17.01.2008 Florian UhligStrangeness at SIS Energies
Update from Kaos
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
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)
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)
17.01.2008 Florian UhligStrangeness at SIS Energies
Midrapidity Distribution
• Select point which are inside cm=90°±10°
17.01.2008 Florian UhligStrangeness at SIS Energies
Inclusive Invariant Cross Sectionat Midrapidity
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
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-
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
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
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°
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
17.01.2008 Florian UhligStrangeness at SIS Energies
Polar Anisotropy
• No effect of KN-potentials seen• Polar anisotropy caused by rescattering ?• Different emission times ?
17.01.2008 Florian UhligStrangeness at SIS Energies
Azimuthal Particle Emission
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))
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
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
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
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
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
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
17.01.2008 Florian UhligStrangeness at SIS Energies
pt dependence of v2
17.01.2008 Florian UhligStrangeness at SIS Energies
pt dependence of v2
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
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 ?
17.01.2008 Florian UhligStrangeness at SIS Energies
Equation of State
17.01.2008 Florian UhligStrangeness at SIS Energies
Passing time