Nuclear medium modifications of properties of kaons measured around threshold with FOPI

Transcription

1 FOPI Nuclear medium modifications of properties of kaons measured around threshold with FOPI Krzysztof Piasecki Institute of Experimental Physics, University of Warsaw Physics motivation Experimental status a decade ago New experimental findings Summary 1

2 Probing partial restoration of chiral symmetry Gell-Mann Oakes Renner relation: FOPI AA 2 m 2 f K K = mu+ ms 2 u u+ s s + Θ (m 2s ) Decay constant Mass M. Kotulla et al., Physik Journal 8 (2009) 3 Chiral effective field theory w/ couple-channels UK-N K+ K p=0 U K- attracted, K+ repelled = F M.F. M. Lutz, PPNP 53 (2004) 125 UK+N J. Schaffner-Bielich et al. NPA 625(1997) 325 First approaches: Potential Potential only on average 2

3 In-medium modifications via K /K+ RBUU RBUU 36 < θcm < 44 F. Laue et al., Eur. Phys. J. A 9, 397 (2000) Experimental status a decade ago 150 < θcm < 165 K. Wiśniewski et al., Eur. Phys. J. A 9, 515 (2000) Effect itself appears to be confirmed but probed within very narrow slice of phase space Statistics too limited for providing uncertainties of extracted UKN. 3

4 1.7A GeV v1, v2 = Coefficients of Fourier expansion Experimental status a decade ago -1.2 < y0 < -0.6 FOPI analysis: v1 (K+) as function of pt for 2 systems at 1.5 2A GeV Preference for UK+N 20 MeV No information on UK N 1.0A GeV KaoS analysis: Fit to dn/dϕ (K+) for 2 systems at 1 2A GeV Preference for UK+N No information on UK N K < y0 < 0.2 Fragmentary insight, coarse results Y. Shin et al., Phys.Rev.Lett 81, 1576 (1998) dn v 1 cos ϕ + 2 v 2 cos(2 ϕ) +... dϕ P. Crochet et al., Phys. Lett. B 486 (2000) 6 In-medium modifications via Flow 4

5 f meson : a missing player (ss) : m = 1.02 GeV Eb, threshold = 2.6 GeV ct = 50 fm (SIS-18: sub-threshold only) 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 K from ϕ decay (mostly in vacuum) mixes with K from collision zone. A decade ago the ϕ/k SIS energies was not known 5

6 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+ v [cm/ns] p / q [GeV/c] t d p K+ p+ K- p- e+ e- p+ v [cm/ns] 6

7 In-medium modifications via Flow: what s new? Flow of K+ and K from 1.9A GeV UK+N = +20 MeV IQMD UK N = -45 MeV 0 MeV UK+N = +20 MeV HSD UK N = -50 MeV 0 MeV v1 : Rather weak Semiperipheral Central V. Zinyuk et al., Phys. Rev. C90, (2014) Centrality 56% UK+N potential. Preference for UK N MeV. 7

8 In-medium modifications via Flow: what s new? UK+N = +20 MeV IQMD UK N = -45 MeV 0 MeV UK+N = +20 MeV HSD UK N = -50 MeV 0 MeV V. Zinyuk et al., Phys. Rev. C90, (2014) Flow of K+ and K from 1.9A GeV, cont. v2: first results od rapidity scan, but predicted sensitivity to UKN too weak, compared to experimental results 8

9 In-medium modifications via K /K+ : what s new? Ratio of K over K+ from 1.9A GeV, centrality 56% New data (full dots) : wide phase space coverage N(K ) / N(K+) < cos θnn < < cos θnn < more statistics To be compared with Transport Models < cos θnn < < cos θnn < preliminary < cos θnn < < cos θnn < EK,NN (GeV) For 1.9A GeV, see: P. Gasik et al (FOPI), EPJ A 52, 177 (2016) 9

10 KP et al., PRC 91, (2015) Contribution of ϕ decays to K f mesons from AA 1.9A GeV Measured in K+K decay channel (BR=50%) Found in 3 systems (small samples). f/k = 0.36 ± 0.05 Since BR (f K+K ) = 50%, About 18% K originates from f meson decays, occuring mostly outside medium. Energy spectra of f mesons reconstructed and fitted in 2 cases. K from f meson decays: colder than these emitted directly from collision zone. Teff = 108 ± 18 ± 16 MeV No data on θ anisotropy (low statistics) One can subtract contribution from K spectra, and obtain K /K+ of particles solely from the medium KP et al., PRC 94, (2016) 0.36 ± < JCM <

11 Phase space distribution of K /K+ without ϕ component Ratio of K over K+ (direct emissions) from 1.9A GeV, centrality 56% N(K ) / N(K+) K Total = K Direct + K From ϕ < cos θnn < < cos θnn < < cos θnn < < cos θnn < preliminary < cos θnn < K Direct = K Total K From ϕ To be compared with Transport Models in case if ϕ emission is not well reproduced < cos θnn < EK,NN (GeV) 11

12 Summary Within last decade a new generation of K+, measurements was performed thanks to the installation of high resolution ToF detector. Directed and elliptic flow of K+, and K across (y, pt) compared to HSD, IQMD models. In-medium potentials: K+ weak, K moderate. K /K+ ratio: wide scan of phase space f meson yield about 18% of K originate from decays of f. Ready for extraction of in-medium potentials via comparison to transport model predictions. New data on 1.65A GeV : analysis has started.. 12

13 Backup slides 13

14 In-medium modifications of K+/0 at r < r0 g, p, p Beam p (p=1.15 GeV/c) + A K0 + p (p=2.25 GeV/c) + A K+ + FOPI ANKE p + A K+ + pp = 2.25 GeV/c CBUU transport code VKN = 0 MeV VKN = 10 MeV VKN = 20 MeV M.L. Benabderrahmane et al., PRL 102, (2009) ANKE Z. Rudy et al., EPJA 23, 379 (2005) M. Kotulla et al., Physik Journal 8 (2009) 3 14

15 F. Uhlig et al. (KaoS), Phys. Rev. Lett. 95, (2005) 15

16 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 pa MUL K FOPI FOPI A Ni+Ni, 1.9A GeV A. Förster et al., PRC 75, (2007) KaoS A K0 : secondary processes involved M.Merschmeyer et al., PRC 76, (2007) If primary: K+0 near-threshold production processes: Nbeam + Ntarget, predominantly via ΔN, ΔΔ K+,0 Y B pn, pδ K+,0 Y Ntarget has Fermi motion Y = [L,S] UKN involved (increases K mass lower yields) secondary processes are involved 16

17 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) = m K ± (ρ 0 ) 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 17

18 2-source model of f emission K+K simulation in PLUTO source temperature : TIN 1.76A GeV Experiment : Conjecture : ( )» 100 MeV T (direct K ) = T (K+) Slope of daughter K : TOUT (K )» 60 MeV K from f (HADES) K direct Inclusive K simulation M. Lorenz, PoS (BORMIO2010) 038 f admixture reduces T(K ) from 89 MeV to 74 MeV 18

19 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 19

20 2-source model of f emission Experiment : Particle K+ Teff 84 ± ± ± 18 ± 16 K KP et al., Phys. Rev. C 91, (2015) 1.9A GeV (FOPI, KaoS) f contribution to K : indication that ~10 MeV above Tinclusive 20

21 Modifications of K0 in AA collisions K 0S from Ar A GeV K 0S ct = 2.7 cm K 0L ct = 15.3 m IQMD transport calc. : No potential UK0N = 46 MeV HADES UKN at r ~ 2 r0 seems to be stronger than for p A K0 + at r r0 G. Agakichiev et al., Phys. Rev. C 82, (2010) 21

22 Effect of f decays on K slopes Ar+KCl (Hades) Ni+Ni (Fopi) Al+Al (Fopi) Previously: Difference of K+,K slopes explained by UKN potentials Present studies: About 50% can be explained by K+K decays 22

23 Apart C. Hartnack et al. Phys. Rep. 510, 119 (2012) Apart 23

24 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 K 0 n [B] = p, n, N, N*, Δ [Y] = Λ, Σ C.B. Dover, G.E. Walker Phys. Rep. 89 (1982) 1 24

25 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 25

26 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:

27 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 27

28 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) p+y Σ* Λ* K + B Q: Can we see them? 28

29 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 J. Phys. G: Nucl. Part. Phys. 25 (1999) 1859 FOPI / KAOS UrQMD fits quite well too 29

30 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 30

31 f/k- within the statistical model approach FOPI J. Cleymans et al. PLB 603, 146 (2004) G. Agakishiev et al., PRC 80, (2009) 31