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TWIST

TWIST. Goal: A high precision measurement of the positron ( T e ) and ( cos  e ) spectrum from -decay to test the SM predictions for the weak interaction. The T RIUMF W eak I nteraction S ymmetry T est. Outline. Physics motivation Discovery potential for TWIST Experimental method

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TWIST

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  1. TWIST Goal:A high precision measurement of the positron (Te) and (cose) spectrum from -decay to test the SM predictions for the weak interaction The TRIUMF Weak Interaction Symmetry Test

  2. Outline • Physics motivation • Discovery potential for TWIST • Experimental method • Analysis approach • Systematics studies • 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. TWISTphysics motivation -- test the Standard Model for -decay … Most general interaction does not presuppose the W • S,V,T = scalar, vector or tensor interactions • R, L=right and left handed leptons (e, m, or t)

  5. Couplings in the present Standard Model

  6. Current measured couplings --

  7. e e+ spectrum in x, cose Spectral shape in x, cose is characterized in terms of four parameters -- ,  , ,  P is the muon polarization (L. Michel, A. Sirlin)

  8. TWIST -- • will measure the e+spectral shape to very high precision rate • will extract , ,  to a few parts in 104 e+Reduced Energy (x) cose e+ spectrum in x, cose •  is being measured at PSI

  9. SM PDG Current status -- TWIST will measure , ,  in two steps -- 10-3 in 2004; ~3x10-4 in 2005/6

  10.    ~500 timesTWIST sensitivity Spectral effects with changes in , , , 

  11. withand all other couplings = 0 implies non-standard model couplings Search for deviations from SM --

  12. Search for deviations from SM -- … and also for

  13. describes decay of n-handed into an m-handed e+ Chirality of the muon decay…

  14. describes decay of a right-handedinto a right-handedorleft-handede+ = 0 by SM which can be shown to be equivalent to to the following combination of  -- A determination of  and  gives a model-independent test for the existence of right-handed couplings to muons, i.e., Coupling to right-handed muons…

  15. Anticipated TWIST sensitivity to right-handed currents in muon decay PDG TWIST preliminary TWIST final d • Existing limits • Discovery region PDG x

  16. Left/Right Symmetric Model Two weak bosons with mass eigenstates M1 and M2 Left/Right mixing angle;

  17. Left/Right Mixing constraints – Anticipated TWIST Sensitivity Mixing angle 

  18. The TWISTprogram: • Collect high precision data to obtain the e+ spectrum from -decay as a function of x and cose • Detailed study of systematic errors in TWIST • Extract the best values of the spectral parameters ,  , , simultaneously (the first time this has been done) • Obtain a precision in , ,  (a) of 10-3 and (b) a few parts in 104 (~10-3 precision for ) • Compare ,  , ,  from our fit with Standard Model values

  19. Obtain high precision data on the e+ spectrum Highly polarized + + stop in Al target(several kHz) Unbiased + (scintillator) trigger

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

  21. m e+ Typical decay event

  22. TWIST Data • High data rates (few kHz)  Data sets of 109 muon decay events in ~ two weeks • TWIST is systematics limited. (High data rates and computational resources are essential for studying systematic effects.) • In 2002-03, ~6 x 109 muon decay events on tape. • Standard data set ~ 300M triggers  ~58M useful events (smaller samples for some systematics studies) Reconstructed muon decay spectrum

  23. Determination of, , ,  Accelerator data are collected Monte Carlo data are generated • Event Analysis • Event classification (31 types) • Helix fit to events within fiducial volume • Extract e+ momentum and angle spectrum in bins of x and cose Fit Accelerator data spectrum Monte Carlo data spectrum , , , 

  24. Determination of, , ,  Data spectrum is fit to Monte Carlo spectrum -- From the fit , , ,  are determined. Blind Analysis: o, o, o, o are generated randomly (once) and remain hiddenuntil the end of the experiment.

  25. Evaluating Systematic Errors Accelerator data are collected Accelerator data are collected • Event Analysis • Event classification (31 types) • Helix fit to events within fiducial volume • Extract e+ momentum and angle spectrum in bins of x and cose Fit Accelerator data spectrum Accelerator data spectrum , , , 

  26. Evaluating Systematic Errors Monte Carlo data are generated Monte Carlo data are generated • Event Analysis • Event classification (31 types) • Helix fit to events within fiducial volume • Extract e+ momentum and angle spectrum in bins of x and cose Fit Monte Carlo data spectrum Monte Carlo data spectrum , , , 

  27. Evaluating Systematic Errors Monte Carlo data are generated Monte Carlo data are generated • Event Analysis • Event classification (31 types) • Helix fit to events within fiducial volume • Extract e+ momentum and angle spectrum in bins of x and cose • Event Analysis • Event classification (31 types) • Helix fit to events within fiducial volume • Extract e+ momentum and angle spectrum in bins of x and cose Fit Monte Carlo data spectrum Monte Carlo data spectrum , , , 

  28. Evaluating Systematic Errors • Methodology: • Exaggerate possible sources of systematic error - • Take accelerator data sets under a different conditions • Generate Monte Carlo runs with different settings • Analyze same data with different calibrations • (Use full (or nearly full) data set for each test) • Fit two data sets; measure the effect on, , ,  • Scale the effect by the exaggeration factor

  29. Evaluating Systematic Errors Examples • Chamber gas density: muon stopping distribution • Different magnetic field: energy calibration • Magnetic field shape • Alignments • Beam properties • Detector response: • STR: HV, drift cell geometry • Efficiency, fiducial region • Resolution • Cross talk • TWIST simulation (GEANT) …and more…

  30. Evaluating Systematic Errors Present Status Preliminary … and many more at this level… No show-stoppers!

  31. CompareMC TWIST Simulation Validation Monte Carlo data are generated Accelerator data are collected Monte Carlo data are generated • Event Analysis • Event classification (31 types) • Helix fit to events within fiducial volume • Extract e+ momentum and angle spectrum in bins of x and cose Monte Carlo data spectrum Monte Carlo data spectrum

  32. CompareA-data TWIST Simulation Validation Accelerator data are collected Accelerator data are collected • Event Analysis • Event classification (31 types) • Helix fit to events within fiducial volume • Extract e+ momentum and angle spectrum in bins of x and cose Accelerator data spectrum Monte Carlo data spectrum Accelerator data spectrum

  33. Compare changes CompareMC CompareA-data TWIST Simulation Validation • Test the simulation independently of, , ,  • Take accelerator data sets under a different conditions • Generate Monte Carlo data sets with same conditions • Analyze data sets with the same analysis package • Compare the differences -- • Determine the sensitivity for each physics/detector effect in , , , 

  34. TWIST Simulation Validation Examples • Chamber gas density: muon stopping distribution • Different magnetic field: energy calibration • pmax vs e • 2 and confidence level distributions • hits per plane • muon stopping distribution • delta production cross-section • energy loss • multiple scattering • …and more…

  35. Compute power - WestGrid • At University of British Columbia • 504 dual-3Ghz Xeon nodes • 10 TB global disk storage • Robot tape archiving system • Many tens of 108 events analyzed • Many tens of 108 events simulated & analyzed • ~70 ms/event (simulation) • ~30 ms/event (reconstruction) • >5000 CPU days used • (www.westgrid.ca) Funded by the Canada Foundation for Innovation, Alberta Innovation and Science, BC Advanced Education,and the participating research institutions.

  36. The TWISTtimeline: • 2004 • Data in hand for measurement of ,  to 10-3 • Study of systematic errors (for 10-3) nearly complete • Publish measurement of , at 10-3 in2004. • Take data for measurement of P - for precison of10-3 -publish 2004/05 • 2005/06 • Take data for measurement of ,  , ,  to a precision of a few parts in 104(~10-3 precision for ) BOTTOM LINE: Compare ,  , ,  from our fit with Standard Model values New Physics?

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