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### P and T violating correlationin muon and beta decays

Oscar Naviliat-Cuncic

LPC-Caen (IN2P3/CNRS-ENSI) and

Université de Caen Basse-Normandie

context and plan

describe some searches for signatures of NP in weak decays, specifically sensitive to P and/or T violation

- CP-even, P-odd correlation (muon decay)
- CP-odd, P-odd correlation (neutron decay)

1. The longitudinal e+ polarizationin polarized muon decay

(initially motivated by the sensitivity of P -/P + measurements in nuclear beta decay)

ne

GF

m

e

- beyond SM: include all Lorentz invariants
- decay amplitude parametrized by

- in the SM (all others are zero)

4-fermions point-like interaction:

(W.Fetscher PLB 173(86)102)

g = S,V,T interactions

e,m = L,R helicity of charged fermions

parameterization of observables

Observables commonly expressed in terms of Michel parameters:

status

the parameter x’’ enters the angular/energy dependence of PL by the combination:

(present PDG value)

PL

Pm

e+

m+

longitudinal e+ polarizationsensitivity vs x and q for Pm = 0.95

x = Ee /E0 reduced positron energy

→ measure near q = p and x = 1

relation to exotic couplings

relative measurement

compare e+ polarizations between polarized and unpolarized muons:

avoids the precise determination of the polarimeter analyzing power

sensitivity coefficient:

r -, r 0: rates of positrons incident on the polarimeter

for polarized and unpolarized muon decays (measured)

implementation

- produce polarized muons
- maintain/destroy the muon polarization
- select backward emitted positrons near the end point
- measure the longitudinal polarization

realization

pE3 area

muons are naturally produced 100%

polarized from pion decay at rest

“surface muons”

(contamineted by “cloud muons”)

> 44 MeV/c e+

Spectrometer

Polarimeter

Wien filter

(B < 0.0004 T)

monitor

telescopes

Al or S

target

experimental setupe+/m+ velocity separation

N(e+)/N(m+) < 0.12

m stop rate: 3x107 s-1 at 1.6 mA

muon polarization

Hanle method

(with two plastic telescopes)

polarization vs muon momentum

“surface muons”

at 28.5 MeV/c: Pm = 0.94(1)

use two muon stop targets:

Al: Pm = 0.94 “polarized”

S: Pm = 0.10 “unpolarized”

energy and angular selection

selector tracker refocus

pe = 50 MeV/c

60% transmission

for Ee > 44 MeV

12 < q < 13

dump of beam positons

pe = 29 MeV/c

2

3

2

e+

1

z

3

d12

d23

silicon trackerdetermine momentum from helix geometry

redundancy constraint!

- 3 planes with 4 detectors each

- 60x60 double SSD 1 mm pitch 300 mm thick

resolution Dpe = 1.15(1) MeV/c

WC

BGO

WC

scintillator

Vacoflux foils with opposite

magnetization

positron polarimeteruse two processes:

- Bhabha scattering

- Annihilation in flight

(have analyzing powers with opposite signs)

BHA: Aeff ~ 0.037

AIF: Aeff ~ -0.015

(incl. fraction of polarized electrons and foil orientation)

but similar FOM (luminosity)

CoNiFe foils: 75x15x0.1 cm3 with 0.75mm active region to reduce Brehmstralung events

hodoscope and calorimeter

- 7x7 plastic scintillators (x and y)
- 90x7 cm2 with single PM readout

- 127 BGO crystals, 55mm diam, 20cm long
- external magnetic shielding
- temperture stabilized DT = ±2°
- resolution DE/E = 10% at 42 MeV

measuring conditions

- two magnetized foils with opposite magnetizations (simultaneous)
- two directions of magnetization for each foil
- two orientations of the polarimeter: +45°, -45°
- two analyzing processes with opposite analyzing powers (BHA, AIF)
- two stop targets for polarized and unpolarized muons
- measure energy dependence of the longitudinal polarization

typical trigger rates:

- total 15 kHz
- AIF 60/s
- BHA 250/s

(consistent with MC simulations)

cluster recognition, event reconstruction,cuts, ratios, asymmetries…

- triggers defined from scintillators and BGO
- SSD readout is slave
- event type sorted from hits in MWPCs, Hodoscope and BGO

preliminary results

(X. Morelle, PhD)

asymmetries of ratios under inversion of foils magnetization

PRELIMINARY!

x” = 1.020 ± (0.062)stat ± (…)sys

(factor of 6 improvement if sys remains negligible)

status

- experiment did not acquired the planned statistics
- no present plans to make a new run

people and institutions

J.Egger, N.Danneberg, J.Deusch, W.Fetscher, F.Foroughi, J.Govaerts, M.Hadri, Ch.Hilbes, K.Kirch, P.Knowles, K.Koehler, A.Kozela, J.Lang, M.Markiewicz, R.Medve, X.Morelle, O.Naviliat-Cuncic, A.Ninane, R.Prieels, L.Simons, J.Sromicki and P.Van Hove

- Institut de Physique Nucléaire, UCL, Louvain-la-Neuve, Belgium
- Institut für Teilchenphysik, ETH, Zurich, Switzerland
- Paul Scherrer Institut, PSI, Villigen, Switzerland
- Département de Physique, Uni-Fribourg, Switzerland
- Laboratoire de Physique Corpusculaire, Caen, France

(thanks to R.Prieels)

related projects

TRIUMF Weak Interaction Symmetry Test: “TWIST”

http://twist.triumf.ca/~e614/experiment.html

tracking of e+ from polarized muon decay

goal: detemine r, d, Pmx with a relative precision at the 10-4 level

prelim. results expected in 2004

Pp

e

pe

p

the R coefficientdecay rate function:

- the coefficients A, R, N, … probe the dynamics
- JTW parameterization: Ci , C’i(i = S, V, A, T )

R and D in neutron decay

D: P-even T-odd R: P-odd T-odd

DFSI = 1.310-5 (10-6) RFSI = 910-4 (510-6)

Pp

e

pe

p

measuring principlehighest sensitivity to R for mutually perpendicular vectors

Mott scattering

experimental concept

(J. Sromicki NIM A 440 (2000) 609)

- produce polarized cold neutron beam
- observe neutron decay in flight
- track low energy decay electrons
- use large angle Mott scattering
- trigger with “opposite” scintillator

realization

- Spallation neutron source SINQ
- target: “zircalloy” (Zr-Pb)
- D2O moderator
- liquid D2 vessel cold source

FUNSPIN area

polarized cold neutron beam

- A. Schebetov et al.
- NIM A 497 (2003) 479
- J. Zejma et al.
- to be submitted to NIM A

- flux: 2×108 /(cm2·s·mA)
- ‹P› ≈ 97 %

FUNSPIN area

Mott scattering analysis

cross section and Sherman function in Au

… Pb is better (higher Z) and cheaper!

- 1mm evaporated Pb layer on 2mm mylar

- 2 or 3 bands for 50x50cm2 active surface

vertex signals

- after vertex reconstruction with VETO condition on
- the hodoscope at the vertex side S/B > 10:1
- inclusion of hot spots of the setup geometry is in
- progress to further improve S/B

comments

2. precision goal:R =510-3

1. polarimetry control

- “up-down” asymmetry probes R
- “left-right” asymmetry probes N

the simultaneous measurement of N ≠ 0 provides a control of the polarimeter

Exclusion plot on S and T frombeta decay experiments (±1s)

interpretation

P. Herczeg 2004: constraints on |Im(aLS)| from Rp are hard to beat with Rn

Rn at 10-2 would require fine-tuned cancellations

→ make life less exciting…

… important considerations for new generation experiments

status and outlook

- The Mott polarimeter for the measurement of R in neutron decay
- is complete.
- The commissioning run in autumn 2003 was successful.
- The first data taking run starts next month.
- The measurement of R with an accuracy of 10-2 is expected to be achieved within one year.
- The sensitivity goal of 510-3 seems feasible;
- will be checked after first complete data analysis.

people, institutions, support

G.Ban, M.Beck, A.Bialek, K.Bodek, T.Brys, A.Czarnecki, W.Fetscher, P.Gorel, K.Kirch, St.Kistryn, A.Kozela, A.Lindroth, O.Naviliat-Cuncic, J.Pulut, A.Serebrov, N.Severijns, E.Stephan and J.Zejma

- Laboratoire de Physique Corpusculaire, Caen
- Institute of Physics, Jegellonian University, Cracow
- Institute of Nuclear Physics, Cracow
- University of Alberta, Edmonton
- St Petersburg Nuclear Physics Institute, Gatchina
- University of Silesia, Katowice
- Catholic University Leuven, Leuven
- Paul Scherrer Institute, Villigen
- Institute of Particle Physics, ETH Zurich

support for PhD students

(thanks to K. Bodek and P. Gorel)

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