experimental study of hadron mass k. ozawa (university of tokyo) (university of tokyo) contents:...

Experimental study of hadron mass

K. Ozawa (University of Tokyo)Contents:

Physics motivationCurrent results

Future ExperimentsSummary

Origin of quark mass

2010/5/24 Weizmann 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 dynamically generated by the strong interaction.

This mechanism is actively studied both theoretically and experimentally.

Current quark masses generated by

spontaneous symmetry breaking (Higgs field)

Constituent quark masses should be generated byQCD dynamical effects

2

Figure by Prof. I. Tserruya

Naïve Theory

2010/5/24 Weizmann seminar, K. Ozawa 3

High TemperatureHigh Density

Quark – antiquark pairs make a condensate and give a potential. Chiralsymmetry is breaking, spontaneously.

Chiral symmetry exists.Mass ~ 0 (Higgs only)

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

q

q

Vacuum Vacuum

When T and r is going down,

p as a Nambu-Goldstone boson.

Experimental approach?


When chiral symmetry is restored, mass of chiral partner should be degenerated.

Dm will decrease in finite r/T matter.

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

be restored (partially).

Vacuumr 0T 0

In finite /r T

Chiral properties can be studied at finite density and temperature.

However, measurements of chiral partner is very difficult.We can measure only mass modification of narrow resonance.

mass

(JP = 1-)

a1 (JP = 1+)1250

770

/r T

Dm

Dm = 0Degenerate

Observable?


Predicted “spectra”

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

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

r- meson

5

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

- meson

As the first step, measurements in hot/dense matter are compared with predicted mass spectra.

CURRENT EXPERIMENTS


Generate hot/dense media

heavy ion reactions:A+AV+X

mV(>>0;T>>0)

SPS

LHC

RHIC

72010/5/24 7Weizmann seminar, K. Ozawa

Measurements of Vector Meson mass spectra in hot/dense medium will provide QCD information.

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

Hot matter experiments

SPS-CERES results


D. Miskowiec, QM05 talk

Existing of Mass modification is established.

PLB663, 43 (2008)

NA60 Results @ SPS

9

PRL 96, 162302 (2006)


[van Hees+R. Rapp ‘06]

Next,We should try to understand QCD nature

of the modification.

Spectrum is well reproduced with collisional broadening.

Muon pair invariant mass in Pb-Pb 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 RHICClear initial conditionClear Time develop

calculated by Hydrodynamics

No concluding remarks at this moment.New data with New detector (HBD) can answer it.

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

arXiv:0706.3034

New detector!


signal electron

Cherenkov blobs

partner positronneeded for rejection

e+

e-

qpair openingangle

~ 1 m

Constructed and installed by Weizmann and Stony Brook group.

~20 p.e.

few p.e.

Hadron

Single electron

Great performance!

Now, Nucleus!

elementary reaction:, p, V+XmV(=0;T=0)

, . p - beams

J-PARCCLAS

At Nuclear Density


Stable systemSaturated density

Experiments, CBELSA/TAPS KEK-E325 @KEK-PS (Japan)CLAS g7 @ J-Lab

Cold matter experiments

Results from CBELSA/TAPS

disadvantage:

• p0-rescattering

advantage:

• p0g large branching ratio (8 %)

• no -contribution ( 0 : 7 10-4)

g g

gg

w p0

p

gA + X

p0g

2ppm

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

after background subtraction

%.mm 03

TAPS, w p0g with g+A

2009/2/22 NQCD symposium, K. Ozawa 14m = m0 (1 - /0) for = 0.13

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 - /0) for = 0.092010/5/24 Weizmann seminar, K. Ozawa 17

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.

mr = m0 (1 - /0) for = 0.02 ± 0.02

No peak shift of r

Only broadening is observed

g w/ /r f

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

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 effects

Note: • similar momentum range• E325 can go lower slightly


We need to have a new experiment to investigate the problem.

CLAS

KEK

R.S. Hayano and T. Hatsuda, Ann. Rev.


Results: f e+e-

Cu

bg<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.

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

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

Excess!!

bg<1.25 (Slow) 1.25<bg<1.75 1.75<bg (Fast)


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

mf = m0 (1 - /0) for = 0.0321

Target/Momentum dep.

NEW EXPERIMENT@ J-PARC



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.

23


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

24

Hadron Hall


Hadron HallNP-HALL

56m(L)×60m(W)

Upgrade of E325Large statistics

25

Stopped w for Clear mass

modification

Upgrade of KEK-E325• Large acceptance (x5 for pair )• Cope with high intensity beam and high rate (x10)• Good mass resolution ~ 5 MeV/c2

• Good electron ID capability

2010/5/24 Weizmann seminar, K. Ozawa 26100 times higher statistics!!

What can be achieved?


Pb

fModified f

[GeV/c2]

f from Proton

Invariant mass in medium

ff

ff

ff

ff

p dep

.

High resolution

Dispersion relation

Detector components


Tracker~Position resolution 100μmHigh Rate(5kHz/mm2)Small radiation length(~0.1% per 1 chamber)

Electron identificationLarge acceptanceHigh pion rejection @ 90% e-eff.

100 @ Gas Cherenkov25 @ EMCal

R&D Items


Develop 1 detector unit and make 26 units.① GEM foil

③ Hadron Blind detectorGas Cherenkov for electron-ID

② GEM Tracker

Ionization (Drift gap)+ Multiplication (GEM)

High rate capability + 2D strip readout

CsI + GEMphoto-cathode

50cm gas(CF4) radiator~ 32 p.e. expectedCF4 also for multiplication in GEM

GEM foils

• Dry etching method is developed in Japan.– Hole shape is improved and

cylindrical hole GEM has better Gain stability.

– Thicker GEM foils is generated.


wet etching dry etching

Hole shape

A hole with cylindrical

shape

A hole with double-conical

shape

WetDry

10

100

1000

10000

250 275 300 325 350 375 400

Gai

n

Δ Vgem/ 2 (100μ ) ・Δ Vgem （50μ ）[V]

100μ ｍ(single)

50μ ｍ(triple)

100mm1 foil

50mm3 foils

Applied Voltage per 50 mm [V] 300 350

102

103

Thicker GEM foil

Stability of GEM gain

GEM Tracker


Gas: Ar/CO2

2D readout: kapton t=25mm(Cu: t=4mm both side) 290 mm

Test @ KEK

σ~105μm

Residual [mm]

HBD: in the beginning…


1~2 photo electronsToo small…

dE/dx (Blind ON)

dE/dx + Light (Blind OFF)

Compare Measured Charge w/wo Cherenkov light blind

Charge [A.U.]

This part of evaporated CsI looks gone!!Low Q.E.?

Exp 2: stopped w meson


g g

gp

w p0

n

p-A + N+X

p0g

2ppm

To generate stopped modified w meson, beam momentum is ~ 1.8 GeV/c. (K1.8 can be used.)As a result of KEK-E325,9% mass decreasing (70 MeV/c2) can be expected.

Focus on forward 　 (~2°).

Generate w meson using p beam.Emitted neutron is detected at 0.Decay of w meson is detected.

If p momentum is chosen carefully, momentum transfer will be ~ 0.

w m

om

entu

m [

GeV

/c]

0.2

0.4

0 2 4p momentum [GeV/c]

0


Experimental setupp-p wn @ 1.8 GeV/c

p0 g gg

Target: Carbon 6cmSmall radiation lossClear calculation of w bound state Ca, Nb, LH2 are under consideration.

Neutron DetectorFlight length 7m60cm x 60 cm (~2°)Gamma DetectorAssume T-violation’s 75% of 4pSKS for charge sweep

Beam Neutron

Gamma Detector

Detectors


Timing resolutionTiming resolution of 80 ps is achieved (for charged particle).It corresponds to mass resolution of 22 MeV/c2.

Neutron EfficiencyIron plate (1cm t) is placed.Efficiency is evaluated using a hadron transport code, FLUKA.Neutron efficiency of 25% can be achieved.

Neutron Detector EM calorimeter

CsI EMCalorimeterExisting detector + upgrade

（ D.V. Dementyev et al., Nucl. Instrum. Meth. A440(2000), 151 ）

912

mass resolution of 18 MeV/c2 can be achieved.

Expected results


H. Nagahiro et al, Calculation for 12C(p-, n)11Bw

Final spectrum is evaluated based on a theoretical calculation and simulation results.

Expected Invariant mass spectrum

Stopped w is selected by forward neutron

Generation of w is based on the above theoretical calculation.

Detector resolution is taken into account.

Yield estimation is based on 100 shifts using 107 beam.

Estimated width in nucleus is taken into account.

“Mass” correlation?


Neutron energy spectrum

Interact w. nuclei andMass modification

No interactNo mass mod.

Smearing

Correlation to invariant mass reconstructed by p0g (Mass @ decay)

Expected Missing mass spectrum(Mass @ generation)

Non-correlation? Same mass?

Summary• According to the theory, Hadron mass is

generated as a results of spontaneous breaking of chiral symmetry.

• Many experimental efforts are underway to investigate this mechanism. Some results are already reported.– Next, we need to extract QCD information.

• New experiments for obtaining further physics information are proposed.– Explore large kinematics region– Measurements with stopped mesons


experimental study of hadron mass k. ozawa (university of tokyo) (university of tokyo) contents:...

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