sketch of a competitive experiment on dense nuclear matter
DESCRIPTION
Sketch of a competitive experiment on dense nuclear matter in the (future) Nuclotron energy range (2-5 AGeV). Helmholtz Summer School 2006, Dubna, Student Seminar Peter Senger, GSI. 1. The physics case: Nuclear equation of state at high baryon densities - PowerPoint PPT PresentationTRANSCRIPT
Sketch of a competitive experiment on dense nuclear matter in the (future) Nuclotron energy range (2-5 AGeV)
1. The physics case: Nuclear equation of state at high baryon densities Search for a first order phase transition between hadronic matter and quark matter
2. Observables: Yield, spectra and collective flow of hadrons incl. (multi-) strange particles Event-by-event fluctuations of particle yields and mean transverse momenta Excitation functions (1-5 AGeV), system size and centrality dependence
3. Estimation of feasibility Particle production cross sections in heavy ion collisions Reaction rates
4. Experimental conditions and requirements Beam energy and intensity Detectors (tracking, momentum determination, particle identification) Efficiencies, signal-to background
Helmholtz Summer School 2006, Dubna, Student Seminar Peter Senger, GSI
Baryon density in central cell (Au+Au, b=0 fm): HSD: mean field, hadrons + resonances + strings QGSM: Cascade, hadrons + resonances + strings
Transport calculations: energy densities
C. Fuchs, E. Bratkovskaya, W. Cassing
Ch. Fuchs, Tübingen
“Trajectories” from UrQMD
L. Bravina, M. Bleicher et al., PRC 1998
The critical point
gasliquid
coexistence
Below Tc: 1. order phase transitionabove Tc: no phase boundary
At the critical point:Large density fluctuations,critical opalescence
Event-by-event analysis by NA49: 5% most central Pb+Pb collisions at 158 AGeV
C. Blume et al., nucl-ex/0409008 (CERN NA49)
Strangeness production in central Pb+Pb collisions
Multistrange hyperons from p+Be, p+Pb and Pb+Pb at 158 AGeV/c
Strangeness enhancement: F. Antinori et al, Nucl. Phys. A 661 (1999) 130c
Thermal production of multistrange hyperons ?
Production processes of multistrange hyperons
0 (s d u) m =1116 MeV
- (s s d) m =1321 MeV
- (s s s) m =1672 MeV
Production processes and thresholds
pp K+ 0 p ( Ep 1.6 GeV ) pp K+K-pp (Ep 2.5 GeV)
pp K+ K+ - p ( Ep 3.7 GeV )
pp K+K+K+- p ( Ep 7.0 GeV )
In heavy ion collisions: “cooking” of multistrange hyperons ?Strangeness exchange reactions:2) 0 K- -0 0 K+ +0
3) - K- - - + K+ + +
Enhanced yield at high densities
pp 0 0 pp ( Ep 7.1 GeV )
pp + - pp ( Ep 9.0 GeV )
pp + - pp ( Ep 12.7 GeV )
Hyperon properties
Particle Quark content
Mass (GeV/c2)
Lifetime
c (cm)
Multiplicity at 6 GeV
Decay channel
BR
uds 1.116 7.89 9.7 p - 63.9%
- dss 1.321 4.91 0.118 - 99.9%
- sss 1.672 2.46 ~710-4 K- 67.8%
Particle multiplicities for central Au+Au collisionsfrom UrQMD calculations
Au+Au 5 AGeV central minimum bias 8.2 2
0.06 0.015 0.0002 0.00005
R = reactions/secNB = beam particles/sec = cross section [barn = 10-24cm2]NT /F = target atoms/cm2 = NA · ·d/A with Avogadros Number NA = 6.02·1023· mol-1,
material density [g/cm3], target thickness d [cm] atomic number A = efficiency
Reaction rate: R = NB · · NT/F ·
Determination of target thickness
Reaction cross section: R = · (2 ·R)2 = 4 ·(r0·A1/3)2 with r0=1.2 fmAu+Au collisions: A=197 R = 6.1 barn, 1 barn = 10-24 cm2
Reaction probability for Au+Au collisions: R/NB = R · NT/F
= 6.1 b · 6.02·1023··d/A = 6.1 ·10-24 cm2 · 6.02·1023·19.3 g/cm3·d/197 = 1%
target thickness d = 0.027 cm
Production cross sections for min. bias Au+Au collisions at 5 AGeV:(Λ) = M(Λ) x R = 2 x 6.1 b = 12.2 b(Ξ) = M(Ξ) x R = 0.015 x 6.1 b = 0.09 b(Ω) = M(Ω) x R = 0.00005 x 6.1 b = 0.0003 b
Particle production probabilities for min. bias Au+Au at 5 AGeV:R(Λ)/NB = (Λ)·NA··d/A = (Λ) [b]·1.6·10-3 = 2·10-2
R(Ξ)/NB = (Ξ)·NA··d/A = (Ξ) [b]·1.6·10-3 = 1.4·10-4
R(Ω)/NB =(Ω)·NA··d/A = (Ω) [b]·1.6·10-3 = 4.8·10-7
R(Λ)/NB = (Λ)·NA··d/A· = ?
Acceptances and Efficiencies
= · p · Det · Trigg · DAQ · analysis
with = angular acceptance
p = momentum acceptance
Det = detector efficiencies
Trigg = trigger efficiencies
DAQ = deadtime correction of DAQ
analysis = efficiency of analysis (track finding, cuts for background suppression , ...)Typical values: 0.5, p 0.8, Det 0.9, Trigg 0.9, DAQ 0.5, analysis 0.3,
0.05
Typical particle detection probabilities in Au+Au at 5 AGeV:
R(Λ)/NB = (Λ)·NA··d/A· = 2·10-2·0.05 = 1·10-3
R(Ξ)/NB = (Ξ)·NA··d/A· = 1.4·10-4·0.05 = 7·10-6
R(Ω)/NB =(Ω)·NA··d/A· = 4.8·10-7·0.05 = 2.4·10-8
Required particle yield for a competitive physics analysis: (differential values like v2 as function of pT): 1 Mio particles
Required number of beam particles (integrated luminosity):for Λ: NB x sec = 106/ 1·10-3 = 1·109
for Ξ : NB x sec = 106/ 7·10-6 = 1.4·1011
for Ω: NB x sec = 106/ 2.4·10-8 = 4.2·1013
Required beam time for a Au-beam intensity of NB = 106/sec: for Λ: t = 1·103 sec = 17 minfor Ξ : t = 1.4·105 sec = 1.6 dfor Ω: t = 4.2·107 sec = 500 d
These numbers refer to one collision system and one beam energy only. Systematic studies require excitation functions (several beam energies) with different collision systems !
Dipolemagnet
tracking chambers
6 m
Possible experiment layout
Silicontracker
Time-of-flight wall(RPC)
needed: fast detectors
Tracking chambers are needed to match tracks in Silicon detector to hits in TOF wall
Silicon tracker in magneticdipole field measures tracks (particle numbers) and curvature (particle momentum).
TOF wall measures Time-of-flight for mass determination.
Ξ - Hyperons at AGS: Au+Au 6 AGeV
• Threshold production of Xi measured• Main detector: TPC with PID capabilities• Measured in 4 centrality bins• ~ 250 Xi measured• Results consistent with UrQMD• Neural network algorithm used for the bgd suppression
Invariant mass distributions Ξ-
• Invariant mass resolution is improved with the dca cut
• σ = 1.7 MeV
• Signal yield: 264
Before cutsAfter impact
parameter cut
After dca cut
All cuts
Invariant mass distributions Ω-
• Invariant mass resolution is improved with the dca cut
• σ = 2.2 MeV
• Signal yield: 486
Before cutsAfter impact
parameter cut
After dca cut
All cuts
Results on Ω- without PIDStatistics: 1.4 108 events
Invariant mass distributions Ω- with perfect PID
Before cutsAfter impact
parameter cut
After dca cut
All cuts
Results on Ω- with perfect PID
Statistics: 1.4 108 events
Conclusions
• Multistrange hyperon measurements seem feasible in Au+Au collision at 5 AGeV
• Track reconstruction, momentum determination and particle identification is required
• Beam intensities of better than NB = 106/sec are needed