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

drgill@triumf.ca

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