International Workshop on Particle Physics at Neutron Sources 2018 1 Naoki Nagakura 1 , Katsuya Hirota 2 , Sei Ieki 1 , Takashi Ino 3 , Yoshihisa Iwashita 4 , Masaaki Kitaguchi 5 , Ryunosuke Kitahara 6 , Jun Koga 7 , Kenji Mishima 3 , Aya Morishita 7 , Yusuke Nakano 2 , Hideyuki Oide 8 , Hiroki Okano 2 , Hidetoshi Otono 9 , Yoshichika Seki 10 , Daiichiro Sekiba 11 , Tatsushi Shima 12 , Hirohiko M. Shimizu 2 , Naoyuki Sumi 7 , Hirochika Sumino 13 , Kaoru Taketani 3 , Tatsuhiko Tomita 7 , Hideaki Uehara 7 , Takahito Yamada 1 , Satoru Yamashita 14 , Mami Yokohashi 4 , Tamaki Yoshioka 9 The Univ. of Tokyo 1 , Nagoya Univ. 2 , KEK 3 , ICR, Kyoto Univ. 4 , KMI, Nagoya Univ. 5 , Kyoto Univ. 6 , Kyushu Univ. 7 , CERN 8 , RCAPP, Kyushu Univ. 9 , J-PARC Center, Japan Atomic Energy Agency 10 , The Univ. of Tsukuba 11 , RCNP, Osaka Univ. 12 , GCRC, The Univ. of Tokyo 13 , ICEPP, The Univ. of Tokyo 14 Precise Neutron Lifetime Measurement Using Pulsed Neutron Beams at J-PARC
Motivation 8.4 sec (3.8σ) which predicts light element synthesis in the early universe 1. input parameter to Big Bang Nucleosynthesis (BBN) theory, neutron lifetime (τ n ) is a fundamental parameter in the weak interaction Particle Data Group 2017 879.6 ± 0.6 sec 888.0 ± 2.2 sec neutrons 2 and count the remaining store ultra-cold neutrons UCN storage method from β decay detector and detect protons inject neutrons into in-flight method we plan to measure τ n using different method with precision of 1 sec 8.4 sec (3.8σ) deviation between the result of two previous methods 2. determine V ud element in CKM matrix
J-PARC / BL05 spallation pulsed neutron beam in MLF (Materials and Life science experimental Facility) at J-PARC polarized beam branch of BL05 polarization ：~ 95% neutron flux：3.9×10 7 /sec•cm 2 (@1 MW) energy ：~ 10 meV（cold neutron） 3 facilities beamline MLF BL05 polarized beam branch neutron J-PARC bird’s eye view
Setup 4 neutron ・detect electrons from βdecay ・ pulsed neutron beam from accelerator 30 cm 40 cm 1 m Time Projection Chamber drift direction MWPC flipper magnetic mirror neutron polarized form neutron bunches Spin Flip Chopper detect e - from β decay He + CO 2 gas shutter m c 0 3
Measurement principle TPC detects both 3 He(n, p) 3 H と β decay at the same time 5 : number of events N ε : selection efficiency σ : 3 He(n, p) 3 H cross section 3 He(n, p) 3 H β decay ν e - p +782 keV n 3 H +764 keV n p 3 He total neutron flux can be evaluated using 3 He(n, p) 3 H σ(v) v = σ(v 0 ) v 0 = 5333(7) barn × 2200 m/s v : neutron velocity ρ : 3 He number density
6 flipper ON 5 bunch mode flipper off to detector mirror magnetic coil flipper dump Spin Flip Chopper filpper OFF polarized neutron sensitive length bunch length is about half of TPC operate in 5 bunch mode by controlling neutron polarization Spin Flip Chopper can form neutron bunches with arbitrary length flipper on
Time Projection Chamber (TPC) anode (1720 V) ：24 ch 30 cm 1 m MWPC structure 6 mm MWPC cathode (0V) ：40 ch×2 7 field (0V) ：24 ch neutron drift direction 4 He (85 kPa) + CO 2 (15 kPa) + 3 He (100 mPa) • • count neutron β decay and 3 He(n, p) 3 H at the same time • low background material（ PEEK ：PolyEthel Ethel ketone） • inside walls covered by 6 LiF to absorb scattered neutrons • no magnetic field is applied m c 0 3
Acquired data 2016/5 200 Ⅳ 2016/4 173 72.7 200 Ⅴ 50 97 69.4 200 Ⅵ 2016/6 114 71.1 200 combined statistical uncertainty for τ n ~ 10 sec 17.5 2016/4 8 I gas No. month 3 He pressure [mPa] beam data time [hour] MLF power [kW] 2014/5 Ⅲ 101 35.3 300 Ⅱ 2015/4 86 15.8 500 we took physics data for 6 different gas cinditions in 2014-2016
Background subtraction 9 βdecay like event at TPC shutter open (beam in data) shutter close (beam dump data) subtracted neutron bunch is completely inside TPC β decay events is counted only in the fiducial time fiducial time
Monte Carlo simulation 10 detector setup in beamline is constructed at Geant4 system evaluate selection efficiency and background amount simulation processes ・β decay ・ 3 He(n, p) 3 H ・ 55 Fe X-ray（energy calibration) ・commic rays（drift velocity calibration） ・neutron scattering ・γ-ray from inside wall electrton track (view from TPC top)
11 Separation of βdecay and 3 He(n, p) 3 H two kinds of signal events ( βdecay and 3 H(n, p) 3 H ) in the TPC can be separated by maximum energy deposit among all wires linear scale log scale 25 keV
12 DC gas scattering βdecay background gas scattering DC n βdecay axis beam γ region Gas scattering background signal log scale linear scale (48 cm from TPC center) DC=4 wires gas scattering bkg ~ large DC βdecay ~ small DC DC : D istance from beam C enter TPC, and prompt γ becomes background scattered neutron interacts with a wall of the background
Results 13 uncertainty values and their uncertainties for gas Ⅵ (~11 days data taking) % Preliminary
Combined results 14 combined results of 6 gas data Ⅰ Ⅱ Ⅲ Ⅳ Ⅴ Ⅵ 2014 2015 2016 Preliminary
Results 15 our result 1.1σ deviation from PDG2017 value（880.2±1.0 sec） Preliminary
Data taking status 9 1.2 2017A 9 150 0.78 2017B 300 4 3.7 2018A 6 300~500 ~ 4 all combined statistical uncertainty ~ 4 sec (0.5%) 200 2016A 16 neutron [×10 11 ] we continue taking physics data year gas set number MLF power [kW] total incident 2014A 0.21 1 300 0.23 2015A 1 500 new
upgrade plan1: SFC upgrade magnetic mirros in SFC 600 days after upgrade (1 MW) current setup (1 MW) at 1 MW operation 100 days for 1 sec statistic error become 5 times total neutron flux is expected to increase in size of flippers and 17 shutter neutron MWPC flipper mirror magnetic neutron polarized 100 days
upgrade plan2: low-pressure operation background for βdecay (～4%) gas scattering βdecay new amplifier (power comsumption ~ 1/50) power-consumption amplifier is required For low-pressure operation, high gain and low at low-pressure（He+CO 2 = 50 kPa）operation This background can be reduced by half at current TPC gas condition (He+CO 2 = 100 kPa) gas scattering event is a main 18 bkg gas scattering DC n βdecay axis beam γ DC bkg
19 Conclusion input parameter to the BBN theory and V ud determination and our first result is • neutron lifetime is an important parameter in the weak interaction • significant deviation between two previous types of measurement • we use different method at J-PARC to measure the neutron lifetime, Preliminary • upgrade projects are undergoing to achieve our goal precision of 1 sec
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