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TWIST

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A precision test of the weak interaction in the Standard Model ... Robert Tribble. Maxim Vasiliev. Valparaiso. Don Koetke. Paul Nord. Shirvel Stanislaus ... – PowerPoint PPT presentation

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Title: TWIST


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_at_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 AM Carl Gagliardi Jim
Musser Robert Tribble Maxim Vasiliev Valparaiso D
on Koetke Paul Nord Shirvel Stanislaus
Deceased
Graduate Students
also UNBC
also UVic
also Saskatchewan
also LANL
4
TWIST Motivation testing the Standard Model
Most general interaction does not presuppose
the W
5
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 JHEP0303063,2003
hep-ph/0206036
6
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
Anticipated TWIST sensitivity to R-H currents in
muon decay
TWIST final
d
  • Existing limits
  • Discovery region

x
9
Left/Right Symmetric Extensions 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
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
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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
Planar drift chambers sample positron track
Use 44 drift planes, and 12 PC planes
15
Typical decay event
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 r, d, x and h used in MC
    generation
  • can be done in straightforward way
  • avoids human bias in analysis of systematics

17
Technology
WestGrid 10003GHz
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
10-3 r d x h
Alignment Translation 0.10 0.08 0.13 5.8
Rotation 0.07 0.05 0.28 3.9
Chamber HV 0.05 0.03 0.06 2.6
Cell Geometry 0.28 0.21 0.36 16.
Gas Density 0.15 0.11 0.20 8.5
Calibration Trigger time 0.13 0.09 0.16 7.0
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 r and d
  • 2004 data run
  • data on Pmx at 10-3 (and h?) this summer/fall
  • at least 3 PhDs granted by 2005
  • Final parts in10-4 data publications2005/2006
  • Need More Graduate Students Now

21
Summary
  • The TWIST experiment is near end of phase 1
  • Anticipate preliminary measurements at 0.1 of
  • r and d (this summer)
  • Pmx (Data during the summer/fall of 2004)
  • Final precision on r and d 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
    complements b 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
  • gtgt 1011 ms in final sample
  • - can loosen many cuts presently used!
  • for example, tof(removes cloud ms) and
  • target stop(removes stops in depolarizing
    materials)

Existing limit lt2.6x10-6 (1x10-10) bracket
is for particular decay of X0
24
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
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26
GEANT verification eloss, mulscat and muon range
slides go here!
27
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
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