Experimental study of hadron mass K. Ozawa (University of Tokyo) (University of Tokyo) Contents: Physics motivation Current results Future Experiments Summary

Origin of quark mass 2010/5/24 Weizmann seminar, K. Ozawa 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 by QCD dynamical effects 2 Figure by Prof. I. Tserruya

Naïve Theory 2010/5/24 Weizmann seminar, K. Ozawa 3 High Temperature High Density Quark – antiquark pairs make a condensate and give a potential. Chiral symmetry is breaking, spontaneously. Chiral symmetry exists. Mass ~ 0 (Higgs only) Vacuum contains quark antiquark condensates. So called “QCD vacuum”. q q Vacuum When T and  is going down,  as a Nambu-Goldstone boson.

Experimental approach? 2010/5/24 Weizmann seminar, K. Ozawa 4 When chiral symmetry is restored, mass of chiral partner should be degenerated. m will decrease in finite /T matter. “QCD vacuum”, i.e. quark condensates can be changed in finite density or temperature. Then, chiral symmetry will be restored (partially). “QCD vacuum”, i.e. quark condensates can be changed in finite density or temperature. Then, chiral symmetry will be restored (partially). Vacuum   0 T  0 In finite  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. However, measurements of chiral partner is very difficult. We can measure only mass modification of narrow resonance. mass  (J P = 1 - ) a 1 (J P = 1 + )  mm m = 0 Degenerate Observable?

2010/5/24 Weizmann seminar, K. Ozawa Predicted “ spectra ” several theories and models predict spectral function of vector mesons () in hot and/or dense matter. –Lowering of in-medium mass –Broadening of resonance R. Rapp and J. Wambach, EPJA 6 (1999) 415  - 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. As the first step, measurements in hot/dense matter are compared with predicted mass spectra.

CURRENT EXPERIMENTS 2010/5/24 Weizmann seminar, K. Ozawa 6

Generate hot/dense media heavy ion reactions: A+A  V+X m V (  >>  0 ;T>>0) SPS LHC RHIC /5/24 7 Weizmann seminar, K. Ozawa Measurements of Vector Meson mass spectra in hot/dense medium will provide QCD information. Leptonic (e + e -,  +  - ) decays are suitable, since lepton doesn’t have final state interaction. Hot matter experiments

SPS-CERES results 2010/5/24 Weizmann seminar, K. Ozawa 8 D. Miskowiec, QM05 talk Existing of Mass modification is established. PLB663, 43 (2008)

NA60 SPS 9 PRL 96, (2006) 2010/5/24 9 Weizmann seminar, K. Ozawa [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 s NN =19.6 GeV

RHIC&PHENIX 2010/5/24 Weizmann seminar, K. Ozawa 10

RHIC RHIC 2010/5/24 Weizmann seminar, K. Ozawa 11 Black Line –Baseline calculations Colored lines –Several models Low mass M>0.4GeV/c 2 : –some calculations OK M<0.4GeV/c 2 : not reproduced –Mass modification –Thermal Radiation Advantages of RHIC Clear initial condition Clear Time develop calculated by Hydrodynamics Advantages of RHIC Clear initial condition Clear 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 s NN =200 GeV arXiv:

New detector! 2010/5/24 Weizmann seminar, K. Ozawa 12 signal electron Cherenkov blobs partner positron needed for rejection e+e+ e-e-  pair 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,   V+X m V (  =  0 ;T=0) , . p - beams J-PARC CLAS At Nuclear Density /5/24 13 Weizmann seminar, K. Ozawa Stable system Saturated density Experiments, CBELSA/TAPS (Japan) CLAS J-Lab Cold matter experiments

Results from CBELSA/TAPS disadvantage:  0 -rescattering advantage:  0  large branching ratio (8 %) no  -contribution (    0  : 7  )       p  A   + X  00 D. Trnka et al., PRL 94 (2005) after background subtraction TAPS,    0  with +A 2009/2/22 NQCD symposium, K. Ozawa 14 m  = m 0 (1 -   /  0 ) for  = 0.13

KEK-PS 12 GeV proton induced. p+A   + X Electrons from decays are detected. Target Carbon, Cupper 0.5% rad length 2010/5/2415 Weizmann seminar, K. Ozawa KEK E325

E325 Spectrometer 2010/5/2416 Weizmann seminar, K. Ozawa

Mass spectra measurements m  = m 0 (1 -   /  0 ) for  = /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 e+e-e+e- e+e-e+e-  /  The excess over the known hadronic sources on the low mass side of  peak has been observed. M. Naruki et al., PRL 96 (2006) KEK E325,  e + e -

CLAS J-Lab 2010/5/24 Weizmann seminar, K. Ozawa 18 Induce photons to Liquid dueterium, Carbon, Titanium and Iron targets, generate vector mesons, and detect e+e- decays with large acceptance spectrometer. m  = m 0 (1 -   /  0 ) for  = 0.02 ± 0.02 No peak shift of  Only broadening is observed   /  R. Nasseripour et al., PRL 99 (2007)

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  without nuclear matter effects Note: similar momentum range E325 can go lower slightly 2010/5/24 Weizmann seminar, K. Ozawa 19 We need to have a new experiment to investigate the problem. CLAS KEK R.S. Hayano and T. Hatsuda, Ann. Rev.

2010/5/24 Weizmann seminar, K. Ozawa Results:   e + e - Cu  <1.25 (Slow) Invariant mass spectrum for slow  mesons of Cu target shows a excess at low mass side of . Measured distribution contains both modified and un-modified mass spectra. So, modified mass spectrum is shown as a tail. 20 First measurement of  meson mass spectral modification in QCD matter. R. Muto et al., PRL 98(2007) Excess!!

 <1.25 (Slow) 1.25<  < <  (Fast) 2010/5/24 Weizmann seminar, K. Ozawa Mass modification is seen only at heavy nuclei and slowly moving  Mass Shift: m  = m 0 (1 -   /  0 ) for  = Target/Momentum dep.

NEW J-PARC 2010/5/24 Weizmann seminar, K. Ozawa 22

2010/5/24 Weizmann seminar, K. Ozawa 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:3.3x10 14 ppp, 15A (2×10 14 ppp, 9A) E Linac = 400MeV (180MeV) Beam Power: 750kW (270kW) Numbers in parentheses are ones for the Phase 1. 23

2010/5/24 Weizmann seminar, K. Ozawa 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

2010/5/24 Weizmann seminar, K. Ozawa Hadron Hall NP-HALL 56m(L)×60m(W) Upgrade of E325 Large statistics 25 Stopped  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/c 2 Good electron ID capability 2010/5/24 Weizmann seminar, K. Ozawa times higher statistics!!

What can be achieved? 2010/5/24 Weizmann seminar, K. Ozawa 27 Pb  Modified  [GeV/c 2 ]  from Proton Invariant mass in medium         p dep. High resolution Dispersion relation

Detector components 2010/5/24 Weizmann seminar, K. Ozawa 28 Tracker ~Position resolution 100μm High Rate(5kHz/mm 2 ) Small radiation length (~0.1% per 1 chamber) Electron identification Large acceptance High pion 90% e-eff. Gas Cherenkov EMCal

R&D Items 2010/5/24 Weizmann seminar, K. Ozawa 29 Develop 1 detector unit and make 26 units. ① GEM foil ③ Hadron Blind detector Gas Cherenkov for electron-ID ② GEM Tracker Ionization (Drift gap) + Multiplication (GEM) High rate capability + 2D strip readout CsI + GEM photo-cathode 50cm gas(CF 4 ) radiator ~ 32 p.e. expected CF4 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 wet etching dry dry etching Hole shape cylindrical A hole with cylindrical shape double-conical A hole with double-conical shape Wet Dry 100m 1 foil 50m 3 foils Applied Voltage per 50 m [V] Thicker GEM foil Stability of GEM gain

GEM Tracker 2010/5/2431 Weizmann seminar, K. Ozawa Gas: Ar/CO 2 2D readout: kapton t=25m (Cu: t=4m both side) 290 m KEK σ~ 105 μm Residual [mm]

HBD: in the beginning… 2010/5/24 Weizmann seminar, K. Ozawa 32 1~2 photo electrons Too 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  meson 2010/5/24 Weizmann seminar, K. Ozawa 33       n   A   + N+X  00 To generate stopped modified  meson, beam momentum is ~ 1.8 GeV/c. (K1.8 can be used.) As a result of KEK-E325, 9% mass decreasing (70 MeV/c 2 ) can be expected. Focus on forward (~2°). Generate  meson using beam. Emitted neutron is detected at 0. Decay of  meson is detected. If  momentum is chosen carefully, momentum transfer will be ~ 0.  momentum [GeV/c]  momentum [GeV/c] 0

2010/5/2434 Weizmann seminar, K. Ozawa Experimental setup  - p   1.8 GeV/c   0    Target: Carbon 6cm Small radiation loss Clear calculation of  bound state Ca, Nb, LH 2 are under consideration. Neutron Detector Flight length 7m 60cm x 60 cm (~2°) Gamma Detector Assume T-violation’s 75% of 4 SKS for charge sweep Beam Neutron Gamma Detector

Detectors 2010/5/24 Weizmann seminar, K. Ozawa 35 Timing resolution Timing resolution of 80 ps is achieved (for charged particle). It corresponds to mass resolution of 22 MeV/c 2. Neutron Efficiency Iron plate (1cm t) is placed. Efficiency is evaluated using a hadron transport code, FLUKA. Neutron efficiency of 25% can be achieved. Neutron DetectorEM calorimeter CsI EMCalorimeter Existing detector + upgrade （ D.V. Dementyev et al., Nucl. Instrum. Meth. A440(2000), 151 ） 912 mass resolution of 18 MeV/c 2 can be achieved.

Expected results 2010/5/24 Weizmann seminar, K. Ozawa 36 H. Nagahiro et al, Calculation for 12 C( , n) 11 B  Final spectrum is evaluated based on a theoretical calculation and simulation results. Expected Invariant mass spectrum Stopped  is selected by forward neutron Generation of  is based on the above theoretical calculation. Detector resolution is taken into account. Yield estimation is based on 100 shifts using 10 7 beam. Estimated width in nucleus is taken into account.

“Mass” correlation? 2010/5/24 Weizmann seminar, K. Ozawa 37 Neutron energy spectrum Interact w. nuclei and Mass modification No interact No mass mod. Smearing Correlation to invariant mass reconstructed by    decay) Expected Missing mass spectrum 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 2010/5/24 Weizmann seminar, K. Ozawa 38