Experimental study of vector mesons in nuclear medium at J-PARC

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1 Experimental study of vector mesons in nuclear medium at J-PARC K. Aoki KEK / J-PARC New Perspectives on Photons and Dileptons in Ultra Relativistic Heavy-Ion Collisions at RHIC and LHC

2 CONTENTS Motivation Probe: Vector meson e + e - decay Results of KEK E325 experiment J-PARC E16 experiment. The experimental setup Beam line status Status of detector construction. 2

3 Physics motivation Study on the origin of hadron mass. Spontaneous breaking of the chiral symmetry of QCD vacuum. Relevant parameters: chiral condensates <`qq> 0, <(`qq)^2> 0, spontaneous chiral sym. Breaking. They depend on temperature and density. Broken symmetry is expected to be (partially) restored, even at norm. nucl. Density. Measure spectral change of vector meson in nucl. medium. Vacuum Normal nuclear density Density 3

Probe: Vector meson e + e - invariant mass Example: p + A f + X Proton beam Proton beam Nucleus f Nucleus f e - e + e - Decays in vacuum Without modification. e + Decays in nuclei.

4 Probe: Vector meson e + e - invariant mass Example: p + A f + X Proton beam Proton beam Nucleus f Nucleus f e - e + e - Decays in vacuum Without modification. e + Decays in nuclei. With mass modified. + = Mass Mass Mass Lepton pair in the final state. small final state interaction. Well-known Inv. mass In vacuum + Modified mass In nuclei. = Observed invariant mass. 4

Heavy ion collisions High temperature arxiv:1509.04667 (2015) PHENIX CERES/NA45 NA60 (dimuon) STAR Phys. Lett.

5 Heavy ion collisions High temperature arxiv: (2015) PHENIX CERES/NA45 NA60 (dimuon) STAR Phys. Lett. B 666,425(2008) PRL 96, (2006) They observe excess in low mass region. Explained by rho broadening scenario. 5

6 At around normal nuclear density. CLAS g7 results of ρ meson. g + A r X (up to 3.8 GeV) Conclusion on ρ meson No mass shift. ρ ω g+ 2 H g+ 12 C φ Phys. Rev. C78, (2008) ρ ω φ Broadening, consistent with expectation from collisional broadening. f meson. Low stat. ρ ω g+ 56 Fe g+ 48 Tl φ BG subtracted (event mix-technique) 6

KEK E325 results of ρ and ω mesons At around norm. nucl. density. p + A rwf X (12 GeV) Linear dependence of mass on density is assumed. m (ρ) m(vac) = 1 k( ρ ρ 0 ) ρ 0 : Normal nucl.

7 KEK E325 results of ρ and ω mesons At around norm. nucl. density. p + A rwf X (12 GeV) Linear dependence of mass on density is assumed. m (ρ) m(vac) = 1 k( ρ ρ 0 ) ρ 0 : Normal nucl. Density m(ρ): mass at density ρ k : param. to be determined. k = 0.092±0.002 obtained. 9% mass reduction in norm. nucl. density Fit without modification unsuccessful Fit with r,w modification successful p + 64 Cu r?? r w w f 7

8 KEK-E325 results of f meson The world s first results of f modification. Nuclear target C, Cu e + f 12GeV (10 9 /spill) Proton beam e - bg < 1.25 f meson Conclusion: Mass decreases in nuclei!! KEK-E325 results Blue line represents mass distribution without mass modification. Under the assumption of linear bg = p/m of f dependence of mass and width on density. Mass: % Width: x p + 64 Cu At normal nuclear density Red: 64 Cu target Blue: 12 C target 8

9 What shall we do next? There exists modification in e+e- mass spectrum. The origin is not clear. We decided to pursue this problem using The same reaction as KEK-E325 (p+a f X) with high stat x 100. with better resolution. s= 5 MeV for f J-PARC E16 p + A f + X, f e+e- 9

Separated peak. Narrow (3.4 MeV) Lower stat.

10 J-PARC E16 compared to other methods. J-PARC E16 p + A f + X, f e+e- e+e- decay Small final state interactions Small branching ratio f meson Separated peak. Narrow (3.4 MeV) Lower stat. Other experiments Hadronic decay (π+π-, π 0 g,,) Suffer from final state interactions Large branching ratio. These disadvantages are overcome by collecting high statistics r/w mesons Overlapping peaks. Wide (r 150MeV) higher stat. r 10 w

11 J-PARC E16 = 100 x KEK-E325 Systematic study is possible. bg (=p/m) dependence. Target size dependence KEK Target A Radius (A^(1/3)) p 1 1 C Cu 64 4 Pb J-PARC 11

12 J-PARC E16 = 100 x KEK-E325 Dispersion relation can be obtained. Dispersion relation for r mesons S.H. Lee Phys.Rev.C57,927(2007) Kondratyuk, et al. PhysRev C58,1078( 98) Post, Mosel Nucl.Phys. A699,169( 02) Calc by S.H. Lee Phys.Rev.C57,927(2007) Was extrapolated to 3GeV/c 12

13 Double peak, not a tail. Distinct peak, not tail. Mass modification unambiguously shown. bg < 1.25 s = 10MeV Slower f meson x 2 better resolution. bg < 0.5 s = 5MeV Target A ~r 3 ~r p 1 1 C Cu 64 4 Pb

14 f KEK J-PARC E16 = 100 x KEK-E325 J-PARC Calc by S.H. Lee was extrapolated to 3GeV/c These three information can give further insights on this matter, thanks to High statistics in f, No peak near f. Without complicated overlap. 14 Qualitatively new information can be obtained.

15 J-PARC E16 Collaboration RIKEN KEK S. Yokkaichi (spokesperson) H. En yo F. Sakuma K. Aoki Y. Morino R. Muto K. Ozawa S. Sawada M. Sekimoto RCNP T.N. Takahashi Hiroshima Univ. K. Shigaki Univ. of Tokyo K. Kanno Y. Komatsu S. Masumoto H. Murakami W. Nakai Y. Obara T. Shibukawa Kyoto Univ. M. Naruki CNS (Univ. of Tokyo) Osaka Univ. H. Hamagaki Y.S. Watanabe JASRI A. Kiyomichi Univ. Tsukuba T. Chujo Esumi JAEA BNL T. Chujo S. Esumi T. Sakaguchi R. Honda 15

16 J-PARC (Proton Accelerator Research Complex) Linac 400MeV Neutrino beams to Super K (T2K) RCS 3GeV Borrowed from Tadashi Koseki s slide 16

Beam Line at J-PARC Hadron Hall 30GeV proton --- 24 kw (3x10 13

17 Beam Line at J-PARC Hadron Hall 30GeV proton kw (3x10 13 ppp) as of Switch Yard Hadron Hall Proton beam (30GeV) LINE-A T1 target K1.8BR K1.8 K 0 E16 spectrometer ~10 10 ppp is stealed from LINE-A To LINE-A To LINE-B 1.1T x 3.6 m 1.1T x 1.4 m 1.6T x 2.2 m 17

18 Beam view Lambertson Magnet 3.6m long In beam direction Coil Field Hole ( to high-p beam line) Field free hole ( to line-a) coil 18

19 To LINE-A To LINE-B Magnetic Septums Magnetic Septum 2 Coil (dipole field) Lambertson magnet and Septums are at Tsukuba. Will be transported to J-PARC 19

20 Beam Line Magnets in SY : Construction & Alignment are completed K. Ozawa, J-PARC PAC With slight modification 2014/12/04 20

21 Beamline magnets in Hadron Hall. Construction completed Alignment needs to be done. E16 Spectrometer magnet 21

(defined as) 1 5 X 5 J-Parc E16 10 10 / spill 30 GeV fyield ~2000 ~ 2

22 To achieve 100 times in statistics. Proton beam KEK- E / spill 12GeV X 10 X 2(x-sec) Acceptance (defined as) 1 5 X 5 J-Parc E / spill 30 GeV fyield ~2000 ~ 2 x 10 5 yield x 100 High rate capability ~5kHz/mm 2 Large acceptance spectrometer KEK E325 J-PARC E16 22

23 The J-PARC E16 spectrometer Magnet (used for KEK E325) A module 26 module in total. 8 modules for the 1 st physics run. X 26 23

24 100 x 100 [mm 2 ] 200 x 200 [mm 2 ] 300 x 300 [mm 2 ] 600 x 600 [mm 2 ] A module of the spectrometer e - Reuse from TRISTAN/TOPAZ GTR (trackers) 100 mm resolution 5kHz/mm2 rate capability Hadron Blind Detector (Cherenkov Detector.) Pion rejection ~ 100 PbGl Calorimeter Pion rejection ~25 HBD 24

GTR (GEM Tracker) Ionization electrons in the

25 GTR (GEM Tracker) Ionization electrons in the drift gap are collected and amplified by GEMs. Charge collected on to 2D strip readout. X: 350um pitch Sensitive to bending direction. 100 um resolution required. Y: 1400um pitch Mesh electrode Drift Gap GEM GEM GEM readout X1 X2 X3 3 mm Trigger Y1 Y2 25

26 Residual sigma [um] GTR algorithm Timing method (~100um achieved.) Distance in drift field dir. Can be obtained using flight time. COG Method (better at 0 deg) 2D fit (COG + Timing) 300 Timing method COG method 2D fit Required Incident angle [degree] 26

27 HBD (Hadron Blind Detector) Based on PHENIX HBD. CF4 serves as radiator and amplification gas Radiator 50 cm. / p.e. ~ 11 Gas Electron Multiplier (GEM) for amplification CsI is evaporated on top GEM Photocathode (> ~6eV) Trigger 300x300mm 2 GEM with CsI 27

28 HBD pions electrons Cluster size - 1 Cluster size - 1 Pion rejection factor of 100 with 80% electron efficiency achieved at beam test. Using charge threshold and cluster size. Cluster size analysis 28

29 HBD GLOVEBOX prototype CsI photocathode have to be treated in dry environment. HBD chamber (production type) 29

30 LG (Lead Glass Calorimeter) Reuse from TOPAZ ~300 at the 1 st stage. ~1000 in total We have all we need. Expected Rejection Power ~25 offline (energy dep. th.) ~10 online (fixed th.) We ve got all we need. 30

31 FM Magnet J-PARC E16 spectrometer (E16 spectrometer Mag.) Was the FM-Cyclotron at U-Tokyo. KEK E325 used it at KEK. It is in E16 configuration at J-PARC. As of Mar KEK-E325 config. As of Oct J-PARC E16 Config. 31

32 DAQ Detectors 32 FTSW: Frontend Timing Switch.

33 Purchased parts Detectors 8/8 8/8 7/8 2/8 5/8 1/1 7/8 2/8 3/8 8/8 8/8 33 FTSW: Frontend Timing Switch.

34 Pictures of Readout electronics E16 GTR preamp 256 channels. 58 x 65 mm 2 E16 HBD preamp 50mm SRS ADC Belle II FTSW Trigger/clock distributor. Belle II UT3 Trigger decision TRG-MRG 34

35 Schedule 2007 Stage 1 approval (at 2 nd J-PARC PAC) Detector R&D High-p construction budget approval 2014 TDR submitted. Production of detectors (1/3 part of detector) will be ready for data taking. Due to the budgetary condition, we start 1/3 of the full design and add the rest later f (80 shifts of physics run) High-p beam line construction will finish. Physics run 35

36 SPECTRAL FUNCTIONS? BLUE LINE: Breit-Wigner convoluted with Gauss BLUE AREA: Bremsstrahlung at target and detector materials. Red AREA: internal radiative corrections. SIMULATION In case of KEK E325 Obviously the moments of this spectra is not what theorists want. Once we know the spectral function, we can calculate how it looks in real data. However, can we do it in the opposite way? (deconvolute)? 36

37 Criticisms which KEK E325 takes Absolute normalization of mixed event. They are quite confident on that! A track primitive : GTR3 x HBD x LG PHYSICS TRIGGER: a track x a track x open angle >60deg NORMALIZATION TRIGGER: a track p+ p reference spectrum p + p reference will be taken (2 nd stage) What else? 37

38 Summary Study on the origin of hadron mass through spectral change of vector mesons in nuclear medium. Many measurements for hot/cold system. There exists some modification. Yet origin is not clear. J-PARC E16 pursue it by collecting 100 times more statistics compared to KEK-325, and obtain new clear information. Dispersion relation / double peak / system size dep. We start with 1/3 of the design configuration and physics run is anticipated in Detector R&D done. Mass production started. Beam line components have been constructed. We are working hard to make the experiment happens. 38

arxiv: v1 [nucl-ex] 3 Feb 2015

arxiv: v1 [nucl-ex] 3 Feb 2015 arxiv:1502.00703v1 [nucl-ex] 3 Feb 2015 Study of in-medium mass modification at J-PARC K. Aoki 1 for the J-PARC E16 Collaboration 1 KEK, High Energy Accelerator Research Organization, Tsukuba, Ibaraki