# Presentation: 173869

## Particle physics with intense muon beams

- A.M. Baldini - INFN Pisa

## Layout of this talk

- Precise measurements of muon lifetime (GF)
- High precision experiments mesuring the carachteristics of the normal muon decay
- (C)LFV experiments (muon rare decays mainly)
- 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)

- 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)

## T-violation (2)principle of themeasurement 

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

## e: SUGRA indications

- SUSY SU(5) predictions
- BR (e)  10-14  10-13
- 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

- combined LEP results favour tan>10

## Connection with -oscillations

- 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**

- in the Standard Model !!

## Signal and background

- e = 180°
- Ee = E = 52.8 MeV
- Te = T

- signal
-   e 

- background

- correlated
-   e 

- accidental
-   e
-   e 
- ee  
- eZ  eZ

- 	

## 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 					            310-14
- allows  *BR *(e)  10-13  but needs

- FWHM

- Need  a DC beam here

## The MEG experiment at PSI

- Easy signal selection with  + at rest

- 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

## Summary and Time Scale

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

- 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

## Calculation of B-e/Be

- Calculation of B-e/Be

## Sindrum II setup

## Sindrum II gold target

## Beam related background

- Moderator: range  about 1⁄2 range 

## Sindrum II results

-  Decay In Orbit

- 2% FWHM resolution

## MECO (P. Yamin)

- Large acceptance pion capture in a SCS
- Muon transport (60 – 120 MsV/c)  in a curved solenoid
- Long detector solenoid with muon stpping target and tracking system

## MECO (2)

-  1011 /s
-  900 KeV (FWHM) electron resolution, dominated by interactions in the target
-  < 10-9 extinction between bursts (beam background)
- Sensitivity to B10-16

- 50% duty cycle

## 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

## 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

## 4. g-2(L. Roberts)

- a = 11 659 204(7)(5) x 10-10 (0.7 ppm)
- a for negative muons (CPT test)

## Muon anomaly vs theory

##  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

## Illustration of the beam needs for the different kinds of experiments

## 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...