原子核媒質中の中間子質量測定の現状と将来

原子核媒質中の中間子質量測定の

現状と将来

小沢　恭一郎（東京大学）Contents:

Physics motivationCurrent results

Future ExperimentsSummary

ハドロン質量の起源

2009/1/8 J-PARC seminar, K. Ozawa

1

10

100

1000

10000

100000

1000000

u d s c b t

QCD Mass

Higgs Mass

95% of the (visible) mass is generated by the strong interaction, dynamically. Only 5% of the mass is due to the Higgs field.

Current quark masses generated by

spontaneous symmetry breaking (Higgs field)

Constituent quark masses generated byQCD dynamical effects (spontaneous chiral symmetry breaking ).

The hadron mass is strongly related to chiral properties of “QCD medium”, which can be

changed as a function of Temperature and Density.2

QCD medium

2009/1/8 J-PARC seminar, K. Ozawa 3

High TemperatureHigh Density

Quark – antiquark pairs make a condensate and give a potential.Symmetry is breaking.

Quark is not confined.Mass ~ 0 (Higgs only)

It looks real “vacuum”.

Quark is confined.Vacuum contains quark antiquark condensates.So called “QCD vacuum”.

q

q

Vacuum VacuumWhen T and r are going down,

p as a Nambu-Goldstone boson.

How to study?


Mass of chiral partner should be degenerated in restored medium. – r (JP = 1-) m=770 MeV ：　 a1 (JP = 1+) m=1250 MeV

– N (1/2+) m=940 MeV 　：　 N* (1/2-) m=1535 MeV ？

Dm will decrease in finite r/T matter.However, measurements of chiral partner is very difficult

“QCD vacuum”, i.e. quark condensates can be changed in finite density or temperature.Then, chiral symmetry will

be restored (partially).

Vacuumr 0T 0

Connect hadron properties and quark condensate using QCD and/or phenomenology.

In finite r/T Chiral properties can be studied at finite density and

temperature.What is observable?

Theoretical efforts• Nambu-Jona-Lasino model

– Nambu and Jona-Lasino, 1961– Vogl and Wise, 1991– Hatsuda and Kunihiro, 1994

• Chiral Perturbation theory– Weinberg 1979– Gasser and Leutwyler, 1984, 1985

• QCD sum rule– Shifman et al., 1979– Colangelo and Khodjamirian, 2001– Hatsuda and Lee, 1992

• Lattice QCD– Wilson, 1974– Karsch, 2002

• Empirical models– Potential model (De Rujula et al., 1975), Bag model (Chdos et al., 1974)

• In addition, Collisional broadening, nuclear mean field …2009/1/8 J-PARC seminar, K. Ozawa 5

‘

G.E.Brown and M. Rho,PRL 66 (1991) 2720

0

**

8.0qq

qq

mm rr

T.Hatsuda and S. Lee,PRC 46 (1992) R34

18.0;1mm

0

B

V

*V

rr

Vector meson mass


Predicted “spectra”

• several theories and models predict spectral function of vector mesons (r, w, f).– Lowering of in-medium mass– Broadening of resonance

R. Rapp and J. Wambach, EPJA 6 (1999) 415

r- meson

6structure due to coupling to S11,P13 resonances

P. Muehlich et al. , Nucl. Phys. A 780 (2006) 187

w- meson

As the first step, experiments try the comparison between

predicted spectra and measurements.

MEASUREMENTS


Create QCD medium

heavy ion reactions:A+AV+X

mV(r>>r0;T>>0)

SPS

LHC

RHICelementary reaction:

, p, p V+XmV(r=r0;T=0)

, p. p - beams

J-PARCCLAS

At Nuclear Density

82009/1/8 8J-PARC seminar, K. Ozawa

Measurements of Vector Meson mass spectra in QCD medium will provide QCD condensates information.

Leptonic (e+e-, m+m-) decays are suitable, since lepton doesn’t have final state interaction.

Results @ SPS

9

PRL 96, 162302 (2006)


[van Hees+R. Rapp ‘06]

(NA60)

Next,We should try to extract of a quark condensate information from the data.

Spectrum is reproduced with collisional broadening.

Muon pair invariant mass in In-In at sNN=19.6 GeV

RHIC&PHENIX


Results @ RHIC


• Black Line– Baseline calculations

• Colored lines– Several models

Low mass• M>0.4GeV/c2:

– some calculations OK• M<0.4GeV/c2:

not reproduced– Mass modification– Thermal Radiation

Advantages of RHICQGP generatedClear initial conditionTime developing

calculated by Hydrodynamics

No concluding remarks at this moment.Currently, we are working for detector upgrade.

Electron pair invariant mass in Au-Au at sNN=200 GeV

arXiv:0706.3034

Then, Nucleus• Stable system

– No (small) need for time development

• Saturated density

ECT*-WS, K. Ozawa

Link vector meson masses and the quark condensate. Link meson bound states and the quark condensate.

Two approaches,


Bound State (Emitted Proton/Neutron)p, p,

Nucleon Hole

TargetDecay

Meson

p bound stateK. Suzuki et al., Phys. Rev. Let., 92(2004) 072302

p bound state is observed in Sn(d, 3He) pion transfer reaction.

Reduction of the chiral order parameter, f*p(r)2/fp2=0.64 at the normalnuclear density (r = r0 ) is indicated.


p as a NG boson

13New exp. is in preparation at RIKEN

D. Jido et al., arXiv:0805.4453PLB670 (2008) 109

Jido-san et al. shows that p-nucleus scattering length is directly connected to quark condensate in the medium.

Mass spectra measurements• 現在までに主に 4 例の実験結果

– TAGX 実験– CBELSA/TAPS 実験– KEK 陽子シンクロトロン（ KEK-E325 実験 )– J-Lab CLAS 実験

• 軽い原子核と重い原子核で比較することで、媒質効果を導き出す。

14

得られるものは、自由空間中で崩壊した粒子の分布との重ね合せ

予想される質量分布（ KEK実験、銅標的の場合）


注意

15J-PARC seminar, K. Ozawa

INS-ES TAGX experiment

E STT modelPresent

work

Previouswork

800-960MeV

700-710 MeV

672±31MeV

960-1120MeV

730MeV

743±17MeV

Eγ~0.8-1.12.GeV, sub/near-threshold ρ0 production• PRL80(1998)241,PRC60:025203,1999.: mass reduced in

invariant mass spectra of 3He(γ, ρ0)X ,ρ0 --> π+π−• Phys.Lett.B528:65-72,2002: introduced cosq analysis to

quantify the strength of rho like excitation • Phys.Rev.C68:065202,2003. In-medium r0 spectral function

study via the H-2, He-3, C-12 (,p+ p-) reaction.

2009/1/8

Try many models, and channels Δ, N*, 3π,…

CBELSA/TAPS

disadvantage:

• p0-rescattering

advantage:

• p0 large branching ratio (8 %)

• no r-contribution (r p0 : 7 10-4)

w p0

p

A w + X

p0

2ppm pw

D. Trnka et al., PRL 94 (2005) 192203after background subtraction

%.mm 03

mw = m0 (1 - r/r0) for = 0.13

TAPS, w p0 with +A


E325 @ KEK-PS12 GeV proton induced.

p+A f + XElectrons from f decays are detected.

TargetCarbon, Cupper0.5% rad length


KEK E325

E325 Spectrometer


Mass spectra measurements

mr = m0 (1 - r/r0) for = 0.092009/1/8 J-PARC seminar, K. Ozawa 19

Induce 12 GeV protons to Carbon and Cupper target, generate vector mesons, and detect e+e- decays with large acceptance spectrometer.

Cu we+e-

re+e-

w/r/f

The excess over the known hadronic sources on the low mass side of w peak has been observed.

M. Naruki et al., PRL 96 (2006) 092301

KEK E325, r/w e+e-

CLAS g7a @ J-Lab


Induce photons to Liquid dueterium, Carbon, Titanium and Iron targets, generate vector mesons, and detect e+e- decays with large acceptance spectrometer.

R. Nasseripour et al., PRL 99 (2007) 262302

mr = m0 (1 - r/r0) for = 0.02 ± 0.02

No peak shift of r Only broadening is observed

w/r/f

Contradiction?• Difference is significant

• What can cause the difference?– Different production process– Peak shift caused by phase

space effects in pA?• Need spectral function of r

without nuclear matter effectsNote:

• similar momentum range• E325 can go lower slightly


In addition, background issue is pointed out by CLAS

CLAS KEK

Background is not an issue• Combinatorial background is evaluated by a mixed event

method.• Form of the background is determined by acceptance and

reliable.• We should be careful on normalization.


Absolute normalization using like-sign pairs

CLAS KEKNormalized using mass region above f. There is enough statistics

The problem:Each experiment can’t apply another method.


Results: f e+e- (E325)

Cu

b<1.25 (Slow)Invariant mass spectrum for slow f mesons of Cu target shows a excess at low mass side of f.

Measured distribution contains both modified and un-modified mass spectra. So, modified mass spectrum is shown as a tail.

23

First measurement of f meson mass spectral modification in QCD matter.

R. Muto et al., PRL 98(2007) 042581

Excess!!

Mass Shift:mf = m0 (1 - r/r0) for = 0.03

b<1.25 (Slow) 1.25<b<1.75 1.75<b (Fast)


Mass modification is seen only at heavy nuclei and slowly moving f Mass Shift:

mf = m0 (1 - r/r0) for = 0.0324

Target/Momentum dep.

NEXT STEP@ J-PARC


Condensates to Spectrum


We should revisit the relation between quark condensate and vector meson spectrum

q

q

Vacuum Vacuum

QCD sum rule

Average of Imaginary part of P(w2)

vector meson spectral function

T.Hatsuda and S. Lee,PRC 46 (1992) R34

03.0;10

*

rr B

V

V

mm

Prediction

Spectrum

mV

Original idea by Hatsuda and Lee shows the relation

Assume

Using this relation,

Spectrum to condensate


Evaluate quark condensate using QCD-SR.

Experimental requirements

1. High statics2. Clear initial condition

Not comparison btw models and measurements.

q

q

Vacuum Vacuum

QCD sum rule

Average of Imaginary part of P(w2)

vector meson spectral function

Replace by average of measured spectra

p

Condensates and Spectrum

Let’s go to J-PARC


• Beam Energy ： 50 ＧｅＶ(30GeV for Slow

Beam)• Beam Intensity: 3.3x1014ppp, 15mA

(2×1014ppp, 9mA)

Hadron Hall


New exp 1: High Statistics• Extended to vertical direction

Side viewPlain view

KEK spectrometer

Cope with 10 times larger beam intensity!!100 times higher statistics!! 29


Beam LineNP-HALL

56m(L)×60m(W)

ここでやります。お願いします。

30

What can be achieved?


Pb

fModified f

[GeV/c2]

f from Proton

Invariant mass in medium

ff

fff

ff

f

p dep.

High resolution

calculate quark condensate

New exp 2: Clear Initial condition


-50 MeV/c2

DM = 0 MeV/c2

-100 MeV/c2

0 2 4 6p momentum [GeV/c]

w m

omen

tum

[GeV

/c]

0

0.2

0.4Mass dependence(Mw = 783 MeV/c2)

Stopped w meson

p

w p0

n

A w + X

p0

2ppm pw

As a result of KEK-E325,We can expect 9% mass decreasing.It corresponds to 70 MeV/c2.To generate stopped modified w meson, beam momentum is ~ 2 GeV/c. (K1.8 can be used.)

Generate w meson using p + p.Emitted neutron is detected at 0.Decay of w meson is detected.If p momentum is chosen carefully, momentum transfer will be ~ 0.

Invariant mass in medium

Expected results


Δ Ｅ /E = 3 %/√E

Expected Invariant mass spectrum

DM=0

DM=9%

DM=13%

Show mass shift at p=0.

Emitted Neutron

p

p0 decayBound w

Dm

Initial condition is measured by forward neutron.w can be bounded in nucleus.

RELATED EXPERIMENT @ J-PARC


Chiral symmetry with Baryon


h bound stateN*(1535)

KS-KL s-wave resonance (Chiral Unitary model)Chiral partner of nucleon (Chiral Doublet model)

h – N is strongly coupled with N*

How to study N* experimentally?

h in nucleus makes N* and hole

Generate slowly moving h in nucleus

LOI by K. Itahashi et. al

Calc. by H. Nagahiro

35

Experiment for h


LOI by K. Itahashi et. al Calc. by H. Nagahiro, D. Jido, S. Hirenzaki et. al

Forward neutron is detected.missing mass distribution is measured.

In addition, measurements of invariant mass of N* decay

Simulation

36

f bound state?


Cu

b<1.25 (Slow)

Bound?

ssuud

K+

Λ

Φ

p ud

sus

Experiment 1:fp -> K+L

Experiment 2:pp -> ff

See details in Dr. Ohnishi’s LOI37

Summary• According to the theory, Hadron mass is

generated as a results of spontaneous breaking of chiral symmetry.

• An experimental efforts are underway to investigate this mechanism. Some results are already reported.– Still, there are problems to extract physics

information. • New experiments for obtaining further

physics information are proposed.– Explore large kinematics region– Measurements with stopped mesons– Measurements of bound states


Back up


質量の起源

ＨｉｇｇｓＱＣＤ

Chiral symmetry


The lagrangian does not change under the transformation below .

This symmetry is called as Chiral symmetry.

V(q)

q

Symmetric in rotation

GluonDivide with chirality Neglect (if m ~0)quark mass

Breaking of symmetry


Potential is symmetric andGround state (vacuum) is at symmetric position

Potential is still symmetric, however,Ground state (vacuum) is at non-symmetric position

This phenomenon is called spontaneous symmetry breaking

When the potential is like V(f) = f4,

dV ~ self energy of ground state ~ mass

If the interaction generate additional potential automatically,V’(f) = -a*f2


Performance of the 50-GeV PS• Beam Energy ： 50 ＧｅＶ

(30GeV for Slow Beam)

(40GeV for Fast Beam)

• Repetition: 3.4 ~ 5-6s• Flat Top Width ： 0.7 ~ 2-3s• Beam Intensity: 3.3x1014ppp, 15mA

(2×1014ppp, 9mA) ELinac = 400MeV (180MeV)

• Beam Power: 750kW (270kW)

Numbers in parentheses are ones for the Phase 1.

43


Linac

J-PARC• Cascaded Accelerator Complex:

3GeV Rapid Cycling (25Hz) Synchrotron

50GeV Synchrotron

Materials and Life Science Facility

Hadron Hall (Slow Extracted Beams)

Neutrino Beamline to Super-Kamiokande

44


1g/cm2

1g/cm2

C Cu

421 ,, ZBackgroundZBremshAV

Experimentalists face to reality - E325 simulation- e+e-

KEK-E325 Targetmaterial beam

(p/spill)Interaction length(%)

radiation length(%)

C 0.64x109 0.2% 0.4%Cu X4 0.05% X4 0.5% X4

simulation

Issue: Final state interaction

disadvantage:

• p0-rescattering

J.G.Messchendorp et al., Eur. Phys. J. A 11 (2001) 95

w p0

p

A w + X

p0

2ppm pw


no distortion by pion rescattering expected in mass range of interest;

further reduced by requiring Tp>150 MeV

Yield EstimationSummary plot of p-p wn for backward w (G. Penner and U. Mosel, nucl-th/0111024,J. Keyne et al., Phys. Rev. D 14, 28 (1976))

0.14 mb/sr @ s = 1.8 GeV same cross section is assumed.

Beam intensity107 / spill, 3 sec spill length)

Neutron Detector acceptanceDq = 1°(30 cm x 30 cm @ 7m

Gamma Detector acceptance75 % for single, 42% for tripleBranching Ratio: 8.9%

Optimistic obtained yield is 316502009/1/8 J-PARC seminar, K. Ozawa 47

原子核媒質中の 中間子質量測定の 現状と将来

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原子核媒質中の中間子質量測定の現状と将来