1. TWIST – the TRIUMF Weak Interaction Symmetry Test  Designed to achieve ~ 0.01% in the shape of the  decay spectrum  Several data sets of 10 9 events each  A precision test of the weak interaction in the Standard Model A precision study of the  + decay spectrum D.R.Gill TRIUMF drgill@triumf.ca

2. Outline  Motivation  Overview of the experiment  Analysis status  Timeline

3. The TWIST Collaboration TRIUMF Ryan Bayes† Yuri Davydov Jaap Doornbos Wayne Faszer David Gill Peter Gumplinger Robert Henderson Jingliang Hu John A. Macdonald § Glen Marshall Dick Mischke†† Art Olin Robert Openshaw Tracy Porcelli‡ Jean-Michel Poutissou Renee Poutissou Grant Sheffer Bill Shin ‡ ‡ Alberta Andrei Gaponenko Peter Kitching Rob MacDonald Maher Quraan Nathan Rodning § John Schaapman Glen Stinson British Columbia Blair Jamieson Mike Hasinoff Montreal Pierre Depommier Regina Ted Mathie Roman Tacik Kurchatov Institute Vladimir Selivanov Vladimir Torokhov Texas A&M Carl Gagliardi Jim Musser Robert Tribble Maxim Vasiliev Valparaiso Don Koetke Paul Nord Shirvel Stanislaus Graduate Students § Deceased ‡ also UNBC† also UVic‡ ‡ also Saskatchewan† † also LANL

4. … Most general interaction does not presuppose the W S,V,T = scalar, vector or tensor interactions R, L = right and left handed leptons (e,  or  ) TWIST Motivation – testing the Standard Model e±e± ±±

5. Expanded in terms what have become known as the Michel parameters e + Reduced Energy e + angle (Cosine) These shape parameters of the spectrum are what TWIST is studying! Modified by radiative corrections. Now several calculations to 2 nd order exist {hep-ph/0206036} See Arbuzov JHEP0303:063,2003 rate

6. Plenty of room for surprises Present knowledge of couplings; SM PDG

7. The Michel Parameter -  The parameter  largely determines the shape of the positron energy spectrum The effect of large deviations in  on the shape of the energy spectrum. The effect shown is roughly 500 times the TWIST sensitivity -positive definite terms  fewer required experiments -can conspire so  = ¾  measure parameters simultaneously

8. Existing limits - Discovery region Anticipated TWIST sensitivity to R-H currents in muon decay TWIST final PDG TWIST preliminary  

9. Left/Right Symmetric Extensions of the Standard Model Two weak bosons with mass eigenstates M 1 and M 2 Parity violation at low energy is presumably due to In general, the models may include a CP violating phase (  ), and a left/right mixing parameter 

10. For Left/Right Symmetric extensions  is sensitive to the Left/Right mixing  to the mixing and to the W R mass  and  are unchanged by Left/Right extensions with manifest symmetry A measurement of  and  determines the W R mass and its mixing For

11. W R Mass (GeV)  (left/right Mixing) Left/Right Mixing constraints – Anticipated TWIST Sensitivity Anticipated TWIST  result Manifest l/r symmetry Discovery potential Anticipated TWIST sensitivity due only to the P   measurement D0 & CDF with various assumptions re CKM R

12.  decay p pbar collider  decay Complementary

13. The Experiment  Highly polarized muons enter the spectrometer one at a time  Unbiased trigger on muon entering system  Data sets of 10 9 muon decay events in roughly two weeks (modern computing)  The experiment is systematics limited. The high data rate is a must for systematics studies The large acceptance makes possible measurements of Michel parameters under differing conditions – therefore improving the reliability of the result.

14. Chambers & half detector Planar drift chambers sample positron track Use 44 drift planes, and 12 PC planes 

15. Typical decay event  e+e+

16. Analysis Concept Fit real data to Monte Carlo generated data many effects of reconstruction cancel MC must reproduce the detector response well TWIST detector thin so effects small Useful for systematics search/study systematics comparisons can be done directly fit data to data or MC to MC Hide values of  and  used in MC generation can be done in straightforward way avoids human bias in analysis of systematics

17. Technology Spectrum is linear in  and  so fit is the fit parameter where - number in momentum/angle bin i  MC  hidden Generate  beam, track to stop, get e + kinematics from box, track e + through detector Fit data to this spectrum Determine  and  Open Safe WestGrid: 1000*3GHz

18. Type 1 (Monte Carlo or data) Analysis 1 (Monte Carlo or data) Analysis 1 Fit mc to mc or data to data Type 1 (Monte Carlo or data) Analysis 1 Type 1 (Monte Carlo or data) Fit uncorrelated samples Detect & evaluate systematic Fit correlated samples Enhance & evaluate systematic Use in systematics studies Type 2 Analysis 2

19. Systematics study status Preliminary Sample from correlated data to data fits 10 -3  Alignment Translation0.100.080.135.8 Rotation0.070.050.283.9 Chamber HV0.050.030.062.6 Cell Geometry0.280.210.3616. Gas Density0.150.110.208.5 Calibration Trigger time0.130.090.167.0 Long list at this level – No showstopper found

20. Timeline  6x10 9 muon decay events are in hand  complete 10 -3 analysis this summer!  publish determination of  and   2004 data run  data on P   at 10 -3  and  this summer/fall  at least 3 PhD’s granted by 2005  Final parts in10 -4 data & publications:2005/2006  Need More Graduate Students Now

21. Summary  The TWIST experiment is near end of phase 1  Anticipate preliminary measurements at ~0.1% of:   and  (this summer)  P   (Data during the summer/fall of 2004)  Final precision on  and  and P   at ~  0.02%  TWIST is exploring significant new space where evidence may be found to challenge the standard model  For left/right symmetric models, TWIST has a mass reach which is comparable to - and which complements  decay experiments and direct searches at the Tevatron

22. Left/Right Symmetric Extensions to the Standard Model Expect a non zero g RR and g LR If tensor and scaler couplings are excluded (as unnecessary) from these extensions, then-

23. ‘Familons’ Search for a bump in the momentum spectrum long lived  narrow peak zero mass  at spectrum upper end >> 10 11  ’s in final sample - can loosen many cuts presently used! for example, tof(removes cloud  ’s) and target stop(removes stops in depolarizing materials) Existing limit <2.6x10 -6 (1x10 -10 ) bracket # is for particular decay of X 0

24. Chiral fermions localized at different points in extra dimension; “split fermions” geometrical explanation of mass hierarchy Extra dimensions Chang, Ho and Ng {PRD66,(2002)076004} 5 th dimension Fermion L(2) Fermion R(1) Our Brane Improvements in  and  to 10 -3 or 10 -4 will “define width of split”  not part of TWIST program - PSI

25. Sample size usually ~300M triggers  ~58M useful events  and  at ~6x10 -4 {statistics} smaller samples for alignment, GEANT verification etc. Goals  and  at 10 -3 systematics at same level( make the effect large)  source (beamline tune) detector performance (HV lowered from optimum) up/downstream symmetry (insert “junk” downstream) momentum scale (modify solenoid field) analysis codes (high and low rate data) GEANT verification (  ’s far up/downstream) alignment Stopping target material(depolarization) determine how to move to P   at 10 -3 and all at 10 -4 Data sets taken 2002 & 2003  6x10 9 triggers on tape}

26. GEANT verification eloss, mulscat and muon range slides go here!

27. Spectrum shape analysis procedure Concept and Technology of last two steps! Classify event(31 types) Fit helix to extract momentum vs angle spectrum Compare different samples and different analyses Extract systematic corrections or errors Biases?

28. TWIST – RF Cuts Backgrounds (extrapolated from higher momentum) Cloud Muons polarization ~ -0.3 flux ~ 1% Flight time through beamline ++ e+  Flight time through the channel show the time that pions are stopped in the pion production target prior to their decay  RF period ~ 1.5 pion lifetimes makes the TRIUMF beam perfect for TWIST