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Progress Report to PAC3J-PARC E06 Experiment (TREK)Measurement of T-violating Transverse Muon Polarization (PT) in K+→p0m+n DecaysJ. ImazatoJuly 6, 2007

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.

Outline

- Statistical sensitivity estimate
- Systematic error estimate
- Polarimeter misalignments
- Other systematics
- R&D for the detector upgrade
- Collaboration/Cost/Funding/Beam
- Summary

Transverse polarization in Km3

K+→p0m+ndecay

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

are small.Non-zero PTis 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.

PT measurement

Use of upgraded E246 detector

PT measured as the azimuthal

asymmetry of the m+ decay e+

Ncw - Nccw

Afwd(bwd) = ; AT = (Afwd - Abwd) / 2

Ncw - Nccw

Factors for statistical sensitivity

_

- K+ beam intensity × Run time
- K+ stopping efficiency (estop~0.30according to a MC )
- K+→p0m+n event rate with m+ in the polarimeter ❶
- E246 experience + MC calculation
- m+→e+nn event rate with e+ detected, and

polarization analyzing power : a = AT / PT❷

- MC calculation for the new active polarimeter

In determining the sensitivity,❶and❷are separable.

They are shown next step by step.

Positron asymmetry measurement

- E246:
- p0- forward (fwd)
- and backward (bwd)
- integral analysis

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

Optimume+measurement

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

FoM = AT√Ne+

- Eeth = 38 MeV
- cosqeth = 0.34
- a = 0.38

(cf. 0.27 in E246)

Optimum p0 measurement

- cosqT ≈ cosqp0
- up to finite m+ acceptance qm+

- cosqpth = 0.30
- <cosqp0> = 0.68
- PT = AT/ 0.258

- Optimization of qpth by FoM of
- FoM = <cosqp0> √Npo

Km3 event rate and sensitivity

- Standard event selection conditions as in E246 :
- 65 < Mgg < 185 MeV/c2
- 3500 < M2TOF < 18,000 (MeV/c2)2
- pm+ <185 MeV/c
- m+ incident into the polarimeter
- qm+p0 < 160o
- M2missing > -15,000 (MeV/c2)2

⇒ Detector acceptanceW(Km3) = 1.14 ×10-2

N(Km3) = N(K+)・estop・Br(Km3)・ W(Km3)

= 3.3 × 109 (total E06 good events)

- MC calculation for 108 events and using PT =AT / 0.258 :

dPT = 6.9 / √N(Km3)

= 1.2 ×10-4

Summary of statistical sensitivity

- dPT =1.2×10-4 for the fwd+bwd integral analysis compared with dPT = 1.8×10-4 given in the proposal .
- Significant gain due to qe 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 dPT = 1.0×10-4 (fwd+bwd) and dPT = 0.8×10-4 (including left+right).

Update of run time

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

2005 design

2007 design

- K+ beam intensity @ 9mA p on T1 is now 2.1×106 /s
- Necessary run time is now 1.4×107 s.

( It was 1.0×107 s in the proposal.)

Acc = 6.0 msr %Dp/p

Acc = 4.5 msr %Dp/p

Source of ErrorS12 fwd/bwddPTx 104e+ 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 <0.1m+ counter f-offset x o <0.1MWPC f-offset (C4) x o 2.0CsI misalignment o o 1.6B offset (e) x o 3.0B rotation (dx) x o 0.4B rotation (dz) x x5.3K+ stopping distribution o o <3.0m+ multiple scattering x x7.1Decay plane rotation (qr) x o 1.2Decay plane rotation (qz) x x0.7Kp2 DIF background x o 0.6K+ DIF background o x < 1.9Analysis - - 3.8Total 11.4

- Cancellation by

S12 and/or

fwd/bwdalmost

all systematics

- except for :
- m+ field alignment
- m+ multiple scattering
- decay plane shifts
- due to
- K+ stopping distribution
- Detector inefficiency
- distribution etc.

Suppression of systematic errors in E06

Old errors

- m+ field alignment : dPT < 10-4
- PT analysis free from misalignment
- m+ multiple scattering : dPT < 0
- no longer relevant with the active polarimeter
- decay plane shifts : dPT < 10-4
- correction for PT only with statistical uncertainty
- active polarimeter e+ analysis : dPT < 10-4
- Perfect fwd/bwd cancellation mechanism

Newcomer

- dPTsyst ~ 0.1 dPTsyst (E246) ~10-4

e+ asymmetrydue topolarimeter misalignment

Rotation about

Component r-axis z-axis

Polarimeter erez

Muon field drdz

fwd - bwd : vanishes for

er , ez , dr when t-integrated

fwd - bwd : not vanishing

for dz !

spurious AT ?

Misalignment analysis using Km3

Asymmetry analysis in terms of q0 : in plane spin angle from z-axis

PT

PT+dz

PT+dr

PT+dz+dr

Asum(q0)

Asub(q0)

- Ddz ~ Ddr ~ 3×10-4 for misalignment determination
- dPT < 1.2×10-4 for PT determination from Asub

Systematic error (1) associated withmisalignment analysis

- Simulation calculation with:

PT= 0 and dz = dr= 5o = 87 mr

==> dPT= (2±7)×10-4 for 108 events

- Essentially statistical error of PT
- No significant effect beyond the statistical error
- In reality, dz ~ dr ~ 1 mr :
- dPTsystshould be < 10-4

- PT can be deduced regardless of the existence of the polarimeter misalignments, er, ez, dr and dz.
- But, how much is the systematic error induced in this misalignment analysis?

Systematic error (2) due to Kp2 BG

Momentum resolutions

Consistency

MC simulation

- Cancellation in gap integration
- ==> averaging to < 1/10 (<0.02%)
- p0 - fwd/bwd cancellation

==> suppression to < 1/10 (<0.002%)

dPT < 10-4

- Dangerous p+ -> m+n background with a PT component
- Substantial reduction due to the addition of the C0 chamber

Systematic error (3) associated with decay plane rotation correction

- Two rotation angles of qz and qr
- Relation: dPT ~ 0.5 <q>due to PN and PL admixture
- <qr> isfwd/bwd cancelling, but

<qz> isnot fwd/bwd cancelling.

- PTwill be corrected for <qz> and <qr>

qz distribution in E246

<qz>= -0.004±0.12 mr

- Statistical error of the correction
- d<qz> = s(qz) /√Ntotal
- dPT (<qz>) ≪dPTstat ~ 10-4

dPT (<qz>) ≪ 10-4

dPT (<qr>) ~dPTstat&fwd/bwd

≪ 10-4

-1 0 +1

0

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 Dr = rfwd - rbwd

- symmetrization of r with bias
- rfwd(r,y,z) = rbwd(r,y,z)
- PTfwd = PT + dPT’
- PTbwd = -PT+ dPT” No problem
- Cancellation power will be calculated using data.

m+ stopping

distribution

in the stopper

Dr = rfwd - rbwd

was a few % in E246

dPTshould be < 10-4

Stopper mSR study (Canada, Japan)

- Muon spin behavior was studied for candidate stopper

materials

Typical TF precession pattern

- TRIUMF surface muon beam with full polarization
- E1120 experiment to study mSR 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

CsI(Tl) readout (INR)

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

Cosmic ray test

Energy Timing

st =3ns

- Very good timing characteristics were confirmed

Fiber target (INR, KEK)

- Target cross section

- Light yield test of the fiber

Pulse height

spectrum

Pulse shape

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

20 cm + clear fiber + MPPC

- MPPC radiation hardness test

at RCNP

- Increasing leakage current

with dose

- Design of shielding

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
- Dx = 90 mm
- Rate capability
- Readout electronics

Amplitude vertical

Amplitude horizontal

Residualx(mm)

Muon field magnet (KEK)

TOSCA 3D calculation

Collaboration

- International cooperation in detector construction

- 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

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

Beamline preparation

K1.1

- 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.

K1.1-BR

T1

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 :

Time schedule

- Totally dependent on the K1.1-BR beamline installation and funding of the experiment.
- In the proposal we presented:

20091) 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.

Theory impact

- A clean search for CP violation via Higgs dynamics.
- Direct CP violation presumably unsuppressed by DI=1/2 rule

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

-- unless enhanced couplings to leptons!

(I. Bigi, CERN Flavor WS, 2007 )

Summary

- We have shown with MC studies that E06 can reach at least the statistical sensitivity of dPT =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.

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.

PAC3

K+Stopping efficiency

GEANT3 calculation

- Optimum degrader

thickness

- Target diameter of
- d=8cm
- d=6cm
- d=4cm
- FOM is maximum at

800 MeV/c

- estop=0.25~0.30

Stopped beam method

- Double ratio experiment
- AT = (Afwd - Abwd) / 2
- Ncw - Nccw
- Afwd(bwd) =
- Ncw - Nccw
- PT = AT / {a <cosqT>}
- a : analyzing power
- <cosqT> : attenuation factor
- Imx = PT / KF
- KF :kinematic factor

PT = - 0.0017 ± 0.0023(stat) ± 0.0011(syst)

( |PT | < 0.0050 : 90% C.L. )

Imx = - 0.0053 ± 0.0071(stat) ± 0.0036(syst)

( |Imx | <0.016 : 90% C.L. )

bwd -p0 (g )

fwd -p0 (g )

Statistical error dominant

Target of E06

- E246 detector is upgraded for E06

Sensitivity improvement in E06

- We aim at a sensitivity of dPT ~10-4
- dPTstat ~0.05 dPTstat (E246) ~10-4 with

1) ×30 beam intensity,

2) ×10 detector acceptance, and

- Higher analyzing power

dPTsyst ~ 0.1 dPTsyst (E246) ~10-4by

1) Precise calibration of misalignments using data

2) Correction of systematic effects

- Precise fwd-bwd cancellation of systematics by data

symmetrization

(Estimate of cancellation power using data)

- Most crucial systematics are misalignment of :

Muon polarimeter and muon field distribution

E246 muon polarimeter

One-sector view

Cross section

B

y(cm)

_

m+ →e+ne nm

W(e+) ∝ 1 + A cos q

- Passive polarimeter with
- Al muon stopper
- Left/Right positron counters
- simple analysis and systematics

Active muon stopoper

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

- Parallel plate stopper with
- Gap wire chambers

Number of plates 31

Plate material Al, Mg or alloy

Plate thickness ~ 2 mm

Plate gap ~ 8 mm

Ave. density 0.24 rAl

m+ stop efficiency ~ 85%

- Small systematics for

L/Re+ asymmetry measurement

- Fit for p0fwd/bwd measurement
- Simple structure

Tracking system

- E246 J-PARC E06
- C0 (cylindrical) and C1(planer) are GEM chambers

Rad.hardness test of MPPC

- MPPC 400 pixel type
- Irradiation of up to 36 Gy

- Increase of leakage current

proportional to dose

Beam halo simulation

- GEANT4 simulation
- 10 cm-f BeO degrader + 6 cm-fTarget

K+ flux distribution

p+

m+

e+

n

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

APD readout of CsI(Tl)

- E246 CsI(Tl)
- 5 x 5mm APD
- CR measurement
- 1.5 ms width

Tracking system alignment

Use of a collimator system

Misalignment analysis

- Time-integrated asymmetry function

- Effects of ez and er vanish.
- q0 determination event-by-event

using Km3 form factors.

- Ambiguity of q0 determination

is not problematic.

Correction for decay plane rotation

- Two rotation angles of qz and qr
- Relation: dPT ~ 0.5 <qz>, ~ 0.5 <qr>
- PTwill be corrected for <qz> and <qr>
- <qr> isfwd/bwd cancelling, but

- <qz> isnot fwd/bwd cancelling.

- Statistical error of the correction
- d<qz> = s(qz)/√Ntotal
- dPT(<qz>) ≪dPTstat ~ 10-4

qz distribution in E246

<qz>= -0.004±0.12 mr

-1 0 +1

0

Data symmetrization

- Suppression of systematic errors -

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

- m+ stopping distributions
- rfwd(r,y,z) ≠rbwd(r,y,z)
- ⇩
- rfwd(r,y,z) = rbwd(r,y,z)
- PTfwd = PT + dPT’
- PTbwd = -PT+ dPT”
- eliminates systematics
- in the polarimeter

Group members

: core members (younger people)

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