We present the combined results on electron-pair production in 158 GeV/n Pb-Au (\(\sqrt{s}\) = 17.2 GeV) collisions taken at the CERN SPS in 1995 and 1996, and give a detailed account of the data ...analysis. The enhancement over the reference of neutral meson decays amounts to a factor of 2.31 \(\pm0.19 (stat.)\pm0.55 (syst.)\pm0.69 (decays)\) for semi-central collisions (28\(\%\)\(\sigma/\sigma_{geo}\)) when yields are integrated over m > 200 MeV/c2 in invariant mass. The measured yield, its stronger-than-linear scaling with \(N_{\rm ch}\), and the dominance of low pair pt strongly suggest an interpretation as thermal radiation from pion annihilation in the hadronic fireball. The shape of the excess centring at \(m\approx\) 500 MeV/c2, however, cannot be described without strong medium modifications of the \(\rho\) meson. The results are put into perspective by comparison to predictions from Brown-Rho scaling governed by chiral symmetry restoration, and from the spectral-function many-body treatment in which the approach to the phase boundary is less explicit.
In this work the thermal stability of the electronic surface passivation of
remote plasma-enhanced chemical vapour deposited (RPECVD) silicon nitride (SiN) films is investigated with the aim to ...establish a cost-effective screen-printing and firing-through-the-SiN process for bifacial silicon (Si) solar cells. As a key result, RPECVD SiN films provide an excellently thermally stable surface passivation quality if they feature a refractive index in the range between 2.0 and 2.2. After a short anneal above 850°C the surface recombination velocity on 1.5
Ωcm p-type float-zone (FZ) Si remains at a very low level of about 20
cm/s. First bifacial silicon solar cells with screen-printed rear contacts on 1.5
Ωcm p-type FZ Si yield a very promising rear efficiency of 13.4%.
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 e
+e
−-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'97 1.
Event-by-event fluctuations at SPS Appelshäuser, Harald; Sako, Hiro; Adamová, D. ...
Nuclear physics. A,
04/2005, Letnik:
752
Journal Article
Recenzirano
Odprti dostop
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.
We report preliminary results of the first measurement of low-mass electron pairs in 160 GeV/nucleon PbAu collisions at central rapidities in a wide multiplicity range. This work is the continuation ...of our systematic studies on pair production in p-Be, p-Au and SAu interactions. The motivation for this effort derives from a new source of lowmass dileptons recently observed in SAu and S-W collisions by CERES and HELIOS/3, respectively. The results obtained in the analysis of the PbAu data confirm our previous finding that pair production in the mass range 0.2 < m
ee
< 1.5 GeV/
c
2 is enhanced over the contributions from hadron decays while no significant excess could be observed for m
ee
≲ 2m
π
. A comparison of the results for different multiplicity bins favours a non-linear dependence of the e
+e
−-yield on the accompanying charged particle densities.
A study of elliptic flow and two-particle azimuthal correlations of charged particles (\(0.5 < p_{{\text{T}}} < 2.5\) GeV/c) and high-\(p_{\rm T}\) pions (\(1.2 < p_{{\text{T}}} < 3.5\) GeV/c) in Pb ...+ Au collisions at 158A GeV/c, close to midrapidity, is presented. Elliptic flow (v2) rises linearly with \(p_{\rm T}\) to a value of about 10\(\%\) at 2 GeV/c. Beyond \(p_{\rm T}\approx\) 1.5 GeV/c, the slope decreases and possibly indicates a v2 saturation at high \(p_{\rm T}\). Two-pion azimuthal anisotropies for \(p_{\rm T} > \) 1.2 GeV/c exceed the v2 values by about 60\(\%\) in semicentral collisions. This non-flow component is attributed to near-side and away-side jetlike correlations. While the near-side peak remains constant with centrality 0.23\(\pm\)0.03 rad, as expected for fragmentation, the away-side peak experiences broadening and disappears in central collisions.
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