Vector meson study for the CBM experiment at FAIR/GSI Anna Kiseleva GSI Germany, PNPI Russia   Motivation   The muon detection system of CBM   Vector meson identification (ρ 0, ω, φ, J/ψ)   The low-mass vector meson problem (soft muons)   acceptance of ρ 0 at MUCH   possible solution   preliminary results   Outlook

Dilepton Sources in Heavy-Ion Collisions Signatures of the quark-gluon plasma: anomalous suppression of charmonium In-medium spectral function using penetrating probes

D.Adamova et al., PRL 91 (2003) Calculations by R. Rapp: thick dashed line: unmodified rho thick dashed-dotted line: in-medium dropping rho mass thick solid line: in-medium spread rho width Di-electron measurements (CERES/CERN)

5-week-long run in Oct.–Nov ~ 4 × ions delivered in total In+In 158 A GeV Di-muon measurements (NA60)

CBM detector: e + e - setup ECAL TOF TRD3 TRD2 STS RICH STS: track and vertex reconstruction RICH: electron identification. TRD: identification of high-energy electrons RPC-TOF: time-of-flight measurement ECAL: electron and photon identification TRD1 A+A collisions at 10 – 45 AGeV

CBM detector: μ + μ - setup ECAL TOF TRD3 TRD2 STS MUCH TRD1

MUonCHamber system (MUCH) FeC cm STS   First design study   absorbers:   4 Fe + 1 C   increasing thickness   full thickness ~ 1m Fe   detectors:   2 layers between absorbers   1 – in front of MUCH   2 – behind last absorber

Tracks π-π- π+π+ 1 central Au+Au event at 25 AGeV beam energy (top view of the STS + MUCH system)

Yields for central Au+Au at 25 A GeV J /  (3095 MeV)  0 (770 MeV)  (782 MeV)  (1020 MeV)  + (140 MeV)  - (140 MeV) 1.95× %4.6× × ×10 -4 —— ~1×10 -6 ~1× × × multiplicity branching ratio of  channel per event

Cuts for background suppression J/ψ ➙ μ + μ - Bg GeV/c μ+μ+ J/ψ μ-μ- ptpt ptpt z Single particle cut: transverse momentum p t J/ψ ➙ μ + μ - p+p+ ➙ p-p- ➙

Bg Pair cuts: 1. opening angle   μ+μ+ J/ψ μ-μ- z º 2. scalar product Bg (GeV/c) 2 μ+μ+ J/ψ μ-μ- z Cuts for background suppression p+p+ ➙ p-p- ➙ p + ➙ p-p- ➙ J/ψ ➙ μ + μ - p+p+ ➙ p-p- ➙

Comparison of J/ψ to ρ 0 ρ0ρ0 Bg opening angle (°) transverse momentum (GeV/c) scalar product (GeV/c) 2 J/ψ J/ψ ➙ μ + μ - ρ0➙μ+μ-ρ0➙μ+μ-

Invariant mass spectra J/ψ ρ0ρ0 ω φ opening angle ptpt scalar productJ/ψ > 12 o > 1[-2.4, -2.05] ρ, ω, φ > 12 o > 0.23[-0.26, 0.04]   full STS tracking:   STS digitization   track finding   momentum reconstruction   primary vertex cut   MUCH tracking:   100μm position resolution   STS track extrapolation   track finding and matching

J/ψ acceptance 4π4πsts much p t > 1GeV/c 1m Fe sts: > 4 sts hits much: sts + first much 1m Fe: behind 1m Fe

ρ 0 acceptance 4π4πsts much1m Fe sts: > 4 sts hits much: sts + first much 1m Fe: behind 1m Fe

Momentum distribution 1.3 much1m Fe 1.3

Momentum Dependent Track Selection (MDTS)

MUCH detector model for MDTS study μ-π-μ-π- μ+π+μ+π+

Absorber thickness vs. momentum absorber thickness, cm μ +, μ - π +, π -

Application: preliminary results μ+μ+ μ-μ- 65 cm ρ0ρ0 ~ 1m Fe 2 hard muons

μ-μ- Application: preliminary results μ+μ+ ρ0ρ0 65 cm ~ 1m Fe 1 hard + 1 soft muons

absorber thickness, cm μ +, μ - π +, π - Application: preliminary results

Application: preliminary results J.Vassiliev 2 hard muons 1 soft + 1 hard muon full STS and MUCH tracking

ρ 0 acceptance J.Vassiliev 2 hard muons 1 soft + 1 hard muon

Outlook   Study of different absorber materials, for example tungsten (W)   Tuning of momentum dependent muon identification