Precision Measurement of Muon Capture on the ProtonmCap experiment - + p m+ nPetersburg Nuclear Physics Institute (PNPI), Gatchina,RussiaPaul Scherrer Institut, PSI, Villigen, SwitzerlandUniversity of California, Berkeley, UCB and LBNL, USAUniversity of Illinois, Urbana-Champaign, USAUniversite Catholique de Louvain, BelgiumTU Munich,Garching, GermanyBoston University, USAUniversity of Kentucky, USA@ PSImCapSteven ClaytonAPS April MeetingMay 2, 2004

Muon Capture and gPChPTlOP (ms-1)gPRMCmCap expected errorSaclay exptheoryOMC Saclayupdate from Gorringe & Fearingprecise QCD (ChPT prediction)no overlap theory & OMC & RMC

experimental challengesm- e+ne+m - p () m+ np(Rich) physics effects Interpretation: where does capture occur ? Critical because of strong spin dependence of V-A interaction

Background: Wall stops and diffusion Transfer to impurities mp+Z mZ +p Rate and statistics (BR = 10-3) mSR effect for m+

LTLSmppmppmpmpmLorthoLparaF=0F=1J=1J=0n+nn+nn+nmCap

mCap Experimental Strategy ImCap New idea: active target of ultra-pure H2 gas 10 bar measure t+ and t- S = 1/- - 1/+ , tm to 10-5eSCe

Lifetime or Disappearance Method

Our experiment observes e+ and e decay products. Muon capture reduces the lifetime compared to the + lifetime by 0.15% !High precision measurement of the lifetime difference:TPCePC1ePC2log(counts)time+ 1010 events

mCap Experimental Strategy IIPhysics Unambiguous interpretation At low density (1% LH2) mostly capture from mp(F=0) atomic state. Clean muon stop definition: Wall stops and diffusion eliminated by 3-D muon tracking In situ gas impurity control (cZ

mCap Experimental Setup Key ideas: active target of ultra-pure H2 gas 10 bar for muons, separate large tracking detector for electrons.mCapScintillator(t = 0)Wire ChambersTime Projection Chamber(target)Wire ChambersHodoscopeMuonDetectorsElectronDetectorse

The Time Projection Chamber tracks muon stops in 3D.p

Event Displaym StopBeam ViewSide View

Impurity Monitoringm StopImpurity CaptureBeam ViewSide View

mCap Time Projection Chamber in Clean Room

mCapAssembly: March August

Data-Taking: September mid-October.commissioning / first physics2003 Run

Time Spectra 2003

mCap Status and PlansmCap2003 Commissioning Run: achieved high purity ~109 m- events in 2 weeks analysis of data to get LS to ~4% by end of 20042004 Upgrades: install 2nd electron wire chamber install gas recirculation systemThe Fall 2004 Production Run should collect 1010 m+ events and 1010 m- events, giving LS to ~1%.

mCap Collaboration Website:www.npl.uiuc.edu/exp/mucapture/Steven Claytonsmclayto@uiuc.edu

Muon Capture and gPChPTlOP (ms-1)gPRMCmCap expected errorSaclay exptheoryOMC Saclayupdate from Gorringe & FearingTRIUMF exp, 2004precise QCD (ChPT prediction)no overlap theory & OMC & RMC

mCap experimental setup Key ideas: active target of ultra-pure H2 gas 10 bar for muons, separate large tracking detector for electrons.mCapmSC(t = 0)mPC1mPC2TPCePC2ePC1eSC (Hodoscope)MuonDetectorsElectronDetectorse

Event Displayx directionAnodesStripsm Stop

Impurity Monitoringx directionAnodesStripsm StopImpurity Capture