Dielectron Measurements Research Articles

Low-mass dielectron measurement in pp and Pb–Pb collisions in ALICE

We report on the first dielectron measurement in pp collisons at = 7 TeV with the ALICE detector system. The results are compared to the expected hadronic sources. The hadronic cocktail agrees to the measured dielectron continuum within statistical and systematic uncertainties. The status of the dielectron measurement in Pb–Pb collisions at = 2.76 TeV is addressed.

Dilepton Measurements at STAR

In the study of hot and dense nuclear matter, created in relativistic heavy-ion collisions, dilepton measurements play an essential role. Leptons, when compared to hadrons, have only little interaction with the strongly interacting system. Thus, dileptons provide ideal penetrating probes that allow the study of such a system throughout its space-time evolution. In the low mass range (Mll < 1.1 GeV/c2), the dominant source of dileptons originates from the decay of vector mesons which may see effects from chiral symmetry restoration. In the intermediate mass range (1.1 < Mll < 3.0 GeV/c2), the main contributions to the mass spectrum are expected to originate from the thermal radiation of a quark-gluon plasma as well as the decays of charm mesons. In the high mass range (Mll > 3.0 GeV/c2), dilepton measurements are expected to see contributions from primordial processes involving heavy quarks, and Drell-Yan production.With the introduction of the Time-of-Flight detector, the STAR detector has been able to perform large acceptance, high purity electron identification. In this contribution, we will present STAR's recent dielectron measurements in the low and intermediate mass range for RHIC beam energies ranging between 19.6 and 200 GeV. Compared to electrons, muon measurements have the advantage of reduced bremsstrahlung radiation in the surrounding detector materials. With the upcoming detector upgrades, specifically the muon detector (MTD), STAR will be able to include such measurements in its (di-)lepton studies. We will discuss the future dilepton program at STAR and the physics cases for these upgrades.

Dielectron measurements during heavy ion collisions at $$\sqrt {s_{NN} }$$ = 200 GeV in the PHENIX experiment at RIHC

The production of dielectron pairs is measured in PHENIX experiment during p + p, d + Au, Cu + Cu, and Au + Au collisions at \(\sqrt {s_{NN} }\) = 200 GeV. In the mass region between φ and J/ψ mesons, the yield is consistent with expectations from correlated production. In the mass region below φ mesons, the p + p and d+ Au spectra are well described by known contributions from light meson decays. In contrast, the Au + Au minimum bias spectrum in this region is enhanced by a factor of 4.7, concentrated at low pT < 1.5 GeV/s and rapidly rising with centrality. Existing theoretical models cannot describe the observed enhancement.

The STAR Dilepton Physics Program

Dileptons provide ideal penetrating probes of the evolution of strongly-interacting matter. With the Time-of-Flight upgrade, STAR is in a unique position to provide large-acceptance dielectron measurements. We discuss preliminary dielectron results for Au+Au collisions at $\sqrt{s_\mathrm{NN}}$=19.6 - 200 GeV, and compare to recent model calculations. With upcoming detector upgrades STAR will further improve its dielectron measurements as well as include dimuon measurements.

Dielectron measurements by PHENIX using the HBD

Abstract PHENIX presents first dielectron spectra for p + p and Au + Au collisions measured using the HBD detector. The p + p results are compatible with cocktail calculations that take into account the modified aperture of PHENIX due to a change in the magnetic field configuration. The Au + Au results are compared to the expected yield of dielectrons from meson decays (hadronic cocktail) in centrality selections 20–40% and 60–92%. Our results do not show any significant deviations from these predictions and are compatible with previous measurements published by PHENIX.

Measurement of low mass dielectrons with the HBD upgrade of PHENIX

The PHENIX experiment was upgraded with the Hadron Blind Detector (HBD) for the measurement of low-mass electron pairs. The HBD reduces the combinatorial background by providing additional electron identification in a field-free region close to the vertex and by exploiting the small opening angle of the π0 Dalitz and conversion pairs. The HBD was successfully operated during Run 9 and Run 10 at the RHIC in the measurements of e+e− pairs in p+p and Au+Au collisions, respectively. This paper reports on the present status of the dielectron analysis in Au+Au collisions at = 200 GeV.

Dielectron continuum production from = 200 GeV p+p and Au+Au collisions at STAR

We present the first STAR dielectron measurement in 200 GeV p+p and Au+Au collisions. Results are compared to hadron decay cocktails to search for vector meson in-medium modification in the low mass region and quark–gluon plasma thermal radiation in the intermediate mass region. The ω → e+e− spectra and the transverse mass distribution in the intermediate mass region are also discussed.

Probing resonance matter with virtual photons

In the energy domain of 1 − 2 GeV per nucleon, HADES has measured rare penetrating probes (e+e−) in C+C, Ar+KCl, p+p, d+p and p+Nb collisions. For the first time the electron pairs were reconstructed from quasi-free n+p sub-reactions by detecting the proton spectator from the deuteron breakup. An experimentally constrained N+N reference spectrum was established. Our results demonstrate that the gross features of di-electron spectra in C+C collisions can be explained as a superposition of independent N+N collisions. On the other hand, a direct comparison of the N+N reference spectrum with the e+e−invariant mass distribution measured in the heavier system Ar+KCl at 1.76 GeV/u shows an excess yield above the reference, which we attribute to radiation from resonance matter. Moreover, the combined measurement of di-electrons and strangeness in Ar+KCl collisions has provided further intriguing results which are also discussed.

Electromagnetic Probes and Heavy Flavor in PHENIX

Abstract These proceedings summarize the di-electron spectrum measurements by PHENIX in p + p and A u + A u collisions at s N N = 200 GeV , along with a comparison to the expectations from hadronic sources and various model predictions. An overview of the latest PHENIX results on open heavy flavor and quarkonia production, measured through the electron and muon channels at mid-rapidity and forward/backward rapidity for p + p , d + A u and A u + A u collisions is also presented.

Systematic study of the optimization potential for di-electron measurements in the CBM experiment

In this paper, we present a systematic investigation of an optimization of the di-electron setup of the CBM experiment for the measurement of low-mass vector mesons, and establish a limit on pion misidentification.

QUARKONIA MEASUREMENTS WITH THE CENTRAL DETECTORS OF ALICE

A Large Ion Collider Experiment – ALICE will become operational with the startup of the Large Hadron Collider – LHC at the end of 2007. One focus of the physics program is the measurement of quarkonia in proton-proton and lead-lead collisions. Quarkonia states will be measured in two kinematic regions and channels: di-muonic decays will be measured in the forward region by the muon arm, the central part of the detector will measure di-electronic decays. The presented studies show the expected performance of the di-electron measurement in proton-proton and central lead-lead collisions.

Di-electron measurements in C+C reactions at [formula omitted] with HADES

The High Acceptance DiElectron Spectrometer HADES has been recently commissioned at GSI, Darmstadt. It has been designed for systematic studies of hadron properties inside nuclear matter. We report first preliminary results on invariant masses e + e - -pairs which were measured in 12 C + 12 C collisions at E kin = 2 GeV ⋅ A . The analysis methods are briefly outlined and a comparison with detailed Monte-Carlo simulations is shown.