Measurements of the A dependence and pseudorapidity interval (δη) dependence of midrapidity ET distributions in a half-azimuth (Δφ=π) electromagnetic calorimeter are presented for p+Be, p+Au, O+Cu, Si+Au, and Au+Au collisions at the BNL-AGS (Alternating-Gradient Synchrotron). The shapes of the upper edges of midrapidity ET distributions as a function of the pseudorapidity interval δη in the range 0.3 to 1.3, roughly centered at midrapidity, are observed to vary with δη, like multiplicity—the upper edges of the distributions flatten as δη is reduced. At the typical fixed upper percentiles of ET distributions used for nuclear geometry characterization by centrality definition—7 percentile, 4 percentile, 2 percentile, 1 percentile, 0.5 percentile—the effect of this variation in shape on the measured projectile Ap dependence for 16O, 28Si, 197Au projectiles on an Au target is small for the ranges of δη and percentile examined. The ET distributions for p+Au and p+Be change in shape with δη; but in each δη interval the shapes of the p+Au and p+Be distributions remain indentical with each other—a striking confirmation of the absence of multiple-collision effects at midrapidity at AGS energies. The validity of the nuclear geometry characterization versus δη is illustrated by plots of the ET(δη) distribution in each δη interval in units of the measured 〈ET(δη)〉p+Au in the same δη interval for p+Au collisions. These plots, in the physically meaningful units of “number of average p+Au collisions,” are nearly universal as a function of δη, confirming that the reaction dynamics for ET production at midrapidity at AGS energies is governed by the number of projectile participants and can be well characterized by measurements in apertures as small as Δφ=π, δη=0.3.
ET is defined as the sum of Ei*Sin(THETAi) taken over all particles emittedon an event. The full ETARAP acceptance of the half-azimuth calorimeter, 1.22 < ETARAP < 2.5, is subdivided into eight nominally equal bins of 0.16 in pseudorapidity.
ET is defined as the sum of Ei*Sin(THETAi) taken over all particles emittedon an event. The full ETARAP acceptance of the half-azimuth calorimeter, 1.38 < ETARAP < 2.34, is subdivided into eight nominally equal bins of 0.16 in pseudorapidity.
ET is defined as the sum of Ei*Sin(THETAi) taken over all particles emittedon an event. The full ETARAP acceptance of the half-azimuth calorimeter, 1.54 < ETARAP < 2.18, is subdivided into eight nominally equal bins of 0.16 in pseudorapidity.
Dijet production has been studied in neutral current deep inelastic e+p scattering for 470 < Q**2 < 20000 GeV**2 with the ZEUS detector at HERA using an integrated luminosity of 38.4 pb**{-1}. Dijet differential cross sections are presented in a kinematic region where both theoretical and experimental uncertainties are small. Next-to-leading-order (NLO) QCD calculations describe the measured differential cross sections well. A QCD analysis of the measured dijet fraction as a function of Q**2 allows both a precise determination of alpha_s(M_Z) and a test of the energy-scale dependence of the strong coupling constant. A detailed analysis provides an improved estimate of the uncertainties of the NLO QCD cross sections arising from the parton distribution functions of the proton. The value of alpha_s(M_Z), as determined from the QCD fit, is alpha_s(M_Z) = 0.1166 +- 0.0019 (stat.) {+ 0.0024}_{-0.0033} (exp.)} {+ 0.0057}_{- 0.0044} (th.).
The differential dijet cross section dsig/dZP1.
The differential dijet cross section dsig/dlog10(x).
The differential dijet cross section dsig/dlog10(xi).
A measurement is presented of dijet and 3-jet cross sections in low-|t| diffractive deep-inelastic scattering interactions of the type ep -> eXY, where the system X is separated by a large rapidity gap from a low-mass baryonic system Y. Data taken with the H1 detector at HERA, corresponding to an integrated luminosity of 18.0 pb^(-1), are used to measure hadron level single and double differential cross sections for 4
Average values, over the specified interval, of the differential hadron level dijet cross section as a function of Q**2.
Average values, over the specified interval, of the differential hadron level dijet cross section as a function of the average transverse momentum of the two jets in the c.m.frame.
Average values, over the specified interval, of the differential hadron level dijet cross section as a function of the average pseudorapidity of the two jets in the lab frame.
Differential cross sections for dijet photoproduction in association with a leading neutron using the reaction e^+ + p --> e^+ + n + jet + jet + X_r have been measured with the ZEUS detector at HERA using an integrated luminosity of 6.4 pb^{-1}. The fraction of dijet events with a leading neutron in the final state was studied as a function of the jet kinematic variables. The cross sections were measured for jet transverse energies E^{jet}_T > 6 GeV, neutron energy E_n > 400 GeV, and neutron production angle theta_n < 0.8 mrad. The data are broadly consistent with factorization of the lepton and hadron vertices and with a simple one-pion-exchange model.
The differential dijet cross section as a function of ET for the inclusive data set. The second DSYS error is due to the uncertainty in the calorimeter energy scale.
The differential dijet cross section as a function of ET for the neutron-tagged data set. The second DSYS error is due to the uncertainty in the calorimeter energy scale.
The differential dijet cross section as a function of ETARAP for the inclusive data set. The second DSYS error is due to the uncertainty in the calorimeterenergy scale.
The first measurement of inclusive Ds+- photoproduction at HERA has been performed with the ZEUS detector for photon-proton centre-of-mass energies 130 < W < 280 GeV. The measured cross section for 3 < pt(Ds) < 12 GeV and |eta(Ds)|< 1.5 is sigma(ep -> Ds X) = 3.79 +- 0.59 (stat.) +0.26-0.46 (syst.) +- 0.94 (br.) nb, where the last error arises from the uncertainty in the Ds decay branching ratio. The measurements are compared with inclusive D*+- photoproduction cross sections in the same kinematic region and with QCD calculations. The Ds cross sections lie above a fixed-order next-to-leading order calculation and agree better with a tree-level O(alpha,alpha_s^3) calculation that was tuned to describe the ZEUS D* cross sections. The ratio of Ds+- to D*+- cross sections is 0.41 +- 0.07 (stat.) +0.03-0.05 (syst.) +- 0.10 (br.). From this ratio, the strangeness-suppression factor in charm photoproduction, within the LUND string fragmentation model, has been calculated to be gamma_s = 0.27 +- 0.05 +- 0.07 (br.). The cross-section ratio and gamma_s are in good agreement with those obtained in charm production in e+e- annihilation.
The differential cross section as a function of PT. The mean values of PT are given as the average values of an exponential fit to the PT distribution in each bin. There is an additional 25 PCT systematic error due to the D/S --> PHI PI branching ratio uncertainty.
The differential cross section as a function of pseudorapidity. There is anadditional 25 PCT systematic error due to the D/S --> PHI PI branching ratio un certainty.
The total inclusive cross section. CT.= The second systematic error (DSYS) is due to the branching ratio uncertainty.
The inclusive production of D*+- mesons in photon-photon collisions has been measured using the OPAL detector at LEP at e+e- centre-of-mass energies of 183 and 189GeV. The D* mesons are reconstructed in their decay to D0pi+ with the D0 observed in the two decay modes Kpi+ and Kpi+pi-pi+. After background subtraction, 100.4+-12.6(stat) D*+- mesons have been selected in events without observed scattered beam electron ("anti-tagged") and 29.8+-5.9 (stat) D*+- mesons in events where one beam electron is scattered into the detector ("single-tagged"). Direct and single-resolved events are studied separately. Differential cross-sections as functions of the D* transverse momentum p_t and pseudorapidity \eta are presented in the kinematic region 2
Differential PT distribution for anti-tagged events for both D* decay modesand combined.
Differential ETARAP distribution for anti-tagged events for both D* decay modes and combined.
Integrated cross section using the anti-tagged events for D* production in the kinematic range of the experiment.
First inclusive measurements of isolated prompt photons in photoproduction at the HERA ep collider have been made with the ZEUS detector, using an integrated luminosity of 38.4 pb$^{-1}$. Cross sections are given as a function of the pseudorapidity and the transverse energy ($\eta^\gamma$, \eTg) of the photon, for $\eTg > $ 5 GeV in the $\gamma p$ centre-of-mass energy range 134-285 GeV. Comparisons are made with predictions from Monte Carlo models having leading-logarithm parton showers, and with next-to-leading-order QCD calculations, using currently available parameterisations of the photon structure. For forward $\eta^\gamma$ (proton direction) good agreement is found, but in the rear direction all predictions fall below the data.
The differential cross section for inclusive photoproduction of isolated photons.
Differential cross sections as a function pseudorapidity for the inclusive photoproduction of isolated photons with transverse energy from 5 to 10 GeV.
The production of D*+-(2010) mesons in deep inelastic scattering has been measured in the ZEUS detector at HERA using an integrated luminosity of 37 pb^-1. The decay channels D*+ -> D0 pi+(+c.c.), with D0 -> K- pi+ or D0 ->K- pi- pi+ pi+, have been used to identify the D mesons. The e+p cross section for inclusive D*+- production with 1
The measured cross section for D* production. The first is derived from theK2PI final state and the second from the K4PI final state.
The differential cross section w.r.t. Q**2 from the K2PI final state. The asymmetric errors are the quadratic sum of the statistical and systematic errors. The statistical errors are also shown separately.
The differential cross section w.r.t. X from the K2PI final state. The asymmetric errors are the quadratic sum of the statistical and systematic errors. The statistical errors are also shown separately.
Inclusive production of $\mathrm{D^{*\pm}}$ mesons in two-photon collisions was measured by the L3 experiment at LEP. The data were collected at a centre-of-mass energy $\sqrt{s} = 189$ GeV with an integrated luminosity of $176.4 \mathrm{pb^{-1}}$. Differential cross sections of the process $\mathrm{e^+e^- \to D^{*\pm} X}$ are determined as functions of the transverse momentum and pseudorapidity of the $\mathrm{D^{*\pm}}$ mesons in the kinematic region 1 GeV $< p_{T}^{\mathrm{D^*}} < 5 $ GeV and $\mathrm{|\eta^{D^*}|} < 1.4$. The cross section integrated over this phase space domain is measured to be $132 \pm 22(stat.) \pm 26(syst.)$ pb. The differential cross sections are compared with next-to-leading order perturbative QCD calculations.
The measured cross sections, as a function of PT over the bin ranges and the differential cross sections after bin-centre corrections.
The measured cross sections, as a function of pseudorapidity over the bin ranges and the differential cross sections after bin-centre corrections.
Integrated cross section in the visible kinematic region.
High transverse momentum pi0-mesons have been measured with the H1 detector at HERA in deep-inelastic ep scattering events at low Bjorken-x, down to x <~ 4.10^{-5}. The measurement is performed in a region of small angles with respect to the proton remnant in the laboratory frame of reference, namely the forward region, and corresponds to central rapidity in the centre of mass system of the virtual photon and proton. This region is expected to be particularly sensitive to QCD effects in hadronic final states. Differential cross-sections for inclusive pi0-meson production are presented as a function of Bjorken-x and the four-momentum transfer Q^2, and as a function of transverse momentum and pseudorapidity. A recent numerical BFKL calculation and predictions from QCD models based on DGLAP parton evolution are compared with the data.
Axis error includes +- 5/5 contribution (Trigger efficiency).
Axis error includes +- 5/5 contribution (Trigger efficiency).
Axis error includes +- 5/5 contribution (Trigger efficiency).
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