New results on muon radiative decay

New results on muon radiative decay (PhD thesis Emmanuel Munyangabe, Aug 2012) Dinko Počanić University of Virginia APS Division of Nuclear Physics Fall 2012 Meeting Newport Beach, CA, 24 27 October 2012

D. Počanić (UVa) Muon radiative decay: Outline 26 Oct 12 (DNP12) 2 / 13 Outline PIBETA/PEN program, motivation and apparatus Basic theory of muon decay Results of the new analysis

D. Počanić (UVa) Muon radiative decay: Program and motivation 26 Oct 12 (DNP12) 3 / 13 PIBETA/PEN program of π, µ rare decay measurements π + π 0 e + ν e.................................. PIBETA ( 99 01) SM checks via q-l universality and CKM unitarity π + e + ν e γ(or e + e ).......... PIBETA ( 99 04), PEN ( 06 10) F A /F V, π polarizability (χpt calibration) tensor coupling besides V A (?) µ + e + ν e ν µ.................................. TWIST ( 03 04) departures from V A in L weak µ + e + ν e ν µ γ(or e + e )............PIBETA ( 04), PEN ( 06 10) departures from V A in L weak { π + e + PEN ( 06 10) ν e...................................... PiENu ( 06 ) e-µ universality pseudoscalar coupling besides V A ν sector anomalies, Majoron searches, m h+, PS l-q s, V l-q s,... search for signs of SUSY (MSSM)

D. Počanić (UVa) Muon radiative decay: Program and motivation 26 Oct 12 (DNP12) 4 / 13 Observed pion and muon decays Decay Branching ratio Decay label π + µ + ν(γ) 0.9998770 (4) (π µ2 ) τ µ + νγ 2.00 (25) 10 4 (π µ2γ ) 26 ns e + ν(γ) 1.230 (4) 10 4 (π e2 ) e + νγ 7.39(5) 10 7 (π e2γ ) π 0 e + ν 1.036 (6) 10 8 (π e3, π β ) e + νe + e 3.2 (5) 10 9 (π e2ee ) π 0 γγ 0.98798 (32) τ e + e γ 1.198 (32) 10 2 (Dalitz) 85 as e + e e + e 3.14 (30) 10 5 e + e 6.2 (5) 10 8 µ + e + ν ν(γ) 1.0 τ e + ν νγ 0.014 (4) 2.2 µs e + ν νe + e 3.4 (4) 10 5

D. Počanić (UVa) Muon radiative decay: Apparatus 26 Oct 12 (DNP12) 5 / 13 PIBETA/PEN apparatus stopped π + beam active target counter 240-detector, spherical pure CsI calorimeter central tracking beam tracking digitized waveforms stable temp./humidity BC π + beam VACUUM pure CsI mtpc AD AT PMT PEN detector 2009-10 PH MWPC1 MWPC2 ~3 m flightpath 10 cm

D. Počanić (UVa) Muon radiative decay: Theory of muon decay 26 Oct 12 (DNP12) 6 / 13 Muon decay parameters: µ e ν e ν µ d 2 Γ dx d(cos θ) = m µ 4π 3 W eµg 4 F 2 x 2 x0 2 [ F IS (x) + P µ + cos θ F AS (x) ] [ 1 + P ] e +(x, θ) ˆζ Isotropic part: Anisotropic part: F IS (x) = x(1 x) + 2 9 ρ(4x 2 3x x 2 0 ) + η x 0 (1 x) F AS (x) = 1 3 ξ x 2 x 2 0 (1 x + 23 [ )]) δ 4x 3 + ( 1 x 20 1 where x = E e E max, x 0 = m e E max, and E max m µ 2,.

D. Počanić (UVa) Muon radiative decay: Theory of muon decay 26 Oct 12 (DNP12) 7 / 13 Parameters of radiative muon decay: µ e ν e ν µ γ d 3 B(x, y, θ) dx dy 2π d(cos θ) = f 1(x, y, θ) + ηf 2 (x, y, θ) + (1 4 3 ρ)f 3(x, y, θ) ρ = 3 4 3 4 [ g V LR 2 + g V RL 2 + 2 g T LR 2 + 2 g T RL 2 ] + R(gRL S g RL T + g LR S g LR T ) SM 3 4, η = where x = ( grl V 2 + glr V 2) + 1 ( glr S 8 + 2g LR T 2 + grl S + 2g RL T 2) ( + 2 glr T 2 + grl T 2) SM 0. E e E max and y = E γ E max.

D. Počanić (UVa) Muon radiative decay: New analysis 26 Oct 12 (DNP12) 8 / 13 Radiative muon decay, µ + e + ν νγ, new analysis of 2004 data (thesis E. Munyangabe) t = t e t γ CsI Time Coincidence Entries/0.5 ns 1200 1000 800 600 400 200 100 3 10 σ = 0.71 ns N0. of Events = 518813 ± 946 0-10 -8-6 -4-2 0 2 4 6 8 10 t = [t - t γ ] (ns) + 3 e 10 Signal MC Misid Events cut 80 Signal MC + Misid. events cos θ eγ 60 40 DATA(measured) 20 0-1 -0.8-0.6-0.4-0.2 0 0.2 0.4 0.6 0.8 1 Cos θ

D. Počanić (UVa) Muon radiative decay: New analysis 26 Oct 12 (DNP12) 9 / 13 Radiative muon decay, µ + e + ν νγ, new analysis of 2004 data (thesis E. Munyangabe) 60000 50000 40000 30000 cut Signal MC Misid Events Signal MC + Misid. events DATA(measured) E γ 20000 10000 0 15 20 25 30 35 40 45 50 55 Photon Energy [MeV] 40000 Signal MC E e + 35000 30000 25000 cut Misid Events Signal MC + Misid. events DATA(measured) 20000 Split clumps very well accounted for! 15000 10000 5000 10 15 20 25 30 35 40 45 50 55 Positron Energy [MeV]

D. Počanić (UVa) Muon radiative decay: New analysis 26 Oct 12 (DNP12) 10 / 13 RMD preliminary results: B exp (thesis E. Munyangabe) Preliminary RMD branching ratio for E γ > 10 MeV, θ eγ > 30 : B exp = 4.365 (9) stat (42) syst 10 3, 29 improved precision B SM = 4.342 (5) stat-mc 10 3 Systematic uncertainty budget: Quantity (based on > 500k RMD events) Rel. syst. uncert. (%) Photon energy calibration 0.73 Background subtraction 0.14 Positron energy threshold 0.26 Positron energy calibration 0.18 Photon energy threshold 0.41 Cosine opening angle 0.29 Time window selection 0.12 Misidentified events 0.03 Total relative syst. uncert. 0.96

D. Počanić (UVa) Muon radiative decay: New analysis 26 Oct 12 (DNP12) 11 / 13 RMD preliminary results: η (thesis E. Munyangabe) χ 2 18 16 14 12 10 8 6 4 η = 0.006 ± 0.017 χ 2 /NDF = 0.8 η: Most sensitive phase space subset: 13 MeV < E γ < 45 MeV, and 10 MeV < E e + < 43 MeV, yields: 2-0.08-0.06-0.04-0.02 0 0.02 0.04 0.06 0.08 η Quantity δ η Photon energy calibration 0.016 Background subtraction 0.003 Positron energy calibration 0.005 Cosine opening angle 0.006 Time window selection 0.002 Misidentified events 0.0003 Total systematic uncert. 0.018 η = 0.006 (17) stat (18) syst or, in terms of an upper limit: { 0.023 (68%CL) η < 0.029 (90%CL) Systematic uncertainty budget for η.

D. Počanić (UVa) Muon radiative decay: New analysis 26 Oct 12 (DNP12) 12 / 13 History of η 4 New world avg Our result is almost 4 more precise than the best previous experiment (Eichenberger et al, 84). 3 2 This work PDG world avg Eichenberger 1984 (Further improvement expected with PEN data) 1 Bogart 1967 0 η 0.2 0.4

D. Počanić (UVa) Muon radiative decay: New analysis 26 Oct 12 (DNP12) 13 / 13 Current and former PIBETA and PEN collaborators L. P. Alonzi a, K. Assamagan a, V. A. Baranov b, W. Bertl c, C. Broennimann c, S. Bruch a, M. Bychkov a, Yu.M. Bystritsky b, M. Daum c, T. Flügel c, E. Frlež a, R. Frosch c, K. Keeter a, V.A. Kalinnikov b, N.V. Khomutov b, J. Koglin a, A.S. Korenchenko b, S.M. Korenchenko b, M. Korolija d, T. Kozlowski e, N.P. Kravchuk b, N.A. Kuchinsky b, D. Lawrence h, W. Li a, J. S. McCarthy a, R. C. Minehart a, D. Mzhavia b,f, E. Munyangabe a, A. Palladino a,c, D. Počanić a, B. Ritchie h, S. Ritt a,c, P. Robmann g, O.A. Rondon-Aramayo a, A.M. Rozhdestvensky b, T. Sakhelashvili f, P. L. Slocum a, L. C. Smith a, N. Soić d, U. Straumann g, I. Supek d, P. Truöl g, Z. Tsamalaidze f, A. van der Schaaf g, E.P. Velicheva b, V.P. Volnykh b, Y. Wang a, C. Wigger c, H.-P. Wirtz c, K. Ziock a. a Univ. of Virginia, USA c PSI, Switzerland e Swierk, Poland g Univ. Zürich, Switzerland b JINR, Dubna, Russia d IRB, Zagreb, Croatia f IHEP, Tbilisi, Georgia h Arizona State Univ., USA Home pages: http://pibeta.phys.virginia.edu http://pen.phys.virginia.edu