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Muon Capture: Status and Prospects 1 Peter Kammel Department of Physics and Center for Experimental Nuclear Physics and Astrophysics, University of Washington http://www.npl.washington.edu/muon/ Representing the MuCap/MuSun collaborations PSI2013, Sept 2013 MuCap MuSun Search for Exotics in and Capture Basic QCD Symmetries “ Calibrating the Sun”
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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
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3 Muon Capture Form factors Muon Capture on the Nucleon - + p + n rate S at q 2 = -0.88 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
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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
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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
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“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
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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 RMC @ TRIUMF exp theory TRIUMF 2006 OMC@ Saclay
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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
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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
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e t MuCap Technique
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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
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MuCap Strategy 12 Precision technique Clear Interpretation Clean stops in H 2 Impurities < 10 ppb Protium D/H < 10 ppb All requirements simultaneously
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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 2 2.0 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 )
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MuCap Strategy Gas continuously purified TPC monitors impurities Impurity doping calibrates effect 14 2004: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
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Experiment at PSI 15 Kicker Separator Quadrupoles MuCap detector TPC Slit E3 beamline Muon On Request
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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 -2 / ~10 -6 /
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Time Distributions are Consistent No azimuth dependence 17 fitted is constant Data run number (~3 minutes per run) 4/6/2012 17 Run groups
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Disappearance Rate Disappearance Rate 18
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Determination of S 19 molecular formation bound state effect MuCap: precision measurement MuLan
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Capture Rate S (MuCap) = 714.9 ± 5.4 stat ± 5.1 syst s -1 S (theory) = 712.7 ± 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) -1.275 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
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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
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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 ± 1.4 10 4 /s Saclay 11.1 ± 1.9 10 4 /s TRIUMF
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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
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Part III: Heavy Search 24 Ideas only ++ + 12 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
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Part III: Heavy at PSI? 25 Ideas only Early experiment: + 3 He → t + |U h | 2 ≤ 10 -3 Key improvements MuSun TPC size and cryo operation Resolution Digitizer and DAQ Detection ? Large improvement potential
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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
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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
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