Some New Results in Heavy Flavor Physics

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Some New Results in Heavy Flavor Physics

• G.Borissov, Lancaster University, UK
• representing DØ Collaboration

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Many new results in heavy flavors physics

• Properties of top quark
• Bs lifetime from Bs?J/? f
• Br(Bs ? µµ-)
• Bd oscillations
• Signals in Bs ? µ ?Ds
• ?b lifetime
• B masses
• Properties of X(3872)
• Bc lifetime

in this talk
talk of A.Nomerotski
Thanks to excellent performance of Tevatron
accelerator and DØ detector
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Tevatron Performance

• Peak luminosity above 1?1032 cm-2sec-1 achieved
• Reliable operation of accelerator in stores 120
  hours/week
• Expected peak luminosity 3?1032 cm-2sec-1 by
  2007
• delivered luminosity to each experiment 4-8 fb-1
  by the end of 2009

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Integrated Luminosity

• Almost 0.5 fb-1 recorded in DØ
• Most of analyses use only 30-50 of this
  statistics
• more events available ? big room for
  improvement.

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Top quark Studies
Provide important constraints on the SM Higgs
mass and new physics contribution
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Top Quark Mass Measurement

• New statistics from Run II (160 pb-1)
• 191 events with lepton 4 jets selected
• 4 topological variables used to separate ttbar
  and Wjets background. They are combined into a
  single discriminant.

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Measurement Methods

• 4 Jets and W can be combined into 2 top quarks in
  12 possible ways
• Two alternative measurement methods used
• Template method
• apply cut on discriminant
• select best mass hypothesis among all jet
  permutations
• Ideogram method
• discriminant is used to compute the purity of
  ttbar candidate on event by event basis
• use all jet permutations with weight depending on
  the ?2 of each combination hypothesis.

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Top Quark Mass Results

• Consistent preliminary results are obtained (160
  pb-1)
• Leading systematic uncertainty is from ttbar
  modeling, can be improved in the futre
• In addition, new result published (Nature (429),
  638 (2004)) using Run I data (single most precise
  mass measurement)

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Br(t?Wb)/Br(t ?Wq)

• This ratio should be close to 1 in the SM,
  assuming unitarity of CKM matrix
• Should be verified experimentally
• Measurement is performed using a double tagging
  technique with b-tagging applied to the t-tbar
  sample (lepton plus jets).

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RBr(t?Wb)/Br(t ?Wq) Result

• Two b-tagging methods are used
• Counting signed impact parameter
• Secondary vertex Tagger
• Consistent preliminary results are obtained
• This result is consistent with R1.

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Bs Studies

• Properties of Bs are not well known yet
• This particle is not accessible at ?(4s)
• Have many interesting features
• Bs oscillation
• Lifetime difference of CP-even and CP-odd state
• CP violation very small in SM, thus can be
  sensitive to the new physics
• Rare decays may be enhanced
• Bs is abundantly produced at Tevatron and can be
  reconstructed in both semileptonic and exclusive
  decays

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Bs lifetime measurement

• In this measurement the decay Bs? J/? f is used
• In parallel, the lifetime of Bd in Bd? J/? K is
  measured very similar topology
• Simultaneous measurement of Bd and Bs lifetimes
  reduces systematics in t(Bs) / t(Bd) ratio
• Important step towards measurement of lifetime
  difference of CP-even and CP-odd Bs states.

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Signal selection
220 pb-1 of DØ Run II data used
ct/s(ct) gt 5
ct/s(ct) gt 5
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Lifetime fit
Two dimensional unbinned likelihood fit is used
Systematic uncertainties
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Bs Lifetime Results
(FNAL-PUB-04/225-E, submitted to PRL)
This result agrees with other measurements of
t(Bs)
Experiment t(Bs)
DØ, this measurement 1.4440.098-0.0900.020
CDF (Run II) prelim 1.369 0.1000.008-0.010
CDF(Run I) semileptonic 1.36 0.0900.06-0.05
ALEPH 1.47 0.14 0.08
DELPHI 1.420.14-0.13 0.03
OPAL 1.500.16-0.15 0.04
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Search for Bs?µµ-
Standard Model prediction
Rare B decays to leptons have very small expected
branching rates in SM. They can be significantly
higher in different SM extensions.
Br(Bd?ll-) Br(Bs?ll-)
l e (3.42.3) 10-15 (8.03.5) 10-14
lµ (1.50.9) 10-10 (3.40.5) 10-9
lt (3.11.9) 10-8 (7.41.9) 10-7
Current 90CL limits
Example SO(10) symmetry breaking model
Br(Bd?ll-) Br(Bs?ll-)
l e lt 5.9 10-6 lt 5.4 10-5
lµ lt 1.5 10-7 lt5.8 10-7
lt lt 2.5 lt 5.0
Contours of constant Br(Bs?µµ-)
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Data sample

• DØ has very efficient di-muon triggers
• Use data collected in 2002 - April 2004
• Sample corresponds to 250 pb-1 integrated
  luminosity.

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Event Preselection
About 38000 candidates remain after preselection
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Discriminating Variables

• Pointing angle angle between Bs momentum and
  direction from primary to secondary vertex
• Transverse decay length significance LT/s(LT)
• Isolation

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Optimization Procedure

• 80 pb-1 of data is used to optimize the
  selection
• Signal band is defined as m(BsDØ) 180 MeV (90
  MeV is Bs?µµ- resolution in MC)
• Signal distributions are taken from MC and
  background from side bands
• Perform random grid search of 3 discriminating
  variables and maximize the sensitivity to the
  signal.
• Signal region in data is kept as a black box,
  open it only after finalizing and fixing the
  selection procedure
• Number of events in side bands is used to
  estimate the background for Bs?µµ-

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Surviving Events
cut Signal MC exp. background Signal
Pointing angle 8016 57314 580
Decay length significance 3847 4.31.2 5
Isolation 3746 3.71.1 4
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Normalization Channel

• B?J/? K (J/? ?µµ-) is used for normalization
• muon selection efficiency cancels in the ratio
• Systematics from discriminating variables
  significantly reduced.

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Systematic uncertainties
Br(Bs?µµ-) Result
This measurement Existing limit (CDF)
90 CL lt 3.810-7 lt 5.810-7
95 CL lt 4.610-7 lt 7.510-7
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Preparing for Bs oscillations

• Bs oscillation measurement very interesting and
  very difficult task
• Requires both selection of Bs signal and tagging
  its initial state (b or bbar)
• Currently DØ selects Bs in semileptonic decays
• We also develop methods of Bs selection in
  hadronic decays

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Initial State Tagging

• Three different methods are developed
• Opposite muon tagging
• Opposite jet charge tagging
• Same side tagging
• Their performance is verified in data using Bd
  oscillation

Same side tagging result
Tagging e D eD2
opposite muon 0.05 0.46 0.010
Same side 0.75 0.12 0.010
Same side Jet charge 0.68 0.15 0.015
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Conclusions

• Many new results in heavy flavor physics are
  obtained by DØ collaboration
• All of them are competitive or the worlds best
  measurements
• DØ will continue research in this direction with
  the main emphasis on studies complementary to
  B-factories those, involving B hadron states
  not produced at the ?(4s).