Search for the K  pp bound state via the in-flight 3 He(K ,n) reaction MESON2014 Yuta Sada for the E15 collaboration RCNP, Osaka Univ & RIKEN 1

Contents Kaonic nuclei J-PARC E15 experiment Setup Preliminary result ▫Exclusive 3 He(K ,  p)n events Summary 2

3 Kaonic nuclei 3 FINUDA DISTO B = 105±2±5 MeV  = 118±8±10MeV B = 115±6±4 MeV  = 67±14±3 MeV 6 Li, 7 Li, 12 C target, stop K− reaction  p invariant mass p+p → X +K +, X →  + p reaction missing-mass & invariant mass These bumps are really K  pp? ⇒ We need more results on various reactions about K  pp!! Bound state of anti-kaon and nuclei with strong interaction K bar N is attractive in isospin=0 o Low energy KN scattering experiments o Kaonic hydrogen X-ray measurements o Existence of  1405) 27MeV below K - p threshold => Kaonic nuclei (K  pp) exists or not??

4 Chiral & energy dependentBinding energy[MeV] Width[MeV] A. Dote, T. Hyodo, W. Weise(2008,2009) Y. Ikeda, H. Kamano, T. Sato(2010) N. Barnea, A. Gal, E.Z. Liverts(2012)1641 Phenomenological potential (energy independent) Binding energy[MeV] width[MeV] T. Yamazaki, Y. Akaishi(2002)4861 N.V. Shevchenko, A. Gal, J. Mares(2007) Y. Ikeda, T. Sato (2007,2009) S. Wycech, A.M. Green (2009) Theoretical calc. of K bar NN(K - pp) There are large difference in theoretical models. Energy dependent models suggest shallow bound??

5 J-PARC E15 experiment in-flight 3 He(K -, n) reaction & its exclusive measurement => Search for K - pp bound states both via formation & Decay 5 K - 1.0GeV/c 3 He Formation Kpp cluster Neutron  p p -- Mode to decay charged particles Decay Missing mass Spectroscopy via neutron Invariant mass reconstruction We are able to detect all particles from formation & decay of K - pp!!

J-PARC K1.8BR beam line[Jun. 2012] beam dump beam sweeping magnet CDS 3 He-target beam line spectrometer neutron counter & TOFstop/proton counter 6 3 He(K -,N) reaction Primary- beam intensity Duration Kaons on target March, 2013 (Run#47) 14.5 kW (18 Tppp, 6s) 30 h1.1 x 10 9 May, 2013 (Run#49c) 24 kW (30 Tppp, 6s) 88 h5.1 x 10 9 K-K- n K-K- p

7 7 CDC Hodoscope And Solenoid To detect the decay particles from 3 HeTarget Momentum reconstruction Particle identification Size : 99 x 30 x 700 mm 3 (W x T x L) Configuration : 36 modules PMT : fine-mesh type (H8409) Cell Drift length~9mm Layer 15 layers Read out : 1816 ch Gas : Ar-C 2 H 6 (50:50) CDC (15 layers, 1816ch) + CDH (36 seg) + 0.7T solid angle: 60% of 4  Mass resolution (Kpp) ~10MeV/c 2 Cylindrical Detector System

PID & Tracking efficiency Tracking eff Total eff =94.0% There is no geometrical asymmetry! Mass^2 [(GeV/c2)^2]Phi angle[rad] Momentum[GeV/c] Tracking eff.] P K   /K/p/d are clearly separated 8  of Mass^2 [(GeV/c2)^2] Momentum[GeV/c] PKPK

There are two purposes 1. K - pp search : K He ⇒ n+K - pp →  p 2. Study of multi-Nucleon 3 He target =>Measurement of In-flight K- multi-nucleon absorption is NEW!!   stopped [1] ▫2nucleon absorption &FSI (50%/  stopped ) are clearly seen ▫3nucleon absorption <3% /  stopped   in-flight [2],[3] ▫2nucleon absorption 0.85 ± 0.17mb (266 MeV/c) ▫3nucleon absorption 3.7 ± 0.6 mb(220 MeV/c) ▫2NA/3NA ~25% 9 [1] D. Gotta, etal., Phys. Rev. C (1995) [2] P. Weber etal., Nucl. Phys A501 (1989) [3] G. Backenstoss etal., Phys. Rev. Lett (1985) 3 He(K -,  p)n reaction

Exclusive 3 He(K -,  p)n events K -3 He   (  0 )pn events can be identified exclusively ▫# of  (  0 )pn events: ~190   0 pn contamination: ~20% 10 n 1GeV/c K - beam p  p missing n  CDS Preliminary

To check  pn events phase space distribution ▫To plot in this figure, kinematics is fixed. ▫Checking 3 nucleon absorption or 2 nucleon absorption 3 He(K -,  p)n: Dalitz plot T neutron T proton T  If events are distributed uniformly => 3NA is dominant 11

K - pp form.: K -3 He  (K - pp)n, K - pp   p 2NA: e.g. K -3 He   pn s 3 He(K -,  p)n: Dalitz plot 12 2NA+2step: e.g. K -3 He    pn s,  0 n s   n 2NA+2step: e.g. K -3 He    np s,  0 p s   p Events are scattered widely in the phase-space of K He->  +p+n =>3NA is dominant!! Preliminary

3 He(K -,  p)n: Invariant Mass total CS : ~200  b ▫when phase-space distributions are assumed Excess around the threshold? 13 ~190 events IM(  p) (~ 0.1% of total cross section of K -3 He) IM(  n) Preliminary

3 He(K -,  p)n: Comparison with Phase-Space data cannot be reproduced only by the phase-space? 14 cos(  p)cos(  n) pp p pnpn Preliminary

Summary J-PARC E15 experiment ▫We have performed the 1 st physics experiment (we accumulated 5.1 x 10 9 Kaons on  He target ) ▫All detectors performance have been archived as designed value Preliminary results ▫Exclusive 3 He(K ,  p)n events  First measurement of in-flight K - multi-nucleon absorption !!  Our data suggest that 3NA processes are dominant in 3 He(K -,  p)n reaction.  Total CS of 3 He(K -,  p)n event (3NA) is estimated to be ~200  b. i.e. 0.1% of total CS of K- 3 He interaction  If we assume all events mainly come from 3NA processes, there is an excess around K+p+p threshold. 15

Thank you for your attention J-PARC E15 collaboration 16

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Experimental situation FINUDA  NE =>positive? ▫Stopped nuclei ->  p invariant mass DISTO =>positive? ▫p + p  (  + p) + K 2.85GeV HADES =>negative? ▫p + p  (  + p) + K 3.5GeV And LEPS experiment =>negative? ▫photon -induced reaction J-PARC E27 experiment =>positive? ▫d(  +, K + Situation is not clear. We need more studies of K bar NN in various reaction channels!! FINUDA B.E. = 115MeV  = 67MeV DISTO B.E. = 103MeV  = 118MeV HADES 18

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3 He(K ,  pn NC ) reaction Events are less than 20 20

Beam line performance K/  ratio: 0.45  beam 21

Neutron counter 3 He(K -,n)X missing mass[GeV/c 2 ] Resolution [MeV/c 2 ] K+p+p threshold  ~10 MeV/c Resolution is estimated with width of  peak 22

Semi-Inclusive 3 He(K -,n)X M.M. spectrum Integrated luminosity of K He: 540  b -1 Semi-Inclusive : (CDC-track > 1) is required to determine the reaction vertex 23 (  lab =0 o )

CANNOT be explained by any experimental effects nor well-known “elementally” processes 24 (  lab =0 o ) excess Semi-Inclusive 3 He(K -,n)X M.M. spectrum DISTO/FINUDA

3 He(K -,n): non-mesonic 2NA? non-mesonic-2NA reactions ▫K He  Y (*) +N+N s  N/  N branches are negligibly small! large contribution of Y* branches? ▫Spectral shape of  (1405) is “simple BW with PDG values”  reproduce the excess with  (1405)n of ~5mb/sr BW shape with PDG values 25

B.E. (MeV)  (MeV) 95% C.L. (mb/sr)FINUDA11567~0.2 DISTO103118~0.3 FINUDA DISTO 26 3 He(K -,n): deeply-bound K - pp search No clear structure was found in B.E. ~ 100 MeV/c 2 95% C.L. of d  /d  (  lab =0 o ) is ~0.3 mb/sr

3NA  pn ~75% 3NA  0pn ~20% 3NA  pn  ~4% else(i.e2NA+  ) ~1% M.M of 3 He(K -,  p)X [GeV/c 2 ] 27 3NA  pn 3NA  0pn 3NA  pn  Preliminary Fitting 3NA/2NA +  events produced MC Decomposition of “missing neutron” region M.M of 3 He(K -,  p)X [GeV/c 2 ]