Tau and Hadronic Physics at B Factories

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Tau and Hadronic Physicsat B Factories

• IOP B Factories Meeting
• Jenny Williams
• Manchester University
• 19 November 2003

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Outline

• ? physics
• General ? properties
• Rare/forbidden decay searches
• ?c measurements in 2 photon events
• Measurement of the ?c width
• Observation of ?c(2S)
• Hadron production at ?s below 10.58 GeV
• Motivation for Initial State Radiation studies
• J/? production using ISR events
• Other final states from ISR

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? Physics at B Factories
Cross section for e ?e ??? ?? ? at ?(4S) ? 0.9
nb ? similar number of ?s to Bs

• SVT/SVD allows precise determination of ? decay
  vertex
• ? is the only lepton heavy enough to decay
  hadronically
• Final states are low-multiplicity
• lots of ? s allows for studies of rare processes

BR(??1prong) ? 85 BR(??3prong) ? 15
3-3 topology tau event Red positive
tracks Green negative tracks Blue neutrals
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? Analyses at B Factories

• Branching ratio measurements
• ?? ? Ks ?? ??, K? ?0 ?
• ?? ? ?? ? , ? h? ?, ? h? ?, ? ?? ?
• ?? ? 5 tracks, 7 tracks
• Searches
• Second class currents ?? ?? ?? ?
• ?? ? ?? ?, e? ?, l l l, ???, e??
• CP violation
• Electric dipole moment
• CP violation in decays
• e? e? ? ?? ??
• Other measurements
• ? lifetime
• tau neutrino mass

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Tau Lifetime
Motivation Test of lepton universality
Decay-length measurement technique requires
precise vertex info
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? Lifetime Measurement
decay length (measure this)
?-momentum (from MC)
?-mass (use PDG value)
?? (cm)
World average (CLEO, LEP) ?? ? 290.6 ? 1.1 fs
Preliminary
Consistent with world average and competitive
with LEP results
Mean decay length ?? ? 240.7?1.3 ?m
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????0?

• ???? spectral function measurement important
  for determining hadronic corrections to g-2

B(???h ?????) ? 25.23 ? 0.05(stat ) ? 0.23(sys )?
B(?????????) ? 24.78?0.05(stat )?0.53(sys
)?0.03(K?)? where PDG value of B (???K?????) ?
0.45 ?0.03 is subtracted.
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Rare Tau Decays

• High luminosity and large ? cross section at
  ?(4S)
• ? Can study rare processes
• Found neutrino oscillations ? now important to
  look for charged lepton flavour violation (LFV)
• Neutrinoless LFV decays allowed
• in various SUSY models
• Searches at B factories
• Lepton flavour violation
• ????, e?, lll, mh, eh
• CP violation in tau decays
• (Beyond SM process)
• Second class currents

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Search for ????, e?
Blind analyses blinding signal region in the ?E
m plane
???? simulation (BABAR)
?E Evis?Ebeam m mass of trackphoton
mEC
?E
mEC

• ???? enhanced by 0 (105-106)
• over ??e?
• Current limits on BR(????)
• SM mn ? O (10-34)
• SUSY ? O (10-6)

ISR
?E
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Results of t?mg, eg Searches

• Belle (79 million tau-pairs)
• Br(t?mg)lt3.1x10-7
• not-m tag
• 54 events in 5s region
• Efficiency 11.0
• Likelihood fit

• Belle (79 million tau-pairs)
• Br(t?eg)lt3.6x10-7 (prelim)
• not-e tag
• 20 events in 5s region
• Efficiency 6.8
• Likelihood fit

• BABAR (56 million tau-pairs)
• Br(t?mg)lt2.0x10-6
• e- or r-tag
• 13 evts in 3s region, 7.8 exp
• Efficiency 5.2 ? 0.5
• Cut-based analysis

• BABAR
• Cut-based analysis underway

• CLEO (12.6 million tau-pairs)
• Br(t?mg)lt1.1x10-6
• Likelihood fit
• 53 events in 10s region
• Efficiency 15.2

• CLEO (4.2 million tau-pairs)
• Br(t? eg)lt2.7x10-6
• Bayesian counting method
• eg 0 observed/2.00.5 exp

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Lepton Flavour Violation t?mh

• Can place limits on constrained MSSM
  Higgs-mediated model
• M. Sher, PR D66 057301 (2002) K.S. Bubu and C.
  Kolda, PRL 89, 241802 (2002)
• A. Dedes, J. Ellis, and M. Raidal, PL B549, 159
  (2002)
• Br(t ? mh) 8.4 times larger than Br(t ? mmm)
• CLEO (4.7fb-1, using h ? gg mode)
• Br(t?mh) lt 9.610-6
• Br(t?eh) lt 8.210-6

• Belle (84.3 fb-1)
• Two h decay-modes
• h?gg (Br 39.4)
• h?pp-p0 (Br 22.6)

K.S. Bubu and C. Kolda, PRL 89, 241802 (2002)
90 CL Br(t?mh) lt 3.4 ?10-7
Br(t?eh) lt 6.9x10-7 (prelim)
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gg Production of hc and hc(2S)

• ?c is the lowest-lying charmonium state
• Measure hc and hc(2S) mass and total width
• hc produced in e?e? ? e?e? g g ? e?e?hc and
  reconstructed in hc ? KS K p , where KS ? p p?

Perturbative QCD calculations give?
Gtot(hc)  (25.4  6) MeV/c 2
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J/? as a Calibration Peak
KsK?? final state also seen in J/? production
through initial state radiation. Determine
properties of ?c mass by measuring mass and width
differences between J/? and ?c
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BABAR 88 fb-1 Number of events ?c
1766?70 J/? 262?26
Preliminary
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Mass and Width of ?c
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hc(2S) Mass and Width
Preliminary

• Previous ?c(2S) measurements
• inconsistent
• Same procedure as
• ?c measurement
• ????c?KsK?? , Ks ?????

Preliminary
86  23 events under the peak
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hc(2S) Mass
PDG(2003) uses this only for average 3654 10 MeV
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Hadronic Physics at Lower ?s

• Initial State Radiation (ISR) processes
  effectively give us a variable ECM energy ee-
  collider without actually varying beam energies

?s lt M?
?s M?

• Due to high luminosity at B factories, can get
  competitive results in many measurements
• Hard ISR photon must be detected and well
  measured, and well separated from any track
• About 10 ISR photon reconstruction efficiency

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Motivation

• Low Mass particle spectroscopy can improve on
  branching ratios and mass and width measurements
  of low mass hadrons
• Measure hadronic contributions for Standard
  Model tests, including
• muon anomalous magnetic moment g?-2
• g?-2 has dominant theoretical uncertainties
  from hadronic vacuum polarization which cant be
  calculated at low energies

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Measurement of R
Can measure R over a range of energies with a
single experiment ? no normalisation
uncertainties Not much data exists so far in 1.4
3.4 GeV region
R
??s
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4? ?
Topology four charged tracks hard photon ( 1C
fit in 4p hyp.)
Preliminary
BABAR 89.4 fb -1
(see note below)
Very preliminary Not finally normalized

• very clean sample (background2 )
• whole mass range is covered
• large statistics (75k events)

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4? in the J/? and ?(2S) Regions
BABAR preliminary
N(J/? ? 4?) 303 ? 23 N(?(2S) ? 2?2m) 611 ? 30
J/??4?
?(2S)?J/?2??2?2?
BJ/? ?4?(PDG) (4.0 ? 1.0) x 10-3 ? factor
of 2.5 better error
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J/y Production in ISR Events

• Study ISR e e- ? ? ??- events in the ??- mass
  range around the J/? mass (2.8 ? 3.2 GeV/c2)
• High statistics ?
• fully reconstruct both
• muons and photon

Preliminary
Preliminary Results
PDG
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ISR J/y Production - Interference
Interference between J/? production and
non-resonant component
Line shape with/without interference convoluted
with detector resolution

• Effects the shape of the distribution but has
  very little effect on the total cross section
• Taken into account as a systematic error (0.3)

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pp-p0g
Preliminary BABAR results
J/y
w
p0
f
Signal ISR photon 2 charged tracks 2
photons Good agreement between data and Monte
Carlo
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ISR Summary

• ISR is useful for studying low-energy hadronic
  cross sections and vector meson production
• Can measure hadronic contributions to photon
  propagator
• contribute to g-2 determination
• contribute to Higgs mass limits
• Most precise determination of J/? ee and total
  width
• Many channels available to study
• Much scope for new studies and high-statistics
  data around 1-4 GeV

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Summary

• Excellent prospects for t physics at B factories
• High luminosity provides many t s
• Good laboratory for rare decay searches
• Two-photon production of ?c, ?c(2S)
• Measurement of mass and width of ?c and ?c(2S)
• ISR events for lower ECM studies
• Hadronic cross section measurements
• Measure R(s) over a wide range of CMS energies

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A few extra slides
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Analysis Regions

• Sidebands Regions used to estimate background
  present in signal.
• Grand Sideband Region used to develop
  selection.
• Signal Region ellipse centred on (0,m?) with
  half-axes

-1.0 ? ?E ? 0.5 GeV 1.5 ? mec ? 2.1 GeV
?E -2s?E , 3s?E mec -3smec , 3smec Belle use
5sigma region
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???? Results
Events inside the signal region
13 Cut-based. Redoing with likelihood fit and
more events Side band analysis expects
7.8 1.4 events This leads to a limit
of BR(t?µ?) ? 2.0?10-6_at_ 90CL
(preliminary) Probability for 7.8 1.4
events fluctuating to 13 or more events in the
absence of signal 7.6
Final unblinded run on Data
Preliminary
Comparable with upper values of SUSY predictions
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Energy Spectrum of ? States
From CLEO
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Is it hc(21S0) ?

• Quantum numbers not measured rigorously but
• JP 0 excluded by final state
• ISR excluded decay products
• concentrated in forward hemisphere
• like ?c and in contrast to J/?
• (ee- asymmetric collider ? larger
• acceptance for J/? decay products
• in backward hemisphere)
• PTtot peaked at zero, characteristics
• of quasi-real photons fusion
• ? rules out J1 state
• Jgt2 disfavored for low mass
• charmonium states
• ? Supporting evidence for JPC 0- state

3.60 lt m(KsKp) lt3.66 GeV
Preliminary
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Analysis of t?lll
Belle 87.1fb-1, preliminary

• Belle (87.1fb-1)
• Blinded analysis
• Count with signal box
• Br lt 1.43.1x10-7
• Efficiency 9.210.1
• Expected BG in signal box lt 1 event

• BABAR
• Analysis under way

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High Lumi Prospects for ? Studies
Br(LFV) lt10-7 lt10-8 lt10-9 t?mh, eh,
lll SUSY, Higgs

• For ??mg, eg background contribution is not
  negligible.
• ? Br lt 3 x 10-8 at 3ab-1
• Main BG sources tau-pair with initial rad.,
  beam BG and t?rn
• ???/e?, 3-lepton mode BG is still small.
• ? Br lt 1 x 10-8 at 3ab-1
• Issue for higher luminosity
• Background reduction