physics goals and status of feasibility studies of the cbm experiment

Physics goals and

status of feasibility studies

of the CBM experiment

Claudia Höhne

GSI Darmstadt, Germany

Claudia Höhne International workshop: TRDs – Present & Future, Romania, 2005

Outline

• motivation for CBM

• physics topics

• high baryon densities ( in medium properties of hadrons)

• deconfinement

• critical point

• CBM detector

• feasibility studies (special emphasis on TRD)

• tracking

• fluctuations

• J/, low mass vector mesons

• D-mesons

• outlook


Mapping the QCD phase diagram of strongly interacting matter with heavy ion collisions

• high T, low B

top SPS, RHIC, LHC

• low T, high B

SIS

• intermediate range ?

low energy runs SPS, AGS limited in observables, statistics

SIS 300 @ GSI ! 2nd generation experiment needed!

Highest baryon densities!

→ in medium properties of hadrons

Deconfinement?

Critical point?

Motivationcritical endpoint: [Z.Fodor, S.Katz, JHEP 0404:050 (2004)][S.Ejiri et al., hep-lat/0312006]

SIS100/300


Physics topics and observables

physics topics

deconfinement at high B ?

softening of EOS ?

Critical point ?

in-medium properties of hadrons

onset of chiral symmetry restoration at high B

observables

strangeness production: K,

charm production: J/, D

flow excitation function

event-by-event fluctuations

e+e-

open charm

TRD !

PID!


Deconfinement: Strangeness production[NA49, C.Blume et al., nucl-ex/0409008]

• s-production mechanism different in hadronic / partonic scenario

• maximum of strangeness production at 30 AGeV

• CBM energy range: 15 – 35/45 AGeV (depending on A)

• verify and extend energy dependence!


Deconfinement: J/ suppression

• screening of cc pairs in partonic phase

• anomalous J/ suppression observed at top-SPS and RHIC energies

• signal of deconfinement?

• energy dependence?!

[E. Scomparin for NA 60, QM05]


Deconfinement: charm production[G

ore

nste

in e

t al J. P

hys. G

28

(20

02

) 21

51

]

Predictions of open charm yield for central A+A collisions differ by orders of magnitude for different production scenarios, especially at low energies

D-meson, J/

central Au+Au

cc N


Deconfinement: collective flow

• collapse of v1 and v2 flow of protons at lower energies signal for first order phase transition?!

• full energy dependence needed!central

midcentral

peripheral

[NA49, PRC68, 034903 (2003)]


In medium modifications: → l+l-

within acceptance

• high quality data at low and high energies now coming in from NA60 (SPS, 158 AGeV, In+In) and HADES (SIS, 2 AGeV, C+C)

• enhancement of low-mass dilepton pairs!

[R. Holzmann for HADES, QM05][E. Scomparin for NA 60, QM05]


In medium modifications: → e+e-

• intermediate energies with highest baryon densities?

• pioneering measurement of CERES

• study full energy dependence!

CERES [Phys. Rev. Lett. 91, 042301 (2003)]


D-mesons in medium[W. Cassing, E. Bratkovskaya, A. Sibirtsev, Nucl. Phys. A 691 (2001) 745]

SIS18 SIS100/ 300


various QCD inspired models predict a change of the D-mass in a hadronic medium

• in analogy to kaon mass modification, but drop for both, D+ and D-

• substantial change (several 100 MeV) already at =0

• effect for charmonium is substantially smaller

[Mishra et al ., Phys. Rev. C 69, 015202 (2004) ]

D-mesons in medium (II)


Consequence of reduced D mass: DD threshold drops below charmonium states

[Mishra et al., Phys. Rev. C 69, 015202 (2004) ]

• decay channels into DD open for ’, c, J/

broadening of charmonium states suppression of J/ lepton pair channel (large fraction of J/ from higher states) (slight) enhancement of D mesons

D-mesons in medium J/


Critical point: fluctuations

• dynamical fluctuations of the K/ ratio increasing towards lower energies

• p/ due to resonance decays, reproduced by UrQMD

[C.Roland et al., nucl-ex/0403035]


Critical point: fluctuations (II)

• mean-pt (pT) fluctuations rather constant

• changing fluctuations of net electric charge dyn?

importance of resonance decays?!

[CERES, NPA 727, 97 (2003)][H. Appelshaeuser and H. Sako for CERES, nucl-ex/0409022]


detector requirements

Systematic investigations:A+A collisions from 8 to 45 (35) AGeV, Z/A=0.5 (0.4) (up to 8 AGeV: HADES)p+A and p+p collisions from 8 to 90 GeV

observables detector requirements & challenges

strangeness production: K,

charm production: J/, D

flow excitation function

event-by-event fluctuations

e+e-

open charm

tracking in high track density environment (~ 1000)

hadron ID

lepton ID

myons, photons

secondary vertex reconstruction

(resolution 50 m)

large statistics: large integrated luminosity:

high beam intensity (109 ions/sec.) and duty cycle

beam available for several months per year

high interaction rates (10 MHz)

fast, radiation hard detector

efficient trigger

rare signals!


The CBM experiment

• tracking, momentum determination, vertex reconstruction: radiation hard silicon pixel/strip detectors (STS) in a magnetic dipole field

• electron ID: RICH & TRD (& ECAL) suppression 104

• hadron ID: TOF (& RICH)

• photons, 0, : ECAL

• high speed DAQ and trigger

beam

targetSTS

(5, 10, 20, 40, 60, 80, 100 cm)TRDs(4,6, 8 m)

TOF(10 m)

ECAL(12 m)

RICH

magnet


TRD – tasks & challenge

Tasks:

• electron identification, suppression > 100

• tracking global tracking, matching to STS, TOF (ECAL)

J/ meson, low-mass vector mesons

particle identification with TOF: (multi-)strange hadrons

flow, correlations, fluctuations of identified particles

Challenge:

• high counting rates (up to 100-150 kHz/cm2)

• self triggered, fast readout (10 MHz)

• large area (3 stations at 4,6,8,m 25, 50, 100 m2)

• good position resolution (~200 m)


TRD – design

• layers: radiator (foils or fibres/foams) + readout

• MWPCs (ALICE)

• GEMs

• straw tubes (ATLAS)

Ongoing R&D!

• design studies (segmentation, padsize, ordering,...) started:

3-6 stations

3 stations, 3 layers each




TRD - simulation

• simulation of TRDs (simplified geometry, (1.7 – 2.2) % X0)

• e/ separation studied in dependence on• number of layers• thickness and compositions of the active gas• radiator parameters – foil & gap thickness


CBM simulation framework

• C++ based simulation framework in development for detailed detector simulation, feasibility studies, design optimization

• tracking !


STS tracking

• set of silicon tracking stations inside magnetic field („heart of CBM“)

• 2-3 vertex detectors with high resolution, minimum thickness (e.g. MAPS)

• outer stations: Si-strip, (hybrid pixel detectors in addition?)

so far: simple standard layout with 7 stations (3 + 4) in use

MAPSStripHybrids

Should deliver unambiguous seeds

High resolution tracking

With large coverage

Ultimate vertex resolution

optimization of layout started

tracking!!


STS tracking (II)

Challenge: high track density 600 charged particles in 25o

task

• track reconstruction for tracks with 0.1 GeV/c < p 10-12 GeV/c and with a momentum resolution of order 1% at 1 GeV/c

• primary and secondary vertex reconstruction (resolution 50 m)

• V0 track pattern recognition (hyperons, e+e- pairs from -conversion)


STS tracking (III)

• several trackers under study (cellular automaton, Hough transform, conformal mapping, 3D track following)

• problem: high hit densities: fakes, pile-up in MAPS?

I. Kisel, CA, all tracks, NSTS > 3 ... including 10 pile-up events in MAPS


TRD - tracking

• standalone TRD - tracking J/ trigger!

• global tracking (standalone + matching, STS track extrapolation)

work has just started ...

will finally lead to layout of detectors (padsize, station&layer ordering, ...)

pad layout used so far

• rectangular pads:

300-500 m x 3-30 mm

• odd layers rotated by 90°


TRD – tracking (II)

• track finding: STS track following

• track fitting: Kalman filter

• input: UrQMD events, central Au+Au @ 25 AGeV

Momentum distribution of tracks requiring > 4 hits in STS

• hit rates 800-1000 per event per layer

• large number of secondaries!


TRD – tracking (III)

• 9 layers in 3 stations, 2.2% X0

• efficiency for tracks with 9 TRD hits


TRD – tracking (IV)Compare to:

• 12 layers in 3 stations, 2.2% X0

• efficiency for tracks with 12 TRD hits slight improvement for low momenta!

• connect to TOF hits: efficiency/ purity of PID?

• impact on fluctuation measurements?


CBM: dynamical fluctuations

4 acceptance identified

particles

K/ 3.2 0.3 2.6 0.6

p/ -5.3 0.07 -5.9 0.1

datamixed events

2 2dyn data mixed

UrQMD:central Au+Au collisionsat 25 AGeV


CBM: charmonium measuremente+e- channel (+- also under investigation)assumptions: ideal tracking

momentum resolution 1%

2·1010 central Au + Au UrQMD 25 AGeV + GEANT3

e+e-

different -suppression, pt> 1 GeV

10-2

10-3

10-4

no (red)

-suppression 10-4

-suppression 10-4

• implement reconstructed tracks

• PID


CBM: → e+e-

track segment

reconstructed no PID

reconstructed PID

main problem: background e !

no tracking in field free region for rejection of close pairs!

N/event Decay BR

36 e+ e- 5.×10-3

38 e+ e- 0

e+ e-

5.9×10-4

7.07×10-5

1.28 e+ e- 3.1×10-4

0 28 e+ e- 4.44×10-5


CBM: → e+e- (II)• detailed study of cut strategies, still on ideal MC level


CBM: ?

• alternative: measure J/ and low-mass vector mesons in +- channel?

• 2 options studied: detector behind TOF, rejection of from -decay via kink analysis (TRD!)

Fe/C absorbers behind STS, tracking stations in between + at end (TRD?)

problem: from soft! also stopped ...first promising results from kink studies for J/!


CBM: D0 → K-+ (~4%, c = 124m)

• rather advanced studies available including tracking, secondary vertex reconstruction (65 m resolution), cut strategies for online D selection (only tracking informnation from STS used, no PID)

event reduction by factor 1000:10 MHz 10 kHz

D0+ D0 multiplicity from HSD: 1.5·10-4 per central Au+Au event at 25 AGeV


CBM: D+ K-++ (9%, c = 317 m)

• first studies started, similar strategy as for D0

• feasibility of reconstructing 3 particle vertices shown

• c (c=62 m, pK-+ (5%))?

efficiency ~ 5.3%


Outlook

• detector design and optimization

• R&D on detector components

• feasibility studies of key observables

detailed studies started by now!

• physics workshop, GSI Dec. 15th-16th, 2005

• CBM collaboration formed and still increasing

• technical Status Report submitted in January 2005

• exciting physics lie ahead of us!


Croatia: RBI, Zagreb

Cyprus: Nikosia Univ. Czech Republic:Czech Acad. Science, RezTechn. Univ. Prague France: IReS Strasbourg

Germany: Univ. Heidelberg, Phys. Inst.Univ. HD, Kirchhoff Inst. Univ. FrankfurtUniv. Mannheim Univ. MarburgUniv. MünsterFZ RossendorfGSI Darmstadt

Romania: NIPNE Bucharest

Russia:CKBM, St. PetersburgIHEP ProtvinoINR TroitzkITEP MoscowKRI, St. PetersburgKurchatov Inst., MoscowLHE, JINR DubnaLPP, JINR DubnaLIT, JINR DubnaPNPI GatchinaSINP, Moscow State Univ.

Spain: Santiago de Compostela Univ. Ukraine: Univ. Kiev

Hungaria:KFKI BudapestEötvös Univ. Budapest

Italy: INFN Frascati

Korea:Korea Univ. SeoulPusan National Univ.

Norway:Univ. Bergen

Poland:Jagiel. Univ. Krakow Silesia Univ. KatowiceWarsaw Univ.Warsaw Tech. Univ. Portugal: LIP Coimbra

CBM collaboration

physics goals and status of feasibility studies of the cbm experiment

Documents

trds present future

low energy

high energies

energy dependence

low energies dmeson

low mb

hadronic medium

medium modifications