Low Mass Vector Mesons Research Articles

Commissioning of a hadron blind detector for dielectron measurement in pA reactions at J-PARC

The J-PARC E16 experiment measures mass spectra of low-mass vector mesons, ρ, ω, and ϕ, in nuclei via e + e - decays. Vector mesons are produced in pA reactions. A spectrometer with a large acceptance and a high-intensity beam up to 1 × 1010 protons per ∼2-sec duration pulse are utilized to collect a sufficient number of vector mesons. We have developed a spectrometer, which has two types of electron identification detectors: a hadron blind detector (HBD) and a lead-glass calorimeter. Commissioning runs have been performed at the J-PARC high-momentum beam line. The HBD successfully observed on average 11 ± 1 photoelectrons for an incident electron. We achieved the pion rejection of 0.9 ± 0.2% with the electron detection efficiency of 61 ± 4% for the HBD, which was consistent of the expected performance.

Low-mass electron pairs from Au+Au collisions at 1.23A GeV with HADES

Lepton pairs are considered as an ideal probe to access the microscopic properties of strongly-interacting matter under extreme conditions of temperature and density. The spectral distribution of lepton pairs in the region below the low mass vector mesons is characterized by an excess radiation above contributions from late meson decays, the so-called hadronic cocktail. It is theoretically understood as a thermal radiation based on Vector Meson Dominance assuming a strong broadening of the in-medium spectral function due to coupling to baryons and anti-baryons.In continuation of a systematic investigation of the emissivity of strongly interacting matter, HADES has recently measured the dielectron emission in Au+Au collisions at 1.23A GeV beam energy. The first measurement for Au+Au completes the systematics of dilepton production in NN/pA/AA collisions in the SIS18 energy range.This contribution will present new results for the Au+Au system based on a data sample of 5.0 billion events of the 40% most central collisions.

Measurement of dielectrons in pp, p–Pb and Pb–Pb collisions with ALICE at the LHC

Dielectrons are penetrating probes which carry unaffected information on the hot and dense medium created in ultra-relativistic heavy-ion collisions. The low-mass region of the dielectron spectrum (mπ0 < mee < mρ) is sensitive to virtual photon production and in-medium modifications of low-mass vector meson spectral functions. These modifications are connected to the restoration of chiral symmetry, which is expected at high temperature. Dielectrons are also sensitive to heavy-flavor production.In these proceedings, we present the preliminary results of dielectron measurements in pp collisions at = 7 TeV, in p–Pb collisions at = 5.02 TeV and in central (0-10%) Pb–Pb collisions at = 2.76 TeV with the ALICE experiment at the LHC. The expected scenario and perspectives for the dielectron measurement after the ALICE upgrade are also discussed.

Experimental overview on hadronic resonance production in high-energy nuclear collisions

I summarize recent results of low-mass vector meson measurements in high-energy nuclear collisions.

Low-mass vector meson production at forward rapidity in p+p and d+Au collisions at $$\sqrt{s_{\rm NN}}$$ s NN = 200 GeV from a multiphase transport model

Low-mass vector meson (\(\rho , \omega \), and \(\phi \)) production at forward rapidity in p+p and d+Au collisions at \(\sqrt{s_{{\rm NN}}}\) = 200 GeV is studied within the framework of a multiphase transport model (AMPT). Detailed investigations, including the transverse momentum and the rapidity dependence of low-mass vector meson production in the AMPT model, show that the hadron interaction process is important for a quantitative description of the \(\rho \) and \(\omega \) data. But for the \(\phi \) meson, the strange quark production in the AMPT model with the string melting scenario describes the data reasonably well, while the default AMPT model under-predicts the data. The \({\rm N}(\phi )/{\rm N} (\rho + \omega )\) ratio from the AMPT model with the string melting scenario perfectly describes the data in p+p collisions. For the d+Au collisions, an increased trend of this ratio vs. transverse momentum and the number of participants are observed from the AMPT model. Our results indicate that a precise measurement of the \({\rm N}(\phi )/ {\rm N} (\rho + \omega )\) ratio in d+Au and Au+Au collisions will shed more light on the strangeness production and its dynamics in quark–gluon plasma.

Testing of Track Point Resolution of Gas Electron Multiplier with Pion Beam at CERN SPS

The future Compressed Baryonic Matter (CBM) Experiment at FAIR, Germany will measure charmonium and low mass vector mesons by their muonic decay channel with a Muon Chamber (MUCH) detector. Operation of CBM-MUCH at high interaction rate requires a detector with large acceptance, high granularity and high rate capability. First few detector stations at MUCH will use Gas Electron Multiplier (GEM) technology [1, 2] . We have conducted a test experiment with prototype detectors using triple GEM at CERNSPS with 150 GeV/c Pion beam. In CBM experiment, tracks are reconstructed using the hits recorded in a number of Silicon Tracking Stations (STS) placed inside a dipole magnet. Later those tracks are projected onto muon chambers for further reconstruction required for muon detection. The beam undergoes multiple scattering inside the absorbers so tracking may be effected. We report here the estimate of the track-point resolution of the GEM detector using a self-trigger read out ASIC.

Low mass dilepton production in pp, p–Pb and Pb–Pb collisions with ALICE

Low mass vector meson ( ρ, ω, ϕ ) production provides key information on the hot and dense state of strongly interacting matter produced in high-energy heavy-ion collisions (called Quark-Gluon Plasma, QGP). Strangeness enhancement is one of the possible signatures of the Quark-Gluon Plasma formation and can be accessed through the measurement of ϕ meson production with respect to ρ and ω mesons. The production dynamics and hadronization process in relativistic heavy-ion collisions can be probed through the measurement of the ϕ nuclear modification factor.We present results on the low mass dimuon analysis in pp, p–Pb and Pb–Pb collisions. In pp collisions at √ s = 2.76 TeV the ϕ differential cross section as a function of the transverse momentum has been measured, serving as a baseline for Pb–Pb data.The ϕ yield and the nuclear modification factor R pPb at forward and backward rapidity have been measured for p–Pb collisions at √ s = 5.02 TeV. At forward rapidity, R pPb increases as a function of p T , saturating for p T > 3 GeV/ c at R pPb ~ 1. At backward rapidity, R pPb shows an increase as a function of the transverse momentum up to a factor of 1.6 for p T ~ 3-4 GeV/ c , followed by a decrease at higher p T .The ϕ yield and nuclear modification factor R AA have been measured for Pb–Pb collisions at √ s NN = 2.76 TeV in the intermediate p T region 2 p T c , as a function of the number of participating nucleons. Remarkable differences are observed in the comparison between the results at forward rapidity in the dimuon channel and the ones measured in the same p T range at midrapidity in the hadronic channel ϕ → KK .In the dielectron channel at midrapidity, the invariant mass distributions in the range 0 m ee c 2 are compared with the expected hadronic sources for pp collisions at √ s = 7 TeV, and for p–Pb collisions at √ s NN = 5.02 TeV. Latest results of the analysis of Pb–Pb collisions at √ s NN = 2.76 TeV are presented.

Design and performance simulation of a segmented-absorber based muon detection system for high energy heavy ion collision experiments

A muon detection system (MUCH) based on a novel concept using a segmented and instrumented absorber has been designed for high-energy heavy-ion collision experiments. The system consists of 6 hadron absorber blocks and 6 tracking detector triplets. Behind each absorber block a detector triplet is located which measures the tracks of charged particles traversing the absorber. The performance of such a system has been simulated for the CBM experiment at FAIR (Germany) that is scheduled to start taking data in heavy ion collisions in the beam energy range of 6–45AGeV from 2019. The muon detection system is mounted downstream to a Silicon Tracking System (STS) that is located in a large aperture dipole magnet which provides momentum information of the charged particle tracks. The reconstructed tracks from the STS are to be matched to the hits measured by the muon detector triplets behind the absorber segments. This method allows the identification of muon tracks over a broad range of momenta including tracks of soft muons which do not pass through all the absorber layers. Pairs of oppositely charged muons identified by MUCH could therefore be combined to measure the invariant masses in a wide range starting from low mass vector mesons (LMVM) up to charmonia. The properties of the absorber (material, thickness, position) and of the tracking chambers (granularity, geometry) have been varied in simulations of heavy-ion collision events generated with the UrQMD generator and propagated through the setup using the GEANT3, the particle transport code. The tracks are reconstructed by a Cellular Automaton algorithm followed by a Kalman Filter. The simulations demonstrate that low mass vector mesons and charmonia can be clearly identified in central Au+Au collisions at beam energies provided by the international Facility for Antiproton and Ion Research (FAIR).

Low-mass vector-meson production at forward rapidity inp+pcollisions ats=200 GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured low-mass vector-meson, ω, ρ, and ϕ, production through the dimuon decay channel at forward rapidity (1.2<|y|<2.2) in p+p collisions at s=200 GeV. The differential cross sections for these mesons are measured as a function of both pT and rapidity. We also report the integrated differential cross sections over 1<pT<7 GeV/c and 1.2<|y|<2.2: dσ/dy(ω+ρ→μμ)=80±6(stat)±12(syst) nb and dσ/dy(ϕ→μμ)=27±3(stat)±4(syst) nb. These results are compared with midrapidity measurements and calculations.4 MoreReceived 23 May 2014DOI:https://doi.org/10.1103/PhysRevD.90.052002© 2014 American Physical Society

Energy Dependence of the Electroproduction of Low Mass Vector Mesons

The energy dependence of the electroproduction of low mass vector mesons has been analyzed. Two pomeron model is used assuming that the pomeron is a Regge pole. Regge amplitude for the photoproduction processes is extended to include the electroproduction. In this case the residues of the two poles are functions of the virtuality of the photon. These functions are extracted from the experimental data using the chi- square method. A reasonable fit to the data is obtained including these functions in the two pomeron model

Energy Dependence of the Electroproduction of Low Mass Vector Mesons

The energy dependence of the electroproduction of low mass vector mesons has been analyzed. Two pomeron model is used assuming that the pomeron is a Regge pole. Regge amplitude for the photoproduction processes is extended to include the electroproduction. In this case the residues of the two poles are functions of the virtuality of the photon. These functions are extracted from the experimental data using the chi- square method. A reasonable fit to the data is obtained including these functions in the two pomeron model

The CBM-RICH detector

The main task of the future Compressed Baryonic Matter experiment (CBM), to be operatedat the FAIR facility at GSI, Darmstadt, is the exploration of theproperties of super-dense nuclear matter. The search for in-mediummodifications of hadrons, the study of the transition from densehadronic matter to quark-gluon matter, and the possible location of acritical endpoint in the QCD phase diagram of strongly interactingmatter are the most important physics goals of CBM. Detailedmeasurements of di-leptons stemming from low-mass vector-mesons andcharmonium have a large potential to shed light on the existence ofsuch effects.The Ring Imaging Cherenkov detector of the CBM experiment aims at aclean and efficient electron identification. It is foreseen to useCO2 as radiator gas and equip the detector with a focussing mirrorsystem and multi-anode photomultiplier tubes as photon detector. Inthis paper we present selected results of R&D studies and beam testmeasurements of the detector prototype performed in fall 2011 and 2012at the CERN/PS with a mixed electron-pion beam.

Low mass vector meson production in pp and Pb-Pb collisions measured with ALICE at the LHC

Vector mesons are key probes of the hot and dense state of strongly interacting matter produced in heavy ion collisions. Their dileptonic decay channel is particularly suitable for these studies, since dileptons have negligible final state interactions in hadronic matter. In particular, strangeness production can be studied through the measurement of muon pairs coming from the decay of ϕ mesons. The ALICE apparatus at the LHC can access vector mesons produced at forward rapidity (2.5 < y < 4) through their decays in muon pairs. We present results on vector meson production in pp and Pb-Pb collisions at = 2.76 TeV. The ϕ meson production cross section is measured in pp collisions. In Pb-Pb collisions, a measurement of the ϕ/(ρ + ω) ratio and of the 0 nuclear modification factor as a function of the collision centrality is obtained.

The Compressed Baryonic Matter experiment

The Compressed Baryonic Matter (CBM) experiment is a next-generation fixed target detector which will operate at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt. The goal of this experiment is to explore the QCD phase diagram in the region of high net baryon densities using high-energy nucleus-nucleus collisions. Its research program includes the study of the equation-of-state of nuclear matter at high baryon densities, the search for the deconfinement and chiral phase transitions and the search for the QCD critical point. The CBM detector is designed to measure both bulk observables with a large acceptance and rare diagnostic probes such as charm particles, multi-strange hyperons, and low mass vector mesons in their di-leptonic decay. The physics program of CBM will be summarized, followed by an overview of the detector concept, a selection of the expected physics performance, and the status of preparation of the experiment.

Investigation of surface homogeneity of mirrors for the CBM-RICH detector and low-mass di-electron feasibility studies

The Compressed Baryonic Matter (CBM) experiment at the future FAIR facility will investigate high net-baryon density matter at moderate temperatures in A+A collisions from 4-45 AGeV. One of the key observables of the CBM physics program is electromagnetic radiation as a probe of strongly interacting matter in heavy-ion collisions, carrying undistorted information on its conditions to the detector. This includes detailed investigations of low-mass vector mesons in their di-electron channel. A clean and efficient identification of electrons is required for such measurements. In CBM the electron identification will be performed by a Ring Imaging Cherenkov detector and several layers of Transition Radiation Detectors. The RICH detector will be operated with CO2 radiator gas, MAPMTs as photodetector and spherical glass mirrors as focusing elements. A high quality of the mirrors in terms of reflectivity and surface homogeneity is required. In the first part of the contribution results on measurements of the mirror surface homogeneity are presented. Results on the feasibility studies of low-mass di-electron measurements with realistic detector response are discussed in the second part of the contribution.

The Compressed Baryonic Matter experiment

The Compressed Baryonic Matter (CBM) experiment is a next-generation fixed-target detector which will operate at the future Facility for Antiproton and Ion Re- search (FAIR) in Darmstadt. The goal of this experiment is to explore the QCD phase diagram in the region of high net baryon densities using high-energy nucleus-nucleus col- lisions. Its research program includes the study of the equation-of-state of nuclear matter at high baryon densities, the search for the deconfinement and chiral phase transitions and the search for the QCD critical point. The CBM detector is designed to measure both bulk observables with a large acceptance and rare diagnostic probes such as charm parti- cles, multi-strange hyperons, and low mass vector mesons in their di-leptonic decay. The physics program of CBM will be summarized, followed by an overview of the detector concept, a selection of the expected physics performance, and the status of preparation of the experiment.

Study of the MPD detector capabilities for electron-positron pair measurements at the NICA collider

One of the main tasks of the NICA/MPD physics program is a study of low-mass vector mesons ρ, ω, ϕ by measuring their dileptonic decay channels. In this paper, the current status of simulations of electron-positron pair measurements in MPD is presented and the detector performance for such measurements is discussed.

Compressed baryonic matter experiment at FAIR

The Compressed Baryonic Matter (CBM) experiment is being planned at the Facility for Antiproton and Ion Research (FAIR), under realization next to the GSI laboratory in Darmstadt, Germany. Its physics programme addresses the QCD phase diagram in the region of highest net baryon densities. Of particular interest are the expected first order phase transition from partonic to hadronic matter, ending in a critical point, and modifcations of hadron properties in the dense medium as a signal of chiral symmetry restoration. Laid out as a fixed-target experiment at the synchrotrons SIS-100/SIS-300, providing magnetic bending power of 100 and 300 T/Fm, the CBM detector will record both proton-nucleus and nucleus-nucleus collisions at beam energies up to 45 AGeV. Hadronic, leptonic and photonic observables will be measured in a large acceptance. The nuclear interaction rates will reach up to 10 MHz to measure extremely rare probes like charm near threshold. This requires the development of novel detector systems, trigger and data acquisition concepts as well as in- novative real-time reconstruction techniques. A key observable of the physics program is a precise measurement of lowmass vector mesons and charmonium in their leptonic decay channel. In CBM, electrons will be identified using a gaseous RICH detector combined with several TRD detectors positioned after a system of silicon tracking stations which are located inside a magnetic dipole field. The concept of the RICH detector, results on R & D as well as feasibility studies and invariant mass distributions of charmonium will be discussed.

Di-muon measurements with the CBM experiment at FAIR

The planned Compressed Baryonic Matter (CBM) experiment at the upcoming FAIR center at GSI, Darmstadt is aiming at the investigation of baryonic matter at high density produced in relativistic heavy-ion collisions. The research program comprises the exploration of the QCD phase diagram at high net baryon densities and moderate temperatures, the search for the de-confinement phase transition, and in-medium modifications of hadrons. The proposed key observables include the measurement of charmonia and low mass vector mesons which can be measured via their decay into the dilepton channel. In this paper, we discuss the physics motivation, detector concepts, and feasibility studies of the di-muon measurements.

Di-electron spectroscopy in CBM

Di-electron spectroscopy is considered to be one of the major programs of the Compressed Baryonic Matter (CBM) experiment at the future FAIR accelerator at Darmstadt. In this contribution, the analysis strategy for the reconstruction of low-mass vector mesons with the proposed CBM detector setup is discussed. Results from feasibility studies will be presented and compared with data from existing dilepton experiments.