Neutron Lifetime From Beam Experiments M. Scott Dewey National Institute of Standards and Technology Gaithersburg, MD, USA Solvay Workshop 2014 Outline of Presentation • A brief introduction to the neutron lifetime • Status of current beam measurements • J-PARC measurement • BL2 at NIST • Future beam measurements • BL3 at NIST • Conclusions Vud and the CKM Matrix Measurements of tn and b-decay angular correlation coefficients yield |Vud|: Measurements of ft values for superallowed 0+→0+ b-decay also yield |Vud|: How to Measure τn … 𝑁(𝑡) = 𝑁0 Direct Observation of Exponential Decay: Similar in principle to Freshman Physics Majors measuring radionuclide half lives -- only a lot harder. “Bottle” Experiments: −𝑡 𝜏𝑛 𝑒 Observe the decay rate of N0 neutrons and the slope of  N (t )  ln   is  1 t n  t   Form two identical ensembles of neutrons and then count how many are left after different times. N (t1 )  e t1 t2  t n N (t2 ) Beam Experiments: Decay rates within a fiducial volume are measured for a beam of well known fluence. Decay Detector N (t )   N tn t Neutron Beam Fiducial Volume Neutron Detector The State of the Neutron Lifetime Beam Average t n  888.0  2.1s Storage Average t n  879.6  0.8s Note: This average contains result from Yue et al Phys. Rev. Lett. 111, 222501 (2013) The Present Precise measurement of neutron lifetime with pulsed neutron beam at JPARC Kenji MISHIMA (KEK) T. Yamada1#, N. Higashi1, K. Hirota2, T. Ino3, Y. Iwashita4, R. Katayama1, M. Kitaguch5, R. Kitahara6, K. Mishima3, H. Oide7, H. Otono8, R. Sakakibara2, Y. Seki9, T. Shima10, H. M. Shimizu2, T. Sugino2, N. Sumi11, H. Sumino12, K. Taketani3, G. Tanaka11, S. Yamashita13, H. Yokoyama1, and T. Yoshioka8 Univ. of Tokyo1, Nagoya Univ.2, KEK3, ICR, Kyoto Univ.4, KMI, Nagoya Univ.5, Kyoto Univ.6, CERN7, RCAPP, Kyushu Univ.8, RIKEN9, RCNP, Osaka Univ.10, Kyushu Univ.11, GCRC, Univ. of Tokyo12, ICEPP, Univ. of Tokyo13 Principle of our experiment Cold neutrons are injected into a TPC. The neutron b-decay and the 3He(n,p)3H reaction are measured simultaneously. Principle （Kossakowski,1989） Count events during time of bunch in the TPC Neutron bunch shorter than TPC p ν 3He(n,p)t Neutron bunch e β-decay τn v εe : lifetime of neutron : velocity of neutron : detection efficiency of electron 3He(n,p)3H εn ρ σ : detection efficiency of 3He reaction : density of 3He : cross section of 3He reaction σ0=cross section@v0, v0=2200[m/s] This method is free from the uncertainties due to external flux monitor, wall loss, depolarization, etc. Our goal is measurement with 1 sec uncertainty. 8 Setup Set up of our experiment in “NOP” beam line. 20 cm Iron shield TPC in the vacuum chamber Inside of Lead shielding Spin Flip Chopper In a Lead Sheald Inside of Cosmic ray Veto TPC in a Vacuum chamber Gas line DAQ 9 chronological table 2008 2009 2010 嶋TPC 1st JPARC symposiu m 2011 G10-TPC Design the G10-TPC 2012 (Low noise Amp) Upgrade of analysis framework for physics run Data taking2012 (commissioning) SFC shielding upgrade Design and development of Large TPC Analysis for commissioning data Measurement of Beam profile First detection of he first beam accept at Neutron β-decay the “NOP” Beam line 100 kW Design and development of Large SFC Design and development of DAQ system BG survey 20 kW 2015 2016 2017 LARGE PEEK-TPC TPC Basic properties test Development of software (Analysis framework, Geant4) Development of DAQ system Material test (PEEK) MLF Power 2014 PEEK-TPC Design the PEEK TPC, First detection of 3He(n,p) reaction 2013 Beam intensity is estimated to be 18 times. Commissioning for the new system Data Taking 2014 Data taking for 1sec level Today 200 Earthquake 200 kW kW Accident 300 kW of hadron hall 300 kW 600 kW? Increasing size the Spin Flip Chopper is planed at 2014/2015. Intensity will be 18 times by a designed value. We will start physics run to 1sec at 2016/2017 10 The NIST Beam Lifetime Experiment II (BL2) n | ddu tn  W 2 F G 4908.7(1.9) s 2 2 GV  3GA p | duu National Institute of Standards and Technology Physical Measurement Laboratory e e The NIST beam lifetime experiment a,t detector B = 4.6 T Precision aperture p detector Neutron beam n 6LiF deposit Beam fluence measurement Neutron monitor • Proton trap Decay product counting volume +800 V ( ) ( ) Proton trap electrostatically traps decay protons and directs them to detector via B field • Neutron monitor measures incident neutron rate by counting n + 6Li reaction products (a + t) Alpha-Gamma Determining tn Proton rate measured as function of trap length Proton detection efficiency n + 6Li reaction product counting Neutron flux monitor efficiency for NIST 2005 Error Budget Most significant improvement Other major improvements Nico et al Phys. Rev. C 71 055502 (2005) Using AG to calibrate the neutron monitor HPGe detector Totally absorbing 10B target foil Neutron monitor PIPS detector with aperture Alpha-Gamma device HPGe detector Neutron monitor efficiency uncertainty budget Projected Error Budget (BL2) Most significant improvement 0.5s 0.1s Other major improvements 0.2s 0.6s t n  1.0s The Future Nab Si detectors • 15 cm diameter • Full thickness: 2 mm • Dead layer ≤ 100 nm • 127 pixels Conclusions • Moving forward the goal is a reliable measurement of the neutron lifetime at the 0.1—0.2 s level • It is likely that there will be two efforts in the US during the coming decade • BL3: a beam experiment designed to achieve an uncertainty of < 0.2 s. • UCNtau: a magnetic bottle experiment • Both experiments will be seeking funding in the next 1—2 years