MEG Run 2008 液体キセノンガンマ線検出器 東京大学 素粒子物理国際研究セン ター 西村 康宏、 他 MEG コラボレー ション 2008 年秋季物理学会＠山形大学小白川キャンパス

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス 2 abstract set up to measure performance –  0 beam test –detector set up estimate resolution –data set in 2008 –energy resolution –timing resolution –position resolution

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス 3 How to estimate  detector performance resolution of timing, position, energy for all acceptance. around    e +  signal region, that is 52.8MeV!! (98.8%) ~60% ~40% 2.9MeV + 0.4MeV n:8.9MeV,  :129.4MeV ~ 82.95MeV n  00 --   p 54.9MeV  available from  - beam  - and  + beam line are almost the same setup PSI 590MeV Proton Cyclotron  liq. Xenon detector target    (1MHz) area map

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス 4  0 run 2  energy distribution depends on opening angle We need targets contained proton and tag counter opposite Liquid Xenon detector liquid Xenon detector 9x24 PMTs in inner face removable liquid H2 target L = 75mm  = 50mm  < 6.5 o -- 0.07% / crystal  < 6 o NaI(Tl) x 9bars 62.5x62.5x305mm from the same beam line as  +    ~ 9% Xe energy [MeV] NaI energy [MeV] opening angle Xe energy [GeV] back to back

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス 5 detector and target for  0 run Hydrogen target –hydrogen is kept liquid by a liquid helium flow –a thin 135 um mylar window –keep ~20K 60 o NaI detector –the same acceptance as liquid xenon detector by moving stage –3x3 APDs are used for each crystal to avoid the influence of strange magnetic field –monitor and control temperature to stabilize gain of APD movable tag counter 60 o 120 o plastic counter –timing calibration of liquid xenon detector –2 plastic scintillator by 2PMTs in front of centre NaI –Lead converter with 5mm thickness

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス 6 data taken in 2008 We had  0 runs in 2007, but limited region of acceptance. –~ 1/12 of inner surface First attempt to scan all inner face in Aug –We can estimate entire performance of liquid xenon detector. in 2008 (3x8) = 24 set, 24 different position of NaI 300k (or 200k) events per 1 set ~ 6hours LED, alpha. cosmic ray run ~ 3hours / day monitoring gain, Q.E. everyday inner face of liquid xenon detector

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス 7 estimation of energy resolution the number of photons is regarded as energy here: –used Q.E. by alpha source and simulation –used gain by LED –weighted by active area of PMT. scan by a selected region –discarded shallow depth use events of depth > 2cm –by each 1PMT window on inner face 6.2cm x 6.2cm mesh x (9x24) cuts the same window as each PMT energy (a.u.) estimate resolution by fitting function: –exponential for lower peak and gaussian for upper peak parameterized resolution: –upper sigma and FWHM

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス 8 calibration of energy scale investigate energy scale for all over acceptance monitoring energy scale for a long time –17.6MeV  from LiF target to monitor scale, light yield, etc. triggered by all acceptance of detector at the same run –in pi0 runs, taken the limited region at the same time : scanning by 3x3 pmts set to monitor stability frequency ~ 1 series data taken / a few days –different beam line enables the frequent monitor the change of energy scale can be corrected –results in pi0 run should be always useful for a long term Cockcroft Walton accelerator proton Xenon detector 10 6  (isotropic) at Ep = 440keV,  =14 keV,  peak = 5 mb energy (A.U.) 17.6MeV peak

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス MeV peak by position –54.9MeV from  0 decay –17.6MeV form LiF the similar dependence by position between 17.6MeV and 54.9MeV gamma ray, calibrate energy scale by each point. normalized energy scale by horizontal normalized energy scale by vertical very preliminary 2008 Cockcroft Walton 00 very preliminary

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス MeV energy resolution by position energy resolution by position after energy scale correction resolution very preliminary

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス 11 distribution of energy resolution energy resolution –calculated by 9x24 mesh –  upper average : 2.4% –FWHM average : 6.6%  upper (%) FWHM (%) except for edge

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス 12 timing reconstruction reference counter opposite of liquid xenon detector: 7.2mm thickness plastic scintillator with 2PMTs x 2 and 5mm Lead converter in front of NaI reference time : Tref = Ttc –Tg1 + Tg2 reconstructed timing using 2  dT pmt + T offset = (T pmt – T propagation – T timewalk ) - Tref subtracted time of light propagation in liquid xenon, offset related to electronics. time walk is estimated by chi square fitting. sigma of dT pmt contains the time spread due to  0 spread in target and also that of Tref  - beam spread –  xy ~ 8mm Ttc Tg1 Tg2 1/sqrt(Np.e.) dT pmt + T offset [ns] dT pmt (  ) [ns] 69ps 

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス 13 time resolution timing resolution by position and depth. timing resolution : 131ps (in  = 160ps - 69ps - 60ps –70ps in plastic counter in front of NaI detector –60ps spread in pion target resolution horizontal [cm] vertical [cm] depth [cm] 160ps

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス 14 Pb collimator for position reconstruction used  from  0 decay but not tagged by NaI Lead collimator of 1.8cm thickness with 1cm width vertical, or horizontal slits, 2x3 PMT size 1.1M events, no tagged by NaI in trigger horizontal vertical horizontal PMT vertical How to reconstruct 1 st conversion point –use light distribution in inner face point : peak position depth : width of light

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス 15 some results results of horizontal slits reconstructed position : actual position < ~ 0.1 ~ 0.2cm difference Edge : resolution = 0.51, 0.52 [cm] Slit : sigma = 0.72, 0.74, 0.80  resolution : 0.63, 0.65, 0.72 [cm] (after considered slit width) projection vertical [cm] horizontal [cm] vertical [cm]

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス 16 summary estimated resolution of liquid xenon detector –position resolution 0.5cm sigma –timing resolution 131ps sigma –energy resolution 2.4%  upper, 6.6%FWHM these results are very preliminary! –some efficient correction remain and will improve. depth correction pile up rejection etc...

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス 17

2008 / 9 / 20 日本物理学会 2008 年秋季大会＠山形大学小白川キャンパス 18 correction by opening angle not correct or correct energy scale by opening angle % % resolutions of all PMTs (inner face) opening angle by PMT windows in 3x3 PMTs reconstructed energy [MeV] by opening angle this is not a final result, but effect from trigger can be removed. in 3x3 PMTs on LXe NaI is opposite here Energy scale differs about ~1%