124 research outputs found
Low-mass e+e- pair production in 158 A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse momentum
We report a measurement of low-mass electron pairs observed in 158
GeV/nucleon Pb-Au collisions. The pair yield integrated over the range of
invariant masses 0.2 < m < 2.0 GeV is enhanced by a factor of 3.5 +/- 0.4
(stat) +/- 0.9 (syst) over the expectation from neutral meson decays. As
observed previously in S-Au collisions, the enhancement is most pronounced in
the invariant-mass region 300-700 MeV. For Pb-Au we find evidence for a strong
increase of the enhancement with centrality. In addition, we show that the
enhancement covers a wide range in transverse momentum, but is largest at the
lowest observed pt.Comment: 17 pages, 4 figures, submitted to Phys.Lett.
Modification of the rho meson detected by low-mass electron-positron pairs in central Pb-Au collisions at 158 A GeV/c
We present a measurement of pair production in central Pb-Au
collisions at 158 GeV/. As reported earlier, a significant excess of the
pair yield over the expectation from hadron decays is observed. The
improved mass resolution of the present data set, recorded with the upgraded
CERES experiment at the CERN-SPS, allows for a comparison of the data with
different theoretical approaches. The data clearly favor a substantial
in-medium broadening of the spectral function over a density-dependent
shift of the pole mass. The in-medium broadening model implies that
baryon induced interactions are the key mechanism to in-medium modifications of
the -meson in the hot fireball at SPS energy.Comment: Revised versio
Recent results from Pb-Au collisions at 158 GeV/c per nucleon obtained with the CERES spectrometer
During the 1996 lead run time, CERES has accumulated 42 million events,
corresponding to a factor of 5 more statistics than in 1995 and 2.5 million
events of a special photon-run. We report on the results of the low-mass
ee-pair analysis. Since the most critical item is the poor
signal-to-background ratio we also discuss the understanding of this
background, in absolute terms, with the help of a detailed Monte Carlo
simulation. We show preliminary results of the photon analysis and summarize
the results of the hadron analysis preliminarily reported on already at QM'97Comment: 10 pages, 9 figures, Proceedings of the XIV Int. Conf. on
Nucleus-Nucleus Collisions,Quark Matter 99, Torino, Italy, May 10 - 15, 199
Event-by-event fluctuations at SPS
Results on event-by-event fluctuations of the mean transverse momentum and
net charge in Pb-Au collisions, measured by the CERES Collaboration at
CERN-SPS, are presented. We discuss the centrality and beam energy dependence
and compare our data to cascade calculations.Comment: 4 pages, 4 figures, proceedings to INPC2004 Goteborg, Swede
New Results on Pb-Au Collisions at 40 AGeV from the CERES/NA45 Experiment
In 1999 the CERES/NA45 ran at the CERN SPS with a beam energy of 40
GeV/nucleon. The data set comprises about 8.7 millions Pb-Au events with a
trigger selection corresponding to approximately the most central 30% of the
geometrical cross section. Results on low-mass electron pair analysis are
presented.
The upgrade of the experimental setup with the radial drift TPC has allowed
to enhance hadron physics capabilities of the experiment. New results on hadron
spectra (including Lambda) and flow are presented.Comment: Talk at the International Nuclear Physics Conference INPC2001,
Berkeley, CA, July 29th - August 3rd 200
Enhancement of low-mass dileptons in heavy-ion collisions
Using a relativistic transport model for the expansion stage of S+Au
collisions at 200 GeV/nucleon, we show that the recently observed enhancement
of low-mass dileptons by the CERES collaboration can be explained by the
decrease of vector meson masses in hot and dense hadronic matter.Comment: 12 pages, RevTeX, 3 figures available from [email protected]
Dilepton Production at SPS-energy Heavy Ion Collisions
The production of dileptons is studied within a hadronic transport model. We
investigate the sensitivity of the dilepton spectra to the initial
configuration of the hadronic phase in a ultrarelativistic heavy ion collision.
Possible in medium correction due to the modifications of pions and the pion
form factor in a hadronic gas are discussed.Comment: Dedicated to Gerry Brown in honor of the 32nd celebration of his 39th
birthday. 31 pages Latex including 13 eps-figures, uses psfig.sty and
epsf.st
Event-by-event fluctuations of the mean transverse momentum in 40, 80, and 158 A GeV/c Pb-Au collisions
Measurements of event-by-event fluctuations of the mean transverse momentum
in Pb-Au collisions at 40, 80, and 158 A GeV/c are presented. A significant
excess of mean p_T fluctuations at mid-rapidity is observed over the
expectation from statistically independent particle emission. The results are
somewhat smaller than recent measurements at RHIC. A possible non-monotonic
behaviour of the mean p_T fluctuations as function of collision energy, which
may have indicated that the system has passed the critical point of the QCD
phase diagram in the range of mu_B under investigation, has not been observed.
The centrality dependence of mean p_T fluctuations in Pb-Au is consistent with
an extrapolation from pp collisions assuming that the non-statistical
fluctuations scale with multiplicity. The results are compared to calculations
by the RQMD and UrQMD event generators.Comment: 28 pages, 10 figure
An improved method for measuring muon energy using the truncated mean of dE/dx
The measurement of muon energy is critical for many analyses in large
Cherenkov detectors, particularly those that involve separating
extraterrestrial neutrinos from the atmospheric neutrino background. Muon
energy has traditionally been determined by measuring the specific energy loss
(dE/dx) along the muon's path and relating the dE/dx to the muon energy.
Because high-energy muons (E_mu > 1 TeV) lose energy randomly, the spread in
dE/dx values is quite large, leading to a typical energy resolution of 0.29 in
log10(E_mu) for a muon observed over a 1 km path length in the IceCube
detector. In this paper, we present an improved method that uses a truncated
mean and other techniques to determine the muon energy. The muon track is
divided into separate segments with individual dE/dx values. The elimination of
segments with the highest dE/dx results in an overall dE/dx that is more
closely correlated to the muon energy. This method results in an energy
resolution of 0.22 in log10(E_mu), which gives a 26% improvement. This
technique is applicable to any large water or ice detector and potentially to
large scintillator or liquid argon detectors.Comment: 12 pages, 16 figure
Enhanced production of low-mass electron-positron pairs in 40-AGeV Pb-Au collisions at the CERN SPS
We report on first measurements of low-mass electron pairs in Pb-Au collisions at the lower SPS beam energy of 40 AGeV. The pair yield integrated over the range of invariant masses 0.2 e+ e- annihilation with a modified rho-propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature.We report on first measurements of low-mass electron pairs in Pb-Au collisions at the lower SPS beam energy of 40 AGeV. The pair yield integrated over the range of invariant masses 0.2<m<1 GeV/c^2 is enhanced by a factor of 5.1+-1.3(stat)+-1.0/1.5(syst data/decays) over the expectation from neutral meson decays, more than previously observed at the higher energy of 158 AGeV. The results are discussed with reference to model calculations based on pi+ pi- -> e+ e- annihilation with a modified rho-propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature
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