Dilepton measurements with CBM Volker Friese v.friese@gsi.de CBM - PowerPoint PPT Presentation

Dilepton measurements with CBM Volker Friese v.friese@gsi.de CBM Forum on Dilepton Measurements in Heavy-Ion Collisions GSI, Febraury 27, 2007

The CBM Experiment "Standard" setup with electron detectors Volker Friese CBM Forum, GSI, February 2007 2

CBM : Overview of Observables • Identified hadrons ( π , K, p) STS + TOF spectra, yields • Hyperons ( Λ , Ξ , Ω ) STS (+ TOF) • Open charm (D 0 , D ± ) STS (+ TOF) flow • Direct photons ECAL • Charmonium ( ψ , ψ ' ) STS + RICH + TRD • Low-mass vector mesons STS + RICH (+ TRD + TOF) fluctuations • Charmonium ( ψ , ψ ' ) STS + MuCH (+ TRD + TOF) • Low-mass vector mesons STS + MuCH (+ TRD + TOF) from p+p to Pb+Pb from 10 AGeV to 35 (45) AGeV Volker Friese CBM Forum, GSI, February 2007 3

Measuring Electron Pairs with CBM • electron identification – RICH ( - 12 GeV) – TRD (1 GeV - ) • background – mis-identified hadrons – Dalitz decays – γ conversion pairs • no electron identification before the magnetic field suppression of electronic background non-vertex: by tracking for charmonium: single electron p t for LVM: dedicated cut strategy for rejection of conversion and Dalitz Volker Friese CBM Forum, GSI, February 2007 4

Electron Identification in RICH Ring finding efficiency vs. momentum Pattern recognition in the PM plane Volker Friese CBM Forum, GSI, February 2007 5

Electron Identification in RICH ring radius vs. momentum composition of tracks identified as electrons (UrQMD events) Volker Friese CBM Forum, GSI, February 2007 6

Improvement of Electron ID by TRD and TOF RICH-identified electrons RICH and TRD-identified electrons Volker Friese CBM Forum, GSI, February 2007 7

Pion Suppression and Electron Efficiency p [GeV] Volker Friese CBM Forum, GSI, February 2007 8

Background topology for LVM Track Segment Global Track + − π 0 → γ e e f a s + − ρ → 0 e e k i e g p n γ → + − e e a a medium i l r Track Fragment Track Fragment - x, y position; no charge information - reconstructed track Track Segment - identified in RICH Global Track Volker Friese CBM Forum, GSI, February 2007 9

LVM: Efficiency of cuts, S/B ratio ω / φ region π 0 -Dalitz region Enhancement region ε Rejection of background from Dalitz and conversion by cuts on distance to closest neighbour pair opening angle pair invariant mass S/B single electron p t Volker Friese CBM Forum, GSI, February 2007 10

LVM: Current Status identified electrons after background rejection ω π 0 η ω ρ φ Results include full event reconstruction and electron identification Volker Friese CBM Forum, GSI, February 2007 11

LVM: Phase Space Coverage after all cuts good mid-rapidity coverage y CM Volker Friese CBM Forum, GSI, February 2007 12

Charmonium in the Di-electron channel pairs / pairs / pairs / 8 350 15 AGeV 35 AGeV 25 AGeV 50 7 2.5 x 10 9 events 4 x 10 8 events 300 10 10 events 6 40 250 5 30 200 4 150 3 20 100 2 10 50 1 0 0 0 2.6 2.8 3 3.2 3.4 3.6 3.8 4 2.8 3 3.2 3.4 3.6 3.8 4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 2 2 2 m ( GeV/c ) m ( GeV/c ) m ( GeV/c ) inv inv inv Results for central Au+Au collisions J/ ψ yield from HSD Full event reconstruction and electron identification in RICH and TRD Single electron p t > 1.2 GeV Volker Friese CBM Forum, GSI, February 2007 13

Measuring Muons with CBM Replace RICH by absorber- detector system "Compact" design with 5 Fe absorbers and 15 detector different absorber concepts layers under study Volker Friese CBM Forum, GSI, February 2007 14

Muon Option: Results for LVM signals: ρ � ω � φ � η � η Dalitz � — background — background+signals Results include full tracking through STS and absorbers Muons are identified after the last absorber Volker Friese CBM Forum, GSI, February 2007 15

LVM: Efficiency and Phase Space Rapidity coverage Signal efficiency vs. inv. mass Mid-rapidity coverage can be improved by allowing "soft tracks" (crossing 4 of 5 absorbers) Volker Friese CBM Forum, GSI, February 2007 16

Charmonium in the Di-Muon Channel Entries J/ ψ 2 S/B = 100 10 = 20 MeV σ 10 1 2.8 3 3.2 3.4 3.6 3.8 2 m GeV/c inv High momentum of charmonium daughters allows a clean identification High quality signal expected Volker Friese CBM Forum, GSI, February 2007 17

Muon Measurement: Detector Issues Very high hit rates after first absorber Coordinate resolution ≈ 100 µm required for tracking through the absorber system Possible solutions GEM / micromegas / MWPC depending on station number / distance from beam Volker Friese CBM Forum, GSI, February 2007 18

Summary • Both electron and muon option give access to low-mass vector mesons and charmonium • Feasibility studies are based on full event reconstruction and electron / muon identification. They are still subject to further optimisation. • Performance on low-mass VM is similar for electrons and muons; mid-rapidity coverage is more difficult for muons • Performance on charmonium is better for muons: higher charmonium states probably not measurable with electrons • Electron measurements rely on established detector technology (RICH, TRD) • Detector issues for muon measurements not yet solved Volker Friese CBM Forum, GSI, February 2007 19