TWIST – the TRIUMF Weak Interaction Symmetry Test

1. TWIST – the TRIUMF Weak Interaction Symmetry Test A precision study of the m+ decay spectrum • Designed to achieve ~ 0.01% in the shape of the m decay spectrum • Several data sets of 109 events each • A precision test of the weak interaction in the Standard Model 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 § Deceased Graduate Students † also UVic ‡ also UNBC ‡ ‡ also Saskatchewan † † also LANL

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

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

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

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

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

9. Two weak bosons with mass eigenstates M1 and M2 Left/Right SymmetricExtensions of the Standard Model Parity violation at low energy is presumably due to In general, the models may include a CP violating phase (w), and a left/right mixing parameter z

10. For Left/Right Symmetric extensions For • r is sensitive to the Left/Right mixing • to the mixing and to the WRmass d and h are unchanged by Left/Right extensions with manifest symmetry A measurement of r and x determines the WR mass and its mixing

11. D0 & CDF with various assumptions re CKMR Left/Right Mixing constraints – Anticipated TWIST Sensitivity Anticipated TWIST sensitivity due only to the Pmx measurement Anticipated TWIST r result z (left/right Mixing) Manifest l/r symmetry Discovery potential WR Mass (GeV)

12. Complementary b decay p pbar collider m decay

13. The Experiment • Highly polarized muons enter the spectrometer one at a time • Unbiased trigger on muon entering system • Data sets of 109 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 m Planar drift chambers sample positron track Use 44 drift planes, and 12 PC planes

15. m e+ Typical decay event

16. Analysis Concept • Fit real data to Monte Carlo generated data • many effectsof 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 r, d, x and h used in MC generation • can be done in straightforward way • avoids human bias in analysis of systematics

17. is the fit parameter where - number in momentum/angle bin i Generate m beam, track to stop, get e+ kinematics from box, track e+ through detector lMC hidden r,d,x,h Fit data to this spectrum Determine Dr, Dd, Dx and Dh Open Safe Technology WestGrid: 1000*3GHz Spectrum is linear in r, h, x and xd so fit

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

19. Systematics study status Sample from correlated data to data fits Preliminary Long list at this level – No showstopper found

20. Timeline • 6x109 muon decay events are in hand • complete 10-3 analysis this summer! • publish determination of randd • 2004 data run • data on Pmxat 10-3(andh?) 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: • randd (this summer) • Pmx (Data during the summer/fall of 2004) • Final precision on randd and Pmx 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 complementsb decay experiments and direct searches at the Tevatron

22. Left/Right Symmetric Extensions to the Standard Model Expect a non zero gRR and gLR 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 • >> 1011m’s in final sample • - can loosen many cuts presently used! • for example, tof(removes cloud m’s) and • target stop(removes stops in depolarizing materials) Existing limit <2.6x10-6 (1x10-10) bracket # is for particular decay of X0

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

25. Data sets taken 2002 & 2003 {S~6x109 triggers on tape} Goals r and d at 10-3 systematics at same level( make the effect large) m 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 (m’s far up/downstream) alignment Stopping target material(depolarization) determine how to move to Pmx at 10-3 and all at 10-4 Sample size usually ~300M triggers  ~58M useful events r and d at ~6x10-4{statistics} smaller samples for alignment, GEANT verification etc.

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

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

28. TWIST – RF Cuts Flight time through beamline • 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 Backgrounds (extrapolated from higher momentum) Cloud Muons polarization ~ -0.3 flux ~ 1% p+ e+