MuCap High-Precision Measurement of Muon Capture on the Proton m BVR35 Progress report presented by Claude Petitjean, PSI 12 Febuary 2004 http://www.npl.uiuc.edu/exp/mucapture/
MuCap Experiment experimental goal principle of measurement apparatus time projection chamber (TPC) data from run in fall 2003 some results milestones reached in 2003 upgrades for run in fall 2004 Beam request 2004
MuCap collaboration V.A. Andreev, A.A. Fetisov, V.A. Ganzha, V.I. Jatsoura, A.G. Krivshich, E.M. Maev, O.E. Maev, G.E. Petrov, G.N. Schapkin, G.G. Semenchuk, M. Soroka, A.A. Vorobyov Petersburg Nuclear Physics Institute (PNPI), Gatchina 188350, Russia P.U. Dick, A. Dijksman, J. Egger, D. Fahrni, M. Hildebrandt, A. Hofer, L. Meier, C. Petitjean, R. Schmidt Paul Scherrer Institute, PSI, CH-5232 Villigen, Switzerland T.I. Banks, T.A. Case, K.M. Crowe, S.J. Freedman, F.E. Gray, B. Lauss University of California Berkeley, UCB and LBNL, Berkeley, CA 94720, USA K.D. Chitwood, S.M. Clayton, P.T. Debevec, D. W. Hertzog, P. Kammel, B. Kiburg, R. McNabb, F. Mulhauser, C. J. G. Onderwater, C. Ozben, C.C. Polly, A. Sharp, D. Webber University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA L. Bonnet, J. Deutsch, J. Govaerts, D. Michotte, R. Prieels Université Catholique de Louvain, B-1348 Louvain-La-Neuve, Belgium R. M. Carey. J. Paley Boston University, Boston, MA 02215, USA T. Gorringe, M. Ojha, P. Zolnierzcuk University of Kentucky, Lexington, KY 40506, USA Cap F.J. Hartmann Technische Universität München, D-85747 Garching, Germany
Experimental goal measure the rate Λ s of muon capture on the proton p n to 1% precision. Muon capture is a semileptonic weak interaction process, and occurs predominantly from the hyperfine singlet atomic bound state. a 1% measurement of Λ s determines g p the weak nucleonic charged current induced pseudoscalar form factor to < 7% precision. The QCD prediction (Heavy Baryon Chiral Pert. Theory) is ~2% precise.
problem of previous experiments interpretation of rate S due to formation of ppµ molecules in lq hydrogen n+ S p F=0 p F=1 T and badly known rate OP of ortho-para transitions pp OP pp J=1 J=0 ortho para n+ n+
g P 20 17.5 15 12.5 interpretation of g P vs OP Muon Capture and g P update from Gorringe & Fearing RMC ChPT 10 7.5 5 Cap proposed OMC Saclay 2.5 Saclay exp theory New TRIUMF exp ---------o--------- 20 40 60 80 100 120 OP (ms -1 )
Experimental Technique Lifetime Method For µ, muon capture competes with muon decay: e e (99.85%) ( p ) n (0.15%) This rate decreases the observed µ lifetime from the vacuum lifetime, which we measure separately with µ + : e e (100%) Thus we need 10 ppm measurements of the µ+/- lifetimes or a statistics of at least 10 10 for both µ-decays
Experimental Technique Lifetime or Disappearance Method Since our experiment can only observe e + and e decay products, muon capture produces a small downward deflection of the µ lifetime curve from the µ + vacuum lifetime curve : log(counts) µ + µ time The capture rate is easily calculated from the measured lifetimes: 1 1 s ( )' ( )'
Technical tasks of MuCap experiment tasks goals to be reached ultra-clean 10-bar hydrogen gas target 0.01 ppm Z>1 impurities deuterium depleted hydrogen ( protium ) < 1 ppm deuterium 100% stop identification no wall stops TPC clean electron identification & tracking 2 cylindrical wire chambers unique µ e decay assignment µ-stop e-vertex matching high data rate 30 khz µ stops high statistics > 10 10 events for µ + and µ - µsr under control for µ + 50-100 Gauss magnetic field
Experimental Setup Apparatus Muon Detectors µsc µpc1 µpc2 TPC µ beam epc1 Electron Detectors epc2 e-detectors cover 75% of 4π esc (Hodoscope)
assembly/tests: March-Aug 2003 data-taking: Sept-Oct 2003
TPC design drawing with glass frames and ceramic structure bakeable to 130 C U cathodes = 5-6 kv E = 2 kv/cm - v drift = 0.5 cm/µs sensitive volume (12 x 15 x 30) cm 3
Online display of µ beam, µ stops in TPC and e in epc1 epc1/esc(phi,z)
event display of muon stops & electrons
event display of µ stop + impurity capture
development of impurities during the 2 good data weeks full scale 1 ppm
summed decay time spectra showing pile-up suppression
µ decay time spectra of 1 week with clean protium filling
MuCap 2003: exponential fits to each esc counter pair ] -1 Rate [s Decay-Rate Fits vs. esc Segment Number 2 4510 x10 4508 λ fit (assuming 50 MHz clock) 4506 4504 4502 4500 4498 2 4 6 8 10 12 14 16 esc Segment Number e-detector Accidentals Fraction 0.16 0.14 0.12 0.1 0.08 0.06 0.04 Accidentals 100 0.02 0 2 4 6 8 10 12 14 16 esc Segment Number
MuCap 2003: µsr enhanced fit of µ + decay time spectra
milestones 2003 protium production with < 0.5 ppm deuterium ultra-clean protium gas filling (< 0.1 ppm impurities) after installation of a new Palladium filter new TPC@4.8 kv stable operation (perfect µ stop detector!) full e detector consisting of epc1 and esc new frontend electronics for epc1 new compressor electronics for deadtime free epc1 data collection new DAQ running with 4 MB/s data rate (80% duty cycle) new µsr magnet with ~50 Gauss field new slow control system full electronics for TPC, wire chambers and plastic counters collimated muon beam injection system analysis software in mature development
upgrades for 2004 protium: maintain < 0.5 ppm deuterium & < 0.1 ppm Z>1 impurities new gas circulation, cleaning & diagnostics (Gatchina) e-detector: include new epc2 ( vertex tracking) tune TPC to 5.5 kv ( online control of µd diffusion) new 0.5 mm Beryllium window ( increase good µ stops x 2) µ-detectors: new outside µpc1&2 ( reduce µ-absorption/range-tails) µ-beam: new tune in πe3 area ( < 3% momentum spread) new spare TPC from Gatchina ( >6 kv to see e tracks) upgrade DAQ for larger data flow ( ~100% duty cycle) upgrade µsr magnet with Alu coils ( reduce scattering of e) new online data analysis goal for 2004: collect a significant part of 10 10 pileup-protected good µ-decays for µ + and µ -
protium gas circulation and purifying system (Gatchina)
MCstudy of µ stop distributions for various beam windows
MuCap experiment: time plans of upgrades for 2004 run
MuCap experiment: beam request for 2004 In 2004 we hope to approach closely the goal formulated in the proposal: a measurement of the µp singlet capture rate to ± 1% accuracy To accomplish this goal, we need area πe3 for the following activities: - setup of beamline with el.stat. separator, assemble full apparatus and electronics, test all components in the beam: 2 weeks - tune new 35 MeV/c muon beam: 1 week - test & optimize complete detector with beam: 1 week - data production towards 10 10 good µ - & µ + decays: 2 x 2.5 weeks - contingency for beam losses or other failures 1 week we request 10 weeks in area πe3 (preferably in Oct-Dec 2004, at the end of the 2004 production cycle)