Muon Capture: Status and Prospects 1 Peter Kammel Department of Physics and Center for Experimental Nuclear Physics and Astrophysics, University of Washington Representing the MuCap/MuSun collaborations PSI2013, Sept 2013 MuCap MuSun Search for Exotics in  and  Capture Basic QCD Symmetries “ Calibrating the Sun”

Part I: MuCap  + p  n +  Understanding hadrons from fundamental QCD  Symmetries of Standard Model  Basic astrophysics reactions in 2-nucleon case 2 Precision experiments meet first principle theory

3  Muon Capture  Form factors Muon Capture on the Nucleon  - + 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

Pseudoscalar Form Factor g P Foundations for mass generation chiral perturbation theory of QCD 4 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 based prediction (2-3% level) basic test of QCD symmetries recent lattice results g P experimentally least known nucleon FF solid QCD based prediction (2-3% level) basic test of QCD symmetries recent lattice results Kammel & Kubodera, Annu. Rev. Nucl. Part. Sci., 60 (2010), 327 Gorringe, Fearing, Rev. Mod. Physics 76 (2004),31

50 Years of Effort to Determine g P 5 “ 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. Rev. Nucl. 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 6  S = 710 s -1  T = 12 s -1  ortho =506 s -1  para =200 s -1

7 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 8 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 10 ppm 9 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 gas density of 1% LH 2 density mostly p  atoms during muon lifetime 11 Precision technique Clear Interpretation Clean stops in H 2 Impurities < 10 ppb Protium D/H < 10 ppb All requirements simultaneously

MuCap Strategy 12 Precision technique Clear Interpretation Clean stops in H 2 Impurities < 10 ppb Protium D/H < 10 ppb All requirements simultaneously

13 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  Gas continuously purified  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 15 Kicker Separator Quadrupoles MuCap detector TPC Slit  E3 beamline Muon On Request

Muon Defined by TPC TPC side view Signals digitized into pixels with three thresholds (green, blue, red) b) Large angle  -p scatter c) Delayed capture on impurity  O  N /  ~10 -6 / 

Time Distributions are Consistent No azimuth dependence 17 fitted  is constant Data run number (~3 minutes per run) 4/6/ Run groups

Disappearance Rate Disappearance Rate 18

Determination of  S 19 molecular formation bound state effect MuCap: precision measurement MuLan

Capture Rate  S (MuCap) = ± 5.4 stat ± 5.1 syst s -1  S (theory) = ± 3.0 gA ± 3.0 RC s -1 Pseudoscalar Coupling g P (MuCap) = 8.06 ± 0.48  s(ex) ± 0.28  s(th) for g A (0)  g P (MuCap)  8.34 By-product (reverse logic, i.e. assuming ChPT) CPT   + /   - to 20 ppm (4 fold improvement) MuCap Results 20 PDG12 updated Czarnecki, Marciano, Sirlin calculation recent calculations APS Editor's spotlight PSI p ress release Physics World

Precise and Unambiguous MuCap Result Verifies Basic Prediction of Low Energy QCD 21 g P (theory) = 8.26 ± 0.23 g P (MuCap) = 8.06 ± 0.55

Resolve RMC Puzzle? Improved RMC measurement Improved op measurement physics capture n(t) sensitive promising conditions  ~0.1 MuSun TPC development  =0.05 higher density need tests interesting if definitive measurement (3x smaller uncertainty) 22 pp  (L=1, I=1)  pp  (L=0, I=0) ortho para small components Auger emission in molecular cluster 4.1 ± /s Saclay 11.1 ± /s TRIUMF

Part II: MuSun  + d  n + n + MuSun Determine strength of axial-current from theoretical clean 2-N system  build nuclear physics from QCD  essential ingredient in fundamental astrophysics reactions 23 p p  d e + e d  p p e - x d  p n x

Part III: Heavy Search 24 Ideas only + C → h + n + 11 C (NC) e+e+ ++  e p → n e + (CC) e  e n p → d  x +  LSND 98 Gninenko 11 consistent with Karmen, MiniBoone  h <10 -9 s

Part III: Heavy at PSI? 25 Ideas only Early experiment:  + 3 He → t + |U  h | 2 ≤ Key improvements MuSun TPC size and cryo operation Resolution Digitizer and DAQ  Detection ? Large improvement potential

Part III: Dark Photons Popular scenario: SU(3) x SU(2) x U(1) x U’(1) V coupling via kinetic mixing: L int =  e J  V  connection to DM “explains” muon g-2 anomaly Worldwide effort Bump hunt in  *→l + l - missing energy … 26 Ideas only Standard Model Hidden Sector messenger

Part III: Dark Photons at PSI? Part III: Dark Photons at PSI? Reactions Capabilities Excellent  beams Simple, clean and low energy reactions Two body recoil with 3 He TPC, model-independent High resolution e/  detectors, Mu3e, MEG Brainstorming meeting in Jan ? 27 Ideas only Kammel, Pospelov