Lead-Glass Electromagnetic Calorimeters for di-lepton measurement

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1 Lead-Glass Electromagnetic Calorimeters for di-lepton measurement Megumi Naruki (Kyoto workshop 2015/3/10 1

2 Hadron Mass Heavy Ion Collision vs Cold Nuclear Matter Relativistic Heavy Ion Collisions T c ~ 170 MeV RHIC SPS large modification complicate space-time evolution Critical point Hadron Gas KEK/J-PARC/JLAB HADES Neutron Stars Baryon Density stable system rather small modification nuclei Quark Gluon Plasma Color Superconductor 2

3 Dilepton Measurement directly access to the properties of vector mesons Low Mass Range (LMR) M ee < 1.1 GeV/c 2 in-medium modification of vector mesons possible connection to CSB Heavy Ion Collision vs Low-Energy pa reaction Width cτ ρ/ω vs φ ρ MeV 1.3 fm large effect overlap ω 8.44 MeV 24 fm light quarks u, d strange charm φ 4.26 MeV 47 fm single peak 3

4 KEK-PS E325 experiment measures Invariant Mass of e + e -, K + K - in 12GeV p + A ρ,ω,φ + X reactions first dilepton measurement at the normal nuclear density Expected Invariant Mass distribution of ρ/ω ω ω ρ ρ assuming Δm/m=-16% at ρ 0 Decay in vacuum In Copper Nuclei 4

5 KEK-PS EP1-B E325 Spectrometer ppp simultaneous extraction to the east experimental hall primary proton beam up to 12GeV/c intensity ~ 10 9 ppp well focused on target 6

6 Experimental Tips Invariant Mass of e + e -, K + K - in 12GeV p + A ρ,ω,φ + X reactions background suppression small branch: Br(V ee) ~ 10-4 thin target + intense proton beam to suppress BG from γ conversion. ~0.1g/cm 2 double-stage electron identification counters simultaneous measurement of electron/kaon pairs Br(φ ee)/br(φ KK) is sensitive to mass modification thin materials in an overlapped region of ee/kk acceptances slowly moving mesons ρ/ω/φ (p lab 2GeV/c Large Acceptance Spectrometer 7

7 Detector Setup Forward LG Calorimeter Hodoscope Rear LG Calorimeter Aerogel Cherenkov Forward TOF Side LG Calorimeter Barrel Drift Chamber B Cylindrical DC Rear Gas Cherenkov Vertex Drift chamber Front Gas Cherenkov 1m 8

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9 Electron ID Counters e-π separation in the momentum range of GeV/c GC iso-butane n= FLG LG X 0 =1.7cm ΔE/E=15%/ E double-stage E-ID Counters Gas Cerenkov detectors + Lead-Glass EM Calorimeters rejection factor ~10-2 for each counter 12

10 Lead-Glass Block reused TOPAZ SF6W + PMT(R1652) Lead Glass SF6W property Radiation Length 1.7cm Density 5.2g/cm3 Critical Energy 12.6MeV Moliere Unit 2.8cm Index X rad 13

11 LG Performance purity of electron sample resolution Energy vs Momentum E/p resolution: 15%/ E efficiencies: 94% for Forward and Rear LG Calorimeters pion contamination: 2% at 94% efficiency 14

12 Invariant Mass Spectrum of e + e - the region GeV/c 2 is excluded from the fit. C w e + e - w e + e - c2/dof=163/140 (8%) Cu c2/dof=156/140 (16%) f e + e - f e + e - the excess over the known hadronic sources on the low mass side of w peak has been observed. M. Naruki et al., PRL 15

13 Invariant mass spectra of φ e + e βγ<1.25 (Slow) 1.25<βγ< <βγ (Fast) Large Nucleus Small Nucleus Rejected at 99% confidence level R. Muto et al., PRL 98(2007)

14 Model Calculation Cu Δm/m = 1-3.4%ρ 0 ΔΓ/Γ = ρ 0 Δm/m = 1 9.2%ρ 0 ΔΓ/Γ = 0 the tendency of the excess for C and Cu are well reproduced by 9.2%/3.4% mass decrease and 0/3.6 times width broadening for ρ/ω and φ, respectively. 19

15 J-PARC E16 at High-p line SM1: branched by 5 Vertical Bend K1.8BR K x3 KL K1.1BR Experimental Area at SM1 protons branch off from the primary line 30 GeV primary proton (10 /s, /s) 8 GeV primary proton for COMET secondary particles (~20 GeV/c) beam dump 20

16 E-ball Spectrometer ppp x 0.1% target = 10 7 interaction GEM Tracker electron ID : HBD + Lead Glass Calorimeter radius1.76m gap : 91cm field 8kG velocity dependence A dependence (p Pb) systematic study of mass modification

17 Expected Signal 22 momentum dependence of mass f f f f f f f f

18 E16 : development & achieved performance Hadron Blind Cherenkov Detector (HBD) Lead-Glass EM Calorimeter GEM Tracker position resolution 100 mm is achieved to keep the ~5 MeV mass resolution for the f mesons. pion suppression down to ~0.1% is achieved with the combination of the two stage of electron-id counters; HBD & LG Experiment will start in early The spectromter magnet should be reconstructed and located at the new Highmomentum beam line, which is under construction and completed in JFY 2016.

19 Lead Glass from TOPAZ / E frames were decomposed at KEK warehouse 1000 LG blocks are secured

20 Lead Glass in reality 1000 LG units from TOPAZ (secured) Geometry determined (w.r.t. magnetic fringe field) Achieved performance (with beam test ) Pion fake trigger rate (at a given threshold) 9-11% for GeV/c pi (10% required) Electron efficiency 90% at 0.4 GeV/c (better for higher momenta) Energy resolution 15% at 1 GeV (not important)

21 LG performance Online - pion suppression down to 10% w/ the trigger threshold which keeps 90% of electron efficiency at 0.4GeV/c Offline - pion suppresion down to 5% (2%) at 0.4(1.0) GeV/c w/ 90% electron efficiency

22 Summary KEK PS-E325 experiment measured e+e- pairs in 12GeV p+a reactions to investigate invariant mass of vector mesons decaying in nuclear matter. Lead-Glass calorimeters well worked for the 2 nd identification counter. Effort in studying the spectral function of vector mesons is ongoing at J-PARC. The construction of a new LG calorimeters will start this month. 27