Rare decay studies in the PEN experiment

Transcription

1 Rare decay studies in the PEN experiment Dinko Počanić University of Virginia 7th Int l Workshop on Chiral Dynamics Newport News, VA, 6 Aug 2012

2 D. Počanić (UVa) PEN experiment: Outline 6 Aug 12 (CD12) 2 / 25 Outline Prior results π + π 0 e + ν (π β decay) π + e + νγ (RPD) Radiative muon decay, µ + e + ν νγ (new) The π e2 decay, π + e + ν e Status and prospects Summary

3 D. Počanić (UVa) PEN experiment: Outline 6 Aug 12 (CD12) 3 / 25 Known and measured pion and muon decays Decay BR π + µ + ν (4) (π µ2 ) µ + νγ 2.00 (25) 10 4 (π µ2γ ) e + ν (4) 10 4 (π e2 ) e + νγ 7.39(5) 10 7 (π e2γ ) π 0 e + ν (6) 10 8 (π e3, π β ) e + νe + e 3.2 (5) 10 9 (π e2ee ) π 0 γγ (32) e + e γ (32) 10 2 (Dalitz) e + e e + e 3.14 (30) 10 5 e + e 6.2 (5) 10 8 µ + e + ν ν 1.0 e + ν νγ (4) e + ν νe + e 3.4 (4) 10 5

4 D. Počanić (UVa) PEN experiment: Outline 6 Aug 12 (CD12) 4 / 25 Recent measurements of π, µ allowed decay π + π 0 e + ν e PIBETA ( 99 01) SM checks related to 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)

5 D. Počanić (UVa) PEN experiment: Prior results 6 Aug 12 (CD12) 5 / 25 Prior results (the PIBETA experiment)

6 D. Počanić (UVa) PEN experiment: Prior results 6 Aug 12 (CD12) 6 / 25 PIBETA result for π + π 0 e + ν (π β ) decay [PRL 93, (2004)] B exp-t πβ = [1.040 ± (stat) ± (syst)] 10 8, B exp-e πβ = [1.036 ± (stat) ± (syst) ± (π e2 )] 10 8, McFarlane et al. [PRD 1985]: B = (1.026 ± 0.039) 10 8 SM Prediction (PDG): B = (90% C.L.) ( excl. rad. corr.) Most sensitive test of CVC/radiative corr. in a meson to date! PDG 2012: V ud = (22) PIBETA: V ud = (25) or V ud = (30).

7 D. Počanić (UVa) PEN experiment: Prior results 6 Aug 12 (CD12) 7 / 25 PIBETA result for π + e + νγ (RPD): QED IB terms: SM and SD V, A terms: A tensor interaction, too? Exchange of S=0 leptoquarks P Herczeg, PRD 49 (1994) 247

8 D. Počanić (UVa) PEN experiment: Prior results 6 Aug 12 (CD12) 8 / 25 Summary of PIBETA results on π eνγ [PRL 103, (2009)] F V = ± (14 ) F A = ± exp (F CVC V ) (16 ) a = 0.10 ± 0.06 (q 2 dep of F V ) ( ) < F T < % C.L. B πe2γ (E γ > 10 MeV, θ eγ > 40 ) = 73.86(54) 10 8 (17 ) Above results will be improved with the new PEN data analysis. Note: F V is related to pion polarizability and π 0 lifetime (at L.O.) α E = β M = (2.783 ± exp ) 10 4 fm 3 { τ π 0 = (8.5 ± 1.1) current PDG avg: 8.4 (4) s PrimEx PRL 10: 8.32 (23)

9 D. Počanić (UVa) PEN experiment: Rad. muon decay (new anal.) 6 Aug 12 (CD12) 9 / 25 Radiative muon decay: µ + e + ν νγ PIBETA: 2004 runs ( PEN: runs )

10 D. Počanić (UVa) PEN experiment: Rad. muon decay (new anal.) 6 Aug 12 (CD12) 10 / 25 Radiative muon decay, µ + e + ν νγ, (new analysis of 2004 data) CsI Time Coincidence Entries/0.5 ns σ = 0.71 ns N0. of Events = ± Signal MC Misid Events Signal MC + Misid. events cut DATA(measured) t = [t - (ns) + t γ ] e Cos θ cut Signal MC Misid Events Signal MC + Misid. events DATA(measured) cut Signal MC Misid Events Signal MC + Misid. events DATA(measured) Photon Energy [MeV] Positron Energy [MeV]

11 D. Počanić (UVa) PEN experiment: Rad. muon decay (new anal.) 6 Aug 12 (CD12) 11 / 25 RMD preliminary results, cont d. Preliminary result for RMD branching ratio (thesis E. Munyangabe): B exp = (9) stat. (42) syst. 10 3, 29 B SM = (5) stat-mc 10 3 (for E γ > 10 MeV, θ eγ > 30 ) χ η = ± χ 2 /NDF = η NB: preliminary results! Analysis of PS subset: 13 MeV < E γ < 45 MeV, and 10 MeV < E e + < 43 MeV, yields η= (17) stat. (18) syst., or η< (68%CL). 4 better than best previous experiment (Eichenberger et al, 84).

12 D. Počanić (UVa) PEN experiment: The π e2 decay 6 Aug 12 (CD12) 12 / 25 The π e2 decay: π + e + ν Primary motivation for PEN (data runs )

13 D. Počanić (UVa) PEN experiment: The π e2 decay 6 Aug 12 (CD12) 13 / 25 π + e + ν e decay (π e2 ): SM calculations; measurements Early evidence for V A nature of weak interaction. Modern SM calculations: Re/µ π Γ(π e ν(γ)) = = Γ(π µ ν(γ)) CALC (5) 10 4 Marciano and Sirlin, [PRL 71 (1993) 3629] (2) 10 4 Finkemeier, [PL B 387 (1996) 391] (1) 10 4 Cirigliano and Rosell, [PRL 99 (2007) ] Experimental world average [PDG] is about 40 less accurate: Γ(π e ν(γ)) Γ(π µ ν(γ)) EXP = 1.230(4) 10 4 ; PEN goal: R R Strong SM helicity suppression amplifies sensitivity to PS terms ( door for New Physics) by factor 2m π /m e (m u + m d ) tests lepton universality: in SM e, µ, τ differ by Higgs couplings only; there could also be new S or PS bosons with non-universal couplings (New Physics). R π e/µ

14 D. Počanić (UVa) PEN experiment: The π e2 decay 6 Aug 12 (CD12) 14 / 25 Reach of π e2 decay beyond the SM (New Physics) L NP = [ ± π + 2Λ 2 V ūγ α d ± [ ± π 2Λ 2 ūd ± S π 2Λ 2 A π 2Λ 2 P ] ūγ α γ 5 d ēγ α (1 γ 5 )ν ] ūγ 5 d ē(1 γ 5 )ν, (Λ i... scale of NP) CKM unitarity and superallowed Fermi nuclear decays currently limit: Λ V 20 TeV, and Λ S 10 TeV. At R π e/µ /Rπ e/µ = 10 3, π e2 decay is directly sensitive to: Λ P 1000 TeV and Λ A 20 TeV, and indirectly, through loop effects to Λ S 60 TeV. In general multi-higgs models with charged-higgs couplings λ eν λ µν λ τν, at 0.1 % precision, R π eµ probes m H ± 400 GeV.

15 D. Počanić (UVa) PEN experiment: The π e2 decay 6 Aug 12 (CD12) 15 / 25 MSSM calculations (R parity cons.) [Ramsey-Musolf et al., PR D76 (2007) ] CURRENT UL (90% c.l.) CURRENT UL (90% c.l.) minimal selectron, smuon masses: Re Μ SUSY R e Μ PEN GOAL lowest mass chargino: Re µ SUSY R e µ PEN GOAL Min mel,mµ L GeV CURRENT UL (90% c.l.) m GeV mχ1 slepton mass degeneracy: Re µ SUSY R e µ PEN GOAL Higgsino mass param s. µ, mũl : mel mµ L (R parity violating scenario constraints also discussed.)

16 D. Počanić (UVa) PEN experiment: Status and prospects 6 Aug 12 (CD12) 16 / 25 Other processes and limits; status of PEN From π eν, additional constraints on: pseudoscalar and vector leptoquarks, neutrino sector anomalies through lepton universality, heavy neutrinos. Expected improvements over prior PIBETA results on Radiative pion decay π eνγ (a critical PEN systematic): F V, F A, a, F T, Radiative muon decay, µ eν νγ (another key PEN systematic), limits on non-(v A) terms via: Branching ratio, Michel parameter η. Current status of PEN: Data acquisition runs in 2008, 2009, 2010 (completed). Collected: > 22 M π e events, > 200 M π µ e events. Comprehensive, blinded maximum likelihood analysis in progress.

17 D. Počanić (UVa) PEN experiment: Status and prospects 6 Aug 12 (CD12) 17 / 25 The 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 PH MWPC1 MWPC2 ~3 m flightpath 10 cm

18 0.5*tgt_wf.mu3.mean-0.5*tgt_wf.pi3.mean {tgt_wf.fitattempt==1 && tgt_wf.subtintegral_left<10e3 && tgt_wf.subtintegral_middle<170e3 && tgt_wf.subtintegral_right<40e3 && 0.5*tgt_wf.e3.mean-0.5*tgt_wf.mu3.mean>10 && 0.5*tgt_wf.e3.mean-0.5*tgt_wf.mu3.mean<70 && trak.ecsi[0]<48} χ 2 / ndf Constant 5 Pion decays in TGT (MeV) E e τ π µ = 26.21(5) ns trigger-weighted events / ns τ π e = 26.02(8) ns positron E vs t Time between pion and positron (ns) 0.3 / top: bottom: muons positrons pion decay time [ns] Events Measurement π decay curve t µ - t π (ns) D. Počanić (UVa) PEN experiment: Status and prospects 6 Aug 12 (CD12) 18 / 25

19 Mean RMS Underflow Overflow Integral Target waveform fitting: (1) Shape (filter) wf signals, (2) Use predicted π stop (DEG) and e + (PH) wf s, (3) Fit with 2 and 3-peak wf s; compare χ 2 values. Raw + shaped wf s Shaped wf s + predicted fits Mean Typical 2-peak π e event Blue trace: no third (muon) signal t (0.5 ns) t (0.5 ns) t (0.5 ns) Typical 3-peak π µ e event Blue trace: putative third (muon) signal t (0.5 ns) D. Počanić (UVa) PEN experiment: Status and prospects 6 Aug 12 (CD12) 19 / 25

20 D. Počanić (UVa) PEN experiment: Status and prospects 6 Aug 12 (CD12) 20 / 25 Selected PEN distributions (2008 data run) 2 peak χ π + µ + e χ 2 3 peak π + e Events per Cell decaytime (ns) π µ e π e χ π eνγ t = t e t γ PEN 2008 data P/B t (ns) PEN improvements over PIBETA data: suppression of muon decay events; superior P/B ratio for π eνγ; full GEANT4 description with synthetic MC data.

21 D. Počanić (UVa) PEN experiment: Status and prospects 6 Aug 12 (CD12) 21 / 25 Key PEN systematic: low E tail response 3 10 background background subtracted Entries subtracted 0 error error pie simulation 2008 π µ e (DIF bgd) π e background subtracted background Entries 0subtracted error error pie simulation total energy [MeV] total energy [MeV]

22 D. Počanić (UVa) PEN experiment: Status and prospects 6 Aug 12 (CD12) 22 / 25 C A C A D B D B RPD: SD + amplitude RPD: SD amplitude C D A B Thanks to low accidental bgds, and strong suppression of µ decays, RPD: IB amplitude PEN data will enable evaluation of region D in π + e + νγ decay (RPD), i.e., new information on SD.

23 D. Počanić (UVa) PEN experiment: Status and prospects 6 Aug 12 (CD12) 23 / 25 Constraints from PIBETA on pion FF s 150 χ 2 Contours F A Form Factor x σ 2σ 1σ Tight constraint on F V + F A (SD + term); weak constraint on F V F A Need to constrain SD! 100 F V CVC = 259(9) x 10-4 Region D in PEN! F V Form Factor x

24 D. Počanić (UVa) PEN experiment: Summary 6 Aug 12 (CD12) 24 / 25 Study of allowed π and µ decays in PEN A significant experimental effort is under way (in PEN and in other experiments) to make use of the unparalleled theoretical precision in the weak interactions of the lightest particles. Information obtained is complementary to expected collider results, and valuable for their proper interpretation. Improvements in precision for π eν, π eνγ (F V, FT ul ), and µ eν νγ. to be achieved in the near future. Great projects for graduate students and postdocs applications are invited.

25 D. Počanić (UVa) PEN experiment: Summary 6 Aug 12 (CD12) 25 / 25 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, E. Munyangabe a, 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: