The energy dependence of the photon-proton total cross section, sigma-tot, was determined from ep scattering data collected with the ZEUS detector at HERA at three values of the center-of-mass energy, W, of the gamma-p system in the range 194<W<296 GeV. This is the first determination of the W dependence of sigma-tot from a single experiment at high W. Parameterizing sigma-tot proportional to W^(2 epsilon), epsilon = 0.111 +/- 0.009 (stat.) +/- 0.036 (syst.) was obtained.
Ratios of the cross sections for 3 energy bins. The first DSYS error isthe uncorrelated uncertainty and the second is the correlated uncertainty.
Fitted power law energy dependence.
Exclusive rho^0 electroproduction at HERA has been studied with the ZEUS detector using 120 pb^{-1} of integrated luminosity collected during 1996-2000. The analysis was carried out in the kinematic range of photon virtuality 2 < Q^2 < 160 GeV$^2, and gamma^* p centre-of-mass energy 32 < W < 180 GeV. The results include the Q^2 and W dependence of the gamma^* p --> rho^0 p cross section and the distribution of the squared-four-momentum transfer to the proton. The helicity analysis of the decay-matrix elements of the rho^0 was used to study the ratio of the gamma^* p cross section for longitudinal and transverse photon as a function of Q^2 and W. Finally, an effective Pomeron trajectory was extracted. The results are compared to various theoretical predictions.
Measurement of the spin density matrix element r_04_00 as a function of Q**2.
Measurement of the spin density matrix element RE(r_04_10) as a function of Q**2.
Measurement of the spin density matrix element r_04_1-1 as a function of Q**2.
J/psi production in d+Au and p+p collisions at sqrt(s_NN) = 200 GeV has been measured by the PHENIX experiment at rapidities -2.2 < y < +2.4. The cross sections and nuclear dependence of J/\psi production versus rapidity, transverse momentum, and centrality are obtained and compared to lower energy p+A results and to theoretical models. The observed nuclear dependence in d+Au collisions is found to be modest, suggesting that the absorption in the final state is weak and the shadowing of the gluon distributions is small and consistent with Dokshitzer-Gribov-Lipatov-Altarelli-Parisi-based parameterizations that fit deep-inelastic scattering and Drell-Yan data at lower energies.
J/PSI differential cross section in P+P reactions( times di-lepton branching ratio B=5.9%) as a function of rapidity.
J/PSI nuclear modification factor RDA,as a function of rapidity.
Total cross-section for J/PSI production in P P reactions. The total cross section is estimated using a pythia calculation, normalized to our data. The di-lepton branching ratio used is 5.9%.The systematic error given is due to the fit. The choice of the PDF and model was estimated to have little impact in the value of the total cross section.
Exclusive electroproduction of $\phi$ mesons has been studied in $e^\pm p$ collisions at $\sqrt{s}=318 \gev$ with the ZEUS detector at HERA using an integrated luminosity of 65.1 pb$^{-1}$. The $\gamma^*p$ cross section is presented in the kinematic range $2<Q^2<70 \gev^2$, $35<W<145 \gev$ and ${|t|}<0.6 \gev^2$. The cross sections as functions of $Q^2$, $W$, $t$ and helicity angle $\theta_h$ are compared to cross sections for other vector mesons. The ratios $R$ of the cross sections for longitudinally and transversely polarized virtual photons are presented as functions of $Q^2$ and $W$. The data are also compared to predictions from theoretical models.
Exclusive GAMMA* P --> PHI P cross section in the Q**2 range 2 to 3 GeV**2.
Exclusive GAMMA* P --> PHI P cross section in the Q**2 range 3 to 5 GeV**2.
Exclusive GAMMA* P --> PHI P cross section in the Q**2 range 5 to 9 GeV**2.
The PHENIX experiment has measured mid-rapidity transverse momentum spectra (0.4 < p_T < 4.0 GeV/c) of single electrons as a function of centrality in Au+Au collisions at sqrt(s_NN) = 200 GeV. Contributions to the raw spectra from photon conversions and Dalitz decays of light neutral mesons are measured by introducing a thin (1.7% X_0) converter into the PHENIX acceptance and are statistically removed. The subtracted ``non-photonic'' electron spectra are primarily due to the semi-leptonic decays of hadrons containing heavy quarks (charm and bottom). For all centralities, charm production is found to scale with the nuclear overlap function, T_AA. For minimum-bias collisions the charm cross section per binary collision is N_cc^bar/T_AA = 622 +/- 57 (stat.) +/- 160 (sys.) microbarns.
Value of the Alpha power as used in a fit of dN/dy versus Ncoll of the form A*Ncoll^Alpha, where N is the non photonic electron yield and Ncoll the number of p+p collisions This value only includes data from Au+Au collisions The value of Alpha = 1 is the expectation in the absence of medium effects.
Value of the Alpha power as used in a fit of dN/dy versus Ncoll, of the form A*Ncoll^Alpha, where N is the non photonic electron yield and Ncoll the number of p+p collisions This value is calculated including previous data of p+p collisions, measured by PHENIX, in addition of the Au+Au data The value of Alpha = 1 is the expectation in the absence of medium effects.
Spectrum in transverse momentum of electrons created in open heavy flavor decays, for minimum bias events.
The exclusive electroproduction of J/psi mesons, ep->epJ/psi, has been studied with the ZEUS detector at HERA for virtualities of the exchanged photon in the ranges 0.15<Q^2<0.8 GeV^2 and 2<Q^2<100 GeV^2 using integrated luminosities of 69 pb^-1 and 83 pb^-1, respectively.The photon-proton centre-of-mass energy was in the range 30<W<220 GeV and the squared four-momentum transfer at the proton vertex |t|<1.The cross sections and decay angular distributions are presented as functions of Q^2, W and t. The effective parameters of the Pomeron trajectory are in agreement with those found in J/psi photoproduction. The spin-density matrix elements, calculated from the decay angular distributions, are consistent with the hypothesis of s-channel helicity conservation. The ratio of the longitudinal to transverse cross sections, sigma_L/sigma_T, grows with Q^2, whilst no dependence on W or t is observed. The results are in agreement with perturbative QCD calculations and exhibit a strong sensitivity to the gluon distribution in the proton.
Cross sections for exclusive J/PSI production as a function of W in the Q**2 region 0.15 to 0.18 GeV**2.
Cross sections for exclusive J/PSI production as a function of W in the Q**2 region 2 to 5 GeV**2.
Cross sections for exclusive J/PSI production as a function of W in the Q**2 region 5 to 10 GeV**2.
The scale dependence of the evolution of photoproduction cross sections with the photon-proton centre of mass energy W is studied using low Q~2 < 0.01 GeV~2 e~+p interactions collected by the H1 experiment at HERA. The value of the largest transverse momentum of a charged particle in the photon fragmentation region is used to define the hard scale. The slope of the $W$ dependence of the cross section is observed to increase steeply with increasing transverse momentum. The result is compared to measurements of the Q~2 evolution of the W dependence of the virtual photon-proton cross section. Interpretations in terms of QCD and in terms of Regge phenomenology are discussed.
The gamma p cross section is parameterized as CONST*(W**2)**POWER.
We present results from the initial run of Fermilab experiment E706. The data include incident π− and p beams at 500 GeV/c on Be and Cu targets, and span the kinematic ranges of transverse momentum and rapidity of 3.5≤pT≤10 GeV/c and −0.7≤yc.m.≤0.7, respectively. We have measured cross sections for π0 and direct-photon production, as well as the ηπ0 production ratio. From the data on Be and Cu, we have extracted the nuclear dependence of π0 production, parametrized as Aα. The cross sections are compared with next-to-leading-log QCD predictions for different choices of the QCD momentum scales and several sets of parton distribution functions.
No description provided.
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We have used the Fermilab 30-in. bubble-chamber-hybrid spectrometer to study neutral-strange-particle production in the interactions of 200-GeV/c protons and π+ and K+ mesons with nuclei of gold, silver, and magnesium. Average multiplicities and inclusive cross sections for K0 and Λ are measured, and a power law is found to give a good description of their A dependence. The exponent characterizing the A dependence is consistent with being the same for K0 and Λ production, and also the same for proton and π+ beams. Average K0 and Λ multiplicities, as well as their ratio, have been measured as functions of the numbers of projectile collisions νp and secondary collisions νs in the nucleus, and indicate that rescattering contributes significantly to enhancement of Λ production but not to K0 production. The properties of events with multiple K0's or Λ's also corroborate this conclusion. K0 rapidities are in the central region and decrease gently with increasing νp, while Λ rapidities are in the target-fragmentation region and are independent of νp. K0 and Λ multiplicities increase with the rapidity loss of the projectile, but their rapidities do not.
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We present new measurements of π0 production at high transverse momenta (pT) for π− and p interactions on Be and Cu targets at 500 GeV/c. The observed dependence of the yields as a function of pT and rapidity (y) is compared with expectations from leading-log QCD over a kinematic range in which the inclusive cross sections fall by more than 4 order of magnitude.
No description provided.
A dependence parameterized as A**POWER for both Pi- and P interactions.
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