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 3-parameter fit to the no-tag data.
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 3-parameter fit to the single-tag data.
Inclusive D^{*+-} production in two-photon collisions is studied with the L3 detector at LEP, using 683 pb^{-1} of data collected at centre-of-mass energies from 183 to 208 GeV. Differential cross sections are determined as functions of the transverse momentum and pseudorapidity of the D^{*+-} mesons in the kinematic region 1 GeV < P_T < 12 GeV and |eta| < 1.4. The cross sections sigma(e^+e^- -> e^+e^-D^{*+-}X) in this kinematical region is measured and the sigma(e^+e^- -> e^+e^- cc{bar}X) cross section is derived. The measurements are compared with next-to-leading order perturbative QCD calculations.
Visible D*+- production cross section in the given phase space range. Data are given for each D* decay channel, and the average.
Total cross section for open charm production. Data are given for each D* decay channel, and the combined average. The second systematic (DSYS) error is the uncertainty on the extrapolation from the visible to the full phase space region.
The measured D*+- production cross section in the region ABS(ETARAP) < 1.4.The DSIG/DPT points refer to the centre of the bin and the SIG points are the integrated over the bin.
K^+K^- production in two-photon collisions has been studied using a large data sample of 67 fb^{-1} accumulated with the Belle detector at the KEKB asymmetric e^+e^- collider. We have measured the cross section for the process gamma gamma -> K^+ K^- for center-of-mass energies between 1.4 and 2.4 GeV, and found three new resonant structures in the energy region between 1.6 and 2.4 GeV. The angular differential cross sections have also been measured.
Cross section for two photon production of K+ K- in the polar angular region ABS(COS(THETA*)) < 0.6.
Differential cross sections DSIG/DCOS(THETA) for the W range 1.40 to 1.56 GeV.. Statistical errors only.
Differential cross sections DSIG/DCOS(THETA) for the W range 1.56 to 1.72 GeV.. Statistical errors only.
Diffractive dissociation of quasi-real photons at a photon-proton centre of mass energy of W 200 GeV is studied with the ZEUS detector at HERA. The process under consideration is gamma p -> X N, where X is the diffractively dissociated photon system of mass M_X and N is either a proton or a nucleonic system with mass M_N < 2GeV. The cross section for this process in the interval 3 < M_X < 24 GeV relative to the total photoproduction cross section was measured to be sigma~partial_D / sigma_tot = 6.2 +- 0.2(stat) +- 1.4(syst)%. After extrapolating this result to the mass interval of m_phi~2 < M_X~2 < 0.05 W~2 and correcting it for proton dissociation, the fraction of the total cross section attributed to single diffractive photon dissociation, gamma p -> X p, is found to be sigma_SD / sigma_tot = 13.3 +- 0.5(stat) +- 3.6(syst)%. The mass spectrum of the dissociated photon system in the interval 8 < M_X < 24 GeV can be described by the triple pomeron (PPP) diagram with an effective pomeron intercept of alpha_P(0) = 1.12 +- 0.04(stat) +- 0.08(syst). The cross section for photon dissociation in the range 3 < M_X < 8 GeV is significantly higher than that expected from the triple pomeron amplitude describing the region 8 < M_X < 24 GeV. Assuming that this discrepancy is due to a pomeron-pomeron-reggeon (PPR) term, its contribution to the diffractive cross section in the interval 3 < M_X < 24 GeV is estimated to be f_PPR = 26 +- 3(stat) +- 12(syst)%.
Fraction of the total photoproduction cross section attributed to the photon dissociation.
The fraction of the total photoproduction cross section due to single dif fractive photon dissociation, in the mass range M_phi**2 < M_DD < X >**2 < 0.05 *W**2.
Identification of the diffractive processes was performed on the basis of the shape of reconstructed hadronic mass spectrum. No rapidity-gap was required.
The final states K S 0 K S 0 π + π − and K S 0 K ∓ π 0 π ± , produced in two-photon reactions, have been studied using the ARGUS detector at the e + e − storage ring DORIS II at DESY. The reaction γγ→ K ∗+ K ∗− has been observed for the first time. Its cross section is about eight times larger than that for γγ→ K ∗0 K ∗0 , but it has a similar W γγ dependence.
No description provided.
Topological cross section.
Topological cross section.
The reaction γγ → 2 π + 2 π − 2 π 0 has been studied using the ARGUS detector at the e + e − storage ring DORIS II at DESY. Production of ω mesons is observed and, in particular, the reaction γγ → ωω is seen for the first time. The cross section for γγ → ωω has an enhancement at ∼ 1.9 GeV/ c 2 of about 10 nb. The cross sections for γγ → 2 π + 2 π − 2 π 0 and γγ → ωπ + π − π 0 are also given.
Topological cross section. 14 pct systematic uncertainty not included.
Cross section for (omega omega) production. Additional 25 pct systematic error not included.
Cross section for (omega pi+ pi- pi0) where (omega omega) events have been removed. Additional 15 pct systematic error not included.
Quasi-elastic (z >0.95) photo-production of psi' mesons has been observed at HERA for photon-proton centre-of-mass energies in the range 40 to 160 GeV. The psi' mesons were identified through their decays to l+l- and to J/psi pi+ pi-, where the J/psi subsequently decays to l+l-, the lepton l being either a muon or an electron. The cross-section for quasi-elastic photoproduction was measured to be [18.0 +- 2.8 (stat) +- 3.0(syst)] nb at a photon-proton centre-of-mass energy of 80 GeV. The ratio of the psi' to J/psi quasi-elastic cross-sections is 0.150 +- 0.027 (stat) +- 0.022 (syst).
Overall value for photoproduction cross section combining the different decay modes and data sample.. 1994 and 1995 data.. The second systematic error is from the branching ratio uncertainties.
Combined cross section from PSI(3685) --> J/PSI(1S) < E+ E- > PI+ PI- and PSI(3685) --> J/PSI(1S) < MU+ MU- > PI+ PI- modes using both the 1994 and 1995 data.. The second systematic error is from the branching ratio uncertainties.
Cross section from PSI(3685) --> J/PSI(1S) < E+ E- > PI+ PI- mode.
Elastic $\rho~0$ photoproduction has been measured using the ZEUS detector at HERA. Untagged photoproduction events from $ep$ interactions were used to measure the reaction $\gamma p \rightarrow \rho~0 p$ ($\rho~0 \rightarrow \pi~+ \pi~-$) at photon-proton centre-of-mass energies between 60 and 80GeV and $|t|<0.5$GeV$~2$, where $t$ is the square of the four-momentum transferred at the proton vertex. The differential cross section $d\sigma/dM_{\pi\pi}$, where $M_{\pi\pi}$ is the invariant mass of the two pions, and the integrated cross section, $\sigma_{\gamma p\rightarrow \rho~0 p}$, are presented; the latter was measured to be $14.7\pm 0.4(\mbox{stat.})\pm2.4(\mbox{syst.})\mu\mbox{b}$. The differential cross section $d\sigma/dt$ has an approximately exponential shape; a fit of the type $A~{\prime}_{t} \exp{(-b~{\prime}_{t}|t| + c~{\prime}_{t} t~2)}$ yields a $t$-slope $b~{\prime}_{t}= 9.9\pm1.2(\mbox{stat.})\pm 1.4(\mbox{syst.})\mu\mbox{b}$. The results, when compared to low energy data, show a weak energy dependence of both $\sigma_{\gamma p\rightarrow \rho~0 p}$ and of the $t$-slope. The $\rho~0$ is produced predominantly with transverse polarisation, demonstrating that $s$-channel helicity conservation holds at these energies.
Integrated cross section for exclusive rho0 <pi+ pi-> production where 2Mpi < Mpi pi < Mrho + 5width0.
No description provided.
Applying the Spital and Yennie method to each t bin. No errors given.
The electroproduction of J/psi and psi(2S) mesons is studied in elastic, quasi-elastic and inclusive reactions for four momentum transfers 2 < Q^2 < 80 GeV^2 and photon-proton centre of mass energies 25 < W < 180 GeV. The data were taken with the H1 detector at the electron proton collider HERA in the years 1995 to 1997. The total virtual photon-proton cross section for elastic J/psi production is measured as a function of Q^2 and W. The dependence of the production rates on the square of the momentum transfer from the proton (t) is extracted. Decay angular distributions are analysed and the ratio of the longitudinal and transverse cross sections is derived. The ratio of the cross sections for quasi-elastic psi(2S) and J/psi meson production is measured as a function of Q^2. The results are discussed in terms of theoretical models based upon perturbative QCD. Differential cross sections for inclusive and inelastic production of J/psi mesons are determined and predictions within two theoretical frameworks are compared with the data, the non-relativistic QCD factorization approach including colour octet and colour singlet contributions, and the model of Soft Colour Interactions.
Cross section for elastic J/PSI photoproduction in W bins.
Cross section for elastic J/PSI photoproduction in W bins.
Cross section for elastic J/PSI photoproduction in W bins.
The elastic electroproduction of rho mesons is studied at HERA with the H1 detector for a photon virtuality in the range 1 < Q^2 < 60 GeV^2 and for a hadronic centre of mass energy in the range 30 < W < 140 GeV. The shape of the pipi mass distribution in the rho resonance region is measured as a function of Q^2. The full set of rho spin density matrix elements is determined, and evidence is found for a helicity flip amplitude at the level of 8 +- 3 % of the non-flip amplitudes. Measurements are presented of the dependence of the cross section on Q^2, W and t (the four-momentum transfer squared to the proton). They suggest that, especially at large Q^2, the gamma^*p cross section develops a stronger W dependence than that expected from the behaviour of elastic and total hadron-hadron cross sections.
Average values of the spin density matrix elements measured for the 1996 data sample.
Spin density matrix elements measured for 3 Q**2 values for the 1996 data sample.
Spin density matrix elements measured for 3 W values for the 1996 data sample.
Data were taken at the energy 2 E = 990 MeV to search for multibody events, with the same large solid angle detector which has been used for the measurement of the ϱ , ω and φ production by e + e − annilations. Assuming a π + π − π 0 π 0 production by the quasi two-body process e + e − → ϱ → ωπ 0 we give the correspondi ng cross section σ (e + e − → π + π − π 0 π 0 ) = (1.1 ± 0.5) 10 −32 cm 2 . Since no events with 3 and 4 charged pions have been observed σ (e + e − → π + π − π 0 π − ) ⩽ 1.5 × 10 −33 cm 2 .
RATIO TO MUON PAIR PRODUCTION CALCULATED FROM CROSS SECTION. INCLUDING SYSTEMATIC ERRORS.
The pion form factor is measured in the reaction e + e − → π + π − for center of mass energies in the range 480–1100 MeV. Our results are first analysed in terms of the conventional Vector Meson Dominance formalism, and then taking into account the ωπ inelastic channel. The result of this later formalism is a pion form factor ( F π ) which fits quite well all the existing data on F π both in the timelike and spacelike regions, and pion mean square radius of 〈 r π 2 〉 = 0.460 ± 0.011 fm 2 or 〈r π 2 〉 1 2 = 0.678 ± 0.008 fm .
No description provided.
The reaction γγ → 2 π + 2 π − π 0 has been studied using the the ARGUS detector at the e + e − storage ring DORIS II at DESY. The production of the vector-meson pair ωϱ 0 is observed for the first time. The cross section for γγ → ωϱ 0 and the topological cross section for γγ → 2 π + 2 π − π 0 are given. The angular distribution in ωϱ 0 events do not indicate any specific dominant spin-parity; they are consistent with isotropic production and decay of the ω and ϱ 0 mesons over the available W γγ range.
Topological cross section.
OMEGA RHO0 Production cross section.
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).
The first observation of open b production in ep collisions is reported. An event sample containing muons and jets has been selected which is enriched in semileptonic b quark decays. The visible cross section \sigma(ep -> b \bar{b}X -> \mu X') for Q^2 < 1 GeV^2, 0.1 < y < 0.8 is measured to be 0.176+-0.016(stat.)+0.026-0.017(syst.) nb for the muons to be detected in the range 35 deg < \theta^\mu < 130 deg and \pt^\mu > 2.0 GeV in the laboratory frame. The expected visible cross section based on a NLO QCD calculation is 0.104+-0.017 nb. The cross sections for electroproduction with Q^2<1 GeV^2 and photoproduction are derived from the data and found to be \sigma(ep-> e b\bar{b}X) = 7.1+-0.6(stat.)+1.5-1.3(syst.) nb and \sigma(\gamma p-> b\bar{b} X) = 111+-10(stat.)+23-20(syst.) at an average <W_{\gamma p}> \sim 180 GeV, respectively.
The visible BQ BQBAR --> MUON X cross section in the stated kinematic range.
The total electroproduction and photoproduction cross sections extrapolated to the full phase space.
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.
Cross section for ABS(COS(THETA*)) < 0.3.
Cross section under assumptions of spin 2, helicity 2 production.
Cross section under assumption of spin 0 production.
The elastic electroproduction of phi mesons is studied at HERA with the H1 detector for photon virtualities 1 < Q^2 < 15 GeV^2 and hadronic centre of mass energies 40 < W < 130 GeV. The Q^2 and t dependences of the cross section are extracted (t being the square of the four-momentum transfer to the target proton). When plotted as function of (Q^2 + M_V^2) and scaled by the appropriate SU(5) quark charge factor, the phi meson cross section agrees within errors with the cross sections of the vector mesons V = rho, omega and J/psi. A detailed analysis is performed of the phi meson polarisation state and the ratio of the production cross sections for longitudinally and transversely polarised phi mesons is determined. A small but significant violation of s-channel helicity conservation (SCHC) is observed.
The measured ratio of PHI to RHO0 production.
The cross section for elastic PHI meson electro-production calculated by multiplying the PHI/RHO0 cross section ratio by the RHO0 cross section accurately measured in the earlier H1 publication (EPJ C13,371).
The corrected T distribution of elastic PHI meson production for W around 75 GeV and Q2 in the range 2.5 to 15 GeV**2 (mean = 4.8 GeV**2). Statistical error only.
Exclusive production of proton-antiproton pairs by two photon scattering at CM energies between 2.0 GeV and 3.1 GeV has been measured with the TASSO detector at the e + e − storage ring PETRA. The angular distribution is flat within the accepted CM angular range | cos Θ ∗ |⩽0.7 . The integrated cross section (| cos Θ ∗ |⩽0.6) drops from about 4 nb at 2 GeV to less than 0.5 nb above 3 GeV. For the two-photon production of the η c (2984) and its subsequent decay into proton-antiproton the upper limit Γ(η c →γγ)· B (η c → p p )<0.32 keV (95% CL) is found.
No description provided.
No description provided.
UPPER LIMIT FOR THE PRODUCT OF THE ETA/C --> GAMMA GAMMA WIDTH AND THE BRANCHING RATIO OF ETA/C --> P AP IS DETERMINED TO BE 0.32 KEV WITH 90 PCT CL.
We present the results of a measurement of the cross section oof the reaction e + e − → π + π − π + π − from 890 to 1100 MeV in the center of mass, obtained with a magnetic detector at the Orsay Storage Ring ACO. With respect to previous experiments, the present one offers the possibility of reconstructing events with at least one constraint and his improved statistics. We find that our measurement of the cross section for e + e − → π + π − π + π − is compatible with quasi two-body production of π A 1 ( m A1 = 1.1 GeV, Γ A1 ∼ 0.2−0.3 GeV), through the ϱ and ϱ′(1600) intermediate states. We were able to states. We were able to determine the cross section of this reaction at the energy of the φ meson and consequently an upper limit on the branching ratio of φ → π + π − π + π − .
UPPER LIMIT FOR PHI --> 4PI.
We present the results obtained with the magnetic detector DM1 at the Orsay storage ring ACO for the reaction e + e − → π + π − π 0 from 483 to 1100 MeV in the center of mass. Our data show without ambiguity an interference effect between the ω and φ mesons, which corresponds to a negative coupling constant product ratio Re( g γω g ω →3 π / g γφ g φ →3 π ) ; however our measurements above the φ, performed using kinematical analysis, can only be explained by a higher energy contribution. In addition, the parameters of the ω have been obtained with an improved accuracy compared to other experiments, and particularly the branching ratio B ω →e + e − = (6.75±0.69) × 10 −5 . We confirm that the reaction e + e − → π + π − π 0 proceeds essentially via a quasi-two-body state ϱπ , at the energy of the φ.
FITTED CROSS SECTION AT OMEGA PEAK IS 1410 +- 130 NB AND AT PHI PEAK IS 615 +- 55 NB.
With the H1 detector at the ep collider HERA, D* meson production cross sections have been measured in deep inelastic scattering with four-momentum transfers Q^2>2 GeV2 and in photoproduction at energies around W(gamma p)~ 88 GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe the differential cross sections within theoretical and experimental uncertainties. Using these calculations, the NLO gluon momentum distribution in the proton, x_g g(x_g), has been extracted in the momentum fraction range 7.5x10^{-4}< x_g <4x10^{-2} at average scales mu^2 =25 to 50 GeV2. The gluon momentum fraction x_g has been obtained from the measured kinematics of the scattered electron and the D* meson in the final state. The results compare well with the gluon distribution obtained from the analysis of scaling violations of the proton structure function F_2.
Total cross section for DIS D*+- production in the specified kinemtaic range.
DIS cross section as a function of the transverse D* momentum in the laboratory frame.
DIS cross section as a function of the transverse D* momentum in the hadronic centre-of-mass frame.
The inclusive e^+ p single and double differential cross sections for neutral and charged current processes are measured with the H1 detector at HERA. The data were taken in 1999 and 2000 at a centre-of-mass energy of \sqrt{s} = 319 GeV and correspond to an integrated luminosity of 65.2 pb^-1. The cross sections are measured in the range of four-momentum transfer squared Q^2 between 100 and 30000 GeV^2 and Bjorken x between 0.0013 and 0.65. The neutral current analysis for the new e^+ p data and the earlier e^- p data taken in 1998 and 1999 is extended to small energies of the scattered electron and therefore to higher values of inelasticity y, allowing a determination of the longitudinal structure function F_L at high Q^2 (110 - 700 GeV^2). A new measurement of the structure function x F_3 is obtained using the new e^+ p and previously published e^\pm p neutral current cross section data at high Q^2. These data together with H1 low Q^2 precision data are further used to perform new next-to-leading order QCD analyses in the framework of the Standard Model to extract flavour separated parton distributions in the proton.
The NC cross section DSIG/DQ**2. There is an additional 1.5 PCT normalization uncertainty.
The CC cross section DSIG/DQ**2. There is an additional 1.5 PCT normalization uncertainty.
The NC cross section DSIG/DX for Q**2 > 1000 GeV**2. There is an additional 1.5 PCT normalization uncertainty.
The final state K + K − π + π − has been studied in γγ interactions using the ARGUS detector at the e + e − storage ring DORIS II at DESY. Production of the vector meson pair K ∗0 (892) K ∗0 (892) is observed for the first time. The cross section for K + K − π + π − , K ∗0 K − π + +c.c. and K ∗0 K ∗0 are all found to be of the order of a few nb. In the W γγ range accessible, a mean upper limit of 0.5 nb at 95% CL is derived for φϱ 0 production.
TOPOLOGICAL CROSS SECTION.
(K*0 K*BAR0) cross section.
(K*0 K- PI+ + CC) CROSS SECTION WITH (K*0 K*BAR0) REMOVED.
We have measured the inclusive branching ratio for B→ψX to be (1.09±0.16±0.21)%, and the exclusive branching ratios for B−→ψK− and B¯ ¯0 *0 to be (0.09±0.05)% and (0.41±0.18)%, respectively. The mass difference between neutral and charged B mesons is 1.1±2.1 MeV, while the difference between the mass of Υ(4S) and twice the mean B-meson mass is 18.5±3.0 MeV. The ψ momentum distribution implies a substantial two-body decay (in agreement with direct measurements), but also some combination of B→ψX with MX>1.5 GeV, and B→ψ’X.
No error for cross-section given in text.
No description provided.
Cross sections for elastic photoproduction of J/Psi and Upsilon mesons are presented. For J/Psi mesons the dependence on the photon-proton centre-of-mass energy W_gammap is analysed in an extended range with respect to previous measurements of 26<=W_gammap<= 285 GeV. The measured energy dependence is parameterized as sigma_gammap proportional W_gammap^delta with delta=0.83+-0.07. The differential cross section dsigma/dt for J/Psi mesons is derived, its dependence on W_gammap and on t is analysed and the effective trajectory (in terms of Regge theory) is determined to be alpha(t)=(1.27+-0.05)+(0.08+-0.17)*t/GeV^2. Models based on perturbative QCD and on pomeron exchange are compared to the data.
The cross sections for the elastic photoproduction of J/PSI particles.
Differential cross section, DSIG/DT, for the elastic photoproduction of J/PSI particles.
The slope of the DSIG/DT distribution.
We present a study of J ψ meson production in collisions of 26.7 GeV electrons with 820 GeV protons, performed with the H1-detector at the HERA collider at DESY. The J ψ mesons are detected via their leptonic decays both to electrons and muons. Requiring exactly two particles in the detector, a cross section of σ(ep → J ψ X) = (8.8±2.0±2.2) nb is determined for 30 GeV ≤ W γp ≤ 180 GeV and Q 2 ≲ 4 GeV 2 . Using the flux of quasi-real photons with Q 2 ≲ 4 GeV 2 , a total production cross section of σ ( γp → J / ψX ) = (56±13±14) nb is derived at an average W γp =90 GeV. The distribution of the squared momentum transfer t from the proton to the J ψ can be fitted using an exponential exp(− b ∥ t ∥) below a ∥ t ∥ of 0.75 GeV 2 yielding a slope parameter of b = (4.7±1.9) GeV −2 .
No description provided.
No description provided.
QED background subtracted.
The cross section for the elastic photoproduction of \r0\ mesons ($\gamma p \rightarrow \rho~0 p$) has been measured with the H1 detector at HERA for two average photon-proton centre-of-mass energies of 55 and 187GeV. TheFcenterline lower energy point was measured by observing directly the $\rho~{0}$ decay giving a cross section of $9.1\pm 0.9\,(\stat)\pm 2.5\,(\syst)\;\mu$b. The logarithmic slope parameter of the differential cross section, ${\rm d}\sigma/{\rm d}t$, is found to be $10.9 \pm 2.4\,(\stat) \pm 1.1\,(\syst)\;$GeV$~{-2}$. The \r0\ decay polar angular distribution is found to be consistent with s-channel helicity conservation. The higher energy cross section was determined from analysis of the lower part of the hadronic invariant mass spectrum of diffractive photoproduction and found to be $13.6\pm 0.8\,(\stat)\pm 2.4\,(\syst)\;\mu$b.
PI+ PI- cross section.
RHO0 cross section by selecting Mpipi to lie between 2Mpi and Mrho + 5width0.
No description provided.
We have measured the cross section of the radiative process e+e- -> pi+pi-gamma with the KLOE detector at the Frascati phi-factory DAPHNE, from events taken at a CM energy W=1 GeV. Initial state radiation allows us to obtain the cross section for e+e- -> pi+pi-, the pion form factor |F_pi|^2 and the dipion contribution to the muon magnetic moment anomaly, Delta a_mu^{pipi} = (478.5+-2.0_{stat}+-5.0_{syst}+-4.5_{th}) x 10^{-10} in the range 0.1 < M_{pipi}^2 < 0.85 GeV^2, where the theoretical error includes a SU(3) ChPT estimate of the uncertainty on photon radiation from the final pions. The discrepancy between the Standard Model evaluation of a_mu and the value measured by the Muon g-2 collaboration at BNL is confirmed.
Differential cross section for $e^+e^-\rightarrow\pi^+\pi^-\gamma$, with $50^o<\theta_\gamma<130^o$
Statistical covariance matrix for differential cross section for $e^+e^-\rightarrow\pi^+\pi^-\gamma$, with $50^o<\theta_\gamma<130^o$
Inverse statistical covariance matrix for differential cross section for $e^+e^-\rightarrow\pi^+\pi^-\gamma$, with $50^o<\theta_\gamma<130^o$
We report an improved measurement of the inverse muon decay process, ν μ +e→ μ − + ν e , at the Fermilab Tevatron. The rate of this reaction with respect to the ν μ -N charged current interaction is measured to be (0.1245±0.0057(stat.)±0.0031 (sys.)) × 10 −2 . The measurement confirms the standard model predictions for the Lorentz structure of the weak current, the helicity of the neutrino, and the energy dependence of the cross section.
Data from the Quadruple Triplet Neutrino beam (QTB).
Data from the Narrow Band Beam(NBB).
Weighted average of the QTB and NBB data.
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 ET differential jet cross section in the virtual-photon CM frame.
The ET differential jet cross section in the virtual-photon CM frame.
The ET differential jet cross section in the virtual-photon CM frame.
The reaction γγ→K + K − π + π − π 0 has been observed for the first time, using the ARGUS detector at the e + e − storage ring DORIS II at DESY. The cross section shows an enhancement for W γγ close to 3 GeV/ c 2 . Searches for γγ→ωφ and for γγ→φφ leading to this final state, as well as for γγ→φφ→2K + 2K − , have been performed. The derived upper limits for ωφ and φφ production are compatible with q q q q model predictions.
TOPOLOGICAL CROSS SECTION.
95 PCT CL UPPER LIMITS.
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.
Inclusive production of $D^*(2010)$ mesons in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 81.9 pb$^{-1}$. The decay channel $D^{* +}\to D^0 \pi^+ $ with $D^0\to K^-\pi^+$ and corresponding antiparticle decay were used to identify $D^*$ mesons. Differential $D^*$ cross sections with $1.5<Q^2<1000$ GeV$^2$ and $0.02<y<0.7$ in the kinematic region $1.5<p_T(D^*)<15$ GeV and $|\eta(D^*)|<1.5$ are compared to different QCD calculations incorporating different parameterisations of the parton densities in the proton. The data show sensitivity to the gluon distribution in the proton and are reasonably well described by next-to-leading-order QCD with the ZEUS NLO QCD fit used as the input parton density in the proton. The observed cross section is extrapolated to the full kinematic region in $p_T(D^*)$ and $\eta(D^*)$ in order to determine the open-charm contribution, $F_2^{\rm charm}(x,Q^2)$, to the proton structure function, $F_2$. Since, at low $Q^2$, the uncertainties of the data are comparable to those from the QCD fit, the measured differential cross sections in $y$ and $Q^2$ should be used in future fits to constrain the gluon density.
Overall total cross section. The second DSYS error is due to the uncertainty in the BR for D* and D0 decay.
Measured differential cross section as a function of Q**2.
Measured differential cross section as a function of X.
We have studied the properties of pion production in the reaction γ →3 π + 3 π − in the energy range 1.6⩽ W γγ ⩽7.5 GeV with the CELLO detector at PETRA. We present the topological cross section both for Q 2 ≈0 (anti-tag) and Q 2 ≈0 (single-tag). The Q 2 dependence of the cross section is flatter than the GVDM prediction. The distribution of the production angle of the pions in the CMS peaks at small angles, indicating a peripheral process. In accordance with the VDM picture the p T distribution of the pions manifests an exponential fall-off. Like sign pion pairs were found to be Bose-Einstein correlated. We use this correlation to estimate the spatial dimensions of the interaction region.
No description provided.
No description provided.
No description provided.
The first observation of neutral pion production in π e inelastic scattering is presented. The cross section at 300 GeV for | t ‖>62;10 −3 (GeV / c ) 2 is 2.11 ± 0.47 nb, in good agreement with the theory of PCAC anomalies with 3 quark colours.
No description provided.
The production of D * and D mesons has been studied in e + e − annihilations at √s = 29GeV. The data, corresponding to an integrated luminosity of 300 pb −1 , were obtained using the HRS detector at PEP. The cross section is measured to be R (D 0 + D + ) = 2.40±0.35 and we determine the electroweak asymmetry to be −9.9 ± 2.7%, which corresponds to an axial vector coupling constant product g e g c = 0.26 ± 0.07.
No description provided.
No description provided.
No description provided.
We have measured the production cross section for K s 0 in e + e − annihilation from 3.6 to 5.0 GeV center of mass energy. A substantial increase of the K s 0 yield is observed around 4 GeV in qualitative agreement with the charm hypothesis.
THE DATA GIVEN HERE AT 9.3 GEV AND ABOVE ARE REPORTED IN C. BERGER ET AL., PL 104B, 79 (1981). THE 12.0 AND 30 GEV DATA WERE TAKEN AT PETRA.
No description provided.
No description provided.
The production of $\phi$ mesons in the reaction $e~{+}p \rightarrow e~{+} \phi p$ ($\phi \rightarrow K~{+}K~{-}$), for $7 < Q~2 < 25$ GeV$~2$ and for virtual photon-proton centre of mass energies ($W$) in the range 42-134 GeV, has been studied with the ZEUS detector at HERA. When compared to lower energy data at similar $Q~2$, the results show that the $\gamma~*p \rightarrow \phid p$ cross section rises strongly with $W$. This behaviour is similar to that previously found for the $\gamma~*p \rightarrow \rho~0 p$ cross section. This strong dependence cannot be explained by production through soft pomeron exchange. It is, however, consistent with perturbative QCD expectations, where it reflects the rise of the gluon momentum density in the proton at small $x$. The ratio of $\sigma (\phi) / \sigma (\rho~0)$, which has previously been determined by ZEUS to be 0.065 $\pm$ 0.013 (stat.) in photoproduction at a mean $W$ of 70 GeV, is measured to be 0.18 $\pm $ 0.05 (stat.) $\pm$ 0.03 (syst.) at a mean $Q~2$ of 12.3 GeV$~2$ and mean $W$ of $\approx$ 100 GeV and is thus approaching at large $Q~2$ the value of 2/9 predicted from the quark charges of the vector mesons and a flavour independent production mechanism.
No description provided.
Additional 32 PCT Systematic error.
Additional 32 PCT Systematic error.
At the electron-proton collider HERA the inclusive $D~{*\pm}$ meson photoproduction cross section has been measured with the H1 detector in two different, but partly overlapping, kinematical regions. For the first, where $\langle W_{\gamma p}\rangle \approx 200$\ GeV and $Q~2 < 0.01\,\gev~2$, the result is $\sigma(\gamma p \rightarrow c \bar{c} X) = (13.2 \pm 2.2 ~{+2.1}_{-1.7}\, ~{+9.9}_{-4.8})\,\mu b$. The second measurement for $Q~2 < 4\,\gev~2$ yields $\sigma(\gamma p \rightarrow c \bar{c} X) = ( 9.3 \pm 2.1 ~{+1.9}_{-1.8}\, ~{+6.9}_ {-3.2} )\,\mu b$ at $\langle W_{\gamma p}\rangle \approx 142$\,GeV and $\sigma(\gamma p \rightarrow c \bar{c} X) = ( 20.6 \pm 5.5 ~ {+4.3}_{-3.9}\, ~{+15.4}_{-7.2})\,\mu b$ at $\langle W_{\gamma p} \rangle \approx 230$\,GeV, respectively. The third error accounts for an additional uncertainty due to the proton and photon parton density parametrizations. Differential cross sections are presented as a function of the $D~{*\pm}$ transverse momentum and rapidity. The results compare reasonably well with next-to-leading order QCD calculations. Evidence for diffractive photoproduction of charm quark is presented.
Tagged events.
Untagged events.
Second systematical errors are due to the dependence on the parton density parametrizations. Tagged events.
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.
Production cross section for all D0 mesons, those not originating fom D* decays and those originating from D* decays.
Production cross section for additional D* mesons (not decaying to D0) and all D* mesons.
Production cross section for D+ mesons.
Nucleon structure functions obtained from neutrino and anti-neutrino scattering on iron nuclei at high energies (Ev=30 to 250 GeV) are presented. These results are compared with the results of other lepton-nucleon scattering experiments. The structure functions are used to test the validity of the Gross-Llewellyn-smith sum rule, which measures the number of valence quarks in the nucleons, and to obtain leading and second order QCD fits.
Measured charged current total cross section.
No description provided.
No description provided.
From a study of peripheral interactions wherein a negative pion of 12 or 18 GeV/c incident on a nucleon produced a pair of high-momentum pions, the pion-pion s-wave interaction was deduced. Normalizing to to the ϱo production cross sections, a pion-pion cross section falling smoothly from 50 mb (300 MeV) to 20 mb (600 MeV) is observed. The forward-backward asymmetry is negative for low dipion masses.
The errors are statistical only.
The errors are statistical only.
No errors are given.
We present the analysis of the inclusive $K^{0}$ production in p+p and p+Nb collisions measured with the HADES detector at a beam kinetic energy of 3.5 GeV. Data are compared to the GiBUU transport model. The data suggest the presence of a repulsive momentum-dependent kaon potential as predicted by the Chiral Perturbation Theory (ChPT). For the kaon at rest and at normal nuclear density, the ChPT potential amounts to $\approx 35$ MeV. A detailed tuning of the kaon production cross sections implemented in the model has been carried out to reproduce the experimental data measured in p+p collisions. The uncertainties in the parameters of the model were examined with respect to the sensitivity of the experimental results from p+Nb collisions to the in-medium kaon potential.
The K0 production cross section in P P collisions.
The K0 production cross section in P + NB collisions. The uncertainty given on SIG(P NB --> K0 X) is the dominating absolute normalization uncertainty.
The ratios R vp and R vp of the neutral current to charged current cross sections for neutrino and antineutrino interactions on protons have been measured in BEBC. The beam was the CERN SPS 400 GeV wideband beam. The bubble chamber, equipped with the standard External Muon Identifier, was surrounded with an additional plane of wire chambers (Internal Picket Fence), which was added to improve neutral current event identification. For a total transverse momentum of the charged hadrons above 0.45 GeV/ c and a charged multiplicity of at least 3, it was found that R vp = 0.384 ± 0.015 and R vp = 0.338 ± 0.014 ± 0.016, corresponding to a value of sin 2 θ w (M w MS of 0.225 ± 0.030 . Combining the results from hydrogen and an isoscalar target, the differences of the neutral current chiral coupling constants were found to be u 2 l − d 2 L = −0.080 ± 0.043 ± 0.012 and u 2 R − d 2 R = 0.021±0.055±0.028.
No description provided.
A maximum likelihood analysis of ARGUS data on two-photon production of π + π + π 0 π 0 π − π − is presented. A small fraction of events is due to the production of omega pairs. The γγ → ωω cross section has its maximum value close to threshold.
Results of maximum liklihood analysis.
Double-tagged interactions of photons with virtualities Q^2 between 10 GeV^2 and 200 GeV^2 are studied with the data collected by DELPHI at LEPII from 1998 to 2000, corresponding to an integrated luminosity of 550 pb^{-1}. The gam* gam* -> mu+mu- data agree with QED predictions. The cross-section of the reaction gam* gam* -> hadrons is measured and compared to the LO and NLO BFKL calculations.
Measured cross section for the process E+ E- --> E+ E- HADRONS.
Measured cross section for the process GAMMA* GAMMA* --> HADRONS.
Differential cross section for GAMMA* GAMMA* --> MU+ MU-.
We report the first observation of an orbitally excited baryon, the Λ(1520), in quark and gluon fragmentation. The production rate is found to be (1.15±0.21±0.16)×10 −2 and (0.80±0.17 −0.13 +0.10 )×10 −2 Λ (1520) hyperons per event in direct ϒ decays and in the continuum, respectively. In contrast to the observed situation for ground state baryons, the production of the Λ(1520) in direct ϒ decays shows little or no enhancement with respect to continuum production.
Full X range uses extrapolation from fit to dsig/dz distribution.
No description provided.
UPSI(1S) DECAYS.
The process γγ→π+π−π+π− has been investigated in reactions of the typee+e−→e+e−π+π−π+π− in the single tag mode. The range of the four momentum squared of one of the virtual photons was 0.28 GeV2/c2≦Q2≦3.6 GeV2/c2, the average being 〈Q2〉=0.92 GeV2/c2; the other photon was quasi real. The reaction is mainly described by the channels γγ→ρ0ρ0 and γγ→4π (phase space), occuring with about equal probability. TheQ2-dependence of the cross section is in agreement with the ρ form factor.
Data read from graph.. Additional overall systematic error 25%.
Data read from graph.. Additional overall systematic error 25%.. The Q**2 approx 0 datum is deduced from the earlier TASSO paper, Brandelik et al, Phys. Lett. 97B(1980)448, (<a href=http://durpdg.dur.ac.uk/scripts/reacsearch.csh/TESTREAC/red+1151> RED = 1151 </a>) on rho0 rho0 production.
Cross-sections and angular distributions for the production of events with single and multiple photons are measured from data recorded with the OPAL detector at the recently upgraded LEP collider. The measured cross-sections are generally consistent with Standard Model expectations for the e + e − → ν v γ(γ) and e + e − → γγ ( γ ) processes. Six events with an acoplanar photon pair and large missing mass are found. The observed number of events is larger than expected from e + e − → ν ν γγ ; however, the missing mass distribution is compatible with the Z 0 resonance. Deviations from QED are constrained by the data on e + e − → γγ ( γ ). Lower limits are set at 95% confidence level on the QED cut-off parameters Λ + and Λ − of 152 GeV and 142 GeV, respectively, and also on the mass of an excited electron of 147 GeV.
No description provided.
No description provided.
No description provided.
The processes e + e − → e + e − and μ + μ − have been studied at PETRA using the JADE detector. The data, which were collected at s -values of up to 1300 GeV 2 have been analysed in terms of an electro-weak extension of QED to obtain values for the weak vector and axial vector couplings in the lepton sector. The values obtained agree with the predictions of the standard Salam-Weinberg model and the data are further analysed in terms of this model to obtain the limits 0.10 < sin 2 ϑ w < 0.40 (68% CL). The mass of the neutral weak gauge boson is deduced to be greater than 51 GeV/ c 2 .
No description provided.
No description provided.
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