lead-glass electromagnetic calorimeters for di-lepton … · 2015. 3. 10. · j-parc e16 at high-p...
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Lead-Glass Electromagnetic Calorimeters for di-lepton measurement
Megumi Naruki (Kyoto Univ.) @ELPH workshop 2015/3/10
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Relativistic Heavy Ion Collisions
Baryon Density nuclei
Color Superconductor
Critical point
Quark Gluon Plasma
Hadron Gas
Neutron Stars
T c ~
170
MeV
RHIC
SP
S
KEK/J-PARC/JLAB HADES
large modification complicate space-time evolution
stable system rather small modification
Hadron Mass Heavy Ion Collision vs Cold Nuclear Matter
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Dilepton Measurement
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Width cτ ρ/ω vs φ
ρ 149.2 MeV 1.3 fm large effect overlap
ω 8.44 MeV 24 fm
φ 4.26 MeV 47 fm single peak light quarksu, d
strange charm
Low Mass Range (LMR) Mee< 1.1 GeV/c2
in-medium modification of vector mesons possible connection to CSB Heavy Ion Collision vs Low-Energy pA reaction
directly access to the properties of vector mesons
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KEK-PS E325 experiment measures Invariant Mass of e+e-, K+K-
in 12GeV p + A → ρ,ω,φ + X reactions
Expected Invariant Mass distribution of ρ/ω
Decay in vacuum In Copper Nuclei
ω
ρ
assuming Δm/m=-16% at ρ0
first dilepton measurement at the normal nuclear density
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ω
ρ
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KEK-PS EP1-B
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• simultaneous extraction to the east experimental hall • primary proton beam up to 12GeV/c • intensity ~ 109 ppp
• well focused on target
E325 Spectrometer
‘97-2002
1012 ppp
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Experimental Tips Invariant Mass of e+e-, K+K-
in 12GeV p + A → ρ,ω,φ + X reactions
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background suppression small branch: Br(Vàee) ~ 10-4
à thin target + intense proton beam to suppress BG from γ conversion. ~0.1g/cm2
double-stage electron identification counters
simultaneous measurement of electron/kaon pairs Br(φàee)/Br(φàKK) is sensitive to mass modification à
thin materials in an overlapped region of ee/KK acceptances
slowly moving mesons ρ/ω/φ (plab~2GeV/c) Large Acceptance Spectrometer
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Forward LG Calorimeter
Rear LG Calorimeter
Side LG Calorimeter
Hodoscope
Aerogel Cherenkov
Forward TOF
Front Gas Cherenkov
Rear Gas Cherenkov
Barrel Drift Chamber
Cylindrical DC
Vertex Drift chamber 1m
B
Detector Setup
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Electron ID Counters
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e-π separation in the momentum range of 0.4 – 2.7 GeV/c
GC iso-butane n=1.00127
LG X0=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
FLG
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Lead-Glass Block reused TOPAZ’ SF6W + PMT(R1652)
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Lead Glass SF6W property
Radiation Length 1.7cm
Density 5.2g/cm3
Critical Energy 12.6MeV
Moliere Unit 2.8cm
Index 1.8
7.4
X rad
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LG Performance
resolution: 15%/√E efficiencies: 94% for Forward and Rear LG Calorimeters pion contamination: 2% at 94% efficiency
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purity of electron sample
Energy vs Momentum E/p
resolution
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Invariant Mass Spectrum of e+e-
C Cu
the excess over the known hadronic sources on the low mass side of w peak has been observed.
f àe+e- f àe+e-
wàe+e- wàe+e-
the region 0.60-0.76GeV/c2 is excluded from the fit.
c2/dof=163/140 (8%)
c2/dof=156/140 (16%)
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M. Naruki et al., PRL
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Invariant mass spectra of φà e+e−
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βγ<1.25 (Slow) 1.25<βγ<1.75 1.75<βγ (Fast)
Larg
e N
ucle
us
Smal
l Nuc
leus
Rejected at 99% confidence level R. Muto et al., PRL 98(2007)042501
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Model Calculation
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.
Cu
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Δm/m = 1 - 3.4%ρ0 ΔΓ/Γ = 1 + 2.6ρ0
Δm/m = 1 – 9.2%ρ0 ΔΓ/Γ = 0
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J-PARC E16 at High-p line
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SM1: branched by 5°
3.9° 5.8°x3
beam dump Experimental Area
Vertical Bend
K1.8
K1.8BR
K1.1BR
KL
at SM1 protons branch off from the primary line ・30 GeV primary proton (1010/s, 1012/s) ・8 GeV primary proton for COMET ・secondary particles (~20 GeV/c)
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E-ball Spectrometer
radius1.76m gap : 91cm field 8kG
velocity dependence A dependence (p à Pb) àsystematic study of mass modification
1010 ppp x 0.1% target = 107 interaction GEM Tracker electron ID : HBD + Lead Glass Calorimeter
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Expected Signal 22
f f
f f f
f f
f
momentum dependence of mass
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E16 : development & achieved performance
Hadron Blind Cherenkov Detector (HBD)
Lead-Glass EM Calorimeter position resolution 100 mm is achieved to keep the ~5 MeV mass resolution for the f mesons.
GEM Tracker
The spectromter magnet should be re-constructed and located at the new High-momentum beam line, which is under construction and completed in JFY 2016.
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 2017.
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Lead Glass from TOPAZ / E362
17 frames were decomposed at KEK warehouse 1000 LG blocks are secured
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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 0.4-4.0 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)
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LG performance l Online
- pion suppression down to 10% w/ the trigger threshold which keeps 90% of electron efficiency at 0.4GeV/c
l Offline - pion suppresion down to 5%
(2%) at 0.4(1.0) GeV/c w/ 90% electron efficiency
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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 2nd 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.
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