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Study of in medium mass modification for the φ meson using

φ meson bound states in nucleus

J-PARC 50 GeV PS PAC2010/07/17

Hiroaki OhnishiRIKEN

For the P29 experiment

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Study of in medium mass modification for the φ meson using

φ meson bound states in nucleus

P.B"uhler1, C. Curceanu2, C. Guaraldo2, O.Hartmann1,K.Hicks3, M.Iwasaki4,5, T.Ishiwatari1, P.Kienle6, J.Marton1,R.Muto7, M.Maruki7, M.Niiyama4, H.Noumi8, H.Ohnishi4,S.Okada2, A.Romero Vidal2, A.Sakaguchi9, F. Sakuma4,

S. Sawada7, D. Sirghi2, F. Sirghi2, K. Suzuki1,D.J. Tedeschi10, K.Tsukada4, O. Vazquez Doce2, E. Widmann1,

S. Yokkaichi4 and J. Zmeskal1

29 members from 10 institute

J-PARC 50 GeV PS PAC2010/07/17

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Goal of experiments at J-PARC to investigate in medium modification of meson

φ-meson bound state measurement of binding energy and width

Question is how to measure the mass shift which can be compared with theoretical prediction?

Origin of mass shift and contribution of chiral symmetry restoration to the mass of vector meson

(need input from theory..)

the invariant mass study of φ→ ee in nucleus

(J-PARC E16)

(J-PARC P29)

ω-meson in nuclear media measurement line shape of ω meson (ω π0γ)

(J-PARC P26)

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Outline

Introduction:Why we believe the φ meson bound states exist

The binding energy?The width of bound state?theoretical progress on φ mesic nuclei

Experimental methodConcept for the measurementConceptual design for the detector

Answers to the questions from previous PAC:

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φ mesons in nuclear media- experimental situation

Invariant mass spectra for φ mesonin heavy nucleus shows

3.4% mass shift3.6 times width broadening

when only the slowly moving phi mesons with respect to the target nuclei were selected (βγφ<1.25)

δmφ = -35 MeV @ ρ=ρ0

Existence ofattractive interaction

between φ-N

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φ-N scattering length (QCD sum rules)

QCD sum rules calculation tells us that the interaction between φ-N is attractive!

results

Attraction!

Expected mass shift of φfor this analysis is

~ 1-2%(@ ρ=ρ0) = -10 MeV to 20 MeV

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φ meson width broadening in nucleus?

Transparency ratio, TA=σγA-φX/A(σγp-φX),

NPA765(2006)188-196

Data : PLB 608(2005)215γA→φX : Extracted σφN =30 mb

Analysis : NPA 765(2006)188σφN expected (Theo.) ~10 mbdiscrepancy between σφNmeasured and expected is explained by width broadening of φ in nuclear media by factor 16!(Γ in nucleus ~70 MeV)

But …..recently very interesting results wew published from LEPS-Spring8 and CLAS-JLab

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φ meson width broadening in nucleus?

Why absorption of φ takes place on deuteron? Huge φmeson width broadening in nuclear matter really happen?

φ meson absorption? by nuclear matter?even with deuteron (single nucleon??)

Nuclear transparency rationmeasured with deuteron shows

0.73±0.058

Experiment : γd→φ X Extracted φN cross section

σφN = 20 mbAgain σφN Expected,

σφN = 11 mb (upper limit)How to explain this discrepancy?Again width broadening of φ mesonin nuclear matter even on deuteron?

[dσd/dt] / [2 x dσp/dt]=

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φ meson in nucleus

φ-N interaction could be attractive.φ-meson width will be broaden in nucleus, but how much is still not known.(How to explain large σφN measured by γd reaction)

Let’s measure it, but how?If ….Mass shift of φ meson exist an order of ~ 30 MeVand only small width broadening in nuclear matter

φ-meson nucleus bound state will be formed!

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Very recent theoretical progresson φ mesic nuclei

Possibility of φ mesic nuclei formation has beendiscussed in this paper,

If attractive potential is strong enough,then one can see the peak? Structuredue to the bound state formation…

～ required Λ in final state

Progress of Theoretical Physics (2010) accepted.

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φ meson production for bound state formation experiment?

φ production via p(p,φ)φ reaction

Very interesting production processDouble φ 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 φ meson in the reaction, its partner will also be a φ meson Missing mass spectroscopy can beperformed for the forward going φmeson

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Concept for the experiment

Anti-proton

Nuclear target Reaction

φ mesonbound state

Outgoingφ meson

K+

Λ

Decay

Strangeness tag!!

Missing mass

Spectroscopy

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Conceptual design of the detectorLarge solid angle charged particle spectrometer (with large gap dipole magnet)

Large acceptance forforward going φ meson(for missing mass analysis)

Large solid angle for the decay particles, K+ and/or Λ,from φ mesic nucleus

ToF wall+Cherenkov

CDC

Main spectrometer

K-K+

AntiprotonAntiproton

beambeam3.6m

6.0 m

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Typical event display

Y [c

m]

P~450 MeV/c

K+

~500 MeV/c

Y [cm]

K+

~500 MeV/c

K−

~500 MeV/c

π−

~100 MeV/c

p + Cu φ + φNi (Bφ = 30 MeV)“φ”+”p” K+ + Λ

( proton & φ at rest )All decay processes are isotropic.

X [c

m]Detector simulation

using GEANT4 based onconceptual detector design

is in progress

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Questions from previous PAC

Original comments on PAC report

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Event rate estimationSummary is shown as Table-1 in the submitted addendum

This number evaluated by use of GEANT4(G4) simulation takes in to account not only the detector acceptance (geometry) but alsoa) branching ratio of φ meson ( Br(φ→K+K-) = 49.2%)b) expected decay branching ratio of bound state

( Br(φN→ΛX) = 76 % )c) branching ratio of Λ (by GEANT4) ( Br(Λ→π-p ) = 63.9%)d) in-flight decay of charged Kaons (by GEANT4)

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Expected number of φ meson bound states on Carbon target

30 kW 0.1 x 106 anti-proton/spill

Running time assumption: 1000 spill/hour, 7 hours/shift, 120 shifts

Nφ-bound states ~ 20

100 kW 0.4 x 106 anti-proton/spillNφ-bound states ~ 80

270 kW 1.0 x 106 anti-proton/spillNφ-bound states ~ 200

If J-PARC 50 GeV-PS operated with

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Questions from previous PAC

Original comments on PAC report

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Previous PAC meeting

The meaning of “background free” is not clarified or even really not discussed deeply

Background for the measurement is reconsidered

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Signal and background

Background processes(Physical background)

φ meson production process in p-p annihilationwith anti-proton momentum = 1.1 GeV/c

x 10

x 20pp φφ (signal) 2.5 μb

φππ 25 μbKKππ 500 μb

signal process is only “double strangeness pairs”production event, therefore if we could identify φ meson + additional strangeness, i.e. K or Λ,the signal left in data sample will be background free, but …..

pp →φππ

Experimental background should be taken into account, such as wrong particle ID etc. andDouble strangeness pairs production by secondary interaction, i.e.

πN→ΛX

Acceptance evaluated usingGEANT4 based detector simulation

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Signal + experimental background Analysis procedure

Missing mass reconstructed using forward φ mesonPossible background processes

pp→φππ (x 10 more cross section than φφ production) pp→KKpp (x200 more cross section than φφ production) Two nucleons absorption: p”pn” → φKΛ (assumed 10% of φφ yield)Secondary Λ production by pion from pp→φππ event

Assumption for the signal Δmφ = 35 MeVΓφ = 15 MeV

Missing mass distribution Estimated to be 1.6% in Carbon target

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Signal + experimental background Analysis procedure

Missing mass reconstructed using forward φ mesonPossible background processes

pp→φππ (x 10 more cross section than φφ production) pp→KKpp (x200 more cross section than φφ production) Two nucleons absorption: p”pn” → φKΛ (assumed 10% of φφ yield)Secondary Λ production by pion from pp→φππ event

Assumption for the signal Δmφ = 35 MeVΓφ = 15 MeV

Missing mass distribution Estimated to be 1.6% in Carbon target

Required a Λ to be detected in the final state together with φ meson

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Signal + experimental backgroundbefore and after Λ requirement in final state

Background rejection factor, an order of 10-3, can be achieved once we required Λ in final state.

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Missing mass distribution with different φ meson width in nucleus

We can be identify up to Γφ ~ 10xΓφ vac

Threshold Threshold

Δmφ = 35 MeVΓφ = 15 MeV

Δmφ = 35 MeVΓφ = 43 MeV

(10xΓφ vac)

Δmφ = 35 MeVΓφ = 85 MeV

(20xΓφ vac)

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Expected number of φ meson bound states on Carbon target

30 kW operation 0.1 x 106 anti-proton/spill

Running time assumption: 1000 spill/hour, 7 hours/shift, 120 shifts

Nφ-bound states ~ 20

100 kW operation 0.4 x 106 anti-proton/spillNφ-bound states ~ 80

270 kW operation 1.0 x 106 anti-proton/spillNφ-bound states ~ 200

Δmφ = 35 MeVΓφ = 15 MeV

Is the φ-N interaction attractive?

Evidence for bound state?

Confirmation of bound state?

100 kW/120 shifts

Δmφ = 35 MeVΓφ = 15 MeV

270 kW/120 shifts

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Questions from previous PAC

Original comments on PAC report

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Double φ meson production in pbarannihilation

pbar-p → φφ reaction is really happeningin nucleus????φ production process :

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

Kaon loopIf such hadron loops are maincomponent of φφ production, the process may be suppressed in nuclear medium.

Two nucleon absorption?pbar-”pN” →φΛK

p

p

φ

φ

Kp

p

φ

φK

K

uud

uud

p

p

s

ss

s

φ

φ

No experimental data nor theoretical calculations do existWe want to measure it with light nucleus as 1st step

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Double φ meson productionLarge φ-N cross section has been measuredon γ-d interaction ( LEPS/Spring-8, CLAS/JLab) Need to confirmed whether this is only special case for γ-n interaction or not.

Step-1 for the experiment: To test the double strangeness production of pbarannihilation on nuclei, we would like to start with light nucleus, i.e. deuteron.

confirmation that pbar-p→φφ production really happened on nucleusinvestigation of basic information for φ-N interaction

J-PARC 50 GeV-PS: 100 kW operation = 740 events/120 shifts

Step-2Search for φ meson bound state in nuclei

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Questions from previous PAC

Original comments on PAC report

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Consideration on beam line

K1.8 BR(exist)beam intensity~ 0.7M/spill

K1.1/K1.1BR(not completed)beam intensity~ 1.0M/spill

What we need for the proposed experimentp beam with the beam momentum 0.9 -1.1 GeV/cLength of the beam line is not a problem.

No decay in flight of beam particle ☺

Main difference is beam intensity! We need 1.8 times more beam time,if we perform the experiment at K1.8BR

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K1.1 BR

K1.8 BR

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Summary

Based on the results reported by KEK-PS E325(mass shift of φ meson) strongly suggested that the production of the φ mesic nucleus can be possible. The most promising elementary process for the φ mesic nucleus production will be pp→φφ channel.Experiment can be performed both K1.1/K1.1BR or K1.8BR. However, K1.1/K1.1BR will be better because higher beam intensity will be expected on K1.1/K1.1BR than K1.8BR.

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Summary

To test the double strangeness production of p annihilation on nuclei, we would like to start with deuteron target. (Step 1)

100 kW, J-PARC-PS operation ~700 φφ events on deuteron

Once the double φ meson production is establish, we will switch the experiment mode to search for φ mesic nuclei (Step 2)

100 kW, J-PARC-PS operation ~80 bound state events on Carbon

270 kW, J-PARC-PS operation ~200 bound state events on Carbon

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Thank you very much!