Download - Experimental study of hadron mass
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
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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
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Figure by Prof. I. Tserruya
Naïve Theory
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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 VacuumWhen T and r is going down,
p as a Nambu-Goldstone boson.
Experimental approach?
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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
r (JP = 1-)
a1 (JP = 1+)1250
770
r/T
DmDm = 0
Degenerate
Observable?
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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
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P. Muehlich et al. , Nucl. Phys. A 780 (2006) 187
w- meson
As the first step, measurements in hot/dense matter are compared with predicted mass spectra.
CURRENT EXPERIMENTS
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Generate hot/dense media
heavy ion reactions:A+AV+X
mV(r>>r0;T>>0)
SPS
LHC
RHIC
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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
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D. Miskowiec, QM05 talk
Existing of Mass modification is established.
PLB663, 43 (2008)
NA60 Results @ SPS
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PRL 96, 162302 (2006)
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[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
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Results @ RHIC
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• 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!
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signal electron
Cherenkov blobs
partner positronneeded for rejection
e+
e-
qpair opening
angle
~ 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, p V+XmV(r=r0;T=0)
, p. p - beams
J-PARCCLAS
At Nuclear Density
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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:
• 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
TAPS, w p0 with +A
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E325 @ KEK-PS12 GeV proton induced.
p+A f + XElectrons from f decays are detected.
TargetCarbon, Cupper0.5% rad length
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KEK E325
E325 Spectrometer
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Mass spectra measurements
mr = m0 (1 - r/r0) 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
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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 - r/r0) for = 0.02 ± 0.02
No peak shift of r Only broadening is observed
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 effectsNote:
• similar momentum range• E325 can go lower slightly
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We need to have a new experiment to investigate the problem.
CLASKEK
R.S. Hayano and T. Hatsuda, Ann. Rev.
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Results: f e+e-
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.
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First measurement of f meson mass spectral modification in QCD matter.
R. Muto et al., PRL 98(2007) 042581
Excess!!
b<1.25 (Slow) 1.25<b<1.75 1.75<b (Fast)
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Mass modification is seen only at heavy nuclei and slowly moving f Mass Shift:
mf = m0 (1 - r/r0) for = 0.0321
Target/Momentum dep.
NEW EXPERIMENT@ J-PARC
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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.
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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
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Hadron Hall
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Hadron HallNP-HALL
56m(L)×60m(W)
Upgrade of E325Large statistics
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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
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What can be achieved?
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Pb
fModified f
[GeV/c2]
f from Proton
Invariant mass in medium
ff
fff
ff
f
p dep.
High resolution
Dispersion relation
Detector components
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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
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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.2010/5/24 Weizmann seminar, K. Ozawa 30
wet etching dry etching
Hole shape
A hole with cylindrical
shape
A hole with double-conical
shape
WetDry
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Gain
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
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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…
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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
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p
w p0
n
p-A w + N+X
p0
2ppm pw
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
omen
tum
[GeV
/c]
0.2
0.4
0 2 4p momentum [GeV/c]
0
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Experimental setupp-p wn @ 1.8 GeV/c
p0
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
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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 calorimeterCsI EMCalorimeter
Existing 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
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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?
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Neutron energy spectrum
Interact w. nuclei andMass modification
No interactNo mass mod. Smearing
Correlation to invariant mass reconstructed by p0 (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
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