With the H1 detector at the ep collider HERA, D* meson production cross sections have been measured in deep inelastic scattering with four-momentum transfers Q^2>2 GeV2 and in photoproduction at energies around W(gamma p)~ 88 GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe the differential cross sections within theoretical and experimental uncertainties. Using these calculations, the NLO gluon momentum distribution in the proton, x_g g(x_g), has been extracted in the momentum fraction range 7.5x10^{-4}< x_g <4x10^{-2} at average scales mu^2 =25 to 50 GeV2. The gluon momentum fraction x_g has been obtained from the measured kinematics of the scattered electron and the D* meson in the final state. The results compare well with the gluon distribution obtained from the analysis of scaling violations of the proton structure function F_2.
Total cross section for DIS D*+- production in the specified kinemtaic range.
DIS cross section as a function of the transverse D* momentum in the laboratory frame.
DIS cross section as a function of the transverse D* momentum in the hadronic centre-of-mass frame.
Single particles and jets in deeply inelastic scattering at low x are measured with the H1 detector in the region away from the current jet and towards the proton remnant, known as the forward region. Hadronic final state measurements in this region are expected to be particularly sensitive to QCD evolution effects. Jet cross-sections are presented as a function of Bjorken-x for forward jets produced with a polar angle to the proton direction, theta, in the range 7 < theta < 20 degrees. Azimuthal correlations are studied between the forward jet and the scattered lepton. Charged and neutral single particle production in the forward region are measured as a function of Bjorken-x, in the range 5 < theta < 25 degrees, for particle transverse momenta larger than 1 GeV. QCD based Monte Carlo predictions and analytical calculations based on BFKL, CCFM and DGLAP evolution are compared to the data. Predictions based on the DGLAP approach fail to describe the data, except for those which allow for a resolved photon contribution.
Forward Jet cross section. Axis error includes +- 7/7 contribution (Dependence of the model used to correct the data).
Forward Di-jet cross section. Axis error includes +- 7/7 contribution (Dependence of the model used to correct the data).
Data from Figure 3a on charged particle production
A measurement of charm and beauty dijet photoproduction cross sections at the ep collider HERA is presented. Events are selected with two or more jets of transverse momentum $p_t^{jet}_{1(2)}>11(8)$ GeV in the central range of pseudo-rapidity $-0.9<\eta^{jet}_{1(2)}<1.3$. The fractions of events containing charm and beauty quarks are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 central vertex detector. Differential dijet cross sections for charm and beauty, and their relative contributions to the flavour inclusive dijet photoproduction cross section, are measured as a function of the transverse momentum of the leading jet, the average pseudo-rapidity of the two jets and the observable $x_{\gamma}^{obs}$. Taking into account the theoretical uncertainties, the charm cross sections are consistent with a QCD calculation in next-to-leading order, while the predicted cross sections for beauty production are somewhat lower than the measurement.
Total dijet CHARM cross section in the defined kinematic range.
Total dijet BOTTOM cross section in the defined kinematic range.
Measured CHARM cross section as a function of PT.
The production of forward jets has been measured in deep inelastic ep collisions at HERA. The results are presented in terms of single differential cross sections as a function of the Bjorken scaling variable (x_{Bj}) and as triple differential cross sections d^3 \sigma / dx_{Bj} dQ^2 dp_{t,jet}^2, where Q^2 is the four momentum transfer squared and p_{t,jet}^2 is the squared transverse momentum of the forward jet. Also cross sections for events with a di-jet system in addition to the forward jet are measured as a function of the rapidity separation between the forward jet and the two additional jets. The measurements are compared with next-to-leading order QCD calculations and with the predictions of various QCD-based models.
Single differential forward jet cross section as a function of Bjorken X.
Triple differential cross section.
Triple differential cross section.
Differential dijet cross sections are measured in photoproduction in the region of photon virtualities Q^2 < 1 GeV^2 with the H1 detector at the HERA ep collider using an integrated luminosity of 66.6 pb^{-1}. Jets are defined with the inclusive k_T algorithm and a minimum transverse momentum of the leading jet of 25 GeV is required. Dijet cross sections are measured in direct and resolved photon enhanced regions separately. Longitudinal proton momentum fractions up to 0.7 are reached. The data compare well with predictions from Monte Carlo event generators based on leading order QCD and parton showers and with next-to-leading order QCD calculations corrected for hadronisation effects.
Bin averaged cross sections for dijet photoproduction shown separately for high and low X(C=GAMMA).
Bin averaged cross sections for dijet photoproduction shown separately for high and low X(C=GAMMA) and for dijet mass > 65 GeV.
Bin averaged cross sections for dijet photoproduction shown separately for high and low XP.
The production of neutral strange hadrons is investigated using deep-inelastic scattering events measured with the H1 detector at HERA. The measurements are made in the phase space defined by the negative four-momentum transfer squared of the photon 2 < Q^2 < 100 GeV^2 and the inelasticity 0.1 < y < 0.6. The K_s and Lambda production cross sections and their ratios are determined. K_s production is compared to the production of charged particles in the same region of phase space. The Lambda - anti-Lambda asymmetry is also measured and found to be consistent with zero. Predictions of leading order Monte Carlo programs are compared to the data.
Visible cross section for the production of K0S and LAMBDA(BAR).
Ratio of strange baryon to meson production.
Ratio of K0S to charged hadron production.
Measurements are reported of the production of dijet events with a leading neutron in ep interactions at HERA. Differential cross sections for photoproduction and deep inelastic scattering are presented as a function of several kinematic variables. Leading order QCD simulation programs are compared with the measurements. Models in which the real or virtual photon interacts with a parton of an exchanged pion are able to describe the data. Next-to-leading order perturbative QCD calculations based on pion exchange are found to be in good agreement with the measured cross sections. The fraction of leading neutron dijet events with respect to all dijet events is also determined. The dijet events with a leading neutron have a lower fraction of resolved photon processes than do the inclusive dijet data.
Differential e p photoproduction cross section as a function of the jet transverse energy.
Differential e p photoproduction cross section as a function of JET pseudorapidity.
Differential e p photoproduction cross section as a function of JET X(C=GAMMA).
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