Precision Measurement of Muon Capture on the Proton “ m Cap experiment”

1. Precision Measurement of Muon Capture on the Proton“mCap experiment” - + p  m+ n Steven Clayton APS April Meeting May 2, 2004 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 mCap

2. Muon Capture and gP gP update from Gorringe & Fearing RMC ChPT mCapexpected error OMC Saclay Saclay exp theory lOP (ms-1) precise QCD (ChPT prediction) no overlap theory & OMC & RMC

3. experimental challenges - p ()  m+ n m- e+ne+m p • (Rich) physics effects • Interpretation: where does capture occur ? • Critical because of strong spin dependence of V-A interaction m LS LT pm pm n+n F=0 F=1 Lortho • Background:Wall stops and diffusionTransfer to impuritiesmp+Z mZ+p • Rate and statistics (BR = 10-3) • mSR effect for m+ ppm n+n J=1 Lpara ppm n+n J=0 mCap

4. mCap Experimental Strategy I New idea: active targetof ultra-pure H2 gas 10 bar measure t+ and t-S = 1/- - 1/+ , tm to 10-5 • “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% ! log(counts) ePC2 1010events μ+ ePC1 μ – TPC time High precision measurement of the lifetime difference: e eSC mCap

5. mCap Experimental Strategy II • Physics • Unambiguous interpretationAt low density (1% LH2) mostly capture frommp(F=0) atomic state. • Clean muon stop definition:Wall stops and diffusion eliminated by 3-D muon tracking • In situ gas impurity control(cZ<10-8, cd<10-6)hydrogen chambers bakeable to 150 C, continuous purification TPC monitors impurities in-situ 10-8 sensitivity with gas chromatograph • m+SR: calibrated with transverse field 70 G 100% LH2 1 % LH2 ppmO pm ppmP ppmO pm ppmP time (ms) • Statistics • 1010 decay events: Complementary analysis methods mCap

6. mCap Experimental Setup Key ideas: active targetof ultra-pure H2 gas 10 bar for muons, separate large tracking detector for electrons. Scintillator (t = 0) Time Projection Chamber (target) Muon Detectors Wire Chambers μ Wire Chambers Electron Detectors Hodoscope mCap e

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

8. m Stop Distribution Beam View Side View Event Display mStop Beam View Side View

9. Impurity Capture Yield vs. Time Yield per m Stop Time Impurity Monitoring Impurity Capture mStop Beam View Side View

10. mCap Time Projection Chamber in Clean Room

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

12. Time Spectra 2003

13. mCap Status and Plans • 2003 Commissioning Run: • achieved high purity • ~109m- events in 2 weeks • analysis of data to get LS to ~4% by end of 2004 • 2004 Upgrades: • install 2nd electron wire chamber • install gas recirculation system • The Fall 2004 Production Run should collect 1010m+ events and 1010m- events, giving LS to ~1%. mCap Collaboration Website: www.npl.uiuc.edu/exp/mucapture/ Steven Clayton smclayto@uiuc.edu mCap

14. Muon Capture and gP gP update from Gorringe & Fearing RMC ChPT mCapexpected error OMC Saclay TRIUMF exp, 2004 Saclay exp theory lOP (ms-1) precise QCD (ChPT prediction) no overlap theory & OMC & RMC

15. mCap experimental setup Key ideas: active targetof ultra-pure H2 gas 10 bar for muons, separate large tracking detector for electrons. mSC (t = 0) mPC1 Muon Detectors mPC2 TPC μ Electron Detectors ePC1 eSC (Hodoscope) ePC2 mCap e

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

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