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

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

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

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

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

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

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

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

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

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

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

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)

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

Expected Signal 22

f f

f f f

f f

f

momentum dependence of mass

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.

Lead Glass from TOPAZ / E362

17 frames were decomposed at KEK warehouse 1000 LG blocks are secured

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)

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

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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