Di-lepton spectroscopy in CBM Claudia Höhne, GSI Darmstadt CBM collaboration

Claudia Höhne Quark Matter Conference, February 2008, India2 Outline Introduction & motivation physics case of CBM dileptons at maximum baryon densities Detector concept of CBM overall concept dilepton measurement: electrons - muons Simulations detector performance & challenges feasibility studies Summary CBM posters on Di-leptons T. GalatyukDi-electron spectroscopy in CBM K. AntipinSystematic study of the optimization potential for di-lepton measurements in the CBM experiment A. Kiseleva, P. Bhaduri Muon measurement with the CBM experiment at FAIR

Claudia Höhne Quark Matter Conference, February 2008, India3 Physics case Compressed Baryonic FAIR – high  B, moderate T: searching for the landmarks of the QCD phase diagram first order deconfinement phase transition chiral phase transition (high baryon densities!) QCD critical endpoint in A+A collisions from 2-45 AGeV starting in 2015 (CBM + HADES) physics program complementary to RHIC, LHC rare probes! (charm, dileptons) (interaction rates up to 10 MHz!) [Andronic et al. Nucl. Phys. A 772, 167 (2006). with the CBM energy range we will reach net baryon densities of (6-12)  0 excitation energy densities  * of (0.8-6) GeV/fm 3 for time spans of ~6 fm/c (  *=  -m N  ) → get access to the electromagnetic radiation from the fireball by the study of dileptons!

Claudia Höhne Quark Matter Conference, February 2008, India4  -meson spectral function  -meson couples to the medium: "melts" close to T c and at high  B vacuum lifetime  0 = 1.3 fm/c dileptons = penetrating probe connection to chiral symmetry restoration? particular sensitive to baryon density p n  ++  p   e +, μ + e -, μ -  "SPS" "FAIR" [R. Rapp, priv. com. (CBM physics book)] illustrate sensitivity to modifications caused by the baryonic component of the medium:  -meson spectral function weighted by 1/M to resemble the dilepton rate, Bose-factor will further amplify the low-mass part m < 0.4 GeV/c 2 of special interest! no measurement between 2-40 AGeV beam energy yet!

Claudia Höhne Quark Matter Conference, February 2008, India5 Charm production at threshold [W. Cassing et al., Nucl. Phys. A 691 (2001) 753] HSD simulations CBM will measure charm production at threshold → after primordial production, the survival and momentum of the charm quarks depends on the interactions with the dense and hot medium! → direct probe of the medium! charmonium in hot and dense matter? relation to deconfinement? relation to open charm? no measurement of charmonium below 160 AGeV beam energy yet!

Claudia Höhne Quark Matter Conference, February 2008, India6 Physics topics and Observables Onset of chiral symmetry restoration at high  B in-medium modifications of hadrons ( , ,   e + e - (μ + μ - ), D) Deconfinement phase transition at high  B excitation function and flow of strangeness (K, , , ,  ) excitation function and flow of charm (J/ψ, ψ', D 0, D ,  c ) charmonium suppression, sequential for J/ψ and ψ' ? The equation-of-state at high  B collective flow of hadrons particle production at threshold energies (open charm) QCD critical endpoint excitation function of event-by-event fluctuations (K/π,...) mostly new measurements CBM Physics Book (theory) in preparation

Claudia Höhne Quark Matter Conference, February 2008, India7 The CBM experiment tracking, momentum determination, vertex reconstruction: radiation hard silicon pixel/strip detectors (STS) in a magnetic dipole field hadron ID: TOF (& RICH) photons,  0,  : ECAL electron ID: RICH & TRD   suppression  10 4 PSD for event characterization high speed DAQ and trigger → rare probes! muon ID: absorber + detector layer sandwich  move out absorbers for hadron runs aim: optimize setup to include both, electron and muon ID STS + MVD RICH TRD TOF ECAL magnet absorber + detectors

Claudia Höhne Quark Matter Conference, February 2008, India8 STS tracking – heart of CBM Challenge: high track density  600 charged particles in  25 o Task track reconstruction: 0.1 GeV/c < p  GeV/c  p/p ~ 1% (p=1 GeV/c) primary and secondary vertex reconstruction (resolution  50  m) V 0 track pattern recognition D + →  +  + K - (c  = 312  m) D 0 → K -  + (c  = 123  m) silicon pixel and strip detectors add detectors for particle identification behind the STS → challenge for di-leptons!

Claudia Höhne Quark Matter Conference, February 2008, India9 Challenges of the di-electron measurement clean electron identification (  suppression ≥ 10 4 ) large background from physical sources  -conversions in target and STS,  0 Dalitz decays → use excellent tracking and two hit resolution (≤ 100  m) in first pixel detectors in order to reject this background: → optimize detector setup (STS, B-field), use 1‰ interaction target TRD high rates! → reduce gas gap RICH high ring densities and interaction rates → MAPMTs + fast self triggered read out electronics prototype:double-sided pad plane

Claudia Höhne Quark Matter Conference, February 2008, India10 Challenges of the di-muon measurement major background from ,K decays into , punch through of hadrons and track mismatches → use TOF information to reject punch through K,p → compact layout to minimize K,  decays → use excellent tracking to reject ,K decays in the STS by kink detection → absorber-detector sandwich for continous tracking low momentum  ! 125 cm Fe ≡ 7.5 I → p > 1.5 GeV/c 225 cm Fe ≡ 13.5 I → p > 2.8 GeV/c

Claudia Höhne Quark Matter Conference, February 2008, India11 Muon detector R&D first double GEM under test at VECC, Kolkatta up to 1 hit/cm 2 in first muon chambers! high rate capability required! detector technology still under discussion: Si-pad (first plane), Micromega, GEMs,... first TGEM production and test at PNPI, St. Petersburg

Claudia Höhne Quark Matter Conference, February 2008, India12 CbmRoot simulation framework investigation of both options in detailed simulations: detector simulation (GEANT3 implemented through VMC) full event reconstruction:- track reconstruction, add RICH, TRD and TOF info - tracking through the muon absorber result from feasibility studies in the following: central Au+Au collisions at 25 AGeV beam energy (UrQMD)

Claudia Höhne Quark Matter Conference, February 2008, India13 Low mass vector mesons invariant mass spectra electrons: pt > 0.2 GeV/c background dominated by physical sources (75%), 1‰ int. target muons: intrinsic p>1.5 GeV cut (125 cm Fe absorber), background dominated by misidentified muons, 1% int. target electrons: 200k events muons: 4 ∙10 8 events All e + e - Comb. bg ρ  e + e -   e + e - φ  e + e - π 0  γ e + e -   π 0 e + e - η  γ e + e -   m = 14 MeV/c 2   m = 11 MeV/c 2 25 AGeV central AuAu

Claudia Höhne Quark Matter Conference, February 2008, India14 Phase space coverage  -meson 25 AGeV beam energy: midrapidity = 2 electrons: full coverage muons: acceptance forward shifted, weak for low-pt intrinsic p>1.5 GeV cut (125 cm Fe absorber) muons electrons 25 AGeV central AuAu

Claudia Höhne Quark Matter Conference, February 2008, India15 Coverage in pt and m inv Dilepton pair coverage in pt and m inv (signal pairs): electrons: acceptance also for low pt and lowest masses (no pt-cut) muons: cutoff at 2  threshold electronsmuons 25 AGeV central AuAu

Claudia Höhne Quark Matter Conference, February 2008, India16 electrons: 4 ∙10 10 events J/   m = 27 MeV/c 2  '  m = 29 MeV/c 2 J/  and  ' invariant mass spectra electrons: p 1.2 GeV, 1‰ interaction target (25  m Au) muons: 225 cm Fe absorber, pt > 1 GeV/c, 1% int. target muons: 3.8 ∙10 10 events J/   m = 22 MeV/c 2  '  m = 23 MeV/c 2 25 AGeV central AuAu

Claudia Höhne Quark Matter Conference, February 2008, India17 Phase space coverage J/  meson 25 AGeV beam energy: midrapidity = 2 full phase space well covered muonselectrons 25 AGeV central AuAu

Claudia Höhne Quark Matter Conference, February 2008, India18 Yields and S/B multiplicitytotal efficiency S/Binteraction rate [MHz] yield/10 weeks  → e+e-  +  % 2.8% ∙ ∙ 10 6  → e+e-  +  % 4% ∙ ∙ 10 6  → e+e-  +  % 7% ∙ ∙ 10 6 J/  → e+e-  +  ∙ % 13% to ∙ ∙ 10 6  '→ e+e-  +  ∙ % 16% to ∙ ∙ 10 3 S/B ratio in a 2  region around the peak, for  from GeV/c 2 no trigger for low-mass vector mesons, a factor 10 maybe achievable for muons trigger for J/ , rate in dielectron channel depends on interaction length of target (segmented target?) central Au+Au, 25 AGeV minbias = 1/5 central overall similar performance of electron and muon channel! 25 AGeV central AuAu

Claudia Höhne Quark Matter Conference, February 2008, India19 Summary: Dileptons in CBM dileptons are only one of several very interesting physics topics of CBM CBM: comprehensive measurement of A+A interactions from AGeV including rare probes (charm, dileptons), flow, correlations, fluctuations measurement of dileptons (low and high masses) very interesting at FAIR: CBM: AGeV, HADES 2-10 AGeV highest baryon densities reached, phase border to partonic phase restoration of chiral symmetry? critical point? charm production at threshold? charm propagation in-medium? dileptons from  to  ' measurable in electron and muon channel similar performance – although background is of very different origin good phase-space coverage low-mass dielectrons even down to lowest masses and pt detector development started CBM will (hopefully) not be limited by statistics systematic uncertainties might be limiting in the end → a measurement of both, muons and electrons will be the best systematic study we can ever do!

Claudia Höhne Quark Matter Conference, February 2008, India20 Germany: Univ. Heidelberg, Phys. Inst. Univ. HD, Kirchhoff Inst. Univ. Frankfurt Univ. Mannheim CBM collaboration Russia: IHEP Protvino INR Troitzk ITEP Moscow KRI, St. Petersburg China: CCNU Wuhan USTC Hefei Croatia: University of Split RBI, Zagreb Portugal: LIP Coimbra Romania: NIPNE Bucharest Poland: Krakow Univ. Warsaw Univ. Silesia Univ. Katowice Nucl. Phys. Inst. Krakow LIT, JINR Dubna MEPHI Moscow Obninsk State Univ. PNPI Gatchina SINP, Moscow State Univ. St. Petersburg Polytec. U. Ukraine: Shevchenko Univ., Kiev Univ. Münster FZ Rossendorf GSI Darmstadt Czech Republic: CAS, Rez Techn. Univ. Prague France: IPHC Strasbourg Hungaria: KFKI Budapest Eötvös Univ. Budapest India: Aligarh Muslim Univ., Aligarh IOP Bhubaneswar Panjab Univ., Chandigarh Univ. Rajasthan, Jaipur Univ. Jammu, Jammu IIT Kharagpur SAHA Kolkata Univ Calcutta, Kolkata VECC Kolkata Univ. Kashmir, Srinagar Banaras Hindu Univ., Varanasi Korea: Korea Univ. Seoul Pusan National Univ. Norway: Univ. Bergen Kurchatov Inst. Moscow LHE, JINR Dubna LPP, JINR Dubna 51 institutions, > 400 members Dresden, September 2007 Cyprus: Nikosia Univ.

Claudia Höhne Quark Matter Conference, February 2008, India21 Backup

Claudia Höhne Quark Matter Conference, February 2008, India22 Acceptance in pt and m inv 0.2 GeV/c 2 pair detection probablitity/ efficiency versus invariant mass for different pt-bins: electrons: acceptance also for low pt and lowest masses (no pt-cut) muons: cutoff at 2  threshold (plot "hard-hard" and "hard-soft" pairs) electronsmuons 25 AGeV central AuAu

Claudia Höhne Quark Matter Conference, February 2008, India23 Detector performance - muons particleMC tracks/event (after 125 cm Fe) reconstructed tracks/event (after 125 cm Fe) p  K  all background tracks punch through and track mismatches ( .K decay!)

Claudia Höhne Quark Matter Conference, February 2008, India24 STS tracking - simulation excellent track reconstruction, momentum resolution achieved optimization of layout ongoing, material budget ≥ 3.2 mm Si equivalent (x/X 0 ≥ 3.4%) tracking efficiencymomentum resolution 25 AGeV central AuAu

Claudia Höhne Quark Matter Conference, February 2008, India25 Detector concept: electrons TRD: 3 x 4 TRD layers appr. at 4, 6, 8 m behind the target, fast gas detectors also used as intermediate tracking detectors towards TOF detector development builds upon knowledge gained from ALICE TOF: RPCs, 80ps time resolution RICH: gaseous RICH detector, size still to be optimized aim: "simple, compact and robust" → N 2 radiator, glass mirrors, MAPMT as photodetector N hits /ring = 22, N 0 ~ 150 cm -1, e = 6.2 cm,  R = 2.5% ~ 90 rings per central collision, 25 AGeV Au+Au (occupancy ~2-4%)

Claudia Höhne Quark Matter Conference, February 2008, India26 Target – electrons number of  -conversions versus target thickness ~ 350 for 25 AGeV, central Au+Au collisions  0 →  (98.8%) rejection only by opening angle (difficult with magnetic field) can be dominant background even for J/  → use high quality, high intensity beam from FAIR and work with 1‰ interaction target! low-mass vector mesons: no trigger possible → higher rate in order to saturate DAQ J/  : trigger required! max. beam intensity 10  ions/s → 1% target max. interaction rate 10 MHz 1‰ 1MHz or use segmented target 25  m → ~3 e ± per event 25  m ≡ 1‰ interaction length

Claudia Höhne Quark Matter Conference, February 2008, India27 Performance of combined e-ID use TRD and TOF detectors for further electron identification combined purity of identified electrons ~96% p [GeV/c]

Claudia Höhne Quark Matter Conference, February 2008, India28 suppression of low momentum muons! → low-mass vector mesons: 125 cm Fe absorber: cutoff at 1.5 GeV/c "hard  " 90 cm 1 GeV/c "soft  " → charmonium: 225 cm Fe absorber 2.8 GeV/c mismatches → include TOF information (distorted for background) depending on detector layout, tracking cuts: ~ 0.4 identified  ± /event (125 cm Fe) reconstruction efficiency for tracks passing the absorber ~70% (125 cm Fe) Detector performance - muons J/    p absorption of muons from different sources in dependence on absorber thickness (Fe)

Claudia Höhne Quark Matter Conference, February 2008, India29  -meson spectral function (II) "SPS" "FAIR" [R. Rapp, priv. com. (CBM physics book)] illustrate sensitivity to modifications caused by the baryonic component of the medium:  -meson spectral function weighted by a factor 1/M to resemble the dilepton rate, Bose-factor will further amplify the low-mass part region with m < 0.4 GeV/c 2 of special interest!

Claudia Höhne Quark Matter Conference, February 2008, India30  -meson spectral function [Rapp, Wambach, Adv. Nucl. Phys. 25 (2000) 1, hep-ph/ ]  -meson couples to the medium: "melts" close to T c and at high  B vacuum lifetime  0 = 1.3 fm/c dileptons = penetrating probe  -meson spectral function particular sensitive to baryon density connection to chiral symmetry restoration? p n  ++  p   e +, μ + e -, μ - 

Claudia Höhne Quark Matter Conference, February 2008, India31  0 mass distribution generated including: –Breit – Wigner shape around the pole mass; –1/M 3, to account for vector dominance in the decay to e + e - ; –Thermal phase space factor Simulation of vector mesons MesonN/eventDecay modeBR  36  e + e -  5.×10 -3  23  e + e - 4.7×10 -5  38  e + e -  0  e + e - 7.7× ×10 -5  1.28  e + e ×10 -4 input: vector mesons generated with Pluto, embedded into central Au+Au collisions, 25 AGeV beam energy from UrQMD full event reconstruction and particle identification, appr. realistic detectors descriptions: always work in progress!

Claudia Höhne Quark Matter Conference, February 2008, India32 First test beam data → hit density? without Pb converter with Pb converter (1.5 cm ~ 3X 0 ) crucial issue for Muon detectors hit densities after absorbers? (reliability of simulation?) first results from  test beam (6 GeV/c) at CERN, PS on high granularity gas detectors (ALICE prototypes): → increase hit density in GEANT 3 appr. by factor 2 ADC counts

Claudia Höhne Quark Matter Conference, February 2008, India33 STS TRD TOF RICH ECAL MVD ZDC MUCH ASCII Urqmd Pluto Track finding digitizers Hit Producers Dipole Map Active Map const. field CBM Code ROOT Run Manager Virtual MC Geant3 Geant4 FLUKA Event Generator Magnetic Field Detector base IO Manager Tasks RTDataBase Oracle Conf, Par, Geo Root files Conf, Par, Geo Root files Hits, Digits, Tracks G4VMC FlukaVMC G3VMC Geometry Application Cuts, processes STT MUO TOF DCH EMC MVD TPC DIRC ASCII EVT DPM Track finding digitizers Hit Producers Dipole Map Solenoid Map const. field Panda Code Event Display Track propagation common developments some features Always in close contact Close contact