 meson in nucleus at J-PARC Hiroaki Ohnishi RIKEN New Frontiers in QDC Exotic Hadron Systems and Dense Matter – Mini Symposium on Exotic hadrons Feb/23/2010 phi meson production at JPARC

This talk is based on the submitted proposal to J-PARC

Introduction

My personal questions  What is the meaning of mass ?  What is the meaning of mass in nuclear media?  i.e. If mass reduction of vector meson exist, what is the meaning?  Is there any clear relations between Chiral order parameter mass reduction of mesons in nuclear media

 meson in nuclear media  why are we focusing on  meson?  Quark content : ~100% ss  Mass shift on  meson in nuclear matter is directly connecting (?) to the in medium change of strange quark condensate (or gluon condensate?) Direct access to the chiral symmetry restoration in the strangeness sector can be possible via  meson   meson in nuclear media will give us unique information on strange content of nucleon and nuclear matter

 mesons in nuclear media - theoretical situation  Mass of vector meson in nuclear media will be decreasing when density increasing (QCD Sum rule) (if no width broadening ?)  Very small mass shift but significant broadening of decay width (Chiral SU(3) ….) T. Hatsuda, H. Shiomi and H. Kuwabara Prog. Theor. Phys. 95(1996)1009 NPA 624(1997)527

 mesons in nuclear media - experimental situation  mass shift (~3%) of  meson have been observed by KEK-PS E325. ( with the width getting 3.6 times bigger then the width in vacuum) - PRL 98(2007)04501  photo production of  meson from Li, C, Al, and Cu at LEPS/SPRING-8    N in nuclear media getting much bigger (~35 mb) than in free space ( huge width broadening ) - PLB608(2005)215   meson production in 158 GeV/c In-In collisions at CERN/SPS (NA60)  mass shift and width broadening are not identified in hot nuclear matter (within detector resolution) - EPJ C64(2009)1-18 What is really happening on  meson in nuclear media ~2GeV/c

Considering mass reduction in nuclear media  Strong attractive force exist between KbarN This is confirmed by measurement of 2p->1s x-ray energy in Kaonic hydrogen atom M.Iwasaki et al., PRL78 (1997) s 2p only Coulomb int keV  E = -323 eV  = 407 eV  The strong attraction between KbarN lead to the conclusion of mass reduction of Kbar(K-) in nuclear media. Nucl.Phys.A617(1997)449 Mass reduction = attractive force exist ??? = attractive potential ?

 -N bound state?   -N bound state has already been discussed in year 2000, however totally independent starting point.  Meson-Nucleon bound state with “ QCD van der Waals ” attractive force (Originally this idea is developed for the discussion of  c -N bound state) Binding energy obtained with this analysis is 1.8 MeV/n. Assume : B EA = B EN x A 2/3 ( like the case of hyper nucleus ) binding energy for Copper nucleus (for example) ~ 28 MeV.

 -N bound state?  Results from Chiral SU(3) quark model Experiment to search for such bound state has been performed, (at CLAS),But no experimentally evidence for existence of such (quasi-) bound state

Goal of the experiment   -meson bound state  measurement of binding energy and width  Question is how to measure mass shift which can be compared with theoretical prediction?? Origin of mass shift and contribution of chiral symmetry restoration in the mass of vector meson (need helps from theory..)  the invariant mass study of  → ee in nucleus (J-PARC E16) (J-PARC P29) This part is missing!!!

Experimental method

How to identify  meson bound state  Formation of  mesic nucleus will be identified with missing mass analysis. a b   Need to find good elementary process for  meson production  ( ,K) reaction for hyper nucleus formation  produced f meson momentum must be small (up to a few hundred MeV/c)

How to produce  with low momentum efficiently?   production via p(p,  )  reaction  Very interesting production process  Double  meson production will be dominant around threshold ( 0.9 GeV/c<p<1.4 GeV/c)  Only less than 10% physical background  Momentum transfer ~ 200 MeV/c  Once we detect one  meson in the reaction, partner will also be  meson  Missing mass spectroscopy can be done with forward going  meson ~2GeV/c KEK-E325  meson  distribution  meson production cross section will be smaller than KEK E325, but using pbar, could produce slow  meson efficiently

How to produce  with low momentum efficiently?  Huge Background However, once one can identify third strangeness in the event, then event sample will be almost background free  meson production with anti-proton will be primary candidate of the elementary process for the  mesoic-nucleus production.

How to ensure  meson is really in nucleus  Let ’ s focusing on decay mode  Mass of the  meson will be decreasing about 30 MeV.  i.e MeV – 30 MeV = 989 MeV ~ 2 x M Kaon Main decay mode for Φmeson, Φ → K+K-, will be suppress.  However, Φ meson is in nucleus. There are many nucleon surrounding them MeV – 30 MeV MeV(proton) ＝ 1927 MeV > M Kaon +M Λ i.e. Φp → K + Λ will be a dominant decay mode, if  meson is in nucleus. (This mode is not suppressed by OZI role ) s s u u d K+ Λ Φ p u d s u s i.e. K +  in final state will be a good signal to ensure  meson in medium

Concept for the experiment Anti-proton Nuclear target Reaction  meson bound state Outgoing  meson Missing mass Spectroscopy K+K+  Decay Strangeness tag!!

Very recent theoretical progress on  mesic nucleus  Posibility of  mesic nuclei formation has been discussed in this paper, arXiv: v1 [nucl-th] 13 Jan 2010 If attractive potential is strong enough, some hope to see the peak? Structure due to the bound state formation …

Concerning for the experiment  pbar-p →  reaction is really happening in nucleus????   production process :  Direct production process  OZI rule viorated  Anomalous large cross section  This process can be expected even in nucleus.  Kaon loop  According to a theoretical calculation, Kaon loop process contributes 2  b to 4  b of cross section.  If such hadron loops are main component of  production, its process may suppress in nuclear medium (??).  Theoretical calculation or experimental evidence is important. p p   K p p   K K u uuduuduuduud p p s s   Probably we need to measure cross section of pbar-p →  in light nucleus as 1 st step

Detector concept and signal expected

Experimental method Slow  meson Fast Φmeson Φ Φmesic nucleus Φ Bound Anti proton Nucleus  ～１ GeV/c ～ 0.3GeV/c K+K+ K-K- How to produce and detect  mesic nucleus? K+K+  Missing mass using reconstructed forward going  coincidence with K+ and  from target Momentum of  produced by this reaction If we choose pbar momentum = 1.0 – 1.3 GeV/c momentum of the f will be 200 – 260 MeV/c Just select  produced to 180°in CM

Conceptual design of the detector  Large solid angle charged particle spectrometer (with large gap dipole magnet) Large acceptance for forward going  meson (for missing mass analysis) Large solid angle for the decay particles, K+ and , from  mesic nucleus ToF wall Antiproton beam CDC Target Region Main spectrometer Target surrounded by trigger counter target beam K- K+

Conceptual design of the detector target beam ToF wall = Resistive Plate Chamber (RPC) FOPI ToF Wall will be a model < 65 ps time resolution Working well under the magnetic field Target Region Aerogel cherenkov counter n~1.2 will be used CDC Candidate of spectrometer magnet RIKEN 4 th -cyclotron magnet now used as historical monument 220 cm pole diameter

Typical event display Y [cm] P ~450 MeV/c K + ~500 MeV/c Y [cm] K + ~500 MeV/c K  ~500 MeV/c   ~100 MeV/c p + Cu   +  Ni (B  = 30 MeV) “  ”+”p”  K + +  ( proton &  at rest ) All decay processes are isotopic. X [cm] Detector simulation using GEANT4 based on conceptual detector design is in progress

Anyway, how the signal looks like?  If life is simple enough (I knew life is complicated)  Assumption in the simulation:  bound state with 30 MeV B.E. exist  Spectrometer missing mass resolution = 18 MeV (  )  Fermi momentum in nucleus is taking into account in the simulation    in nucleus assumed to be broaden 10 time more than natural width Blue triangle: Missing mass spectra of unbound  Red circle : Expected signals CuCC2H4 Beam10 6 Mass number Carge number Cross section (Z 2/3 x s pp ) [mb] Target thickness [g/cm 2 ] Acceptance of forward KK Acceptance of decay particle Averaged Sticking probability Analysis and DAQ efficiency x x x x x x10 -2 N/A 0.7 Expected yield/120 shift~200~290610

Summary  Based on the results reported by KEK-PS E325 (mass shift of  meson) strongly suggested that the production of  mesic nucleus can be possible.  The most promising elementary process for the  mesic nucleus production will be pp →  channel.  Na ï ve event rate estimation tells us that ~200 events candidate for  mesic nucleus will be produce per 40 days,with beam intensity, 1x10 6 /spill, for 1.1 GeV/c anti-proton.