We have measured the cross section of four charged pion production in photon-photon interactions in the invariant mass range 1.0≦Wγγ≦3.2 GeV and up toQ2=16 GeV2. For 1.2 GeV≦Wγγ≦1.7 GeV the process is dominated by ρ0ρ0 production with a rapid rise in cross section around 1.2 GeV, well below the nominal ρ0ρ0 threshold. The observed distributions in the two particle masses and in the production and decay angles are well described by an incoherent sum of the phase-space subprocesses γγ →ρ0ρ0, →ρ0π+π−, and →π+π−π+π−. A spin-parity analysis of the ρ0ρ0 system showsJP=2+ to dominate, although 0+ is also possible forWγγ≦1.4 GeV. Negative partity states are excluded.
Fractions of subprocesses from 2-parameter fit to the no-tag data in limited energy range. The Q=1R contribution is set equal to zero.
Fractions of subprocesses from 2-parameter fit to the single-tag data in limited energy range. The Q=1R contribution is set equal to zero.
Inclusive charged-current interactions of high-energy neutrinos and antineutrinos have been studied with high statistics in a counter experiment at the CERN Super Proton Synchrotron. The energy dependence of the total cross-sections, the longitudinal structure function, and the nucleon structure functionsF2,xF3, and\(\bar q^{\bar v} \) are determined from these data. The analysis of theQ2-dependence of the structure functions is used to test quantum chromodynamics, to determine the scale parameter Λ and the gluon distribution in the nucleon.
STUCTURE FUNCTIONS ARE EVALUATED ASSUMING R=SIG(L)/SIG(T)=0.1 AND M(W) IS INFINITE. NO CORRECTION FOR FERMI MOTION APPLIED. ERRORS ARE STATISTICAL AND SYSTEMATIC POINT-TO-POINT ERRORS. IN ADDITION OVER-ALL SCALE ERROR OF 6 PCT. FOR F2 , 8 PCT. FOR XF3.
Measurements of charged pion and kaon production in central Pb+Pb collisions at 40, 80 and 158 AGeV are presented. These are compared with data at lower and higher energies as well as with results from p+p interactions. The mean pion multiplicity per wounded nucleon increases approximately linearly with s_NN^1/4 with a change of slope starting in the region 15-40 AGeV. The change from pion suppression with respect to p+p interactions, as observed at low collision energies, to pion enhancement at high energies occurs at about 40 AGeV. A non-monotonic energy dependence of the ratio of K^+ to pi^+ yields is observed, with a maximum close to 40 AGeV and an indication of a nearly constant value at higher energies.The measured dependences may be related to an increase of the entropy production and a decrease of the strangeness to entropy ratio in central Pb+Pb collisions in the low SPS energy range, which is consistent with the hypothesis that a transient state of deconfined matter is created above these energies. Other interpretations of the data are also discussed.
The energy dependence of the K+/PI+ ratio at y = 0 in PB PB and AU AU collisions. This table includes the present NA49 data as well as other data CT.= The commmon systematic error on the NA49 points is +-7%. including PHENIX and AGS data.
The energy dependence of the K-/PI- ratio at y = 0 in PB PB and AU AU collisions. This table includes the present NA49 data as well as other data includingPHENIX and AGS data, and preliminary E895 data.. The commmon systematic error on the NA49 points is +-7%.
The energy dependence of the ratio of the K+ to PI+ multiplicities in full phase space from PB PB and AU AU collisions. This table includes the present NA49 data as well as other data including AGS data.. The commmon systematic error on the NA49 points is +-7%.
We report a measurement of the inclusive D/D̄ production cross section in 800 GeV/ c proton-proton interactions. The experiment used the high resolution bubble chamber LEBC exposed to an 800 GeV/ c proton beam at the Fermilab MPS. We obtain σ( D/ D ̄ )=59 −15 +22 μ b (statistical errors), having analysed 25% of the total data sample. Comparison with 400 GeV/ c pp dat a obtained with LEBC at CERN shows a D/D̄ cross section increase by a factor of 1.7 −0.5 +0.7 . This is in good agreement with fusion model calculations.
PAGE FROM PREPRINT. It was made the assumption that the increase in cross section with energy is the same for neutral and chareged d-meson (with following weights).
Neutral current single pi0 production induced by neutrinos with a mean energy of 1.3 GeV is measured at a 1000 ton water Cherenkov detector as a near detector of the K2K long baseline neutrino experiment. The cross section for this process relative to the total charged current cross section is measured to be 0.064 +- 0.001 (stat.) +- 0.007 (sys.). The momentum distribution of produced pi0s is measured and is found to be in good agreement with an expectation from the present knowledge of the neutrino cross sections.
Ratio of single PI0 NC cross section to the total CC cross section. For reference the total CC cross section is calculated to be 1.1 x 10**-38 CM**2/nucleon averaged over the K2K neutrino beam energy.
We present measurements of the total production rates and momentum distributions of the charmed baryon $\Lambda_c^+$ in $e^+e^- \to$ hadrons at a center-of-mass energy of 10.54 GeV and in $\Upsilon(4S)$ decays. In hadronic events at 10.54 GeV, charmed hadrons are almost exclusively leading particles in $e^+e^- \to c\bar{c}$ events, allowing direct studies of $c$-quark fragmentation. We measure a momentum distribution for $\Lambda_c^+$ baryons that differs significantly from those measured previously for charmed mesons. Comparing with a number of models, we find none that can describe the distribution completely. We measure an average scaled momentum of $\left< x_p \right> = 0.574\pm$0.009 and a total rate of $N_{\Lambda c}^{q\bar{q}} = 0.057\pm$0.002(exp.)$\pm$0.015(BF) $\Lambda_c^+$ per hadronic event, where the experimental error is much smaller than that due to the branching fraction into the reconstructed decay mode, $pK^-\pi^+$. In $\Upsilon (4S)$ decays we measure a total rate of $N_{\Lambda c}^{\Upsilon} = 0.091\pm$0.006(exp.)$\pm$0.024(BF) per $\Upsilon(4S)$ decay, and find a much softer momentum distribution than expected from B decays into a $\Lambda_c^+$ plus an antinucleon and one to three pions.
LAMBDA/C+ differential production rate per hadronic event for the continuum at cm energy 10.54 GeV.
The integrated number of LAMBDA/C+'s per hadronic event for the continuum at cm energy 10.54 GeV.
LAMBDA/C+ differential production rate per UPSILON(4S) decay at cm energy 10.58 GeV.
The shapes of jets with transverse energies, E_T(jet), up to 45 GeV produced in neutral- and charged-current deep inelastic e+p scattering (DIS) at Q**2 > 100 GeV**2 have been measured with the ZEUS detector at HERA. Jets are identified using a cone algorithm in the eta-phi plane with a cone radius of one unit. The jets become narrower as E_T(jet) increases. The jet shapes in neutral- and charged-current DIS are found to be very similar. The jets in neutral-current DIS are narrower than those in resolved processes in photoproduction and closer to those in direct-photon processes for the same ranges in E_T(jet) and jet pseudorapidity. The jet shapes in DIS are observed to be similar to those in e+e- interactions and narrower than those in pbarp collisions for comparable E_T(jet). Since the jets in e+e- interactions and e+p DIS are predominantly quark initiated in both cases, the similarity in the jet shapes indicates that the pattern of QCD radiation within a quark jet is to a large extent independent of the hard scattering process in these reactions.
Comparison of the differential jet shape with those from E+E- interactions obtained in a comparable data from OPAL (Alees et al. ZP C63 (94) 197).
Electron-proton elastic scattering cross sections have been measured at four-momentum transfers between 1.0 and 3.0 (GeV/ c ) 2 and at electron scattering angles between 10° and 20° and at about 86° in the laboratory. The proton electromagnetic form factors G E and G M were determined. The results indicate that G E ( q 2 ) decreases faster with increasing q 2 than G M ( q 2 ).
Axis error includes +- 2.5/2.5 contribution (Due to counting statisticss, separation of elastic events, beam monitoring, incident energy, scattering angle, proton absorption, solid angle, target length and density).
The cross section for dijet photoproduction at high transverse energies is presented as a function of the transverse energies and the pseudorapidities of the jets. The measurement is performed using a sample of ep-interactions corresponding to an integrated luminosity of 6.3 pb^(-1), recorded by the ZEUS detector.Jets are defined by applying a k_T-clustering algorithm to the hadrons observed in the final state. The measured cross sections are compared to next-to-leading order QCD calculations. In a kinematic regime where theoretical uncertainties are expected to be small, the measured cross sections are higher than these calculations.
The dijet cross section for the x(gamma)>0.75 range as a function of the pseudorapidity of the jet with the other jet fixed. This data is for a restricted range of y, (W = 212 to 277 GeV).
The DIS diffractive cross section, $d\sigma^{diff}_{\gamma^* p \to XN}/dM_X$, has been measured in the mass range $M_X < 15$ GeV for $\gamma^*p$ c.m. energies $60 < W < 200$ GeV and photon virtualities $Q^2 = 7$ to 140 GeV$^2$. For fixed $Q^2$ and $M_X$, the diffractive cross section rises rapidly with $W$, $d\sigma^{diff}_{\gamma^*p \to XN}(M_X,W,Q^2)/dM_X \propto W^{a^{diff}}$ with $a^{diff} = 0.507 \pm 0.034 (stat)^{+0.155}_{-0.046}(syst)$ corresponding to a $t$-averaged pomeron trajectory of $\bar{\alphapom} = 1.127 \pm 0.009 (stat)^{+0.039}_{-0.012} (syst)$ which is larger than $\bar{\alphapom}$ observed in hadron-hadron scattering. The $W$ dependence of the diffractive cross section is found to be the same as that of the total cross section for scattering of virtual photons on protons. The data are consistent with the assumption that the diffractive structure function $F^{D(3)}_2$ factorizes according to $\xpom F^{D(3)}_2 (\xpom,\beta,Q^2) = (x_0/ \xpom)^n F^{D(2)}_2(\beta,Q^2)$. They are also consistent with QCD based models which incorporate factorization breaking. The rise of $\xpom F^{D(3)}_2$ with decreasing $\xpom$ and the weak dependence of $F^{D(2)}_2$ on $Q^2$ suggest a substantial contribution from partonic interactions.
Diffractive structure function F2(D3).
Exclusive production of $\rho^0$ and $J/\psi$ mesons in e^+ p collisions has been studied with the ZEUS detector in the kinematic range $0.25 < Q^2 < 50 GeV^2, 20 < W < 167 GeV$ for the $\rho^0$ data and $2 < Q^2 < 40 GeV^2, 50 < W < 150 GeV$ for the $J/\psi$ data. Cross sections for exclusive $\rho^0$ and $J/\psi$ production have been measured as a function of $Q^2, W$ and $t$. The spin-density matrix elements $r^{04}_{00}, r^1_{1-1}$ and $Re r^{5}_{10}$ have been determined for exclusive $\rho^0$ production as well as $r^{04}_{00}$ and $r^{04}_{1-1}$ for exclusive $J/\psi$ production. The results are discussed in the context of theoretical models invoking soft and hard phenomena.
The spin-density martix elements deletermined for various values of W and Q**2 for the RHO0 BPC sample.
Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 82 pb^{-1}. Charm has been tagged by reconstructing D^{*+}, D^0, D^{+} and D_s^+ (+ c.c.) charm mesons. The charm hadrons were measured in the kinematic range p_T(D^{*+},D^0,D^{+}) > 3 GeV, p_T(D_s^+)>2 GeV and |\eta(D)| < 1.6 for 1.5 < Q^2 < 1000 GeV^2 and 0.02 < y < 0.7. The production cross sections were used to extract charm fragmentation ratios and the fraction of c quarks hadronising into a particular charm meson in the kinematic range considered. The cross sections were compared to the predictions of next-to-leading-order QCD, and extrapolated to the full kinematic region in p_T(D) and \eta(D) in order to determine the open-charm contribution, F_2^{c\bar{c}}(x,Q^2), to the proton structure function F_2.
The extracted values of F2(CC) from a combination of the production cross section of D0 (not coming from D*+ decay), D_ and D/S+.
The production of energetic neutrons in $ep$ collisions has been studied with the ZEUS detector at HERA. The neutron energy and $p_T^2$ distributions were measured with a forward neutron calorimeter and tracker in a $40 \pb^{-1}$ sample of inclusive deep inelastic scattering (DIS) data and a $6 \pb^{-1}$ sample of photoproduction data. The neutron yield in photoproduction is suppressed relative to DIS for the lower neutron energies and the neutrons have a steeper $p_T^2$ distribution, consistent with the expectation from absorption models. The distributions are compared to HERA measurements of leading protons. The neutron energy and transverse-momentum distributions in DIS are compared to Monte Carlo simulations and to the predictions of particle exchange models. Models of pion exchange incorporating absorption and additional secondary meson exchanges give a good description of the data.
Normalized double differential cross sections for leading neutron production in the photoproduction sample. Statistical errors only are given.
A detailed analysis is presented of the diffractive deep-inelastic scattering process $ep\to eXY$, where $Y$ is a proton or a low mass proton excitation carrying a fraction $1 - \xpom > 0.95$ of the incident proton longitudinal momentum and the squared four-momentum transfer at the proton vertex satisfies $|t|<1 {\rm GeV^2}$. Using data taken by the H1 experiment, the cross section is measured for photon virtualities in the range $3.5 \leq Q^2 \leq 1600 \rm GeV^2$, triple differentially in $\xpom$, $Q^2$ and $\beta = x / \xpom$, where $x$ is the Bjorken scaling variable. At low $\xpom$, the data are consistent with a factorisable $\xpom$ dependence, which can be described by the exchange of an effective pomeron trajectory with intercept $\alphapom(0)= 1.118 \pm 0.008 {\rm (exp.)} ^{+0.029}_{-0.010} {\rm (model)}$. Diffractive parton distribution functions and their uncertainties are determined from a next-to-leading order DGLAP QCD analysis of the $Q^2$ and $\beta$ dependences of the cross section. The resulting gluon distribution carries an integrated fraction of around 70% of the exchanged momentum in the $Q^2$ range studied. Total and differential cross sections are also measured for the diffractive charged current process $e^+ p \to \bar{\nu}_e XY$ and are found to be well described by predictions based on the diffractive parton distributions. The ratio of the diffractive to the inclusive neutral current $ep$ cross sections is studied. Over most of the kinematic range, this ratio shows no significant dependence on $Q^2$ at fixed $\xpom$ and $x$ or on $x$ at fixed $Q^2$ and $\beta$.
Details of systematic errors from the Minimum Bias data sample taken in 1997. D_UNC ==> uncorrelated systematic error. D_LAR ==> LAr hadronic energy scale. D_ELE ==> SPACAL electromagnetic energy scale. D_THETA ==> scattered electron angle. D_NOISE ==> calorimeter noise treatment. D_XPOM ==> reweighting the simulation in X(pomeron). D_BETA ==> reweighting the simulation in BETA. D_BG ==> background subtraction. D_PLUG ==> plug energy scale. Q**2 ==> reweighting the simulation in Q**2. SPA ==> SPACAL hadromic energy scale.
Details of systematic errors from the Minimum Bias data sample taken in 1997. D_UNC ==> uncorrelated systematic error. D_LAR ==> LAr hadronic energy scale. D_ELE ==> SPACAL electromagnetic energy scale. D_THETA ==> scattered electron angle. D_NOISE ==> calorimeter noise treatment. D_XPOM ==> reweighting the simulation in X(pomeron). D_BETA ==> reweighting the simulation in BETA. D_BG ==> background subtraction. D_PLUG ==> plug energy scale. Q**2 ==> reweighting the simulation in Q**2. SPA ==> SPACAL hadromic energy scale.
Details of systematic errors from the complete ('all') data sample taken in 1997. D_UNC ==> uncorrelated systematic error. D_LAR ==> LAr hadronic energy scale. D_ELE ==> SPACAL electromagnetic energy scale. D_THETA ==> scattered electron angle. D_NOISE ==> calorimeter noise treatment. D_XPOM ==> reweighting the simulation in X(pomeron). D_BETA ==> reweighting the simulation in BETA. D_BG ==> background subtraction. D_PLUG ==> plug energy scale. Q**2 ==> reweighting the simulation in Q**2. SPA ==> SPACAL hadromic energy scale.
Deep-inelastic positron-proton interactions at low values of Bjorken-x down to x \approx 4.10^-5 which give rise to high transverse momentum pi^0 mesons are studied with the H1 experiment at HERA. The inclusive cross section for pi^0 mesons produced at small angles with respect to the proton remnant (the forward region) is presented as a function of the transverse momentum and energy of the pi^0 and of the four-momentum transfer Q^2 and Bjorken-x. Measurements are also presented of the transverse energy flow in events containing a forward pi^0 meson. Hadronic final state calculations based on QCD models implementing different parton evolution schemes are confronted with the data.
The inclusive PI0 cross section as a function of the scaled pion energy in 3 regions of Bjorken X.
The inclusive PI0 cross section as a function of the scaled pion energy in 3 regions of Q**2.
The production of the neutral strange hadrons $K^{0}_{S}$, $\Lambda$ and $\bar{\Lambda}$ has been measured in $ep$ collisions at HERA using the ZEUS detector. Cross sections, baryon-to-meson ratios, relative yields of strange and charged light hadrons, $\Lambda$ ($\bar{\Lambda}$) asymmetry and polarization have been measured in three kinematic regions: $Q^2 > 25 \gev^2$: $5 < Q^2 < 25 \gev^2$: and in photoproduction ($Q^2 \simeq 0$). In photoproduction the presence of two hadronic jets, each with at least $5 \gev$ transverse energy, was required. The measurements agree in general with Monte Carlo models and are consistent with measurements made at $e^+ e^-$ colliders, except for an enhancement of baryon relative to meson production in photoproduction.
Asymmetry in LAMBDA/LAMBDABAR production in DIS events as a function of pseudorapidity (lab). for Q**2 > 25 GeV**2.
LAMBDA/K0S production ratio in photoproduction events as a function of transverse momentum (lab). for data from the fireball-enriched sample where the highest energy jet contributes no more than 30% to the total energy.
LAMBDA/K0S production ratio in photoproduction events as a function of transverse momentum (lab). for data from the fireball-depleted sample where the highest energy jet contributes at least 30% to the total energy.
Cross sections for e^+p neutral current deep inelastic scattering have been measured at a centre-of-mass energy of sqrt{s}=318 GeV with the ZEUS detector at HERA using an integrated luminosity of 63.2 pb^-1. The double-differential cross section, d^2sigma/dxdQ^2, is presented for 200 GeV^2 < Q^2 < 30000 GeV^2 and for 0.005 < x < 0.65. The single-differential cross-sections dsigma/dQ^2, dsigma/dx and dsigma/dy are presented for Q^2 > 200 GeV^2. The effect of Z-boson exchange is seen in dsigma/dx measured for Q^2 > 10000 GeV^2. The data presented here were combined with ZEUS e^+p neutral current data taken at sqrt{s}=300 GeV and the structure function F_2^{em} was extracted. All results agree well with the predictions of the Standard Model.
The reduced cross section SIG(C=RED) for Q**2 in the range 15000 to 25000 GeV**2 corrected to the electroweak Born level.
Dijet production has been studied in neutral current deep inelastic e+p scattering for 470 < Q**2 < 20000 GeV**2 with the ZEUS detector at HERA using an integrated luminosity of 38.4 pb**{-1}. Dijet differential cross sections are presented in a kinematic region where both theoretical and experimental uncertainties are small. Next-to-leading-order (NLO) QCD calculations describe the measured differential cross sections well. A QCD analysis of the measured dijet fraction as a function of Q**2 allows both a precise determination of alpha_s(M_Z) and a test of the energy-scale dependence of the strong coupling constant. A detailed analysis provides an improved estimate of the uncertainties of the NLO QCD cross sections arising from the parton distribution functions of the proton. The value of alpha_s(M_Z), as determined from the QCD fit, is alpha_s(M_Z) = 0.1166 +- 0.0019 (stat.) {+ 0.0024}_{-0.0033} (exp.)} {+ 0.0057}_{- 0.0044} (th.).
The measured values of ALPHA_S determined from the QCD fit to the measured dijet fraction. The first systematic (DSYS) error is the systematic uncertainty not associated with the energy scales of the jets, the second is associated with the energy scales and the third DSYS error is the total theoretical uncertainty.
The production of neutrons carrying at least 20% of the proton beam energy ($\xl > 0.2$) in $e^+p$ collisions has been studied with the ZEUS detector at HERA for a wide range of $Q^2$, the photon virtuality, from photoproduction to deep inelastic scattering. The neutron-tagged cross section, $e p\to e' X n$, is measured relative to the inclusive cross section, $e p\to e' X$, thereby reducing the systematic uncertainties. For $\xl >$ 0.3, the rate of neutrons in photoproduction is about half of that measured in hadroproduction, which constitutes a clear breaking of factorisation. There is about a 20% rise in the neutron rate between photoproduction and deep inelastic scattering, which may be attributed to absorptive rescattering in the $\gamma p$ system. For $0.64 < \xl < 0.82$, the rate of neutrons is almost independent of the Bjorken scaling variable $x$ and $Q^2$. However, at lower and higher $\xl$ values, there is a clear but weak dependence on these variables, thus demonstrating the breaking of limiting fragmentation. The neutron-tagged structure function, ${{F}^{\rm\tiny LN(3)}_2}(x,Q^2,\xl)$, rises at low values of $x$ in a way similar to that of the inclusive \ff of the proton. The total $\gamma \pi$ cross section and the structure function of the pion, $F^{\pi}_2(x_\pi,Q^2)$ where $x_\pi = x/(1-\xl)$, have been determined using a one-pion-exchange model, up to uncertainties in the normalisation due to the poorly understood pion flux. At fixed $Q^2$, $F^{\pi}_2$ has approximately the same $x$ dependence as $F_2$ of the proton.
The XL bins, their acceptance and the acceptance uncertainty. The RH columnshows the contribution from the energy-scale uncertainty - this is completely c orrelated between the bins.
We report our final results from the analysis of the full high statistics sample of events of the reaction ν μ + e − → μ − + ν c collected with the CHARM II detector in the CERN wide-band neutrino beam during the years 1988 to 1991. From a signal of 15758 ± 324 inverse muon decay events we derived, inthe Born approximation, a value of (16.51 ± 0.93) × 10 −42 cm 2 GeV −1 for the asymptotic cross section slope σ E ν , in goodagreement with the Standard Model prediction of 17.23 × 10 −42 cm 2 GeV −1 . The result constrains the scalar coupling of the electron and the muon to | g LL S | 2 < 0.475 at 90% CL.
23.8 is mean neutrino beam energy.
Born approximation of the asymptotic cross section slope obtained by applying radiative corrections, which amount to a 3% effect.. Error is combined statistics and systematics.. 23.8 is mean neutrino beam energy.
A new method is employed to measure the neutral current cross section up to Bjorken-x values of one with the ZEUS detector at HERA using an integrated luminosity of 65.1 pb-1 for e+p collisions and 16.7 pb-1 for e-p collisions at sqrt{s}=318 GeV and 38.6 pb-1 for e+p collisions at sqrt{s}=300 GeV. Cross sections have been extracted for Q2 >= 648 GeV2 and are compared to predictions using different parton density functions. For the highest x bins, the data have a tendency to lie above the expectations using recent parton density function parametrizations.
Breakdown of the uncorrelated and correlated systematic errors for the 96-97 E+ P NC scattering data.
We measured the inclusive electron-proton cross section in the nucleon resonance region (W < 2.5 GeV) at momentum transfers Q**2 below 4.5 (GeV/c)**2 with the CLAS detector. The large acceptance of CLAS allowed for the first time the measurement of the cross section in a large, contiguous two-dimensional range of Q**2 and x, making it possible to perform an integration of the data at fixed Q**2 over the whole significant x-interval. From these data we extracted the structure function F2 and, by including other world data, we studied the Q**2 evolution of its moments, Mn(Q**2), in order to estimate higher twist contributions. The small statistical and systematic uncertainties of the CLAS data allow a precise extraction of the higher twists and demand significant improvements in theoretical predictions for a meaningful comparison with new experimental results.
No description provided.
Resonance production in the γγ reactionse+e−→e+e+e−π0π0 ande+e−π0η has been studied with the JADE detector at PETRA. The decay widths into γγ of thef2(1270),a0(980) anda2(1320) were measured to be\(\Gamma _{\gamma \gamma } (f_2 (1270)) = 3.19 \pm 0.09_{ - 0.38}^{ + 0.22} \) Kev,Γλλ(a0(980))=0.28±0.04±0.10 KeV/BR(a0(980)→π0η) andΓλλ(a2(1320))=1.01±0.14±0.22KeV. For thef0(975) andf4(2050) upper limits of the widths were obtained,Γλλ(f0(975))<0.6 KeV, andΓλλ(f4(2050))<1.1 KeV, both at the 95% C.L. Assuming that the spin 0 background under thef2(1270) is small, thef2(1270) was found to be produced exclusively in a helicity 2 state. The helicity 0 contribution is <15% at the 95% C.L. The cross section forλλ→π0π0 in the mass range 2.0–3.5 GeV/c2 was measured for the first time. Since the cross section forλλ→π+π− is a factor ∼2 larger, ππ production in this range can be interpreted as taking place via isospin 0 production.
Data read from graph.. Event distributions uncorrected for angular acceptance and the efficiency with energy of the detector RE = GAMMA GAMMA --> PI0 PI0.
Data read from graph.. Event distributions uncorrected for angular acceptance and the efficiency with energy of the detector RE = GAMMA GAMMA --> PI0 PI0.
The x and Q 2 dependence of the single photon exchange cross section d 2 σ /d Q 2 d x and the proton structure functions F 2 ( x , Q 2 ) and R ( x , Q 2 ) have been measured in deep inelastic muon proton scattering in the region 0.02 < x < 0.8 and 3 < Q 2 < 190 GeV 2 . By comparing data at different incident muon energies R was found to have little kinematic dependence and an average value of −0.010 ± 0.037 (stat.) ± 0.102 (stat.). The observed deviations from scaling gave the value of Λ MS , the QCD mass scale parameter, to be 105 −45 +55 (stat.) −45 +85 (syst.) MeV. The fraction of the momentum of the nucleon carried by gluons was found to be ∼56% at Q 2 ∼22.5 GeV 2 . It is shown that to obtain a description of the data for F 2 ( x , Q 2 ) together with that measured in deep inelastic electron-proton scattering at lower Q 2 it is necessary to include additional higher twist contributions. The value of Λ MS remains unchanged with the inclusion of these contributions which were found to have an x -dependence of the form x 3 /(1 − x ).
No description provided.
Earlier measurements at LEP of isolated hard photons in hadronic Z decays, attributed to radiation from primary quark pairs, have been extended in the ALEPH experiment to include hard photon productioninside hadron jets. Events are selected where all particles combine democratically to form hadron jets, one of which contains a photon with a fractional energyz≥0.7. After statistical subtraction of non-prompt photons, the quark-to-photon fragmentation function,D(z), is extracted directly from the measured 2-jet rate. By taking into account the perturbative contributions toD(z) obtained from anO(ααs) QCD calculation, the unknown non-perturbative component ofD(z) is then determined at highz. Provided due account is taken of hadronization effects nearz=1, a good description of the other event topologies is then found.
2-jet events. Variable Z has been defined as E(gamma)/(E(gamma)+E(had)), where E(gamma) is the energy of the hard photon in 'photon-jet', E(had) is the energy of the rest hadrons in jet. Ycut is jet resolution parameter (see paper).
2-jet events. Variable Z has been defined as E(gamma)/(E(gamma)+E(had)), where E(gamma) is the energy of the hard photon in 'photon-jet', E(had) is the energy of the rest hadrons in jet. Ycut is jet resolution parameter (see paper).
2-jet events. Variable Z has been defined as E(gamma)/(E(gamma)+E(had)), where E(gamma) is the energy of the hard photon in 'photon-jet', E(had) is the energy of the rest hadrons in jet. Ycut is jet resolution parameter (see paper).
Deep inelastic scattering and its diffractive component, ep -> e'gamma*p ->e'XN, have been studied at HERA with the ZEUS detector using an integrated luminosity of 4.2 pb-1. The measurement covers a wide range in the gamma*p c.m. energy W (37 - 245 GeV), photon virtuality Q2 (2.2 - 80 GeV2) and mass Mx. The diffractive cross section for Mx > 2 GeV rises strongly with W: the rise is steeper with increasing Q2. The latter observation excludes the description of diffractive deep inelastic scattering in terms of the exchange of a single Pomeron. The ratio of diffractive to total cross section is constant as a function of W, in contradiction to the expectation of Regge phenomenology combined with a naive extension of the optical theorem to gamma*p scattering. Above Mx of 8 GeV, the ratio is flat with Q2, indicating a leading-twist behaviour of the diffractive cross section. The data are also presented in terms of the diffractive structure function, F2D(3)(beta,xpom,Q2), of the proton. For fixed beta, the Q2 dependence of xpom F2D(3) changes with xpom in violation of Regge factorisation. For fixed xpom, xpom F2D(3) rises as beta -> 0, the rise accelerating with increasing Q2. These positive scaling violations suggest substantial contributions of perturbative effects in the diffractive DIS cross section.
Cross section for the diffractive scattering process GAMMA* P --> DD X for a diffractive mass of 3.0 GeV and Q**2 = 2.7 GeV**2.
We report on a high statistics measurement of the total and differential cross sections of the process gamma gamma -> pi^+ pi^- in the pi^+ pi^- invariant mass range 0.8 GeV/c^2 < W < 1.5 GeV/c^2 with 85.9 fb^{-1} of data collected at sqrt{s}=10.58 GeV and 10.52 GeV with the Belle detector. A clear signal of the f_0(980) resonance is observed in addition to the f_2(1270) resonance. An improved 90% confidence level upper limit Br.(eta'(958) -> pi^+ pi^-) < 2.9 x 10^{-3} is obtained for P- and CP-violating decay of the eta'(958) meson using the most conservative assumption about the interference with the background.
No description provided.
Data collected at the Z resonance using the DELPHI detector at LEP are used to determine the charged hadron multiplicity in gluon and quark jets as a function of a transverse momentum-like scale. The colour factor ratio, \cacf, is directly observed in the increase of multiplicities with that scale. The smaller than expected multiplicity ratio in gluon to quark jets is understood by differences in the hadronization of the leading quark or gluon. From the dependence of the charged hadron multiplicity on the opening angle in symmetric three-jet events the colour factor ratio is measured to be: C_A/C_F = 2.246 \pm 0.062 (stat.) \pm 0.080 (syst.) \pm 0.095 (theo.)
Charged multiplicity in events with a hard photon, as a function of the apparent centre-of-mass energy (SQRT(S)) of the hadronic system. The errors shown are statistical only.
The interaction of virtual photons is investigated using double tagged gammagamma events with hadronic final states recorded by the ALEPH experiment at e^+e^- centre-of-mass energies between 188 and 209 GeV. The measured cross section is compared to Monte Carlo models, and to next-to-leading-order QCD and BFKL calculations.
Differential cross section as a function of the relative energy of the scattered electrons.
Di-jet producion is studied in collisions of quasi-real photons at e+e- centre- of-mass energies sqrt(s)ee from 189 to 209 GeV at LEP. The data were collected with the OPAL detector. Jets are reconstructed using an inclusive k_t clustering algorithm for all cross-section measurements presented. A cone jet algorithm is used in addition to study the different structure of the jets resulting from either of the algorithms. The inclusive di-jet cross-section is measured as a function of the mean transverse energy Etm(jet) of the two leading jets, and as a functiuon of the estimated fraction of the photon momentum carried by the parton entering the hard sub-process, xg, for different regions of Etm (jet). Angular distribution in di-jet events are measured and used to demonstrate the dominance of quark and gluon initiated processes in different regions of phase space. Furthermore the inclusive di-jet cross-section as a function of |eta(jet)| and |delta eta (jet)| is presented where eta(jet) is the jet pseudo-rapidity. Different regions of the xg+ -xg- -space are explored to study and control the influence of an underlying event. The results are compared to next-to-leading order perturbative QCD calculations and to the predictions of the leading order Monte Carlo generator PYTHIA.
The di-jet cross section as a function of the mean transverse energy of thedi-jet system for the full X(C=GAMMA+) and X(C=GAMMA-) region.
The di-jet cross section as a function of the mean transverse energy of thedi-jet system for the region where either X(C=GAMMA+) or X(C=GAMMA-) are < 0.75 .
The di-jet cross section as a function of the mean transverse energy of thedi-jet system for the region where both X(C=GAMMA+) and X(C=GAMMA-) are < 0.75.
During 1993 and 1995 LEP was run at 3 energies near the Z$^0$peak in order to give improved measurements of the mass and width of the resonance. During 1994, LEP o
Measurement of the observed Born cross section for the 1992-1995 data from the ISR events. SPRIME is the reduced energy after the ISR.
Di-jet production is studied in collisions of quasi-real photons radiated by the LEP beams at e+e- centre-of-mass energies 161 and 172 GeV. The jets are reconstructed using a cone jet finding algorithm. The angular distributions of direct and double-resolved processes are measured and compared to the predictions of leading order and next-to-leading order perturbative QCD. The jet energy profiles are also studied. The inclusive two-jet cross-section is measured as a function of transverse energy and rapidity and compared to next-to-leading order perturbative QCD calculations. The inclusive two-jet cross-section as a function of rapidity is compared to the prediction of the leading order Monte Carlo generators PYTHIA and PHOJET. The Monte Carlo predictions are calculated with different parametrisations of the parton distributions of the photon. The influence of the `underlying event' has been studied to reduce the model dependence of the predicted jet cross-sections from the Monte Carlo generators.
Transverse energy flow outside the jets in the rapidity region abs(etarap*)<1.
Fraction of the transverse energy of the jets inside a cone of radious 0.5 around the jet axis as a function of the mean ET of the jets.
Fraction of the transverse energy of the jets inside a cone of radious 0.5 around the jet axis as a function of the jet rapidity.
In Phys. Lett. B 753, 629-638 (2016) [arXiv:1507.08188] the BESIII collaboration published a cross section measurement of the process $e^+e^-\to \pi^+ \pi^-$ in the energy range between 600 and 900 MeV. In this erratum we report a corrected evaluation of the statistical errors in terms of a fully propagated covariance matrix. The correction also yields a reduced statistical uncertainty for the hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon, which now reads as $a_\mu^{\pi\pi\mathrm{, LO}}(600 - 900\,\mathrm{MeV}) = (368.2 \pm 1.5_{\rm stat} \pm 3.3_{\rm syst})\times 10^{-10}$. The central values of the cross section measurement and of $a_\mu^{\pi\pi\mathrm{, LO}}$, as well as the systematic uncertainties remain unchanged.
Results of the BESIII measurement of the cross section $\sigma^{\rm bare}_{\pi^+\pi^-(\gamma_{\rm FSR})} \equiv \sigma^{\rm bare}(e^+e^-\rightarrow\pi^+\pi^-(\gamma_{\rm FSR}))$ and the squared pion form factor $|F_\pi|^2$. The errors are statistical only. The value of $\sqrt{s'}$ represents the bin center. The 0.9$\%$ systematic uncertainty is fully correlated between any two bins.
Results for the bare cross section $\sigma^\text{bare}_{\pi^+\pi^-}$ and the pion form factor together with their statistical uncertainties. The systematical uncertainties are given by 0.9% (see <a href="https://inspirehep.net/literature/1385603">arXiv:1507.08188</a>).
Bare cross section $\sigma^\mathrm{bare}(e^+e^-\to\pi^+\pi^-(\gamma_\mathrm{FSR}))$ of the process $e^+e^-\to\pi^+\pi^-$ measured using the initial state radiation method. The data is corrected concerning final state radiation and vacuum polarization effects. The final state radiation is added using the Schwinger term at born level.
A precise measurement of the cross section of the process $e^+e^-\to\pi^+\pi^-(\gamma)$ from threshold to an energy of 3GeV is obtained with the initial-state radiation (ISR) method using 232fb$^{-1}$ of data collected with the BaBar detector at $e^+e^-$ center-of-mass energies near 10.6GeV. The ISR luminosity is determined from a study of the leptonic process $e^+e^-\to\mu^+\mu^-(\gamma)\gamma_{\rm ISR}$, which is found to agree with the next-to-leading-order QED prediction to within 1.1%. The cross section for the process $e^+e^-\to\pi^+\pi^-(\gamma)$ is obtained with a systematic uncertainty of 0.5% in the dominant $\rho$ resonance region. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the measured $\pi\pi$ cross section from threshold to 1.8GeV is $(514.1 \pm 2.2({\rm stat}) \pm 3.1({\rm syst}))\times 10^{-10}$.
Bare cross-section $e^+e^-\rightarrow\pi^+\pi^-(\gamma)$ The cross section values (nb) for 337 CM energy intervals (GeV) from 0.3 to 3 GeV. The cross section is bare (excluding vacuum polarization) and includes the emission of final state photons. ***WARNING*** The quoted errors are from the diagonal elements of the statistical covariance matrix (reported the Table titled "Bare cross-section statistical covariance") and added quadratically with the systematic uncertainties (reported in the Table titled "Bare cross-section systematic uncertainties"). These errors can be used when plotting the results as they are representative of the precision achieved. However, any calculation involving the cross section over some energy range MUST use, to be meaningful, the full statistical covariance matrix and the proper correlations of the systematic uncertainties. ***WARNING***
Bare cross-section $e^+e^-\rightarrow\pi^+\pi^-(\gamma)$ systematic uncertainties contributions and total systematic uncertainties, for 337 CM energy intervals (GeV), from 0.3 to 3 GeV. All systematics contributions are each 100% correlated in all energy bins.
Bare cross-section $e^+e^-\rightarrow\pi^+\pi^-(\gamma)$ statistical covariance matrix, for 337x337 CM energy intervals (GeV), from 0.3 to 3 GeV.
We report on measurements of hadronic and leptonic cross sections and leptonic forward-backward asymmetries performed with the L3 detector in the years 1993-95. A total luminosity of 103 pb^-1 was collected at centre-of-mass energies \sqrt{s} ~ m_Z and \sqrt{s} ~ m_Z +/- 1.8 GeV which corresponds to 2.5 million hadronic and 245 thousand leptonic events selected. These data lead to a significantly improved determination of Z parameters. From the total cross sections, combined with our measurements in 1990-92, we obtain the final results: m_Z = 91189.8 +/- 3.1 MeV, Gamma_Z = 2502.4 +/- 4.2 MeV, Gamma_had = 1741.1 +/- 3.8 MeV, Gamma_l = 84.14 +/- 0.17 MeV. An invisible width of Gamma_inv = 499.1 +/- 2.9 MeV is derived which in the Standard Model yields for the number of light neutrino species N_nu = 2.978 +/- 0.014. Adding our results on the leptonic forward-backward asymmetries and the tau polarisation, the effective vector and axial-vector coupling constants of the neutral weak current to charged leptons are determined to be \bar{g}_V^l = -0.0397 +/- 0.0017 and \bar{g}_A^l = -0.50153 +/- 0.00053.Including our measurements of the Z -> b \bar{b} forward-backward and quark charge asymmetries a value for the effective electroweak mixing angle of sin^2\bar{\theta}_W = 0.23093 +/- 0.00066 is derived. All these measurements are in good agreement with the Standard Model of electroweak interactions. Using all our measurements of electroweak observables an upper limit on the mass of the Standard Model Higgs boson of m_H < 133 GeV is set at 95% confidence level.
Forward-Backward Asymmetries of e+ e- production from the 1995 data in the fiducial volume THETA from 44 to 136 degrees and including an acollinearity cut of PSI < 25 degrees. The errors are statistical only and there is an additional correlated absolute error of 0.0025 to be added. The right most column is the s-channel contribution in the full solid angle.
The transition between photoproduction and deep-inelastic scattering is investigated in jet production at the HERA ep collider, using data collected by the H1 experiment. Measurements of the differential inclusive jet cross-sections dsigep/dEt* and dsigmep/deta*, where Et* and eta* are the transverse energy and the pseudorapidity of the jets in the virtual photon-proton centre of mass frame, are presented for 0 < Q2 < 49 GeV2 and 0.3 < y < 0.6. The interpretation of the results in terms of the structure of the virtual photon is discussed. The data are best described by QCD calculations which include a partonic structure of the virtual photon that evolves with Q2.
The inclusive virtual photon-proton jet cross section.
The total and the differential cross sections for the reaction e + e − → γγ ( γ ) have been measured with the DELPHI detector at LEP using an integrated luminosity of 36.9 pb −1 . The results agree with the QED predictions and consequently there is no evidence for non-standard channels with the same experimental signature. The lower limits obtained on the QED cutoff parameters are Λ + > 143 GeV and Λ − > 120 GeV, and the lower bound on the mass of an excited electron with an effective coupling constant λ γ = 1 is 132 GeV/ c 2 . Upper limits on the branching ratios for the decays Z 0 → γγ , Z 0 → π 0 γ , Z 0 → ηγ and Z 0 → γγγ have been determined to be 5.5 × 10 −5 , 5.5 × 10 −5 , 8.0 × 10 −5 , and 1.7 × 10 −5 respectively. All the limits are at the 95% confidence level.
1990 energies are 88.223, 89.222, 90.217, 91.217, 92.209, 93.208 and 94.202 GeV.. 1991 energies are 88.465, 89.460, 90.208, 91.225, 91.954, 92.953, and 93.703 GeV.. 1992 energy is 91.278 GeV.
We report a high-statistics measurement of differential cross sections for the process gamma gamma -> pi^0 pi^0 in the kinematic range 0.6 GeV <= W <= 4.0 GeV and |cos theta*| <= 0.8, where W and theta* are the energy and pion scattering angle, respectively, in the gamma gamma center-of-mass system. Differential cross sections are fitted to obtain information on S, D_0, D_2, G_0 and G_2 waves. The G waves are important above W ~= 1.6 GeV. For W <= 1.6 GeV the D_2 wave is dominated by the f_2(1270) resonance while the S wave requires at least one additional resonance besides the f_0(980), which may be the f_0(1370) or f_0(1500). The differential cross sections are fitted with a simple parameterization to determine the parameters (the mass, total width and Gamma_{gamma gamma}B(f_0 -> pi^0 pi^0)) of this scalar meson as well as the f_0(980). The helicity 0 fraction of the f_2(1270) meson, taking into account interference for the first time, is also obtained.
Differential cross section for W = 2.14, 2.18 and 2.22 GeV.
Exclusive rho rho production in two-photon collisions involving a single highly virtual photon is studied with data collected at LEP at centre-of-mass energies 89GeV < \sqrt{s} < 209GeV with a total integrated luminosity of 854.7pb^-1 The cross section of the process gamma gamma^* -> rho rho is determined as a function of the photon virtuality, Q^2 and the two-photon centre-of-mass energy, Wgg, in the kinematic region: 1.2GeV^2 < Q^2 < 30GeV^2 and 1.1GeV < Wgg < 3GeV.
Production cross sections as a function of Q**2. The differential cross sections are corrected to the centre of each bin.
Production cross section for the two photon data as a function of Q**2.
Differential cross section for non-resonance and RHO0 RHO0 data corrected to the centre of each bin.
Compton scattering of quasi-real virtual photons, gamma e+- -> gamma e+-, is studied with 0.6fb-1 of data collected by the L3 detector at the LEP e+e- collider at centre-of-mass energies root(s')=189-209GeV. About 4500 events produced by the interaction of virtual photons emitted by e+- of one beam with e-+ of the opposite beam are collected for effective centre-of-mass energies of the photon-electron and photon-positron systems in the range from root(s')= 35GeV up to root(s')=175GeV, the highest energy at which Compton scattering was ever probed. The cross sections of the gamma e+- -> gamma e+- process as a function of root(s') and of the rest-frame scattering angle are measured, combined with previous L3 measurements down to root(s')~20GeV, and found to agree with the QED expectations.
The measured angular distribution over the photon-electron centre of mass energy range 35 to 175 GeV.
The measured Compton scattering cross section using the full data sample including the lower energy data from Acciarri et al. PL B439(1998)183. Errors are combined statistics and systematics.
The production of hard di-jet events in photoproduction at HERA is dominated by resolved photon processes in which a parton in the photon with momentum fraction x_gamma is scattered from a parton in the proton. These processes are sensitive to the quark and gluon content of the photon. The differential di-jet cross-section dsigma/dlog(x_gamma) is presented here, measured in tagged photoproduction at HERA using data taken with the H1 detector, corresponding to an integrated luminosity of 7.2 pb^(-1). Using a restricted data sample at high transverse jet energy, E_(T,jet)>6 GeV, the effective parton density f_gamma,eff(x_gamma) = [q(x_gamma) + bar(q)(x_gamma) +9/4g(x_gamma)] in the photon in leading order QCD is measured down to x_gamma=0.05 from which the gluon density in the photon is derived.
The di-jet photoproduction cross section for ET > 6 GeV after pedestal energy subtraction.
Dijet cross sections as functions of several jet observables are measured in photoproduction using the H1 detector at HERA. The data sample comprises e^+p data with an integrated luminosity of 34.9 pb^(-1). Jets are selected using the inclusive k_T algorithm with a minimum transverse energy of 25 GeV for the leading jet. The phase space covers longitudinal proton momentum fraction x_p and photon longitudinal momentum fraction x_gamma in the ranges 0.05<x_p<0.6 and 0.1<x_gamma<1. The predictions of next-to-leading order perturbative QCD, including recent photon and proton parton densities, are found to be compatible with the data in a wide kinematical range.
Differential ep cross section for dijet production as a function of the average transverse energy the two jets.
Differential ep cross section for dijet production as a function of the maximum transverse energy the leading jet.
Differential ep cross section for dijet production as a function of the average pseudorapidity the two jets in two transverse energy regions and in the Y region 0.1 to 0.5.
The differential cross section for the process $\gamma \gamma \to \eta \pi^0$ has been measured in the kinematic range $0.84 \GeV < W < 4.0 \GeV$, $|\cos \theta^*|<0.8$, where $W$ and $\theta^*$ are the energy and $\pi^0$ (or $\eta$) scattering angle, respectively, in the $\gamma\gamma$ center-of-mass system. The results are based on a 223 fb$^{-1}$ data sample collected with the Belle detector at the KEKB $e^+ e^-$ collider. Clear peaks due to the $a_0(980)$ and $a_2(1320)$ are visible. The differential cross sections are fitted in the energy region $0.9 \GeV < W < 1.46 \GeV$ to obtain the parameters of the $a_0(980)$. Its mass, width and $\Gamma_{\gamma \gamma} \B (\eta \pi^0)$ are measured to be $982.3 ^{+0.6}_{-0.7} ^{+3.1}_{-4.7} \MeV/c^2$, $75.6 \pm 1.6 ^{+17.4}_{-10.0} \MeV$ and $128 ^{+3}_{-2} ^{+502}_{-43} \eV$, respectively. The energy and angular dependences above 3.1 GeV are compared with those measured in the $\pi^0 \pi^0$ channel. The integrated cross section over $|\cos \theta^*|<0.8$ has a $W^{-n}$ dependence with $n = 10.5 \pm 1.2 \pm 0.5$, which is slightly larger than that for $\pi^0 \pi^0$. The differential cross sections show a $\sin^{-4} \theta^*$ dependence similar to $\gamma \gamma \to \pi^0 \pi^0$. The measured cross section ratio, $\sigma(\eta \pi^0)/\sigma(\pi^0 \pi^0) = 0.48 \pm 0.05 \pm 0.04$, is consistent with a QCD-based prediction.
The differential cross section as a function of angle for W = 1.25 GeV.
The production of two high-p_T jets in the interactions of quasi-real photons in e+e- collisions at sqrt{s_ee} from 189 GeV to 209 GeV is studied with data corresponding to an integrated e+e- luminosity of 550 pb^{-1}. The jets reconstructed by the k_T cluster algorithm are defined within the pseudo-rapidity range -1 < eta < 1 and with jet transverse momentum, p_T, above 3 GeV/c. The differential di-jet cross-section is measured as a function of the mean transverse momentum ptmean of the jets and is compared to perturbative QCD calculations.
Distribution of the total energy outside the reconstructed jets for the completed data samples. Also tabulated is the estimated background.
Distribution of the total energy outside the reconstructed jets for the 'Dir' domain. Also tabulated is the estimated background.
Distribution of the total energy outside the reconstructed jets for the 'SR' domain. Also tabulated is the estimated background.
The reaction gamma p --> K0 Sigma+ was measured in the photon energy range from threshold up to 2.6 GeV with the SAPHIR detector at the electron stretcher facility, ELSA, in Bonn. Results are presented on the reaction cross section and the polarization of the Sigma+ as a function of the kaon production angle in the centre-of-mass system, cos(Theta_K^{c.m.}), and the photon energy. The cross section is lower and varies less with photon energy and kaon production angle than that of gamma p --> K+ Sigma0. The Sigma+ is polarized predominantly at cos(Theta_K^{c.m.}) \approx 0. The data presented here are more precise than previous ones obtained with SAPHIR and extend the photon energy range to higher values. They are compared to isobar model calculations.
Polarization parameter of the SIGMA+ as a function of angle in two photon energy ranges.