The latest measurements of the cross sections for neutral and charged current deep inelastic scattering in e+/-p collisions at HERA with longitudinally polarised lepton beams are presented. The measured cross sections are compared with the predictions of the Standard Model. Next-to-leading-order QCD analyses of HERA data are also presented. The analyses yield the parton distribution functions of the proton and are extended to also extract electroweak parameters. The determinations from HERA are compared with those from LEP and the Tevatron.
HERA measurements of diffractive ep scattering - the quasi-elastic scattering of the photon in the proton colour field - are summarised. Emphasis is placed on the most recent data.
New precision measurements of inclusive diffractive deep-inelastic ep scattering interactions, performed by the H1 and ZEUS collaborations at the HERA collider, are discussed. A new set of diffractive parton distributions, determined from recent high precision H1 data, is presented.
This contribution covers three recent results on deep-inelastic scattering at HERA: (i) new measurements of the proton longitudinal structure function $F_L$ from H1 and ZEUS experiments, (ii) a dedicated NC cross section measurement from ZEUS in the region of high Bjorken $x$, and (iii) preliminary combination results of all HERA inclusive data published up to now by H1 and ZEUS, taking into account the experimental correlations between measurements.
This article summarizes a talk given at the International Symposium on Multiparticle Dynamics 1999 in Providence/USA. It provides an overview on the variety of measurements of the hadronic final state in jet production for deep-inelastic scattering and photoproduction at HERA.
Inclusive jet production in neutral and charged current deep inelastic scattering, in photoproduction and the transition region has been studied with the ZEUS and H1 detectors at HERA. The measurements have been compared to next-to-leading-order QCD calculations which are used to make determinations of the strong coupling constant.
A brief survey is given of recent HERA results in jet production and prompt photon production, together with the evaluation of the QCD coupling constant alpha_s.
Measurements of vector mesons at HERA allow a detailed study of diffractive and non-diffractive production mechanisms, fragmentation and decay branching ratios. Results are presented on hadronic resonance measurements. In addition, the first observation of two meson states at masses around 1500 MeV and 1700 MeV are reported using inclusive KsKs production in deep inelastic ep scattering in ZEUS at HERA.
Recent results from the \emph{ep} collier HERA are presented. Inclusive dijet cross sections have been measured in neutral current deep inelastic scattering, for virtualities of the exchanged boson in the range $125 < Q^{2} < 20\,000\; GeV^{2}$ and in photoproduction, $Q^{2} \sim 0 GeV^{2}$. The measurements are compared to perturbative QCD calculations at next-to-leading order.
Inclusive non-diffractive photoproduction of rho(770)^0, K^*(892)^0 and phi(1020) mesons is investigated with the H1 detector in ep collisions at HERA. The corresponding average γp centre-of-mass energy is 210 GeV. The mesons are measured in the transverse momentum range 0.5<p_T<7 GeV and the rapidity range |y_{lab}|<1. Differential cross sections are presented as a function of transverse momentum and rapidity, and are compared to the predictions of hadroproduction models.
A simultaneous NLO QCD fit of the parton density functions (PDFs) of the proton and of the strong coupling $α_{S}(M_{Z})$ is presented. The analysis is based on combined H1 and ZEUS inclusive DIS cross section measurements together with inclusive jet cross section measurements provided by both H1 and ZEUS collaborations. The inclusion of the jet data significantly reduces the correlation between the gluon PDF and the strong coupling, improving the precision of the gluon PDF and providing an accurate determination of $α_{S}(M_{Z})$ using DIS data from HERA only.
A combination is presented of the inclusive deep inelastic cross sections measured by the H1 and ZEUS Collaborations in neutral and charged current unpolarised ep scattering at HERA during the period 1994-2000. The data span six orders of magnitude in negative four-momentum-transfer squared, Q^2, and in Bjorken x. The combination method used takes the correlations of systematic uncertainties into account, resulting in an improved accuracy. The combined data are the sole input in a NLO QCD analysis which determines a new set of parton distributions, HERAPDF1.0, with small experimental uncertain…
Recent precision measurements of diffractive neutral current deep inelastic ep scattering are performed by the H1 and ZEUS Collaborations at the HERA collider in a wide range of photon virtuality Q2. The first measurements of the large rapidity gap cross sections in charged current processes at high Q2 are also presented. The results are compared with model predictions based on parton density functions obtained from a DGLAP QCD fit to the data.
In this article, recent measurements of diffraction in deep inelastic scattering are presented along with QCD fits to extract the partonic structure of the exchange. These so-called diffractive parton density functions can then be used in predictions for other processes to test factorisation in diffraction. This is an important verification of QCD and has significance for predicting exotic signals such as diffractive Higgs production at the LHC.
The diffractive dissociation of virtual photons, gamma*p -> Xp, has been studied in ep interactions at HERA with the H1 and ZEUS detectors. The data are presented in terms of the diffractive structure function F2D and of the diffractive cross sections dsigma/dt and dsigma/dMX. The t-dependence of the cross section is measured. The Pomeron intercepts extracted from diffractive and inclusive ep interactions are compared. The result is further interpreted studying the dependence of the ratio between the diffractive to the inclusive cross section on the photon-proton center of mass energy. Recent …
The diffractive dissociation of virtual photons, gamma*p -> Xp, has been studied with the ZEUS detector at HERA by requiring a large rapidity gap between X and the outgoing proton, by analysing the mass distribution, M_X, of the hadronic final state, as well as by directly tagging the proton. At low values of the proton momentum loss, the diffractive structure function measurements obtained with the three methods are consistent, provided the different treatment and contributions of proton-dissociative events are taken into account.
The photoproduction of isolated photons, both inclusive and together with a jet, has been measured with the ZEUS detector at HERA using an integrated luminosity of $374\, \mathrm{pb}^{-1}$. Differential cross sections are presented in the isolated-photon transverse-energy and pseudorapidity ranges $6 < E_T^γ< 15$ GeV and $-0.7 < η^γ< 0.9,$ and for jet transverse-energy and pseudorapidity ranges $4 < E_T^{jet} < 35$ GeV and $-1.5 < η^{jet} < 1.8,$ for exchanged-photon virtualities $Q^2 < 1$ GeV$^2$. Differential cross sections are also presented for inclusive isolated-photon production as funct…
First inclusive measurements of isolated prompt photons in photoproduction at the HERA ep collider have been made with the ZEUS detector, using an integrated luminosity of 38.4 pb$^{-1}$. Cross sections are given as a function of the pseudorapidity and the transverse energy ($η^γ$, \eTg) of the photon, for $\eTg > $ 5 GeV in the $γp$ centre-of-mass energy range 134-285 GeV. Comparisons are made with predictions from Monte Carlo models having leading-logarithm parton showers, and with next-to-leading-order QCD calculations, using currently available parameterisations of the photon structure. Fo…
The single-inclusive cross-section for jet production in deep inelastic e-p scattering (DIS) at HERA is measured for photon virtualities Q^2 between 5 and 100 GeV^2, differentially in Q^2, in transverse jet energy E_T, in E_T^2/Q^2 and in pseudorapidity eta_LAB. In most of the phase space these data are well described by QCD calculations in next-to-leading order (NLO) using a renormalization scale mu_R=E_T. Significant discrepancies are observed only for jets in the proton beam direction with E_T below 20 GeV and Q^2 below 20 GeV^2.
Inclusive K0SK0S production in ep collisions at HERA was studied with the ZEUS detector using an integrated luminosity of 0.5 fb-1. Enhancements in the mass spectrum were observed and are attributed to the production of f2(1270)/a02(1320), f'2(1525) and f0(1710). Masses and widths were obtained using a fit which takes into account theoretical predictions based on SU(3) symmetry arguments, and are consistent with the PDG values. The f0(1710) state, which has a mass consistent with a glueball candidate, was observed with a statistical significance of 5 standard deviations. However, if this state…
A measurement of the inclusive deep-inelastic neutral current e+p scattering cross section is reported in the region of four-momentum transfer squared, 12<=Q^2<=150 GeV^2, and Bjorken x, 2x10^-4<=x<=0.1. The results are based on data collected by the H1 Collaboration at the ep collider HERA at positron and proton beam energies of E_e=27.6 GeV and E_p=920 GeV, respectively. The data are combined with previously published data, taken at E_p=820 GeV. The accuracy of the combined measurement is typically in the range of 1.3-2%. A QCD analysis at next-to-leading order is performed to determine the …
A measurement of the inclusive ep scattering cross section is presented in the region of low momentum transfers, 0.2 GeV^2 < Q^2 < 12 GeV^2, and low Bjorken x, 5x10^-6 < x < 0.02. The result is based on two data sets collected in dedicated runs by the H1 Collaboration at HERA at beam energies of 27.6 GeV and 920 GeV for positrons and protons, respectively. A combination with data previously published by H1 leads to a cross section measurement of a few percent accuracy. A kinematic reconstruction method exploiting radiative ep events extends the measurement to lower Q^2 and larger x. The data a…
The inclusive photoproduction of D\ast mesons and of D\ast-tagged dijets is investigated with the H1 detector at the ep collider HERA. The kinematic region covers small photon virtualities Q2 < 2 GeV2 and photon-proton centre-of-mass energies of 100 < Wgp < 285 GeV. Inclusive D\ast meson differential cross sections are measured for central rapidities |eta(D\ast)| < 1.5 and transverse momenta pT (D\ast) > 1.8 GeV. The heavy quark production process is further investigated in events with at least two jets with transverse momentum pT (jet) > 3.5 GeV each, one containing the D\ast meson. Different…
HERA jet data, in addition to combined HERA inclusive data, are input to the HERAPDF NLO QCD analysis in order to further constrain the gluon PDF and to allow an accurate evaluation of $α_S(M_Z)$
A combination of the inclusive diffractive cross section measurements made by the H1 and ZEUS Collaborations at HERA is presented. The analysis uses samples of diffractive deep inelastic ep scattering data at a centre-of-mass energy sqrt(s) = 318 GeV where leading protons are detected by dedicated spectrometers. Correlations of systematic uncertainties are taken into account, resulting in an improved precision of the cross section measurement which reaches 6% for the most precise points. The combined data cover the range 2.5 < Q2 < 200 GeV2 in photon virtuality, 0.00035 < xIP < 0.09 in proton …
Inclusive-jet and dijet differential cross sections have been measured in neutral current deep inelastic ep scattering for exchanged boson virtualities Q2 > 125 GeV2 with the ZEUS detector at HERA using an integrated luminosity of 82 pb-1. Jets were identified in the Breit frame using the kt cluster algorithm. Jet cross sections are presented as functions of several kinematic and jet variables. The results are also presented in different regions of Q2. Next-to-leading-order QCD calculations describe the measurements well. Regions of phase space where the theoretical uncertainties are small hav…
The H1 and Zeus collaborations have measured the inclusive diffractive DIS cross section ep -> eXp and these measurements are in good agreement within a normalisation uncertainty. Diffractive parton density functions (DPDFs) have been extracted from NLO QCD fits to inclusive measurements of diffractive DIS and the predictions of these DPDFs are compared with measurements of diffractive dijets in DIS, testing the validity of the factorisation approximations used in their extraction. H1 then use these diffractive dijets in DIS data to provide further constraints in a combined QCD fit, resulting …
Inclusive production cross sections are measured in deep inelastic scattering at HERA for meson states composed of a charm quark and a light antiquark or the charge conjugate. The measurements cover the kinematic region of photon virtuality 2 < Q^2 < 100 GeV^2, inelasticity 0.05 < y < 0.7, D meson transverse momenta p_t(D) > 2.5 GeV and pseudorapidity |eta(D)| < 1.5. The identification of the D-meson decays and the reduction of the combinatorial background profit from the reconstruction of displaced secondary vertices by means of the H1 silicon vertex detector. The production of charmed mesons…
A new ZEUS measurement of inclusive-jet and dijet cross-sections in the Breit frame performed in deep-inelastic ep scattering data is presented. The data correspond to an integrated luminosity of about 82 ${\rm pb^{-1}}$ and are resctricted to the kinematic regime $Q^2 >$125${\rm GeV^2}$ and -0.65$< \cosγ_{had} <$0.65, where $Q^2$ is the photon virtuality and $\cosγ_{had}$ corresponds to the polar angle of the hadronic system. The cross-sections are measured as functions of various kinematic and jet observables and are compared to NLO QCD calculations which describe the data well within all un…
Inclusive ep double differential cross sections for neutral current deep inelastic scattering are measured with the H1 detector at HERA. The data were taken with a lepton beam energy of 27.6 GeV and two proton beam energies of Ep = 460 and 575 GeV corresponding to centre-of-mass energies of 225 and 252 GeV, respectively. The measurements cover the region of 6.5 *10^{-4}<=x<= 0.65 for 35<=Q^2<=800 GeV^2 up to y = 0.85. The measurements are used together with previously published H1 data at Ep = 920 GeV and lower Q2 data at Ep = 460, 575 and 920 GeV to extract the longitudinal proton structure f…
Recent measurements of inclusive and semi-inclusive measurements from the HERA collaborations are presented. The measurements include neutral current structure functions $F_2$, $F_L$ and $xF_3$; the charged current cross section including first measurements of the dependence on electron polarisation; and measurements of the heavy quark structure functions $F_2^{c\bar{c}}$ and $F_2^{b\bar{b}}$.
Inclusive jet cross sections are measured in photoproduction at HERA using the H1 detector. The data sample of e+ p -> e+ + jet + X events in the kinematic range of photon virtualities Q^2 < 1 GeV^2 and photon-proton centre-of-mass energies 95 < W_gammap < 285 GeV represents an integrated luminosity of 24.1 pb^-1. Jets are defined using the inclusive k_T algorithm. Single- and multi-differential cross sections are measured as functions of jet transverse energy E_T^jet and pseudorapidity η^jet in the domain 5 < E_T^jet < 75 GeV and -1 < η^jet < 2.5. The cross sections are found to be in good ag…
Inclusive photoproduction cross-sections of the neutral mesons eta, rho^0, f_0(980) and f_2(1270) have been measured by H1 and compared to the photoproduction of pi^+ in ep collisions at HERA. Also, inclusive KsKs production and evidence for a narrow baryonic state decaying to Ksp have been observed by ZEUS at HERA.
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 10 GeV$^2\le Q^2\le100$~GeV$^2$ and $0.01\le y\le0.7$ of $σ(ep\to c\barcX) = (17.4 \pm 1.6 \pm 1.7 \pm 1.4)$~nb is derived. A first measurement of the charm contribution F2_charm(x,Q^2) to the proton structure function for Bjorken $x$ between $8\cdot10^{-4}$ …
In this talk, I present the brand new results from the H1 and ZEUS Collaborations on the combination of all previously published inclusive deep inelastic cross sections at HERA for neutral and charged current $e^\pm p$ scattering for zero beam polarisation and the corresponding parton distributions functions, HERAPDF 2.0, at up to next-to-next-to-leading order (NNLO). The results also include a new precise determination at next-to-leading order (NLO) of the strong coupling constant $α_s(M^2_Z)=0.1184\pm 0.0016$ (excluding scale uncertainties) based on a simultaneous fit to the combined inclusi…
Inclusive jet differential cross sections have been measured in neutral current deep inelastic e+p scattering for boson virtualities Q**2>125 GeV**2. The data were taken using the ZEUS detector at HERA and correspond to an integrated luminosity of 38.6 pb-1. Jets were identified in the Breit frame using the longitudinally invariant K_T cluster algorithm. Measurements of differential inclusive jet cross sections are presented as functions of jet transverse energy (E_T,jet), jet pseudorapidity and Q**2, for jets with E_T,jet>8 GeV. Next-to-leading-order QCD calculations agree well with the measu…
Single- and double-differential inclusive dijet cross sections in neutral current deep inelastic ep scattering have been measured with the ZEUS detector using an integrated luminosity of 374 pb^-1. The measurement was performed at large values of the photon virtuality, Q^2, between 125 and 20000 GeV^2. The jets were reconstructed with the k_T cluster algorithm in the Breit reference frame and selected by requiring their transverse energies in the Breit frame, E_T,B^jet, to be larger than 8 GeV. In addition, the invariant mass of the dijet system, M_jj, was required to be greater than 20 GeV. T…
A measurement of inclusive jet cross-sections in deep-inelastic ep scattering at HERA is presented based on data with an integrated luminosity of 21.1 pb^-1. The measurement is performed for photon virtualities Q^2 between 5 and 100 GeV^2, differentially in Q^2, in the jet transverse energy E_T, in E_T^2/Q^2 and in the pseudorapidity eta_lab. With the renormalization scale mu_R = E_T, perturbative QCD calculations in next-to-leading order (NLO) give a good description of the data in most of the phase space. Significant discrepancies are observed only for jets in the proton beam direction with …
Differential photoproduction cross sections are measured for events containing D* mesons. The data were taken with the H1 detector at the ep collider HERA and correspond to an integrated luminosity of 51.1 pb-1. The kinematic region covers small photon virtualities Q^2 < 0.01 GeV^2 and photon-proton centre-of-mass energies of 171 < W_gammap < 256 GeV. The details of the heavy quark production process are further investigated in events with one or two jets in addition to the D* meson. Differential cross sections for D* jet production are determined and the correlations between the D* meson and …
Inclusive phi-meson production in neutral current deep inelastic e+p scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 45 pb^{-1}. The phi mesons were studied in the range 10<Q2<100 GeV2, where Q2 is the virtuality of the exchanged photon, and in restricted kinematic regions in the transverse momentum, p_T, pseudorapidity, eta, and the scaled momentum in the Breit frame, x_p. Monte Carlo models with the strangeness-suppression factor as determined by analyses of e+e- annihilation events overestimate the cross sections. A smaller value of the strangen…
Inclusive e\pmp single and double differential cross sections for neutral and charged current deep inelastic scattering processes are measured with the H1 detector at HERA. The data were taken at a centre-of-mass energy of \surds = 319GeV with a total integrated luminosity of 333.7 pb-1 shared between two lepton beam charges and two longitudinal lepton polarisation modes. The differential cross sections are measured in the range of negative fourmomentum transfer squared, Q2, between 60 and 50 000GeV2, and Bjorken x between 0.0008 and 0.65. The measurements are combined with earlier published u…
The inclusive cross section for the photoproduction of neutral pions has been measured as a function of the transverse momentum, rapidity, and Feynman x of the pizero mesons at an average photon--proton centre-of-mass energy of 208 GeV and for photon virtualities below Q^2=0.01 GeV^2. The pizero measurement extends the range covered by previous charged particle measurements at HERA by two units of rapidity in the photon direction down to a value of -5.5 in the gamma p centre-of-mass frame. The pizero transverse momentum distribution is well described over the whole measured range by a power la…
For the first time, differential inclusive-jet cross sections have been measured in neutral current deep inelastic ep scattering using the anti-kT and SIScone algorithms. The measurements were made for boson virtualities Q^2 > 125 GeV^2 with the ZEUS detector at HERA using an integrated luminosity of 82 pb^-1 and the jets were identified in the Breit frame. The performance and suitability of the jet algorithms for their use in hadron-like reactions were investigated by comparing the measurements to those performed with the kT algorithm. Next-to-leading-order QCD calculations give a good descri…
Differential inclusive-jet cross sections have been measured for different jet radii in neutral current deep inelastic ep scattering for boson virtualities Q^2 > 125 GeV^2 with the ZEUS detector at HERA using an integrated luminosity of 81.7 pb^-1. Jets were identified in the Breit frame using the k_T cluster algorithm in the longitudinally inclusive mode for different values of the jet radius R. Differential cross sections are presented as functions of Q^2 and the jet transverse energy, E_T,B^jet. The dependence on R of the inclusive-jet cross section has been measured for Q^2 > 125 and 500 G…
Recent measurements of inclusive and semi-inclusive deep inelastic scattering in electron-proton collisions at HERA are reviewed. These measurements are used to determine the parton distribution functions (PDFs) of the proton, a necessary input to theory predictions for hadron colliders. An introduction to the PDF determination with an emphasis on HERA PDFs is presented. Theory predictions based on HERAPDF are compared to a selection of recent LHC and Tevatron measurements. The impact of jet and charm production measurements on the PDFs is discussed.
A new measurement of the inclusive DIS ep cross section using H1 data from the year 2000 is performed and combined with published results using 1996/97 data. The new data covers the region of Q2 from 12 to 150 GeV2 at HERA with unprecedented accuracy. The structure Function F2 is extracted and studied. A QCD analysis, H1PDF 2009, is performed including the new and published H1 inclusive measurements.
Inclusive jet differential cross sections for the reaction e+ p --> e+ + jet + X with quasi-real photons have been measured with the ZEUS detector at HERA. These cross sections are given for the photon-proton centre-of-mass energy interval 134 < W < 277 GeV and jet pseudorapidity in the range -1 < eta(jet) < 2 in the laboratory frame. The results are presented for three cone radii in the eta-phi plane, R=1.0, 0.7 and 0.5. Measurements of dsigma/deta(jet) above various jet-transverse-energy thresholds up to 25 GeV and in three ranges of W are presented and compared to next-to-leading order (NLO…
Inclusive transverse momentum spectra of charged particles in photoproduction events in the laboratory pseudorapidity range $-1.2<η<1.4$ have been measured up to $p_{T}=8\GeV $ using the ZEUS detector. Diffractive and non--diffractive reactions have been selected with an average $γp$ centre of mass (c.m.) energy of $\langle W \rangle = 180\GeV$. For diffractive reactions, the $p_{T}$ spectra of the photon dissociation events have been measured in two intervals of the dissociated photon mass with mean values $\langle M_{X} \rangle = 5$ GeV and $10$ GeV. The inclusive transverse momentum spectra…
The ZEUS inclusive cross-section data from HERA-I, for charged and neutral current processes, taken with $e^+$ and $e^-$ beams, have been used in a new NLO QCD analysis to extract the parton distribution functions (PDFs) of the proton within a single experiment. The precision of the high-$x$ gluon determination is improved by using ZEUS differential cross-section data on inclusive jet production in $e^+p$ scattering and di-jet production in $γ-p$ scattering
A QCD fit analysis to the combined HERA-I inclusive deep inelastic cross sections measured by the H1 and ZEUS collaborations for $e^\pm p$ scattering resulting into a competitive NLO PDF set, HERAPDF1.0 is presented. HERAPDF at NNLO fits are presented as well, resulting, however, in a worse description of the combined HERA data. In addition, a preliminary analysis including the HERA II measurements of lower proton-beam energies is performed. The effect of including the new data on the determination of HERA parton distribution functions is analysed, using fits similar to those performed for HER…
The first measurement of inclusive Ds+- photoproduction at HERA has been performed with the ZEUS detector for photon-proton centre-of-mass energies 130 < W < 280 GeV. The measured cross section for 3 < pt(Ds) < 12 GeV and |eta(Ds)|< 1.5 is sigma(ep -> Ds X) = 3.79 +- 0.59 (stat.) +0.26-0.46 (syst.) +- 0.94 (br.) nb, where the last error arises from the uncertainty in the Ds decay branching ratio. The measurements are compared with inclusive D*+- photoproduction cross sections in the same kinematic region and with QCD calculations. The Ds cross sections lie above a fixed-order next-to-leading o…
Inclusive jet cross sections in photoproduction for events containing a $D^*$ meson have been measured with the ZEUS detector at HERA using an integrated luminosity of $78.6 {\rm pb}^{-1}$. The events were required to have a virtuality of the incoming photon, $Q^2$, of less than 1 GeV$^2$, and a photon-proton centre-of-mass energy in the range $130<W_{γp}<280 {\rm GeV}$. The measurements are compared with next-to-leading-order (NLO) QCD calculations. Good agreement is found with the NLO calculations over most of the measured kinematic region. Requiring a second jet in the event allowed a more …
A measurement of inclusive charged particle distributions in deep inelastic $ep$ scattering for $γ^* p$ centre-of-mass energies $75< W < 175$~GeV and momentum transfer squared $10< Q^2 < 160$~GeV$^2$ from the ZEUS detector at HERA is presented. The differential charged particle rates in the $γ^* p$ centre-of-mass system as a function of the scaled longitudinal momentum, $x_F$, and of the transverse momentum, $p_t^*$ and $<\!\!p_t^{*\,2}\!\!>\,\,$ , as a function of $x_F$, $W$ and $Q^2$ are given. Separate distributions are shown for events with (LRG) and without (NRG) a rapidity gap with respe…
Previously published data on inclusive neutral and charged current e+p and e-p deep inelastic scattering from HERA have been combined. The new, model-independent method of combining the measured cross sections takes full account of correlated systematics in a coherent way, leading to significantly reduced uncertainties in the combined measurement across the (x, Q^2) plane. The combined cross section data have been used as the sole input for a new next-to-leading order QCD fit to extract the parton distribution functions (PDFs) of the proton. The PDFs extracted have greatly reduced experimental…
The H1 and ZEUS Collaborations have performed new next-to-leading order QCD analyses to determine the parton density functions of the proton. QCD fits are performed using inclusive neutral and charged deep inelastic scattering cross sections from HERA-I. The fits include a full treatment of experimental systematic uncertainties, taking into account point-to-point correlations. The extracted parton densities are in agreement with those from global fits. Since HERA inclusive data provide no direct information on the high-x gluon, an independent fit has been performed by the ZEUS Collaboration in…
We calculate the cross section of J/psi plus jet associated production in ep deep-inelastic scattering within the factorization formalism of nonrelativistic quantum chromodynamics. Our analytic results disagree with previous analyses, both for the colour-singlet and colour-octet channels. Our theoretical predictions agree reasonably well with recent data taken by the H1 Collaboration at DESY HERA, significantly better than those obtained within the colour-singlet model.
Inclusive photoproduction of D*+- mesons has been measured for photon-proton centre-of-mass energies in the range 130 < W < 280 GeV and a photon virtuality Q^2 < 1 GeV^2. The data sample used corresponds to an integrated luminosity of 37 pb^-1. Total and differential cross sections as functions of the D* transverse momentum and pseudorapidity are presented in restricted kinematical regions and the data are compared with next-to-leading order (NLO) perturbative QCD calculations using the "massive charm" and "massless charm" schemes. The measured cross sections are generally above the NLO calcul…
Recent ZEUS measurements of inclusive-jet and dijet cross sections in neutral current deep inelastic ep scattering at HERA are presented. The data correspond to more than a two-fold increase in statistics compared to previous studies. The cross sections are measured in the Breit frame, for boson virtualities of Q^2 > 125 GeV^2, as functions of various kinematic and jet observables. The data are found to be well described by NLO QCD and have the potential to constrain the gluon density in the proton. Two new extractions of the strong coupling, alpha_s, are also presented: the first is determine…
We investigate the effect of including the HERA run I + II combined cross section data on the MMHT2014 PDFs. We present the fit quality within the context of the global fit and when only the HERA data are included. We examine the changes in both the central values and uncertainties in the PDFs. We find that the prediction for the data is good, and only relatively small improvements in $χ^2$ and changes in the PDFs are obtained with a refit at both NLO and NNLO. PDF uncertainties are slightly reduced. There is a small dependence of the fit quality on the value of $Q^2_{\min}$.
Recent results on diffraction at HERA are presented, focusing on the measurement of the inclusive diffractive cross section and on the study of two and three jets in diffractive ep scattering.
