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Sketch of a competitive experiment on dense nuclear matter

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

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Sketch of a competitive experiment on dense nuclear matter

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  1. 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  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

  2. Transport calculations: energy densities Baryon density in central cell (Au+Au, b=0 fm): HSD: mean field, hadrons + resonances + strings QGSM: Cascade, hadrons + resonances + strings C. Fuchs, E. Bratkovskaya, W. Cassing

  3. Ch. Fuchs, Tübingen

  4. “Trajectories” from UrQMD L. Bravina, M. Bleicher et al., PRC 1998

  5. Event-by-event analysis by NA49: 5% most central Pb+Pb collisions at 158 AGeV liquid gas coexistence Below Tc: 1. order phase transition above Tc: no phase boundary At the critical point: Large density fluctuations, critical opalescence The critical point

  6. Strangeness production in central Pb+Pb collisions C. Blume et al., nucl-ex/0409008 (CERN NA49)

  7. 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

  8. Thermal production of multistrange hyperons ?

  9. Production processes of multistrange hyperons Production processes and thresholds pp  K+0p ( 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 ) 0(s d u) m =1116 MeV - (s s d) m =1321 MeV - (s s s) m =1672 MeV pp 0 0pp ( Ep  7.1 GeV ) pp + -pp ( Ep  9.0 GeV ) pp + -pp ( Ep  12.7 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

  10. Hyperon properties

  11. 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

  12. Reaction rate:R = NB · · NT/F· • R = reactions/sec • NB = 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

  13. Determination of target thickness Reaction cross section: R = · (2 ·R)2 = 4 ·(r0·A1/3)2 with r0=1.2 fm Au+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

  14. 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· = ?

  15. 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

  16. 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 min for Ξ : t = 1.4·105 sec = 1.6 d for 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 !

  17. Possible experiment layout TOF wall measures Time-of-flight for mass determination. needed: fast detectors tracking chambers Dipole magnet Time-of-flight wall (RPC) Silicon tracker Tracking chambers are needed to match tracks in Silicon detector to hits in TOF wall Silicon tracker in magnetic dipole field measures tracks (particle numbers) and curvature (particle momentum). 6 m

  18. 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

  19. Invariant mass distributions Ξ- After impact parameter cut Before cuts • Invariant mass resolution is improved with the dca cut • σ = 1.7 MeV • Signal yield: 264 After dca cut All cuts

  20. Invariant mass distributions Ω- After impact parameter cut Before cuts • Invariant mass resolution is improved with the dca cut • σ = 2.2 MeV • Signal yield: 486 After dca cut All cuts

  21. Results on Ω- without PID Statistics: 1.4 108 events

  22. Invariant mass distributions Ω- with perfect PID After impact parameter cut Before cuts After dca cut All cuts

  23. Results on Ω- with perfect PID Statistics: 1.4 108 events

  24. 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

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