meson in nucleus at J-PARC

Hiroaki OhnishiRIKEN

New Frontiers in QDC 2010-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 <qq>

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 <ss> (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. KuwabaraProg. 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.I

was

aki e

t al

.,

PR

L78

(199

7) 3

067

1s

2p

only Coulomb int. -8.6 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 : BEA = BEN 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 bedone 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 modeMass of the meson will be decreasing about 30 MeV. i.e. 1019 MeV – 30 MeV = 989 MeV ~ 2 x MKaon

Main decay mode for Φmeson, Φ→K+K-, will be suppress.However, Φ meson is in nucleus.

There are many nucleon surrounding them. 1019 MeV – 30 MeV + 938 MeV(proton)　　　　　　　　　　　　　　　　　＝ 1927 MeV > MKaon+MΛ

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

uud

K+

Λ

Φ

p ud

s

us

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

mesonbound state

Outgoing meson

Missing

mass

Spectroscop

y

K+

Decay

Strangeness

tag!!

Very recent theoretical progresson mesic nucleus

Posibility of mesic nuclei formation has beendiscussed in this paper,

arXiv:1001.2235v1 [nucl-th] 13 Jan 2010

If attractive potential is strong enough,some hope to see the peak? Structuredue to the bound state formation…

Concerning for the experiment pbar-p → reaction is really happening

in nucleus???? production process :

Direct production process OZI rule vioratedAnomalous large cross section This process can be expected even in nucleus.

Kaon loopAccording to a theoretical calculation,

Kaon loop process contributes 2b to 4b 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

uud

uud

p

p

s

ss

s

Probably we need to measure cross section of pbar-p → in light nucleus as 1st step

Detector conceptand

signal expected

Experimental method

Slow meson

Fast Φmeson

Φ

Φmesic nucleus

Φ Bound

Antiproton

Nucleus

～１ GeV/c～ 0.3GeV/c

K+

K-

How to produce and detect mesic nucleus? 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/cmomentum 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 forforward 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

targetbeam

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 4th-cyclotron magnetnow 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 onconceptual 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

Cu C C2H4Beam 106 106 106

Mass numberCarge numberCross section (Z2/3 x spp ) [mb]Target thickness [g/cm2]Acceptance of forward KK Acceptance of decay particleAveraged Sticking probabilityAnalysis and DAQ efficiency

63.529232.05x10-2

8x10-2

0.130.7

1267.92.05x10-2

8x10-2

0.130.7

112.42.07x10-2

3x10-2

N/A0.7

Expected yield/120 shift ~200 ~290 610

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.

Naïve event rate estimation tells us that ~200 events candidate for mesic nucleus will be produce per 40 days,with beam intensity, 1x106/spill, for 1.1 GeV/c anti-proton.