The charged multiplicity distributions and the mean charged multiplicity have been investigated in inclusive neutral current deep inelastic $ep$ scattering with the ZEUS detector at HERA, using an integrated luminosity of 38.6 pb$^{-1}$. The measurements were performed in the current region of the Breit frame, as well as in the current fragmentation region of the hadronic centre-of-mass frame. The KNO-scaling properties of the data were investigated and the energy dependence was studied using different energy scales. The data are compared to results obtained in $\epem$ collisions and to previous DIS measurements as well as to leading-logarithm parton-shower Monte Carlo predictions.
Multiplicity distributions measured in the current region of the Breit frame for the bin of 2*E(Breit,current region) = 1.5 to 4.
Multiplicity distributions measured in the current region of the Breit frame for the bin of 2*E(Breit,current region) = 4 to 8.
Multiplicity distributions measured in the current region of the Breit frame for the bin of 2*E(Breit,current region) = 8 to 12.
Diffractive photoproduction of dijets was measured with the ZEUS detector at the ep collider HERA using an integrated luminosity of 77.2 pb-1. The measurements were made in the kinematic range Q^2 < 1 GeV^2, 0.20 < y < 0.85 and x_pom < 0.025, where Q^2 is the photon virtuality, y is the inelasticity and x_pom is the fraction of the proton momentum taken by the diffractive exchange. The two jets with the highest transverse energy, E_T^jet, were required to satisfy E_T^jet > 7.5 and 6.5 GeV, respectively, and to lie in the pseudorapidity range -1.5 < eta^jet < 1.5. Differential cross sections were compared to perturbative QCD calculations using available parameterisations of diffractive parton distributions of the proton.
Differential cross section DSIG/DY for diffractive photoproduction of dijets as a function of Y.
Differential cross section DSIG/DM(P=5_6_7) for diffractive photoproduction of dijets as a function of M(P=5_6_7).
Differential cross section DSIG/DX(NAME=POMERON) for diffractive photoproduction of dijets as a function of X(NAME=POMERON).
Jet cross sections were measured in charged current deep inelastic e+-p scattering at high boson virtualities Q^2 with the ZEUS detector at HERA II using an integrated luminosity of 0.36 fb^-1. Differential cross sections are presented for inclusive-jet production as functions of Q^2, Bjorken x and the jet transverse energy and pseudorapidity. The dijet invariant mass cross section is also presented. Observation of three- and four-jet events in charged-current e+-p processes is reported for the first time. The predictions of next-to-leading-order (NLO) QCD calculations are compared to the measurements. The measured inclusive-jet cross sections are well described in shape and normalization by the NLO predictions. The data have the potential to constrain the u and d valence quark distributions in the proton if included as input to global fits.
Differential polarized inclusive jet cross sections as a function of jet pseudorapidity.
Differential polarized inclusive jet cross sections as a function of jet pseudorapidity.
Differential polarized inclusive jet cross sections as a function of jet transverse energy.
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.
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.
The double differential cross section for the 96-97 E+ P NC scattering data.
The double differential cross section for the 96-97 E+ P NC scattering data.
The double differential cross section for the 96-97 E+ P NC scattering data.
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.
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Mean values and differential distributions of event-shape variables have been studied in neutral current deep inelastic scattering using an integrated {luminosity} of 82.2 pb$^{-1}$ collected with the ZEUS detector at HERA. The kinematic range was $80 < Q^2 < 20 480\gev^2$ and $0.0024 < x < 0.6$, where $Q^2$ is the virtuality of the exchanged boson and $x$ is the Bjorken variable. The data are compared with a model based on a combination of next-to-leading-order QCD calculations with next-to-leading-logarithm corrections and the Dokshitzer-Webber non-perturbative power corrections. The power-correction method provides a reasonable description of the data for all event-shape variables studied. Nevertheless, the lack of consistency of the determination of $\alpha_s$ and of the non-perturbative parameter of the model, $\albar$, suggests the importance of higher-order processes that are not yet included in the model.
Mean value of the event shape variable 1-THRUST(C=T).
Mean value of the event shape variable B(C=T).
Mean value of the event shape variable RHO**2.
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.
Measurement of the proton structure function F2 at Q**2 = 2.7 GeV**2.
Measurement of the proton structure function F2 at Q**2 = 4.0 GeV**2.
Measurement of the proton structure function F2 at Q**2 = 6.0 GeV**2.
Deep inelastic scattering and its diffractive component, $ep \to e^{\prime}\gamma^* p \to e^{\prime}XN$, have been studied at HERA with the ZEUS detector using an integrated luminosity of 52.4 pb$^{-1}$. The $M_X$ method has been used to extract the diffractive contribution. A wide range in the centre-of-mass energy $W$ (37 -- 245 GeV), photon virtuality $Q^2$ (20 -- 450 GeV$^2$) and mass $M_X$ (0.28 -- 35 GeV) is covered. The diffractive cross section for $2 < M_X < 15$ GeV rises strongly with $W$, the rise becoming steeper as $Q^2$ increases. The data are also presented in terms of the diffractive structure function, $F^{\rm D(3)}_2$, of the proton. For fixed $Q^2$ and fixed $M_X$, $\xpom F^{\rm D(3)}_2$ shows a strong rise as $\xpom \to 0$, where $\xpom$ is the fraction of the proton momentum carried by the Pomeron. For Bjorken-$x < 1 \cdot 10^{-3}$, $\xpom F^{\rm D(3)}_2$ shows positive $\log Q^2$ scaling violations, while for $x \ge 5 \cdot 10^{-3}$ negative scaling violations are observed. The diffractive structure function is compatible with being leading twist. The data show that Regge factorisation is broken.
Proton structure function F2 at Q**2 = 25 GeV**2.
Proton structure function F2 at Q**2 = 35 GeV**2.
Proton structure function F2 at Q**2 = 45 GeV**2.
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.
No description provided.
No description provided.
No description provided.
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