B Physics at D0: An update

1
B Physics at D0 An update

• Vivek Jain
• Cornell University
• Oct 1, 2004

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Outline

• Introduction
• D0 detector
• Recent Results
• New states
• Rare decays
• Lifetimes
• Mixing
• Conclusions

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Why B physics?

• Understanding structure of flavour dynamics is
  crucial 3 families, handedness, mixing angles,
  masses, any unified theory will have to
  account for it
• Weak decays, especially Mixing, CP violating and
  rare decays provide an insight into
  short-distance physics
• Short distance phenomena are sensitive to
  beyond-SM effects
• Test bed for QCD, e.g., form factors,
  calculations of B hadron lifetimes, spectroscopy

5
B physics at the Tevatron

• At Ecm 2 TeV
• At Z pole
• At ?(4S)
• All species produced,

Environment not as clean as at electron
machines Low trigger efficiencies
6
B Physics Program at D0

• Unique opportunity to do B physics during the
  current run
• Complementary to program at B-factories (KEK,
  SLAC, CLEO..)
• mixing,
• Rare decays Large tanß
  SUSY models enhance rate
• Beauty Baryons, lifetime,
• expt 0.800.06 (SL
  modes), theory 0.95
• , , B lifetimes, B semi-leptonic,
  CP violation studies
• Quarkonia - production,
  polarization

b production cross-section In Run I, measd.
Rates x(2-3) higher
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DZero Detector

• Trackers
• Silicon Tracker ?lt3
• Fiber Tracker ?lt2
• Magnetic field 2T

• Muon system with coverage ?lt2 and good shielding

8
CFT
Readout by VLPC High QE, very low dark
noise Excellent PE resolution Each pixel has 1mm
radius well matched to fiber Operated at 8-9
( 0.05)K
8 Layers Axial, Stereo ( 3) Radius 20-50 cm
Good S/N. Signal 5-9 pe Fast enough to be in
L1 trigger
9
VLPC performance Signal ON LED was set to 2 pe
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All tracks
Analysis cuts pTgt0.7 GeV
s(DCA)53µm _at_ Pt1GeV and better _at_ higher Pt
data
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pT spectrum of soft pion candidate in D?D0?
100 events/pb-1
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Excellent Lepton Acceptance
Muon ID

• Overall efficiency (from data)
• plateaus at about 85-90
• - at pT 4.5 GeV
• pT 3.5 GeV
• - at pT 2.5 GeV

MC
Muon system in Level 1
of reconstructed muon
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Electron ID

• Calorimeter goes out to
• Low pT electron ID is in progress
• At present, we can detect electrons with pTgt3
  GeV and
• Average efficiency is about 75
• Working to extend to higher values of
  and lower pT
• threshold use for tagging initial state
  flavour

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All trigger components have simulation software
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Triggers for B physics

• Robust and quiet di-muon and single-muon triggers
• Large coverage hlt2, pgt1.5-5 GeV depends on
  Luminosity and trigger
• Variety of triggers based on - Muon purity _at_ L1
  90 - all physics!
• L1 Muon L1 CTT (Fiber Tracker)
• L2 L3 filters
• Typical total rates at medium luminosity (40 1030
  s-1cm-2)
• Di-muons 50 Hz / 15 Hz / 4 Hz _at_
  L1/L2/L3
• Single muons 120 Hz / 100 Hz / 50 Hz _at_ L1/L2/L3
  (prescaled)
• Current total trigger bandwidth
  
• 1600 Hz / 800 Hz / 60 Hz _at_
  L1/L2/L3

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Recent Results

• Many new analyses used 250-350 pb-1
• Single muon triggers have variable prescales,
  non-trivial to determine luminosity for analyses
  using these triggers
• Have more data on tape, but not yet analyzed
• Details at www-d0.fnal.gov/Run2Physics/ckm/

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Basic particles
Plot is for illustrative purpose
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282693
7217127
62441
350 pb-1
Large exclusive samples
Impact parameter cuts
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Bs
No IP cuts Use for lifetime
33725
?b
250 pb-1
Will reprocess w/ tracking optimized for
long-lived part. (yield will 50)
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Observation of X(3872)
5.2? effect
In 2003, Belle saw a new particle at ? 3872
MeV/c2, observed in B decays B ? K X(3872),
X(3872) ? J/? ? ?- Belles discovery has
been confirmed by CDF and DØ. DØ (accepted by
PRL) 522 100 events ?M 0.7749 ? 0.0031
(stat) ? 0.003 (syst) GeV/c2
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Charmonium
J_PC
(Estia Eichten)
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What kind of particle is the X ? - charmonium
? 1 ³D3, 2 ³P2 - an exotic meson molecule
? - something else ? Compare X candidates to
?(2S), e.g. - split into two ? regions -
decay length, isolation, helicity
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No significant differences between ?(2S) and X
have been observed yet. This comparison will be
more useful once we have models of the production
and decay of, e.g., meson molecules that
predict the observables used in the comparison.
ylt1
Iso1
Hel(µµ)lt0.4
pTgt15
Hel(pp)lt0.4
dllt0.01 cm
Observation of the charged analog X ? J/? ? ?0
would rule out charmonium Observation of
radiative decays X ? ? ?c would favour charmonium
Belles results rule out 1 ³D3, 2 ¹P1, ³D2, ¹D2,
0-, 1 Use Dzeros calorimeter to identify low
energy ?0 and ? work in progress.
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Spectroscopy L1 B (and D) mesons

• For Hadrons with one heavy quark, QCD has
  additional symmetries as
• (Heavy Quark Symmetry)
• Spin of the heavy quark decouples and meson
  properties are given by the light degrees of
  freedom
• Each energy level in the spectrum of such mesons
  has a pair of degenerate states

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Lessons from charm (I)
For non-strange L1 Charm mesons jq 1/2, 3/2
have been seen
The wide states were observed via Dalitz plot
analysis in
Belle hep-ex/0307021
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D at D0
Preliminary result on product branching
ratio Br(B ? D10,D20 ? ? X) ? Br(D10,D20 ?
D ?-) 0.280 ? 0.021 (stat) ? 0.088 (syst)
measured by normalizing to known Br (B ? D ? ?
X)
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Lessons from charm (II) Ds
Eichten
For L1 Ds mesons, preferred decay modeDK jq
3/2 -gt DK, DK
jq 1/2 below DK threshold, decay to
Mass/widths unexpected! Maybe B or Bs
have similar behaviour
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Previous results on B
Probably not the natural width of these states

• Previous experiments did not resolve the four
  states
• ltPDG massgt 56988 MeV
• Theoretical estimates for M(B1) 5700 - 5755 and
  for
• M( ) 5715 to 5767. Width 20 MeV

Experiment B reconstruction BJ mass (MeV) BJ width
ALEPH exclusive 569518 5316
CDF (µD)p 571020 -----
DELPHI inclusive B p 573221 14528
OPAL inclusive B p 568111 11624
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Signal reconstruction (I)

• Search for narrow B - Use B hadrons in the
  foll. modes and add coming from the
  Primary Vertex
• Since ?M between B and B0 is expected to be
  small compared to resolution, we combine all
  channels (e.g., ?M for B/B0 0.330.28 MeV)

7217127 events
2826 93 events
624 41 events
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Signal Reconstruction (II)

• Dominant decays modes of
• (
  forbidden by J,P conserv.)
• (ratio of the two modes expected
  to be 11)
• To improve resolution, we measure mass difference
  between and B, ?M

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Signal reconstruction (III)

• Now, ?M(B - B) 45.780.35 MeV small
• Thus, if we ignore , ?M shifts down 46
  MeV,

• We get three peaks
• M( ) M(B) 46 MeV
• M( ) M(B) 46 MeV
• M( ) M(B) - in correct place

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First observation of the separated states
From fit N All B 536114 events
7s signif.
27359 events
Interpreting the peaks as (98)
13130 events
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Consistency checks
B0
B
required to have large Impact parameter
signific. relative to Primary vertex No Signal
(as expected)
3236 events
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Results of fit - Preliminary
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Standard Model predictions
Exptl. Results 90 (95) CL
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Beyond Standard Model

• First proposed by Babu/Kolda as a probe of SUSY
  (hep-ph 9909476)
• Branching fraction depends on tan(ß) and charged
  Higgs mass
• Branching fraction increases as
• in 2HDM (MSSM)

Other models also have enhanced rates,
e.g., Dedes, Nierste hep-ph 0108037 mSUGRA
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Experimental challenge
(?L? 200 pb-1)
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Optimization Procedure blind analysis

• 80 pb-1 of data was used to optimize cuts
• After pre-selection, three additional variables
  were used to discriminate bkgd. from signal -
• Isolation Since most of b-quarks mom. is
  carried by the B-hadron, track population around
  it is low
• Decay Length significance Lxy/dLxy remove
  combinatoric background, e.g., fake muons
• Pointing angle Angle, a, between B_s decay
  vector and B_s momentum vector

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Result of optimization
Isolation gt 0.56
Pointing angle lt 0.20
(rad)
dLxy/ dL gt 18.5
Background prediction from sidebands in (MB
2s) 3.7 1.1 events
Punzi (physics/0308063)
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Opened the box (July 8 04)
(?L 240 pb-1)
Nothing remarkable about the four events look
like background!
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Calculate upper limit (I)

• To calculate limit on branching fraction,
  normalize to

PDG
Feldman-Cousins
MC 0.2290.016
MC
0.2700.034 (PDG)
Since our signal region overlaps Bd, can have
contamination R theoretical expectation for
ratio of Br. frac. of Bd /Bs - set R0 If
limit will be better
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Upper Limit - Preliminary
The 95 (90) C.L. upper limit
Currently, the most stringent limit on this decay
channel
If we use Bayesian approach, we get 4.7 (3.8)
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Excluded by D0 Run II 240 pb-1
Implications of this result
4.6E-7 (95CL)
Dermisek et al Hep-ph 0304101 Dark Matter
and Minimal SO10 with soft SUSY breaking
Contours of constant
Allowed by Dark Matter constraints
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Observation of Bc

• Last of ground state mesons to be definitively
  observed!
• Theory Lifetime 0.3-0.5 ps
• Theory Mass 6.4 GeV 0.3
• Only previous evidence CDF RunI result

Mass 6.40.390.13 GeV
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Take advantage of easy-to-trigger-on final
state events come via the dimuon triggers
m-
m
n
Select 231 J/ymX candidates Background estimated
with J/ytrack data control sample, separated
into prompt and non-prompt components
m
Bc
PV
47
Do combined likelihood fit to invariant mass and
pseudo-proper time distribution


signal 951211
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Background-only fit

D2log(likelihood) is 60 for 5 degrees of freedom
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Other properties
Bc
b
c

Forms weakly decaying charmed hadron
c
b
Probability 4th m within f 90 degrees of Bc
candidate 52 Probability 4th m within f 90
degrees of background 1
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Lifetimes of B hadrons

• Use modes with J/? final states, semi-leptonic
  decays
• Predictions available from theory via OPE
  calculations
• These calculations are rooted in QCD
• Expansion is in inverse powers of heavy quark
  mass
• Predictions are semi-quantitative for Charm
• For B-hadrons, predictions are on much firmer
  footing

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?(B)/?(B0) from semileptonic decays
Novel idea Signal with Imp. Param cuts
D0 sample ? K ?- anything B
82 B0 16 Bs 2 D
sample ? D0 ?- anything B 12
B0 86 Bs 2
Estimates based on measured branching
fractions and isospin relations.
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Group events into 8 bins of Visible Proper Decay
Length (VPDL) Measure ri N(? D-)/N(? D0) in
each bin i. Minimize Additional inputs to
the fit - sample compositions (previous
slide) - K-factors (from MC) missing
particles K pT(?D0) / pT(B)
separately for different decay modes -
Relative reconstruction e for different B decay
modes (from MC) - Slow pion reconstruction e
flat for pT(D0) gt 5 GeV (one of our cuts)
- Decay length resolution (from MC) - ?(B)
1.674 ? 0.018 ps PDG Fix in fit
one example VPDL bin
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Preliminary result ?(B)/?(B0) 1.093 ? 0.021 ?
0.022 (stat) (syst)
Adding more data
Syst. dominated by - time dependence of slow
? reconstruction eff. - relative reconstruction
efficiency CY - Br(B ? ? ? D- ? X) -
K-factors - decay length resolution differences
D0 ? D The prelim. DØ meas. is one of the most
precise results
Not updated
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2D fit Mass and Lifetime (100)
Also did,
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Summary of ?b results
World Average
1.2290.080 ps
0.7980.052
Theory 0.900.05
World Average uses semi-leptonic modes
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2D fit Mass and Lifetime
Single best measurement
Most existing meas. use SL mode
Also did,
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Summary of Bs results
World Average
1.4610.057 ps
0.9510.038
Theory 1.000.01
ltWorldgt contains final states with different
amts. of CP e-states
60
Mixing is high priority

• 2nd order weak transition

• ?lt0 disfavoured by current limit on ?ms (gt14.4/ps)

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Bs CP 1 CP -1 Lifetimes

• B0s?J/? f unknown mixture of CP 1 CP -1
  states
• In Standard Model ??s/?s may be as large as 0.1
  ( )
• Gs ( GLight GHeavy)/2 ?Gs
  GLight - GHeavy
• In the case of untagged decay, the CP
  specific terms evolve like
• CP - even ( A0(0)2 A(0)2 ) exp(
  -GLightt)
• CP - odd A-(0)2 exp( -GHeavyt)
• Flavor specific final states (e.g. B0s?l?Ds )
  provide
• Gfs Gs - (?Gs)2 / 2Gs ? ( (?Gs)3 / Gs 2
  )

DZ Beauty03
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In progress
Bs Lifetimes, transversity variable ?T
The CP-even and CP-odd components have
different decay distributions. The
distribution in transversity variable ?T and
its time evolution is d?(t)/d cos?T 8
(A0(t)2 A(t)2) (1 cos2?T) A-(t)2 2
sin2?T 3 linear polarization states J/? and
f polarization vectors
longitudinal (0) to the B direction of motion
transverse and parallel () and
(- ) to each other

• MC distributions for CP 1 CP -1 for
  accepted events (D0)

DZ Beauty03
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How to measure ?m
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In search of BS oscillations
(Amplitude method)
Fit data to
Fit for A as a function of ?ms
Measurement A 1 Sensitivity 1.645?A 1
(95) Limit A lt 1 - 1.645?A (95)
Current limit ?ms gt 14.4 ps-1 _at_95 CL
65
Compare A for ?m15 ps-1
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Significance of mixing measurement

• We need
• Final State reconstruction
• Ability to measure B decay length
• B flavour at decay and production

67
Flavour tagging

• Use flavour-specific decays to get flavour of B
  at decay
• To get flavour of B at production use

Same side
Opposite side
neutrino
Jet charge
Trigger lepton
Fragmentation pion
b-hadron
B
D
PV
Soft lepton
Lxy
68
MC
(B MC)
Require Q gt 0.2
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Combined tags analysis - Bd
200pb-1

• Data sample split into two sets
• Tagged by soft muons (SLT)
• Tagged by combined jetQSST algorithm
• Combined algorithm produces non-zero answer if
• Event not tagged by SLT
• At least one of jetQ and SST gives a non-zero
  answer
• jetQ and SST give same answer (? better
  dilution)

70
Combined tagger result
200pb-1
Simultaneous fit to SLT and
jetQSST asymmetries

• Chief systematics
• D ? sample composition
• D pion tagging probability
• Charged B dilution determination

SLT
Preliminary results
?md0.456 ? 0.034 (stat)? 0.025 (syst) ps-1
D0 (44.8 ? 5.1) SLT
D0 (14.9 ? 1.5) jetQSST D?
(27.9 ? 1.2) jetQSST ? (5.0 ? 0.2)
SLT ? (68.3 ? 0.9) jetQSST
jetQSST
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• One can reconstruct in hadronic and
  semi-leptonic modes
• Hadronic modes, e.g.,
• Pros Very good proper time resolution
• Cons Low branching fraction (
  ), triggers
• Semi-leptonic modes, e.g.,
• Pros Large Branching fraction
  , triggers
• Use both Muon Electron final
  states
• Cons Poorer proper time resolution

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SL modes have large yields
DS ??? BR (3.6?0.9)
9481 events in 250pb-1
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BS ? DS ? X

• BR (3.3?0.9)
• (BR comparable to Ds? ??)
• But larger backgrounds
• D- ? K ?- ?-
• D- ? K ?-
• non-resonant D- ? K ?- ?-
• 4933 events in 200 pb-1
• Significant increase in total BS yield

Other DS decays are being studied too
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Mixed BS candidate in Run 164082 Event 31337864

• Two same sign muons are detected
• Tagging muon has ?1.4
• See advantage of muon system with large coverage
• MKK1.019 GeV, MKKp1.94 GeV
• PT(µBs)3.4 GeV PT(µtag)3.5 GeV

Y, cm
X, cm
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Progress report

• Studying electrons as an initial state flavour
  tag
• Hadronic modes Bs -gt Ds pi
• New triggers online very effective for hadr.
  Decays
• If nature is kind, and ?m is on the low side, we
  could have
• a shot at it with the SL mode
• Some upgrades are planned
• Layer 0 new Silicon layer at r 2.5 cm.
  Significant
• improvement in proper time resolution
  (mid-2005)
• Double trigger bandwidth/reconstruction farms
  and write
• more data to tape in proposal stage

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Conclusions and Outlook

• Lot of progress in the previous year
• Accelerator performing reasonably well.
• Expect 500 pb-1 by the end of the calendar
  year
• B physics group producing competitive results
• Exciting times ahead

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Backup slides
78

Need to precisely determine the CKM matrix

• Elements of the CKM matrix can be written as
• ? Cabbibo angle (0.22), A (0.85),
• Magnitude of CP violation is given by ?

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• Unitarity of the CKM matrix leads to relationship
  between various terms
• One such relation

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If CKM matrix is unitary, leads to triangles in
the ?, ? plane
Vtd
Vub
Vcb
CA
BA
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• Study of B hadrons yields
• B mixing
• ? can be inferred from CP violation
• Within the SM, CP conserving decays sensitive to
  
  
  
• gt 0 can be inferred from limit on Bs mixing
• Complementary meas. of ?, from
• New phenomena might affect K and B differently

can tell if ? is non-zero
83
Winter 2004 HFAG avg. (fit does not include
results on Sin(2ß))
84
Pre-shower detectors help in e-ID
Barrels and Disks
85
SMT
6 barrels 4 layers SSDS, 2/90 stereo
zlt0.6 m, r 2.7-10 cm 12 central F
disks DS, 144 wedges,
stereo
4 forward H disks 96 wedges, z 1.1/1.2 m r
9.5-20 cm
Tracking to ? 3 (? 6)
793K channels, rad hard to 1 MRad 2-3
fb-1 S/N gt 10, 1 MIP 25 ADC counts Hit
resolution 10µ
86

• J/y mass is shifted by 22 MeV
• Observe dependence on Pt and on material crossed
  by tracks
• Developed correction procedure based on field
  material model
• Finalizing calibration of momentum scale using
  J/y, Ks, D0
• NOT yet used

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Track triggers very important for B physics -
Trk/muon match at L1 - Trks are fed to L2
Silicon track trigger - Trk/Pre-shower match
89
Silicon Track Trigger is being commissioned Trigge
r is online as yet not used for physics

• Performs final silicon cluster filtering and
  track fitting
• Lookup table used to convert hardware (e.g.,
  channel, etc.) to physical coordinates ( )
• 8 300-MHz 32-bit integer Texas Instruments DSPs
  perform a linearized track fit
• Fit using precomputed matrix stored in lookup
  table

90
Accelerator performance
Run Ib Run IIa Run IIb
bunches 6X6 36X36 140X133
(TeV) 1.8 1.96 1.96
1.6E31 8E31 2-5E32
Bunch x-ing (ns) 3500 396 132(?)
Int./x-ing 2.8 2.4 2-5

• Have

Currently
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Basic Particles
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Inclusive B lifetime using
Standard technique no IP cuts. Poor S/B
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Aside Where do the Bs go?
Factor events for 2 fb-1
3E11
2 b quarks/event 6E11
6E10
1.8E8
7.2E6
3.6E6
Single µ Trig. Eff lt 1 lt3.6E4
Reco. Eff. lt10 lt3.6E3
Flavour Tag µ comes for free
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jq1/2, J0, 1 - B, B
For L0, two states with

• For L1, get two pairs of degenerate doublets,
• jq1/2, J0, 1 -
• jq3/2, J1, 2 -
• HQS also constrains the strong decays of these
  states
• jq 1/2 decay via S-wave, hence expected to be
  wide
• jq 3/2 decay via D-wave, hence narrow

These four L1 states are collectively known as
B or
Strong decays
97
Lessons from Charm (III)

• For charm mesons, M(D)-M(D) 140-145 MeV
• For bottom, M(B)-M(B) 46 MeV
• Theory Splitting within a doublet has 1/m_Q
  corrections
• M( )-M( ) 32-37 MeV (jq3/2 doublet)
• Could expect this to be 10-15 MeV for M(
  )-M( )
• For non-strange charm, M(D)-M(D) 550-600 MeV
• Would expect similar behaviour for B mesons

98
Signal Reconstruction (V)

• We fit the ?M signal with 3 relativistic
  Breit-Wigner functions convoluted with Gaussians
• N Number of events in the three peaks
• Fraction of in all events
• Branching fraction of
• From theory fix and
• From MC fix resolution of ?M10.5 MeV

99
Sample composition

B meson lifetimes and branching rates from
PDG K-factor distributions, decay length
resolution, reconstruction efficiencies from MC
D sample
D0 sample
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2D lifetime fits
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Quarkonia at D0

• Have older results on J/Psi production. Will
  update
• - Cross-section as a function of pT and ?
  
• Started to look at Upsilon production
  characteristics
• - We presented a preliminary pT distribution
  at QWG03
• and more recently at PHENO04
• - Next step is to determine production
  absolute cross-section
• and polarization studies

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