The Status of Hyperball-J Akio Sasaki Dept. of Phys. Tohoku Univ. 23/9/2011

Contents Introduction Details of Hyperball-J Test of the PWO Suppressor Summary

Setup for J-PARC E13 Experiment Tag hypernuclear production Detect hypernuclear  ray Reaction-γ coincidence Fig1. K1.8 beam line at J-PARC K － ( p =1.5 GeV/c )  - ( p ~1.4 GeV/c ) 0 m 5 m Target 2.5T SKS magnet Hyperball-J K1.8 beam line beam particle ： K - （ Up to 10 MHz ）

Hyperball-J Features  Large photo-peak efficiency  ε~6.1% for 1MeV  -ray with 32 Ge detectors  Radiation-hard Ge detector  Mechanical cooling  Fast background suppressor  PWO counters Operation under high-rate beam Higher photo-peak efficiency Hyperball2  Hyperball-J Crystal temp. ： 67 K : 92 K (Liquid N 2 ) Placement of crystals 13 cm A new detector array for hypernucler γ-ray spectroscopy experiment PWO crystal (Scintillation counter) Ge crystal Pulse Tube Refrigerator Target Fig. Lower-half part of Hyperball-J   Target center Spherical Target center Plane

Background Suppressor for γ-ray Detection Anti-coincidence of Ge and PWO  We can suppress these events. Anti-coincidence of Ge and PWO  We can suppress these events. Beam Charged particle (C) High energy charged particle (B) Cascade shower caused by high energy gamma-ray Λ n π0π0  0 from  /K  decay  0  two  rays PWO counter Target Produced hypernucleus Ge detector  -ray (A) Compton scattering of gamma rays e-e-

Differences between PWO and BGO CrystalBGOPWO Effective atomic number 7576 Density[g/cm 3 ] Decay constant [ns]300~6 Light yield [NaI=100]15~1 Low efficiency for low energy γ rays of ~ 100 keV To increase light yield  Cool down (1 p.e.) Typical pulse shape for 661keV gamma ray (b) PWO New Developed (a) BGO Conventional Dead time ~ 1.5μs Dead time ~50ns Cooling power is essential Fast background suppressor # of photo-electron Doped PWO Number of photo electrons for 661-keV  ray Number of photo electrons for 661-keV  ray Temperature (  C) Increase 3%/K Crystal Temperature( ℃ )

Cooling System for PWO Crystals Cu plate for cooling PWO case with PWO crystals installedAssemble PMTs and magnetic shield. Ge1 Coolant(ethylene glycol) IN OUT Copper PMTs

Cooling Test 40 K peak(1460keV) Pedestal Single photo-electron 35.7 p.e p.e. Energy spectrum of gamma ray from 40 K Red : Coolant off (room temp. 12 ℃ ) Blue : Coolant -15 ℃ Light yield increment times Assuming PWO crystals’ light yield increasing by 3%/K. PWO crystal’s temp. corresponds to  5 ℃ when coolant is -15 ℃ ch The number of PWO crystals  ~250 Dense placement of PWO Crystals Direct measurement is difficult

Coolant Temp. no cooling 0 ℃ -15 ℃ All PWO Crystals’ Temp PWO Crystal # Crystal Temp.(Degree Celsius) Ge1 Ge PWO crystals’ temp. coolant -15 ℃ ) ~ -5 ℃ on average. Room temperature : 12 ℃ (tested in winter)  Efficiency for 100keV gamma ray ~ 90% Crystal’s temperature( ℃ ) Estimated efficiency for 100 keV  ray

Assembling Hyperball-J Units ~ 3 m Whole Frame Mount two units

Suppression Test (Using 60 Co source) ・ Ge ADC ・ PWO TDC Trigger : Ge Off-line suppression Ge Top view B-typeE-type 60 Co source PWO crystal Ge crystal 140 mm 200 mm 300 mm 130 mm

Suppression Performance (B-type Unit) Black:w/o suppression Blue : w/ suppression Ge and PWO signals coincidence  Suppress this event Analysis Energy(keV) Ge Top view B-type Ge ADC spectrum

Suppression Performance (E-type Unit) Black:w/o suppression Red : w/ suppression Ge and PWO signals coincidence  Suppress this event Analysis Energy(keV) Ge Top view E-type Ge ADC spectrum

Present Status and Schedules of Hyperball-J We have moved SKS magnet to SksMinus position (E13 configuration). K1.8 Beam line Hyperball-J Long stability test of germanium detectors. Other PWO units under assembling. Schedule June, 2012 Full Univ. Transfer to J-PARC. September, 2012 Ready for beam run.Schedule June, 2012 Full Univ. Transfer to J-PARC. September, 2012 Ready for beam run.

Summary ・ We are preparing for hypernuclear gamma-ray spectroscopy (J-PARC E13) experiment. ・ Performance test of Hyperball-J.  Test for cooling PWO crystals.  Cooling system are working well.  Suppression performance  Worked well for both B- and E-types Other types will be soon assembled and tested.

Back up

Set up (Side view) PWO crystal Ge crystal Solid angle from Ge to PWO is larger in B-type. 60Co source E-typeB-type

Schematic view around Ge crystal PWO crystal Cu plate (for cooling) Insulator Outer metal case Plastic case Ge crystal Dew condensation occurs on the surface of plastic case

Energy spectrum w/o suppression Blue : B-type Red : E-type

Compare B-type and E-type Geometry of PWO counters results in differences of suppression performance. Blue: B-type w/ suppression Red: E-type w/ suppression Normalized by the number of count around 1.33 MeV peak. GeGe GeGe GeGe GeGe GeGe GeGe GeGe GeGe Ge Top view B-typeE-type

B-type Energy(keV) (arbitary unit) Experimental result Simulation

E-type Energy(keV) (arbitary unit) Experimental result Simulation

Energy Spectrum ・実験と同じ検出器配置 ・ PWO の efficiency=1 ・線源位置から１イベントご とに 同時に２本のガンマ線を出 す (1173keV と 1333keV) Simulation Experimen t

Center of target position ~20 degree ~95 degree Theta(rad) Energy(MeV) Cross section(arbitary units) Theta(rad) Energy(MeV) Theta(rad) Compton scattering (0.1 MeV gamma ray )

Center of target position ~20 degree ~95 degree Theta(rad) Energy(MeV) Cross section(arbitary units) Compton scattering (1 MeV gamma ray )

TDC spectrum of PWO counters triggered by Ge detector. TDC Spectrum

Ge detector with mechanical cooler Pulse-tube cooler － Low mechanical vibration Energy resolution(FWHM) 3.1 MeV (LN 2 : 3.1 keV) Time resolution(FWHM) 5.8 MeV (LN 2 : 5.7 ns) Water cooling for refrigerator － enhance cooling power → Crystal temp. ： 67 K (LN 2 : 92 K) Slim and compact design － dense placement of detectors Cold head Pulse tube refrigerator Pulse-tube refrigerator Fuji electrics, Co.) (Fuji electrics, Co.) Weight : ~11 kg Cooling power : 2.5 Pulse-tube refrigerator Fuji electrics, Co.) (Fuji electrics, Co.) Weight : ~11 kg Cooling power : 2.5

Improvement of light yield Efficiency for 100-keV  ray ( Doped PWO, -25  C ) : 98 % Light yield is large enough when doped and cooled Light yield with doping and cooling Light yield with doping and cooling Pure PWO → Doped PWO ×2 Room temp. → - 25  C ×4 Doped PWO Number of photo electrons for 661-keV  ray Number of photo electrons for 661-keV  ray Temperature (  C)

Compare with suppression

Case for PWO PWO counters are mounted in cases of 4 types (B,E,C,L) with cooling system Ge detector x 2 PWO counter x 21 coolant Outer case (SUS) Inner support (Acrylic) Copper plate Insulator (Aelo-gelc) Ge detector PWO crystal Assembling all cases in progress Assembling all cases in progress PWO crystal

Differences between PWO and BGO CrystalBGOPWO Effective atomic number 7576 Density[g/cm 3 ] Decay constant [ns]300~6 Light yield [NaI=100]15~1 The lower light yield becomes a problem for low energy γ rays of ~ 100 keV. To increase light yield  Cool down (1 p.e.) Fig ： Typical pulse shape for 661keV gamma ray Short dead time Fast background suppressor (b) PWO New Developed (a) BGO Conventional Dead time ~ 1.5μs Dead time ~50ns Cooling power is essential # of photo-electron Doped PWO Number of photo electrons for 661-keV  ray Number of photo electrons for 661-keV  ray Temperature (  C) Increase 3%/K Crystal Temperature( ℃ )

Status of Hyperball-J SKS magnet Hyperball-J

3 stages for detector mount 1. inner 2. mid 3. outer beam direction 1 m Detector units is mounted to stage. Ge detector PWO case Detector geometry

Radiation hardness Radiation hardness E. Hull and R. H. Pehl et al. IUCF Ann. Rep. 143, (1993) Energy MeV of damaged Ge detector Energy MeV of damaged Ge detector Temp. with LN 2 cooling Temp. of Ge crystal (K) Energy resolution (keV) Energy peak of a Ge detector FWHM FWTM w/o damage w damage Use mechanical cooler to obtain lower temp. FWTM FWHM Low energy tail ( Asymmetric shape )

PWO crystals A total of 246 piece 204 have been acquired 4 sizes 25 x 20 x 200t (88 %) 31 x 20 x 200t (71 %) 34 x 20 x 200t (65 %) 40 x 20 x 200t (55 %) PMT Φ33 mm Wrapping scheme Teflon 0.1mm ESR film (3M) mm Black sheet 0.1 mm ■average of 6 crystals (Covered ratio?) Wrapped PWO crystals and PMT

Improvement of light yield Pure PWO Doped PWO Number of photo electrons for 661-keV  ray Number of photo electrons for 661-keV  ray Efficiency for 100-keV  ray ( Doped PWO, -25  C ) : 98 % Light yield is large enough when doped and cooled Light yield with doping and cooling Light yield with doping and cooling Pure PWO → Doped PWO ×2 Room temp. → - 25  C ×4 Temperature (  C)

Design of Hyperball-J Ge detector densely placed → Large solid angle （ 26 % ） Placement of crystals 13 cm Beam Target center Spherical Target center Plane