We present transverse momentum (p_T) spectra of charged hadrons measured in deuteron-gold and nucleon-gold collisions at \sqrts = 200 GeV for four centrality classes. Nucleon-gold collisions were selected by tagging events in which a spectator nucleon was observed in one of two forward rapidity detectors. The spectra and yields were investigated as a function of the number of binary nucleon-nucleon collisions, \nu, suffered by deuteron nucleons. A comparison of charged particle yields to those in p+p collisions show that the yield per nucleon-nucleon collision saturates with \nu for high momentum particles. We also present the charged hadron to neutral pion ratios as a function of p_T.
<p>Charged hadron spectra for centrality selected d+Au collisions.</p>
<p>Charged hadron spectra for centrality selected d+Au collisions.</p>
<p>Charged hadron spectra for centrality selected d+Au collisions.</p>
Forward jet cross sections have been measured in neutral current deep inelastic scattering at low Bjorken-x with the ZEUS detector at HERA using an integrated luminosity of ${81.8 \rm pb}^{-1}$. Measurements are presented for inclusive forward jets as well as for forward jets accompanied by a dijet system. The explored phase space, with jet pseudorapidity up to 4.3 is expected to be particularly sensitive to the dynamics of QCD parton evolution at low x. The measurements are compared to fixed-order QCD calculations and to leading-order parton-shower Monte Carlo models.
Differential cross section DSIG/DQ**2 in bins of Q**2 .
Differential cross section DSIG/DX in bins of X .
Differential cross section DSIG/DET(P=4) in bins of ET(P=4) .
Three- and four-jet final states have been measured in photoproduction at HERA using the ZEUS detector with an integrated luminosity of 121 pb^-1. The results are presented for jets with transverse energy E_T^jet>6 GeV and pseudorapidity |eta^jet|<2.4, in the kinematic region given by the virtuality of the photon Q^2<1 GeV^2 and the inelasticity 0.2<y<0.85 and in two mass regions defined as 25<M_nj<50 GeV and M_nj>50 GeV, where M_nj is the invariant mass of the n-jet system. The four-jet photoproduction cross section has been measured for the first time and represents the highest-order process studied at HERA. Both the three- and four-jet cross sections have been compared with leading-logarithmic parton-shower Monte Carlo models, with and without multi-parton interactions. The three-jet cross sections have been compared to an order(alpha alpha_s^2) perturbative QCD calculation.
Cross section D(SIG)/M(P=4_5_6) as a function of M(P=4_5_6) .
Cross section D(SIG)/M(P=4_5_6_7) as a function of M(P=4_5_6_7) .
Cross section D(SIG)/X(C=GAMMA,OBS) as a function of X(C=GAMMA,OBS) in two jet invariant mass regions, 25 to 50 and > 50 GeV .
The cross section for the process $e^+e^- \to K^+K^-$ was measured in the energy range $\sqrt{s}$ = 1.04--1.38 GeV in the SND experiment at VEPP-2M $e^+e^-$ collider. The measured cross section is described by the Vector Meson Dominance model with contributions from the light vector mesons $\rho$, $\omega$, $\phi$ and their lowest excitations. The mean statistical accuracy of the measurement is 4.4 %, and the systematic uncertainty is 5.2 %.
The measured cross section and charged kaon form factor.
The cross section for high-E_T dijet production in photoproduction has been measured with the ZEUS detector at HERA using an integrated luminosity of 81.8 pb-1. The events were required to have a virtuality of the incoming photon, Q^2, of less than 1 GeV^2 and a photon-proton centre-of-mass energy in the range 142 < W < 293 GeV. Events were selected if at least two jets satisfied the transverse-energy requirements of E_T(jet1) > 20 GeV and E_T(jet2) > 15 GeV and pseudorapidity requirements of -1 < eta(jet1,2) < 3, with at least one of the jets satisfying -1 < eta(jet) < 2.5. The measurements show sensitivity to the parton distributions in the photon and proton and effects beyond next-to-leading order in QCD. Hence these data can be used to constrain further the parton densities in the proton and photon.
Cross section D(SIG)/(ET(P=4)+ET(P=5))/2 as a function of (ET(P=4)+ET(P=5))/2 for X(C=GAMMA,OBS) > 0.75 .
Cross section D(SIG)/(ET(P=4)+ET(P=5))/2 as a function of (ET(P=4)+ET(P=5))/2 for X(C=GAMMA,OBS) <= 0.75 .
Cross section D(SIG)/ET(P=4) as a function of ET(P=4) for X(C=GAMMA,OBS) > 0.75 .
We report the measurement of Lamda and Anti-Lamda yields and inverse slope parameters in d + Au collisions at sqrt(s_NN) = 200 GeV at forward and backward rapidities (y = +- 2.75), using data from the STAR forward time projection chambers. The contributions of different processes to baryon transport and particle production are probed exploiting the inherent asymmetry of the d + Au system. Comparisons to model calculations show that the baryon transport on the deuteron side is consistent with multiple collisions of the deuteron nucleons with gold participants. On the gold side HIJING based models do not describe the measured particle yields while models with initial state nuclear effects and/or hadronic rescattering do. The Multi-Chain Model can provide a good description of the net baryon density in d + Au collisions at RHIC, and the derived parameters of the model agree with those from nuclear collisions at lower energies.
(Color online) a) Invariant mass distribution of $\Lambda$ candidates on the deuteron side with estimated $K_{s}^{0}$ background distribution, b) and c) show the background subtracted $\Lambda$ and $\overline{\Lambda}$ invariant mass distributions. The widths of the peaks are due to the limited momentum resolution of the detectors, and are reproduced by simulations.
(Color online) a) Invariant mass distribution of $\Lambda$ candidates on the deuteron side with estimated $K_{s}^{0}$ background distribution, b) and c) show the background subtracted $\Lambda$ and $\overline{\Lambda}$ invariant mass distributions. The widths of the peaks are due to the limited momentum resolution of the detectors, and are reproduced by simulations.
(Color online) a) Invariant mass distribution of $\Lambda$ candidates on the deuteron side with estimated $K_{s}^{0}$ background distribution, b) and c) show the background subtracted $\Lambda$ and $\overline{\Lambda}$ invariant mass distributions. The widths of the peaks are due to the limited momentum resolution of the detectors, and are reproduced by simulations.
The first observation of (anti)deuterons in deep inelastic scattering at HERA has been made with the ZEUS detector at a centre-of-mass energy of 300--318 GeV using an integrated luminosity of 120 pb-1. The measurement was performed in the central rapidity region for transverse momentum per unit of mass in the range 0.3<p_T/M<0.7. The particle rates have been extracted and interpreted in terms of the coalescence model. The (anti)deuteron production yield is smaller than the (anti)proton yield by approximately three orders of magnitude, consistent with the world measurements.
Measured invariant cross section for P production.
Measured invariant cross section for DEUT production.
Measured invariant cross section for PBAR production.
Inclusive dijet and trijet production in deep inelastic $ep$ scattering has been measured for $10<Q^2<100$ GeV$^2$ and low Bjorken $x$, $10^{-4}<x_{\rm Bj}<10^{-2}$. The data were taken at the HERA $ep$ collider with centre-of-mass energy $\sqrt{s} = 318 \gev$ using the ZEUS detector and correspond to an integrated luminosity of $82 {\rm pb}^{-1}$. Jets were identified in the hadronic centre-of-mass (HCM) frame using the $k_{T}$ cluster algorithm in the longitudinally invariant inclusive mode. Measurements of dijet and trijet differential cross sections are presented as functions of $Q^2$, $x_{\rm Bj}$, jet transverse energy, and jet pseudorapidity. As a further examination of low-$x_{\rm Bj}$ dynamics, multi-differential cross sections as functions of the jet correlations in transverse momenta, azimuthal angles, and pseudorapidity are also presented. Calculations at $\mathcal{O}(\alpha_{s}^3)$ generally describe the trijet data well and improve the description of the dijet data compared to the calculation at $\mathcal{O}(\alpha_{s}^2)$.
Two jet cross section D(SIG)/DQ**2 as a function of Q**2.
Two jet cross section D(SIG)/DX as a function of X.
Two jet cross section D(SIG)/DET(P=4,RF=CM) as a function of ET(P=4,RF=CM).
We report on the observed differences in production rates of strange and multi-strange baryons in Au+Au collisions at sqrts = 200 GeV compared to pp interactions at the same energy. The strange baryon yields in Au+Au collisions, then scaled down by the number of participating nucleons, are enhanced relative to those measured in pp reactions. The enhancement observed increases with the strangeness content of the baryon, and increases for all strange baryons with collision centrality. The enhancement is qualitatively similar to that observed at lower collision energy sqrts =17.3 GeV. The previous observations are for the bulk production, while at intermediate pT, 1 < pT< 4 GeV/c, the strange baryons even exceed binary scaling from pp yields.
Midrapidity E(i) as a function of $<N_{part}>$ for $\Lambda$, $\bar{\Lambda}$ ($|y| < 1.0$), $\Xi^{-}$, $\bar{\Xi}^{+}$ ($|y| < 0.75$). Error bars on the data points represent those from the heavy ions. Stat. and syst. errors added in quadrature. Grand Canonical Model arrows(values in brackets), for $\Lambda$ E(2.6) and T(165 MeV) for $\bar{\Lambda}$ E(2.2) and T(170 MeV), for $\Xi$ E(10.7) and T(165 MeV), for anti-$\Xi$ E(7.5) and T(170 MeV).
Midrapidity E(i) as a function of $<N_{part}>$ for $\Omega^{-}+\bar{\Omega}^{+}$ ($|y| < 0.75$). Error bars on the data points represent those from the heavy ions. Stat. and syst. errors added in quadrature.
Midrapidity E(i) as a function of $<N_{part}>$ for inclusive $p$ ($|y| < 0.5$). Error bars on the data points represent those from the heavy ions. Stat. and syst. errors added in quadrature.
We report the first measurement of the opening angle distribution between pairs of jets produced in high-energy collisions of transversely polarized protons. The measurement probes (Sivers) correlations between the transverse spin orientation of a proton and the transverse momentum directions of its partons. With both beams polarized, the wide pseudorapidity ($-1 \leq \eta \leq +2$) coverage for jets permits separation of Sivers functions for the valence and sea regions. The resulting asymmetries are all consistent with zero and considerably smaller than Sivers effects observed in semi-inclusive deep inelastic scattering (SIDIS). We discuss theoretical attempts to reconcile the new results with the sizable transverse spin effects seen in SIDIS and forward hadron production in pp collisions.
Measured and calculated asymmetries vs. di-jet pseudorapidity sum for $+\hat{z}$ (left) and $−\hat{z}$ (right) beams. (a,b): Fraction of the calculated di-jet cross section with a quark (gluon) from the $+\hat{z}$ $(−\hat{z})$ beam. (c,d): Unweighted asymmetries compared with pQCD calculations [20] (histograms) for two models of quark Sivers functions fitted to SIDIS results [8]. (e,f): Asymmetries for $|\sin\zeta|$-weighted yields, compared with calculations [20, 21] based on twist-3 quark-gluon correlations. Vertical (horizontal) bars on the data indicate statistical uncertainties (bin widths). The systematic error bands exclude a $\pm12\%$ beam polarization normalization uncertainty.
Measured and calculated asymmetries vs. di-jet pseudorapidity sum for $+\hat{z}$ (left) and $−\hat{z}$ (right) beams. (a,b): Fraction of the calculated di-jet cross section with a quark (gluon) from the $+\hat{z}$ $(−\hat{z})$ beam. (c,d): Unweighted asymmetries compared with pQCD calculations [20] (histograms) for two models of quark Sivers functions fitted to SIDIS results [8]. (e,f): Asymmetries for $|\sin\zeta|$-weighted yields, compared with calculations [20, 21] based on twist-3 quark-gluon correlations. Vertical (horizontal) bars on the data indicate statistical uncertainties (bin widths). The systematic error bands exclude a $\pm12\%$ beam polarization normalization uncertainty.
Measured and calculated asymmetries vs. di-jet pseudorapidity sum for $+\hat{z}$ (left) and $−\hat{z}$ (right) beams. (a,b): Fraction of the calculated di-jet cross section with a quark (gluon) from the $+\hat{z}$ $(−\hat{z})$ beam. (c,d): Unweighted asymmetries compared with pQCD calculations [20] (histograms) for two models of quark Sivers functions fitted to SIDIS results [8]. (e,f): Asymmetries for $|\sin\zeta|$-weighted yields, compared with calculations [20, 21] based on twist-3 quark-gluon correlations. Vertical (horizontal) bars on the data indicate statistical uncertainties (bin widths). The systematic error bands exclude a $\pm12\%$ beam polarization normalization uncertainty.
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