TWIST – the TRIUMF Weak Interaction Symmetry Test Designed to achieve ~ 0.01% in the shape of the...
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Transcript of TWIST – the TRIUMF Weak Interaction Symmetry Test Designed to achieve ~ 0.01% in the shape of the...
TWIST – the TRIUMF Weak Interaction Symmetry Test
Designed to achieve ~ 0.01% in the shape of the decay spectrum
Several data sets of 109 events eachA precision test of the weak interaction in
the Standard Model
A precision study of the + decay spectrum
D.R.Gill TRIUMF
Outline
MotivationOverview of the experimentAnalysis statusTimeline
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 ‡ ‡
AlbertaAndrei Gaponenko
Peter Kitching
Rob MacDonald
Maher Quraan
Nathan Rodning §
John Schaapman
Glen Stinson
British ColumbiaBlair Jamieson
Mike Hasinoff
MontrealPierre Depommier
ReginaTed Mathie
Roman Tacik
Kurchatov InstituteVladimir Selivanov
Vladimir Torokhov
Texas A&MCarl Gagliardi
Jim Musser
Robert Tribble
Maxim Vasiliev
ValparaisoDon Koetke
Paul Nord
Shirvel Stanislaus
Graduate Students
§ Deceased
‡ also UNBC† also UVic ‡ ‡ also Saskatchewan † † also LANL
… 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)
|| ~ 2
,,
,,jei
LRji
TVSij egrate
TWIST Motivation – testing the Standard Model
e±
±
Expanded in terms what have become known as the Michel parameters
e+ Reduced Energye+ angle (Cosine)
)34(
3
21)cos(
13)34(
3
233~ 2 xxP
xx
xxxxrate o
These shape parametersof the spectrum arewhat TWIST is studying!
Modified by radiative corrections. Now several calculations to 2nd order exist
{hep-ph/0206036}
See Arbuzov JHEP0303:063,2003
rate
0.55|g|
0.424|g|
0.125|g|
0.066|g|
SLL
SRL
SLR
SRR
0.110|g|
0.060|g|
0.033|g|
VRL
VLR
VRR
0|g|
0.122|g|
0.036|g|
0|g|
TLL
TRL
TLR
TRR
0.96|g| VLL
Plenty of room for surprises
Present knowledge of couplings;
SM PDG
013.0007.0
0030.00079.00027.1
0028.00026.07486.0
0026.07518.0
0.0
0.1
4/3
4/3
1985
1987
1988
1969
T
RLSRL
TRL
SRL
TLR
SLR
TLR
SLR
TRL
TLR
VRL
VLR
gggggggg
gggg
****
2222
ReReReRe43
||||2||||43
43
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
Existing limits- Discovery region
Anticipated TWIST sensitivity to R-H currents in muon decay22222 ||||
41
||3||||41 V
RRSRR
TLR
VLR
SLRLRRR ggggg QQQR
916
31
121
RQ
TWIST final
PDG
PDG
TWIST preliminary
Left/Right Symmetric Extensions of the Standard Model
)sin()cos(
)sin()cos(
21
21
MMeM
MMM
iW
W
R
L
Two weak bosons with mass eigenstates M1 and M2
1L
R
W
W
m
mParity violation at low energy is presumably due to
In general, the models may include a CP violating phase (), and a left/right mixing parameter
For Left/Right Symmetric extensions
is sensitive to the Left/Right mixing
to the mixing and to the WRmass
and are unchanged by Left/Right extensions with manifest symmetry
A measurement of and determines the WR mass and its mixing
04
3
23
4
221
214
3
4
24
2
R
L
R
L
m
m
m
m
2
RLV
RR mmg1 V
RLVLR ggFor
WR 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 variousassumptions re CKMR
424
R
LLud
Rud
L
R
M
M
V
V
g
g
R
LLud
Rud
L
R
M
Mfunction
V
V
g
g22
424
1
R
LLud
Rud
L
R
M
M
V
V
g
g
decay
p pbar collider
decay
Complementary
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.
Chambers & half detectorPlanar drift chambers sample
positron track
Use 44 drift planes, and 12 PC planes
Typical decay event
e+
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 smallUseful for systematics search/study• systematics comparisons can be done directly fit data to data or MC to MCHide values of and used in MC generation• can be done in straightforward way• avoids human bias in analysis of systematics
TechnologySpectrum is linear in and so fit
MCdatai
MCidatai
NNN
MCdata is the fit parameterwhere
iN - 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 spectrumDetermine and Open Safe
WestGrid: 1000*3GHz
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
Systematics study status
Preliminary
Sample from correlated data to data fits 10-3
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 7.0Long list at this level – No showstopper found
Timeline6x109 muon decay events are in hand complete 10-3 analysis this summer!publish determination of and
2004 data rundata on Pat 10-3 andthis summer/fall
at least 3 PhD’s granted by 2005Final parts in10-4 data & publications:2005/2006Need More Graduate Students Now
SummaryThe TWIST experiment is near end of phase 1Anticipate 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
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-
2
RLV
RR mmg1 V
RLVLR gg
0
22 ||2||4
3 VLR
VLL gg 222 ||||2||
4
3 VRR
VLR
VLL ggg
222 2|| VLR
VRR
VLL ggg
‘Familons’
0XeSearch for a bump in the momentum spectrum• long lived narrow peak• zero mass at spectrum upper end• >> 1011 ’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 X0
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}
5th dimension
Fermion L(2)
Fermion R(1) OurBrane
Improvements in and to 10-3 or 10-4 will “define width of split” not part of TWIST program - PSI
Sample size usually ~300M triggers ~58M useful events and at ~6x10-4 {statistics} smaller samples for alignment, GEANT verification etc.
Goalsand 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)alignmentStopping target material(depolarization)
determine how to move to Pat 10-3 and all at 10-4
Data sets taken 2002 & 2003 6x109 triggers on tape}
GEANT verification eloss, mulscat and muon range slides go here!
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?
TWIST – RF Cuts
Backgrounds (extrapolated from higher momentum)
Cloud Muonspolarization ~ -0.3flux ~ 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