A search for deeply-bound kaonic nuclear states by in-flight ...

A search for deeply-bound kaonic nuclear states by in-flight ...

Recent results and future prosp bar ects of the K NN search via the (K-,N) reaction at J-PARC F. Sakuma, RIKEN for the J-PARC E15 collaboration Results of the E15 1st physics run Future prospects of E15 Summary Achievements and Perspectives in Low-Energy QCD with Strangeness, ECT*, 2014 10/27-31 Kaonic Nuclei Kaonic nucleus is a bound state of nucleus and anti-kaon (KbarNN, KbarNNN, KbarKbarNN, ...) Density [1/fm3] Y.Akaishi & T.Yamazaki, PLB535, 70(2002).

T.Yamazaki, A.Dote, Y.Akiaishi, PLB587, 167 (2004). 2 K-pp Bound State K-pp : the simplest Kbar-nuclear state A.Gal, NPA914(2013)270 Y.Ichikawa, EXA2014 All theoretical studies predict existence of the K-pp However, B.E. and G are controversial 3 Experimental Principle of E15 A search for the simplest kaonic nucleus, K-pp, using 3He(in-flight K-,n) reaction

two-nucleon absorption CAN be discriminated kinematically 4 hyperon decays Experimental Setup m 5 1 5 E15 1st Stage Physics-Run Production run of ~1% of the approved proposal w as successfully performed in 2013. All detector systems worked well as designed. Primary-beam

intensity Secondary-kaon intensity Duration Kaons on target (w/ tgt selection) March, 2013 14.5 kW (18 Tppp, 6s) 80 k/spill 30 h

1.1 x 109 May, 2013 24 kW (30 Tppp, 6s) 140 k/spill 88 h 5.3 x 109 (Run#47) (Run#49c) * production target: Au 50% loss, spill length: 2s, spill duty factor: ~45%, K/pi ratio: ~1/2

* ~70% of beam kaons hit the fiducial volume of 3He target 6 Summary of E15 1st FINUDA/DISTO 3 He(K-,n)X M.M. Formation Channel Semi-Inclusive 3He(K-,n)X No significant bump structure in the deeply bound region Excess below the threshold attributed to 2NA of L*n? Decay Channel

Exclusive 3He(K-,Lp)n Hint of the excess around the threshold Cannot be from 2NA of L*n (final state = Lpn) Lp I.M. of 3He(K-,Lp)n preliminary 7 Formation Channel, Semi-Inclusive 3He(K-,n)X T.Hashimoto et al., arXiv:1408.5637, submitted to PLB 8

Semi-Inclusive Spectrum Quasi Elastic K- + 3He K- + n + ps + ps ds/dWq=0deg ~ 6mb/sr and Charge-Exchange K- + 3He K0 + n + ds K0 p+ + pds/dWq=0deg ~ 11mb/sr The tail structure is not due to the detector resolution9 Background Evaluation (Phys. BG) (Exp. BG)

evaluated using empty-target data (Exp. BG) 1/b distribution for g/n 10 Spectrum below the Threshold FINUDA/ DISTO No significant bump-structure in the deep-binding region 11 Statistically significant excess just below the threshold

Comparison betw een E15 and Othe r Results M(K+p+p) [email protected] PRL94(2005)212303 A(stopped K-, Lp) [email protected] PRL104(2010)132502 p + p (L + p) + K+ @ 2.85GeV 12 Comparison betw

een E15 and Othe r Results M(K+p+p) [email protected] EXA2014 conference d(p+, K+) @ 1.7GeV/c Bump structure in the deep-binding region reported from other experiments was NOT seen in E15 Excess near the threshold can be seen only in E15 13

U.L. of the deeply-Bound K-pp 95% C.L. CDS tagging eff. K-ppLp Assumptions K-pp Lp decay mode (isotropic decay) K-pp shape = Breit-Wigner U.L. depends on the decay mode 14 95% C.L.

U.L. of the deeply-Bound K-pp K-ppLp [email protected] PLB728(2014)616 g + d K+ + p- + X @ 1.5-2.4GeV E15(K-+3He): (UL) 0.5-5% of QF FINUDA(stopped K-): ~0.1% of stopped K DISTO(p+p): larger than L* @ 2.85GeV LEPS(g+d) (UL) 1.5-26% of gNK+p-Y

Upper limits (CS) can be directly compared with QF yield. 15 Spectrum below the Threshold ? No significant bump-structure in the deep-binding region 16 Statistically significant excess just below the threshold Excess = Elementary Processes? DATA (BG subtracted) The tail structure is NOT

reproduced by well known processes would be attributed to the imaginary part of the attractive KbarN Multi-NA? K-pp? S decay contributions SIM Detector acceptance and all known KN interactions are taken in to account: Cross-section [CERN-HERA-83-02] Fermi-motion Angular distribution Simple assumptions: stot = 2*sK-p + sK-n (~150mb)

17 Excess = pSN, pSNN, etc? Each process is simulated with unreasonably large CS of 100mb contributions in the binding region are negligible 18 Excess = L*N, etc? CS of each process : 20mb/sr @ 0 degrees BW shape with PDG values LN/SN branches are negligibly small (consistent with KEK-PS E548) L(1405)n branch seems to reproduce the excess need rather large CS of ~5mb/sr semi-inclusive measurement would distort the

spectrum by Magas et al., PRC81(2010)024609. L(1405) shape is controversial careful quantitative analysis is required For further study, exclusive measurement of pSN is important. 19 Excess = Loosely-Bound K-pp? DATA (BG subtracted) CDS tagging eff. K-pp? S decay contributions The excess is assumed to be fully attributed to the bound

K-pp state 20 ds/dW(qlab=0o) of the excess is ~ mb/sr (Excess/QF < ~10%) Comparison between E15 and Calc. semi-inclusive DATA (BG subtracted) Koite, Harada, PRC80(2009)055208 DATA (BG subtracted) inclusive

integrated CS: ~mb/sr CS is roughly consistent with KH Loosely-bound K-pp state ??? semi-inclusive inclusive integrated CS: ~0.1 mb/sr Yamagata-Sekihara, et al., PRC80(2009)045204 pSN measurement 21

is an important key Decay Channel, Exclusive 3He(K-,Lp)n 22 Exclusive 3He(K-,Lp)n events CDS preliminary p n missing n

L pp 1GeV/c K- beam K-3HeL(S0)pn events can be i dentified exclusively # of L(S0)pn events: ~190 S0pn contamination: ~20% 23 Dalitz plot preliminary 3NA: e.g. K-3HeLpn

Observed events seem to be scattered widely in the phase-space of K-+3He->L+p+n 24 Dalitz plot preliminary 2NA: e.g. K-3HeLpns 2NA+2step: e.g. K-3HeS0pns, S0nsLn 2NA+2step: e.g. K-3HeLpns, pnspn 2NA+2step: e.g. K-3HeS0nps,

S0psLp K-pp form.: K-3He(K-pp)n, K-ppLp 25 K-induced vs p-induced [1] D. Gotta, et al., PRC51. 496 (1995) [2] P. Weber et al., NPA501 765 (1989) [3] G. Backenstoss et al., PRL55. 2782 (1985) p- stopped [1] 2nucleon absorption &FSI (50%/p 3nucleon absorption <3% /p stopped stopped

) are clearly seen p- in-flight [2],[3] 2nucleon absorption 0.85 0.17mb (266 MeV/c) 3nucleon absorption 3.7 0.6 mb(220 MeV/c) 3NA/2NA ~ 4 in-flight K preliminary stopped p Data suggests that 3NA reactions are dominant? 26 Lp Invariant Mass

preliminary FS = L (S0 ) pn cannot be from 2NA of L*n Excess around the threshold? SIM K-pp 2NA B.E = 50MeV G = 50MeV S0p Lp

3NA Further study is ongoing, such as contribution from 2NA+2step. 27 Comparison with Phase-Space IM(Lp) ~190 events preliminary IM(Ln) preliminary total CS : ~200 mb

(~ 0.1% of total cross section of K-3He) when phase-space distributions are assumed Excess around the threshold? 28 Comparison with Phase-Space cos(Lp) cos(Ln) preliminary preliminary pL

preliminary pp preliminary pn preliminary data cannot be reproduced by the phase-space? 29 Formation + Decay Channel, Kinematically Complete 3He(K-,Lpn)

30 Kinematically-complete measurement of 3He(K -, Lpn) preliminary only ~15 events preliminary Minimum momentum transfer of the 3He(K-,n) reaction would enhance the S=-1 di-baryon production 31 More beam time is required Future Prospects of E15

32 E15 2nd stage (approved) x10 E152nd: 50x109 kaons on target in 2015 The goal of the E152nd 1. derive pSN decay information in 3He(K-,n)X reaction 2. confirm the spectral shape of the Lp invariant-mass by the exclusive measurement of 3He(K-,Lp)n 3. explore the neutron spectrum at qlab=0O with the kinematically complete measurement of 3He(K-,Lpn) 33 FINUDA/DISTO Summary of E15 1st

3 He(K-,n)X M.M. Formation Channel Semi-Inclusive 3He(K-,n)X No significant bump structure in the deeply bound region Excess below the threshold attributed to 2NA of L*n? nd Int erestin g hints o have b f

S =-1 sys e e E1 5 n obta t e m i n 2 wil e Lp I.M. l be pofeHe(K ,Lp)nd in E15 1 st . rforme Decay Channel

d in preliminary Exclusive He(K ,Lp)n 2015. Hint of the excess around 3 3 - - the threshold Cannot be from 2NA of L*n (final state = Lpn) 34

The J-PARC E15 Collaboration 35

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