A measurement is presented of inelastic photo- and electroproduction of J/psi mesons in ep scattering at HERA. The data were recorded with the H1 detector in the period from 2004 to 2007. Single and double differential cross sections are determined and the helicity distributions of the J/psi mesons are analysed. The results are compared to theoretical predictions in the colour singlet model and in the framework of non-relativistic QCD. Calculations in the colour singlet model using a k_T factorisation ansatz are able to give a good description of the data, while colour singlet model calculations to next-to-leading order in collinear factorisation underestimate the data.
Measured differential photoproduction cross section as a function of the squared transverse momentum of the J/PSI.
Measured differential photoproduction cross section as a function of the elasticity of the J/PSI.
Measured photoproduction cross section as a function of the photon-proton centre of mass energy W.
The reaction gamma p -> p pi0 gamma' has been measured with the Crystal Ball / TAPS detectors using the energy-tagged photon beam at the electron accelerator facility MAMI-B. Energy and angular differential cross sections for the emitted photon gamma' and angular differential cross sections for the pi0 have been determined with high statistics in the energy range of the Delta+(1232) resonance. Cross sections and the ratio of the cross section to the non-radiative process gamma p -> p pi0 are compared to theoretical reaction models, having the anomalous magnetic moment kappa_Delta+ as free parameter. As the shape of the experimental distributions is not reproduced in detail by the model calculations, currently no extraction of kappa_Delta+ is feasible.
Total cross section for the background reaction GAMMA P --> P PI0.
Total cross section for the background reaction GAMMA P --> P PI0 PI0.
Angular distribution of the PI0 in the reaction GAMMA P --> P PI0 at beam energy 400 MeV. Inclusive measurement where only the PI0 decay photons are detected.
We present a measurement of the differential cross section for $t\bar{t}$ events produced in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV as a function of the transverse momentum ($p_T$) of the top quark. The selected events contain a high-$p_T$ lepton ($\ell$), four or more jets, and a large imbalance in $p_T$, and correspond to 1 fb${}^{-1}$ of integrated luminosity recorded with the D0 detector. Each event must have at least one candidate for a $b$ jet. Objects in the event are associated through a constrained kinematic fit to the $t\bar{t}\to WbW\bar{b} \to \ell\nu b q\bar{q}'\bar{b}$ process. Results from next-to-leading-order perturbative QCD calculations agree with the measured differential cross section. Comparisons are also provided to predictions from Monte Carlo event generators using QCD calculations at different levels of precision.
Total cross section for TOP TOPBAR production integrating over PT.
The inclusive PT spectra for TOP TOPBAR production.
The pseudorapidity density and multiplicity distribution of charged particles produced in proton-proton collisions at the LHC, at a centre-of-mass energy $\sqrt{s} = 7$ TeV, were measured in the central pseudorapidity region |$\eta$| < 1. Comparisons are made with previous measurements at $\sqrt{s}$ = 0.9 TeV and 2.36 TeV. At $\sqrt{s}$ = 7 TeV, for events with at least one charged particle in |$\eta$| < 1, we obtain dNch/deta = 6.01 $\pm$ 0.01 (stat.) $^{+0.20}_{-0.12}$ (syst.). This corresponds to an increase of 57.6% $\pm$ 0.4% (stat.) $^{+3.6}_{-1.8}$% (syst.) relative to collisions at 0.9 TeV, significantly higher than calculations from commonly used models. The multiplicity distribution at 7 TeV is described fairly well by the negative binomial distribution.
Charged-particle pseudorapidity densities at central pseudorapidity (ETRAP from -1.0 to 1.0) for the INEL>0 class of events. Data are also given for the lower energy ALICE data.
Relative increase in pseudorapidity density between the different energies.
Multiplicity distribution normalized to the bin width in the pseudorapidity region -1.0 to 1.0 for INEL>0 collisions at a centre-of-mass energy of 7000 GeV. See the paper arXiv:1004.3034 for the lower energy data. Note that the statistical as well as the systematic uncertainties are strongly correlated between neighbouring points. See text of paper for details.
Charged particle production has been studied in neutral current deep inelastic ep scattering with the ZEUS detector at HERA using an integrated luminosity of 0.44 fb^-1. Distributions of scaled momenta in the Breit frame are presented for particles in the current fragmentation region. The evolution of these spectra with the photon virtuality, Q^2, is described in the kinematic region 10<Q^2<41000 GeV^2. Next-to-leading-order and modified leading-log-approximation QCD calculations as well as predictions from Monte Carlo models are compared to the data. The results are also compared to e+e- annihilation data. The dependences of the pseudorapidity distribution of the particles on Q^2 and on the energy in the \gamma p system, W, are presented and interpreted in the context of the hypothesis of limiting fragmentation.
Bin averaged scaled momentum spectra in the Q**2 ranges 160 to 320 and 320 to 640 GeV**2.
Bin averaged scaled momentum spectra in the Q**2 ranges 640 to 1280 and 1280 to 2560 GeV**2.
Bin averaged scaled momentum spectra in the Q**2 ranges 2560 to 5120 and 51200 to 10240 GeV**2.
The proton-proton and proton-eta' invariant mass distributions have been determined for the pp -> ppeta' reaction at an excess energy of Q = 16.4 MeV. The measurement was carried out using the COSY-11 detector setup and the proton beam of the cooler synchrotron COSY. The shapes of the determined invariant mass distributions are similar to those of the pp -> ppeta reaction and reveal an enhancement for large relative proton-proton momenta. This result, together with the fact that the proton-eta interaction is much stronger that the proton-eta' interaction, excludes the hypothesis that the observed enhancement is caused by the interaction between the proton and the meson.
Differential cross section as a function of the squared invariant mass of the proton-proton system.
Differential cross section as a function of the squared invariant mass of the proton-etaprime system.
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. The cross sections are described by the predictions of next-to-leading-order QCD.
The measured differential cross-sections $d\sigma/dQ^2$ for inclusive dijet production. The statistical, uncorrelated systematic and jet-energy-scale (ES) uncertainties are shown separately. The multiplicative corrections, ${C_{\rm{QED}}}$, which have been applied to the data and the corrections for hadronisation and ${Z^{0}}$ effects to be applied to the parton-level NLO QCD calculations, ${C_{\rm{hadr}}\cdot C_{\rm{Z^{0}}}}$, are shown in the last two columns.
Inclusive dijet cross-sections ${d\sigma/dx_{\rm{Bj}}}$. Other details as in the caption to Table 1.
Inclusive dijet cross-sections ${d\sigma/d\overline{E^{jet}_{T,B}}}$. Other details as in the caption to Table 1.
The inclusive double-spin asymmetry, $A^p_1$, has been measured at COMPASS in deepinelastic polarised muon scattering off a large polarised NH3 target. The data, collected in the year 2007, cover the range $Q^2 > 1 (GeV/c)^2, 0.004 < x < 0.7$ and improve the statistical precision of $g^p_1(x)$ by a factor of two in the region $x < 0.02$. The new proton asymmetries are combined with those previously published for the deuteron to extract the non-singlet spin-dependent structure function $g^{NS}_1(x,Q^2)$. The isovector quark density, $\Delta_{q3}(x,Q^2)$, is evaluated from a NLO QCD fit of $g^{NS}_1$. The first moment of $\Delta_{q3}$ is in good agreement with the value predicted by the Bjorken sum rule and corresponds to a ratio of the axial and vector coupling constants $|g_A/g_V$ = $1.28\pm 0.07(stat)\pm 0.10$(syst).
Values of $A_1^p$ and $g_1^p$ as a function of $x$ with corresponding average values of $Q^2$.
Values of $g_1^p$ for the 2007 COMPASS proton data at 160 GeV in ($x$, $Q^2$) bins.
We report on a measurement of the Upsilon(1S+2S+3S) -> e+e- cross section at midrapidity in p+p collisions at sqrt(s)=200 GeV. We find the cross section to be 114 +/- 38 (stat.) +23,-24 (syst.) pb. Perturbative QCD calculations at next-to-leading order in the Color Evaporation Model are in agreement with our measurement, while calculations in the Color Singlet Model underestimate it by 2 sigma. Our result is consistent with the trend seen in world data as a function of the center-of-mass energy of the collision and extends the availability of Upsilon data to RHIC energies. The dielectron continuum in the invariant mass range near the Upsilon is also studied to obtain a combined cross section of Drell-Yan plus (b b-bar) -> e+e-.
Unlike-sign pair invariant mass distribution with |y_ee| < 0.5.
Like-sign pair invariant mass distribution with |y_ee| < 0.5.
Background subtracted unlike-sign invariant mass distribution.
We present the results of an elliptic flow analysis of Cu+Cu collisions recorded with the STAR detector at 62.4 and 200GeV. Elliptic flow as a function of transverse momentum is reported for different collision centralities for charged hadrons and strangeness containing hadrons $K_{S}^{0}$, $\Lambda$, $\Xi$, $\phi$ in the midrapidity region $|eta|<1.0$. Significant reduction in systematic uncertainty of the measurement due to non-flow effects has been achieved by correlating particles at midrapidity, $|\eta|<1.0$, with those at forward rapidity, $2.5<|\eta|<4.0$. We also present azimuthal correlations in p+p collisions at 200 GeV to help estimating non-flow effects. To study the system-size dependence of elliptic flow, we present a detailed comparison with previously published results from Au+Au collisions at 200 GeV. We observe that $v_{2}$($p_{T}$) of strange hadrons has similar scaling properties as were first observed in Au+Au collisions, i.e.: (i) at low transverse momenta, $p_T<2GeV/c$, $v_{2}$ scales with transverse kinetic energy, $m_{T}-m$, and (ii) at intermediate $p_T$, $2
Charged hadron azimuthal correlations as a function of pT in 0-60% Cu+Cu and p+p collisions at 200 GeV using TPC and FTPC flow vectors.
Charged hadron azimuthal anisotropy v2 as a function of pT in 0-60% Cu+Cu collisions at 200 GeV using TPC flow vectors, and those with subtracting the azimuthal correlations in p+p collisions.
Charged hadron azimuthal anisotropy v2 as a function of pT in 0-60% Cu+Cu collisions at 200 GeV using FTPC flow vectors, and those with subtracting the azimuthal correlations in p+p collisions.
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