We report the first observation of diffractive $J/\psi(\to \mu^+\mu^-)$ production in $\bar pp$ collisions at $\sqrt{s}$=1.8 TeV. Diffractive events are identified by their rapidity gap signature. In a sample of events with two muons of transverse momentum $p_T^{\mu}>2$ GeV/$c$ within the pseudorapidity region $|\eta|<$1.0, the ratio of diffractive to total $J/\psi$ production rates is found to be $R_{J/\psi}= [1.45\pm 0.25]%$. The ratio $R_{J/\psi}(x)$ is presented as a function of $x$-Bjorken. By combining it with our previously measured corresponding ratio $R_{jj}(x)$ for diffractive dijet production, we extract a value of $0.59\pm 0.15$ for the gluon fraction of the diffractive structure function of the proton.
Diffractive to total J/psi production ratio.
Ratio of diffractive to total J/psi rate, per unit of the fractional momentum loss of the leading (anti)proton, and as a function of x-Bjorken of the struck parton of the (anti)proton adjacent to the rapidity gap and participating in the J/psi production.
Gluon fraction of the diffractive structure function of the (anti)proton.
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.
Differential cross section of leading neutron production.
The semi-inclusive leading neutron structure function for Q**2.
The semi-inclusive leading neutron structure function for Q**2.
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 parton distributions in the proton based on H1 data.
Data from the 2000 running period at Q**2 There is an additional 1.2 PCT overall normalisation uncertainty not included.
Data from the 2000 running period at Q**2 There is an additional 1.2 PCT overall normalisation uncertainty not included.
Data from the 2000 running period at Q**2 There is an additional 1.2 PCT overall normalisation uncertainty not included.
The inclusive production of D*(2010) mesons in deep-inelastic ep scattering is measured in the kinematic region of photon virtuality 100 < Q^2 < 1000 GeV^2 and inelasticity 0.02 < y < 0.7. Single and double differential cross sections for inclusive D* meson production are measured in the visible range defined by |eta(D*)| < 1.5 and p_T(D*) > 1.5 GeV. The data were collected by the H1 experiment during the period from 2004 to 2007 and correspond to an integrated luminosity of 351 pb^{-1}. The charm contribution, F_2^{ccbar}, to the proton structure function F_2 is determined. The measurements are compared with QCD predictions.
Total inclusive cross section for D*+- production.
Single differential cross section DSIG/DPT for D*+- production. The DSYS errors are the uncorrelated and correlated systematicuncertainties respectively.
Single differential cross section DSIG/DETARAP for D*+- production. The DSYS errors are the uncorrelated and correlated systematicuncertainties respectively.
The reduced cross sections for ep deep inelastic scattering have been measured with the ZEUS detector at HERA at three different centre-of-mass energies, 318, 251 and 225 GeV. From the cross sections, measured double differentially in Bjorken x and the virtuality, Q^2, the proton structure functions FL and F2 have been extracted in the region 5*10^-4 < x <0.007 and 20 < Q^2 < 130 GeV^2.
The reduced cross section at Q**2 = 24 GeV**2 for centre-of-mass energy 318.
The reduced cross section at Q**2 = 32 GeV**2 for centre-of-mass energy 318.
The reduced cross section at Q**2 = 45 GeV**2 for centre-of-mass energy 318.
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 are compared with theoretical models which apply to the transition region from photoproduction to deep inelastic scattering.
Reduced cross section as measured in the SVX data sample for Q**2 = 0.20 GeV**2. Additional 3 PCT luminosity uncertainty not included in the total error.
Reduced cross section as measured in the SVX data sample for Q**2 = 0.25 GeV**2. Additional 3 PCT luminosity uncertainty not included in the total error.
Reduced cross section as measured in the SVX data sample for Q**2 = 0.35 GeV**2. Additional 3 PCT luminosity uncertainty not included in the total error.
The production of D+- and D0 mesons has been measured with the ZEUS detector at HERA using an integrated luminosity of 133.6 pb-1. The measurements cover the kinematic range 5 < Q^2 < 1000 GeV^2, 0.02 < y < 0.7, 1.5 < p_T^D < 15 GeV and eta^D < 1.6. Combinatorial background to the D meson signals is reduced by using the ZEUS microvertex detector to reconstruct displaced secondary vertices. Production cross sections are compared with the predictions of next-to-leading-order QCD which is found to describe the data well. Measurements are extrapolated to the full kinematic phase space in order to obtain the open-charm contribution, F2^ccbar, to the proton structure function, F2.
Production cross section for (D+ + D-) mesons.
Production cross section for (D0 + DBAR0) mesons not originating from D*+- decays.
Measured D+- cross section as a function of Q**2.
Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 82 pb^{-1}. Charm has been tagged by reconstructing D^{*+}, D^0, D^{+} and D_s^+ (+ c.c.) charm mesons. The charm hadrons were measured in the kinematic range p_T(D^{*+},D^0,D^{+}) > 3 GeV, p_T(D_s^+)>2 GeV and |\eta(D)| < 1.6 for 1.5 < Q^2 < 1000 GeV^2 and 0.02 < y < 0.7. The production cross sections were used to extract charm fragmentation ratios and the fraction of c quarks hadronising into a particular charm meson in the kinematic range considered. The cross sections were compared to the predictions of next-to-leading-order QCD, and extrapolated to the full kinematic region in p_T(D) and \eta(D) in order to determine the open-charm contribution, F_2^{c\bar{c}}(x,Q^2), to the proton structure function F_2.
Production cross section for all D0 mesons, those not originating fom D* decays and those originating from D* decays.
Production cross section for additional D* mesons (not decaying to D0) and all D* mesons.
Production cross section for D+ mesons.
Measurements are presented of inclusive charm and beauty cross sections in e^+p collisions at HERA for values of photon virtuality 12 \le Q^2 \le 60 GeV^2 and of the Bjorken scaling variable 0.0002 \le x \le 0.005. 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 vertex detector. Values for the structure functions F_2^{c\bar{c}} and F_2^{b\bar{b}} are obtained. This is the first measurement of F_2^{b\bar{b}} in this kinematic range. The results are found to be compatible with the predictions of perturbative quantum chromodynamics and withprevious measurements of F_2^{c\bar{c}}.
Measured NC reduced cross section for charm quarks.
Measuredstructure function F2 for charm quarks.
Measured NC reduced cross section for BOTTOM quarks.
Measurements are presented of inclusive charm and beauty cross sections in e^+p collisions at HERA for values of photon virtuality Q^2 > 150 GeV^2 and of inelasticity 0.1 < y < 0.7. The charm and beauty fractions 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 vertex detector. The data are divided into four regions in Q^2 and Bjorken x, and values for the structure functions F_2^{c\bar{c}} and F_2^{b\bar{b}} are obtained. The results are found to be compatible with the predictions of perturbative quantum chromodynamics.
Charm fraction and cross section.
Bottom fraction and cross section.
The measured reduced neutral current charm cross sections and structure functions obtained using the NLO QCD fit correct for FL.
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