Precision Muon Capture at PSI 1 Peter Kammel Department of Physics and Center for Experimental Nuclear Physics and Astrophysics, University of Washington Chiral Dynamics, Aug 2012 MuCap MuLan MuSun

Outline  e  Strength of Weak Interaction MuLan G F  + p  n +  Basic QCD Symmetries MuCap g P  + d  n + n +  Weak few nucleon reactions  + 3 He  t +  and astrophysics MuSun 2

Muon Lifetime Fundamental electro-weak couplings Implicit to all EW precision physics Uniquely defined by muon decay G F  M Z QED q Extraction of G F from   : Recent two-loop calc. reduced error from 15 to ~0.2 ppm 9 ppm  0.6 ppm 0.37 ppb 23 ppm MuLan Collaboration PRL 106, (2011 )

MuLan Final Results  (R06) = ± 2.5 ± 0.9 ps  (R07) = ± 3.7 ± 0.9 ps  (Combined) = ± 2.2 ps (1.0 ppm)  (R07 – R06) = 1.3 ps New G F G F (MuLan) = (7) x GeV -2 (0.6 ppm) The most precise particle or nuclear or atomic lifetime ever measured

Outline  e  Strength of Weak Interaction MuLan G F  + p  n +  Basic QCD Symmetries MuCap g P  + d  n + n +  Weak few nucleon reactions  + 3 He  t +  and astrophysics MuSun 5

6  Historical: V-A and  -e Universality  Today: EW current key probe for  Understanding hadrons from fundamental QCD  Symmetries of Standard Model  Basic astrophysics reactions Muon Capture on the Proton charged current  - + p   + n Chiral Effective Theories Lattice Calculations

7  Muon Capture  Form factors Capture Rate  S and Form Factors  - + 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. g V, g M from CVC, e scattering g A from neutron beta decay 0.45 % 9 % pre MuCap

Axial Vector g A 8 PDG 2008 g A (0)=−1.2695± PDG 2012 g A (0)=− ± Future ? (Marciano PDG12) g A (0)=−1.275 Axial Mass  A =1 GeV p,  electro production 1.35 nuclear targets

Pseudoscalar Form Factor g P Foundations for mass generation chiral perturbation theory of QCD 9 History  PCAC  Spontaneous broken symmetries in subatomic physics, Nambu. Nobel 2008 State-of-the-art  Precision prediction of ChPT  g P = (8.74  0.23) – (0.48  0.02) = 8.26  0.23 leading order one loop two-loop <1% g P experimentally least known nucleon FF solid QCD prediction (2-3% level) basic test of QCD symmetries recent lattice results g P experimentally least known nucleon FF solid QCD prediction (2-3% level) basic test of QCD symmetries recent lattice results Kammel & Kubodera, Annu. Rev. Nucl. Part. Sci :327 Gorringe, Fearing, Rev. Mod. Physics 76 (2004) 31 Bernard et al., Nucl. Part. Phys. 28 (2002), R1

45 years of effort to determine g P 10 “ Radiative muon capture in hydrogen was carried out only recently with the result that the derived g P was almost 50% too high. If this result is correct, it would be a sign of new physics... ’’ — Lincoln Wolfenstein (Ann.ReNucl.Part.Sci. 2003) OMC RMC  - + p  n + +  Kammel&Kubodera

“Rich” Muon Atomic Physics Makes Interpretation Difficult Strong sensitivity to hydrogen density  rel. to LH 2 ) In LH 2 fast pp  formation, but op largely unknown 11  S = 710 s -1  T = 12 s -1  ortho =506 s -1  para =200 s -1

12 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. Controversial Experiments ChPT OP (ms -1 ) gPgP TRIUMF exp theory TRIUMF 2006 Saclay

MuCap Strategy 13 Precision technique Clear Interpretation Clean stops in H 2 Impurities < 10 ppb Protium D/H < 10 ppb Muon-On-Request All requirements simultaneously

MuCap Strategy   p  n rare, only 0.16% of  e  neutron detection not precise enough Lifetime method   S = 1/   - 1/    measure   to 10ppm 14 Precision technique Clear Interpretation Clean stops in H 2 Impurities < 10 ppb Protium D/H < 10 ppb Muon-On-Request All requirements simultaneously

 e t MuCap Technique

MuCap Strategy At 1% LH 2 density mostly p  atoms during muon lifetime 16 Precision technique Clear Interpretation Clean stops in H 2 Impurities < 10 ppb Protium D/H < 10 ppb All requirements simultaneously

MuCap Strategy 17 Precision technique Clear Interpretation Clean stops in H 2 Impurities < 10 ppb Protium D/H < 10 ppb All requirements simultaneously

18 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, 1.12% LH kV/cm drift field ~5.4 kV on 3.5 mm anode half gap bakeable glass/ceramic materials to prevent muon stops in walls (Capture rate scales with ~Z 4 )

MuCap Strategy  CHUPS purifies the gas continuously  TPC monitors impurities  Impurity doping calibrates effect :c N < 7 ppb, c H2O ~20 ppb 2006 / 2007: c N < 7 ppb, c H2O ~9-4ppb Precision technique Clear Interpretation Clean stops in H 2 Impurities < 10 ppb Protium D/H < 10 ppb Muon-On-Request All requirements simultaneously anodes time

Experiment at PSI 20 Kicker Separator Quadrupoles MuCap detector TPC Slit  E3 beamline Muon On Request

MuCap Data 21 YearStatistics [10 10 muon decays] Comment -- + published * This talk This talk Total~1.21~0.61~60TB raw data + known to 1 ppm from MuLan *V.A. Andreev et al., Phys. Rev. Lett. 99, (2007)

Muon defined by TPC TPC active volume Fiducial volume Front face view muon beam direction vertical direction TPC side view transverse direction vertical direction Signals digitized into pixels with three thresholds (green, blue, red)

Electron defined by Independent e-Tracker  Small, but significant interference with  track  simple, robust track reconstruction and its verification essential 23

Time Distributions are Consistent No azimuth dependence 24 fitted  is constant Data run number (~3 minutes per run) 4/6/ Run groups

Start and stop-time-scans consistency 4/6/

MuCap Results 26 rates with secret offset, stat. errors only

Disappearance rate Disappearance rate 27

Error budget 28 Systematic errorsRun 2006Run 2007 (s -1 )  (s -1 ) (s -1 )  (s - 1 ) High-Z impurities  p scatter  p diffusion Fiducial volume cut 3.0 Entrance counter inefficiencies 0.5 Choice of electron detector def. 1.8 Total

Determination of  S 29 molecular formation bound state effect  S (MuCap prelim) = ± 5.4 stat ± 5.0 syst s -1  S (theory) = ± 4.6 s -1 Czarnecki, Marciano, Sirlin, RC=2.8% MuCap: precision measurement MuLan

g P : Precise and unambiguous MuCap result solves long-standing puzzle 30 g P (theory) = 8.26 ± 0.23 g P (MuCap prelim) = 8.04 ± 0.56

Outline  e  Strength of Weak Interaction MuLan G F  + p  n +  Basic QCD Symmetries MuCap g P  + d  n + n +  Weak few nucleon reactions  + 3 He  t +  and astrophysics MuSun 31 Laura Marcucci, Tuesday

32 Motivation  μ - + d  ν + n + n  μ - + d  ν + n + n measure rate Λ d in μd(  ) atom to <1.5%  simplest nuclear weak interaction process with precise th. & exp. nucleon FF (g P ) from MuCap rigorous QCD calculations with effective field theory  close relation to neutrino/astrophysics solar fusion reaction pp  de +  d scattering in SNO exp.  model independent connection to μd by single Low Energy Constant  model independent connection to μd by single Low Energy Constant (LEC) μ + d determines this LEC in clean 2 N system  2 N system  “ Calibrates the Sun ” reduce LEC uncertainty from 100% to ~20%

33 Precise Experiment Needed

Muon Physics and Interpretation Precision technique Clear Interpretation Clean stops in D 2 Impurities < 1ppb H/D < 100 ppb 34 Optimal conditions complex, can one extract EW parameters ? Muon-Catalyzed Fusion Breunlich, Kammel, Cohen, Leon Ann. Rev. Nucl. Part. Science, 39: (1989)

Precise Experiment Possible? Precision technique Clear Interpretation Clean stops in D 2 Impurities < 1ppb H/D < 100 ppb Active muon target 35

MuSun Detector System 36 Electron Tracker CryoTPC TPC Digitizer Electronics Impurity filtering Liquid Ne Circulation

Fusions in TPC 37 t+p 3 He  run2011, prelim robust muon tracking algorithm at level required !  SC 2  s

Status and Plans Analysis analysis run 2011 data 4.8 x 10 9 good μ- stop 4 x 10 8 μ+ stop events first physics publication study detector upgrades Upgrades detector upgrades 2012 cryo preamp TPC optimization improved purity and monitoring New beam line at PSI Commissioning run 2012 Final runs extended πE1 old πE1

Summary: Evolution of Precision 39 future complete in progress complete = 8.04 ± 0.56 (  p) = 8.2 ± 0.7 (  3 He exp+MKRSV theo )

Collaborations Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia Paul Scherrer Institute (PSI), Villigen, Switzerland University of California, Berkeley (UCB and LBNL), USA University of Illinois at Urbana-Champaign, Urbana, USA University of Washington, Seattle, USA Université Catholique de Louvain, Belgium University of Kentucky, Lexington, USA Boston University, USA Regis University, Denver, USA University of South Carolina, USA Boston University, USA University of Illinois at Urbana-Champaign, Urbana, USA James Madison University, Harrisonburg, USA University of Kentucky, Lexington, USA KVI, University of Groningen, Groningen, The Netherlands Paul Scherrer Institute (PSI), Villigen, Switzerland Regis University, Denver, USA University of Washington, Seattle, USA MuLan MuCap/MuSun Supported by NSF, DOE, Teragrid, PSI and Russian Academy Science

Backup 41

Kicker On Fill Period Measurement Period The MuLan experimental concept… time Number (log scale) kV 12.5 kV Real data 170 Inner/Outer tile pairs 450 MHz WaveForm Digitization Extinction ~ 1000 Accumulation Measuring Period Detector has symmetric design around stops

4/6/2012Brendan Kiburg, University of Washington 43

4/6/2012Brendan Kiburg, University of Washington 44

4/6/2012Brendan Kiburg, University of Washington 45

The interference is time- and space-dependent 4/6/2012Brendan Kiburg, University of Washington 46 N Blue Pixels

First MuSun Production Run 47 Performance 12 weeks incl. setup & tests in x 10 9 good μ - stops 4 x 10 8 μ + stops in fiducial vol. with decay electron 21.2 TB μ - & 2.5 TB μ + of clean data Important upgrades before run  produced new hydrogen-depleted deuterium gas (c p < )  stable HV at 80 kV (no sparks)  improved frontend electronics  gas chromatography w. online sampling  new X-ray detectors (Ge, NaI)  drifttime effect  impurity control

Muons in TPC 48   run2011, prelim  SC 2  s

MuLan Final Errors and Numbers ppm units  (R06) = ± 2.5 ± 0.9 ps  (R07) = ± 3.7 ± 0.9 ps  (Combined) = ± 2.2 ps (1.0 ppm)  (R07 – R06) = 1.3 ps New G F G F (MuLan) = (7) x GeV -2 (0.6 ppm)

Comments Determination of g P  exp. precision at two-loop level  larger g A would shift  S (theory) from 711 to 716 Using g P from HBChPT  CPT test:   + -   20 ppm  g  NN from MuCap  2 nd class currents, beyond standard model couplings 50