Setup for hypernuclear gamma-ray spectroscopy at J-PARC

Gecoolingsystem

target

Setup for hypernuclear gamma-ray spectroscopy at Setup for hypernuclear gamma-ray spectroscopy at J-PARCJ-PARC

K.Shirotori Tohoku Univ. Japanfor the Hyperball-J collaboration

J-PARC E13 hypernuclear J-PARC E13 hypernuclear -ray -ray spectroscopy experimentspectroscopy experiment

Missing mass analysis : Magnetic spectrometerMissing mass analysis : Magnetic spectrometer(identification of hypernuclear bound states )(identification of hypernuclear bound states )

Beam K-Scattered -

-ray measurement by Ge detector array

rays from hypernuclei : rays from hypernuclei : Particle-Particle- coincidence coincidence

((++, K, K+ + ) @ KEK, (K) @ KEK, (K--, , --) @ BNL) @ BNLMagnetic spectrometers + HyperballMagnetic spectrometers + Hyperball UpgradeUpgrade

Hyperball-J

Missing mass analysisMissing mass analysis -ray measurement-ray measurement

(K(K--, , - - ) reaction @ J-PARC) reaction @ J-PARCOptimized magnetic spectrometer + Hyperball-JOptimized magnetic spectrometer + Hyperball-J

SksMinSksMinusus

HyperbalHyperball-Jl-J

To analyze To analyze 1.4 GeV/c1.4 GeV/c (1.1~1.8 GeV/c) scattered (1.1~1.8 GeV/c) scattered --

Large acceptance Large acceptance ~100 msr~100 msr, , 20 degree 20 degree → → Efficient tagging of hypernuclei and angular Efficient tagging of hypernuclei and angular selectivityselectivity Good momentum resolution Good momentum resolution 224 MeV/c (FWHM)4 MeV/c (FWHM)→ → Identification of bound states of hypernucleiIdentification of bound states of hypernuclei (mass resolution ~5 MeV (FWHM) )(mass resolution ~5 MeV (FWHM) )

Modified SKS (Modified SKS (SSuperconducting uperconducting KKaon aon SSpectrometer)pectrometer)

(K(K--, , - - ) reaction @ p) reaction @ pKK = 1.5 GeV/c = 1.5 GeV/c

SDC1~4 : Momentum analysisSDC1~4 : Momentum analysis

STOF : Time-of-flight STOF : Time-of-flight

SAC : SAC : -- identification identification

SFV : KSFV : K-- beam veto beam vetoBeam decay background VetoBeam decay background Veto

SMF : SMF : -- from K from K- - → → - - + + SP0 : SP0 : -- from K from K- - → → - - + + 00

_

Target ~20 g/cm2

1 m

2.2TPrevious condition

SksMinus

Beam K- decay products make serious background ⇒ Same kinematical region to (K-, -) reaction

K-→--+ (5.58%)K-→e-0 (4.87%)K-→-0 (3.27%)K-→-00 (1.73%)

Contribution of three-body Contribution of three-body decay is relatively small.decay is relatively small.

Simulated performanceSimulated performanceAcceptance, Momentum resolution and Particle IDAcceptance, Momentum resolution and Particle ID

Acceptance at 1.4 GeV/c, Acceptance at 1.4 GeV/c, ~130 msr~130 msr Enough angular acceptance,Enough angular acceptance, ~~20 degree20 degree Momentum resolution at 1.4 GeV/c Momentum resolution at 1.4 GeV/c ~2.1 MeV/c (FWHM)~2.1 MeV/c (FWHM)

Rejection of KRejection of K-- beam through background beam through backgroundSAC ~98% + SFVSAC ~98% + SFV

Reaction ID by BAC and SAC (n=1.03) Reaction ID by BAC and SAC (n=1.03) @ trigger@ trigger STOF : Time resolution ~150 ps (rms)STOF : Time resolution ~150 ps (rms)

Large drift chambersOptimized incident beam angle

Beam decay background veto countersBeam decay background veto counters

KK- - → → -- (63.4%) (63.4%)

Muon FilterMuon Filter

_

- (passing through)- (absorbed in the iron)

Sufficient performance to reduce the trigger rate and backgroundSufficient performance to reduce the trigger rate and background

KK- - → → - - 00 (21.1%) (21.1%)

PiZero VetoPiZero Veto

_

_

Wall configuration and simulated efficiencyWall configuration and simulated efficiency

Mechanical cooling by Pulse tubeMechanical cooling by Pulse tubePWO background suppressionPWO background suppressionWaveform readout for pulse shape Waveform readout for pulse shape analysisanalysis

~6%~6% photo peak efficiency @ 1 MeV photo peak efficiency @ 1 MeV

(half picture)

Mechanical coolerMechanical cooler⇒⇒Suppression of the neutron damage effect with Ge crystal below Suppression of the neutron damage effect with Ge crystal below 8585 K K(LN2 cooling ~90 K)(LN2 cooling ~90 K)

~2 keV (FWHM) energy resolution and cooling ~2 keV (FWHM) energy resolution and cooling power of less than 85 K are achieved.power of less than 85 K are achieved.

GeGeCoolerCooler

Pulse Tube refrigeratorPulse Tube refrigerator

PWOPWOCsICsI

PMTPMT

Doped PWO crystalDoped PWO crystalCooling of PWO below 0℃Cooling of PWO below 0℃

W-type

U-type

L-type

-type

The performance of background suppression of the The performance of background suppression of the PWO counter by cooling below 0 is the same as ℃PWO counter by cooling below 0 is the same as ℃of BGO counter.of BGO counter.

But, small light yields (PWO/BGO = 1 /10)But, small light yields (PWO/BGO = 1 /10)

The PWO crystal has very first decay The PWO crystal has very first decay constant ~6 ns. (~300 ns for BGO)constant ~6 ns. (~300 ns for BGO)

To improve energy resolution and recover To improve energy resolution and recover rejected events at high counting ratesrejected events at high counting ratesBaseline shift restorationBaseline shift restorationPileup signals separationPileup signals separation

Pulse height ADCPulse height ADC ⇒ ⇒ FADCFADC (wave form digitization) (wave form digitization)

(after shaping)(after shaping)

In the test experiment, the positron beam is irradiated to In the test experiment, the positron beam is irradiated to Ge detector to make frequent baseline shits by reset Ge detector to make frequent baseline shits by reset signal.signal.⇒⇒The restoration of the baseline shitsThe restoration of the baseline shits

3.7 keV⇒3.7 keV⇒ 3.1 keV (FWHM) 3.1 keV (FWHM) 2.6 keV w/o beam2.6 keV w/o beam

No baseline restorationNo baseline restorationBaseline restorationBaseline restoration

New Ge detectorNew Ge detector

Cooling powerGe crystal temperature less than 85K when biasedLow mechanical vibrationMinimization of microphonics noiseCompact sizeRealization of the planar arrangement of Ge detectors

Hyperball-J Hyperball-J ∞∞-type element-type element

PWO counter and Waveform readout for high counting ratesPWO counter and Waveform readout for high counting rates

SummaryJ-PARC E13 experiment by the (KJ-PARC E13 experiment by the (K--, , --) reaction @ p) reaction @ pKK =1.5 GeV/c =1.5 GeV/c

•Optimal magnetic spectrometerOptimal magnetic spectrometer•New Hyperball system for the high counting rateNew Hyperball system for the high counting rate

Magnetic spectrometer, Magnetic spectrometer, SksMinusSksMinus and newly constructed array, and newly constructed array, Hyperball-JHyperball-JSksMinus performance : More than 100 msr acceptance, 20 degree coverage, ~2 SksMinus performance : More than 100 msr acceptance, 20 degree coverage, ~2 MeV/c momentum resolutionMeV/c momentum resolutionHyperball-J : ~6 % efficiency, Mechanical cooling system, PWO counter, Waveform Hyperball-J : ~6 % efficiency, Mechanical cooling system, PWO counter, Waveform readoutreadout

The experiment will be performed at 2009.The experiment will be performed at 2009.

PWO counter typesPWO counter types

6060Co 1.3 MeV Co 1.3 MeV -ray spectrum-ray spectrum

Several light hypernuclear -ray spectroscopy experiments are planned.

(4He, 7

Li, 10B, 11

B, 19F )

SKS for 1.05 GeV/c (SKS for 1.05 GeV/c (++, K, K++) ) reaction (preaction (pKK = 0.72 GeV/c) = 0.72 GeV/c)

2.7T

Beam K

BAC SACTarget20cm

Decay

Overlap

86%86% of of events detected events detected14 % non-rejected (stopped in 14 % non-rejected (stopped in the iron) by offline analysis the iron) by offline analysis Totally Totally > 99.9 %> 99.9 % Over kill for true π Over kill for true π ~2.5%~2.5%

80%80% of of --00 events detected events detected10 sets10 sets of 3 mm lead plate of 3 mm lead plate and 8 mm scintillation and 8 mm scintillation counter layercounter layer at 1.5 GeV/c at 1.5 GeV/c beam.beam.

SAC

Beam veto (SFV)

BAC

Muon Filter

Neutron damageNeutron damageHigh counting rateHigh counting rate

10 cm10 cm13 cm13 cm

Ge energy spectrumGe energy spectrum1 MeV 1 MeV ray ray

J-PARC