N. Saveljic

Publications (16)8.91 Total impact

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  Available from: Guy Tel-Zur

  Article: e+e--pair production in Pb-Au collisions at 158 GeV per nucleon

  G. Agakichiev, H. Appelshauser, J. Bielcikova, R. Baur, P. Braun-Munzinger, A. Cherlin, S. Damjanovic, A Drees, S Esumi, U. Faschingbauer, [......], G Tel-Zur, I Tserruya, T. Ullrich, C. Voigt, S. Voloshin, C Weber, J. P. Wessels, T. Wienold, J P Wurm, V. Yurevich
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  ABSTRACT: 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/$c^2$ in invariant mass. The measured yield, its stronger-than-linear scaling with $N_{ch}$, and the dominance of low pair $p_t$ strongly suggest an interpretation as {\it thermal radiation} from pion annihilation in the hadronic fireball. The shape of the excess centring at $m\approx$ 500 MeV/$c^2$, 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.
  06/2005;
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  Available from: arxiv.org

  Article: Semihard scattering unraveled from collective dynamics by two-pion azimuthal correlations in 158A GeV/c Pb+Au collisions.

  G Agakichiev, H Appelshäuser, R Baur, J Bielcikova, P Braun-Munzinger, A Cherlin, A Drees, S I Esumi, K Filimonov, Z Fraenkel, [......], H J Specht, J Stachel, H Tilsner, I Tserruya, C Voigt, S Voloshin, C Weber, J P Wessels, J P Wurm, V Yurevich
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  ABSTRACT: Elliptic flow and two-particle azimuthal correlations of charged hadrons and high-p(T) pions (p(T)>1 GeV/c) have been measured close to midrapidity in 158A GeV/c Pb+Au collisions by the CERES experiment. Elliptic flow (v(2)) rises linearly with p(T) to a value of about 10% at 2 GeV/c. Beyond p(T) approximately 1.5 GeV/c, the slope decreases considerably, possibly indicating a saturation of v(2) at high p(T). Two-pion azimuthal anisotropies for p(T)>1.2 GeV/c exceed the elliptic flow values by about 60% in midcentral collisions. These nonflow contributions are attributed to nearside and back-to-back jetlike correlations, the latter exhibiting centrality dependent broadening.
  Physical Review Letters 01/2004; 92(3):032301. · 7.37 Impact Factor
• Article: Hadron physics with CERES: spectra and collective flow

  G. Agakichiev, H. Appelshäuser, R. Baur, P. Braun-Munzinger, F. Ceretto, A. Cherlin, A. Drees, P. Ernst, S. Esumi, U. Faschingbauer, [......], I. Tserruya, Th. Ullrich, C. Voigt, S. Voloshin, C. Weber, J. P. Wessels, Th. Wienold, B. Windelband, J. P. Wurm, V. Yurevich
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  ABSTRACT: Hadronic spectra from interactions of Pb on Au at 158AGeV/c have been measured by the CERES experiment at the CERN SPS. We report on preliminary results on transverse mass spectra of identified pions and negative hadrons as well as spectra of the positive charge excess obtained by subtracting the negative particle distribution from that of positive tracks. We have also performed a study of the event azimuthal anisotropies which give evidence for directed and elliptic flow in non-central collisions.
  Nuclear Physics A 07/1998; 638:467-470. · 1.54 Impact Factor
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  Available from: psu.edu

  Article: CERES results on low-mass electron pair production in Pb--Au collisions

  Ceres Collaboration, G. Agakichiev, R. Baur, P. Braun-Munzinger, F. Ceretto, A Drees, S Esumi, U. Faschingbauer, Z Fraenkel, E. Gatti, [......], Y. Panebrattsev, A Pfeiffer, J Rak, I Ravinovich, S. Razin, P Rehak, M Richter, M. Sampietro, N. Saveljic, J Schukraft
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  ABSTRACT: this paper we present an analysis of the data taken during the SPS Pb-beam period in the fall of 1995. The results confirm previous findings of CERES showing that the pair production in the mass range 0.2 ! m ee ! 1.5 GeV=c
  03/1998;
• Article: pair production in 158A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse momentum

  G. Agakichiev, R. Baur, F. Ceretto, A Drees, S Esumi, U. Faschingbauer, Z Fraenkel, E. Gatti, C. P. De Los Heros, P. Holl, [......], Y. Panebrattsev, A Pfeiffer, J Rak, I Ravinovich, S. Razin, P Rehak, M Richter, M. Sampietro, N. Saveljic, J Schukraft
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  ABSTRACT: y Now at State University New York at Stony Brook Doctoral Thesis of C. Voigt. 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/c 2 is enhanced by a factor of 3.5 Sigma 0.4 (stat) Sigma 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/c 2 . 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 p ? . Three experiments at the CERN Super-Proton Synchrotron (HELIOS-3 [1], NA38 [2] and CERES/NA45 [3]) have observed significantly more dileptons from central collisions of 200 GeV/nucleon sulfur beams with heavy targets than is expected from `conventional sources' [4,5]. The en...
  01/1998;
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  Available from: Gennady Alexeevich Ososkov

  Article: A New Robust Fitting Algorithm For Vertex Reconstruction In The Ceres Experiment

  G. Agakichiev, O. Barannikova, F. Ceretto, U. Faschingbauer, P. Glassel, E Kolganova, G. Ososkov, J Rak, N. Saveljic, I Tserruya
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  ABSTRACT: : In this paper we report on the application of a robust approach based on a reweighted least squares method for the vertex reconstruction of the CERES/NA45 experiment at the CERN SPS for the case of 160 GeV/u Pb+Au collisions and compare its performance with the presently used algorithm based on the minimization of summed Gaussian weights. In the CERES/NA45 experiment a doublet of cylindrical silicon drift detectors (SDD) is used for vertex reconstruction and tracking. The vertex reconstruction algorithm has to cope with a background-contaminated environment. Furthermore, in the case of ultrarelativistic heavy-ion collisions where high event multiplicities occur (dn ch =dj ' 500), the probability of confusing hits from close or intersecting tracks is high. The algorithm needs to provide the precise vertex location even at high occupancies, at a reasonable speed. Our findings are that the robust iterative procedure presented here is about an order of magnitude faster than approaches us...
  10/1997;
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  Available from: Gennady Alexeevich Ososkov

  Article: A new robust fitting algorithm for vertex reconstruction in the CERES experiment

  G. Agakichiev, O. Barannikova, F. Ceretto, U. Faschingbauer, P. Glässel, E. Kolganova, G. Ososkov, Yu. Panebratsev, J. Rak, N. Saveljic, I. Tserruya, Th. Ullrich, J.P. Wurm
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  ABSTRACT: In this paper we report on the application of a robust approach based on a reweighted least squares method for the vertex reconstruction of the CERES/NA45 experiment at the CERN SPS for the case of 160 GeV/u Pb+Au collisions and compare its performance with the presently used algorithm based on the minimization of summed Gaussian weights.In the CERES/NA45 experiment a doublet of cylindrical silicon drift detectors (SDD) is used for vertex reconstruction and tracking. The vertex reconstruction algorithm has to cope with a background-contaminated environment. Furthermore, in the case of ultrarelativistic heavy-ion collisions where high event multiplicities occur (), the probability of confusing hits from close or intersecting tracks is high. The algorithm needs to provide the precise vertex location even at high occupancies, at a reasonable speed. Our findings are that the robust iterative procedure presented here is about an order of magnitude faster than approaches using standard minimization packages, at a comparable or slightly better accuracy.
  Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
• Article: STUDY OF ELECTRON PAIR AND HADRON PRODUCTION WITH IN AND PB BEAMS AT THE CERN SPS. (ADDENDUM 2 TO PROPOSAL SPSC-P-P280).

  G. Agakichiev, H Appelshäuser, R. Baur, J. Bielcikova, P. Braun-Munzinger, A. Cherlin, A Drees, S I Esumi, K. Filimonov, Z Fraenkel, [......], S. Specht, J. Stachel, H. Tilsner, I Tserruya, C. Voigt, S. Voloshin, C Weber, J. P. Wessels, J P Wurm, V. Yurevich
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  ABSTRACT: Hardcopy at DESY
• Article: New results on low-mass lepton pair production in Pb-Au collisions at 158 GeV per nucleon

  B. Lenkeit, G. Agakichiev, H. Appelshäuser, R. Baur, P. Braun-Munzinger, A. Cherlin, F. Ceretto, A. Drees, S. Esumi, U. Faschingbauer, [......], J. Stachel, I. Tserruya, Th. Ullrich, C. Voigt, S. Voloshin, C. Weber, J.P. Wessels, T. Wienold, J.P. Wurm, V. Yurevich
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  ABSTRACT: The CERES/NA45 experiment at the CERN-SPS is dedicated to study the production of e+e−-pairs in ultrarelativistic heavy ion collisions. Compared to extrapolations from results obtained in proton-induced reactions, it has previously observed an enhanced production in S-Au [1] and Pb-Au [2] collisions. To verify this enhancement and to study its properties, higher statistics were accumulated during a runtime in 1996. We report here, for the first time, on the results of this analysis (for details see ref. [3]).
  Nuclear Physics A.
• Article: CERES results on low-mass electron pair production in PbAu collisions

  G. Agakichiev, R. Baur, P. Braun-Munzinger, F. Ceretto, A. Drees, S. Esumi, U. Faschingbauer, Z. Fraenkel, Ch. Fuchs, E. Gatti, [......], J. Stachel, G. Tel-Zur, I. Tserruya, T. Ullrich, C. Voigt, C. Weber, J.P. Wessels, T. Wienold, J.P. Wurm, V. Yurevich
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  ABSTRACT: The CERES/NA45 collaboration measured, at the CERN SPS, low-mass electron pair production in PbAu collisions at 158 A GeV/c incident momentum. In this paper we present an analysis of the data taken during the SPS Pb-beam period in the fall of 1995. The results confirm previous findings of CERES showing that the pair production in the mass range 0.2 <mee < 1.5 GeV/c2, when scaled to the ion case with the event multiplicity, is enhanced over the expected yield from the known hadronic sources in pp collisions. A comparison of the results for different multiplicity bins indicates that the excess increases faster than linearly with charged-particle multiplicity. We also present the transverse-momentum distributions of the observed pairs.
  Nuclear Physics A.
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  Available from: arxiv.org

  Article: Recent results from Pb-Au collisions at 158 GeV/c per nucleon obtained with the CERES spectrometer

  B. Lenkeit, G. Agakichiev, H. Appelshäuser, R. Baur, P. Braun-Munzinger, F. Ceretto, A. Cherlin, A. Drees, S. Esumi, U. Faschingbauer, [......], J. Stachel, I. Tserruya, Th. Ullrich, C. Voigt, S. Voloshin, C. Weber, J.P. Wessels, T. Wienold, J.P. Wurm, V. Yurevich
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  ABSTRACT: 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].
  Nuclear Physics A.
• Article: A new robust fitting algorithm for vertex reconstruction in the CERES experiment

  G. Agakichiev, O Yu Barannikova, F. Ceretto, U. Faschingbauer, P Glässel, E Kolganova, G A Ososkov, Yu A Panebratsev, J Rak, N. Saveljic, T S Ullrich, J P Wurm
• Article: One spin pion asymmetry in d$\uparrow$ + A --> $\pi^{\pm}$ + X processes near $\vartheta_{\pi}$=90$^0$

  G. S. Averichev, G. Agakichiev, Yu T Borzunov, L. G. Efimov, N Ghiordanescu, L. B. Golovanov, Y G Guseinaliev, Yu I Minaev, N S Moroz, S A Nikiforov, [......], G. P. Skoro, E I Shahaliev, S S Shimansky, M. K. Suleimanov, M. V. Tokarev, I O Tsvetkov, N N Trofimov, V. I. Yurevich, I Zborovský, A P Zvinev
• Article: High $p_{T}$ charged-pion production in Pb-Au collisions at 158 AGeV/c

  G. Agakichiev, R. Baur, P. Braun-Munzinger, A Drees, S C Esumi, U. Faschingbauer, Zeev Fraenkel, C Fuchs, P Glässel, C Pérez de los Heros, [......], J J Stachel, G Tel-Zur, Itzhak Tserruya, T S Ullrich, C A Voigt, C Weber, J. P. Wessels, T. Wienold, J P Wurm, V. I. Yurevich
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  ABSTRACT: The CERES/Na45 experiment at CERN SPS measured transverse momentum spectra ofcharged-pions in the range 1<pt<4GeV/c near mid-rapidity in 158 AGeV/c Pb-Aucollisions. The invariant transverse momentum spectra are exponential over theentire observed range. The average inverse slope is 245+/- 5MeV/c, it shows a2.4 0ncrease with centrality of the collision over the 35most centralfraction of the cross section. The pi-/pi+ ratio is constant at 1.028+/-0.005over the pt interval measured.
• Article: Low-mass e+e− pair production in 158 A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse momentum

  G. Agakichiev, R. Baur, P. Braun-Munzinger, F. Ceretto, A. Drees, S. Esumi, U. Faschingbauer, Z. Fraenkel, Ch. Fuchs, E. Gatti, [......], J. Stachel, G. Tel-Zur, I. Tserruya, T. Ullrich, C. Voigt, C. Weber, J.P. Wessels, T. Wienold, J.P. Wurm, V. Yurevich
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  ABSTRACT: 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/c2 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/c2. 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 p⊥.
  Physics Letters B.
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  Available from: Guy Tel-Zur

  Article: Low-mass $e^{+}e^{-}$ pair production in 158 A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse momentum

  G. Agakichiev, R. Baur, P. Braun-Munzinger, F. Ceretto, A Drees, S C Esumi, U. Faschingbauer, Zeev Fraenkel, C Fuchs, E. Gatti, [......], J J Stachel, G Tel-Zur, Itzhak Tserruya, T S Ullrich, C A Voigt, C Weber, J. P. Wessels, T. Wienold, J P Wurm, V. I. Yurevich
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  ABSTRACT: We report a measurement of low-mass electron pairsobserved 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 evidencefor 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.