- LFV and related topics

M. Grassi – INFN Pisa Rome - November 7th , 2005

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-LFV and related topics


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RequestsWe were asked of focusing on the

following items– Physics motivation– Technology aspects– Cost estimates– Manpower– Interest in Italy

… but I’ll discuss mainly the LFV

xx~


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Examples of CLFV processes-LFV

3eeNeN’ee

-LFVlll l lll’ NN’ X

K systemKL eKL 0eK± ±ePrecise measurements

-EDMg-2 decay parameters


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Physics motivationCharged Lepton Flavour Violation (CLFV) processes, like e , eee , e conversion, and also e, , lll , are negligibly small in the extended Standard Model (SM) with massive Dirac neutrinos (BR 10-50)

Super-Symmetric extensions of the SM (SUSY-GUTs) with right handed neutrinos and see-saw mechanism may produce CLFV processes at significant rates

CLFV decays are therefore a clean (no SM contaminated) indication of profound New Physics (mainly SUSY, but also on other exotic scenarios )

and they are experimentally

accessible


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Model independent indicationsEffective interactions:

Dependence upon arbitrary parameters and F

Mag. Mom. Trans.

Direct violat

2

2 4F

3 4πB(μ eγ) = G Λ


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Model independent indicationsThe same effective interaction

implies also a non zero EDM and deviations for the muon g-2 value with respect to the SM predictions

2 2 21 2 3 5( ) ( ) ( )2

ieu ef q f q f q q um

1

2

3

(0) 1(0)(0)

ff af d


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SUSY indications for e

• SUSY SU(5) predictions

BR (e) 10-14 10-13

• SUSY SO(10) predictionsBRSO(10) 100 BRSU(5)

R. Barbieri et al., Phys. Lett. B338(1994) 212R. Barbieri et al., Nucl. Phys. B445(1995) 215

LFV induced by finite slepton mixing through radiative corrections

Experimental limit

small tan() excluded by LEP results


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-oscillation connection

J. Hisano, N. Nomura, Phys. Rev. D59 (1999)116010

Experimental limit

tan()=30

tan()=1

Additional contribution to slepton mixing from V21 (the matrix element responsible for solar neutrino deficit)


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The muon trio

2 2 2

2 2 2

2 2 2

ee e e

e

e

m m mm m mm m m

2em

e

B e

2Re m

B

2I m m

B

eeconv

g-2

EDM

In SUSY models the slepton mixing matrix

links the three processes

L. RobertsY. Kuno


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SU(5) LFV ratios

On large classes of SUSY-GUT

BR(-e conv) 10-2

BR(e)BR(3e) 10-2 BR(e)BR( ) 10+5 BR(e)

J.Hisano et al., Phys.Lett. B391(1997)341

-e:Ti conv

e

<0 >010-11

10-20

10-20


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CLFV comparison

Within the same, or among different

unification models the predictions of CLFV

processes have large variations

J.Ellis et al., Eur.Phys.J. C14(2000)319

BR() x 102

103

BR(

e) x

10-210-2


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Predictions ?• Huge spread of SUSY prediction 10-12 – 10-19

• In R-violating SUSY the dominant process are 3e and -e conv

• Super Symmetry does not exist...

• Extra dimensions theories have parameters values with measurable BR

Choice based on feasibility arguments


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Experimental situation

LFV searches

Orders of magnitude improvement are required:

experimental challenge!


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sector3eeNeN’-EDMg-2ee

• dedicated beams• dedicated experiments• single purpose


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+e+e+e-

CoplanarityVertexingEe = m

Te+ = Te+ = Te-

signal eee

background

correlated e e e

accidental

e ee+e- e+e-

e+ +

e+

+

e+

e-

e+ +

e-

e+

+

e+

e+

e- e-


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+e+e+e- : SINDRUM IPresent limit B(3e ) < 1x10-12

U.Bellgardt et al. Nucl.Phys. B299(1988)1No other experimental proposal

This channel has only charged particles in the final state

The experiment needs only a tracking system but

• Sustain the entire Michel decay rate

• Down to low momentum• 4 coverage

SINDRUM I parameters– beam intensity 6x106 /s– momentum 25 MeV/c– magnetic field 0.33T– acceptance 24%– momentum res. 10% FWHM– vertex res. 2 mm2

FWHM– timing res. ns– target length 220 mm– target density 11 mg/cm2


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+e+e+e- : future• SINDRUM: sensitivity 10-12

background 10-13

• A new experiment should aim to a sensitivity: B 10-16

would require 109 /s butbackground 10-10 (6 order of magnitude !)

• Exercise: detector improvements for just a 104 factor– momentum resolution 10% FWHM 1% FWHM

bckg scales quadratically with momentum resolution– co-planarity test ?– vertex resolution 2 mm2 <1 mm2

– target length 220 mm ?– target density 11 mg/cm2 ?– timing resolution ns 100 ps

(accidental background increases quadratically with the muon stop rate)


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+e+e+e- : summaryNo other experimental proposal

Six orders of magnitude of background reduction are requiredfour orders of magnitude could be achieved, two more?

This is not a relevant item


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+e+

e+ +

e = 180°Ee = E = 52.8 MeVTe = T

signal e

background

correlated physical e

e+ +

accidental

e e

ee eZ eZ e+ +


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+e+ : present

Present limit B(e) < 1.2x10-11 by the MEGA Collab. M.L.Brooks et al. Phys.Rev.Lett. 83(1999)1521

Near to start data-taking experiment: MEG


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+e+ : MEG experimental method

1m

e+

L iq . Xe Scintilla tionDetector

Drift C ham ber

Liq. Xe Scin tilla tionDetector

e+

Tim ing Counter

Stopping TargetThin S uperconducting Coil

M uon Beam

Drift Chamber

Easy signal selection with + at rest

e+ + Ee = E = 52.8 MeV

e = 180°Detector outline

• Stopped beam of 3x107 /sec in a 150 m target

• Liquid Xenon calorimeter for detection (scintillation)

- fast: 4 / 22 / 45 ns- high LY: ~ 0.8 * NaI- short X0: 2.77 cm

• Solenoid spectrometer & drift chambers for e+ momentum

• Scintillation counters for e+ timing


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+e+ : MEG required performances

Exp./Lab Year Ee/Ee (%)

E/E (%)

te (ns)

e

(mrad)

Stop rate (s-1)

Duty cyc.(%)

BR(90% CL)

SIN 1977 8.7 9.3 1.4 - 5 x 105 100 3.6 x 10-9

TRIUMF 1977 10 8.7 6.7 - 2 x 105 100 1 x 10-9

LANL 1979 8.8 8 1.9 37 2.4 x 105 6.4 1.7 x 10-10

Crystal Box 1986 8 8 1.3 87 4 x 105 (6..9) 4.9 x 10-11

MEGA 1999 1.2 4.5 1.6 17 2.5 x 108 (6..7) 1.2 x 10-11

MEG 2006 0.8 4 0.1

5 19 2.5 x 107 100 1 x 10-13

The sensitivity is limited by the by the accidental backgroundThe 310-14

allows BR (e) 10-13 but needs

2 2acc μ e γ eγ eγΔ Δ Δ ΔBR R E E θ t

FWHM


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+e+ : correlated backgroundThe correlated background is smaller than the accidental

one

The correlated background•has a complicate dependence on the photon (y) and positron (x) energy resolutions.•Its rate depends linearly on the R

•The BR is 3x10-15


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+e+ : MEG sensitivity summary

0.6ε 0.70.9ε 0.9ε γ3

sele

0.09 4π Ω s

μ100.3R s102.6T 8μ

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Cuts at 1,4FWHM

Detector parameters

seleμsig

4

RTBRNSignal

seleμ

4RT

1SES 410-14

Single Event Sensitivity

corrBR

2 BR R E E θ t2 2acc μ e γ eγ eγΔ Δ Δ Δ 310-

14 310-15

Backgrounds

Upper Limit at 90% CL BR (e) 110-13

Discovery 4 events (P = 210-3) correspond BR = 210-13


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http://meg.psi.chhttp://meg.pi.infn.it

http://meg.icepp.s.u-tokyo.ac.jp

+e+ : MEG time profile

More details at

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

Planning R & D Assembly Data Taking

nownowLoILoI ProposalProposalRevisedRevised

documentdocument


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+e+ summary

The PSI E5 can deliver up to 3x108 +/s The MEG sensitivity is accidental background limitedWith better detector resolutions a BR of 10-14

would be possible No need, at least for the next 10 years, for a more intense beam


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+e+ comments• Total MEG cost: 7.5 M€• At the limit of present-day technology• Detector completion in spring 2006• Engineering runs 2006• Full statistic 3 years• A few months data taking for a factor 10 improvement

(2007)• Italian collaboration: 4 groups fully committed (adding up

~20 fte)• Near future:

Detector improvementPolarized beam (in case of signal !)


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-e- conversion

Ee = m-EB -ER

Signalcoherent LFV decay (A,Z) e (A,Z)

background

MIO (muon decay in orbit)

(A,Z) e (A,Z)

RPC (radiative pion capture)

(A,Z) (A,Z-1)

e- - (A,Z)

e- -

(A,Z)

-

(A,Z)


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-e- generalities 1 particle in the final state: no accidental Background

chance for pushing down the limit on BR

• Event selection based on e- momentum only• lifetime ~.9 s on Al or .35 s on Ti

Key element: beam quality !– Short (t ~ 10ns) and intense (~ 1013 s) pulses of low

momentum (~ 68 MeV/c) – Long beam off intervals ( t ~ 1 s )– Extremely low contamination (10-9 proton extinction or

FFAG)– Narrow momentum spread (<2 % with FFAG)


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-e- : sensitivity

R.Kitano et al Phys.Rev.D66(2002)096002


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-e- conv. present

Present limit B(e:Au ) < 8x10-13

by the SINDRUM II A. Van der Schaaf, NOON03

New approved experiment: MECOB(e) < 10-16 (2008 ? )

New project LOI to J-PARC: PRISM/PRIMEB(e) < 10-18 (>2010 ? )

cancelled


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-e- : SINDRUM II resultSINDRUM II parameters

– beam intensity 3x107 /s– momentum 53 MeV/c– magnetic field 0.33T– acceptance 7%– momentum res. 2% FWHM– S.E.S 3.3x10-13

– B(e:Au ) 8x10-13


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-e- : PRISM beamPPhase hase RRotated otated IIntense ntense SSlow low MMuon uon sourcesource

•To be operated at J-PARC (Japan) or elsewhere !!! (if J-PARC …)•Based on a FFAG ring•FFAG funded by Osaka Univ.•Ready end 2007


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-e- : PRISM beam

Phase rotation conceptPhase rotation concept• Muon momentum spread reduction by phase rotation down to 2 3 % FWHM

• Intensity 1012 /s (no pions);• Muon momentum 68 MeV/c.

The small energy spread allows very thin targets (<100 m)

If a momentum resolution 350 keV FWHM is reached, the experiment could be sensitive to e conversion with

SES ~ 6x10-19 BR ~ 10-18


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-e- : PRIME detector

Only a LOI has been presented at J-PARC

The detector is in form of conceptual design

The Collaboration seed is formed by Jap and US researchers

Cost ???Timescale ???

The physics channel is a very challenging but really interesting


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-e- and +e+ as probes of New Physics

e conv. is more sensitive for all processes not mediated by photon

e is more sensitive for processes mediated by photons

The motivation is sufficiently strong that both experiments should be done– Relative rates for e and e conv. would give

information on underlying mechanism– A significant rate for e with polarized muons could

give additional information on mechanism


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g-2 and e+e- based predictionAll E821 results were obtained with a “blind” analysis.

~2.7 difference with e+e- based SM prediction

world average

-1011 659 208(6)×10 (0.5 ppm)a


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Future g-2 experiments• Leading role of US groups• E969 @ BNL 0.5 → 0.20 ppm (scientific

approval but not funded)– expected near-term improvement in theory, →

the ability to confront the SM by ~ x 2• The next generation 0.20 → 0.06 ppm

– substantial R&D would be necessary


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A g-2 experiment to ~0.06 ppm?

• Makes sense if the theory can be improved to 0.1 ppm, which is hard, but maybe not impossible.

• With the present storage ring, we already have


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The Physics Case• Scenario 1

– LHC finds SUSY– MEG sees → e

• The trio will have SUSY enhancements– to understand the nature of the SUSY

space we need to get all the information possible to understand the nature of this new theory

a la L. Roberts


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The Physics Case• Scenario 2

– LHC finds Standard Model Higgs at a reasonable mass, nothing else …

• Then precision measurements come to the forefront, since they are sensitive to heavier virtual particles. – μ-e conversion is especially sensitive to other

new physics besides SUSY

a la L. Roberts


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Muon EDM• Present limit ~10-19 e-cm• Could reach 10-24 at a high intensity muon

source• Developments and technology owned by

US groups• We could think of placing the ring not in

the USA! J-PARC already was thought as an opportunity


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Muon channel

Realm of an other WG …


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Conclusion are sensitive probes of physics beyond the Standard

Model

• SUSY theories require cLFV not far from present existing upper limits

• Strong case for experimental searches in all channels, together with improved measurement of g-2 and EDM

+e+ results are expected in 2007

-e- conversion search is planned at the level of 10-18

-e- conversion is not accidental background limited could benefit of new high intensity pulsed beams


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BibliographyGeneral

J.Aysto et al. CERN-TH/2001-231NuFact03 proceedings INFN WG 2004

SINDRUM coll., W Bertl et al. Nucl.Phys. B260(1988)1SINDRUM2 coll., W Honecker et al. Phys.Rev.Lett. 76(1996)200MECO coll., BNL proposal AGS P940 (1997)MEG coll., “The MEG proposal” (2002)-A -A,X

S.N. Gninenko et al.,Mod. Phys. Lett. A17 (2002) 1407, M. Sher et al.,Phys. Rev. D69 (2004) 017302)

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- LFV and related topics