LFV with µ-beams: status and perspectives

Size: px

Start display at page:

Download "LFV with µ-beams: status and perspectives"

Juliet Barton
6 years ago
Views:

1 LFV with µ-beams: status and perspectives Donato Nicolò Università di Pisa & INFN XXXX Rencontres de Moriond 5-12 March 2005

2 Outline Theoretical issues for LFV SUSY predictions Connections with neutrino oscillations Past searches An historical touch Beam intensity, detection resolution & sensitivity µ eγ Signature and background The MEG experiment µ 3e The SINDRUM experiment µ e conversion SINDRUM2 MECO Beam developments and future experiments Conclusions Search for LFV... 2

3 LFV in the Standard Model Neutrino oscillations flavour mixing in lepton sector Extensions of SM with massive Dirac neutrinos allow LFV also with charged leptons (µ eγ, τ eγ, µ eee, µ e) Γ Γ( 2 2 ( µ eγ ) α 2 m 55 sin 2θ 10 2 e ) 2 µ νν π M W larger mass scale needed SUSY not observable! Search for LFV... 3

4 SUSY predictions LFV induced by finite slepton mixing through radiative corrections R. Barbieri et al., Phys. Lett. B338(1994) 212 R. Barbieri et al., Nucl. Phys. B445(1995) 215 P. Ciafaloni et al., Nucl. Phys. B458(1996) 3 SU(5) B (µ eγ) SO(10) ~μ μ ~ χ 0 e Current experimental limit Next goal m 2 ~μ~e fl ~e B SO(10) (m τ /m µ ) 2 B SU(5) tan(β)<3 excluded at 95% C.L. by combined LEP results (hep-ex/ ) Minimal SU(5) SUSY-SUGRA pure SUSY effect (no SM contamination) Search for LFV... 4

5 m 2 (ev 2 ) % CL SUSY with ν R MSSM models with right-handed Majorana neutrinos (see-saw) Additional contribution to slepton mixing from V (the matrix 10 element responsible MSW large angle for solar neutrino deficit) log( m /ev ) (b) Confirmed by KamLAND 90% CL 95% CL 99% CL MSW small angle LMA LOW (see E. Lisi s talk) 2 MSW large angle small mass Search for LFV... 5 sin 2θ log(tan θ) Just so 1 J. Hisano, N. Nomura, Phys. Rev. D59 (1999) ) µ e γ Br( Experimental bound Experimental limit MSW LMA Next goal tan(β)= M MSW LOW ν R2 (GeV) tan(β)=1 Vacuum

The first attempt E.P.Hincks and B. Pontecorvo, Phys.Rev.73(1948)246 published before discovery of - electron spectrum J.Steinberger, PR74(1948)500 - ν µ and ν e G.

6 The first attempt E.P.Hincks and B. Pontecorvo, Phys.Rev.73(1948)246 published before discovery of - electron spectrum J.Steinberger, PR74(1948)500 - ν µ and ν e G.Danby et al., PRL 9(1962)36 Use of cosmic rays as muon beam Lead blocks as moderator and γ- converter Geiger-Müller counters to detect µ and e B(µ eγ) < 10% Search for LFV... 6

7 History of LFV searches Improved by 2 orders of magnitudes per decade Muon intensity Detection resolution Cosmic µ stopped π MEG (2007) MECO (2010) PRIME (?) µ beams 2 orders of magnitudes more needed to constrain SUSY Experimental challenge Search for LFV... 7

8 µ + e + γ: signature and background signal µ e γ e + µ + γ θeγ = 180 Ee = Eγ = 52.8 MeV Te = Tγ correlated µ e γ ν ν ν e + µ + γ ν background accidental µ e ν ν µ e γ ν ν ee γ γ ez ez γ ν e + µ + ν γ Search for LFV... 8

9 Background rate Signal window µ-rate e + -energy γ-energy alignment timing e + -annihilation rad. µ-decay ) ( ln t E E E E E E R N N BR e e e acc acc δ δθ δ δ π α δ γ γ γ γ γ µ µ + = Search for LFV... 9 Continuous beam needed Sensitivity limited by accidental background at high intensities (must be accompanied by improvements in detection techniques)

10 MEG detector layout Beam outline Detector outline 1.8 ma of 590 MeV/c protons (1.1 MW) at PSI (Switzerland) 29 MeV/c muons from π-decay at rest continuous beam ( 10 8 µ/s) Stopped beam of >10 7 µ /sec in a 150 µm target Liquid Xenon calorimeter for γ detection (scintillation) -fast: 4 / 22 / 45 ns -high LY:~ 0.8 * NaI Liq. Xe Scintillation Detector Liq. Xe Scintillation Detector -short X 0 : 2.77 cm Thin Superconducting Coil Muon Beam γ Stopping Target γ Solenoid spectrometer & drift chambers for e + momentum Drift Chamber e + Timing Counter e + Scintillation counters for e + timing Drift Chamber 1m Search for LFV... 10

11 Based on CEX reaction of π - onto a liquid H target π - p π 0 n, π 0 γ γ 54.9 MeV < E(γ) < 82.9 MeV θ>170 ο FWHM = 1.3 MeV E θ>175 o FWHM = 0.3 MeV γ Energy (MeV) MEG calorimeter result o o σ(e γ )/E γ = 4.8% σ(t) = 120 ps opening angle (deg) Search for LFV θ in agreement with the proposal goal

12 µ + e + γ : present and future MEG is going to start taking data in Spring 2006 Revised LoI Proposal document now Planning R & D Assembly Data Taking events expected with BR(µ eγ) BR acc More details at Is within the reach of future experiments? Beam: continuous at 10 9 µ + /s (PSI beam can deliver up to 3x10 8 µ + /s) Better detector resolutions needed to limit accidental background Search for LFV... 12

13 µ + e + e + e - e + µ + Coplanarity Vertexing ΣE e = m µ Te+ = Te+ = Tesignal µ eee e + correlated e µ - e e e ν ν ν e + µ + ν e - background e + e - e + accidental µ e ν ν µ e ν ν e + e - e + e - ν e + µ + ν e - e + ν µ + ν Search for LFV... 13

14 µ + e + e + e - : SINDRUM α m ln 3π B (µ e e e ) µ B(µ e γ) m e 11 4 = Current limit B(µ 3e ) < 1x %CL U.Bellgardt et al. Nucl.Phys. B299(1988)1 Background level To be improved by 3 orders of magnitude to probe SUSY (BR ) would require 10 9 µ + /s but background (6 order of magnitude!) Possible improvements (not to be taken seriously) momentum resolution 10% FWHM 1% FWHM background scales quadratically with momentum resolution co-planarity test? vertex resolution 2 mm 2 <1 mm 2 target length 220 mm? target density 11 mg/cm 2? timing resolution ns 100 ps No other experimental proposal Search for LFV... 14

15 µ - e - conversion signal µ (A,Z) e (A,Z) (A,Z) e - µ - γ E e = m µ -E B E e = MeV for Al E e = MeV for Ti E e = 94.9 MeV for Pb Background (beam related) Muon-decay In Orbit µ (A,Z) e ν ν (A,Z) ν (A,Z) e - µ - ν Radiative Pion Capture π (A,Z) γ (A,Z-1) γ π - (A,Z) Search for LFV... 15

16 µ - e - / µ + e + γ comparison R.Kitano et al Phys.Rev.D66(2002) Search for LFV... 16

17 µ - e - : SINDRUM II result MIO R (E -E B ) -5 signal SINDRUM II parameters beam intensity 3x10 7 µ /s µ momentum 53 MeV/c magnetic field 0.33T acceptance 7% momentum res. 2% FWHM S.E.S 3.3x10-13 B(µ e:au ) 8x10-13 A. Van der Schaaf, NOON03 Search for LFV... 17

18 µ - e - : MECO detector (BNL) Muon Stopping Target Straw Tracker Superconducting Transport Solenoid (2.5 T 2.1 T) Crystal Calorimeter Muon Beam Stop Superconducting Production Muon Solenoid Production (5.0 T 2.5 T) Target Collimators Proton Beam Proton beam from AGS Heat & Radiation Shield Superconducting Detector Solenoid (2.0 T 1.0 T) 4 x incident p/s 1 x stopping µ/s Search for LFV... 18

19 µ - e - : MECO Proton Beam Pulsed beam from AGS to eliminate prompt backgrounds Active time window 0.03 µ s 0.7 µ s 1.35 µ s µ s Extinction of second beam spill 1.0 second accelerator cycle Search for LFV... 19

20 Spectrometer Performance Search for LFV , 91, & 105 MeV e - from target Performance calculated using Monte Carlo simulation of all physical effects Resolution dominated by multiple scattering in tracker ( p/p = 0.8%) Resolution function of spectrometer convolved with theoretical calculation of muon decay in orbit to get expected background.

21 µ - e - : MECO background ~ 0.45 background events for 10 7 s running time with 4x10 13 proton/s sensitivity of ~ 5 signal events for R µe = Source Events Comments µ decay in orbit 0.25 S/N = 20 for R µe = Tracking errors < Radiative µ decay < Beam e - < 0.04 µ decay in flight < 0.03 Without scattering in stopping target µ decay in flight 0.04 With scattering in stopping target π decay in flight < Radiative π capture 0.07 From out of time protons Radiative π capture From late arriving pions Anti-proton induced Mostly from π Cosmic ray induced Assuming 10-4 CR veto inefficiency Total Background 0.45 Assuming 10-9 inter-bunch extinction Search for LFV... 21

µ - e - : PRISM beam High intensity pulsed proton beam Pion capture solenoid Pion decay section Phase rotation (muon energy spread reduction) with a FFAG ring

22 µ - e - : PRISM beam High intensity pulsed proton beam Pion capture solenoid Pion decay section Phase rotation (muon energy spread reduction) with a FFAG ring smaller µ-target better momentum resolution ( p/p = 0.3%) suppression of MIO background ( E 5 ) FFAG approved and financed Ready end 2007 Search for LFV... 22

23 µ - e - : PRIME detector PRISM/PRIME parameters beam intensity 3x10 11 µ /s µ momentum 68 MeV/c momentum res. 350KeV FWHM S.E.S 6x10-19 B(µ e) Search for LFV... 23

24 Preliminary, rough, estimates for a possible SPL pulsed muon beam (J. Aysto et al., CERN-TH/ , A.Baldini, MultiMW may04) Macro duty cycle: 1.2 ms every 20 ms (6% duty cycle) By the help of a chopper 40 ma of protons in bursts of 200 ns can be provided every 2 µs (good microstructure for mu-e conv) R.Garoby This corresponds to 1.5*10 15 GeV (0.5 MW) An extinction factor of 10 8 might be within reach (difficult to be measured): confirmation in 2007 An additional 10 3 might be added to the extinction factor by using a veto counter active only between the p bursts By using GHEISHA to scale #π/p from 8 to 2.2 GeV (HARP results needed) µ/s (tungsten target) Sensitivity down to B=10-18 Need of precise design/estimates Search for LFV... 24

25 Conclusions µ are sensitive probes of physics beyond the Standard Model SUSY-SUGRA theories predicts LFV not far from present existing upper limits Strong case for experimental searches in all channels µ + e + γ results are expected in 2007 (10-13 ) µ - e - conversion search is planned at the level of µ - e - conversion is not accidental background limited could benefit of new high intensity pulsed beams Search for LFV... 25

26 Beam requirements Experiment q µ N µ T µ P µ /P µ I off /I on δt t BR µ + e + e + e < 4 (MeV) < 10 % DC n/a n/a µ + e + γ < 4 (MeV) < 10 % DC n/a n/a µ - e - conv < 80 (MeV) < 5 % < < 100 ns > 1 µs µ - e - conv < 80 (MeV) < 5 % DC n/a n/a Search for LFV... 26

27 Supplementary information Search for LFV... 27

28 µ + e + γ : correlated background The correlated background is smaller than the accidental one The correlated background has a complicate dependence on the photon (y) and positron (x) energy resolutions. depends linearly on the R µ is 3x10-15 Search for LFV... 28

29 MEG spectrometer COnstant Bending RAdius (COBRA) spectrometer Constant bending radius independent of emission angles Gradient field Uniform field High p T positrons quickly swept out Gradient field Uniform field Search for LFV... 29

MEG positron tracker 17 chamber sectors aligned radially with 10 intervals Two staggered arrays of drift cells Chamber gas: He-C 2 H 6 mixture Vernier

30 MEG positron tracker 17 chamber sectors aligned radially with 10 intervals Two staggered arrays of drift cells Chamber gas: He-C 2 H 6 mixture Vernier pattern to measure z-position made of 15 µm kapton foils σ(x,y) ~200 µm (drift time) σ(z) ~ 300 µm (charge division vernier strips) Search for LFV... 30

31 MEG positron timing counter BC404 Two layers of scintillator read by PMTs placed at right angles with each other Outer: timing measurement Inner: additional trigger information Goal achieved on prototype σ time ~ 40 psec (100 ps FWHM) Search for LFV... 31

32 MEG Liquid Xe calorimeter 800 l of Liquid Xe ~800 PMT immersed in LXe Only scintillation light High luminosity Unsegmented volume Experimental check Cooling pipe Refrigerator H.V. Signals Vacuum for thermal insulation Liq. Xe Al Honeycomb window PMT Plasticfiller 1.5m

33 The LP α-sources LEDs Search for LFV... 33

34 Bibliography J.Aysto et al. CERN-TH/ NuFact03 proceedings NuFact02 proceedings MultiMW Workshop, May 2004 SINDRUM coll., W Bertl et al. Nucl.Phys. B260(1988)1 SINDRUM2 coll., W Honecker et al. Phys.Rev.Lett. 76(1996)200 MECO coll., BNL proposal AGS P940 (1997) MEG coll., The MEG proposal (2002) Search for LFV... 34

35 Physics motivation Charged-Lepton Flavour Violation (clfv) processes, like µ eγ, µ eee, µ e conversion, and also τ eγ, are negligibly small in the extended Standard Model (SM) with massive Dirac neutrinos (BR ) Super-Symmetric extensions of the SM (SUSY-GUTs) with right handed neutrinos and see-saw mechanism may produce LFV processes at significant rates clfv decays are therefore a clean (no SM contaminated) indication of Super Symmetry and the expected BR are close to the experimental limits Search for LFV... 35

36 LFV in the Standard Model Neutrino oscillations flavour mixing in lepton sector Extensions of SM with massive Dirac neutrinos allow Lepton Flavour Violation (LFV) processes, like µ eγ, τ eγ, µ eee, µ e conversion with B Super-Symmetric extensions of the SM (SUSY-GUTs) with right handed neutrinos and see-saw mechanism may produce LFV processes at significant rates A µ e γ decay is therefore a clean (no SM contaminated) indication of Super Symmetry but Are these rates accessible experimentally? Search for LFV... 36

37 µ + e + γ : present Present limit B(µ e ) < 1.2x10-11 by the MEGA Collab. M.L.Brooks et al. Phys.Rev.Lett. 83(1999)1521 New under-construction experiment: MEG Search for LFV... 37

38 µ + e + γ : MEG required performances The sensitivity is limited by the by the accidental background BR R E E θ t 2 The acc µ e γ eγ eγ allows BR (µ eγ) but needs FWHM Exp./Lab Year E e /E e (%) E γ /E γ (%) t eγ (ns) θ eγ (mrad) Stop rate (s -1 ) Duty cyc.(%) BR (90% CL) SIN x x 10-9 TRIUMF x LANL x Crystal Box x 10 5 (6..9) MEGA x 10 8 (6..7) 1 x x x x MEG x x Search for LFV... 38

39 The PSI πe5 surface muon beam Primary proton beam 1.8 ma of 590 MeV/c protons (1.1 MW) 30 MeV/c muons from π stop at rest DC beam ( 10 8 µ/s)

40 A exit beam solenoid B gold target C vacuum wall D scintillator hodoscope E Cerenkov hodoscope µ - e - : SINDRUM II detector F inner drift chamber G outer drift chamber H superconducting coil I helium bath J magnet yoke I H J 1m A H D C D G F E B SINDRUM II configuration 2000 Search for LFV... 40

41 µ + e + γ : MEG sensitivity summary Detector parameters Signal Single Event Sensitivity Backgrounds T = ε 0.9 e N sig 7 s ε sel R = µ ( 0.9 ) Cuts at 1,4 FWHM = BR T R µ 3 8 µ s = 0.7 Ω ε e ε 4π γ ε sel Ω 4π ε 0.6 γ = 0.09 SES = Ω -14 T Rµ ε e εγ ε sel 4π 2 BR R E E 2 θ 2 t BR corr acc µ e γ eγ eγ Upper Limit at 90% CL BR (µ eγ) Discovery 4 events (P = ) correspond BR = Search for LFV... 41

42 µ + e + e + e - : SINDRUM α m ln 3π B (µ e e e ) µ B(µ e γ) m e 11 4 = Current limit B(µ 3e ) < 1x %CL U.Bellgardt et al. Nucl.Phys. B299(1988)1 Background level To be improved by 3 orders of magnitude would require 10 9 µ + /s background level 10-7 SINDRUM I future (?) beam intensity 6x10 6 µ + /s 10 9 µ + /s µ + momentum 25 MeV/c magnetic field 0.33T acceptance 24% momentum resolution 10% FWHM <1% FWHM vertex resolution 2 mm 2 FWHM.1 mm 2 FWHM timing resolution ns.1 ns target length 220 mm 1 m target density 11 mg/cm 2? Search for LFV... 42

43 µ - e - : present Present limit B(µ e:au ) < 8x10-13 by the SINDRUM II A. Van der Schaaf, NOON03 New approved experiment: MECO B(µ e) < (2008?) New project LOI to J-PARC: PRISM/PRIME B(µ e) < Search for LFV... 43

44 µ - e - : comparison Background SINDRUM MECO PRISM/PRIME µ decay in orbit MIO Resolution 2% Resolution.8% Resolution.3% (E -E B ) -5 Radiative µ decay Resolution 2% Beam e - µ decay in flight π decay in flight Radiative π capture RPC Anti-proton induced Cosmic ray induced Low momentum Low momentum Low momentum PMC magnet - Cosmic veto Pulsed beam extinction Pulsed beam extinction Pulsed beam extinction Pulsed beam extinction Pulsed beam extinction Cosmic veto FFAG FFAG FFAG FFAG FFAG n/a 10-5 in ROI Search for LFV... 44

Lepton Flavour Violation

Lepton Flavour Violation Search for e at Paul Scherrer Institut Satoshi Mihara ICEPP, Univ. of Tokyo http://meg.icepp icepp.s..s.u-tokyo.ac.jp, http://meg.psi psi.ch,http://meg.pi.,http://meg.pi.infn.it