The e+e- -> e+e- hadrons reaction, where one of the two electrons is detected in a low polar-angle calorimeter, is analysed in order to measure the hadronic photon structure function F2gamma . The full high-energy and high-luminosity data set, collected with the L3 detector at centre-of-mass energies 189-209GeV, corresponding to an integrated luminosity of 608/pb is used. The Q^2 range 11-34GeV^2 and the x range 0.006-0.556 are considered. The data are compared with recent parton density functions.
Cross sections DELTA(SIG)/DELTA(X) in the Q**2 range 11 TO 14 GeV**2.
Cross sections DELTA(SIG)/DELTA(X) in the Q**2 range 14 TO 20 GeV**2.
Cross sections DELTA(SIG)/DELTA(X) in the Q**2 range 20 TO 34 GeV**2.
The production of charm quarks is studied in deep-inelastic electron-photon scattering using data recorded by the OPAL detector at LEP at normal e+e- centre-of-mass energies from 183 to 209 GeV. The charm quarks have been identified by full reconstruction of charged D* mesons using their decays into D0pi with the D0 observed in two decay modes with charged particle final states, Kpi and K3pi. The cross-section sigma(D*) for production of charged D* in the reaction e+e- -> e+e-D*X is measured in a restricted kinematical region using two bins in Bjorken x, 0.0014 < x < 0.1 and 0.1 < x < 0.87. From sigma(D*) the charm production cross-section sigma(e+e- -> e+e- ccbar X) and the charm structure function of the photon F 2,c are determined in the region 0.0014 < x < 0.87 and 5 < Q2 < 100 GeV2. For x > 0.1 the perturbative QCD calculation at next-to-leading order agrees perfectly with the measured cross-section. For x < 0.1 the measured cross-section is 43.8 +- 14.3 +- 6.3 +- 2.8 pb with a next-to-leading order prediction of 17.0+2.9-2.3 p.b
The inclusive D* production cross section.
The inclusive charm quark pair cross section. The second DSYS error is due to extrapolation.
The measured structure function F2(C=CHARM). The second DSYS error is due to extrapolation.
The hadronic structure of the photon F2gamma is measured as a function of Bjorken x and of the photon virtuality Q2 using deep-inelastic scattering data taken by the OPAL detector at LEP at e+e- centre-of-mass energies from 183 to 209 GeV. Previous OPAL measurements of the x dependence of F2gamma are extended to an average Q2 of <Q2>=780GeV2 using data in the kinematic range 0.15 < x < 0.98. The Q2 evolution of F2gamma is studied for 12.1 < <Q2> < 780GeV2 using three ranges of x. As predicted by QCD, the data show positive scaling violations in F2gamma for the central x region 0.10-0.60. Several parameterisations of F2gamma are in qualitative agreement with the measurements whereas the quark-parton model prediction fails to describe the data.
F2 and DSIG/DX for the EE sample in the high Q**2 region as a function of X.
Statistical correlations between the bins in the preceding table.
The measured value of F2 and DSIG/DX for the SW data sample in the Q**2 range 9 to 15 GeV**2.
The photon structure function F2-gamma(x,Q**2) has been measured using data taken by the OPAL detector at centre-of-mass energies of 91Gev, 183Gev and 189Gev, in Q**2 ranges of 1.5 to 30.0 GeV**2 (LEP1), and 7.0 to 30.0 GeV**2 (LEP2), probing lower values of x than ever before. Since previous OPAL analyses, new Monte Carlo models and new methods, such as multi-variable unfolding, have been introduced, reducing significantly the model dependent systematic errors in the measurement.
Results of F2/ALPHAE for the LEP1 data using the SW for Q**2 = 1.9 GeV**2.
Results of F2/ALPHAE for the LEP1 data using the SW for Q**2 = 3.7 GeV**2.
Results of F2/ALPHAE for the LEP1 data using the FD for Q**2 = 8.9 GeV**2.
The structure functions of real and virtual photons are derived from cross section measurements of the reaction e^+e^ -> e^+e^- + hadrons at LEP. The reaction is studied at \sqrt{s} ~ 91 GeV with the L3 detector. One of the final state electrons is detected at a large angle relative to the beam direction, leading to Q^2 values between 40 GeV^2 and 500 GeV^2. The other final state electron is either undetected or it is detected at a four-momentum transfer squared P^2 between 1 GeV^2 and 8 GeV^2. These measurements are compared with predictions of the Quark Parton Model and other QCD based models.
Measured values of F2 for the single-tag data as a function of X for the full Q**2 range.
Measured values of F2 for the single-tag data as a function of Q**2 for different X ranges.
The effective F2 measured in double-tag events as a function of X.
The inclusive production of D*+- mesons in photon-photon collisions has been measured using the OPAL detector at LEP at e+e- centre-of-mass energies of 183 and 189GeV. The D* mesons are reconstructed in their decay to D0pi+ with the D0 observed in the two decay modes Kpi+ and Kpi+pi-pi+. After background subtraction, 100.4+-12.6(stat) D*+- mesons have been selected in events without observed scattered beam electron ("anti-tagged") and 29.8+-5.9 (stat) D*+- mesons in events where one beam electron is scattered into the detector ("single-tagged"). Direct and single-resolved events are studied separately. Differential cross-sections as functions of the D* transverse momentum p_t and pseudorapidity \eta are presented in the kinematic region 2<p_t<12GeV and \eta<1.5. They are compared to next-to-leading order (NLO) perturbative QCD calculations. The total cross-section for the process (e+e- to e+e-ccbar), where the charm quarks are produced in the collision of two quasi-real photons, is measured to be 842+-97(stat)+-75(syst)+-196(extrapolation)pb. A first measurement of the charm structure function F2 of the photon is performed in the kinematic range 0.0014<x<0.87 and 5<Q^2<100 GeV^2, and the result is compared to a NLO perturbative QCD calculation.
Differential PT distribution for anti-tagged events for both D* decay modesand combined.
Differential ETARAP distribution for anti-tagged events for both D* decay modes and combined.
Integrated cross section using the anti-tagged events for D* production in the kinematic range of the experiment.
The production of D*+-(2010) mesons in deep inelastic scattering has been measured in the ZEUS detector at HERA using an integrated luminosity of 37 pb^-1. The decay channels D*+ -> D0 pi+(+c.c.), with D0 -> K- pi+ or D0 ->K- pi- pi+ pi+, have been used to identify the D mesons. The e+p cross section for inclusive D*+- production with 1<Q^2<600 GeV^2 and 0.02<y<0.7 is 8.31 +- 0.31(stat.) +0.30-0.50(syst.) nb in the kinematic region 1.5< pT(D*+-)<15 GeV and |eta(D*+-)|<1.5. Differential cross sections are consistent with a next-to-leading-order perturbative-QCD calculation when using charm-fragmentation models which take into account the interaction of the charm quark with the proton remnant. The observed cross section is extrapolated to the full kinematic region in pT(D*+-) and eta(D*+-) in order to determine the charm contribution, F^ccbar_2(x,Q^2), to the proton structure function. The ratio F^ccbar_2/F_2 rises from ~10% at Q^2 ~1.8 GeV^2 to ~30% at Q^2 ~130 GeV^2 for x values in the range 10^-4 to 10-3.
The measured cross section for D* production. The first is derived from theK2PI final state and the second from the K4PI final state.
The differential cross section w.r.t. Q**2 from the K2PI final state. The asymmetric errors are the quadratic sum of the statistical and systematic errors. The statistical errors are also shown separately.
The differential cross section w.r.t. X from the K2PI final state. The asymmetric errors are the quadratic sum of the statistical and systematic errors. The statistical errors are also shown separately.
The inclusive single and double differential cross-sections for neutral and charged current processes with four-momentum transfer squared Q^2 between 150 and 30,000 GeV2 and with Bjorken x between 0.0032 and 0.65 are measured in e^+ p collisions. The data were taken with the H1 detector at HERA between 1994 and 1997, and they correspond to an integrated luminosity of 35.6 pb^-1. The Q^2 evolution of the parton densities of the proton is tested, yielding no significant deviation from the prediction of perturbative QCD. The proton structure function F_2(x,Q^2) is determined. An extraction of the u and d quark distributions at high x is presented. At high Q^2 electroweak effects of the heavy bosons Z0 and W are observed and found to be consistent with Standard Model expectation.
The structure function, F2, and the reduced cross section, in NC DIS scattering at Q**2 from 150 to 30000 GeV**2 as a function if x and y. Also tabulated are the QED corrections to the data, which have already been applied. The individual corrections used to calculate F2 from the cross sections are given in the following table.
The various corrections to the cross sections used to calcuate the F2 values given in the previous table. See the text of the paper for more details.
The CC double differential cross section and the structure function term PHI(C=CC) - see text of the paper for details - at Q**2 from 150 to 1 5000 GeV**2 as a function of both x and y. Also tabulated are the QED corrections to the data, which have already been applied.
The structure of both quasi-real and highly virtual photons is investigated using the reaction e+e- -> e+e-mu+mu-, proceeding via the exchange of two photons. The results are based on the complete OPAL dataset taken at e+e- centre-of-mass energies close to the mass of the Z boson. The QED structure function F_2^gamma and the differential cross-section dsigdx for quasi-real photons are obtained as functions of the fractional momentum x from the muon momentum which is carried by the struck muon in the quasi-real photon for values of Q**2 ranging from 1.5 to 400 GeV**2. The differential cross-section dsigdx for highly virtual photons is measured for 1.5< Q**2 < 30 GeV**2 and 1.5< P**2 < 20 GeV**2, where Q**2 and P**2 are the negative values of the four-momentum squared of the two photons such that Q**2 > P**2. Based on azimuthal correlations the QED structure functions F_A^gamma and F_B^gamma for quasi-real photons are determined for an average Q**2 of 5.4 GeV**2.
No description provided.
No description provided.
No description provided.
Deep--inelastic scattering events with a leading baryon have been detected by the H1 experiment at HERA using a forward proton spectrometer and a forward neutron calorimeter. Semi--inclusive cross sections have been measured in the kinematic region 2 <= Q^2 <= 50 GeV^2, 6.10^-5 <= x <= 6.10^-3 and baryon p_T <= MeV, for events with a final state proton with energy 580 <= E' <= 740 GeV, or a neutron with energy E' >= 160 GeV. The measurements are used to test production models and factorization hypotheses. A Regge model of leading baryon production which consists of pion, pomeron and secondary reggeon exchanges gives an acceptable description of both semi-inclusive cross sections in the region 0.7 <= E'/E_p <= 0.9, where E_p is the proton beam energy. The leading neutron data are used to estimate for the first time the structure function of the pion at small Bjorken--x.
Semi-inclusive structure function for data with forward proton.
Semi-inclusive structure function for data with forward proton.
Semi-inclusive structure function for data with forward proton.
New measurements at a centre-of-mass energy s ≃183 GeV of the hadronic photon structure function F γ 2 ( x ) in the Q 2 interval, 9 GeV 2 ≤ Q 2 ≤30 GeV 2 , are presented. The data, collected in 1997 with the L3 detector, correspond to an integrated luminosity of 51.9 pb −1 . Combining with the data taken at a centre-of-mass energy of 91 GeV, the evolution of F γ 2 with Q 2 is measured in the Q 2 range from 1.2 GeV 2 to 30 GeV 2 . F γ 2 shows a linear growth with ln Q 2 ; the value of the slope α −1 d F γ 2 ( Q 2 )/dln Q 2 is measured in two x bins from 0.01 to 0.2 and is somewhat higher than predicted.
Measured values of F2/ALPHA as a function of x. The second systematic error (DSYS) is that due to the model dependence and is the difference between the results obtained with PHOJET and TWOGAM. The full systematic error is the quadrature sum of the two systematic errors.
Measurements of the proton structure function $F_2$ for $0.6 < Q^2 < 17 {GeV}^2$ and $1.2 \times 10^{-5} < x <1.9 \times 10^{-3}$ from ZEUS 1995 shifted vertex data are presented. From ZEUS $F_2$ data the slopes $dF_2/d\ln Q^2$ at fixed $x$ and $d\ln F_2/d\ln(1/x)$ for $x < 0.01$ at fixed $Q^2$ are derived. For the latter E665 data are also used. The transition region in $Q^2$ is explored using the simplest non-perturbative models and NLO QCD. The data at very low $Q^2$ $\leq 0.65 {GeV}^2$ are described successfully by a combination of generalised vector meson dominance and Regge theory. From a NLO QCD fit to ZEUS data the gluon density in the proton is extracted in the range $3\times 10^{-5} < x < 0.7$. Data from NMC and BCDMS constrain the fit at large $x$. Assuming the NLO QCD description to be valid down to $Q^2\sim 1 {GeV}^2$, it is found that the $q\bar{q}$ sea distribution is still rising at small $x$ and the lowest $Q^2$ values whereas the gluon distribution is strongly suppressed.
F2.
F2.
F2.
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.
Cross section for diffractive scattering.
Cross section for diffractive scattering.
Cross section for diffracitve scattering.
The hadronic photon structure function F γ 2 is studied in the reaction e + e − →e + e − hadrons at LEP with the L3 detector. The data, collected from 1991 to 1995 at a centre-of-mass energy s ≃91 GeV, correspond to an integrated luminosity of 140 pb −1 . The photon structure function F γ 2 is measured in the Q 2 interval 1.2 GeV 2 ≤ Q 2 ≤9.0 GeV 2 and the x interval 0.002< x <0.2. F γ 2 shows a linear growth with ln Q 2 . The value of the slope α −1 d F γ 2 ( Q 2 )/dln Q 2 is measured to be 0.079±0.011±0.009.
No description provided.
No description provided.
No description provided.
The reactions e + e − → e + e − e + e − and e + e − → e + e − μ + μ − , in a single tag configuration, are studied at LEP with the L3 detector. The data set corresponds to an integrated luminosity of 93.7 pb −1 at s =91 GeV. Differential cross sections are measured for 1.4 GeV 2 ≤Q 2 ≤7.6 GeV 2 . The leptonic photon structure function F γ 2 and azimuthal correlations are measured for e + e − → e + e − μ + μ − . The related structure functions F γ A and F γ B , which originate from interference terms of the scattering amplitudes, are determined for the first time.
The systematic and statistical errors added in quadrature. F2(NAME=FA) AND F2(NAME=FB) are related structure functions FA and FB, which originate from inerference terms of the scattering amplitudes. See text for exact definition and details.
This paper presents the first analysis of diffractive photon dissociation events in deep inelastic positron-proton scattering at HERA in which the proton in the final state is detected and its momentum measured. The events are selected by requiring a scattered proton in the ZEUS leading proton spectrometer (LPS) with $\xl>0.97$, where $\xl$ is the fraction of the incoming proton beam momentum carried by the scattered proton. The use of the LPS significantly reduces the contamination from events with diffractive dissociation of the proton into low mass states and allows a direct measurement of $t$, the square of the four-momentum exchanged at the proton vertex. The dependence of the cross section on $t$ is measured in the interval $0.073<|t|<0.4$~$\gevtwo$ and is found to be described by an exponential shape with the slope parameter $b=\tslopeerr$. The diffractive structure function $\ftwodfour$ is presented as a function of $\xpom \simeq 1-\xl$ and $\beta$, the momentum fraction of the struck quark with respect to $\xpom$, and averaged over the $t$ interval $0.073<|t|<\ftwodfourtmax$~$\gevtwo$ and the photon virtuality range $5<Q^2<20~\gevtwo$. In the kinematic range $4 \times 10^{-4} < \xpom < 0.03$ and $0.015<\beta<0.5$, the $\xpom$ dependence of $\ftwodfour$ is fitted with a form $\xpoma$, yielding $a= \ftwodfouraerr$. Upon integration over $t$, the structure function $\ftwod$ is determined in a kinematic range extending to higher $\xpom$ and lower $\beta$ compared to our previous analysis; the results are discussed within the framework of Regge theory.
The measured distribution of T, the squared momentum transfer to the virtual pluton.
Slope of the T distribution.
The structure function F2(NAME=D4).
A measurement is made of the cross section for the process ep --> eXY in deep-inelastic scattering with the H1 detector at HERA. The cross section is presented in terms of a differential structure function F_2^D(3)(x_P,beta,Q^2) of the proton over the kinematic range 4.5 < Q^2 < 75 GeV^2. The dependence of F_2^D(3) on x_P is found to vary with beta, demonstrating that a factorisation of F_2^D(3) with a single diffractive flux independent of beta and Q^2 is not tenable. An interpretation in which a leading diffractive exchange and a subleading reggeon contribute to F_2^D(3) reproduces well the x_P dependence of F_2^D(3) with values for the pomeron and subleading reggeon intercepts of alpha_P(0)=1.203 \pm 0.020(stat.)\pm 0.013(sys.) ^{+0.030}_{-0.035}(model} and alpha_reg(0)=0.50\pm 0.11(stat.)\pm 0.11 (sys.}^{+0.09}_{-0.10} (model), respectively. A fit is performed of the data using a QCD motivated model, in which parton distributions are assigned to the leading and subleading exchanges. In this model, the majority of the momentum of the pomeron must be carried by gluons in order for the data to be well described.
No description provided.
No description provided.
No description provided.
A small electromagnetic sampling calorimeter, installed in the ZEUS experiment in 1995, significantly enhanced the acceptance for very low x and low Q^2 inelastic neutral current scattering, e^{+}p \to e^{+}X, at HERA. A measurement of the proton structure function F_2 and the total virtual photon-proton (\gamma^*p) cross-section is presented for 0.11 \le Q^{2} \le 0.65 GeV^2 and 2 \times 10^{-6} \le x \le 6 \times 10^{-5}, corresponding to a range in the \gamma^{*}p c.m. energy of 100 \le W \le 230 GeV. Comparisons with various models are also presented.
Measured F2 values with the assumption FL=0. The second systematic error isthe change in F2 assuming a value for FL given by VDM.
Measured F2 values with the assumption FL=0. The second systematic error isthe change in F2 assuming a value for FL given by VDM.
Measured F2 values with the assumption FL=0. The second systematic error isthe change in F2 assuming a value for FL given by VDM.
New measurements are presented of the photon structure function F_2^gamma(Q) at four values of Q^2 between 9 and 59 GeV/c^2 based on data collected with the OPAL detector at centre-of-mass energies of 161-172 GeV, with a total integrated luminosity of 18.1 pb^-1. The evolution of F_2^gamma with Q^2 in bins of x is determined in the Q^2 range from 1.86 to 135 GeV/c^2 using data taken at centre-of-mass energies of 91 GeV and 161-172 GeV. F_2^gamma is observed to increase with Q^2 with a slope of 1/alpha_em dF_2^gamma/dln(Q^2) = 0.10 +0.05 -0.03 measured in the range 0.1 < x < 0.6.
Measured values of F2 for the SW sample.
Measured values of F2 for the FD sample.
F2 for the full X range (0.1 to 0.6) as a function of Q**2. The full SW andFD sample points are tabulated for completeness but are not in the plot or fits . The first three points are previous OPAL data at sqrt(s) = 91 GeV (ZP C74(1997)33).
Deep inelastic electron-photon scattering is studied using e+e- data collected by the OPAL detector at centre-of-mass energies sqrt{s_ee} ~ M_{Z^0}. The photon structure function F_2^gamma(x,Q^2) is explored in a Q^2 range of 1.1 to 6.6 GeV/c^2 at lower x values than ever before. To probe this kinematic region events are selected with a beam electron scattered into one of the OPAL luminosity calorimeters at scattering angles between 27 and 55 mrad. A measurement is presented of the photon structure function F_2^gamma(x,Q^2) at <Q^2> = 1.86 GeV^2 and 3.76 GeV^2 in five logarithmic x bins from 0.0025 to 0.2.
Measurement of the hadron photon structure function. Systematic errors do not contain any effects caused by the four momentum of the quasi-real photon being non zero.
Measurement of the hadron photon structure function. Systematic errors do not contain any effects caused by the four momentum of the quasi-real photon being non zero.
This paper presents measurements of D^{*\pm} production in deep inelastic scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The data have been taken with the ZEUS detector at HERA. The decay channel $D^{*+}\to (D^0 \to K^- \pi^+) \pi^+ $ (+ c.c.) has been used in the study. The $e^+p$ cross section for inclusive D^{*\pm} production with $5<Q^2<100 GeV^2$ and $y<0.7$ is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region {$1.3<p_T(D^{*\pm})<9.0$ GeV and $| \eta(D^{*\pm}) |<1.5$}. Differential cross sections as functions of p_T(D^{*\pm}), $\eta(D^{*\pm}), W$ and $Q^2$ are compared with next-to-leading order QCD calculations based on the photon-gluon fusion production mechanism. After an extrapolation of the cross section to the full kinematic region in p_T(D^{*\pm}) and $\eta$(D^{*\pm}), the charm contribution $F_2^{c\bar{c}}(x,Q^2)$ to the proton structure function is determined for Bjorken $x$ between 2 $\cdot$ 10$^{-4}$ and 5 $\cdot$ 10$^{-3}$.
No description provided.
Integrated charm cross sections in two Q**2 regions.
Distribution of the fractional momentum of the D* in the gamma*-p system.
The results of a measurement of the proton structure function F_2(x,Q~2)and the virtual photon-proton cross section are reported for momentum transfers squared Q~2 between 0.35 GeV~2 and 3.5 GeV~2 and for Bjorken-x values down to 6 10~{-6} using data collected by the HERA experiment H1 in 1995. The data represent an increase in kinematic reach to lower x and Q~2 values of about a factor of 5 compared to previous H1 measurements. Including measurements from fixed target experiments the rise of F_2 with decreasing x is found to be less steep for the lowest Q~2 values measured. Phenomenological models at low Q~2 are compared with the data.
No description provided.
No description provided.
No description provided.
A measurement of the inclusive cross section for the deep-inelastic scattering of positrons off protons at HERA is presented at momentum transfers $8.5 \leq Q~2 \leq 35 GeV~2$ and large inelasticity $y = 0.7$, i.e. for the Bjorken-x range $0.00013 \leq x \leq 0.00055$. Using a next-to-leading order QCD fit to the structure function F_2 at lower y values, the contribution of F_2 to the measured cross section at high y is calculated and, by subtraction, the longitudinal structure function F_{L} is determined for the first time with an average value of $F_L=0.52 \pm 0.03 (stat)$~ {+0.25}_{-0.22}$ (syst) at $Q~2=15.4 GeV~2$ and $x=0.000243$.
Inclusive cross section scaled by the kinematic factor K given by:. X*Q**4/((2*PI*ALPHA**2)*Y+). Y+=2(1-Y)+Y**2.
F2 values corresponding to the cross section measurements. X*Q**4/((2*PI*ALPHA**2)*Y+). Y+=2(1-Y)+Y**2.
Longitudinal structure function measurements.
Deep inelastic electron-photon scattering is studied in the Q2 ranges from 6 to 30 GeV2 and from 60 to 400 GeV2 using the full sample of LEP data taken with the OPAL detector at centre-of-mass energies close to the Z0 mass, with an integrated luminosity of 156.4 pb−1. Energy flow distributions and other properties of the measured hadronic final state are compared with the predictions of Monte Carlo models, including HERWIG and PYTHIA. Sizeable differences are found between the data and the models, especially at low values of the scaling variable x. New measurements are presented of the photon structure function $F_2^{αmma }(x,Q^2)$, allowing for the first time for uncertainties in the description of the final state by different Monte Carlo models. The differences between the data and the models contribute significantly to the systematic errors on $F_2^{αmma }$. The slope ${⤪ d}(F_2^{αmma }/←pha )/{⤪ d ln} Q^2$ is measured to be $0.13_{-0.04}^{+0.06}$.
No description provided.
No description provided.
No description provided.
We have studied azimuthal correlations in singly-tagged e+e− → e+e−μ+μ− events at an average Q2 of 5.2 GeV2. The data were taken with the OPAL detector at LEP at e+e− centre-of-mass energies close to the Z0 mass, with an integrated luminosity of approximately 100 pb−1. The azimuthal correlations are used to extract the ratio $F_{B}^{αmma}/F_{2}^{αmma}$ of the QED structure functions $F_{B}^{αmma}(x,Q^{2})$ and $F_{2}^{αmma}(x,Q^{2})$ of the photon. In leading order and neglecting the muon mass $F_{B}^{αmma}$ is expected to be identical to the longitudinal structure function $F_{L}^{αmma}$. The measurement of $F_{B}^{αmma}/F_{2}^{αmma}$ is found to be significantly different from zero and to be consistent with the QED prediction.
No description provided.
First results on inclusive D0 and D* production in deep inelastic $ep$ scattering are reported using data collected by the H1 experiment at HERA in 1994. Differential cross sections are presented for both channels and are found to agree well with QCD predictions based on the boson gluon fusion process. A charm production cross section for 10GeV$~2\le Q~2\le100$GeV$~2$ and $0.01\le y\le0.7$ of $\sigma\left(ep\rightarrow c\overlinecX\right) = (17.4 \pm 1.6 \pm 1.7 \pm 1.4)$nb is derived. A first measurement of the charm contribution F2_charm(x,Q~2) to the proton structure function for Bjorken $x$ between $8\cdot10~{-4}$ and $8\cdot10~{-3}$ is presented. In this kinematic range a ratio F2_charm/F2= 0.237\pm0.021{+0.043\atop-0.039}$ is observed.
Inclusive D meson production cross sections. The second systematc error represents the model uncertainty.
Inclusive charm meson cross section averaged for the two processes. The second systematc error represents the model uncertainty.
Ratio of cross sections of D0 and D* production.
We present measurements of the structure function \Ft\ in $e~+p$ scattering at HERA in the range $3.5\;\Gevsq < \qsd < 5000\;\Gevsq$. A new reconstruction method has allowed a significant improvement in the resolution of the kinematic variables and an extension of the kinematic region covered by the experiment. At $ \qsd < 35 \;\Gevsq$ the range in $x$ now spans $6.3\cdot 10~{-5} < x < 0.08$ providing overlap with measurements from fixed target experiments. At values of $Q~2$ above 1000 GeV$~2$ the $x$ range extends to 0.5. Systematic errors below 5\perc\ have been achieved for most of the kinematic region. The structure function rises as \x\ decreases; the rise becomes more pronounced as \qsd\ increases. The behaviour of the structure function data is well described by next-to-leading order perturbative QCD as implemented in the DGLAP evolution equations.
No description provided.
No description provided.
No description provided.
A new measurement of the proton structure function $F_2(x,Q~2)$ is reported for momentum transfers squared $Q~2$ between 1.5GeV$~2$ and 5000GeV$~2$ and for Bjorken $x$ between $3\cdot 10~{-5}$ and $0.32$ using data collected by the HERA experiment H1 in 1994. The data represent an increase in statistics by a factor of ten with respect to the analysis of the 1993 data. Substantial extension of the kinematic range towards low $Q~2$ and $x$ has been achieved using dedicated data samples and events with initial state photon radiation. The structure function is found to increase significantly with decreasing $x$, even in the lowest accessible $Q~2$ region. The data are well described by a Next to Leading Order QCD fit and the gluon density is extracted.
Data from shifted vertex sample.
Data from shifted vertex sample.
Data from shifted vertex sample.
The proton and deuteron structure functions F2p and F2d are measured in inelastic muon scattering with an average beam energy of 470 GeV. The data were taken at Fermilab experiment E665 during 1991 and 1992 using liquid hydrogen and deuterium targets. The F2 measurements are reported in the range 0.0008<x<0.6 and 0.2<Q2<75 GeV2. These are the first precise measurements of F2 in the low x and Q2 range of the data. In the high x range of the data where they overlap in x and Q2 with the measurements from NMC, the two measurements are in agreement. The E665 data also overlap in x with the DESY HERA data, and there is a smooth connection in Q2 between the two data sets. At high Q2 the E665 measurements are consistent with QCD-evolved leading twist structure function models. The data are qualitatively described by structure function models incorporating the hadronic nature of the photon at low Q2. The Q2 and the W dependence of the data measure the transition in the nature of the photon between a pointlike probe at high Q2 and a hadronic object at low Q2.
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We report on a measurement of the proton structure function $F_2$ in the range $3.5\times10~{-5}\leq x \leq 4\times10~{-3}$ and 1.5 ${\rm GeV~2} \leq Q~2 \leq15$ ${\rm GeV~2}$ at the $ep$ collider HERA operating at a centre-of-mass energy of $\sqrt{s} = 300$ ${\rm GeV}$. The rise of $F_2$ with decreasing $x$ observed in the previous HERA measurements persists in this lower $x$ and $Q~2$ range. The $Q~2$ evolution of $F_2$, even at the lowest $Q~2$ and $x$ measured, is consistent with perturbative QCD.
Data from shifted vertex analysis. Overall normalization error of 3% is notincluded.
Data from shifted vertex analysis. Overall normalization error of 3% is notincluded.
Data from shifted vertex analysis. Overall normalization error of 3% is notincluded.
The proton and deuteron structure functions F2p and F2d were measured in the kinematic range 0.006<x<0.6 and 0.5<Q~2<75 GeV~2, by inclusive deep inelastic muon scattering at 90, 120, 200 and 280 GeV. The measurements are in good agreement with earlier high precision results. The present and earlier results together have been parametrised to give descriptions of the proton and deuteron structure functions F2 and their uncertainties over the range 0.006<x<0.9.
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Low x domain.
We present a QCD analysis of the proton structure function $F_2$ measured by the H1 experiment at HERA, combined with data from previous fixed target experiments. The gluon density is extracted from the scaling violations of $F_2$ in the range $2\cdot 10~{-4}<x<3\cdot 10~{-2}$ and compared with an approximate solution of the QCD evolution equations. The gluon density is found to rise steeply with decreasing $x$.
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This paper presents an analysis of the inclusive properties of diffractive deep inelastic scattering events produced in $ep$ interactions at HERA. The events are characterised by a rapidity gap between the outgoing proton system and the remaining hadronic system. Inclusive distributions are presented and compared with Monte Carlo models for diffractive processes. The data are consistent with models where the pomeron structure function has a hard and a soft contribution. The diffractive structure function is measured as a function of $\xpom$, the momentum fraction lost by the proton, of $\beta$, the momentum fraction of the struck quark with respect to $\xpom$, and of $Q~2$. The $\xpom$ dependence is consistent with the form \xpoma where $a=1.30\pm0.08(stat)~{+0.08}_{-0.14}(sys)$ in all bins of $\beta$ and $Q~2$. In the measured $Q~2$ range, the diffractive structure function approximately scales with $Q~2$ at fixed $\beta$. In an Ingelman-Schlein type model, where commonly used pomeron flux factor normalisations are assumed, it is found that the quarks within the pomeron do not saturate the momentum sum rule.
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The inclusive A(e,e') cross section for $x \simeq 1$ was measured on $~2$H, C, Fe, and Au for momentum transfers $Q~2$ from 1-7 (GeV/c)$~2$. The scaling behavior of the data was examined in the region of transition from y-scaling to x-scaling. Throughout this transitional region, the data exhibit $\xi$-scaling, reminiscent of the Bloom-Gilman duality seen in free nucleon scattering.
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We present the structure function ratios F2(Li)/F2(D) and F2(C)/F2(D) measured in deep inelastic muon-nucleus scattering at a nominal incident muon energy of 200 GeV. The kinematic range 0.0001 < x < 0.7 and 0.01< Q~2 < 70 GeV~2 is covered. For values of $x$ less than $0.002$ both ratios indicate saturation of shadowing at values compatible with photoabsorption results.
Additional normalization error of 0.004 not included.
Data on F2(C)/F2(DEUT) merged with previous NMC data from Amaudruz et al. 1995, NP B441,3. (<a href=http://durpdg.dur.ac.uk/scripts/reacsearch.csh/TESTREAC/red+3106> RED = 3106 </a>). Additional normalization error of 0.004 not included.
A measurement is presented, using data taken with the H1 detector at HERA, of the contribution of diffractive interactions to deep-inelastic electron-proton scattering. The diffractive contribution to the proton structure function is evaluated as a function of the appropriate deep-inelastic scattering variables using a class of deep-inelastic ep scattering events with no hadronic energy flow in an interval of pseudo-rapidity adjacent to the proton beam direction. The dependence of this contribution on x-pomeron is consistent with both a diffractive interpretation and a factorisable ep diffractive cross section. A first measurement of the deep-inelastic structure of the pomeron in the form of a factorised structure function is presented. This structure function is observed to be consistent with scale invariance.
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The ratio of the deuteron to proton structure functions is measured at very small Bjorken x (down to 10–6) and for Q2>0.001 GeV2 from scattering of 470 GeV muons on liquid hydrogen and deuterium targets. The ratio F2n/F2p extracted from these measurements is found to be constant, at a value of 0.935±0.008±0.034, for x<0.01. This result suggests the presence of nuclear shadowing effects in the deuteron. The dependence of the ratio on Q2 is also examined; no significant variation is found.
F2(N) / F2(P) = 2F2(DEUT)/F2(P) - 1.
F2(N) / F2(P) = 2F2(DEUT)/F2(P) - 1. The systematic uncertainty in the Q**2 dependece is negligible as compared to the statistical uncertainty.
A measurement of the proton structure function $F_{\!2}(x,Q~2)$ is reported for momentum transfer squared $Q~2$ between 4.5 $GeV~2$ and 1600 $GeV~2$ and for Bjorken $x$ between $1.8\cdot10~{-4}$ and 0.13 using data collected by the HERA experiment H1 in 1993. It is observed that $F_{\!2}$ increases significantly with decreasing $x$, confirming our previous measurement made with one tenth of the data available in this analysis. The $Q~2$ dependence is approximately logarithmic over the full kinematic range covered. The subsample of deep inelastic events with a large pseudo-rapidity gap in the hadronic energy flow close to the proton remnant is used to measure the "diffractive" contribution to $F_{\!2}$.
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The gluon momentum density xg ( x , Q 2 ) of the proton was extracted at Q 2 = 20 GeV 2 for small values of x between 4 × 10 −4 and 10 −2 from the scaling violations of the proton structure function F 2 measured recently by ZEUS in deep inelastic neutral current ep scattering at HERA. The extraction was performed in two ways. Firstly, using a global NLO fit to the ZEUS data on F 2 at low x constrained by measurementsfrom NMC at larger x ; and secondly using published approximate methods for the solution of the GLAP QCD evolution equations. Consistent results are obtained. A substantial increase of the gluon density is found at small x in comparison with the NMC result obtained at larger values of x .
Values of F2 and slope of F2 obtained from fits to the ZEUS paper used in the extraction of the gluon momentum distributions.
Gluon momenta distribution at Q**2 = 20.
The ZEUS detector has been used to measure the proton structure functionF2. During 1993 HERA collided 26.7 GeV electrons on 820 GeV protons. The data sample corresponds to an integrated luminosity of 0.54 pb−1, representing a twenty fold increase in statistics compared to that of 1992. Results are presented for 7<Q2<104 GeV2 andx values as low as 3×10−4. The rapid rise inF2 asx decreases observed previously is now studied in greater detail and persists forQ2 values up to 500 GeV2.
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This paper presents our first measurement of the F 2 structure function in neutral-current, deep inelastic scattering using the ZEUS detector at HERA, the ep colliding beam facility at DESY. The data correspond to an integrated luminosity of 24.7 nb −1 . Results are presented for data in range of Q 2 from 10 GeV 2 to 4700 GeV 2 and Bjorken x down to 3.0 × 10 −4 . The F 2 structure function increases rapidly as x decreases.
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A measurement of the proton structure function F 2 ( x , Q 2 ) is presented with about 1000 neutral current deep inelastic scattering events for Bjorken x in the range x ⋍ 10 −2 – 10 −4 and Q 2 > 5 GeV 2 . The measurement is based on an integrated luminosity of 22.5 nb −1 recorded by the H1 detector in the first year of HERA operation. The structure function F 2 ( x , Q 2 ) shows a significant rise with decreasing x .
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We present measurements of the hadronic photon structure functionF2γ(x), in twoQ2 ranges with mean values of 5.9 GeV2 and 14.7 GeV2. The data were taken by the OPAL experiment at LEP, with\(\sqrt s\) close to theZ0 mass and correspond to an integratede+e− luminosity of 44.8 pb−1. In the context of a QCD-based model we find the quark transverse momentum cutoff separating the vector meson dominance (VMD) and perturbative QCD regions to be 0.27±0.10 GeV. We confirm that there is a significant pointlike component of the photon when the probe photon hasQ2>4 GeV2. Our measurements extend to lower values ofx than any previous experiment, and no increase ofF2γ(x) is observed.
Additional overall systematic error 5.9% not included.
Additional overall systematic error 5.9% not included.
The photon structure function F 2 has been measured at average Q 2 values of 73,160 and 390 ( GeV c ) 2 . We compare the x dependence of the Q 2 = 73 ( GeV c ) 2 data with theoretical expectations based on QCD. In addition we present results on the Q 2 evolution of the structure function for the intermediate x range (0.3⩽ x ⩽0.8). The results are consistent with QCD.
X dependence at Q**2 = 73 GeV**2 for light quark data.
X dependence at Q**2 = 73 GeV**2 for total data.
Photon structure function F2 for total data.
A high-statistics measurement of the differential cross-sections for neutrino-iron scattering in the wide-band neutrino beam at the CERN SPS is presented. Nucleon structure functions are extracted and theirQ2 evolution is compared with the predictions of quantum chromodynamics.
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We present a measurement of the hadronic structure function F 2 γ ( x , Q 2 ) of the photon in the Q 2 range from 10 to 100 GeV 2 . Data were taken with the PLUTO detector at the e + e - storage ring PETRA. This measurement and previous PLUTO measurements in the Q 2 range of 1.5 to 16 GeV 2 are compared with higher order QCD calculations. The structure function is consistent with the predicted log Q 2 behaviour when charm contributions are subtracted. The x dependence can be well described for 0.1 < x < 0.9 by the regularization scheme of Antoniadis and Grunberg. Within their scheme the data yield a value of Λ MS = 183 + 65/ −40( stat. ) + 46/ −36( sys. ) MeV for the QCD scale parameter.
Data read from graph.
Data read from graph.
Data read from graph.
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SIG(Q=L)/SIG(Q=T) ASSUMED TO BE 0.
SIG(Q=L)/SIG(Q=T) ASSUMED TO BE 0.
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