Peter Kammel Muon Capture and the Nucleon’s Axial Structure First Results and Future Plans of the MuCap Experiment GFGF gPgP L 1A MuCap “MuSun” project MuLan

 Historical: V-A and  -e Universality  Today: EW current key probe for  Understanding hadrons from fundamental QCD  Symmetries of Standard Model  Basic astrophysics reactions Physics Context charged current MuCap  - + p   + n

Muon Capture on the Proton MuCap  - + p   + n rate   S at q 2 = m  2 Lorentz, T invariance + second class currents suppressed by isospin symm. apart from g P = 8.3 ± 50% All form factors precisely known from SM symmetries and data gPgPgPgP The Black Sheep of Form Factors T. Hemmert Form factors

g P determined by chiral symmetry of QCD: g P = (8.74  0.23) – (0.48  0.02) = 8.26  0.23 PCAC pole term Adler, Dothan, Wolfenstein ChPT leading order one loop two-loop <1% g P basic and experimentally least known EW nucleon form factor solid QCD prediction via HBChPT (2-3% level) basic test of QCD symmetries g P basic and experimentally least known EW nucleon form factor solid QCD prediction via HBChPT (2-3% level) basic test of QCD symmetries Recent reviews: V. Bernard et al., Nucl. Part. Phys. 28 (2002), R1 T. Gorringe, H. Fearing, Rev. Mod. Physics 76 (2004) 31 Pseudoscalar Form Factor g P Pseudoscalar Form Factor g P MuCap n  p --  g  NN FF W

Interpretation of Experiments ?  T = 12 s -1 pμ ↑↓ singlet (F=0)  S = 710 s -1 n+ triplet (F=1) μ pμ ↑↑ ppμ para (J=0)ortho (J=1) λ op  ortho =506 s-1  para =200 s-1 ppμ Interpretation requires knowledge of pp  population Strong dependence on hydrogen density  pp  P pp  O pp 100% LH 2 pp pp  P pp  O 1 % LH 2 time (  s)  λ pp  MuCap

no overlap theory & OMC & RMC large uncertainty in OP  g P  50% ? no overlap theory & OMC & RMC large uncertainty in OP  g P  50% ? Precise Theory vs. 45 Years of Exp. Efforts ChPT OP (ms -1 ) gPgP  - + p   + n + TRIUMF  Cap precision goal exp theory TRIUMF 2006  - + p   + Saclay MuCap

n Lifetime method  →e decays measure   to 10ppm,     S = 1/   - 1/    to 1%  n Unambiguous interpretation at 1% LH 2 density Clean  stop definition in active target (TPC) to avoid wall stops n Ultra-pure gas system and purity monitoring at 10 ppb level n Isotopically pure “protium” MuCap Experimental Strategy fulfill all requirements simultaneously unique MuCap capabilities MuCap log(counts) t e -t  μ+μ+ μ –        S reduces lifetime by  → e PSI, Switzerland

3D tracking w/o material in fiducial volume Muons stop in active TPC target p -- Observed muon stopping distribution E e-e- 10 bar ultra-pure hydrogen, 1.16% LH kV/cm drift field ~5.4 kV on 3.5 mm anode half gap bakeable glass/ceramic materials continuous gas circulation

Time Spectra  -e impact parameter cut huge background suppression diffusion (deuterium) monitoring blinded master clock frequency variety of consistency checks 6 mm Inside TPC MuCap

Results  S MuCap =  13.7 stat  10.7 sys s -1 Average of HBChPT calculations of  S : (MuCap 2007) g P = 7.3 ± 1.1 Apply new rad. correction (2.8%): Czarnecki, Marciano,Sirlin, PRL 2007 further sub percent theory required MuCap   + from PDG and MuLan

MuCap result nearly model independent First precise and unambiguous result Consistent with chiral prediction Does not confirm radiative muon capture (RMC) discrepancy Final result (’06 and ’07 data) will reduce error twofold MuCap result nearly model independent First precise and unambiguous result Consistent with chiral prediction Does not confirm radiative muon capture (RMC) discrepancy Final result (’06 and ’07 data) will reduce error twofold g P Landscape after MuCap 07 Before MuCap experiments inconclusive and mutually inconsistent MuCap  - + p   + n + 

12 “Calibrating the Sun” via Muon Capture on the Deuteron  + d  n + n +  + d  n + n + Goal total  d capture rate to 1% precision Motivation first precise measurement of basic EW reaction in 2N system, benchmark measurement with 10x higher precision impact on fundamental astrophysics reactions (SNO, pp) comparison of modern high precision calculations high precision feasible by  Cap technique and careful optimization model-independent connection via EFT & L 1A “MuSun”

Theory SNPA – EFT (HBChPT,  EFT, hybrid) 1B NN description accurate 2B not well constrained by theory Axial Currents in 2N System n Reactions  + d  n + n + basic solar fusion reaction p + p  d + e + + key reactions for SNO + d  p + p + e - (CC) + d  p + n + (NC) … MEC EFT L 1A EFT: Class of axial current reactions related by single parameter L 1A Quest for L 1A Precision  +d experiment (PK, Chen) best determination of L 1A from 2N system theory: precise enough? reaction soft enough for L 1A ? Ando, Park, Kubodera, Myhrer (2002) Chen, Inoue, Ji, Li (2005) experiment: 1% precision possible ? MuCap technique   E n (MeV) E n (MeV) p (MeV/c) 10 MuSun

Quest for L 1A Precise experiment in 2N system needed

Proposal planned 2007 measurement of absolute rate to <1%  Sun I:  Cap technique, 1% LD 2, 300 K, measure time spectra of capture neutrons monitor populations with fusion and capture reactions First measurement of polarization observables in  +d capture?  Sun II : new cryo TPC Kinetics requires optimized target conditions: T 5% LD 2 density time (  s) 30K, 5%  d(  )  d(  )   He 1% LD K 10% LD 2 30 K MuSun New collaborators welcome ! PSI Oct ‘07, US Nov ‘07 Proposal deadline Jan ‘08

Various ideas: Fusion hep: 3 He + p → 4 He + e + +  4 He → t + n + Dalitz plot ? dd  → 4 He +  +  p wave at low energies n d 3 He  → 4 He+  +p Theoretical motivation should be clarified Can one extract the S factor, which precision needed ? sensitivity study based on MuCap data

Summary MuCap: First precise g P measurement with clear interpretation Consistent with ChPT expectation, does not support RMC puzzle Factor 2-3 additional improvement on the way MuSun muon-deuteron capture, needs g P as input New benchmark in EW reactions in 2N system MuLan: First G F update in 23 years – 2.5x improvement, no surprise in result Factor 10 additional improvement on the way log(counts) time μ+μ+ μ – 20 ppm  10 ppm  1 ppm ??  30 ppm  10 ppm projected

Additional slides

MuCap

MuCap Error Budget

TPC tracks 2 different events seen by TDC and FADC system

45 Years of Experiments to Determine g P  - + p   + n OMC BR~ experiments, typical precision 10-15%, Saclay 4%  - + p   + n +  RMC BR~10 -8, E>60 MeV  He   + 3 H n Beta Decay Correlations … 279±25 events BR  (k>60MeV)=(2.10±0.21)x10 -8 Wright et al. (1998) authors  stat (s -1 ) comment theory 1993Congleton & Fearing13041B theory 1996Congleton & Truhlik1502±321B + 2B exp 1998Ackerbauer et al1496.0±4.0 3 He TPC theory 2002Marcucci et al.1484±81B+2B, T beta constraint rad. corrections?

QCD high q 2 (q > some GeV)short distance <0.1 fm Weakly interacting quarks and gluons asymptotic freedom low q 2 (q 1 fm QCD has chiral symmetry spontaneously broken  is Nambu-Goldstone boson, weakly interacting chiral effective theory ↔ Nuclear Physics Lattice QCD: ab initio calculations issues: continuum transition, etc. physical quark masses not reached Lattice QCD Edwards et al. LHPC Coll (2006)

MuCap Unique Capabilities: Impurities Results n c N, c O < 7 ppb, c H2O ~18-30 ppb n correction based on observed capture yield Diagnostic in TPC rare impurity capture  Z  (Z-1)+n+  Z (C, N, O) ~ (40-100) x  S ~10 ppb purity required Hardware Circulating Hydrogen Ultrahigh Purification System Gas chromatography CRDF 2002, 2005 Imp. Capture x z t

Results Directly from data c d = 1.49 ± 0.12 ppm AMS (2006) c d = 1.44 ± 0.15 ppm On-site isotopic purifier 2006 (PNPI, CRDF)  p + d   d + p (134 eV)  large diffusion range of  d < 1 ppm isotopic purity required MuCap Unique Capabilities:  p,  d diffusion Diagnostic: vs.  -e vertex cut AMS, ETH Zurich e-e- e-e- pp p dp d or to wall  -e impact par cut World Record c d < 0.1 ppm

Axialvector Form Factor g A Axialvector Form Factor g A Exp. History Axial radius Lattice QCD  +N scattering consistent with  electroproduction (with ChPT correction) introduces 0.46% uncertainty to  S (theory) PDG 2006 Edwards et al. LHPC Coll (2006) Bernard et al. (2002) MuCap

 EW current key probe  Understanding hadrons from QCD  Symmetries of Standard Model  Muon Capture  Formfactors MuCap Physics Case MuCap  - + p   + n rate   S at q 2 = m  2 Lorentz, T invariance + second class currents suppressed by isospin symm. apart from g P = 8.3 ± 50% All form factors precisely known from SM symmetries and data gPgPgPgP The Black Sheep of Form Factors T. Hemmert

Future

Quest for L 1A process value (fm 3) method theory Dim.arguments ±6 2 nucleon +d  e + +n+n 3.6 ±4.6reactor, optimistic   +n +p ES, CC, NC 4.0 ±6.3 SNO self calibration  +d  +n+n ±1 ?1%  measurement theory uncertainty 1% 3 nucleon 3 H  3 He+e + +n4.2 ± 0.1 used by EFT*, not by  EFT  3 He  3 H+ ?g P from other source astro Helioseismology7.0 ± 5.9pp fusion, but no other SoMo uncertainties Chen, Heeger, Robertson PRC 67 (2003) Precise experiment in 2N system needed

Various Ideas: Weak Interactions recoil polarization should be included  p: H(n,F)  p: Laser  d: Av g a sensitivity Serebrov  g a ~0.7%

 3 He

MuLan

MuLan Scientific Case n Fundamental electroweak parameters n G F Implicit to all EW precision physics Uniquely related to muon decay Precision  G F  relation no longer theory limited 9 ppm ppm 23 ppm G F  M Z QED MuLan 2004 MuLan Goal theory 17 ppm 18 ppm 90 ppb 30 ppm 9 ppm 18 ppm <0.3 ppm 0.5 ppm 1 ppm <0.3 ppm van Ritbergen and Stuart: 2-loop QED corrections MuLan exp

PSI DC proton beam 590 MeV, 1.7 mA Kicker On Fill Period Measurement Period time Number (log scale) kV 12.5 kV Real data MuLan Experiment “Early-to-late” changes Instrumental shifts Gain or threshold Time response Effective acceptance Residual polarization or precession Pileup Missing events Systematics MuLan

This world average used for MuCap

MuLAN    MuLan  = (21)(11)  s (11ppm)   (World) = (21)  s (9.6 ppm) G F = (6) x GeV -2 (5 ppm) MuLAN    MuLan  = (21)(11)  s (11ppm)   (World) = (21)  s (9.6 ppm) G F = (6) x GeV -2 (5 ppm) MuLan FAST   = (32) (15)  s e-Print: arXiv: [hep-ex] FAST   = (32) (15)  s e-Print: arXiv: [hep-ex]

MuLan Error Budget