Mesons in the medium- what we have learned?

Transcription

1 Mesons in the medium- what we have learned? Mariana Nanova Outline: introduction: meson-nucleus interactions methods for determining meson-nucleus potentials potential parameters for K +, K, K -, η, ω, Φ - A interaction search for meson-nucleus bound states summary & outlook *funded by the DFG within SFB/TR16 International Conference on Exotic Atoms and Related Topics - EXA 217 Vienna, Austria, September 1-15, 217 1

2 meson-nucleus interaction meson nucleus 1.) interaction attractive or repulsive?? 2.) if attractive, interaction strong enough to form meson-nucleus bound state exclusively bound by the strong interaction?? exotic nuclear configurations: nuclear physics: states with excitation energies of several 1 MeV hadron physics: investigate in-medium static properties of mesons mesons investigated: K +, K, K -,η, ω, Φ 2

3 meson-nucleus potential H. Nagahiro, S. Hirenzaki, PRL 94 (25) U(r) = V(r) + i W(r) attractive? absorption repulsive? V(r) = Δm(ρ) ρ(r)/ρ W(r) = -Γ/2 ρ(r)/ρ = -1/2 hc ρ(r) σinel β line shape analysis excitation function momentum distribution meson-nucleus bound states transparency ratio measurement TA= σ γa η X A σ γn η X D. Cabrera et al., NPA733 (24)13 3

4 determining the real part of the η -nucleus potential: comparison with collision/transport model calculations E. Ya. Paryev, J. Phys.G 4 (213)2521 excitation function momentum distribution of the meson: in case of dropping mass - repulsion higher η kinetic energy higher meson yield for given s because of increased phase space large attraction low η kinetic energy due to lowering of the production threshold downward shift of momentum distribution enhancement at low energies for in-medium mass drop: V(ρ=ρ) = - Δm (ρ=ρ) 4

5 determining the imaginary part of the meson-nucleus potential from transparency ratio measurements TA= σ γa η X A σ γn η X transport model calculation: GiBUU collision model calculation P. Mühlich and U. Mosel, NPA 773 (26) 156 E. Ya. Paryev, J. Phys.G 4 (213)2521 γa ωx at E γ =1.5 GeV 1.1 γa η X at E γ =1.9 GeV 1. E γ =1.9 GeV Γ=37 MeV T A C A σinel[mb] W(ρ=ρ) = -Γ/2 (ρ=ρ) = -1/2 hc ρ σinel β 5

6 strategy for determining potential parameters real part of meson-nucleus potential measure meson excitation functions and/or momentum distributions compare with transport and/or collision model calculations for different sets of V V = V(ρ=ρ) imaginary part of meson-nucleus potential measure transparency ratio TA(A,p) compare with transport and/or collision model calculations for different sets of Γmed, σinel Γmed, σinel W = W(ρ=ρ; p=) U(ρ=ρ) = V + i W 6

7 σ η [µb] ELSA C data σ tot σ diff excitation function and momentum distribution for γ C η X E γ thr ) = MeV ) = -25 MeV ) = -5 MeV ) = -75 MeV ) = -1 MeV ) = -15 MeV σ η N =11 mb E γ [MeV] η' photoproduction off C data: M. Nanova et al., PLB 727 (213) 417 calc.: E. Paryev, J. Phys. G 4 (213) 2521 dσ η /dp η [µb/gev/c] C data σ η N =11 mb ) = MeV E γ =15-22 MeV ) = -25 MeV ) = -5 MeV ) = -75 MeV ) = -1 MeV ) = -15 MeV p η [GeV/c ] V η (ρ=ρ) = (4±6) MeV V η (<p η > 1.1 GeV/c;ρ=ρ) = (32±11) MeV data disfavour strong mass shifts 7

8 excitation function and momentum distribution for η' photoproduction off Nb ELSA γ Nb η X data: M. Nanova et al., PRC 94 (216) 2525 [µb] σ η' Nb σ tot σ diff [µb/(gev/c)] 1 Nb = GeV E γ 1 1 η' thr E γ η' σinel = 13 mb V(ρ=ρ ) = MeV V(ρ=ρ V(ρ=ρ V(ρ=ρ V(ρ=ρ V(ρ=ρ ) = - 25 MeV ) = - 5 MeV ) = - 75 MeV ) = -1 MeV ) = -15 MeV η' dσ/dp 1 σ η' inel σ η N =11 mb = 13 mb V(ρ=ρ ) = MeV V(ρ=ρ V(ρ=ρ V(ρ=ρ V(ρ=ρ V(ρ=ρ ) = - 25 MeV ) = - 5 MeV ) = - 75 MeV ) = -1 MeV ) = -15 MeV E γ [GeV] [GeV/c] V η (ρ=ρ) = (4±12) MeV V η (<p η > 1.1 GeV/c;ρ=ρ) = (45±2) MeV data disfavour strong mass shifts p η' 8

9 determining the real part of the η -nucleus potential M. Nanova et al., PRC 94 (216) 2525 excitation function mom. distribution weighted average p-η' coinc. C Nb prelim. } p η m <p η > 6 MeV/c [MeV] V = Δm(ρ=ρ) =-[39±7(stat)±15(syst)] MeV observed mass shift in agreement with QMC model predictions V η'a S. Bass and T. Thomas, PLB 634 (26) 368 9

10 determining the real part of the ω-nucleus potential M. N. and V. Metag, EPJ Web of conf. 13 (216) 27 excitation function C p-ω coinc. average [MeV] V η'a V = Δm(ρ=ρ) =-[29±19(stat)±2(syst)] MeV 1

11 C determining the imaginary part of the η -nucleus potential T A M. Nanova et al., PLB 71 (212) 6.9 TA= mass dependence of TA E γ =1.7 GeV 1 ) [MeV] η' -(Im U σ γa η X A σ γn η X momentum dependence of Γ, W S. Friedrich et al., EPJA 52 (216) 297 PLB 71 (212) 6 EPJA 52 (216) η exp data Γ(ρ )=1 MeV Γ(ρ )=15 MeV Γ(ρ )=2 MeV Γ(ρ )=25 MeV Γ(ρ )=3 MeV Γ(ρ )=35 MeV Γ(ρ )=4 MeV A Γ η (ρ=ρ) =15-25 MeV s - η' s thr [MeV] W = Im U(ρ=ρ,p η =) =-[13±3(stat)±3(syst)] MeV 11

12 summary of information on the η -nucleus potential V. Metag, M. N., E. Paryev, arxiv: , PPNP in press [MeV] imaginary part W a pη' QMC η' chiral unitary lin σ NJL potential depth V [MeV] apη - potential parameters corresponding to the pη scattering length (Czerwinski et al. PRL 113 (214) 624 ) 12

13 determining the real part of the K -nucleus potential HADES: Ar + KCl at AGeV G. Agakishiev et al., PRC9 (214) 5496 K transverse momentum spectra compared to IQMD transport calculations without potential (dashed) and with repulsive potential of +46 MeV (solid curve) V + 4 MeV 13

14 determining the real part of the K - -nucleus potential K+ and K - kinetic energy spectra from Al + Al at 1.94 AGeV FOPI: P. Gasik et al., EPJA 52 (216) 177 VK + +4 MeV VK - -5 MeV?? b.) corrected for feeding of K - spectrum from decay Φ K + K - decays Φ/K - -ratio =.36±.5 Ni+Ni at 1.9 AGeV (FOPI) not reproduced in Φ/K - -ratio =.52±.16 Au + Au at 1.23 AGeV (HADES)} transport calculations make sure other observables are reproduced before deducing potential parameters!! 14

15 determining the real part of the K - -nucleus potential p + C, Cu, Ag, Au K + K - +X K + K - - pairs not from Φ decay ANKE: Yu. T. Kiselev et al., PRC92 (215) 6521 K - -momentum spectra compared to collision model calculations: E. Paryev et al., J. Phys. G 42 (215) 7517 VK - (ρ=ρ) = MeV accounting for systematic uncertainties 15

16 determining the imaginary part of the Φ-nucleus potential M. Hartmann et al., PRC85 (212)3526 ANKE: p + C, Cu, Ag, Au Φ + X at 2.83 GeV momentum dependence of transparency ratio c TA= σ γa ΦX A σ γn ΦX σ γc ΦX 12 σ γn ΦX transparency ratio in-medium width σinel W(ρ=ρ) = -Γ/2 (ρ=ρ) = -1/2 hc ρ σinel β W = - (1-3) MeV for.7 < p Φ <1.5 GeV/c 16

17 real part of the meson-nucleus potential [MeV] V K V. Metag, M. N., E. Paryev, arxiv: , PPNP in press K - K η η' ω φ meson-nucleus real potential: K +, K repulsive: 2-4 MeV K - strongest attraction: - (3-1) MeV η, η, ω, Φ weakly attractive: - (2-5) MeV 17

18 imaginary part of the meson-nucleus potential V. Metag, M. N., E. Paryev, arxiv: , PPNP in press [MeV] W 2 - K η η' ω φ meson-nucleus imaginary potential: η : -1 MeV η, Φ : - 2 MeV ω : - 4 MeV K - : - 6 MeV 18

19 real vs. imaginary part of the meson-nucleus potential V. Metag, M. N., E. Paryev, arxiv: , PPNP in press [MeV] 8 7 V < W imaginary part W ω 3 2 η' η potential depth V [MeV] meson with V > W suitable for search for meson-nucleus quasi-bound states φ V > W 19

20 search for η -mesic states in hadronic reactions missing mass spectrometry: Δmm =2.5 MeV/c 2 FRS@GSI: 12 C(p,d)η 11 C K. Itahashi et al., PETP 128 (212) 61 H. Nagahiro et al., PRC 87 (213)

21 search for η -mesic states in hadronic reactions missing mass spectrometry: Δmm =2.5 MeV/c 2 FRS@GSI: 12 C(p,d)η 11 C K. Itahashi et al., PETP 128 (212) 61 H. Nagahiro et al., PRC 87 (213) 4521 Y. K. Tanaka et al., PRL 117 (216) 2251 no structure in bound state region observed deep η -nucleus potentials V 1 MeV excluded! MeV)] σ/(dωde) [μb/(sr 2 d Residue Deuteron momentum [MeV/c] Counts 4 2 D(p,d)p C(p,d) Eex E [MeV] 2

22 summary of information on the η -nucleus potential Y. Tanaka et al., PRL 117 (216) 2251 [MeV] imaginary part W apη QMC η' chiral unitary lin σ excluded NJL potential depth V [MeV] 21

23 summary of information on the η -nucleus potential Y. Tanaka et al., PRL 117 (216) 2251 [MeV] imaginary part W apη QMC η' chiral unitary lin σ excluded NJL potential depth V [MeV] semi-exclusive experiment in preparation increased sensitivity by studying formation AND decay of η -mesic states 21

24 summary and conclusions meson-nucleus interaction described by complex potential U(r) = V(r) + i W(r) real part of meson-nucleus potential deduced from comparison of measured meson excitation functions or momentum distributions with transport and/or collision model calculations imaginary part of meson-nucleus potential deduced from comparison of measured transparency ratios with transport and/or collision model calculations measured potential parameters indicate favourable conditions ( V >> W ) promising candidates: K -, η, η K - pp clusters; η 11 C mesic nuclei for observing meson-nucleus quasi-bound states extension to charm sector difficult because of high momentum transfer V. Metag, M. N., E. Paryev, arxiv: , PPNP in press 22

25 Thank you! 23

26 back-up slides 24

27 /A [µb] γ π σ -1 1 C data excitation function and momentum distribution for V. Metag et al., PPNP67 (212)53 ω photoproduction off C, Nb GiBUU ) = MeV a.u. 1 C 8 6 M. Thiel et al., EPJA 49 (2313) 132 Nb -2 1 ω thr E γ ) = -2 MeV ) = -4 MeV ) = -55 MeV ) = -94 MeV ) = -125 MeV [GeV] E γ [MeV/c] p π γ V = -[42±17(stat)±2(syst)] MeV 25

28 momentum dependence of ω transparency ratio: Nb/C S. Friedrich et al., EPJA 52 (216) 297 ω T Nb/C PRL 1 (28) this experiment ) [MeV] ω -(Im U PRL 114 (215) EPJA 52 (216) [MeV/c] p ω s ω - s thr [MeV] W(ρ=ρ) = -[48±12(stat)±9(syst)] MeV 26

29 Determining the real part of the ω-nucleus potential: GiBUU transport model simulations J. Weil, U. Mosel and V. Metag, PLB 723 (213 ) 12 sensitive to nuclear density at production point measurement of the excitation function of the meson in case of dropping mass - higher meson yield for given s because of increased phase space due to lowering of the production threshold cross section enhancement π γ excitation function ω π γ E γ thr 27

30 Determining the real part of the ω-nucleus potential: GiBUU transport model simulations J. Weil, U. Mosel and V. Metag, PLB 723 (213 ) 12 sensitive to nuclear density at production point measurement of the excitation function of the meson in case of dropping mass - higher meson yield for given s because of increased phase space due to lowering of the production threshold cross section enhancement π γ excitation function γ+ 93 Nb π γ+x E γ = GeV ω π γ momentum distribution of the meson: in case of dropping mass - when leaving the nucleus hadron has to become on-shell; mass generated at the expense of kinetic energy downward shift of momentum distribution π γ momentum distribution E γ thr 27

31 line shape Analysis: Φ meson p + C, Cu Φ +X at 12 GeV KEK E325: R. Muto et al., PRL 98 (27) 4251 deviation from expected lines shape for slow (βγ < 1.25) Φ mesons V = Δm(ρ=ρ) = -35±7 MeV; W(ρ=ρ) = MeV 28

32 line shape analysis?? γ η determine mass from in-medium decay: e.g., η γγ probability for decay: m = (p1+p2) 2 dpdecay mc = Γdecay dl p 1 hc Γ η γγ = MeV γ = /fm counts Γmed m med Δm Γ m invariant mass probability for absorption: dpabs dl = σabs ρ(r) σabs = 13 mb =.21/fm at ρ=ρ Pdecay 1 times more likely to get absorbed than to decay more favourable decay/absorption ratio only at lower densities near the surface where in-medium modifications are reduced sensitive to nuclear density at decay point Pabs = 1-4 at ρ=ρ 29

33 real and imaginary part of the η-nucleus potential p+d η+ 3 He ANKE: T. Mersmann et al., PRL 98 (27) COSY-11: J. Smirski et al., PLB 649 (27) 258 γ+ 3 He η+ 3 He M. Pfeiffer et al., PRL 92 (24) 2521 F. Pheron et al., PLB 79 (212) 21 very steep rise of cross section near threshold!! indication for a quasi-bound state near threshold?? C. Wilkin et al. PLB 654 (27) 92: pole at Q=-.3 MeV; Γ =.3 MeV J.J.Xie et al.,prc95 (217) 1522: BW structure at mass = -.3 MeV; Γ = 3 MeV V = -(54±6) MeV; W = -(2±2) MeV η-meson binding in the He isotopes talk yesterday by A. Gal (p)d+d η+ 3 He talk yesterday by M. Skurzok (WASA) 3

34 information on the K - -nucleus potential from atomic X-rays potential extracted from level shifts and widths of atomic states arising from the strong interaction E. Friedman, A. Gal, Phys. Rep. 452 (27) 89 S. Hirenzaki et al., PRC 61 (2) 5525 X-rays from kaonic atoms sensitive to the potential at low nuclear densities K - - multi nucleon interaction (talk by J. Mareš) E. Friedman, A. Gal, NPA 959 (217) 66 potentials can reliably be extracted up to 3% and 5% of normal nuclear matter density for real and imaginary part, respectively other approaches needed to access V(ρ=ρ), W(ρ=ρ) (talk yesterday by E. Friedman) 31

35 search for meson-nucleus bound states with Φ and heavier mesons (charm sector) general experimental problem: heavy meson production associated with high momentum transfer probability for nucleus to stay intact FA 2 (q 2 ) minimising momentum transfer: favourable reaction p p X Y pmin(x) m X 2 - mn 2 2 mn M. Faessler, NPA 692 (21) 14c with Y forward and X backward in cm (still 1.4 GeV/c for DD pairs!!) more favourable: two step production p p D* - D + D* - +(Z,A) π +D - (Z,A) J. Yamagata-Sekihara et al., PLB 754 (116) 26 32