We report on measurements by the E864 experiment at the BNL-AGS of the yields of light nuclei in collisions of Au(197) with beam momentum of 11.5 A GeV/c on targets of Pb(208) and Pt(197). The yields are reported for nuclei with baryon number A=1 up to A=7, and typically cover a rapidity range from y(cm) to y(cm)+1 and a transverse momentum range of approximately 0.1 < p(T)/A < 0.5 GeV/c. We calculate coalescence scale factors B(A) from which we extract model dependent source dimensions and collective flow velocities. We also examine the dependences of the yields on baryon number, spin, and isospin of the produced nuclei.
10 pct most central collisions.
10 to 38 pct most central collisions.
38 to 66 pct most central collisions.
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 distribution of the azimuthal angle for the charged hadrons has been studied in the hadronic centre-of-mass system for neutral current deep inelastic positron-proton scattering with the ZEUS detector at HERA. Measurements of the dependence of the moments of this distribution on the transverse momenta of the charged hadrons are presented. Asymmetries that can be unambiguously attributed to perturbative QCD processes have been observed for the first time.
Differential azimuthal angular distributions for different PT cuts.
Mean values of cos(phi) and cos(2pi) as a function of the PT cut.
The dependence of the photon structure on the photon virtuality, Q^2, is studied by measuring the reaction e^+p\to e^+ + {\rm jet} + {\rm jet} + {\rm X} at photon-proton centre-of-mass energies 134 < W < 223 GeV. Events have been selected in the Q^2 ranges \approx 0 GeV^2, 0.1-0.55 GeV^2, and 1.5-4.5 GeV^2, having two jets with transverse energy E_T^{jet} > 5.5 GeV in the final state. The dijet cross section has been measured as a function of the fractional momentum of the photon participating in the hard process, x_gamma. The ratio of the dijet cross section with x_gamma < 0.75 to that with x_gamma > 0.75 decreases as Q^2 increases. The data are compared with the predictions of NLO pQCD and leading-order Monte Carlo programs using various parton distribution functions of the photon. The measurements can be interpreted in terms of a resolved photon component that falls with Q^2 but remains present at values of Q^2 up to 4.5 GeV^2. However, none of the models considered gives a good description of the data.
Dijet cross section for the low ET set of cuts.
Dijet cross section for the high ET set of cuts.
Ratio of Dijet cross sections as a function of Q**2 for XOBS(C=GAMMA) less than to greater than 0.75 for the lower ET cuts.
None
The Dalitz plot parameters G, H, and K are used in the standard parameterization of the matrix element squared (see PDG): M**2 = 1 + G*X + H*X**2 + K*Y**2,where X = (s3-s0)/m(PI)**2 and Y = (s1-s2)/m(PI)**2, s1 = (pK - pPI0)**2, s2 = (pK - pPI0)**2, s3 = (pK - pPI+)**2, s0 = (s1+s2+s3)/3.
The forward-jet cross section in deep inelastic ep scattering has been measured using the ZEUS detector at HERA with an integrated luminosity of 6.36 pb^-1. The jet cross section is presented as a function of jet transverse energy squared, E(T,jet)^2, and Q^2 in the kinematic ranges 10^-2
Forward jet cross section as a function of ET**2/Q**2. The second DSYS error is the uncertainty in the energy scale of the calorimeter.
Measured forward-jet x distribution.
Elastic and proton-dissociative photoproduction of $\rho^0$, $\phi$ and $J/\psi$ vector mesons ($\gamma p\to Vp$, $\gamma p\to VN$, respectively) have been measured in e^+p interactions at HERA up to -t=3 GeV$^2$, where t is the four-momentum transfer squared at the photon-vector meson vertex. The analysis is based on a data sample in which photoproduction reactions were tagged by detection of the scattered positron in a special-purpose calorimeter. This limits the photon virtuality, Q^2, to values less than 0.01 GeV$^2$, and selects a $\gamma p$ average center-of-mass energy of
Differential cross section for proton-dissociative RHO0 photoproduction.
Differential cross section for elastic RHO0 photoproduction.
The ratio of the elastic to proton-dissociative cross sections for RHO0 photoproduction.
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.
We present measurements from Brookhaven Experiment 864 of neutron invariant multiplicity in 11.5 A GeV/c Au+Pb collisions. The measurements span a rapidity range from center-of-mass to beam rapidity (y(beam)=3.2) and are presented as a function of event centrality. The results are compared with E864 measurements of proton invariant multiplicity and an average n/p ratio at hadronic freeze-out of 1.19+-.08 is determined for the rapidity range y=1.6 to y=2.4. We discuss briefly the implications of this ratio within a simple equilibrium model of the collision system.
The errors are statistical and systematic errors added in quadrature. 10% most central events.
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.
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