Experimental data on K
+ meson and proton sideward flow measured with the FOPI detector at SIS/GSI in the reactions Ru+Ru at 1.69
A GeV and Ni+Ni at 1.93
A GeV are presented. The K
+ sideward flow is ...found to be anti-correlated (correlated) with the one of protons at low (high) transverse momenta. When compared to the predictions of a transport model, the data favour the existence of an in-medium repulsive K
+-nucleon potential.
The inclusive charged particle transverse momentum distribution is measured in proton–proton collisions at s=900 GeV at the LHC using the ALICE detector. The measurement is performed in the central ...pseudorapidity region (|η|<0.8) over the transverse momentum range 0.15<pT<10 GeV/c. The correlation between transverse momentum and particle multiplicity is also studied. Results are presented for inelastic (INEL) and non-single-diffractive (NSD) events. The average transverse momentum for |η|<0.8 is 〈pT〉INEL=0.483±0.001 (stat.)±0.007 (syst.) GeV/c and 〈pT〉NSD=0.489±0.001 (stat.)±0.007 (syst.) GeV/c, respectively. The data exhibit a slightly larger 〈pT〉 than measurements in wider pseudorapidity intervals. The results are compared to simulations with the Monte Carlo event generators PYTHIA and PHOJET.
The pseudorapidity density and multiplicity distribution of charged particles produced in proton-proton collisions at the LHC, at a centre-of-mass energy {radical}s = 7 TeV, were measured in the ...central pseudorapidity region |{eta}| < 1. Comparisons are made with previous measurements at {radical} = 0.9 TeV and 2.36 TeV. At {radical}s = 7 TeV, for events with at least one charged particle in |{eta}| < 1, we obtain d N{sub ch}/d{eta} = 6.01 {+-} 0.01(stat.){sub -0.12}{sup +0.20}(syst.). This corresponds to an increase of 57.6% {+-} 0.4%(stat.){sub -1.8}{sup +3.6}%(syst.) relative to collisions at 0.9 TeV, significantly higher than calculations from commonly used models. The multiplicity distribution at 7 TeV is described fairly well by the negative binomial distribution.
Charged-particle production was studied in proton-proton collisions collected at the LHC with the ALICE detector at centre-of-mass energies 0.9 TeV and 2.36 TeV in the pseudorapidity range |{eta}| < ...1.4. In the central region (|{eta}| < 0.5), at 0.9 TeV, we measure charged-particle pseudorapidity density d N{sub ch}/d{eta} = 3.02 {+-} 0.01(stat.){sub -0.05}{sup +0.08}(syst.) for inelastic interactions, and d N{sub ch}/d{eta} = 3.58 {+-} 0.01(stat.){sub -0.12}{sup +0.12}(syst.) for non-single-diffractive interactions. At 2.36 TeV, we find d N{sub ch}/d{eta} = 3.77 {+-} 0.01(stat.){sub -0.12}{sup +0.25}(syst.) for inelastic, and d N{sub ch}/d{eta} = 4.43 {+-} 0.01(stat.){sub -0.12}{sup +0.37}(syst.) for non-single-diffractive collisions. The relative increase in charged-particle multiplicity from the lower to higher energy is 24.7% {+-} 0.5%(stat.){sub -2.8}{sup +5.7}%(syst.) for inelastic and 23.7% {+-} 0.5%(stat.){sub -1.1}{sup +4.6}%(syst.) for non-single-diffractive interactions. This increase is consistent with that reported by the CMS collaboration for non-single-diffractive events and larger than that found by a number of commonly used models. The multiplicity distribution was measured in different pseudorapidity intervals and studied in terms of KNO variables at both energies. The results are compared to proton-antiproton data and to model predictions.
A measurement of direct photon production in {sup 208}Pb+ {sup 208}Pb collisions at 158A GeV has been carried out in the CERN WA98 experiment. The invariant yield of direct photons in central ...collisions is extracted as a function of transverse momentum in the interval 0.5<p{sub T}<4 GeV/c . A significant direct photon signal, compared to statistical and systematical errors, is seen at p{sub T}>1.5 GeV/c . The result constitutes the first observation of direct photons in ultrarelativistic heavy-ion collisions. It could be significant for diagnosis of quark-gluon-plasma formation.
Charged particles and photons have been measured in central Pb+Pb collisions at 158 A GeV in a common (η–ϕ)-phase space region in the WA98 experiment at the CERN SPS. The measured distributions have ...been analyzed to quantify the frequency with which phase space regions of varying sizes have either small or large neutral pion fraction. The measured results are compared with VENUS model simulated events and with mixed events. Events with both large and small charged–neutral fluctuations are observed to occur more frequently than expected statistically, as deduced from mixed events, or as predicted by model simulations, with the difference becoming more prominent with decreasing size of the Δη–Δϕ region.
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