Charged particle multiplicity distributions in positron-proton deep inelastic scattering at a centre-of-mass energy $\sqrt{s}=319$ GeV are measured. The data are collected with the H1 detector at HERA corresponding to an integrated luminosity of $136$ pb${}^{-1}$. Charged particle multiplicities are measured as a function of photon virtuality $Q^2$, inelasticity $y$ and pseudorapidity $η$ in the laboratory and the hadronic centre-of-mass frames. Predictions from different Monte Carlo models are compared to the data. The first and second moments of the multiplicity distributions are determined and the KNO scaling behaviour is investigated. The multiplicity distributions as a function of $Q^2$ and the Bjorken variable $x_{\rm Bj}$ are converted to the hadron entropy $S_{\rm hadron}$, and predictions from a quantum entanglement model are tested.
We present the design and commissioning of a new multiplicity veto for the HERA-B detector, a fixed-target spectrometer originally designed to study the physics of B mesons in proton-nucleus interactions. The HERA-B trigger is a message-driven multi-level track trigger. The first level trigger (FLT) consists of custom-made electronics, and the higher trigger levels are implemented as PC farms. The multiplicity veto has been designed to reject high-multiplicity events before they enter the trigger chain. A veto signal is generated based on the comparison of the number of photons in part of the …
The azimuthal decorrelation angle between the leading jet and scattered lepton in deep inelastic scattering is studied with the ZEUS detector at HERA. The data was taken in the HERA II data-taking period and corresponds to an integrated luminosity of 330 $\rm{pb^{-1}}$. Azimuthal angular decorrelation has been proposed to study the $Q^{2}$ dependence of the evolution of the transverse momentum distributions (TMDs) and understand the small-$x$ region, providing unique insight to nucleon structure. Previous decorrelation measurements of two jets have been performed in proton-proton collisions at…
We study the proposal by Kharzeev-Levin to determine entanglement entropy in Deep Inelastic Scattering (DIS) from parton distribution functions (PDFs) and to relate the former to the entropy of final state hadrons. We find several uncertainties in the current comparison to data, in particular the overall normalization, the relation between charged versus total hadron multiplicity in the comparison to experimental results as well as different methods to determine the number of partons in Deep Inelastic Scattering. We further provide a comparison to data based on leading order HERA PDF as well a…
We provide quantitative predictions for the rapidity, centrality and energy dependencies of inclusive charged-hadron productions for the forthcoming LHC measurements in nucleus-nucleus collisions based on the idea of gluon saturation in the color-glass condensate framework. Our formulation gives very good descriptions of the first data from the LHC for the inclusive charged-hadron production in proton-proton collisions, the deep inelastic scattering at HERA at small Bjorken-x, and the hadron multiplicities in nucleus-nucleus collisions at RHIC.
Collective behaviour of final-state hadrons, and multiparton interactions are studied in high-multiplicity $ep$ scattering at a centre-of-mass energy $\sqrt{s}=318$ GeV with the ZEUS detector at HERA. Two- and four-particle azimuthal correlations, as well as multiplicity, transverse momentum, and pseudorapidity distributions for charged-particle multiplicities $N_{\textrm ch} \geq 20$ are measured. The dependence of two-particle correlations on the virtuality of the exchanged photon shows a clear transition from photoproduction to neutral current deep inelastic scattering. For the multipliciti…
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 center-of-mass frame. The KNO-scaling properties of the data were investigated and the energy dependence of multiplicity distributions was studied using different energy scales. The data are compared to results obtained in e+e- collision…
Two-particle azimuthal correlations have been measured in neutral current deep $\mbox{inelastic}$ $\textit{ep}$ scattering with virtuality $Q^2 > 5$ GeV$^2$ at a centre-of-mass energy $\sqrt{s}=318$ GeV recorded with the ZEUS detector at HERA. The correlations of charged particles have been measured in the range of laboratory pseudorapidity $-1.5 < η< 2.0$ and transverse momentum $0.1 < p_{\textrm{T}}~< 5.0$ GeV and event multiplicities $N_{\textrm{ch}}$ up to six times larger than the average $\left< N_{\textrm{ch}} \right>\approx5$. The two-particle correlations have been measured in terms o…
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…
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…
This talk covers three contributions from H1: "Measurement of the inclusive e^\pm p scattering cross section at high inelasticity y and of the structure function F_L", "Determination of the integrated luminosity at HERA using elastic QED Compton events" and "Inclusive deep inelastic scattering at high Q2 with longitudinally polarized lepton beams at HERA". These are new measurements mainly based on the full HREA-II data but include also those from HERA-I in the combination whenever it is relevant. The main results of these measurements are briefly summarized here.
The final results on the combination of all inclusive deep-inelastic scattering cross section data from the H1 and ZEUS experiments at HERA are reviewed. The parton distribution functions (PDFs) extracted from these data (HERAPDF2.0) and from HERA data on heavy flavour production and jet production are also presented (HERAPDF2.0Jets). The use of various heavy flavour schemes is compared and the sensitivity of the data to cuts on Q2 is explored. When jet data are included in the fits, a competitive value of $α_s(M_Z)=0.1184 \pm 0.0016$ is extracted at NLO, excluding scale uncertainties
The forthcoming LHC measurement of hadron multiplicity in proton-nucleus collisions is a crucial test of the k_t factorization and gluon saturation based models. Here, we provide quantitative predictions for the pseudorapidity distribution of charged particles produced in minimum bias proton-nucleus collisions at the LHC based on the idea of gluon saturation in the color-glass condensate framework. Our formulation gives good descriptions of the LHC and RHIC data for the charged-hadron multiplicities in both proton-proton and nucleus-nucleus collisions, and also the deep inelastic scattering at…
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.
In this technical note we briefly present the analysis of the HERA polarimeters (transversal and longitudinal) as of summer 2011. We present the final reanalysis of the TPOL data, and discuss the systematic uncertainties. A procedure to combine and average LPOL and TPOL data is presented.
