12 sepetmber 2008 paolo walter cattaneo 1 perspectives beyond meg paolo walter cattaneo infn pavia...

12 Sepetmber 12 Sepetmber 20082008

Paolo Walter CattaneoPaolo Walter Cattaneo 11

Perspectives beyond MEG Perspectives beyond MEG

Paolo Walter CattaneoPaolo Walter CattaneoINFNINFN PaviaPavia

Neutrino Oscillation WorkshopNeutrino Oscillation Workshop

Conca Specchiulla, Otranto, Lecce Conca Specchiulla, Otranto, Lecce (ITALY)(ITALY)

6 – 13 September 20086 – 13 September 2008



OutlineOutline• Theoretical motivations for searching for Theoretical motivations for searching for LFVLFV..• The The muonic channelmuonic channel::

ee ( (MEGMEG);); e conversion (e conversion (MECOMECO, , PRIMEPRIME);); conversion conversion (a brief mention)(a brief mention); ; Future perspectives.Future perspectives.

• The The tauonic channeltauonic channel:: , e, e ( (BABARBABAR, , BELLEBELLE);); lll lll ((BABARBABAR, , BELLEBELLE);); Other decays (Other decays ( lh, lh, lhh lhh …) …) ((BABARBABAR, ,

BELLEBELLE);); Future perspectives.Future perspectives.

• Conclusions.Conclusions.



Theoretical Theoretical motivationsmotivations

In theIn the Standard ModelStandard Model withwith massive Dirac massive Dirac neutrinosneutrinos LFV processesLFV processes (as(as e, , , , eee, eee, A A eA .. eA ..) ) are predicted are predicted atat unmeasurably unmeasurably small levels small levels (BR ~ 10(BR ~ 10-50-50).).

However,However, Most of the beyond SM modelsMost of the beyond SM models predict predict such processessuch processes atat much larger ratesmuch larger rates..

Since theSince the SM background is negligibleSM background is negligible, , LFV LFV processes processes areare clear evidences for Physisca clear evidences for Physisca beyond SMbeyond SM..



The The muonicmuonic channel channel



5

1

10-2

10-4

10-16

10-6

10-8

10-10

10-14

10-12

1940 1950 1960 1970 1980 1990 2000 2010

History of Lepton Flavor Violation with History of Lepton Flavor Violation with

- N e-N + e+ + e+ e+ e-

MEGA

SINDRUM2

Bran

chin

g Fr

actio

n Up

per L

imit

MEG goal

-

-N→e-N goal



SUSY predictions for SUSY predictions for e e

LFV induced by LFV induced by finite slepton finite slepton mixingmixing through through radiative radiative correctionscorrections..

MEG goalMEG goalJ. Hisano J. Hisano et al.et al., Phys. Lett. , Phys. Lett. B391B391 (1997) 341(1997) 341

SUSY SU(5) modelSUSY SU(5) modelExperimental Bound (MEGA Coll., PRD Experimental Bound (MEGA Coll., PRD 65 65 (2002) 112002)(2002) 112002)

In SO(10) In SO(10) BRBRSO(10)SO(10) 10 10 BRBRSU(5)SU(5)

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

In general beyond the SM predicts BRBR((ee)) BRBReeeeeeBRBReeeeeeBRBReAeA



ee: Signal and Background: Signal and Background

ee++ ++

ee = = 180°180°

EEee == E E == 52.852.8 MeVMeV

TTee = = TT

signal ee

background

promptprompt

ee

ee++ ++

accidentalaccidental

ee ee ee ee

eZ eZ eZeZ

ee++ ++ Vanishing EVanishing E

energyenergy



Summary of MEG Summary of MEG sensitivitysensitivity

BR BR (( e e )) 1 1 • • 1010-13-13Upper Limit @ 90 % Upper Limit @ 90 %

C.L.C.L.

BRBRaccacc R R •• EEee •• ( (EE22 •• ( (22 •• tt 3 3 • • 1010-15-15Accidental BackgroundAccidental Background

BRBRcorrcorr 11•• 10 10-15-15Correlated BackgroundCorrelated Background

NNsigsig = BR = BR •• T T •• R R •• /4/4 •• e e selsel SignalSignal

SES = 1/(T SES = 1/(T •• R R •• /4/4 •• e e selsel 4 4 • • 1010-14-14Single Event SensitivitySingle Event Sensitivity

4 events4 events ( (P = 2 P = 2 •• 10 10-3-3) correspond to ) correspond to BR =BR = 2 2 • • 1010-13-13DiscoveryDiscovery

ee/E/Eee = 1.0% = 1.0% /E/E = 4.0% = 4.0%

ee 0.6 0.6 0.6 0.6 selsel (0.9) (0.9)33 = 0.7 = 0.7/4/4 = 0.09 = 0.09Detector parametersDetector parameters

RR = 3.0 = 3.0 •• 10 1077 ++/s Duty cycle 100%/s Duty cycle 100%

T = 2.5 T = 2.5 •• 10 107 7 ss

tteeps ps eemradmrad



What next for What next for e e ? ? 1)1)

Which gain in sensitivity can be expected usingWhich gain in sensitivity can be expected usingmore intense muon beamsmore intense muon beams ( ( 10 101010 /s) ? /s) ?

For a 0 background experiment with RFor a 0 background experiment with Rtunabletunable

RRoptopt1/sqrt(T 1/sqrt(T •• /4/4 •• e e selsel ••EEee • • tt• 1/(• 1/(EE• •

SESSESoptopt ((EE• • sqrtsqrtEEee• • ttsqrt(T • sqrt(T • /4/4 • • e e selsel Linear improvements are obtained only with Linear improvements are obtained only with EE andand

At PSI At PSI RRmax max ••as far as as far as RR

max max >>RRopt opt rate is not a limitationrate is not a limitation

A factor 10 to be gained to reach A factor 10 to be gained to reach BRBR(( e e )) 1 • 101 • 10-14-14

Either a detector technology breakthrough orEither a detector technology breakthrough orseveral small (factors 1.5-2.0) improvementsseveral small (factors 1.5-2.0) improvements



Most limiting factorsMost limiting factors: : performances of e.m. performances of e.m.

calorimeter MEG Lxe is state of the art calorimeter MEG Lxe is state of the art

technology technology

SomeSome possible improvementspossible improvements: :

- - high resolution beta spectrometers high resolution beta spectrometers ((EEee/E/Eee = =

0.1 %0.1 %), ), geometrical acceptance ??geometrical acceptance ??;;

- - thinner targetthinner target to improve to improve ( (exploiting higher exploiting higher

intensity muon beamsintensity muon beams), ), off target decay increase pileup off target decay increase pileup

background??background??;;

- - finely segmented active targetfinely segmented active target (to improve e (to improve e

match), match), concept to be developedconcept to be developed; ;

Substantial Substantial RDRD needed !!! needed !!!

What next for What next for e e ? ? 2)2)



3e status3e status

BR(BR( 3e) ~ 3e) ~ BR( BR( e e) ~ 10) ~ 10-2-2 BR( BR( e e))20 year old20 year old limitlimit BR(BR(3e) < 103e) < 10-12-12 (SINDRUM Coll., Nucl. Phys. (SINDRUM Coll., Nucl. Phys.

B299B299 (1988) 1) (1988) 1) BRBRaccacc 1010-13 -13 RRRRmaxmax= 5 = 5 •• 10106 6 /s/s

ExploitExploit E Eee = M = M time coincidencetime coincidence and and coplanaritycoplanarity

Also limited byAlso limited by accidental backgroundaccidental background..((Michel positron and an eMichel positron and an e++ee-- pair produced by Bhabha scattering in the target pair produced by Bhabha scattering in the target))Experimental advantage: Experimental advantage: no photonsno photons

no e.m. calorimeter no e.m. calorimeter.. However: However: very high ratevery high rate in tracking systemin tracking system dead time, trigger & pattern recognition dead time, trigger & pattern recognition problemsproblems; ;

need of need of large modularitylarge modularity..

large angular and momentum acceptance of large angular and momentum acceptance of spectrometerspectrometer



3e the future3e the future

To be competitive with MEG predicted limit To be competitive with MEG predicted limit BR(BR( ee)<)<1010-13-13

BR(BR( 3e) < 3e) <1010-15 -15 !!!!

Total efficiencyTotal efficiency in SINDRUM in SINDRUM Cannot be improved Cannot be improved much!!much!!

To match the BR goal To match the BR goal RR must increase by must increase by 101033 to to RR= 5 = 5 •• 10109 9 /s/s

BrBracc acc increase of a factor 10increase of a factor 106 6 !!!!

MEG timing system improve resolution of factor of 10MEG timing system improve resolution of factor of 10

Recover 10Recover 1055 from tracking and material reduction appears from tracking and material reduction appears extremely difficult.extremely difficult.

No experimet proposal in the last 20 yearsNo experimet proposal in the last 20 years



--A A e e--A: Conversion A: Conversion Mechanism Mechanism

•- - are are stoppedstopped in material foils in material foils ( (AlAl for MECO, for MECO, TiTi for PRIME) forming for PRIME) forming muonic muonic atomsatoms..

•Three possible fates for the muon:Three possible fates for the muon: Nuclear capture;Nuclear capture; Three body decay in orbit;Three body decay in orbit; Coherent LFV decayCoherent LFV decay (extra factor of Z in the rates). (extra factor of Z in the rates).

•Signal is a Signal is a single monochromatic electron: single monochromatic electron:

•EEee = m = mmm – E – E

recoilrecoil – E – Ebinding binding 105.0 MeV (Al), 104.3 MeV (Ti)105.0 MeV (Al), 104.3 MeV (Ti)

• inin Al Al ~ 0.9 ~ 0.9 ss, , in in Ti Ti ~ 0.35 ~ 0.35 ss ( (in vacuum: 2.2in vacuum: 2.2 s).s).



--A A e e--A:A: Signal and Signal and

BackgroundBackground

EEeesigsig== m m– E– EB B - -

EERR

signalsignal (A,Z)(A,Z) e e (A,Z)(A,Z)

main backgroundsmain backgrounds MIO MIO (muon decay in orbit)(muon decay in orbit) (A,Z)(A,Z) ee (A,Z)(A,Z)

EEeemaxmax== mm– E– EB –B – E ERR dN/dEdN/dE

ee

(E(Emaxmax–E–Eee))

55

ee-- -- (A,Z)(A,Z) RMC RMC ((radiative radiative capture capture))

(A,Z)(A,Z) (A,Z-1) (A,Z-1) ee++ ee--

Beam related background!Beam related background!

No coincidenceNo coincidenceno accidental backgroundno accidental background

RPC RPC ((radiative radiative capture capture)) (A,Z)(A,Z) (A,Z-1) (A,Z-1) ee++

EEeemax max > > EEee

sig sig !!!!



Reduction of beam Reduction of beam backgroundbackground

1) Beam pulsing:1) Beam pulsing: Muonic atoms have Muonic atoms have some hundreds of nslifetimesome hundreds of nslifetime use a pulsed use a pulsed beam with beam with buckets short compared to this lifetimebuckets short compared to this lifetime, leave , leave decaydecay andand measure in a delayed time windowmeasure in a delayed time window. .

2) 2) Beam quality:Beam quality:- insert a insert a moderatormoderator to to reduce the reduce the contamination contamination (pion (pion range 0.5 muon range); a range 0.5 muon range); a 101066 reduction factor reduction factor obtained by obtained by

SINDRUM II. SINDRUM II. No more than 10No more than 1055 may stop in the may stop in the target during the full measurement (target during the full measurement ( 1 1 background event); background event);- select select a beam momentum 70 MeV/ca beam momentum 70 MeV/c ( ( decaying in decaying in flight produce low energy electrons).flight produce low energy electrons).



Present limit: SINDRUM II Present limit: SINDRUM II (PSI)(PSI)

SINDRUM II parametersSINDRUM II parameters– beam intensitybeam intensity 3 x 103 x 1077 /s/s

– momentummomentum 53 MeV/c53 MeV/c

– magnetic fieldmagnetic field 0.33T0.33T

– acceptance acceptance 7%7%

– momentum res.momentum res. 2% FWHM2% FWHM

– S.E.SS.E.S 3.3 x 103.3 x 10-13-13

– B(B(--Au Au e e--Au Au ) ) 8 x 10 8 x 10-13-13



The MECO/MU2E The MECO/MU2E Experiment Experiment

•Expected 10Expected 101111 stopping stopping /s (1000–fold increase in/s (1000–fold increase in beam beam intensity) for intensity) for

a proton current of 4 x 10a proton current of 4 x 101313 protons/s (8 GeV) and high Z protons/s (8 GeV) and high Z target.target.

•Curved transport selects low momentum Curved transport selects low momentum (n, (n, removed)removed)

•High rate capability electron detectors in a 1 T fieldHigh rate capability electron detectors in a 1 T field

Crystal Calorimeter

Straw Tracker Stopping

Target Foils

Pion Production Target

Superconducting Solenoids

Proton Beam

Muon Beam

5 T

2.5 T

2 T

1 T

1 T



MECO/MU2E proton MECO/MU2E proton beambeam

Pulsed beam from Pulsed beam from AGS (BNL)/FERMILAB AGS (BNL)/FERMILAB to reduce prompt backgrounds.to reduce prompt backgrounds.

Measurement windowMeasurement window



MECO/MU2E expected MECO/MU2E expected sensitivitysensitivity

Expected Expected 5 signal events5 signal events for 10 for 1077 s (2800 hours) running if s (2800 hours) running if RRee = 10 = 10-16-16

0.600.60 capture probabilitycapture probability

5.05.0Detected events forDetected events for RRee = 10 = 10-16-16

0.190.19Fitting and selection criteria efficiencyFitting and selection criteria efficiency

0.900.90Electron trigger efficiencyElectron trigger efficiency

0.490.49Fraction ofFraction of capture in detection time window capture in detection time window

0.580.58 stopping probabilitystopping probability

0.00430.0043 entering transport solenoid / incident proton entering transport solenoid / incident proton

4 4 10 101313Proton flux (Hz) (50% duty factor, 740 kHz micropulse)Proton flux (Hz) (50% duty factor, 740 kHz micropulse)

101077Running time (s) Running time (s)

FactorFactorContributions to the Signal RateContributions to the Signal Rate

ExpectedExpected ~ 0.45 bck events~ 0.45 bck events ( (0.25 MIO, 0.07 RPC0.25 MIO, 0.07 RPC) ) for 10for 107 7 s running times running time..



PRISM/PRIMEPRISM/PRIME

PRIPRIsmsm M Muonuon E Electron conversion lectron conversion experimentexperimentPPhase hase RRotation otation IIntense ntense SSlow low MMuon sourceuon sourceAt JPARC (Japan) Fixed Field Alternating Gradient (FFAG)(FFAG) synchrotron ready in 2007 High intensity High intensity pulsed proton beam (pulsed proton beam (~ ~ 101014 14 p/sp/s));;

Muon energy spread reductionMuon energy spread reduction (phase rotation)(phase rotation) E 2E 23% FWHM 3% FWHM spreadspread IntensityIntensity 10 101212 /s /s (no pions);(no pions); Muon momentum Muon momentum 68 MeV/c68 MeV/c. . Small Small EE essential to essential to stop enough muonsstop enough muons inin very thin targetsvery thin targets, improving momentum , improving momentum resolution. resolution. If If p p 350 keV (FWHM) , 350 keV (FWHM) , the experiment the experiment can becan be

sensitivesensitive to to BR(BR(e)< 10e)< 10-(18-(1819)19). .



PRIME Detector LayoutPRIME Detector Layout• PRIME=PRISM mu-e conversion

– High field solenoid magnet– Target– Positron tracking chambers– Positron energy calorimeter



A look at the futureA look at the future

High intensity machines under study (like High intensity machines under study (like NUFACTNUFACT at CERN or at CERN or ProtonProtonDriverDriver at Fermilab) should provide at Fermilab) should provide proton beams at the level of proton beams at the level of 10101515 protons/s of some GeV protons/s of some GeV. Secondary beams with . Secondary beams with intensity intensity ~ 10~ 101414 /s/s could be obtained from these machines. could be obtained from these machines.

The The A -> eA -> e--A conversion experiments are A conversion experiments are not limited by accidentalnot limited by accidentalbackground.background. In principle In principle they can benefit of the increased they can benefit of the increased muon beam intensity much better than -> emuon beam intensity much better than -> e experiments. experiments.

We can hope to gain We can hope to gain a couple of order of a couple of order of magnitudesmagnitudes in in

the experimental sensitivity for the experimental sensitivity for LFV muon decaysLFV muon decays in in

respect with present experiments ? respect with present experiments ?



--A A --A,XA,X

The possibility of exploringThe possibility of exploring A,XA,X conversionconversion channel is under investigation channel is under investigation It could complement the It could complement the LFV LFV decaysdecays, as, as , , ee etc.etc.

Need of an intense high energy muon beamNeed of an intense high energy muon beam: :

a) Ea) E 20 GeV 20 GeV b) 10b) 102020 muons/year muons/year ((/neutrino /neutrino

factoryfactory)) production compatible with existing bounds: production compatible with existing bounds: up to several up to several thousands of thousands of ’s’s (depending on (depending on energy) energy)Signal selection based on Signal selection based on angular distribution ofangular distribution of decay productsdecay products (hard hadrons or (hard hadrons or ) and ) and missing momentummissing momentum Backgrounds: Backgrounds: mis-identified hard mis-identified hard fromfrom A A A’A’ , , hard hadronshard hadrons from from targettarget Need of Need of realistic MC simulations and detector design !realistic MC simulations and detector design !



The The tauonictauonic channel channel



GeneralitiesGeneralities

The The channel channel is in principle is in principle very interestingvery interesting for studying for studying

LFV because of the LFV because of the large mass (m large mass (m 17 m 17 m)) Many Many decay channelsdecay channels;; BR’s enhancedBR’s enhanced in respect with in respect with e e by (m by (m/m/m)) with with ~ ~

3 3

Experimental problem: Experimental problem: production & detection of production & detection of large large samplessamples..

To be To be competitive with dedicated experimentscompetitive with dedicated experiments one must one must reach reach

BR(BR() < 10) < 10-(8-(8)) Significant improvements obtained by Significant improvements obtained by B-factoriesB-factories

((BELLE,BABARBELLE,BABAR). ).



Predicted by many new physics models– Normal NP models enhance and l+l-

– Some NP models may enhance other modes– eand el+l are similar

Several measurable BR O(10-8) in parameter space.

Reference SM+ mixing EPJ C8(1999)513 10-40 10-14

SM + heavy Maj R PRD 66(2002)034008 10-9 10-10

Non-universal Z’ PLB 547(2002)252 10-9 10-8

SUSY SO(10) PRD 68(2003)033012 10-8 10-10

mSUGRA+seesaw PRD 66(2002)115013 10-7 10-9

SUSY Higgs PLB 566(2003)217 10-10 10-7

LFV LFV decays: prediction decays: prediction



SUSY predictions for SUSY predictions for LFV LFV decaysdecays

Green: Belle (2008)Green: Belle (2008)Yellow: BaBar Yellow: BaBar (2008)(2008)

Br(ee) / Br() 1/94

Br()/ Br() 1/440

Br(eee) / Br(e) 1/94

Br(e)/ Br(e) 1/440

B-factories are B-factories are -factories too-factories too:

ee



qq _

2photon process f=leptons,quarks

signal

Only tag side has neutrino(s).

Both sides have neutrino(s).

radiative Bhabha process

e+ e

eee

e

many tracks

• e+e- – 1 prong tau decay

(BR~85%)

LFV LFV decays; Signal and decays; Signal and BackgroundBackground



BelleBelle BaBarBaBar BelleBelle BaBarBaBarUL90(10-7)

Lum(fb-1)

UL90(10-7)

Lum(fb-1)

UL90(10-7)

Lum(fb-1)

UL90(10-7)

Lum(fb-1)

0.5 535 0.7 232 e 0.8 401 1.3 339

e 1.2 535 1.1 232 3l 0.2-0.4 535 0.4-0.8 376

0.7 401 1.5 339 lhh 2-16 158 1-5 221

’ 1.3 401 1.3 339 V0 0.6-1.3 543 1.0() 384

1.2 401 1.5 339 eV0 0.6-1.8 543 1.1(e) 384

e 0.9 401 1.6 339 f00.33 671

e’ 1.6 401 2.4 339 ef0 0.34 671

Current status of LFV searchCurrent status of LFV search



• Int. Luminosity at B-factories >1.3 ab-1

– ~1.2x109 -pairs• Super B-factory 10 ab-1/year (50 ab-1)• BR sensitivity

– It depends on background.– l; scale as ~1/L

• ee is irreducible BG.• ~10-8 level at super B-factory

– lll, lX0; scale as ~1/L• O(10-9) level at super B-factory

The future: Super B The future: Super B factories factories

Super-B factories are under design: luminosity 5Super-B factories are under design: luminosity 5 x x 10103535 cm cm-2-2 s s-1-1



The future: LHC The future: LHC

LHCLHC In In one year of data taking at low luminosityone year of data taking at low luminosity, ~ , ~ 10101212 are produced and are produced and several several hundred millions could be used to search for LFV hundred millions could be used to search for LFV decays decays. .

MainMain sources sources:: W -> W -> , Z ->, Z ->, B -> , B -> DD

The The predicted sensitivitiespredicted sensitivities in the in the->-> and and -> 3 -> 3 channels channels

are are BrsBrs ~ 10~ 10-7--7-1010-8-8, at the level of the , at the level of the present B-factories resultspresent B-factories results

(the (the -> 3-> 3 channel has channel has the best signal/noise ratiothe best signal/noise ratio).).



• Existing LFV limits starts challenging New Physics model. The strongest constraint from:– Br(->e) < 1.2 10-11

– Br(ee) < 2.0 10-8

• MEG plans to reach in the next few years– Br(->e) < 1.0 10-13

• Similar constraints from SuperB factory– Br(lll) < 1.0 10-9

• Strongest limit from ->eA (Mu2e-PRISME) – Br(->e) < 1.0 10-17-18

• In future -factory could bring farther improvement down to Br(->e) < 1.0 10-19-20

SummarySummary



On DemandOn Demand



Many possibilities …Many possibilities …

CΛ 3000 TeV

-4HHg =10 ge

Second Higgs

2Z

17

M 3000 TeV/c

B(Z ) 10e

Heavy Z’, Anomalous Z coupling

Supersymmetry

2 13N eNU U 8 10

Heavy Neutrinos

L

2

M

3000 TeV/cd ed

Leptoquarks

After W. Marciano

Predictions at 10-

15



• Most famous SM extension• LFV are generated through slepton mixing.

– Independent parameter for e

• SUSY seesaw (J.Hisano et. al.,PRD 60 (1999) 055008)

– Achievable BR of O(10-7~-8) if tan~60 and mSUSY~1TeV/c2

SUSYSUSY



• When sleptons are heavy (>weak scale),Br() is suppressed.

• Higgs in SUSY enhances other LFV modes, such as 3l, l+hadrons, ...

• Higgs-mediated MSSM– 3 (A.Brignole, A.Rossi, PLB 566 (2003) 217)

– Enhanced if tan is large and Higgs mass is small.

SUSY HiggsSUSY Higgs



SUSY HiggsSUSY Higgs• Higgs-mediated MSSM (M.Sher, PRD 66 (2002) 057301)

– Br() : Br() = 8.4 : 1• Phase space, color factor, mass

• MSSM seesaw (E.Arganda, arXiv:0803.2039v1)

– Large BR of O(10-7) for , ’,

• Need to search for all possible LFV modes– To probe unknown physics and discriminate models



38

decay in vacuum: Ee < mc2/2

decay in bound orbit: Ee < mc2 - ENR - EB

Radiative Muon Capture: - N N(Z-1)

For Al, Emax=102.5 MeV/c2, P(E >100.5 MeV/c2) =410-9

P( e+e-, Ee > 100.5 MeV/c2) = 2.5 10-5

Restricts choice of stopping targets: Mz-1 > Mz

Radiative Pion Capture: - N N(Z-1)

• Branching fraction ~ 1.2% for E > 105 MeV/c2

• P( e+e-, 103.5 < Ee< 100.5 MeV/c2) = 3.5 10-5

• Limits allowed pion contamination in beam during detection time

--A A e e--A:A: Signal and BackgroundSignal and Background



MECO expected sensitivityMECO expected sensitivity

Expected ~ Expected ~ 5 signal events5 signal events for 10 for 1077 s (2800 hours) running if R s (2800 hours) running if Ree = 10= 10-16-16

0.600.60 capture probabilitycapture probability

5.05.0Detected events for Detected events for RRee = 10 = 10-16-16

0.190.19Fitting and selection criteria efficiencyFitting and selection criteria efficiency

0.900.90Electron trigger efficiencyElectron trigger efficiency

0.490.49Fraction of Fraction of capture in detection time window capture in detection time window

0.580.58 stopping probabilitystopping probability

0.0040.00433

entering transport solenoid / incident proton entering transport solenoid / incident proton

4 4 10101313

Proton flux (Hz) (50% duty factor, 740 kHz Proton flux (Hz) (50% duty factor, 740 kHz micropulse)micropulse)

101077Running time (s) Running time (s)

FactorFactorContributions to the Signal RateContributions to the Signal Rate



MECO backgroundMECO background

Without scattering in stopping Without scattering in stopping targettarget

< 0.03< 0.03 decay in flightdecay in flight

Assuming 10Assuming 10-4 -4 CR veto inefficiencyCR veto inefficiency0.0040.004Cosmic ray inducedCosmic ray induced

Mostly from Mostly from --0.0070.007Anti-proton inducedAnti-proton induced

Assuming 10Assuming 10-9 -9 inter-bunch inter-bunch extinction extinction

0.450.45Total BackgroundTotal Background

From late arriving pionsFrom late arriving pions0.0010.001Radiative Radiative capture capture

From out of time protonsFrom out of time protons0.070.07Radiative Radiative capture capture

< 0.001< 0.001 decay in flightdecay in flight

With scattering in stopping targetWith scattering in stopping target 0.040.04 decay in flightdecay in flight

< 0.04< 0.04Beam eBeam e--

< 0.005< 0.005RadiativeRadiative decay decay

< 0.006< 0.006Tracking errorsTracking errors

S/N = 20 for RS/N = 20 for Ree = 10 = 10-16-16 0.250.25 decay in orbitdecay in orbit

CommentsCommentsEventsEventsSourceSource

ExpectedExpected ~ 0.45 ~ 0.45 bck bck eventsevents for for 10107 7 s s running running time.time.



A look at the future: rough A look at the future: rough estimate for a possible pulsed estimate for a possible pulsed

muon beam at muon beam at NUFACT or Fermilab Proton DriverNUFACT or Fermilab Proton Driver

Using Using MECO numbersMECO numbers for scaling: for scaling: MECOMECO Proton DriverProton Driver NUFACTNUFACT

p/s (8 GeV) p/s (8 GeV) 4 x 10 4 x 101313 1 1 2 x 10 2 x 101515 1.5 x 101.5 x 101515

/s (tungsten target)/s (tungsten target) 1 x1 x 10101111 3 3 5 x 10 5 x 1011 11 1 x 101 x 101212

SensitivitySensitivity 2 x 102 x 10-17-17 few x 10few x 10-18-18 1 x 10 1 x 10-18-18

Competitive with PRIME.Competitive with PRIME.(same extinction factor assumed: 10(same extinction factor assumed: 1099)) Power release: Power release: ~ 10 kW many tens of kW~ 10 kW many tens of kW ~ 100 kW ~ 100 kW (need of (need of target coolingtarget cooling to avoid to avoid

melting)melting)Need precise design and estimatesNeed precise design and estimates.. EEpp = 2.2 GeV; scaling by using GHEISHA. = 2.2 GeV; scaling by using GHEISHA.



Beam requirements for Beam requirements for ee

Continuous beamContinuous beam to reduce the to reduce the accidental backgroundaccidental background;; Small momentum biteSmall momentum bite ( (p/p p/p 10 % 10 %) to use ) to use thin targetsthin targets;; Use Use surface muonssurface muons ( (ppss = 29 MeV/c = 29 MeV/c) to maximize the ) to maximize the pion pion stopping stopping raterate in the target (R in the target (R p p3.53.5 for p for p ppss); ); Good Good /e separation/e separation by by Wien filtersWien filters; ; Possible solution to Possible solution to realize an (almost) continuos muon realize an (almost) continuos muon beambeam:: insert insert a thina thin (~ 10 (~ 10-3-3 interaction lengths) interaction lengths) pion pion production production target inside the proton synchrotron target inside the proton synchrotron oror recirculating recirculating LINACLINAC.. Protons Protons recirculate many timesrecirculate many times and end up interacting. and end up interacting. If If they stay in the synchrotron/LINAC for a long timethey stay in the synchrotron/LINAC for a long time, , an almost continuous muon beam can (in principle) be an almost continuous muon beam can (in principle) be obtained.obtained. Problems: - Problems: - target heatingtarget heating;; - - radiation in the target arearadiation in the target area (safety (safety requirements).requirements). See J. See J. ÄÄystystöö et al., “Physics with low-energy muons at a et al., “Physics with low-energy muons at a neutrino neutrino factory complex”, hep-ph/0109217 factory complex”, hep-ph/0109217



Conclusions about Conclusions about ee

The The MEG experimentMEG experiment at PSI is in advanced state of building at PSI is in advanced state of building and and

testing; the testing; the data taking is foreseen for 2006data taking is foreseen for 2006. . The expected The expected MEG sensitivity is down to BR(MEG sensitivity is down to BR( e e) ) 1010-13-13, ,

a a two orders of magnitude improvementtwo orders of magnitude improvement in respect with in respect with

present bound. Many present bound. Many SUSY models predictSUSY models predict LFV in the LFV in the

ee channel at this level channel at this level or even higher. or even higher. A A further improvement in sensitivityfurther improvement in sensitivity by using more by using more intense intense

muon beams is muon beams is not easynot easy because of because of accidental accidental background background

limitationslimitations; ; strong improvements in detector strong improvements in detector technologies technologies

are neededare needed. Moreover, a . Moreover, a continuous beamcontinuous beam must be must be realized.realized.



Conclusions about Conclusions about --A A e e--A conversionA conversion

The The --A A e e--A conversion BRA conversion BR is predicted by many SUSY is predicted by many SUSY theories theories atat measurable levels (~ 10 measurable levels (~ 10-15-15)).. The The --A A e e--AA conversion conversion and the and the ee channels are complementarychannels are complementary in discriminating in discriminating between between LFV theoretical models.LFV theoretical models. Two Two LFV experimentsLFV experiments working in the working in the --AA e e--A conversion A conversion channel channel are in preparation/project: are in preparation/project: MECOMECO and and PRIMEPRIME; ; results are results are expected in some yearsexpected in some years from now. They should from now. They should improve improve the the present limitpresent limit on the on the --AA e e--A BR (~ 10A BR (~ 10-13-13) by at least ) by at least three orders of magnitudethree orders of magnitude. . Since they are not limited by accidental background, Since they are not limited by accidental background, --AA e e--AA conversion experiments can potentially benefitconversion experiments can potentially benefit from the from the muon muon flux increase expected in Neutrino Factories and Muon flux increase expected in Neutrino Factories and Muon FacilitiesFacilities. . The key factors are The key factors are momentum resolutionmomentum resolution and and pion pion extinctionextinction factorfactor. A suitably tuned . A suitably tuned pulsed muon beampulsed muon beam is needed. is needed.



Conclusions about muonic Conclusions about muonic channelchannel ee

- - The The MEG experimentMEG experiment at PSI is in advanced state of building and testing; at PSI is in advanced state of building and testing; data data takingtaking is foreseen for 2006is foreseen for 2006. The expected . The expected MEG sensitivity is down to BR(MEG sensitivity is down to BR( e e) ) 10 10-13-13,, a a two orders of magnitude improvementtwo orders of magnitude improvement in respect with present bound. in respect with present bound. Many Many SUSYSUSY models predictmodels predict LFV in the LFV in the e e channel at this level channel at this level or even higher. or even higher. - A - A further improvement in sensitivityfurther improvement in sensitivity by using more intense by using more intense -beams is -beams is not not easyeasy because of because of accidental background limitationsaccidental background limitations; ; strong improvements in strong improvements in detectordetector technologies are neededtechnologies are needed; a ; a continuous beamcontinuous beam must be realized must be realized..

--A A e e--AA - - The The --A A e e--AA conversion and the conversion and the e e channels are complementarychannels are complementary in in discriminating between LFV theoretical models. Two discriminating between LFV theoretical models. Two --AA e e--A conversion A conversion experiments are in preparation/project: experiments are in preparation/project: MECOMECO and and PRIMEPRIME; ; results are results are expected in some yearsexpected in some years from now. They should from now. They should improve the present limit improve the present limit on the on the --AA e e--A BR (8 x10A BR (8 x10-13-13) by at least ) by at least three orders of magnitudethree orders of magnitude. . - Since they are not limited by accidental background, - Since they are not limited by accidental background, --AA e e--AA conversion conversion experiments can potentially benefitexperiments can potentially benefit from the from the muon flux increase muon flux increase expected inexpected in Neutrino Factories and Muon FacilitiesNeutrino Factories and Muon Facilities. The key factors are . The key factors are momentum momentum resolutionresolution and and pion extinctionpion extinction factorfactor. A suitably tuned . A suitably tuned pulsed muon beampulsed muon beam is needed. is needed.



Conclusions on tauonic Conclusions on tauonic channelchannel

The tauonic channel is The tauonic channel is very promisingvery promising for the search for LFV for the search for LFV processes because processes because the large the large mass enhances the BR’s and opens a mass enhances the BR’s and opens a lot of possible channelslot of possible channels. Experimentally speaking, this channel is . Experimentally speaking, this channel is presently presently not yet competitive (but not so far)not yet competitive (but not so far) from the more from the more studied muonic channel. studied muonic channel.

The B-factory experiments improved the limits on The B-factory experiments improved the limits on LFV LFV decay BR’s by about one order of magnitudedecay BR’s by about one order of magnitude; one or two ; one or two other order of magnitudes should be gained by other order of magnitudes should be gained by Super B-factoriesSuper B-factories, , reaching reaching BR levels which would put severe constraints on BR levels which would put severe constraints on supersymmetric parameter spacesupersymmetric parameter space. To fully benefit of the increase in . To fully benefit of the increase in luminosity, luminosity, a careful background control is neededa careful background control is needed. .

Huge samples of Huge samples of ’s will be produced at LHC’s will be produced at LHC, even at low , even at low luminosity, but only luminosity, but only a sub-sample can be used for LFV studiesa sub-sample can be used for LFV studies. . LFV LFV decays of SUSY particles can be studied together with “usual” LFV decays of SUSY particles can be studied together with “usual” LFV decaysdecays..

12 sepetmber 2008 paolo walter cattaneo 1 perspectives beyond meg paolo walter cattaneo infn pavia...

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