Update from Kaos
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Transcript of Update from Kaos
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17.01.2008 Florian UhligStrangeness at SIS Energies
Update from Kaos
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17.01.2008 Florian UhligStrangeness at SIS Energies
Outline
• Kaon Production– Inclusive results
• Slopes• Polar anisotropy• Multiplicities• Equation of State
– Centrality dependence• K-/K+-Ratio• Polar anisotropy
• Azimuthal Particle Emission
Data: A. Förster et. al, Phys. Rev. C75 (2007) 024906
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17.01.2008 Florian UhligStrangeness at SIS Energies
Setup
• Selective Kaon trigger (ToF, Cherenkov)
• Background reduction (3MWPCs, double ToF measurements)
• Reaction plane reconstruction (Small-Angle Hodoscope) and event characterization – centrality (Large-Angle Hodoscope)
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17.01.2008 Florian UhligStrangeness at SIS Energies
Inclusive Production Cross Section
• Inclusive = no centrality selection
• Extract slopes and total production cross scection with one consistent method
• Lines are result of simultaneous fit
€
Ed3σ
dp3=C 1+ a2 cos
2(θcm )[ ]Ecm exp(−EcmT)
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17.01.2008 Florian UhligStrangeness at SIS Energies
Midrapidity Distribution
• Select point which are inside cm=90°±10°
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17.01.2008 Florian UhligStrangeness at SIS Energies
Inclusive Invariant Cross Sectionat Midrapidity
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17.01.2008 Florian UhligStrangeness at SIS Energies
Slopes
• Fit midrapidity spectra with Maxwell-Boltzmann function
• Slopes are increasing with increasing beam energy
• K+ slope higher than K- slope at same beam energy
• At same centrality K+ slope higher than K- slope
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17.01.2008 Florian UhligStrangeness at SIS Energies
Polar Anisotropy
• Energy dependence is determined at midrapidity
• Normalize data points inv(Ecm, cm) to inv(Ecm, cm=90°)
• Forward-backward preference
• More pronounced for K+ than K-
• Different freeze-out conditions (times and/or potentials) for K+ and K-
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17.01.2008 Florian UhligStrangeness at SIS Energies
Multiplicities
• Results of simultaneous fits are used to extrapolate to phase-space regions not measured
• Calculate total reaction cross section using Glauber calculations
• Strong rise due to the proximity of thresholds in binary NN collisions
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17.01.2008 Florian UhligStrangeness at SIS Energies
• K+ produced in multi step collisions• Baryonic density reached in Au+Au
reactions is 2-3 0 and depends on compression modulus of nuclear matter KN, weak dependence and lower density in C+C collisions
• (M/A)AU/(M/A)C is sensitiv to KN
• Experimental uncertainties partly cancel
• Ratio hardly affected by less known input to transport model calculations
• Models favour soft EoS
Equation of State
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17.01.2008 Florian UhligStrangeness at SIS Energies
Centrality Dependence
• Group data in 5 centrality bins defined by multiplicity in LAH
• Apart calculated using a Glauber calculation
• M=/(fr) with fr beeing the fraction of the total reaction cross section in the bin
• M ~Apart
1.5 AGeV, 40°
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17.01.2008 Florian UhligStrangeness at SIS Energies
K-/K+-Ratio
• Constant K+/K- ratio• K+ produced together with Y to
conserve strangeness• K- produced via strangeness-
exchange reaction YK-N• Production mechanism of K+
and K- coupled by strangeness-exchange reaction
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17.01.2008 Florian UhligStrangeness at SIS Energies
Polar Anisotropy
• No effect of KN-potentials seen• Polar anisotropy caused by rescattering ?• Different emission times ?
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17.01.2008 Florian UhligStrangeness at SIS Energies
Azimuthal Particle Emission
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17.01.2008 Florian UhligStrangeness at SIS Energies
Azimuthal Particle Emission
-180 -90 0 90 180
0
0.2
[Deg]φ
p < 0.15n 0.05 < y
-180 -90 0 90 180
0
0.2
[Deg]φ
p < 0.15n 0.05 < y
0.01± = -0.27 1v
0.01± = -0.02 2v
v1 < 0
+/- 180deg
dN/ddN/d 1 + 21 + 2vv11cos(cos() + 2) + 2vv22cos(2cos(2))
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17.01.2008 Florian UhligStrangeness at SIS Energies
Azimuthal Particle Emission
dN/ddN/d 1 + 21 + 2vv11cos(cos() + 2) + 2vv22cos(2cos(2))
-180 -90 0 90 1800
0.1
[Deg]φ
+
-180 -90 0 90 1800
0.1
[Deg]φ
+
0.01± = 0.03 1v
0.01± = -0.13 2v+/- 90deg
v2 < 0mid-rapiditymid-rapidity
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17.01.2008 Florian UhligStrangeness at SIS Energies
Collective Flow at Target Rapidity
•Protons show expected flow•Nice agreement between KaoS and FOPI
•shadowing of pions - short mean
•Emission time depends on energy
FOPI Data: A. Andronic et al. Phys. Rev., C64:041604, 2001.
KaoS Data: M. Ploskon, PhD Thesis, University Frankfurt, 2005 F.Uhlig, PhD Thesis, TU Darmstadt, 2003
Ni+Ni 1.93 AGeV
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17.01.2008 Florian UhligStrangeness at SIS Energies
Collective Flow of Kaons
• Similar behavior for kaons, but K >>
• K+N-potential
FOPI Daten: P. Crochet et al., Phys. Lett. B 486, 2000RBUU: W. Cassing and E. Bratkoskaya,Phys. Rep. 308, 1999
Ni+Ni 1.93 AGeVNi+Ni 1.93 AGeV
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17.01.2008 Florian UhligStrangeness at SIS Energies
Passing Time
• Decreasing v2 with increasing Ebeam• Scattering/Absorbtion of pions in spectator matter
• Compare different collision systems• Passing time tp=2R/c
Ni+Ni 1.93 AGeV Midrapidity
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17.01.2008 Florian UhligStrangeness at SIS Energies
K+ around Midrapidity
Data: Y. Shin et al., Phys. Rev. Lett. 81 (1998) 1576
RBUU Stony Brook:G.Q.Li et al., Phys. Lett. B 381 (1996)
QMD Tübingen: Z.S. Wang et al., Eur. Phys. J. A5 (1999) 275
KN potential repulsive for K+
Transport calculations:• with potential• w/o potential
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17.01.2008 Florian UhligStrangeness at SIS Energies
K- around Midrapidity
Data: Ni+Ni 1.93 AGeV[F.Uhlig, A. Förster et al.,Phys.Rev.Lett. 95 (2005) 012301
IQMD: Ch. Hartnack
In-Plane flow of K- ???
Semi-central
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17.01.2008 Florian UhligStrangeness at SIS Energies
pt dependence of v2
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17.01.2008 Florian UhligStrangeness at SIS Energies
pt dependence of v2
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17.01.2008 Florian UhligStrangeness at SIS Energies
pt dependence of v2 transport models
A. Mishra et al.,Phys. Rev. C 70 (2004) 044904 W. Cassing et al., Nucl. Phys. A 727 (2003) 59-94
C. Hartnack
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17.01.2008 Florian UhligStrangeness at SIS Energies
Summary• K+ excitation function measured with heavy-ion collisions
favours rather soft EoS• Different freeze-out conditions for K+ and K-
• K+/K- ratio as a function of Apart -> strangeness-exchange – the dominant production channel for K-
• Pion clock – high energetic pions emitted early• Elliptic flow of K+ mesons – evidence for repulsive K+N
potential or rescattering ?• Elliptic flow of K- - an evidence for attractive K-N potential or
rather high sensitivity to emission time ?
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17.01.2008 Florian UhligStrangeness at SIS Energies
Equation of State
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17.01.2008 Florian UhligStrangeness at SIS Energies
Passing time