Charged Leptons as Probes of the Standard Model

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Charged Leptons as Probes of the Standard Model

• J. Michael Roney
• University of Victoria
• (BABAR Collaboration Member)

Lepton-Photon SymposiumDaegu, South Korea
August 13-18, 2007
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What Standard Model sectors can we probe with
charged leptons and how useful is that probing?

• Appropriate questions, especially for the
  LEPTON-photon symposium
• There are recent very high precision measurements
  at low energy of interest but nothing new for
  LP07 (see Sven Heinemeyers review from Monday
  morning)
• the tension between data and SM persists in muon
  g-2
• PRL 97, 030801(2006) Odom et al electron g-2
  defines a to 0.7ppb
• EDMs continue to heavily constrain any physics
  beyond the SM
• Lets start with the basics where new results are
  in
• Quantum Field Theory has CPT invariance built
  into it translates into equal masses
  lifetimes for each particle and antiparticle
• SM silent on particular masses, but foundations
  crumble if e.g. m and m- have different masses
  or lifetimes
• charged leptons are the only bare fermions
  allowing such probes

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SM is silent on actual values of the masses and
lifetimes

• Some are used to define the SM parameter space
  because of their high precision whereas the
  absolute values are required for less
  foundational probing such as the assumption of
  charged current universality
• Present new results on
• m lifetime
• t masses and CPT tests

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Precision m lifetime at PSI byMuLan
Collaboration Phys. Rev. Lett. 99, 032001 (2007)

• Defines GF fundamental SM parameter
• GF a MZ
• 9ppm 0.0007ppm 23ppm

weak intn loop corrections e.g.
van Ritbergen Stuart full 2-loop
QED corrections (1999) allow determination of GF
from m lifetime at 0.3ppm level (Nucl.Phys.B56434
3-390,2000)
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(from D. Hertzog, Moriond07)
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(from D. Hertzog, Moriond07)
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CPT test from m lifetime

• Dominated by lifetime of m- 2.197025(155)ms
  (Bardin 94)
• dont expect much improvement on testing CPT

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CPT

• what about t Lifetime
• 1st CPT on lifetime from BABAR (Lusiani,
  TAU04)
• THIS TEST WOULD BENEFIT FROM HIGH STATISTICS AS
  MANY SYSTEMATICS WOULD CANCEL

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CPT

• t Mass
• BELLE published using 5.8x106 t-pair
  eventst??nn t?3p? n in 414/fb of data PRL
  99,011801(2007) (hep-ex/0608046)

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CPT

• t Mass future?
• A SuperB factory with 100/ab would yield a
  statistical error of 0.023MeV on the mass
  difference 6 x smaller than 0.14MeV systematic
  error BELLE now quotes.
• (Reach 0.15MeV at 2.3/ab)
• To fully exploit 100/ab, would need charge
  asymmetric momentum scales controlled at 10-5
  level. VERY CHALLENGING DETECTOR SYSTEMATICS
  PROBLEM
• Would get CPT test to 2x10-5 level of sensitivity
  and would be most sensitive CPT mass difference
  test after K0(10-18), proton and electron (10-8).
  

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New preliminary t mass from KEDR Collaboration
at the VEPP-4M Collider in Novosibirsk
(hep-ex/0611046)
using enn,mnn,pn,Kn,rn vs - enn t-pair events
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The t mass is needed for probes of charged
current universality involving the t but to
probe the SM in m-t and e-m universality further
requires higher precision measurements of
BR(t?enn) and BR(t?mnn) and improved t lifetime
measurements
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Charged Current Lepton universality

• Charged current universality tau decays

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Lepton universality in Kaon Decays New results
from KLOE at Frascatis DAFNE phi factory for
LP07
can have deviations from SM from e.g. multi-Higgs
effects inducing an effective pseudoscalar
interaction up to the few level in K decays (A.
Masiero, P. Paradisi, R. Petronzio, PRD74 (2006)
011701)
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KLOE Universality results

• Using 1.7fb-1 at the f
• Compare RK to a SM calculation (M. Finkemeier,
  PLB 387 (1996) 391) which includes internal brem
  photons (IB) and ignores contributions from
  structure-dependent direct photon emission (DE).
  Requires care!

IB IBDE
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KLOE Universality results
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Probing the CKM Matrix with t leptons

• CKM Unitarity implies
• strange decays of t provides an additional way of
  probing Vus with a technique having
  uncorrelated experimental and theoretical errors

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Strange and non-Strange ?-Decays
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Extracting Vus
The weighted spectral functions may be written
as When one takes the flavour breaking
difference the D0 terms cancel leaving D?
2. So
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BABAR Branching Ratio for ?-?K-?0?(uses 230/fb)
t-t
qq
?-?
arXiv0707.2922 hep-ex submitted PRD-RC
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BELLEBR, Mass Width ?-? KS?-?
arXiv0706.223 hep-ex submitted to PLB
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BELLE BR ?-?K-h?,?-?K-?0h ?(K-h ?) ?-?p-?0h ?

• preliminary
• decays
• with h

arXiv0708.0733 hep-ex
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BELLE (preliminary) Use ?-?K-?0h sample to get
B(?-? K-h ?) through the K-(892)?K-?0 mode
using BR(K-(892)?K-?0 )1/3
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BABAR Branching Ratios for ?-?h-h-h?
iChannels Selected jDecay Mode
arXiv0707.2981 hep-ex Submitted PRL
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BABAR Branching Ratios for ?-?h-h-h?
??-?-?
?K-?-?
?K-?-K
?K-K-K
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Some Updates to Vus from t
UPDATED ?-?K-?0? arXiv0707.2922
hep-ex ?-?K-?-?? arXiv0707.2981
hep-ex ?-?K0?-? arXiv0706.2231 hep-ex
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Some Updates to Vus from t
UPDATED ?-?K-?0? arXiv0707.2922
hep-ex ?-?K-?-?? arXiv0707.2981
hep-ex ?-?K0?-? arXiv0706.2231 hep-ex
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About the t tension

• Comment 1 B-factory experimental program to
  measure all strange decays of the t in progress
  many modes still to be measured by BABAR and
  BELLE, Vus analysis assumed modes not yet
  measured are negligibly small
• Comment 2Theory errors for R00 require some care
  (Maltman Wolfe hep-ph/0603215) poor
  convergence properties of the integrated D2 OPE
  series for R00
• argues for better behaved weighted spectral
  functions even so, difference is not
  diminished using ALEPH spectral functions
  re-scaled with B-factory BRs even with better
  behaved weighted SF
• Comment 3 The updated Vus analysis doesnt yet
  include the new ?-?K-h?,?-?K-?0h ?(K-h ?)
  results from Belle these lower values will
  increase the tension further
• very active area for both experimentalists and
  theorists

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Lepton Flavour ViolationA bit of historythe
importance of being earnest
in seeing nothing

• 1947 muon established as lepton, excited
  electron ruled out by absence of??e?
• 1958 G. Feinberg leptonic GIM argument
  establishes two neutrino types
• Early weak theory
• BR(??e?)10-4 expected but BR(??e?)lt10-5
• 1950s first ?-N?e-N conversion experiments
• Eem?-Binding Energy105MeV
• and ??eee searches

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History of e-muon LFV Searches
B(µ?e?) lt 1.2x10-11 (MEGA/LAMPF) Brooks et al
PRL 83 1521 (1999) µTi?eTi lt 4x10-12
MEG
MECO(?)
hadronic decays
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By beginning of 21st Century Lepton Flavour
Violation established!

• SNO, SuperK, K2K all see neutrino mixing
  implying massive neutrinos
• We even have parts of the mixing matrix q12,
  q23 experiments,
• such as T2K, preparing to measure q13
• So the SM extended to include massive
  neutrinos predicts LFV
• in the charged lepton sector as well
• well below any conceivable experimental
  sensitivity
• OPPORTUNITY CHARGED LFV IS UNAMBIGUOUS
• SIGNAL OF NEW PHYSICS

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Many SM extensions predict observable Charged LFV

• If see-saw mechanism responsible for small n
  mass, natural to get large Charged LFV
• Heavy Neutrinos
• Supersymmetry

e.g.SO(10) inspired model with SUSY imbedded in
GUT Calibbi et al PRD 74(2006)
univ. gaugino mass
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(requires 107 m/sec)
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The present status of the MEG experiment (T.
Mori)
Liquid Xenon Gamma-Ray Detector All phototubes
installed inside the cryostat final preparations
to start operation toward the end of August
Timing Counters Final assembly in Italy
Installation planned at the end of August
Drift Chambers Installed and ready at the beam
line cosmic ray test soon
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STATUS of MEG
The whole MEG detector will be ready in September
2007 Plan to start an engineering run with muons
after calibration runs in October. Expect to
start taking some physics data toward the end of
the year
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Focus on Lepton Flavour Violation in t decays

• lepton-mass dependent couplings
• parameter space in some models touch current
  limits
• different sensitivity to 2-body 3-body decays
• which mode will be discovered first is
  unknown (e.g. some mSUGRASeesaw (PRD66) has
  parameters having t?µ? t?mmm t?µh
  1.51.08.4)
• Well motivated searches complementary to
  potential LHC discoveries
• Limits (or discovery!) will better constrain
  theories

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General approach in Search for LFV _at_ ee-
colliders
Lab frame
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Signal no neutrinos ? powerful mass and beam
energy information

• mass mµ ? mt
• Babar uses beam energy constrained mass
• ? vertex at µ point of closest approach to
  beamspot in x,y
• (MEC)9MeV
• (cf no mass or vertex constraint ?24MeV)
• Beam Energy
• ?E E ?? -Ebeam 0
• ? (?E)50MeV

signal region typically defined as 2? box or
ellipse
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Summary of t???, ???
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New Babar (prelim) Belle (prelim) results on
t????
optimize event selections for each signal mode
separately accounting for different background
compositions
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New prelim Belle result on t????
Belle update to 535fb-1 increase in lumi by 6.1
fold Efficiency6.0-12.5 ltBkgndgt0.01-0.40
events Total ltBkgndgt0.59?0.31ev Nobs0
events 90CL limits BR(t????)lt(2.0-4.1)x10-8 5-
7 fold improvement over previous limit
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New prelim BABAR results on t????
BABAR update to 376fb-1 for LP07 increase in lumi
by 4.3 fold

• Background PDF
• shapes from
• MC or control
• samples
• PDFs summed
• and fit to data
• in sidebands
• ltBkgdgt from
• integral of PDF
• over signal box

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New prelim Babar results on t????
Efficiency5.5-12.4 ltBkgndgt0.3-1.3 events
total4.2?0.8 events Total Nobs6 events 90CL
limits BR(t????)lt(3.7-8.0)x10-8 2-5 fold lower
limits over previous Babar results
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New Belle results on t??V0
using 543fb-1 Efficiency2.5-4.0 ltBkgndgt0.0
-0.2 events Total ltBkgndgt0.78?0.29ev Nobs3
events 90CL limits BR(t??V0)lt(6.1-18)x10-8
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NEW t??p0/h/h
hep-ex/0610067 PRL 98.061803 (2007)
expected background/channel 0.1-0.3 Total
expected background3.1, Observed2
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Some intepretations within benchmark models
compilation by S. Banerjee (Tau06,hep-ex/0702017)
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LFV in tau decays How far we can go?
It depends on irresidual background levels not
currently a limiting factor t??g future
sensitivity will be affected by ee-?tt-g
?ttag t- ? m-nng irreducible background. When
that limit hit, sensitivity will scale as
1/sqrt(Lumi) . For 75/ab as with SuperB might
expect O(10-9) level ?????, ?hh sensitivity not
likely limited by irreducible backgrounds so
might expect sensitivity to scale as 1/Lumi .For
SuperB might expect O(10-10) level
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Summary

• Charged leptons are probing many sectors of the
  SM
• CPT
• CC Universality
• LFV
• CKM unitarity with Vus - watch this space
• EDM
• g-2 possible hint of something beyond SM?
• Look forward to more precision data from MEG,
  MuLan, Babar, Belle, KEDR, BES, KLOE

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Additional Slides
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Extracting Vus from ?-Spectral Function
Strange and non-strange Hadronic Width May be
written in terms of the spectral density function
or in terms of the 2 point correlator
function
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Extracting Vus
A set of spectral moments has been used in the
FESR as the particular weight functions w For
(k,l)(0,0), R00 is obtained from the BR of
strange decays
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Some Updates to Vus from t
from S. Banerjee (Kaon07)
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Belle result on t?mg summer 06 result
submitted to PLB
94 events in 535 fb-1 within 2? ellipse,
eff5.1 s(90 CL)
2.0 events Brlt4.5x10-8 at 90C.L
2? projection
0705.0650hep-ex submitted to PRB
Unbinned Extended Maximum Likelihood fit
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Belle result on t?eg summer 06 result
submitted to PLB
20 events within 5? in 535 fb-1 within 2?
ellipse, eff3 UEML fit in 2? ellipse signal
events -0.14 (P(nlt-0.14)48) background
evts5.14 s(90 CL) 3.34
events Brlt1.2x10-7 at 90C.L
2? projection
0705.0650hep-ex submitted to PRB
Unbinned Extended Maximum Likelihood fit
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Summary of ? ? l?, l?0, l?, l?, lK0S
90 CL UL (10-7)
L (fb-1)
Lum
L (fb-1)
90 CL UL (10-7)
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Summary of ? ? lhh
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Current exp ULs vs BSM scenarios????
Excluded
SUSY SO(10) seesaw Masiero et al. NJP 6
(2004) 202