Docstoc

A Two Body Decay Search in the TWIST Spectrum

Document Sample
A Two Body Decay Search in the TWIST Spectrum Powered By Docstoc
					Introduction    TWIST Decay Spectra   Fitting Procedure   Systematic Effects   Results   Conclusions




               A Two Body Decay Search in the TWIST
                            Spectrum

                                       R. Bayes 1 2
                              For the T WIST Collaboration
                                   rbayes@triumf.ca

                                      1 Department  of Physics
                                       University of Victoria
                                      2 TRIUMF,     Vancouver


                          Fundamental Symmetries Workshop
                                   July 10, 2010

Ryan Bayes                                                                                     UVIC
T WIST Rare Decays
Introduction   TWIST Decay Spectra   Fitting Procedure   Systematic Effects   Results   Conclusions




Outline

       Introduction

       TWIST Decay Spectra

       Fitting Procedure

       Systematic Effects

       Results

       Conclusions


Ryan Bayes                                                                                    UVIC
T WIST Rare Decays
Introduction   TWIST Decay Spectra    Fitting Procedure        Systematic Effects        Results   Conclusions




Flavour Violation in Muon Decays


                                                      General cLFV decays in
Standard model muon decay                             vacuum
                                 e+
 µ+                                                            flavour symmetry breaking
               W+                                              results in the production of a
                                                               boson
                     νµ
                     ¯           νe                                                 e+

        flavour symmetry an                                µ+
        experimental requirement
                                                                                    X0



Ryan Bayes                                                                                               UVIC
T WIST Rare Decays
Introduction          TWIST Decay Spectra   Fitting Procedure   Systematic Effects           Results                              Conclusions




Kinematics of Two Body Decays
           Signal composed of decay positrons recoiling off X 0 at a
           single momentum                                            ×103
                                                                                                Entries
                                                                                                Mean
                                                                                                RMS
                                                                                                          h_x
                                                                                                                   4.511092e+11
                                                                                                                          37.08
                                                                                                                           10.6




                                                                    400
                                                                    350
         mX = 0 global symmetry breaking                            300
                                                                    250
                                                                    200
                                                                    150
                                                                    100
                                                                     50
                                                                      0
                                                                      10 15 20 25 30 35 40 45 50 55
                                                                                     Momentum (MeV/c)     h_x




                                                                       ×103
                                                                                                Entries         1.109234e+09
                                                                                                Mean                    36.98
                                                                                                RMS                     10.55




                                                                   400
                                                                   350
         mX > 0              local symmetry breaking               300
                                                                   250
                                                                   200
                                                                   150
                                                                   100
                                                                    50
                                                                     0 15 20 25 30 35 40 45 50 55
                                                                     10
                                                                                Momentum (MeV/c)



                    Special case: In the presence of SUSY R-Parity breaking 1
                                    ∂Γ
                                          ∝ (1 + A cos θ) where A = ±Pµ
                                  ∂ cos θ
               1
                   M. Hirsch and A. Vicente, PRD 79,(2009) 055023
Ryan Bayes                                                                                                                              UVIC
T WIST Rare Decays
Introduction   TWIST Decay Spectra   Fitting Procedure   Systematic Effects   Results   Conclusions




TWIST Experiment


                                                            44 planar drift chambers(DC),
                                                            12 proportional chambers(PC
                                                            detector contained in 2 Tesla
                                                            solenoidal magnet
                                                            29.6 MeV/c muons stop in
                                                            high purity metal foil
                                                            Decay positrons tracked
                                                            through symmetric DC stack.



Ryan Bayes                                                                                    UVIC
T WIST Rare Decays
Introduction    TWIST Decay Spectra   Fitting Procedure   Systematic Effects   Results   Conclusions




Detector Operation

               Dimensions known to parts in 105 .
               Magnetic Field known to 0.5 Gauss.




Ryan Bayes                                                                                     UVIC
T WIST Rare Decays
Introduction    TWIST Decay Spectra   Fitting Procedure   Systematic Effects   Results   Conclusions




Detector Operation

               Dimensions known to parts in 105 .
               Magnetic Field known to 0.5 Gauss.




Ryan Bayes                                                                                     UVIC
T WIST Rare Decays
Introduction    TWIST Decay Spectra   Fitting Procedure   Systematic Effects   Results   Conclusions




Detector Operation

               Dimensions known to parts in 105 .
               Magnetic Field known to 0.5 Gauss.




Ryan Bayes                                                                                     UVIC
T WIST Rare Decays
Introduction   TWIST Decay Spectra   Fitting Procedure                Systematic Effects                              Results                 Conclusions




TWIST Analysis
                                                                  simulation of the detector used
        Data spectrum fit to a sum...
                                                                  to account for reconstruction
                                                                  biases and efficiencies
                 =

                                                            4
                                                          10
                                                             3
                                                          10
                                                          102
                                                           10
               +∆ρ×                                         1
                                                             1

                                                         co 0.8                                                                                    3
                                                           sθ   0.6
                                                                      0.4                                                                 2
                                                                            0.2                                                                - yp rec
                                                                                  -0                                             1      = p dec
                                                                                                                                                a

                                                                                    -0.2                                    0   ∆ p tot
                                                                                        -0.4                           -1
                                                                                            -0.6
                                                                                                -0.8             -2
                                                                                                       -1   -3



     +∆ξ×                  +∆ξδ×                                  Long lived X 0 signal
                                                                  dominated by the detector
                                                                  response
Ryan Bayes                                                                                                                                                UVIC
T WIST Rare Decays
Introduction   TWIST Decay Spectra       Fitting Procedure    Systematic Effects     Results    Conclusions




Spectra Used in Search


           All data from TWIST                               Events collected after cuts
           experiment combined for fit                             Silver           2.96 ×108
           Simulated muon decay used                          Aluminum             2.46 ×108
           as background                                           Total           5.42 ×108
           The detector response models
                                                             Estimated Branching Ratio
           µ → e+ X 0 signal.
                          Γ(µ →e     +
           Determine B = Γ(µ+ →e+ νXνµ )
                                      )     +   0
                                                                    σ ∼ 100 - 200 keV/c
                                   e¯
           from response amplitude                                  B∝      √σ
                                                                                   ∼ O(10−6 )
                                                                              N




Ryan Bayes                                                                                            UVIC
T WIST Rare Decays
Introduction                          TWIST Decay Spectra             Fitting Procedure                         Systematic Effects                                  Results      Conclusions




Validation of Method
       Large signal added to simulation
                                    ×10                                                                                                    ×10
                                      -3                                                                                                     -3
           Production Ratio




                                                                                          Normalized Counts Background Subtracted
                                                                                                                                    0.06
                              0.8

                                                                                                                                    0.05

                              0.6
                                                                                                                                    0.04

                                                                                                                                    0.03
                              0.4

                                                                                                                                    0.02
                              0.2
                                                                                                                                    0.01


                               0                                                                                                       0

                                                                                                                                    -0.01
                                28        28.5   29   29.5   30 30.5 31 31.5 32                                                         28       28.5   29   29.5   30   30.5 31 31.5 32
                                                              Peak Momentum (MeV/c)                                                                                       Momentum (MeV/c)


                              Expected B = 7.6 × 10−4
Ryan Bayes                                                                                                                                                                             UVIC
T WIST Rare Decays
Introduction                      TWIST Decay Spectra          Fitting Procedure                                           Systematic Effects    Results         Conclusions




Treatment of Systematic Effects
                       Systematic effects are smooth Exception: Signals at endpoint
                       changes in the spectrum
                           Can only affect signal       Decay endpoint very sensitive
                           amplitude                    to systematic effects
                                Absorbed by decay
                                parameter corrections                                                                  Changes in endpoint look like
                                                                                                                       µ+ → e+ X 0 signal
#" ( ! 10 4)




                 95

                 94
                                                                                                                     ×10
                                                                                                                       -6
                 93                                                                                            30




                                                                                      MC - Data (normalized)
                 92                                                                                            25
                 91                                                                                            20
                 90
                      15   20     25   30    35   40    45       50           55
                                                                                                               15
                                                         Momentum of Signal (MeV/c)
                                                                                                               10
                                                                                                                5
# $ ( ! 10 4)




                101
                                                                                                                0
                100

                 99
                                                                                                                -5
                 98                                                                                            -10
                 97                                                                                            -15
                 96                                                                                            -20
                      15   20     25   30    35   40    45       50           55                                       52.4       52.6    52.8   53    53.2     53.4
                                                         Momentum of Signal (MeV/c)
                                                                                                                                                  Momentum (MeV/c)
Ryan Bayes                                                                                                                                                             UVIC
% ( ! 10 4)




                 70

T WIST Rare Decays
   69
Introduction   TWIST Decay Spectra   Fitting Procedure                                          Systematic Effects                    Results                  Conclusions




Branching Ratios
                                                                                                                                                        Mass of X0 (in MeV/c2 )
                                                                                                     80                  70            60              50      40       30 20
                                                                  25




                                       Branching Ratio (× 10 )
      Signals fit in 50 keV/c




                                       6
                                                                                       90% C.I., A = -1
                                                                  20
                                                                                       90% C.I., A = 0
      steps                                                       15                   90% C.I., A = +1

      Confidence intervals                                         10

                                                                  5
      from method by                                              0
                                                                   10             15            20             25        30           35             40        45       50
      Feldman and Cousins a                                                                                                                          Signal Momentum (MeV/c)

                                                                                                                                                 Mass of X0 (in MeV/c2 )
                                                                             24            22             20        18           16    14         12   10 8 6 4 2      0
                                       Branching Ratio (× 10 )
                                       6                         120
                                                                                       90% C.I., A = -1
                                                                 100
                                                                                       90% C.I., A = 0
                                                                  80                   90% C.I., A = +1
                                                                  60
                                                                  40
                                                                  20
                                                                  0
                                                                        50               50.5              51             51.5              52             52.5        53
                                                                                                                                                     Signal Momentum (MeV/c)




 a
                                                                   Systematic errors included in confidence
     PRD 57, (1998),3873
                                                                   band
Ryan Bayes                                                                                                                                                                 UVIC
T WIST Rare Decays
Introduction          TWIST Decay Spectra   Fitting Procedure   Systematic Effects   Results   Conclusions




Results Summary
                    Average B compiled for p ∈[20 MeV/c,52 MeV/c]

                        Decay signal                             90% Upper Limit
                        A=0                      Average           8.1 ×10−6
                                                 Endpoint          3.3 ×10−5
                        A = -1                   Average           8.4 ×10−6
                                                 Endpoint          6.7 ×10−5
                        A = +1                   Average           5.7 ×10−6
                                                 Endpoint          8.5 ×10−6
                        Bryman, 1986 2           Average            3 ×10−4
                        Jodidio, 1986 3          Endpoint          2.5 ×10−6
               2
                   PRL 57, (1986) 2787
               3
                   PRD 34, (1986) 1967
Ryan Bayes                                                                                           UVIC
T WIST Rare Decays
Introduction     TWIST Decay Spectra   Fitting Procedure   Systematic Effects   Results   Conclusions




Conclusions


               5 × 108 muon decay events used to estimate
                    Γ(µ+ →e+ 0 )
               B = Γ(µ+ →e+ νXνµ )
                             e¯

               Discriminate isotropic and anisotropic decay signals
                    First direct measurement
               Improved upper limit in massive X 0 case by a factor of 32
                    No evidence of signals when A ≥ 0
                    Average of 90% upper limit between 5.7 and 8.4 ppm
               Limits set on massless X 0
                    90% upper limit between 8.5 and 33 ppm



Ryan Bayes                                                                                      UVIC
T WIST Rare Decays
Introduction   TWIST Decay Spectra   Fitting Procedure   Systematic Effects    Results       Conclusions




The T WIST Collaboration
       TRIUMF
       Ryan Bayes ♣                  Alberta                            Kurchatov Institute
       Yuri Davydov                  Andrei Gaponenko                   Vladimir Selivanov
       Wayne Faszer                  Robert MacDonald
                                                                        Texas A&M
       Makoto Fujiwara               British Columbia                   Carl Galiardi
       David Gill                    James Bueno                        Bob Tribble
       Alexander Grossheim           Mike Hasinoff
       Peter Gumplinger                                                 Valpariso
       Anthony Hillairet ♣           Montreal                           Don Koetke
       Robert Henderson              Pierre Depommier                   Shirvel Stanislaus
       Jingliang Hu
                                     Regina                               graduate student
       Glen Marshall
                                     Ted Mathie                           graduated
       Dick Mischke
                                     Roman Tacik                        ♣ also UVic
       Konstantin Olchanski
       Art Olin ♣
       Robert Openshaw                         Funding Support from NSERC and US DOE
       Jean-Michel Poutissou
                                               Additional support from TRIUMF, Russian
       Renée Poutissou
                                               Science Ministry, and NRC
       Grant Sheffer
       Bill Shin                               Computing resources provided by WestGrid
Ryan Bayes                                                                                         UVIC
T WIST Rare Decays

				
DOCUMENT INFO
Shared By:
Categories:
Stats:
views:16
posted:2/14/2011
language:English
pages:16