Download Status report of the MEG experiment: search for m+*e+g

Status and results of the MEG experiment:
search for m+e+g with sensitivity to BR 10-13
A. Baldini INFN Pisa: Venezia:
March 16th 2011
The Standard Model of particle
interactions was explicitily built on the
non observation of this decay (Lepton
Flavour)
Even with the introduction of the recently
discovered neutrino masses SM predicts
the non observability of me g
(BR 10-54)
m e g is an extremely powerfull test for
New Physics models
Lab.
Year
Upper limit
Experiment or Auth.
PSI
1977
< 1.0  10-9
A. Van der Schaaf et al.
TRIUMF
1977
< 3.6  10-9
P. Depommier et al.
LANL
1979
< 1.7  10-10
W.W. Kinnison et al.
LANL
1986
< 4.9  10-11
Crystal Box
LANL
1999
< 1.2  10-11
MEGA
PSI
~2012
~ 10-13
MEG
meg predicted by several models ( mainly (but not only)
SUSY GUTS) @ rates just below the MEGA results
(Paradisi’s talk later)
…
MSSM with
large tanb
Just one recent example
G.Isidori
Signal and background
signal
meg
background
4(5) Measured variables
Physical:
RMD
e+ m+
g
megnn
n
qeg = 180°
Ee = Eg = 52.8 MeV
Te = Tg
e+ m+
n
g
1/10 of the accidental
one
Accidental
(Dominant)
menn
megnn
ee  g g
eZ  eZ g
n
n
e+ m+
g
We have to measure positrons and photons kinematic variables in the most
precise way in order to reduce backgrounds
Detector outline
reminder
Liq. Xe Scintillation
Detector
Liq. Xe Scintillation
Detector
Thin Superconducting Coil
g
Stopping Target
Muon Beam
e+
g
Timing Counter
Stopped pE5 beam of 3 107
m /sec in a 150 mm target
2.
Solenoidal spectrometer &
drift chambers for e+
momentum (DCH)
3.
Scintillation counters for
e+ timing (TC)
4.
Liquid Xenon calorimeter
for g detection (LXe)
(scintillation)
e+
Drift Chamber
Drift Chamber
1m
1.
MEG Physics runs
2008:
3 months of data taking with low efficient Drift Chambers (DCH) system and
varying xenon light yield as a function of (gaseous) purification
Sensitivity = 1.3 x 10-11, 90%UL = 2.8 x 10-11
Published : NPB 834 (2010) 1
2009:
DCH system stable (HV distribution system problem corrected) + Xenon
purified and stable.
2 months of data taken in stable conditions.
Sensitivity: average UL obtained by 100 Toy MC experiments generated
with no signal
2009 analysis
PDF= Probabilty
Distribution Function
10
Michel positrons
Mott scattering device
double turn tracks
g variables
+ 4.4 g from
Am/Be source,
9 MeV g from n
capture (n
generator) in Ni
g
e+ variables
+ Mott scattering device
2009:
BR<1.5 x 10-11 90%CL
Latest on analysis
improved
to compute the background in the analisys box
We plan to present a combined 2009+2010 analysis asap
+ Adopted a
common FC +
profile likelyhood
analysis
approach (PDG)
Relative alignement of g
and e+ ??
Delayed start: DCHs construction, MEG target accidentally broken
Premature end: BTS solenoid magnet problem on beginning of november
Improvements for this year (2011) and later
• TC counter now complete with fibers+APDs
• Improved DAQ and Trigger efficiencies
• New HV system for reducing noise of Drift Chambers system
• New measurement of positrons resolutions with Mott scattering device
• Radiative Decays for better eg alignement
• Improvements in Eg reconsruction by means of detailed understanding of light
transmission in calorimeter
• Improvements in magnetic field knowledge
• beam intensity optimiztion
• Increased positron acceptance
Summary
• With the 2009 data MEG has established an upper limit (90% CL) on
BRmeg of 1.5 x 10-11 with an estimated sensitivity of 6.1 x 10-12
• The analysis methods and systematics were recently improved. It was
however decided not to present a re-analysis of 2009 data only but a
combined analysis of 2009+2010 data in order to get a clearer picture of
the origin of what we observed in 2009
• The expected sensitivity of 2009+2010 data is roughly 1.5 x 10-12
• 2011 data taking will soon start
• Continue to run to reach the expected
sensitivity of few times x 10-13
Backup slides