1 fact03 ny june 6 th 2003 particle physics with intense muon beams a.m. baldini - infn pisa

fact03 NY June 6th 2003 1

Particle physics with intense muon beams

A.M. Baldini - INFN Pisa


Layout of this talk

1. Precise measurements of muon lifetime (GF)

2. High precision experiments mesuring the carachteristics of the normal muon decay

3. (C)LFV experiments (muon rare decays mainly)4. g-2 and EDM

Do these experiments benefit by an increase of the muon intensity ? Statistics vs systematics

J. Aysto et al., CERN-TH/2001-231


1. Measurements of muon lifetime (GF)

• GF is one of the three parameters of the bosonic sector of the standard model

(0,045 ppm), MZ (23 ppm), GF (9 ppm)

• The accuracy is dominated by the knowledge of the muon lifetime (theoretical uncertainty <1ppm)

• True in pure V-A

• Electroweak fits depend on GF M2Z


Experiments

•3 experiments going-on

•RAL (D. Tomono)Need to depolarize the muons (limited coverage)

Detector segmented (MWPC+scint.) to avoid pile-up

Benefits from pulsed structure of the beam (time)

But repetition rate too low (50 Hz) -> statistically limited to 104 events/s to avoid pile-up

In order a 1 ppm accuracy 1012 events are needed

50 Hz ->50 KHz


muLan (G. Onderwater) at PSI

•Scintillator tiles + PMTs

• symmetric detector to reduce polarization effects

•Beam structure created artificially at PSI

•20 muons of the DC beam are used every 10 muon lifetimes

•1012 events collection

This class of experiments could gain an additional order of magnitude by an increase of the muon rate if pile-up and detector timing stability are kept under control


FAST at PSI Use of a pion beam

After a final beam test this year they will take data in 2004 and might be ready with results for fact04


2. TWIST (E614) at TRIUMF (P. Kitching)

)]34(3

21cos[)34(

3

2)1(3

Pdd

d

)parameter fourth (/ termsneglected; / max mmEE ee

Precise measurement of the Michel spectrum


TWIST setup

• is sensitive to right handed W bosons of several hundred GeV: sensitivity better than direct searches (D0)

•Need of a higly polarized muon beam (surface muon beam)

• sensitivity limited by systematic effects


T-violation experiment at PSI (W. Fetscher)

)(

fact03 NY June 6th 2003

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T-violation (2)principle of themeasurement


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3. (C)LFV: History of lepton flavour searches


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e: SUGRA indications

• SUSY SU(5) predictions

BR (e) 10-14 10-

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• SUSY SO(10) predictions

BRSO(10) 100 BRSU(5) R. Barbieri et al., Phys. Lett. B338(1994) 212

R. Barbieri et al., Nucl. Phys. B445(1995) 215

LFV induced by finite slepton mixing through radiative corrections

MEG goal

Experimental limit

combined LEP results favour tan>10


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MEG goal

Experimental limit

Connection with -oscillations

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

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

tan()=30

tan()=1

After SNO After Kamland

-5410R in the Standard Model !!


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Signal and background

e+ +

e = 180°

Ee = E = 52.8 MeV

Te = T

signal e

background

correlated

e

e+ +

accidental

e e

ee

eZ eZ

e+ +


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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 2007 0.8 4 0.15 19 2.5 x 107 100 1 x 10-13

The sensitivity is limited by the by the accidental background

The 310-14

allows BR (e) 10-13 but needs

eγ2

eγ2

γeμacc ΔΔΔΔ tθEERBR

FWHM

Need a DC beam here


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The MEG experiment at PSI

1m

e+

Liq. Xe Scin tilla tionDetector

Drift Cham ber

Liq. Xe Scin tilla tionDetector

e+

Tim ing Counter

Stopping TargetThin S uperconducting Coil

M uon Beam

Drift Cham ber

Easy signal selection with + at rest

e+ + Ee = E = 52.8 MeV

e = 180°Detector outline

• Stopped beam of >107 /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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http://meg.psi.chhttp://meg.pi.infn.it

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

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

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

Summary and Time Scale• This experiment may provide a clean indication of New Physics

• Measurements and detector simulation make us confident that we can reach the SES of 4 x 10-14 to e (BR 10-13)

• Final prototypes will be measured within this year• Large Prototype for energy, position and timing resolutions of s• Full scale Drift Chamber -Transport and degrader-target

• Financed very recently also in Italy (april)+Switzerland (may)• Tentative time profile

More details at

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Planning R & D Assembly Data Taking

nownowLoILoI ProposalProposalRevisedReviseddocumentdocument


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Calculation of B-e/Be


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Sindrum II setup


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Sindrum II gold target


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Beam related background

Moderator: range about ½ range


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Sindrum II results

Decay In Orbit

2% FWHM resolution


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MECO (P. Yamin)

1. Large acceptance pion capture in a SCS

2. Muon transport (60 – 120 MsV/c) in a curved solenoid

3. Long detector solenoid with muon stpping target and tracking system


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MECO (2)

• 1011 /s

• 900 KeV (FWHM) electron resolution, dominated by interactions in the target

• < 10-9 extinction between bursts (beam background)

•Sensitivity to B10-16

50% duty cycle


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PRISM (A. Sato)

•High intensity pulsed proton beam

•Pion capture solenoid

•Pion decay section

•Phase rotation (muon energy spread reduction) by means of an rf field

•Very similar to the front end of the proposed neutrino factories


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MECO (2)

•Intensity 1012 muons/s

•Low momentum (68 MeV/c)

•Narrow energy spread (few % FWHM)

The last characteristic is essential to stop enough muons in thin targets. If the electron momentum resolution can be kept below 350 KeV (FWHM) the experiment can be sensitive to e conversion down to 10-18

Other LFV processes such as muonium-antimuonium oscillations could be studied with improvements of some order of magnitudes wrt previous limits


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4. g-2(L. Roberts)

a = 11 659 204(7)(5) x 10-10 (0.7 ppm)

a for negative muons (CPT test)


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Muon anomaly vs theory


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edm (W.Morse)•P and T violating

•Best limit from g-2 CERN experiment: 3.7 3.4 x 10-19 e.cm

•Letter of intent (Jan 2003) for a dedicated experiment ->10-24 e.cm level

•Disentangle the EDM effect from the g-2 precession by means of a radial electric field

•High intensity beam of 0.5 GeV/c polarized muons: new PRISM; PRISMII


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Illustration of the beam needs for the different kinds of experiments


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Conclusions

•Muons are sensitive probes of physics beyond the standard model

•SUGRA theories need (C)LFV not too far from the existing limits

•Many of the on going measurements will benefit from an increase of the muon flux

•In some cases better experiments should be conceived

•This constitutes a challenge for the field of detectors R&D

•The effort is worthwhile: new physics could be not so far...

1 fact03 ny june 6 th 2003 particle physics with intense muon beams a.m. baldini - infn pisa

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