Transcript Lepton Flavor Violation and Dipole Moments in the Muon System at High Intensity Beams Marco Incagli - INFN Pisa SPSC meeting - Villars -

Lepton Flavor Violation and
Dipole Moments in the Muon
System at High Intensity Beams
Marco Incagli - INFN Pisa
SPSC meeting - Villars - 27 sep 2004
• Precision Physics as complementary to Frontier Energy
Physics
• Precision Measurement relevant if:
– firm predictions (eventually null) from Standard Model
– relevant informations on Standard Model or on
Standard Model extensions can be extracted
– experimentally accessible
– (relatively) low cost
• Muons satisfy all requirements!
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
2
Physics motivations: LFV
• Lepton flavor violation processes (LFV), like meg ,
meee , me conversion , 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 LFV processes at significant rates
m-LFV decays are therefore a clean (no SM contaminated)
indication of New Physics
and
they are accessible experimentally
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
3
Physics motivations : m moments
1. Magnetic Dipole Moment (g-2) :
 measured and predicted with very high accuracy (10 ppb in electron;
0.5 ppm in muon), it represents the most precise test of QED ;
 most extensions of SM predict a contribution to g-2 ;
 a 2.7 s discrepancy between theory and experiment has raised a lot
of interest (and publications) .
2. Electric Dipole Moment (mEDM) :
 Like LFV processes, a positive measurement of m Electric Dipole
Moment (mEDM) would be a signal of physics beyond the SM
Both experiments need a new high intensity muon
source for the next generation of measurements
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
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Connection between LFV and m-moments
• In SUSY, g-2 and EDM probe the diagonal elements of
the slepton mixing matrix, while the LFV decay me
probes the off-diagonal terms
V~e ~e V~e m~ 


V ~~ V ~~ 
mm 
 me
• In case SUSY particles are observed at LHC,
measurements of the LFV decays and of the m-moments
will provide one of the cleanest measarements of tanb
and of the new CP violating phase .
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
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The Anomalous Magnetic Moment : am
Q
E
D
QED Prediction:
g
g
 m  eg m  a
Computed up to 4th order
[Kinoshita et al.]
(5th order estimated [Mohr, Taylor])
m
ie
s m q
2m
a 
Schwinger 1948
(Nobel price 1965)

 0.001161
2
    11614098.1  41321.8 
10
    
  10
n 1   
  3014.2  38.1  0.6 
n
QED
am
Kinoshita-Nio,
hep-ph/0402206
corrected feb 04
QED
Hadronic
Weak
SUSY...
... or other new
physics ?
shad
LBL
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
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Storage ring to measure am
polarized
Electric field
used for focusing
(electrostatic
quadrupoles)
B
(out of plane)
E
Precession of spin and momentum
vectors in E, B fields (in the hyp.
bB=0) :
 

e
 

a  s  m  m c am B  Kb  E

 K  am  1

g 2 1


• At g magic = 29.3, corresponding to Em=3.09 GeV, K=0
and precession is directely proportional to am
am  a B
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
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Muon anomaly (from Hoecker’s presentation at ICHEP04 - Beijing)
Including CMD2 and KLOE e+e- results
Melnikov-Vainshtein, hep-ph/0312226
am SM [e+e– ] = (11 659 182.8 ± 6.3had ± 3.5LBL ± 0.3QED+EW)  10 –
10
BNL E821 (2004) : amexp = (11 659 208.0  5.8) 10 10
Observed Difference with Experiment:
am exp – am SM
not yet published
not yet published
= (25.2 ± 9.2)  10 –10
 2.7 ”standard deviations“
(using e+e- data only)
preliminary
m and m data combined together (CPT)
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
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Possible new physics contribution…




New physics contribution can
affect am through the muon
coupling to new particles
In particular SUSY can easily
predict values which contribute
to am at the 1ppm level
t data can be affected differently
than e+e- data by this new
t
physics
In particular H- exchange is at
the same scale as W- exchange,
while m(H0)>>m(r)
M. Incagli - INFN Pisa
Marciano + others
t
W
Villars SPSC meeting 22-28 sep 2004
t
t
H
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LoI to J-PARC
 An
experiment with
sensitivity of 0.05 ppm
proposed at J-PARC
 At the moment, the
project is scheduled for
Phase2 (>2011)
 Together with the
experiment there must be
an improvement on:
 evaluation of LBL
 experimetal data on
s(had) to cover
m()<s<m(r and
1<s<2 GeV
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
10
New proposal - statistics
•
The new experiment aims to a precision of 0.1-0.05
ppm, which needs a factor of 25-100 more muons
•
This can be achieved by increasing the …
1. … number of primary protons on target  target must
be redisigned
2. … number of bunches
3. … muon injection efficiency which, at E821, was 7%
4. … running time (it was 7months with m- at BNL)
•
The J-PARC proposal is mostly working on items 2 (go
from 12  90 bunches) and 3
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
11
Intermediate step on g-2 …
• As intermediate step between now ( 0.6 ppm) and a
future storage ring ( 0.05) a proposal of upgrading E821,
in order to reach  0.2 ppm, has been submitted to BNL
in July 2004 and defended Sep 9  positive response
from PAC
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
12
Electric Dipole Moment (EDM)
• The electromagnetic interaction Hamiltonian of a particle
with both magnetic and electric dipole moment is:

e  g 
g-2 term

d M  m  g 2m c s  2 m0s
   
H   m  B  d  E where  

e   
 dE  d  
s  m0s
2m c
2

• The existence of dE, in SM, is suppressed because
• dE violates both P and T (and also CP in the CPT hyp.)
• only one weak phase exist in CKM
• This is not the case for SUSY where many CP phases exist
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
13
Limits on EDM
o Up to now EDMs have been measured only on:
1. Neutrons
2. Heavy paramagnetic/diamagnetic atoms/molecules (Tl,Hg,YbF)
o Electron EDM extracted from (2.) : dE(e)<210-27 ecm

New idea to measure directly the EDM on an elementary
particle : muons in storage ring

What value for mEDM if new physics exists in am at 1ppm?
This New Physics would induce a mEDM :
unit conversion
dmNP  amNP tanfCP 1013 e  cm  tanfCP 1022 e  cm
 With new technique expected sensitivity is dm  1024 e  cm
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
14
New approach to mEDM
• Muons in storage ring: combination of g, E, B that cancels
out muon spin (g-2) precession (electric field E must be radial
and Eb=Bb=0) ; only mEDM precession left .
 


a  am B  K (g ) b  E  am B  K (g ) bE zˆ  0 - precession due to am

e    
e
- precession due to mEDM
EDM 
E  b  B 
bBrˆ
mc 2
2m c


NO out of plane
precession
side
view
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
15
Muon ring for mEDM measurement
LOI to J-PARC with
following parameters:
Required
statistics:
P = 500 MeV/c
Bz = 0.25 T
Er = 2MV/m
R = 7m
<R> = 11m
B+E = 2.6 m
Intervals = 1.7 m
n. elements = 16
circunference  40m
NmP2 = 1016
P = Beam
Polarization
 Optimal momentum choice : pm  300-500 MeV
 Below 300 MeV the muon polarization becomes a concern
 Above 500 MeV the radial electric field needed to cancel
out g-2 precession is >20kV/cm
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
16
Systematics
• Basic idea to fight systematics: compare clockwise vs
counter-clockwise results
0 due to choice of b,B,E

e   
1      
 am B   am  2 b  E  E  b  B
 
m c 
g 1 
2


Opposite sign





cw  ccw
b  -b
B  -B
EE
Same sign
• Needs 2 injection points and possibility of changing
polarity of dipole magnets (not necessary for
quadrupoles)
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
17
Summary on m-moments





Both g-2 and mEDM are sensitive to new physics beyond
the SM (maybe behind the corner)
Unique opportunity of studying phases of mixing matrix
for SUSY particles
mEDM first direct probe of dE on elementary particle
The experiments are hard but, in particular the mEDM,
not impossible
A large flux of polarized muons of energy 3 GeV (g-2) or
500 MeV (mEDM) is required
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
18
Lepton Flavor Violation m decays
•
Three relevant processes :
meg
•
m3e
mNeN
Model Indipendent Interactions:
Dipole Transition
e.g. :
slepton mixing
matrix
Direct violation
•
Relative strength depends upon arbitrary parameters L, LF
•
In the hyp. L/LF<<1, as in large class of SUSY-GUT theories:
BR(m-e conv)  10-3 BR(meg) BR(m3e)  10-2 BR(meg)
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
19
m+e+g
signal
meg
background
accidental
me
correlated
e+ m+
g
meg

qeg = 180°
Ee = Eg = 52.8 MeV
e+ m+

g
Te = Tg
M. Incagli - INFN Pisa
meg
ee  g g
eZ  eZ g


e+ m+
g
Villars SPSC meeting 22-28 sep 2004
20
m+e+g : present
Present limit B(me ) < 1.2x10-11 by the MEGA Collab. M.L.Brooks et al. Phys.Rev.Lett.
83(1999)1521
New approved experiment:
MEG @ PSI
• Stopped beam of >107 m
/sec in a 150 mm target
Revised
LoI Proposal document
Planning
R&D
1998
1999
2000
2001
• Liquid Xenon calorimeter
for g detection
(scintillation)
• Solenoid spectrometer &
drift chambers for e+
momentum
2002
now
Assembly
2003
2005
Thin Superconducting Coil
g
Stopping Target
Muon Beam
e+
2006
2007
Liq. Xe Scintillation
Detector
Liq. Xe Scintillation
Detector
g
Timing Counter
e+
Drift Chamber
• Scintillation counters for
e+ timing
M. Incagli - INFN Pisa
2004
Data Taking
Drift Chamber
1m
Villars SPSC meeting 22-28 sep 2004
21
m+e+g : future
• MEG sensitivity : 10-13 with 107 m+/s
• The PSI E5 can deliver up to 3x108 m+/s
• The MEG sensitivity is accidental background limited
• With better detector resolutions a BR of 10-14 would
be possible
but...
Challenging !
No immediate (next 10 years) need for
a more intense beam
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
22
m+e+e+esignal
m  eee
background
accidental
me
e+
e+
m+
e-
Coplanarity
Vertexing
Ee = mm
correlated
meee

+
+
+
e
e m

e-
e+e- e+e
e+ m+
e+
e-
Te+ = Te+ = Te-
M. Incagli - INFN Pisa
me
Villars SPSC meeting 22-28 sep 2004

e+ 
e- m+

23
m+e+e+e- : SINDRUM I
Present limit B(m3e ) < 1x10-12
No other experimental proposal
U.Bellgardt et al. Nucl.Phys. B299(1985)1
SINDRUM I parameters
–
–
–
–
–
–
–
–
–
M. Incagli - INFN Pisa
beam intensity
m momentum
magnetic field
acceptance
momentum resolution
vertex resolution
timing resolution
target length
target density
6x106 m/s
25 MeV/c
0.33T
24%
10% FWHM
 2 mm2 FWHM
 ns
220 mm
11 mg/cm2
Villars SPSC meeting 22-28 sep 2004
24
m+e+e+e : summary
• A new experiment should aim at a sensitivity of 10-15,
which means to increase beam intensity by 103
• Technically not impossible, but uncorrelated background
scales quadratically with the beam intensity, therefore six
orders of magnitude of background reduction, wrt to
SINDRUM I, is required
 four orders of magnitude could be achieved … more?
Challenging !
No immediate (next 10 years) need for
a more intense beam
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
25
m-e- conversion
signal
m (A,Z)  e (A,Z)
background
RPC
 (A,Z)  g (A,Z-1)
g
-
(A,Z)
e- m- g
Ee = mm - EB
M. Incagli - INFN Pisa
MIO
(A,Z)
m (A,Z)  e   (A,Z)

(A,Z)
e m

Villars SPSC meeting 22-28 sep 2004
26
m-e- : present
Present limit B(me:Au ) < 8x10-13
SINDRUM II COLLABORATION
SINDRUM II parameters
•
•
•
•
•
beam intensity
m momentum
magnetic field
acceptance
momentum res.
3x107 m/s
53 MeV/c
0.33T
7%
2%
FWHM
Main background : Radiative Pion Capture (RPC)
 suppressed with an 8mm carbon absorber at the entrance of the
solenoid
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
27
m-e- : future
 Differently from other channels, this one is not limited by
accidentals but by RPC
 Two techinques to improve beam purity proposed for two
next generation experiments:
New approved experiment at BNL:
MECO (E940)
BR(me) < 10-16 (2008 ??)
New project LOI to J-PARC:
PRISM/PRIME
M. Incagli - INFN Pisa
BR(me) < 10-18 (>2008 ??? )
Villars SPSC meeting 22-28 sep 2004
28
me : beam line for MECO

New AGS beam structure:
1. 21013 protons/bucket (71012 for
Pulsed beam from AGS to
eliminate prompt background
g-2 experiment)
2. Short pulses of 30nsec with 1.35
µsec separation between pulses (2
per rotation)
3. Extinction between pulses must be
>109; fast kicker in transport will
divert beam from production
solenoid
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
29
m-e- : MECO detector
Straw Tracker
Muon Stopping
Target
Superconducting
Transport Solenoid
(2.5 T – 2.1 T)
Crystal
Calorimeter
2 x 1013 incident p/sec
Superconducting
Production Solenoid
(5.0 T – 2.5 T)
Superconducting
Detector Solenoid
(2.0 T – 1.0 T)
1 x 1011 stopping µ/sec
~ 5 signal events for 107 s (2800 hours) running if Rme = 10-16
~ 0.45 expected bckg events if extinction factor = 10-9
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
30
m-e- : PRISM beam
PRISM (Phase Rotated Intense
Slow Muon source):
 Pion capture section
 Decay section
 Phase rotation section
 Ejection system
Machine parameters
 Intensity: 1011-1012 m/sec
 Muon momentum : 68 MeV
 Momentum spread :  0.5-1.0 MeV
 Beam repetition : 100 Hz
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
31
m-e- : PRIME detector
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
32
m-e- : summary
• This channel will definitely benefit from an increase in
beam intensity
BUT
• The problem of pion contamination of the muon beam is
the fundamental issue
• Two proposals :
– Beam extinction at <10-9 level (!) - BNL
– New kind of muon extraction technique with circular
(compact) FFAG - PRISM
Very promising channel !
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
33
mEDM and me conversion with “same” beam?
• In mEDM LOI to J-PARC the possibility of accomodating
mEDM and me in the same hall is prospected
• The FFAG system must be projected with the possibility
of providing muons both of 80 and of 400 MeV
me detector
PRISM FFAG
mEDM ring
M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
34
Summary table and Conclusions



Muons have historically played a key role in understanding
the structure of the Standard Model (V-A, QED tests, …)
Muons are fundamental tools to discover and/or to
understand the structure of any physics beyond the SM
All future projects (J-PARC, Fermilab) foresee high intensity
flux of muons to be used in a storage ring and/or LFV exp.
me transitions and mEDM (also g-2) seem very promising
 Europe (CERN) should not loose this opportunity and aim for
a leading role in the field of m decays and m moments

M. Incagli - INFN Pisa
Villars SPSC meeting 22-28 sep 2004
35