645 research outputs found
Anisotropic flow of strange particles at SPS
No full textThe elliptic flow for Lambda hyperons and K0s mesons was measured by the NA49 experiment in semicentral Pb+Pb collisions at 158A GeV. The standard method of correlating particles with an event plane has been used. Measurements of v2 near mid-rapidity are reported as a function of centrality, rapidity and transverse momentum. Elliptic flow of Lambda and K0s particles increases both with the impact parameter and with the transverse momentum. It is compared with v2 for pions and protons as well as with various model predictions. The NA49 results are compared with data from NA45/CERES and STAR experiments
3ΛH and 3Λ¯H‾ production in Pb–Pb collisions at √sNN = 2.76 TeV
No full textThe production of the hypertriton nuclei 3
H and 3
¯ H has been measured for the first time in Pb–Pb
collisions at √sNN = 2.76 TeV with the ALICE experiment at LHC. The pT-integrated 3
H yield in one
unity of rapidity, dN/dy × B.R.
3
H→3He,π− = (3.86 ± 0.77(stat.) ± 0.68(syst.)) × 10−5 in the 0–10% most
central collisions, is consistent with the predictions from a statistical thermal model using the same
temperature as for the light hadrons. The coalescence parameter B3 shows a dependence on the
transverse momentum, similar to the B2 of deuterons and the B3 of 3He nuclei. The ratio of yields
S3 = 3
H/(3He×/p) was measured to be S3 = 0.60±0.13(stat.)±0.21(syst.) in 0–10% centrality events;
this value is compared to different theoretical models. The measured S3 is compatible with thermal
model predictions. The measured 3
H lifetime, τ = 181+54
−39(stat.) ± 33(syst.) ps is in agreement within 1σ
with the world average value.peerReviewe
Measurement of the Lifetime and Λ Separation Energy of _{Λ}^{3}H
No full textThe most precise measurements to date of the _{Λ}^{3}H lifetime τ and Λ separation energy B_{Λ} are obtained using the data sample of Pb-Pb collisions at sqrt[s_{NN}]=5.02 TeV collected by ALICE at the LHC. The _{Λ}^{3}H is reconstructed via its charged two-body mesonic decay channel (_{Λ}^{3}H→^{3}He+π^{-} and the charge-conjugate process). The measured values τ=[253±11(stat)±6(syst)] ps and B_{Λ}=[102±63(stat)±67(syst)] keV are compatible with predictions from effective field theories and confirm that the _{Λ}^{3}H structure is consistent with a weakly bound system
Energy dependence of multiplicity fluctuations in heavy ion collisions
No full textThe energy dependence of multiplicity fluctuations was studied for the most central Pb+Pb collisions at 20A, 30A, 40A, 80A and 158A GeV by the NA49 experiment at the CERN SPS. The multiplicity distribution for negatively and positively charged hadrons is significantly narrower than Poisson one for all energies. No significant structure in energy dependence of the scaled variance of multiplicity fluctuations is observed. The measured scaled variance is lower than the one predicted by the grand-canonical formulation of the hadron-resonance gas model. The results for scaled variance are in approximate agreement with the string-hadronic model UrQMD
A. Mar'in for the CERES Collaboration: G. Agakichiev
No full texts b , T. Wienold b , B. Windelband b , J. P. Wurm f , W. Xie e , V. Yurevich a a JINR, Dubna, Russia b Universitat Heidelberg, Germany c GSI, Darmstadt, Germany d Department for Physics and Astronomy, SUNY Stony Brook, USA e Weizmann Institute, Rehovot, Israel f Max-Planck-Institut fur Kernphysik, Heidelberg, Germany h NPI/ASCR, Rez, Czech Republic i Brookhaven National Laboratory, Upton, USA j CERN, Geneva, Switzerland k Guest at Universitat Heidelberg, Germany The CERES/NA45 experiment at the CERN SPS was upgraded in 1998 by the addition of a cylindrical Time Projection Chamber. The aim is to improve the mass resolution of e + e \Gamma pairs in the ae/!/OE region to<F12
Charged particle production in proton-, deuteron-, oxygen- and sulphur-nucleus collisions at 200 GeV per nucleon
No full textThe 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
Dielectron Mass Spectra From Au+au Collisions At Snn =200 Gev
No full textWe report the STAR measurements of dielectron (e+e-) production at midrapidity (|yee|<1) in Au+Au collisions at sNN=200GeV. The measurements are evaluated in different invariant mass regions with a focus on 0.30-0.76 (ρ-like), 0.76-0.80 (ω-like), and 0.98-1.05 (φ-like) GeV/c2. The spectrum in the ω-like and φ-like regions can be well described by the hadronic cocktail simulation. In the ρ-like region, however, the vacuum ρ spectral function cannot describe the shape of the dielectron excess. In this range, an enhancement of 1.77±0.11(stat)±0.24(syst)±0. 33(cocktail) is determined with respect to the hadronic cocktail simulation that excludes the ρ meson. The excess yield in the ρ-like region increases with the number of collision participants faster than the ω and φ yields. 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Antibaryon production in sulphur nucleus collisions at 200 GeV per nucleon
No full textAntiproton production near midrapidity has been studied in central collisions of S-32 With sulphur, silver and gold nuclei at 200 GeV per nucleon. The measured transverse mass distributions can be described by an exponential with inverse slope parameters of about 200 MeV, similar to those obtained from spectra. The rapidity density increases weakly with the target mass, ranging from 0.4 to 0.7. The ratio near midrapidity is approximately 1.4 on average, significantly larger than the corresponding ratio observed in proton-proton and proton-nucleus collisions
STRANGE PARTICLE-PRODUCTION IN NUCLEAR COLLISIONS AT 200 GEV PER NUCLEON
No full textMultiplicities and spectra of strange particles (LAMBDA, LAMBDABAR, K(S)0, K+ and K-) produced in central S-32+S, S-32+Ag and S-32+Au collisions at 200 GeV per nucleon are presented and compared with data on strange particle production in proton-nucleus and nucleon-nucleon interactions. It is shown that strangeness production in S-32+Ag collisions is enhanced by a factor of two, similar to that found previously in central S-32+S collisions
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