The Physics of CBM Volker Friese GSI Darmstadt CBM-China Workshop, Beijing, 2 November 2009

The Physics of CBM

Volker FrieseGSI Darmstadt

CBM-China Workshop, Beijing, 2 November 2009

The Mission

CBM-China Workshop, Beijing, 2 November 2009Volker Friese 2

study of QCD matter at the highest net baryon densities achievable in the laboratory

search for the 1st order phase transition from confined to deconfined matter

search for restoration of chiral symmetry

search for the critical endpoint of the QCD phase diagram

The Messengers


First collisions (Equilibrated ?) fireballHadronisationChemical freeze-out

Kinematic freeze-outFree streaming particles

The Tools


RICHTRD

TOF ECAL

PSD

absorber +

detectors

Electron + Hadron setup Muon setup

STS+MVD

Hyperons: STS Muons: STS + MUCH+ TOF

Hadrons: STS + TRD + TOF Hyperons: STS Open charm: STS + MVD Electrons: STS + RICH + TRD +

TOF + ECAL Photons: ECAL

The Strategy

CBM-China Workshop, Beijing, 2 November 2009Volker Friese 5Energy density

transversemomentum

volume

charm, strangeness

antibaryons

elliptic flow

e-by-e fluctuations

high pt hadrons

heavy quarkonia

mass and width of ρ,ω,φ

thermal photons and dileptons

Phase transitions will show up in non-monotonic behaviour of observables as function of collision energy

Measure excitation functions of yields, spectral shapes, flow, fluctuations, ....

Yagi, Hatsuda, Miake: Quark-Gluon Plasma (2006)

Observables: Open Charm


charm is produced in first hard collisions: carries informations on all stages of the collision

different predictions of open charm yield in hadronic (HSD) or partonic (pQCD + statistical hadronisation) pictures

no measurements in heavy-ion collisions below RHIC energy

very rare probe at FAIR energies!

W. Cassing et al., Nucl. Phys. A 691 (2001) 753

A. Andronic et al., arXiv:0708.1488

HSD

SHM

Open Charm in Dense Medium


Mass shifts expected for D mesons in dense environment

Reduced effective mass for both D and anti-D

Large effect on yield near production threshold

Opening of strong decay channels for charmonia (?)

Mishra et al, nucl-th/0308082

Open Charm Detection in CBM


Micro-Vertex Detector (2 stations of MAPS) with low material budget and high coordinate resolution

allows vertex resolution of 50 – 80 μm

Open Charm in CBM: D± mesons


excellent S/B ratio for D± decay

good pt and rapidity coverage

good statistics (16 k D+ in 25 d beamtime @ 106 interactions / second

Open Charm: Other Channels


D0 -> K- π+ + c.c.

Λc+ -> p K- π+ Ds

+ -> K- K+ π+

D0 -> K- π- π+ π+

Charmonium


rescaled to 158 GeV

(sequential) charmonium suppression predicted for QGP (Debye screening)

observations by NA50/NA60 and PHENIX, but interpretation debated

no measurements below top SPS energy

ratio hidden / open charm very sensitive to charm production mechanism

J/ψ

Ψ‘

Charmonium in CBM


e+e- μ+μ-

Rarest probe for CBM: requires highest interaction rates (10 MHz)

Measurements via electrin pairs (RICH, TRD, TOF) or muon pairs (MUCH)

Similar performance in both channels: good S/B for J/ψ; ψ‘ will be difficult

see talk by T. Galatyuk

Observables: Strangeness


originally thought sensitive to QGP

but: reasonable description by statistical model

some features at lower SPS energies debated

lack of precision measurements, in particular for multi-strange baryons

Hyperon measurements


Λ Ξ- Ω-

Identified by decay topology in STS + inv. Mass

New and fast rec. Software

Clean signals: almost background free for Λ and Ξ

No identification of secondaries required

simulation and reconstruction: central Au+Au @ 25A GeV

Erotic Exotics: Multi-strange di-baryons


{Ξ0, Λ}

Thermal production yields for hyperon clustersStarted to study {Ξ0, Λ} → ΛΛ

Assuming:

m=mΛ + mΞ

cτ = 3 cm (1-5 cm)

BR = 2 % (1-10 %)

J. Schaffner-Bielich, R. Mattiello and H. Sorge, 1999

J. Steinheimer, priv. comm.

CBM Sensitivity for {Ξ0, Λ}


Thermal multiplicity (7 10-3)

Sensitivity limit: 7 10-6

CBM will see {Ξ0, Λ} with thermal yields

Evene three OOM below the signal will be visible above BG

≈ 30 d data taking at 107 MHz

Observables: Fluctuations


multiplicity net charge mean pt

results on multiplicity, net charge, mean pt so far null or in line with hadronic transport

deviation from transport seen in K/π

finite volume / lifetime of fireball possibly suppresses fluctuations

role of hadronic rescattering?

K/π in CBM


CBM-TOF allows good kaon ID in a large acceptanc region

small acceptance + PID bias introduced in fluctuation measure

central Au+Au @ 25A GeV

Observables: In-Medium Vector Mesons


modification of mass / width expected in dense matter: restoration of chiral symmetry ?

observable for short-lived vector mesons in di-leptonic decay channels

measurements between 2 and 40 A GeV lacking! (maximum density!)

Low-Mass Vector Mesons in CBM


LVM→μμLVM→e+e-

central Au+Au @ 25A GeV

Difficult measurement, but feasible in both electron and muon channels

S/B well above competitors

see talk by T. Galatyuk

Observables: Flow


elliptic flow sensitive to EOS

model predicitions with and without phase transition differ strongly

AMPT model predicts quark number scaling also at FAIR energies (with phase transition)

AMPT model, C. Ko et al.

CBM Physics at SIS-100


temporal offset of SIS-300 w.r.t. SIS-100 possible

physics programme of CBM at SIS-100:

A+A up to 10A GeV

strangeness excitation function (incl. flow)

p+p, p+A up to 29 GeV

open charm

CBM@SIS-100: Open Charm With Proton Beam


cross sections close to threshold unknwon for open charm also in p+p and p+A

provides important restriction of models for A+A

measurement in CBM is possible with proton beam from SIS-300

30 GeV

Acceptance for Kaons @ SIS-100


satisfactory acceptance down to 4A GeV without modification of setup

measurement is possible without intermediate tracker (TRD)

Documents

The Physics of CBM Volker Friese GSI Darmstadt CBM-China Workshop, Beijing, 2 November 2009