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MuCap: From first results to final precision on determining g P Brendan Kiburg 2008 APS April Meeting April 12 th, 2008
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Ordinary Muon Capture is a basic weak charged-current process Process Probes Electroweak Current –Connects with QCD, nucleon structure –Tests SM symmetries q 2 << M W 2, and the hadronic current is parameterized by form factors The Physics of MuCap µ - + p µ + n : rate S, q 2 =-0.88 m µ 2
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g P determined by chiral symmetry of QCD: g P = (8.74 0.23) – (0.48 0.02) = 8.26 0.23 ChPT leading order one loop two-loop <1% g P basic and experimentally least known nucleon form factor solid QCD prediction (2-3% level) 30 years of experiments, no unambiguous results g P basic and experimentally least known nucleon form factor solid QCD prediction (2-3% level) 30 years of experiments, no unambiguous results g P is the least well known form factor Experiments: Proton form factors precisely known from SM symmetries and data (electron scattering, beta decay) Theory: apart from g P
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The muon capture rate depends on its environment pμ ↑↓ singlet (F=0) S ~ 710 s -1 μ ppμ para (J=0)ortho (J=1) λ op ppμ ortho ~ 3/4 S para ~ 1/4 S cZcZ μZ Z is an elemental or isotopic impurity (C,N,O or d) Z ~ Z 4 S
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Lifetime method –10 10 →e decays – measure to 10ppm, S = 1/ - 1/ to 1% 1% LH 2 density makes interpretation unambiguous Active imaging target (TPC) avoids wall stops Online monitoring demonstrates elemental purity <10 ppb Isotope separator produces pure “protium” MuCap Experimental Strategy log(counts) t e -t μ+μ+ μ – S reduces lifetime by 10 -3 → e
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Results S MuCap = 725.0 13.7 stat 10.7 sys s -1 (MuCap 2007) g P = 7.3 ± 1.1 S theory = 710.6 s -1
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MuCap result nearly model independent First precise and unambiguous result Final result (’06 and ’07 data) will reduce g P error twofold MuCap result nearly model independent First precise and unambiguous result Final result (’06 and ’07 data) will reduce g P error twofold g P Landscape after MuCap 07 Before MuCap, experiments inconclusive and mutually inconsistent MuCap - + p + n +
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Several upgrades were needed to reach the final precision Source 2007 Uncertainty (s -1 ) Projected Final Uncertainty (s -1 ) Upgrade Z > 1 impurities5.02CHUPS, FADC µd diffusion1.60.5Isotope Separator µp diffusion0.5 µ + p scattering31 µ pileup veto eff.31 Analysis Methods52 Muon kinetics5.82Neutron Counters Systematic10.73.8 Statistical13.73.7Kicker, MuLan
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CHUPS FADC upgrade on all TPC channels Z>1 Impurities reduced and measured Circulating Hydrogen Ultrahigh Purification System (CHUPS) Gas chromatography c N, c O < 5 ppb, c H2O <10 ppb Diagnostic in TPC Imp. Capture x z t
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Several upgrades were needed to reach the final precision Source 2007 Uncertainty (s -1 ) Projected Final Uncertainty (s -1 ) Upgrade Z > 1 impurities5.02CHUPS, FADC µd diffusion1.60.5Isotope Separator µp diffusion0.5 µ + p scattering31 µ pileup veto eff.31 Analysis Methods52 Muon kinetics5.82Neutron Counters Systematic10.73.8 Statistical13.73.7Kicker, MuLan
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µp + d d + p (134 eV) large diffusion range of d < 1 ppm isotopic purity required Cap Unique Capabilities: p, d diffusion Diagnostic: – vs. -e vertex cut –2007 Result Data: c d = 1.49 ± 0.12 ppm AMS: c d = 1.44 ± 0.15 ppm On-site isotopic separator c d < 0.010 ppm ! –AMS, ETH Zurich e-e- e-e- pp p dp d or to wall -e impact par cut –AMS, ETH Zurich
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Several upgrades were needed to reach the final precision Source 2007 Uncertainty (s -1 ) Projected Final Uncertainty (s -1 ) Upgrade Z > 1 impurities5.02CHUPS, FADC µd diffusion1.60.5Isotope Separator µp diffusion0.5 µ + p scattering31 µ pileup veto eff.31 Analysis Methods52 Muon kinetics5.82Neutron Counters Systematic10.73.8 Statistical13.73.7Kicker, MuLan
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Muon-On-Demand concept Cap Unique Capabilities: Muon-On-Demand Beamline Single muon requirement (to prevent systematics from pile-up) This limits the accepted rate to ~ 7 kHz, PSI beam can provide ~ 70 kHz -- +12.5 kV -12.5 kV Kicker Plates 50 ns switching time detector TPC Fig will be improved ~3 times higher rate dc kicked 2-Dec-2005 Lan kicker TRIUMF rf design 1.6*10 10 good kicked mu-e pairs
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Outlook log(counts) time μ+μ+ μ – 20 ppm 10 ppm 1 ppm ?? 30 ppm 10 ppm 2007 2008-2009 projected MuLan MuCap Future: MuSun needs both, g P and precision lifetimes Hardware upgrades address systematic issues Data is already collected, analysis underway
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MuCap studies the weak charged current : Transition Amplitude : Lepton Current : Nucleon Current : p n q 2 = -0.88m μ 2 << M W 2 n p -- W Weak current probe of the nucleus
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The pseudoscalar form factor g P is the least well known. G-Parity g P only known to about 50% !! Beta Decay Proton EM form Factor, CVC Electron Scattering
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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 pp 100% LH 2 pp pp P pp O 1 % LH 2 time ( s) λ pp MuCap
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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 2 2.0 kV/cm drift field ~5.4 kV on 3.5 mm anode half gap bakeable glass/ceramic materials
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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
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“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 (EFT/SNPA) high precision feasible by Cap technique and careful optimization model-independent connection via EFT & L 1A MEC EFT L 1A proposal end 2007 “MuSun”
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