Low-mass e+e− pair production in 158 A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse momentum

Agakichiev, G.; Baur, Roland; Braun‐Munzinger, P.; Ceretto, F.; Esumi, S.; Faschingbauer, U.; Fraenkel, Z.; Fuchs, C.; Gatti, E.; Glässel, P.; Heros, C. Pérez de los; Holl, P.; Jung, Ch.; Lenkeit, B.; Messer, M.; Panebrattsev, Y.; Pfeiffer, A.; Rak, J.; Ravinovich, I.; Razin, S. V.; Řehák, P.; Richter, Matthias; Sampietro, Marco; Saveljić, N.; Schukraft, J.; Shimansky, S.; Seipp, W.; Socol, E.; Specht, H. J.; Stachel, J.; Tel-Zur, G.; Tserruya, I.; Ullrich, T.; Voigt, Christiane; Weber, C.; Wessels, J. P.; Wienold, T.; Wurm, J.P.; Yurevich, V. I.

doi:10.1016/s0370-2693(98)00083-5

Cited by 215 publications

(44 citation statements)

References 22 publications

(25 reference statements)

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“…We emphasize as well that the behavior of the curves in Fig. 3, which correspond to a finite system, has a similar tendency to the CERES data [1,2]. For comparison, we present in Fig.…”

supporting

confidence: 65%

“…That is why, the dileptons (e + e − and µ + µ − pairs) observed in high-energy heavy ion collisions secure an excellent opportunity for obtaining information on the initial state and the evolution of the system created in a collision. The enhancement with an invariant mass of 200 ÷ 800 MeV observed by the CERES collaboration [1,2] in the production of dileptons has received recently a considerable attention and has been studied in the framework of various theoretical models (for the review, see Ref.[3]). It was found that a large part of the observed enhancement is due to the medium effects (see Refs.…”

mentioning

confidence: 99%

“…To obtain eq. (3), we represent the amplitude A ρ = out|S (2) |in of the reaction under consideration as…”

mentioning

confidence: 99%

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Pion and Quark Annihilation Mechanisms of Dilepton Production in Relativistic Heavy Ion Collisions

Anchishkin

Naryshkin²

2005

Mod. Phys. Lett. A

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We revise the π + π − and qq annihilation mechanisms of dilepton production during relativistic heavy-ion collisions. We focus on the modifications caused by the specific features of intramedium pion states rather than by medium modification of the ρ-meson spectral density. The main ingredient emerging in our approach is a form-factor of the multi-pion (multi-quark) system. Replacing the usual delta-function the form-factor plays the role of distribution which, in some sense, "connects" the 4-momenta of the annihilating and outgoing particles. The difference between the c.m.s. velocities attributed to annihilating and outgoing particles is a particular consequence of this replacement and results in the appearance of a new factor in the formula for the dilepton production rate. We obtained that the form-factor of the multi-pion (multi-quark) system causes broadening of the rate which is most pronounced for small invariant masses, in particular, we obtain a growth of the rate for the invariant mass below two masses of the annihilating particles.Since leptons do not interact practically with the highly excited nuclear matter, they leave the reaction zone after their creation in a relativistic nucleus-nucleus collision without further rescattering. That is why, the dileptons (e + e − and µ + µ − pairs) observed in high-energy heavy ion collisions secure an excellent opportunity for obtaining information on the initial state and the evolution of the system created in a collision. The enhancement with an invariant mass of 200 ÷ 800 MeV observed by the CERES collaboration [1,2] in the production of dileptons has received recently a considerable attention and has been studied in the framework of various theoretical models (for the review, see Ref.[3]). It was found that a large part of the observed enhancement is due to the medium effects (see Refs. [4,5] and references therein). Meanwhile, pion annihilation is the main source of dileptons which come from the hadron matter [6,7]. That is why, the proper analysis of the dilepton spectra obtained experimentally gives important observables which probe the pion dynamics in the dense nuclear matter that exists at the early stage of the collision. The purpose of the present letter is to look once more on the π + π − annihilation mechanism of dilepton production from the hadron plasma by accounting the medium-induced modifications of the dilepton spectrum. In order to do this, we concentrate on the modifications which are due rather to intramedium pion states, than on the discussion of a modification of the ρ-meson spectral density. In accordance with our suggestions, the main features of a pion wave function follow from the fact that pions live a finite time in the *

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“…We emphasize as well that the behavior of the curves in Fig. 3, which correspond to a finite system, has a similar tendency to the CERES data [1,2]. For comparison, we present in Fig.…”

supporting

confidence: 65%

mentioning

confidence: 99%

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Pion and Quark Annihilation Mechanisms of Dilepton Production in Relativistic Heavy Ion Collisions

Anchishkin

Naryshkin²

2005

Mod. Phys. Lett. A

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“…Dilepton spectroscopy allows to measure the in-medium properties without distortion due to final state interactions (FSI). The CERES collaboration at CERN, for example, measured the low-mass e + e − pair production in heavy-ion collisions and observed an enhancement in the mass range of 0.3 GeV/c 2 ≤ m e + e − ≤ 0.7 GeV/c 2 over the yield expected from the known sources in pp collisions [15,16]. More recently, analyzing π + π − pairs the STAR experiment at RHIC observed a decrease of the ρ meson in-medium mass in peripheral Au+Au collisions [17].…”

mentioning

confidence: 99%

Observation of In-Medium Modifications of theωMeson

Trnka¹,

Anton²,

Bacelar³

et al. 2005

Phys. Rev. Lett.

185

101

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The photoproduction of ω mesons on nuclei has been investigated using the Crystal Barrel/TAPS experiment at the ELSA tagged photon facility in Bonn. The aim is to study possible in-medium modifications of the ω meson via the reaction γ + A → ω + X → π 0 γ + X ′ . Results obtained for Nb are compared to a reference measurement on a LH2 target. While for recoiling, long-lived mesons (π 0 , η and η ′ ), which decay outside of the nucleus, a difference in the lineshape for the two data samples is not observed, we find a significant enhancement towards lower masses for ω mesons produced on the Nb target. For momenta less than 500 MeV/c an in-medium ω meson mass of M medium = [722 +2 −2 (stat) +35 −5 (syst)] MeV/c 2 has been deduced at an estimated average nuclear density of 0.6 ρ0.

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“…Fig. 7 shows the dielectron invariant mass distributions measured by NA45 in different colliding systems [22][23][24]. While the more elementary collisions (pBe and p-Au) are reproduced within errors by final state Dalitz and direct decays of neutral mesons as…”

Section: The Pastmentioning

confidence: 99%

CERN achievements in relativistic heavy ion collisions

Brunò

2015

EPJ Web of Conferences

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Abstract. Twenty years after a Letter of Intent by the GSI and LBL groups for the "Study of particle production and target fragmentation in central 20 Ne on Pb reactions, at 12 GeV per nucleon energy of the CERN PS external beam" [1], based on the results found by the NA45/CERES, NA49, NA50, and WA97/NA57 experiments at the SPS, CERN announced compelling evidence for the formation of a new state of matter in heavyion collisions at CERN-SPS energies [2]. Some of the experiments were indeed the 2 nd or 3 rd generation successors of the apparatuses originally proposed by the GSI-LBL collaboration. Actually, the CERN ion program initiated at the SPS with the acceleration of oxygen ions at 60 and 200 GeV/nucleon only in 1986, and continued with sulphur ions at 200 GeV/nucleon up to 1993. The rest is history: lead-ion beams at 160 GeV/nucleon became available at the SPS in 1994; the LHC accelerated and collided lead beams at a center of mass energy per nucleon pair √ s NN = 2.76 TeV in 2010. Heavy ion physics is definitely in the future program of CERN: ALICE will operate a major upgrade of its detectors during the second long shutdown of the LHC, in 2018-2019, and the associated physics program will span the third and fourth LHC runs, till late 2020s.

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Low-mass e+e− pair production in 158 A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse momentum

Cited by 215 publications

References 22 publications

Pion and Quark Annihilation Mechanisms of Dilepton Production in Relativistic Heavy Ion Collisions

Pion and Quark Annihilation Mechanisms of Dilepton Production in Relativistic Heavy Ion Collisions

Observation of In-Medium Modifications of theωMeson

CERN achievements in relativistic heavy ion collisions

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