1

Progress Report to PAC3J-PARC E06 Experiment (TREK)

Measurement of T-violating Transverse Muon Polarization (PT) i

n K+→ DecaysJ. ImazatoJuly 6, 2007

2

Problem assigned by PAC1

The PAC would like the proponent to show that the improvement on the sensitivity and systematic uncertainty below 10-4 is attainable via detailed Monte Carlo studies, e.g. acceptance, B-field offset, detector misalignments and the new polarimeter.

3

Outline

Statistical sensitivity estimateSystematic error estimate

Polarimeter misalignmentsOther systematics

R&D for the detector upgradeCollaboration/Cost/Funding/BeamSummary

4

Transverse polarization in K3

K+→decay

PT is T-odd and spurious effects from final state interaction

are small. Non-zero PT is a signature of T violation. Standard Model contribution to PT : PT(SM) < 10-7

Spurious effects from final state interactions : PT(FSI) < 10-5

There are theoretical models which allow sizeable PT

without conflicting with other experimental constraints.

5

PT measurement

Ncw - NccwAfwd(bwd) = ; AT = (Afwd - Abwd ) / 2 Ncw - Nccw

Use of upgraded E246 detector

PT measured as the azimuthal asymmetry of the + decay e+

6

Statistical sensitivity estimate

7

Factors for statistical sensitivity K+ beam intensity × Run timeK+ stopping efficiency (stop~0.30 according to a MC )

K+→event rate with + in the polarimeter ❶– E246 experience + MC calculation

→e+event rate with e+ detected, and polarization analyzing power : = AT / PT 　　　 ❷

– MC calculation for the new active polarimeter

In determining the sensitivity, ❶ and ❷ are separable.

They are shown next step by step.

_

8

Positron asymmetry measurement

E06:conservative estimate now by fwd/bwdambitious analysis including left/right event-by-event analysis: future option

E246: 0- forward (fwd) and backward (bwd) integral analysis

9

Optimum e+ measurement

Eeth = 38 MeV

coseth = 0.34

= 0.38 (cf. 0.27 in E246)

PT = AT / <cosT> : analyzing power, <cosT> : attenuation factor Figure of Merit (FoM) optimization by a MC simulation using a realistic + stopper condition

FoM = AT√Ne+

10

Optimum 0 measurement

costh = 0.30

<cos> = 0.68 PT = AT / 0.258

Optimization of th by FoM of

FoM = <cos0> √No

cosT ≈ cos0

up to finite + acceptance +

11

K3 event rate and sensitivity Standard event selection conditions as in E246 :

1. 65 < M < 185 MeV/c2

2. 3500 < M2TOF < 18,000 (MeV/c2)2

3. p <185 MeV/c4. + incident into the polarimeter5. < 160o

6. M2missing > -15,000 (MeV/c2)2

⇒ Detector acceptance = 1.14 ×10-2

N(K) = N(K+) ・ stop・ Br(K) ・ = 3.3 × 109 (total E06 good events)

MC calculation for 108 events and using PT =AT / 0.258 : PT = 6.9 / √N(K) = 1.2 ×10-4

13

Summary of statistical sensitivity

PT =1.2×10-4 for the fwd+bwd integral analysis compared with PT = 1.8×10-4 given in the proposal . – Significant gain due to e cut and realistic event selection (The effect of Ee+ threshold was partially included in the proposal.)

We will attack the event-by-event weighted analysis aiming for PT = 1.0×10-4 (fwd+bwd) and PT = 0.8×10-4 (including left+right).

14

Update of run time

K+ beam intensity @ 9A p on T1 is now 2.1×106 /sNecessary run time is now 1.4×107 s. ( It was 1.0×107 s in the proposal.)

K1.1-BR beam optics was changed due to B1 position

2005 design 2007 design

Acc = 6.0 msr %p/p Acc = 4.5 msr %p/p

15

Systematic error estimate

16

Source of Error 12 fwd/bwd PT x 104

e+ counter r-rotation x o 0.5e+ counter z-rotation x o 0.2e+ counter f-offset x o 2.8e+ counter r-offset o o <0.1e+ counter z-offset o o

<0.1+ counter f-offset x o <0.1MWPC-offset (C4) x o 2.0CsI misalignment o o 1.6B offset () x o 3.0B rotation (x) x o 0.4B rotation (z) x x 5.3K+ stopping distribution o o <3.0+ multiple scattering x x 7.1Decay plane rotation (r) x o 1.2Decay plane rotation (z) x x 0.7K2 DIF background x o 0.6K+ DIF background o x

< 1.9Analysis - - 3.8

Total 11.4

E246 systematic errors

Cancellation by 12 and/or fwd/bwd almost all systematics except for :

+ field alignment

+ multiple scattering decay plane shifts due to • K+ stopping distribution • Detector inefficiency distribution etc.

17

Suppression of systematic errors in E06

• + field alignment : PT < 10-4

– PT analysis free from misalignment

• + multiple scattering : PT < 0– no longer relevant with the active polarimeter

• decay plane shifts : PT < 10-4

– correction for PT only with statistical uncertainty

• active polarimeter e+ analysis : PT < 10-4

– Perfect fwd/bwd cancellation mechanism

Old errors

Newcomer

PTsyst ~ 0.1 PT

syst (E246) ~10-4

18

e+ asymmetrydue to

polarimeter misalignment

Rotation aboutComponent r-axis z-axisPolarimeter r z Muon field r z

fwd - bwd : vanishes for r , z , r when t-integrated

fwd - bwd : not vanishing for z !

spurious AT ?

19

Misalignment analysis using K3

z ~ r ~ 3×10- 4 for misalignment determination

PT < 1.2×10- 4 for PT determination from Asub

Asum(0)Asub(0)

Asymmetry analysis in terms of 0 : in plane spin angle from z-axis

PT

PT+z

PT+r

PT+z+r

21

Systematic error (1) associated withmisalignment analysis

PT can be deduced regardless of the existence of the polarimeter misalignments, r, z, r and z.

But, how much is the systematic error induced in this misalignment analysis? Simulation calculation with:

PT = 0 and z = r = 5o = 87 mr ==> PT = (2±7)×10-4 for 108 events Essentially statistical error of PT No significant effect beyond the statistical error In reality, z ~ r ~ 1 mr : PT

syst should be < 10-4

22

Systematic error (2) due to K2 BGDangerous + -> background with a PT componentSubstantial reduction due to the addition of the C0 chamber

Cancellation in gap integration ==> averaging to < 1/10 (<0.02%) 0 - fwd/bwd cancellation ==> suppression to < 1/10 (<0.002%)

PT < 10-4

MC simulation

Momentum resolutions Consistency

23

Systematic error (3) associated with decay plane rotation correction

Two rotation angles of z and r

Relation: PT ~ 0.5 <> due to PN and PL admixture <r> is fwd/bwd cancelling, but <z> is not fwd/bwd cancelling.

PT will be corrected for <z> and <r> 　

Statistical error of the correction <z> = (z) /√Ntotal PT (<z>) ≪ PT

stat ~ 10-4

z distribution in E246 <z>= -0.004±0.12 mr

-1 0 +1 0

PT (<z>) ≪ 10-4

PT (<r>) ~ PTstat& fwd/bwd

≪ 10-4

24

Systematic errors (4) associated with positron analysis

Systematics in the chamber measurement is left-right canceling :

cell inefficiency plate non-uniform thickness etc.

further cancellation by fwd-bwd up to small = fwd -bwd symmetrization of with biasfwd(r,y,z) = bwd(r,y,z) PT

fwd = PT + PT’ PT

bwd = -PT + PT” No problem

Cancellation power will be calculated using data.

= fwd -bwd was a few % in E246

PT should be < 10-4

+ stopping distribution in the stopper

26

R&D of detector upgrade

27

Upgraded elements

29

Stopper SR study (Canada, Japan)

TRIUMF surface muon beam with full polarization E1120 experiment to study SR in Al and Mg alloys Transverse field (TF) and longitudinal field (LF) relaxation rates were

measured with a 0.03 T field. Several candidate stopper materials were confirmed.

Al alloys: A5052, A6063, Mg alloys: AZ31, ZK60, Z6, AM60, AZ91

Muon spin behavior was studied for candidate stopper materials

Typical TF precession pattern

30

CsI(Tl) readout (INR)

Cosmic ray test Energy Timing

First application of APD readout to a large CsI(Tl) calorimeter

Very good timing characteristics were confirmed

t =3ns

31

Fiber target (INR, KEK)

2.5x2.5 mm x 20 cm fiber Tapered coupling to MPPC Yield of ~ 20 p.e. for 90Sr

Target cross section Light yield test of the fiber

20 cm + clear fiber + MPPC

Pulse height spectrum Pulse shape

MPPC radiation hardness test at RCNP

Increasing leakage current with dose Design of shielding

32

C0 and C1 GEM chambers (MIT)

Three chambers were beam-tested at FNAL by MIT GEM Lab.

H- and V-amplitude correlation

Middle residual

• Stable operation• Resolution of x = 90 m• Rate capability• Readout electronics A

mpl

itude

ver

tical

Amplitude horizontal Residual x (mm)

33

Muon field magnet (KEK)TOSCA 3D calculation

34

Collaboration/Funding/Beamline

35

Collaboration• Canada Univ. of Saskatchewan, Univ. of British Columbia, TRIUMF, Univ. of Montreal• U.S.A. MIT, Iowa State Univ., Univ. of South Carolina• Japan KEK, Osaka Univ., Tohoku Univ., Kyoto Univ., NDA- New participation - • Russia INR (group with E246 experience) Altogether • Vietnam Nat. Sci. Univ. in HCMC 35 people

International cooperation in detector construction

Strong support from : (1) TRIUMF detector shop, and (2) MIT GEM Lab.

36

Beamline preparationK1.1

K1.1-BR

K1.1BR uses the upstream part of K1.1.

No budget is allocated for K1.1 in the J-PARC budget, although it is one of the planned secondary lines in Phase 1.

We would like to go ahead with the BR (700-800 MYen), with a possible Canadian contribution to the 0.8 GeV leg.

Once full beam operation has started at T1, it will become very difficult to install the frond end of the channel (B1, Q1, Q2, B2). Timely installation of K1.1/K1.1BR is absolutely necessary.

T1

37

Cost estimate and funding policy

Updated cost estimate :– Detector upgrade etc. 279,710 kYen– Transfer of the SC spectrrometer 182,000 kYen– K1.1BR branch construction 50,000 kYen(These are not very different from the estimates in the proposal.)

Policy for funding :

38

Time scheduleTotally dependent on the K1.1-BR beamline installation a

nd funding of the experiment. In the proposal we presented:

2009 1) Spectrometer setup 2) Field mapping 3) Detector setup 4) Beam tuning

2010-11 5) Engineering run, and 6) Data taking

We would like to pursue the earliest possible schedule aiming to provide the first particle physics output from the hadron hall.

39

Theory impact

A clean search for CP violation via Higgs dynamics.

Direct CP violation presumably unsuppressed by I=1/2 rule

PT ~ [’effect × 20 = 5 x 10-6 × 20 ~ 10-4

-- unless enhanced couplings to leptons!

(I. Bigi, CERN Flavor WS, 2007 )

40

Summary

We have shown with MC studies that E06 can reach at least the statistical sensitivity of PT =1.2×10-4 in the safe fwd+bwd integral analysis.

We have established a PT extraction method in the presence of any polarimeter misalignments.

We have shown that other systematics should be controllable to the level < 10-4.

We have demonstrated the validity of the proposed upgraded detector elements with necessary test experiments.

PAC341

Our request to PAC

The Canadian and American groups are starting budget requests in their countries. The status of stage-2 approval is very necessary for a successful application. The PAC is requested to consider E06 for the stage-2 approval although there are no funds yet in place.

An endorsement of the K1.1BR beamline installation for E06 is desirable. The PAC is also asked to make a strong recommendation to the IPNS/J-PARC management to provide a plan for the K1.1BR construction so that the Canadian group will be able to request money for a contribution to this stopped K+ beamline.

42

END of Slides

43

K+ Stopping efficiency

Optimum degrader thickness Target diameter of

d=8cmd=6cmd=4cm

FOM is maximum at

800 MeV/c

stop=0.25~0.30

GEANT3 calculation

44

Stopped beam method

PT = - 0.0017 ± 0.0023(stat) ± 0.0011(syst) ( |PT | < 0.0050 : 90% C.L. )Im= - 0.0053 ± 0.0071(stat) ± 0.0036(syst) ( |Im| <0.016 : 90% C.L. )

Statistical error dominant

Double ratio experiment

AT = (Afwd - Abwd ) / 2

Ncw - NccwAfwd(bwd) = Ncw - Nccw

PT = AT / {<cosT>} : analyzing power <cosT> : attenuation factor Im = PT / KF

KF : kinematic factor bwd - fwd -

45

Target of E06

E246 detector is upgraded for E06

46

Sensitivity improvement in E06 We aim at a sensitivity of PT ~10-4

PTstat ~0.05 PT

stat (E246) ~10-4 with

1) × 30 beam intensity, 2) × 10 detector acceptance, and3) Higher analyzing power

PTsyst ~ 0.1 PT

syst (E246) ~10-4 by　 1) Precise calibration of misalignments using data

2) Correction of systematic effects3) Precise fwd-bwd cancellation of systematics by dat

a symmetrization (Estimate of cancellation power using data)

Most crucial systematics are misalignment of : Muon polarimeter and muon field distribution

47

E246 muon polarimeterCross section One-sector view

y(cm)

B

+ → e+e W(e+) ∝ 1 + A cos

Passive polarimeter with• Al muon stopper• Left/Right positron counterssimple analysis and systematics

48

Active muon stopoper Identification of muon stopping point/ decay vertex Measurement of positron energy Ee+ and angle e+ Large positron acceptance of nearly 4 Larger analyzing power Higher sensitivity Lower BG in positron spectra

Parallel plate stopper withGap wire chambers Number of plates 31 Plate material Al, Mg or alloy Plate thickness ~ 2 mm Plate gap ~ 8 mm Ave. density 0.24 Al

stop efficiency ~ 85%

Small systematics for L/R e+ asymmetry measurement Fit for 0 fwd/bwd measurement Simple structure

49

Spin relaxation rate

50

Tracking system

E246 J-PARC E06

C0 (cylindrical) and C1(planer) are GEM chambers

51

Tracking performance

52

Rad.hardness test of MPPC

MPPC 400 pixel typeIrradiation of up to 36 Gy

Increase of leakage current proportional to dose

53

Beam halo simulation GEANT4 simulation 10 cm- BeO degrader + 6 cm-Target

K+ flux distribution

+

+

e+

n

54

CsI(Tl) readout CsI(Tl) + APD + Amplifier + FADC Electrons after APD : ~ 2 ×107 @ 100 MeV Max count rate / module : ~ 100 kHz Max K+ decay rate : ~ 20 MHz

- enough for the beam intensity in Phase 1 Noise level : to be tested Module energy resolution : to be tested

-Energy resolution is determined by lateral shower leakage

55

APD readout of CsI(Tl)

• E246 CsI(Tl)• 5 x 5mm APD• CR measurement• 1.5 s width

56

Tracking system alignmentUse of a collimator system

57

CsI(Tl) alignment Use of K+ → with back to back kinematics

azimuthal rotation two tilt angles

58

e+ asymmetrydue to

polarimter misalignmnet

59

Precession patterns due to misalignments

r=1o r=1o

z=1o z=1o

@= 0o

- A kind of normalization -

60

Misalignment analysis

• Effects of z andr vanish.

• 0 determination event-by-event using K3 form factors.

• Ambiguity of 0 determination is not problematic.

Time-integrated asymmetry function

61

dependence of the asymmetry

0-fwd 0-bwd

PT

z=5o r=5o

N

62

Correction for decay plane rotation

• Two rotation angles of z and r

• Relation: PT ~ 0.5 <z>, ~ 0.5 <r>• PT will be corrected for <z> and <r>

　 <r> is fwd/bwd cancelling, but

Statistical error of the correction <z> = (z)/√Ntotal

PT(<z>) ≪ PTstat ~ 10-4

z distribution in E246 <z>= -0.004±0.12 mr -1 0

+1 0

　 <z> is not fwd/bwd cancelling.

63

Data symmetrization

K+ stopping distribution• non-bias cut• small loss of events

- Suppression of systematic errors -

+ stopping distributions fwd(r,y,z) ≠bwd(r,y,z) ⇩fwd(r,y,z) = bwd(r,y,z)

　 PTfwd = PT + PT’

PTbwd = -PT + PT”

eliminates systematics in the polarimeter

64

Group members

: core members (younger people)

65

Trigger rate reduction