Softening of the kaon spectra in 1.9A GeV nucleus-nucleus collisions by f(1020) meson production and decay

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1 FOPI Softening of the kaon spectra in 1.9A GeV nucleus-nucleus collisions by f(1020) meson production and decay Krzysztof Piasecki Institute of Experimental Physics, University of Warsaw Motivation: different T (slopes) of K+ and K vs f mesons Experimental data on f, K production 2-source model of K emission Summary 1

2 Kaon dynamics near threshold K production near threshold (1..2A GeV) In-medium modifications of K+/ mass A. Foerster et al. (KaoS) PRC 75, (2007) U(K+N) U(K N) K+ K J. Schaffner-Bielich et al. NPA 625, 325 (1997) +/ As Kaon escapes the Collision zone, mk m0 K reduces Ekin mk+ m0 K+ increases Ekin Interplay between: KN scattering K absorption In-medium effects K. Wiśniewski et al., Eur. Phys. J. A 9, 515 (2000) 2

3 f meson : a missing player (ss) : m = 1.02 GeV Eb, threshold = 2.6 GeV (SIS-18: sub-threshold only) ct = 50 fm K+K (BR ~ 50%) K IQMD Simulation Au+Au, TLAB = 2A GeV K K+ + t (fm/c) Emission from hot & dense collision zone K Emisson (mainly) from vacuum Q1: How strong is the K+K contribution to K, K+ yields? Q2: Can it modify T of K+/? Can it disturb the extracted UKN potential? 3

4 G. Agakishiev et al., PRC 80, (2009) Experimental data (1) 1.756A GeV Trigger: 35% central collisions f K+ P (K+) : (2.8 ± 0.2 ± 0.1) 10 2 S = 168 evts K P (K ) : (7.1 ± 1.5 ± 0.3) 10 4 minvk+k- [MeV/c2] P (f) = (2.6 ± 0.7 ± 0.1) 10 4 Connection: K+K (BR = 50%) Impact of f on K+ : negligible... φ = 37 ± 13 ± 3 % K 18 ± 6 % of K comes from f decays 4

5 P. Gasik, Ph. D. (IFD UW), draft in preparation Experimental data (2) 1.91A GeV Trigger: 9% most central collisions S = 108 S/B = 1.0 Signif. = 7.4 f 4 P (f) = (2.6 ± 0.7 ± 0.1) 10 4 φ = 35 ± 6 K P (K ) = (9.5 ± 0.8 ± 0.9) 10 4 % 18 ± 3 % of K comes from f decays 5

6 Experimental data (3) 1.91A GeV KP et al., Phys. Rev. C 91, (2015) Trigger: 52% (semi-)central collisions K f P (f) = (4.4 ± 0.7 ± 1.4) 10 4 φ = 44 ± 7 K P (K ) = (9.8 ± 0.2 ± 0.6) % 22 ± 3 % of K comes from f decays 6

7 Kinematic distributions of f 1.76A GeV 1.9A GeV 1.9A GeV f HADES preliminary 0.20 < y < 0.60 Teff = 84 ± 8 MeV 115 < JCM < 145 Teff = 93 ± 14 ± 16 MeV 95 < JCM < 150 Teff = 106 ± 18 ± 16 MeV 7

8 2-source model of f emission K+K simulation in PLUTO source temperature : TIN Experiment : Conjecture : ( )» 100 MeV T (direct K ) = T (K+) Slope of daughter K : TOUT (K )» 60 MeV K from f K direct Inclusive K (HADES) simulation M. Lorenz, PoS (BORMIO2010) A GeV f admixture reduces T(K ) from 89 MeV to 74 MeV 8

9 1.9A GeV (FOPI) dn/dekin, CM [GeV 1] Experiment : Particle Teff 82 ± 7 ± ± 2 ± 9 93 ± 14 ± 16 Ekin, CM [GeV] P. Gasik, Ph. D. (IFD UW), draft in preparation 2-source model of f emission T (K from f) = 58 MeV T (K direct ) = 92 ± 16 MeV f contribution to K : indication that ~10 MeV above Tinclusive 9

10 2-source model of f emission Experiment : Particle K+ Teff K 84 ± ± ± 18 ± 16 KP et al., Phys. Rev. C 91, (2015) 1.9A GeV (FOPI, KaoS) f contribution to K : indication that ~10 MeV above Tinclusive 10

11 Effect of f decays on K slopes Ar+KCl (Hades) Ni+Ni (Fopi) Previously: Al+Al (Fopi) Difference of K+,K slopes explained by UKN potentials Present studies: About 50% can be explained by K+K decays 11

12 Summary Total yields of K+, K and f mesons near free NN thresholds, obtained for: φ negligible + K φ 0.4 K 1.76A GeV 1.91A GeV 1.91A GeV Ekin (or mt) distributions of K+, K : 2-source model of K emission ~ 20% of K originate from f decays A gap between slopes : T (K+) = T (K ) MeV [ direct + f-decays ] : Ar+KCl : Assuming T(K direct) = T(K+), cocktail nearly explains the gap Ni+Ni Al+Al Accounting for f decays indicates that T(K direct)» T(K inclusive) + 10 MeV Extraction of KN potentials via [experiment «transport model] comparison should include the f production data on both sides. 12

13 Backup slides 13

14 FOPI experimental setup Nearly 4p coverage Drift chambers: chambers CDC, Helitron ToF : Plastic Barrel, RPC Forward: Forward Plastic Wall, Zero Degree Direct PID of p±, K±, p, d, t, He 3,4 MMRPC Plastic Barrel p [GeV/c] t d p K+ p / q [GeV/c] t p K+ p+ K- p- e+ e- p+ v (cm/ns) d v (cm/ns) 14

15 K-/K+ : experiment vs transport 1.93A GeV, 9% most central events K : UKN repulsive + (P. Gasik) K : UKN ~attractive K /K+ : promising observable IQMD transport code ρ m K± (ρ) = mk ± (ρ0 ) 1+α± ρ 0 at r=r0 ( ) DmK+ = 40 MeV, DmK- = 100 MeV HSD preliminary 136 < Θcm < 150 transport code K+ as in IQMD K : off-shell G-matrix approach IQMD, NO Pot. HSD, NO Pot. HSD, UK+=40 MeV, K- Not Modified HSD, UK+=40 MeV, UK-= G-Matrix IQMD, UK+=40 MeV, UK-=-100 MeV Clear preference for UKN 0 option UK+ only scenario : insufficient IQMD: potentials used probably too strong 15

16 C. Hartnack et al. Phys. Rep. 510, 119 (2012) M. Kotulla et al., Phys. Jour. 8, 3 (2009) A. Foerster et al. (KaoS) PRC 75, (2007) Apart FOPI AA Apart 16

17 Subthreshold f another sample 1.93A GeV Trigger: 23% most central collisions KP (analysis in progress) 23% central M. Menzel et al. (KaoS), PLB 495 (2000) A GeV, = 118 S S/B = 0.5 Signif. = 6.1 preliminary MINV [GeV/c2] ycm P(K ) / 1 triggered event: (21. ± 4.) 10-4 Number of identified f : 118 P(f) / 1 triggered event: (6.2 ± 1.0) 10-4 φ = 29 ± 7 ± 10 % K 14 ± 3 % K comes from f decays 17

18 f production Apart dependency A. Förster et al., PRC 75, (2007) Ni+Ni 23% (Fopi) Ni+Ni 52% (Fopi) Al+Al (Fopi) Ar+KCl (Hades) Fit: P(f) = N <Ap>a a = A Behaviour different than that for K+-0 and L? BR of different prod. channels is unknown Possible absorption at high <Apart> 18

19 Strangeness production and absorption K+ K- f Production (primary) BB BYK+ BB BBK+K- Tpp pλk+ = 1.58 GeV Tpp ppk+k- = 2.5 GeV Tpp ppk+k- = 2.6 GeV Production (secondary) pb YK+ py (S* ) BKBY NK-L BY BBKpB BK+Kf K+K- pb Bf rb Bf pn* Nf rp f BB BBf H.W. Barz et al. (BUU), Nucl. Phys. A 705 (2002) 223 K+K- f negligible Absorption K+Y pb K-B py fn KL Elastic scat. (char. exch.) K+B K+ B K-B K-B fn fn K+n K0 p K-p K0n [B] = p, n, N, N*, Δ C.B. Dover, G.E. Walker Phys. Rep. 89 (1982) 1 [Y] = Λ, Σ 19

20 f yield BUU predictions BUU calculations for 1.93A GeV, 9% most central collisions f production channels: BB f, B = {N, D} mb f, m = {p, r} pr f negligible H.W. Barz et al. (BUU), Nucl. Phys. A 705 (2002) 223 collision K+ K f BUU: f yield overestimated 20

21 f yield compared to K Ni+Ni 52% (Fopi) Al+Al (Fopi) K+K Ni+Ni 23% (Fopi) Ar+KCl (Hades) ct = 50 fm 1 φ 3 K (BR ~ 50%) ~ % K originates from f decays UrQMD model Resonance states in medium: N* N + f preliminary FOPI J. Steinheimer, M. Bleicher, arxiv:

22 Ni+Ni Al+Al Central A+A C. Alt et al. (NA49), Phys. Rev. C 78, (2008) B. Back et al. (E917), Phys. Rev. C 69, (2004) Excitation function of f inverse slopes Ar+KCl 22

23 Production of Kaons in AA: Primary or secondary? σk = const For pa KX: MUL K = σ inelastic AA KX: Glauber: AA = A NA AA MUL K = A FOPI pa MUL K FOPI A Ni+Ni, 1.9A GeV A. Förster et al., PRC 75, (2007) KaoS K0 : secondary processes involved K+0 near-threshold production processes: Nbeam + Ntarget, predominantly via ΔN, ΔΔ K+,0 Y B pn, pδ K+,0 Y A M.Merschmeyer et al., PRC 76, (2007) If primary: Ntarget has Fermi motion Y = [L,S] UKN involved (increases K mass lower yields) secondary processes are involved 23

24 K+ Primary: (Fermi momentum) NN NK+Y (Y =, S) K+ Secondary: BB BK+ (BB = ND, DD) pb K+Y (B = N,D) C. Fuchs, PPNP 56 (2006) 1 KaoS +QMD Secondary processes involved 24

25 Sub- and near-threshold Production of K in medium: mainly strangeness exchange: BY NNK, 1.5A GeV (IQMD transport code) py K B strong reabsorption: K B py coupled to resonances Σ(1385), (1385) Λ(1405) Σ* Λ* p+y K + B Q: Can we see them? K f(1020) K K+ decay (mostly outside collision zone) Q: How strong is this contribution? K + t (fm/c) In-medium effects: UKN potential or spectral density Q: How strong is this influence? K 25

26 Particle yields vs Statistical Model and UrQMD Al+Al : 8 independent ratios involving Al+Al p, d, p, K+, K, K0s,, K*0, Σ*±, Λ Ni+Ni : 8 independent ratios involving p, d, p+, p-, K+, K-, K0s,, Λ Statistical Model Grand Canonical ensemble; FOPI / KAOS prelim. For S 0, Canonical ensemble calc: THERMUS code S.Wheaton, J.Cleymans, hep-ph/ Ni+Ni UrQMD v 2.3 prelim. SM fitting quite well No equilibration assumed Cascade model no mean field no in-medium effects FOPI / KAOS J. Phys. G: Nucl. Part. Phys. 25 (1999) 1859 UrQMD fits quite well too 26

27 Strange meson excitation functions near threshold FOPI central A+A FOPI HADES C. Alt et al. (NA49), Phys. Rev. C 78, (2008) B. Back et al. (E917), Phys. Rev. C 69, (2004) G. Agakishiev et al., Eur. Phys. J. A (2013) 49: 34 27

28 f/k- within the statistical model approach FOPI J. Cleymans et al. PLB 603, 146 (2004) G. Agakishiev et al., PRC 80, (2009) 28