We present measurements of $\pi^-$ and $\pi^+$ elliptic flow, $v_2$, at midrapidity in Au+Au collisions at $\sqrt{s_{_{\rm NN}}} =$ 200, 62.4, 39, 27, 19.6, 11.5 and 7.7 GeV, as a function of event-by-event charge asymmetry, $A_{ch}$, based on data from the STAR experiment at RHIC. We find that $\pi^-$ ($\pi^+$) elliptic flow linearly increases (decreases) with charge asymmetry for most centrality bins at $\sqrt{s_{_{\rm NN}}} = \text{27 GeV}$ and higher. At $\sqrt{s_{_{\rm NN}}} = \text{200 GeV}$, the slope of the difference of $v_2$ between $\pi^-$ and $\pi^+$ as a function of $A_{ch}$ exhibits a centrality dependence, which is qualitatively similar to calculations that incorporate a chiral magnetic wave effect. Similar centrality dependence is also observed at lower energies.
The distribution of observed charge asymmetry from STAR data.
Pion $v_2${2} as a function of observed charge asymmetry.
$v_2$ difference between $\pi^-$ and $\pi^+$ as a function of charge asymmetry with the tracking efficiency correction, for 30-40% central Au+Au collisions at 200 GeV. The errors are statistical only.
The dissociation of virtual photons, $\gamma^{\star} p \to X p$, in events with a large rapidity gap between $X$ and the outgoing proton, as well as in events in which the leading proton was directly measured, has been studied with the ZEUS detector at HERA. The data cover photon virtualities $Q^2>2$ GeV$^2$ and $\gamma^{\star} p$ centre-of-mass energies $40<W<240$ GeV, with $M_X>2$ GeV, where $M_X$ is the mass of the hadronic final state, $X$. Leading protons were detected in the ZEUS leading proton spectrometer. The cross section is presented as a function of $t$, the squared four-momentum transfer at the proton vertex and $\Phi$, the azimuthal angle between the positron scattering plane and the proton scattering plane. It is also shown as a function of $Q^2$ and $\xpom$, the fraction of the proton's momentum carried by the diffractive exchange, as well as $\beta$, the Bjorken variable defined with respect to the diffractive exchange.
The differential cross section DSIG/DT for the LRG and the LPS data samples.
The fitted exponential slope of the T distribution as a function of X(NAME=POMERON).
The fitted exponential slope of the T distribution as a function of X(NAME=POMERON).
Results on charged pion and kaon production in central Pb+Pb collisions at 20A and 30A GeV are presented and compared to data at lower and higher energies. A rapid change of the energy dependence is observed around 30A GeV for the yields of pions and kaons as well as for the shape of the transverse mass spectra. The change is compatible with the prediction that the threshold for production of a state of deconfined matter at the early stage of the collisions is located at low SPS energies.
Transverse mass spectra for pion production in the central rapidity region for collisions at 20 GeV per nucleon.
Transverse mass spectra for pion production in the central rapidity region for collisions at 30 GeV per nucleon.
Transverse mass spectra for kaon production in the central rapidity region for collisions at 20 GeV per nucleon.
The exclusive photoproduction of J/psi mesons, gamma p->J/psi p, has been studied in ep collisions with the ZEUS detector at HERA, in the kinematic range 20<W<290 GeV, where W is the photon-proton centre-of-mass energy. The J/psi mesons were reconstructed in the muon and the electron decay channels using integrated luminosities of 38 pb^-1 and 55 pb^-1, respectively. The helicity structure of J/psi production shows that the hypothesis of s-channel helicity conservation is satisfied at the two standard-deviation level. The total cross section and the differential cross-section dsigma/dt, where t is the squared four-momentum transfer at the proton vertex, are presented as a function of W, for |t|<1.8 GeV^2. The t distribution exhibits an exponential shape with a slope parameter increasing logarithmically with W with a value b=4.15 \pm 0.05 (stat.)^{+0.30}_{-0.18} (syst.) GeV^-2 at W=90 GeV. The effective parameters of the Pomeron trajectory are alphapom(0) = 1.200 \pm 0.009(stat.)^{+0.004}_{-0.010}(syst.) and alphappom= 0.115 \pm 0.018(stat.)^{+0.008}_{-0.015}(syst.) GeV^-2.
The total exclusive J/PSI photoproduction cross section, the differential cross section extrapolated to t=0 and the slope parameter of the exponential t dependence as afunction of W, the photon-proton c.m. energy, for data from J/PSI muon decay.
The total exclusive J/PSI photoproduction cross section as a function of W,the photon-proton c.m. energy, for data from J/PSI electron decays.
The differential cross section extrapolated to t=0 and the slope parameter of the exponential t dependence for exclusive J/PSI photoproduction as a function of W, the photon-proton c.m. energy for data from J/PSI electron decays.
We report measurements of D ∗± production in interactions between 350 GeV/ c π − particles and nuclei. Reconstruction of the decay D ∗+ → D 0 π + and charge conugate, with D 0 identified via its decays to K − π + and K − π − π + π + , has allowed isolation of a sample of 611 ± 28 D ∗± mesons, produced at positive x F . Assuming a linear A-dependence, the cross-section per nucleon in the region x F > 0 is measured to be 1.41 ± 0.10 ± 0.11 μ b for D ∗+ and 1.84 ± 0.12 ± 0.15 μ b for D ∗− . We present measurements of differential cross-sections with respect to x F and P t 2 , and compare data for D ∗± (vector-meson) production with data for production of charmed pseudoscalar mesons.
No description provided.
Data on D0, DBAR0, D+, and D- meson production are taken from previous publication of this collaboration (see NP B495, 3).
No description provided.
A study has been made of pseudoscalar mesons produced centrally in pp interactions. The results show that the eta and etaprime appear to have a similar production mechanism which differs from that of the pi0. The production properties of the eta and etaprime are not consistent with what is expected from double Pomeron exchange. In addition the production mechanism for the eta and etaprime is such that the production cross section are greatest when the azimuthal angle between the pT vectors of the two protons is 90 degrees.
No description provided.
Resonance production as a function of dPT - the difference in the transverse momentum vectors of the two exchange particles, expressed as a percentage of its total contribution.
T distributions have been fitted to the form D(SIG)/D(T) = const(NAME=ALPHA)*EXP(-SLOPE(C=1)*T) + const(NAME=BETA)*T**2*EXP(-SLOPE(C=2)*T).
The transverse momentum and rapidity distributions of net protons and negatively charged hadrons have been measured for minimum bias proton-nucleus and deuteron-gold interactions, as well as central oxygen-gold and sulphur-nucleus collisions at 200 GeV per nucleon. The rapidity density of net protons at midrapidity in central nucleus-nucleus collisions increases both with target mass for sulphur projectiles and with the projectile mass for a gold target. The shape of the rapidity distributions of net protons forward of midrapidity for d+Au and central S+Au collisions is similar. The average rapidity loss is larger than 2 units of rapidity for reactions with the gold target. The transverse momentum spectra of net protons for all reactions can be described by a thermal distribution with `temperatures' between 145 +- 11 MeV (p+S interactions) and 244 +- 43 MeV (central S+Au collisions). The multiplicity of negatively charged hadrons increases with the mass of the colliding system. The shape of the transverse momentum spectra of negatively charged hadrons changes from minimum bias p+p and p+S interactions to p+Au and central nucleus-nucleus collisions. The mean transverse momentum is almost constant in the vicinity of midrapidity and shows little variation with the target and projectile masses. The average number of produced negatively charged hadrons per participant baryon increases slightly from p+p, p+A to central S+S,Ag collisions.
No description provided.
No description provided.
The value YRAP = 4PI is the extrapolation for 4PI acceptance.
Charmed-meson production by 350 GeV/c π − particles incident on copper and tungsten targets has been studied in the WA92 experiment, performed at the CERN Ω′ spectrometer. Results obtained are reported and discussed. Reconstruction of decays from the set D 0 → K − π + D 0 → K − π − π + π + , D s + → φπ + and charge conjugates has yielded a sample of 7280 ± 108 charmed mesons, produced with χ F > 0, ( χ F ) = 0.18 and〈 p T 2 〉 = 1.86 ( GeV / c ) 2 . Assuming a relationship σ = σ 0 A α between the cross section, σ, per nucleus of mass A and the nucleonic cross section, σ 0 the α value found for the detected charmed particles is 0.95 ± 0.06 ± 0.03. Taking α = 1, the measured cross sections per nucleon for χ F > 0 production are 7.78 ± 0.14 ± 0.52 μ b for D 0 / D 0 , 3.28 ± 0.08 ± 0.29 μ b for D + /D − and 1.29 ± 0.16 ± 0.33 μ b for D s + /D s − . Differential cross sections with respect to χ F and p T 2 have been determined for the various types of charmed meson, and particle-antiparticle asymmetries have been analysed.
No description provided.
No description provided.
Nuclear dependence is fitted by SIG=CONST*A**POWER for CU and WT nuclei.
We present a measurement and comparison of the χc1 and χc2 production cross sections determined from interactions of 300-GeV/c π± and p with a Li target. We find χc1χc2 production ratios of 0.52−0.27+0.57 and 0.08−0.15+0.25 from reactions induced by π± and p, respectively.
The cross section per nucleon.
The cross section per nucleon. The differential cross section is fitted by the equation : D(SIG)/D(PT**2)= CONST*EXP(SLOPE*PT), D(SIG)/D(XL) = CONST*(1-(XL-CONST(C=X0))**2)**POWER(C=1) , and D(SIG)/D(XL) = CONST*(1-ABS(XL-CONST(C=XC)))**POWER(C=2).
The cross section per nucleon. The differential cross section is fitted by the equation : D(SIG)/D(COS(THETA)) = CONST*(1+CONST*COS(THETA)**2), where THETA is the angle between the MU+ and beam momentum in the CHI/C rest frame.
Data on the reactions (K+/π+)p→(K+/π+)pπ+π- and (K+/π+)p→(K+/π+)p2π+2π-, obtained with the European Hybrid Spectrometer, are presented and compared with data at lower energies. The contribution of beam and target diffractive dissociation and double Pomeron exchange, and porperties of these reactions are discussed.
No description provided.
No description provided.
No description provided.
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