Precision Muon Physics Group

1. Precision Muon Physics Group K.D. Chitwood, P. Debevec, S. Clayton, D. Hertzog, P. Kammel, B. Kiburg, R. McNabb, F. Mulhauser, C. C. Polly, A. Sharp, D. Webber Nucleon form factors, chiral symmetry of QCD m Cap experimentgP to < 7% (3%) muon capture on proton- + p  m+ n L to 1 % Basic EW two nucleon reaction, calibrate v-d reactions mD project muon capture on deuteron - + d  m+ n +n L to 1 % Fermi Coupling Constant m Lan experiment GF to < 1ppm muon decay+  e++ne+m t+ to 1 ppm

2. Scientific case • QCD is the theory of strong interactions • non Abelian Gauge theory, running coupling constant, • Precision tests at high energies • strong coupling, confinement at “everyday” energies • Theoretical approaches to low energy domain • QCD inspired models • Lattice QCD • Effective field theories (chiral perturbation theory) systematic expansion around chiral limit “spontaneous broken” symmetry governs dynamics mass generationaccurate QCD prediction and QCD foundation for modelsmodel independent predictions of important reactions Quarkhandedness conserved mCap

3. - + p  m+ n nucleon level elementary level Ja Ja d p n u W W QCD nm m- m- nm Ja = <n|Va- Aa |p> Va= gV(q2) ga + igM(q2)/2M sab qb Aa= gA(q2) gag5 + gP(q2) qa/m g5 Ja = <d|ga (1-g5) |u> • fundamental and least known weak nucleon FF • solid theoretical prediction at 2-3% level • basic test of QCD symmetries • experiments not precise, controversial, 4 s discrepancy to theory • T. Gorringe, H. Fearing, Induced pseudoscalar coupling of the proton weak interaction, nucl-th/0206039, Jun 2002 • V. Bernard et al., Axial Structure of the Nucleon, Nucl. Part. Phys. 28 (2002), R1 gpNN n p p pseudoscalar form factor gP Fp W m- nm mCap

4. mD project m + d  n + n + n n d n W nm m- • fundamental EW 2-body reaction • high impact for fundamental astrophysics reactions • 10x precision improvement feasible by mCap techniques mD

5. MECEFT L1A pEFT: Class of axial current reactions related by single unknown parameter L1A • basic solar fusion reaction • p + p  d + e+ +  • key reactions for solar neutrino detection and supernova neutrino •  + d  p + p + e •  + d  p + n +  • short distance, axial two body currents, ab-inito pEFT(NNLO) vs. SNPA vs. MEEFT md capture close terrestrial analogue • soft enough ? • precision measurement possible ? p n d d p n W W e+ nm m- ne mD

6. Precision Measurement of Muon Capture on the Proton“mCap experiment” - + p  m+ n www.npl.uiuc.edu/exp/mucapture/ 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

7. experimental challenges - p ()  m+ n m- e+ne+m p - = heavy electron • (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 impurities mp+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

8. log(counts) ePC2 μ+ ePC1 μ – TPC time 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% ! 1010events High precision measurement of the lifetime difference: e eSC mCap

9. mCap experimental strategy II • Physics • Unambigous interpretationAt 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<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 10% LH2 1 % LH2 pm pm ppmO ppmO pm ppmO ppmP ppmP ppmP time (ms) • Statistics • 1010 statistics: Complementary analysis methods mCap

10. 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

11. mCap experimental setup: TPC The time projection chamber (TPC), is our active gas-filled target. It detects in muons and reaction products in 3D. m stop rare impurity capture m+Z  Z’+n+n

12. 2003 run Assembly: March → August Data-Taking: September → mid-October. commissioning / first physics mCap

13. time spectra 2003

14. mCap status and plans • Planned schedule mCap • technical proposal spring 2001, received “high priority status” • commissioning 2003 • final detector upgrades 2004 • data run 2003 4% precision • data run 2004 1% precision • …. mCap II or md project Steve’s and Tom’s thesis Contact me if you are interested ! mCap

15. Experimental facility Location Paul Scherrer Institute (PSI), Switzerland Muon Source • PSI accelerator (ring cyclotron) generates 590 MeV proton beam • protons hit graphite target and produce pions • pions decay to muons Muon Beam Properties • Particles: μ+ or μ– • Momentum ~ 30-40 MeV/c • rate ~ 50 kHz