Forward pi^0 Production and Associated Transverse Energy Flow in Deep-Inelastic Scattering at HERA

Deep-inelastic positron-proton interactions at low values of Bjorken-x down to x \approx 4.10^-5 which give rise to high transverse momentum pi^0 mesons are studied with the H1 experiment at HERA. The inclusive cross section for pi^0 mesons produced at small angles with respect to the proton remnant (the forward region) is presented as a function of the transverse momentum and energy of the pi^0 and of the four-momentum transfer Q^2 and Bjorken-x. Measurements are also presented of the transverse energy flow in events containing a forward pi^0 meson. Hadronic final state calculations based on QCD models implementing different parton evolution schemes are confronted with the data.Comment: 27 pages, 8 figures and 3 table

Multi-Jet Event Rates in Deep Inelastic Scattering and Determination of the Strong Coupling Constant

Jet event rates in deep inelastic ep scattering at HERA are investigated applying the modified JADE jet algorithm. The analysis uses data taken with the H1 detector in 1994 and 1995. The data are corrected for detector and hadronization effects and then compared with perturbative QCD predictions using next-to-leading order calculations. The strong coupling constant alpha_S(M_Z^2) is determined evaluating the jet event rates. Values of alpha_S(Q^2) are extracted in four different bins of the negative squared momentum transfer~\qq in the range from 40 GeV2 to 4000 GeV2. A combined fit of the renormalization group equation to these several alpha_S(Q^2) values results in alpha_S(M_Z^2) = 0.117+-0.003(stat)+0.009-0.013(syst)+0.006(jet algorithm).Comment: 17 pages, 4 figures, 3 tables, this version to appear in Eur. Phys. J.; it replaces first posted hep-ex/9807019 which had incorrect figure 4

Measurement of Leading Proton and Neutron Production in Deep Inelastic Scattering at HERA

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.Comment: 30 pages, 9 figures, 2 tables, submitted to Eur. Phys.

Measurement of inclusive jet cross-sections at low Q 2 at HERA ∗

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 ET, in E 2 T/Q 2 and in pseudorapidity ηLAB. In most of the phase space these data are well described by QCD calculations in next-to-leading order (NLO) using a renormalization scale µR = ET. Significant discrepancies are observed only for jets in the proton beam direction with ET below 20 GeV and Q 2 below 20 GeV 2. Jet production in DIS is an ideal testing ground for perturbative QCD (pQCD). Experimental results on (multi) jet production at HERA and elsewhere cover a wide range of Q 2 and have been found to be well described by pQCD in next-to-leading order in the strong coupling constant αS. The study of inclusive jet production, in particular, gives access to a bigger phase space, and avoids phase space regions where pQCD calculations are infrared sensitive. The data presented here close the gap of inclusive jet production at Q 2 below 100 GeV 2. For details on the experimental measurement and on the theory predictions see [1] and references therein. Event Selection and Measured Observables The present analysis is based on a total integrated luminosity of 21.1 pb −1 of e +-p collision data collected with the H1 detector [2] in 96 and 97. DIS events are selected by requiring the presence in the electromagnetic calorimeter of an electron with E&gt; 10 GeV and with an angle above 157 o with respect to the proton beam direction. The kinematic range is then defined by requiring a virtuality Q 2 between 5 and 100 GeV 2 and an inelasticity y between 0.2 and 0.6, as determined from the scattered electron

Control and Mapping of X-Ray Emission in a Laser-Plasma Accelerator

International audienceWe show that the control and the mapping of the x-ray emission reveals unique features of the laser-plasma accelerator physics, including strong correlations between electron and x-ray beams, and density-dependence of electron injection position. (C) 2011 Optical Society of Americ

Measurement of charged particle multiplicity distributions in DIS at HERA and its implication to entanglement entropy of partons

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 $$\eta$$ 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 $$x_{\mathrm{bj}}$$ are converted to the hadron entropy $$S_{\mathrm{hadron}}$$, and predictions from a quantum entanglement model are tested

Measurement of Leading Neutron Production in Deep-Inelastic Scattering at HERA

The production of leading neutrons, where the neutron carries a large fraction x_L of the incoming proton's longitudinal momentum, is studied in deep-inelastic positron-proton scattering at HERA. The data were taken with the H1 detector in the years 2006 and 2007 and correspond to an integrated luminosity of 122 pb^{-1}. The semi-inclusive cross section is measured in the phase space defined by the photon virtuality 6 < Q^2 < 100 GeV^2, Bjorken scaling variable 1.5x10^{-4} < x < 3x10^{-2}, longitudinal momentum fraction 0.32 < x_L < 0.95 and neutron transverse momentum p_T < 0.2 GeV. The leading neutron structure function, F_2^{LN(3)}(Q^2,x,x_L), and the fraction of deep-inelastic scattering events containing a leading neutron are studied as a function of Q^2, x and x_L. Assuming that the pion exchange mechanism dominates leading neutron production, the data provide constraints on the shape of the pion structure function.Comment: 30 pages, 9 figure

Measurement of inclusive jet cross-sections in deep inelastic ep scattering at HERA

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 E_T below 20 GeV and Q^2 below 20 GeV^2. This corresponds to the region in which NLO corrections are largest and further improvement of the calculations is thus of particular interest.Comment: 20 pages, 4 figures and 3 table