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Di-lepton spectroscopy in CBM. Claudia Höhne, GSI Darmstadt CBM collaboration. Outline. Introduction & motivation physics case of CBM dileptons at maximum baryon densities Detector concept of CBM overall concept dilepton measurement: electrons - muons Simulations

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Di lepton spectroscopy in cbm

Di-lepton spectroscopy in CBM

Claudia Höhne, GSI Darmstadt

CBM collaboration


Outline
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. Galatyuk Di-electron spectroscopy in CBM

  • K. Antipin Systematic 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


Physics case
Physics case

  • with the CBM energy range we will reach

  • net baryon densities of (6-12) r0

  • excitation energy densities e* of (0.8-6) GeV/fm3 for time spans of ~6 fm/c (e*=e-mNr)

  • → get access to the electromagnetic radiation from the fireball by the study of dileptons!

  • Compressed Baryonic Matter @ FAIR – high mB, 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).


R meson spectral function
r-meson spectral function

r

e+, μ+

e-, μ-

"SPS"

"FAIR"

  • r-meson couples to the medium: "melts" close to Tc and at high mB

  • vacuum lifetime t0 = 1.3 fm/c

  • dileptons = penetrating probe

  • connection to chiral symmetry restoration?

  • particular sensitive to baryon density

n

p

p

++

  • illustrate sensitivity to modifications caused by the baryonic component of the medium:

  • r-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/c2 of special interest!

no measurement between

2-40 AGeV beam energy yet!

[R. Rapp, priv. com. (CBM physics book)]


Charm production at threshold
Charm production at threshold

  • 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?

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

HSD simulations

no measurement of charmonium

below 160 AGeV beam energy yet!


Physics topics and observables
Physics topics and Observables

  • The equation-of-state at high B

  • collective flow of hadrons

  • particle production at threshold energies (open charm)

  • Deconfinement phase transition at high B

  • excitation function and flow of strangeness (K, , , , )

  • excitation function and flow of charm (J/ψ, ψ', D0, D, c)

  • charmonium suppression, sequential for J/ψ and ψ' ?

  • QCD critical endpoint

  • excitation function of event-by-event fluctuations (K/π,...)

  • Onset of chiral symmetry restoration at high B

  • in-medium modifications of hadrons (,, e+e-(μ+μ-), D)

  • mostly new measurements

  • CBM Physics Book (theory) in preparation


The cbm experiment
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, p0, h: ECAL

  • PSD for event characterization

  • high speed DAQ and trigger → rare probes!

  • electron ID: RICH & TRD

  •  p suppression  104

  • muon ID: absorber + detector layer sandwich

  •  move out absorbers for hadron runs

ECAL

TOF

TRD

RICH

absorber + detectors

magnet

aim: optimize setup to include both, electron and muon ID

STS + MVD


Sts tracking heart of cbm
STS tracking – heart of CBM

Challenge: high track density

 600 charged particles in  25o

  • Task

  • track reconstruction:

  • 0.1 GeV/c < p  10-12 GeV/c

  • Dp/p ~ 1% (p=1 GeV/c)

  • primary and secondary vertex reconstruction (resolution  50 mm)

  • V0 track pattern recognition

silicon pixel

and strip detectors

add detectors for particle identification behind the STS

→ challenge for di-leptons!

D+→ p+p+K- (ct = 312 mm)

D0 → K-p+ (ct = 123 mm)


Challenges of the di electron measurement
Challenges of the di-electron measurement

  • clean electron identification (p suppression ≥ 104)

  • large background from physical sources

  • g-conversions in target and STS, p0 Dalitz decays

  • → use excellent tracking and two hit resolution (≤ 100 mm) in first pixel

  • detectors in order to reject this background:

  • → optimize detector setup (STS, B-field), use 1‰ interaction target

RICH

high ring densities and interaction rates

→ MAPMTs + fast self triggered read out electronics

TRD

high rates!

→ reduce gas gap

prototype:double-sided pad plane


Challenges of the di muon measurement
Challenges of the di-muon measurement

  • major background from p,K decays into mn, punch through of hadrons and track mismatches

  • → use TOF information to reject punch through K,p

  • → compact layout to minimize K,p decays

  • → use excellent tracking to reject p,K decays in the STS by kink detection

  • → absorber-detector sandwich for continous tracking

  • low momentum m!

125 cm Fe ≡ 7.5 lI → p > 1.5 GeV/c

225 cm Fe ≡ 13.5 lI → p > 2.8 GeV/c


Muon detector r d
Muon detector R&D

  • up to 1 hit/cm2 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

first double GEM under test at VECC, Kolkatta


Cbmroot simulation framework
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)


Low mass vector mesons
Low mass vector mesons

25 AGeV

central AuAu

All e+e-

Comb. bg

ρe+e-  e+e-φe+e-

π0 γe+e-  π0e+e-ηγe+e-

  • 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 ∙108 events

w,fsm = 14 MeV/c2

w,fsm = 11 MeV/c2


Phase space coverage
Phase space coverage

25 AGeV

central AuAu

  • r-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)

electrons

muons


Coverage in pt and m inv
Coverage in pt and minv

25 AGeV

central AuAu

  • Dilepton pair coverage in pt and minv (signal pairs):

  • electrons: acceptance also for low pt and lowest masses (no pt-cut)

  • muons: cutoff at 2m threshold

electrons

muons


J/y and y'

25 AGeV

central AuAu

  • invariant mass spectra

  • electrons: p < 13 GeV/c, pt > 1.2 GeV, 1‰ interaction target (25 mm Au)

  • muons: 225 cm Fe absorber, pt > 1 GeV/c, 1% int. target

muons: 3.8 ∙1010 events

electrons: 4 ∙1010 events

J/ysm = 27 MeV/c2

y' sm = 29 MeV/c2

J/ysm = 22 MeV/c2

y' sm = 23 MeV/c2


Phase space coverage1
Phase space coverage

25 AGeV

central AuAu

  • J/y meson

  • 25 AGeV beam energy: midrapidity = 2

  • full phase space well covered

electrons

muons


Yields and s b
Yields and S/B

25 AGeV

central AuAu

  • S/B ratio in a 2s region around the peak, for r from 0.2-0.9 GeV/c2

  • no trigger for low-mass vector mesons, a factor 10 maybe achievable for muons

  • trigger for J/y, rate in dielectron channel depends on interaction length of target (segmented target?)

overall similar performance of electron and muon channel!

minbias = 1/5 central

central Au+Au, 25 AGeV


Summary dileptons in cbm
Summary: Dileptons in CBM

  • dileptons are only one of several very interesting physics topics of CBM

  • CBM: comprehensive measurement of A+A interactions from 10-45 AGeV

  • including rare probes (charm, dileptons), flow, correlations, fluctuations

  • measurement of dileptons (low and high masses) very interesting at FAIR:

  • CBM: 10-45 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 r to y' 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!


CBM collaboration

China:

CCNU Wuhan

USTC Hefei

Croatia:

University of Split

RBI, Zagreb

Univ. Münster

FZ Rossendorf

GSI Darmstadt

Korea:

Korea Univ. Seoul

Pusan National Univ.

Russia:

IHEP Protvino

INR Troitzk

ITEP Moscow

KRI, St. Petersburg

Hungaria:

KFKI Budapest

Eötvös Univ. Budapest

Norway:

Univ. Bergen

Kurchatov Inst. Moscow

LHE, JINR Dubna

LPP, JINR Dubna

Poland:

Krakow Univ.

Warsaw Univ.

Silesia Univ. Katowice

Nucl. Phys. Inst. Krakow

Cyprus:

Nikosia Univ.

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

LIT, JINR Dubna

MEPHI Moscow

Obninsk State Univ.

PNPI Gatchina

SINP, Moscow State Univ.

St. Petersburg Polytec. U.

Czech Republic:

CAS, Rez

Techn. Univ. Prague

France:

IPHC Strasbourg

Portugal:

LIP Coimbra

Romania:

NIPNE Bucharest

Germany:

Univ. Heidelberg, Phys. Inst.

Univ. HD, Kirchhoff Inst.

Univ. Frankfurt

Univ. Mannheim

Ukraine:

Shevchenko Univ. , Kiev

51 institutions, > 400 members

Dresden, September 2007



Acceptance in pt and m inv
Acceptance in pt and minv

25 AGeV

central AuAu

  • 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 2m threshold (plot "hard-hard" and "hard-soft" pairs)

electrons

muons

0.2 GeV/c2


Detector performance muons
Detector performance - muons

  • background tracks

  • punch through and track mismatches (p.K decay!)


Sts tracking simulation
STS tracking - simulation

25 AGeV

central AuAu

  • excellent track reconstruction, momentum resolution achieved

  • optimization of layout ongoing, material budget ≥ 3.2 mm Si equivalent

  • (x/X0≥ 3.4%)

tracking efficiency

momentum resolution


Detector concept electrons
Detector concept: electrons

  • RICH:

  • gaseous RICH detector, size still to be optimized

  • aim: "simple, compact and robust"

  • → N2 radiator, glass mirrors, MAPMT as photodetector

  • Nhits/ring = 22, N0 ~ 150 cm-1, <R>e = 6.2 cm, sR = 2.5%

  • ~ 90 rings per central collision, 25 AGeV Au+Au (occupancy ~2-4%)

  • 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


Target electrons
Target – electrons

  • <p0> ~ 350 for 25 AGeV, central Au+Au collisions

  • p0→ gg (98.8%)

  • rejection only by opening angle

  • (difficult with magnetic field)

  • can be dominant background even for J/y

  • → use high quality, high intensity

  • beam from FAIR and work with

  • 1‰ interaction target!

number of g-conversions versus target thickness

  • low-mass vector mesons:

  • no trigger possible

  • → higher rate in order to saturate DAQ

  • J/y: trigger required!

  • max. beam intensity 109 ions/s

  • → 1% target max. interaction rate 10 MHz

  • 1‰ 1MHz

  • or use segmented target

25 mm → ~3 e± per event

25 mm ≡ 1‰ interaction length


Performance of combined e id
Performance of combined e-ID

  • use TRD and TOF detectors for further electron identification

  • combined purity of identified electrons ~96%

p [GeV/c]

p [GeV/c]


Detector performance muons1
Detector performance - muons

  • suppression of low momentum muons!

  • → low-mass vector mesons: 125 cm Fe absorber: cutoff at 1.5 GeV/c "hard m"

  • 90 cm 1 GeV/c "soft m"

  • → 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 m±/event

  • (125 cm Fe)

  • reconstruction efficiency for tracks

  • passing the absorber ~70%

  • (125 cm Fe)

J/y

w

p

p

absorption of muons from different sources in dependence on absorber thickness (Fe)


R meson spectral function ii
r-meson spectral function (II)

"SPS"

"FAIR"

  • illustrate sensitivity to modifications caused by the baryonic component of the medium:

  • r-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/c2 of special interest!

[R. Rapp, priv. com. (CBM physics book)]


R meson spectral function1
r-meson spectral function

r

e+, μ+

e-, μ-

  • r-meson couples to the medium: "melts" close to Tc and at high mB

  • vacuum lifetime t0 = 1.3 fm/c

  • dileptons = penetrating probe

  • r-meson spectral function particular sensitive to baryon density

  • connection to chiral symmetry restoration?

n

p

p

++

[Rapp, Wambach, Adv. Nucl. Phys. 25 (2000) 1,

hep-ph/9909229]


Simulation of vector mesons
Simulation of vector mesons

  • 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!

  • 0 mass distribution generated including:

    • Breit – Wigner shape around the pole mass;

    • 1/M3, to account for vector dominance in the decay to e+e-;

    • Thermal phase space factor


First test beam data hit density
First test beam data → hit density?

  • crucial issue for Muon detectors

  • hit densities after absorbers?

  • (reliability of simulation?)

  • first results from p test beam (6 GeV/c) at CERN, PS on high granularity gas detectors (ALICE prototypes):

ADC counts

→ increase hit density in GEANT 3 appr. by factor 2

without Pb converter

with Pb converter (1.5 cm ~ 3X0)


STS

Hit

Producers

Hit

Producers

STT

Dipole Map

Dipole Map

Pluto

DPM

TOF

TOF

Solenoid

Map

Active Map

ECAL

EMC

Oracle

Conf,

Par,

Geo

const. field

digitizers

digitizers

Urqmd

EVT

TRD

MUO

const.

field

MVD

MVD

Track finding

Track finding

ASCII

ASCII

ZDC

TPC

MUCH

DIRC

CBM Code

Panda Code

RICH

DCH

Geant3

ROOT

G3VMC

Geant4

G4VMC

Geometry

Virtual MC

Close

contact

FlukaVMC

FLUKA

Root files

Hits,

Digits,

Tracks

some features

Cuts,

processes

Application

IO Manager

Track propagation

Run Manager

RTDataBase

Event

Display

Root files

Conf,

Par,

Geo

Event

Generator

Magnetic

Field

Always in

close

contact

Detector base

Tasks

common

developments


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