1. Precision Measurement of Muon Capture on the Proton “  Cap experiment”  - + p   + n Petersburg Nuclear Physics Institute (PNPI), Gatchina,Russia Paul Scherrer Institut, PSI, Villigen, Switzerland University of California, Berkeley, UCB and LBNL, USA University of Illinois, Urbana-Champaign, USA Universite Catholique de Louvain, Belgium TU Munich,Garching, Germany Boston University, USA University of Kentucky, USA @ PSI  Cap Steven Clayton APS April Meeting May 2, 2004

2. Muon Capture and g P ChPT  OP (ms -1 ) gPgP RMC  Cap expected error Saclay exp theory OMC Saclay update from Gorringe & Fearing precise QCD (ChPT prediction) no overlap theory & OMC & RMC

3. experimental challenges    e+ e +   - p (  )   + n p (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  p+Z   Z +p Rate and statistics (BR = 10 -3 )  SR effect for  + TT SS  pp  pp pp  ortho  para F=0 F=1 J=1 J=0 n+  Cap

4.  Cap Experimental Strategy I  Cap New idea: active target of ultra-pure H 2 gas 10 bar measure   + and   -   S = 1/   - - 1/   +,   to 10 -5 eSC e “Lifetime” or “Disappearance” Method Our experiment observes e + and e – decay products. Muon capture reduces the μ – lifetime compared to the μ + lifetime by 0.15% ! High precision measurement of the lifetime difference: TPC ePC1 ePC2 log(counts) time μ+μ+ μ – 10 10 events

5.  Cap Experimental Strategy II Physics Unambiguous interpretation At low density (1% LH 2 ) mostly capture from  p(F=0) atomic state. Clean muon stop definition: Wall stops and diffusion eliminated by 3-D muon tracking In situ gas impurity control (c Z <10 -8, c d <10 -6 ) hydrogen chambers bakeable to 150 C, continuous purification TPC monitors impurities in-situ 10 -8 sensitivity with gas chromatograph  + SR: calibrated with transverse field 70 G Statistics 10 10 decay events: Complementary analysis methods  Cap pp pp  P pp  O time (  s ) 100% LH 2 1 % LH 2 pp  P pp  O pp

6.  Cap Experimental Setup Key ideas: active target of ultra-pure H 2 gas 10 bar for muons, separate large tracking detector for electrons.  Cap Scintillator (t = 0) Wire Chambers Time Projection Chamber (target) Wire Chambers Hodoscope μ Muon Detectors Electron Detectors e

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

8. Event Display  Stop  Stop Distribution Beam ViewSide View Beam ViewSide View

9. Impurity Monitoring  Stop Impurity Capture Beam ViewSide View Impurity Capture Yield vs. Time Yield per  Stop Time

10.  Cap Time Projection Chamber in Clean Room

11.  Cap Assembly: March → August Data-Taking: September → mid-October. commissioning / first physics 2003 Run

12. Time Spectra 2003

13.  Cap Status and Plans  Cap 2003 Commissioning Run: achieved high purity ~10 9  - events in 2 weeks analysis of data to get  S to ~4% by end of 2004 2004 Upgrades: install 2 nd electron wire chamber install gas recirculation system The Fall 2004 Production Run should collect 10 10  + events and 10 10  - events, giving  S to ~1%.  Cap Collaboration Website: www.npl.uiuc.edu/exp/mucapture/ Steven Clayton smclayto@uiuc.edu

14. Muon Capture and g P ChPT  OP (ms -1 ) gPgP RMC  Cap expected error Saclay exp theory OMC Saclay update from Gorringe & Fearing TRIUMF exp, 2004 precise QCD (ChPT prediction) no overlap theory & OMC & RMC

15.  Cap experimental setup Key ideas: active target of ultra-pure H 2 gas 10 bar for muons, separate large tracking detector for electrons.  Cap  SC (t = 0)  PC1  PC2 TPC ePC2 ePC1eSC (Hodoscope) μ Muon Detectors Electron Detectors e

16. Event Display y direction (drift time) x direction z direction Anodes Strips y direction (drift time) z direction  Stop Distribution  Stop

17. Impurity Monitoring y direction (drift time) x direction z direction Anodes Strips  Stop Impurity Capture