Study of the Bc Meson Properties using BcgJyen Decay at CDF II

1
Study of the Bc Meson Properties using BcgJ/yen
Decay at CDF II

• Masato Aoki
• University of Tsukuba, Japan

2
Periodic Table
Bc meson is the last meson experimentally observed
3
The Bc meson

• Only meson state with differently flavored heavy
  quarks
• (bottom and charm quark)
• Both quarks are heavy
• Similar binding interaction to heavy quarkonia
  families (J/y, U, etc.)
• Other quarkonia decay via strong interaction
• The two quarks have different flavor
• ?Only weak decay is possible
• ?Comparable timescales for decay of two heavy
  constituents
• ?Measurable lifetime but shorter than other B
  mesons (t0.5 ps)

q
q
J/y, U
q
q
Bu, Bd, Bs
4
The Bc properties

• Quarkonia described by Quark Potential models
• Opportunity to test with Bc
• Expect
• Tightly bound f(Bc) 400 MeV
• Ground state mass predictions
  6.1ltM(Bc )lt6.5 GeV/c2
• Rich spectroscopy of narrow states below B-D
  threshold

5
Decay properties

• Three dominant processes
• b decay
• J/y p, J/y Ds, J/y ln
• c decay
• Bs0p, Bs0 ln
• Annihilation
• tnt, DK, multi-p
• Large f(Bc) and Vcb vertex ? 400x larger
  annihilation width than for B

6
Decay properties

• Naïvely expect factorization to apply
• GGbGc Gann.
• Expect t0.4 - 0.7 ps
• However, bound-state effects may be large
• Eichten and Quigg predict t1.3 ps

7
Theoretical calculations

• V. V. Kiselev, hep-ph/0308214 (2003) Review
  paper

Bc observation by CDF(1998)
8
Rich decay modes
hep-ph/0308214(2003)

• Large J/ygmm- rate provides experimental
  signature
• ( For example, BR(BugJ/yK) 0.1 )

9
Hadronic production

• Dominant process is gggBcbc
• Calculation requires 36 diagrams O(as4)
• Contributions from color singlet / octet

Chang et al, PRD, 71 (2005) 074012
curves represent different singlet/ octet
contributions
10
Bc production rate

• Much smaller production rate than other b-hadrons

Theoretical calculation 7.4nb Phys. Lett. B605,
311(2005)
11
Heavy Flavor Physics at CDF

• Huge production cross sections at Tevatron
• sb30 mb
• Currently only Tevatron can produce the Bc meson
• B-factories cannot produce the Bc meson because
  the beam energy is not enough for the Bc
  generation
• Large backgrounds as well
• ? B triggers are necessary
• lepton trigger
• displaced track trigger
• and combined trigger

Typical bb pair production diagrams
quark annihilation
gluon fusion
flavor excitation
gluon splitting
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Bc discovery in CDF Run I (9196)

• Bc signal search using BcgJ/yln (le,m) channel
• 20 Bc signal events were observed in 110 pb-1 of
  J/ygmm trigger data

PRL 81, 2432 (1998) and PRD 58, 112004 (1998)
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The CDF II detector _at_Tevatron
HAD Calorimeter
Muon Chamber

• Silicon Detector
• hlt2.0
• svertex30mm
• Central Outer Tracker
• hlt1.0
• spT/pT0.15 pT
• Muon Chamber
• hlt0.6 (1.0)
• EM, HAD Calorimeter
• hlt1.1(EM), lt0.9(HAD)
• sE/Ev (13.52/ET 32) (EM)
• v (502/ET 32) (HAD)

EM Calorimeter
Silicon Detector
Central Outer Tracker
All of the tracking system are replaced for Run II
14
Bc signature in this analysis

• Use semileptonic decay BcgJ/yen
• ? Larger BR than other triggerable decay modes
• ? statistical advantage
• ? Improved J/ygmm trigger
• pT(m)gt1.5 GeV/c (was 2 GeV/c)
• Factor 5 J/y yield (factor 2 BgJ/y yield)
• ? No narrow mass peak due to missing neutrino
• Bc signal excess above estimated backgrounds
• ? More photon conversion background due to new
  tracking system (more material than Run I)
• Establishing the Bc again and precise
  measurements
• s(Bc)B(Bc?J/yen) / s(Bu)B(BugJ/yK) and
  lifetime
• (Mass to be measured in exclusive channel)

15
J/ygmm trigger data

• Lint 360 pb-1
• pT(mm) gt 3 GeV/c
• Reduce fake
• Reduce prompt
• 2.2M J/y
• Signal window M(mm)-M(PDGJ/y) lt 50 MeV/c2

Additional requirements in this analysis
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Electron reconstruction

• pT(e) gt 2 GeV/c, hlt1.0
• Track-seeded reconstruction Inside-Out
  algorithm
• High reconstruction efficiency for low pT
  electrons
• Calorimeter-seeded algorithm is used for high pT
  physics
• Electron ID using both calorimeter and dE/dx
  measured by COT

17
Calorimeter 10 variables
E/p
EHad/EEm
E/p (shower max)
Ewire/Estrip (shower max)
c2wire (shower max)
c2strip (shower max)
DZ/s (shower max)
QDX/s (shower max)
E (preradiator)
DX (preradiator)

• Red electrons from ggee-
• Blue pions from K0sgpp-

18
Electron ID using calorimeter

• 10 variables from calorimeter
• Form a Joint Likelihood Function
• L cut position is varied not to have any
  dependences for electron efficiency
  (isolation,pT,charge)

70 efficiency
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Isolation

• Isolation is defined by SpT/pT
• pT in the denominator is the pT of the track of
  interest
• SpT in the numerator is the scalar sum of pT of
  all other tracks in the same calorimeter tower
• Calorimeter variables strongly depend on the
  isolation
• Isolation correction is necessary
• BcgJ/yen decay is expected to have similar
  isolation to that for BugJ/yK

CDF Preliminary
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Electron ID using dE/dx
Ze/sZ?1.3

• Energy deposit in COT

p
p
?2GeV
e
?2GeV
m
p
p
K
m
K
e
90 efficiency
e
m
p
p
K
ZeLog((dE/dx)measured/(dE/dx)pred. for e)
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s(Bc)B(Bc?J/yen) / s(Bu)B(BugJ/yK) Measurement
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s(Bc)B(Bc?J/yen) / s(Bu)B(BugJ/yK) measurement
strategy

• Reconstruct mass of J/y-e pair
• Estimate all the backgrounds
• Event counting above the backgrounds
• Estimate the acceptance and efficiency
• Use BugJ/yK as the normalization mode
• ? BugJ/yK has similar topology to Bc?J/yen
• ? Cancel out most of uncertainties

m
m
J/y
J/y
m-
m-
Bu
Bc
n
K
e
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J/ye pair reconstruction
m
J/y
m-
n
Bc
e

• One displaced decay vertex
• Lxy/sLxy gt 3
• Prompt background becomes negligible
• pT(J/y-e) gt 5 GeV/c
• Reduce non-B tracks
• Search window
• Wide mass region due to missing neutrino
• 4 lt M(J/ye) lt 6 GeV/c2

signal region
24
Background Estimates
25
Backgrounds and control samples

• fake J/y
• J/y mass sideband events
• fake electron
• J/y track
• bb (bgeX, bgJ/yX)
• PYTHIA Monte Carlo
• electron from photon conversion
• J/y electron tagged as photon conversion
• prompt J/y
• No control sample. There is no reliable Monte
  Carlo
• Zero lifetime ? killed by Lxy/sLxygt3 requirement

26
Fake J/y background

• Fake J/y background can be estimated by J/y mass
  sideband events
• J/yelectron, J/ytrack, J/yconv.-e have fake
  J/y part each other
• To avoid double counting, fake J/y events
  (sideband events) will be subtracted in the
  following background estimations

27
Fake electron background

• Control sample J/y track
• (after dE/dx requirement)
• Fake rate after eID by calorimeter
• Fake rates for K/p/p
• Control samples from high statistics
  Two displaced Tracks Trigger (TTT) data
• Combine them with proper fraction obtained from
  PYTHIA Monte Carlo
• Nfake N(J/ytrack) x efake

Displaced track trigger
secondary vertex
Long lived particle
d0
primary vertex
particle composition around J/y
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Fake rate estimates for K/p/p
K
K-
p
p-
after eID
after eID

• Control samples in TTT data
• D0gKp for K/p
• Lgpp for proton
• Fit the mass distribution to obtain of events
  before and after eID by calorimeter
• Fake rate N after eID / N before eID

p
p
after eID
29
Particle composition in J/ytrack sample

• PYTHIA Monte Carlo simulation
• Dominant fake source pion

CDF Preliminary
Data
Kaon
Pion
d0.09
PYTHIA
Kaon
Pion
Proton
Proton
after dE/dx requirement
pion fraction from dE/dx fitting ? max difference
0.09
30
Average fake rate
Combine
p, p-
CDF Preliminary
average fake rate
positive charge negative charge
K, K-
lt 0.8
p, p

• The average fake rate is applied to J/ytrack
  after dE/dx cut

31
Systematic uncertainties

• Isolation dependence on fake rate
• 14.5
• Difference between TTT data and J/y trigger data
  (tight requirement on of silicon hits for TTT)
• 7.2
• Particle fraction in PYTHIA
• 1.9
• Sample statistics
• J/ytrack 2.0
• Fake rate 0.9

32
Estimated fake electron background

• From J/ytrack data with fake rate convolution
• 15.43 ? 2.54 events in the signal region

33
Photon conversion electrons
g

• Control sample J/ye tagged as ggee
• Find collinear partner track
• These candidates are removed from the J/ye
  candidate list
• Miss-tracking due to very low pT partner track
• ? Not 100 finding efficiency
• ? Residual photon conversion electrons
• Need to understand the finding efficiency

34
Conversion finding efficiency

• Monte Carlo sample
• B0gJ/yp0
• 98 p0ggg, 2 p0geeg
• etag 50 efficiency
• Residual ggee events
• Systematics study
• Another MC use pT(tracks) in J/ytrack as pT(p0)

35
Systematic uncertainties
CDF Monte Carlo

• pT spectrum
• 43.7
• Lifetime of B0
• 2.0
• Dalitz decay
• 1.0
• Sample statistics
• Finding efficiency 3.8
• J/yconv. e 30.1

36
Estimated residual photon conversion

• From J/yconv-e data and conversion finding
  efficiency
• 14.54 ? 7.75 events in the signal region

37
bb background
quark annihilation
gluon fusion
flavor excitation
gluon splitting

• It is possible to make a common vertex with J/y
  from one B decay and e from another B decay
• bb background

38
bb background estimate

• PYTHIA Monte Carlo simulation
• Validated using bb azimuthal correlation
  information PRD71,092001 (2005)
• Reasonable agreement with data
• Normalization with data N(BugJ/yK)

Azimuthal angle distribution between J/y and
electron with all kinematical requirements
Bc signal MC
Additional requirement Df(J/y-e) lt 90deg.
39
Systematic uncertainties

• Monte Carlo setting (PDF/ISR)
• 31.4
• Isolation dependence on eID efficiency
• 2.9
• Branching ratio of normalization mode BugJ/yK
• 0.9
• Calorimeter fiducial coverage
• 0.9
• Statistics
• MC sample 6.5
• N(BugJ/yK) in MC 1.9
• N(BugJ/yK) in data 1.8
• e(eID by cal) 1.4
• e(eID by dE/dx) 1.0

40
Estimated bb background

• From PYTHIA Monte Carlo
• BugJ/yK for normalization to data
• 33.63 ? 11.38 events in the signal region

41
Summary table
J/y sideband events are subtracted
before the subtraction, data has 203 events and
the fake J/y is 24.53.5
42
M(J/yelectron) data and excess

• Total background 63.614.4 events
• Excess 115 events
• Significance 5.9s

43
Cross check e-track IP w.r.t. J/y vertex
electron

• Lxy(J/y)/sLxy gt 3
• Bc decay vertex position is the same as that for
  J/y (J/y immediately decays)
• Bc should make a peak around IP0

m
IP
m-
PV
Lxy(J/y)
Peak exists!
BugJ/yK
J/y-e
44
s(Bc)B(Bc?J/yen) / s(Bu)B(BugJ/yK) calculation

• Have established the signal !!
• Lets calculate
  s(Bc)B(Bc?J/yen) / s(Bu)B(BugJ/yK)

• acceptance ratio
• efficiency ratio

45
Normalization mode BugJ/yK

• Similar reconstruction criteria as J/ye
• N(Bu)2872?59 was found in the same data

46
Kinematical acceptance ratio

• RK Akin(Bu)/Akin(Bc) 4.421.02

Systematic uncertainties
Largest
47
Reconstruction efficiency ratio

• Most of the efficiencies are expected to be same
  for Bc and Bu
• u electron ID with calorimeter and dE/dx

48
Kinematical limits
-1 lt y(Bc) lt 1
4GeV

• Choose pT(B) gt 4GeV/c, y(B) lt 1 as our cross
  section definition
• (Run1 pT(B) gt 6GeV/c, y(B) lt 1)

49
Result of s?B ratio measurement

• s(Bc)B(Bc?J/yen) / s(Bu)B(BugJ/yK)
• 0.282 ? 0.038(stat.) ? 0.035(yield) ?
  0.065(acc.)
• (pT(B)gt4GeV/c, h(B)lt1)
• Most of the difference to the Run I measurement
  is from the treatment of input pT(Bc) spectrum
• Still consistent with Run I
• Consistent with result from muon channel
• 0.245 0.045(stat.) 0.066(syst.)
  0.080/-0.032(life.)
• The result is consistent with recent QCD
  calculation

0.132 0.031
0.041 0.037
0.032 0.020
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Lifetime Measurement
51
Lifetime measurement strategy

• Release Lxy(J/ye)/sLxy gt 3 requirement
• Cut on Lxy error (sLxy lt 70 mm)
• Use J/y-e events in the signal region(4-6 GeV/c2)
• Estimate of background events using same way as
  s?B ratio measurement
• Un-binned maximum likelihood fit with J/y-e data
• Input pseudo-proper decay length and its error
• Background shapes from each control sample
• Prompt background shape is assumed to be a
  resolution function (Gaussian)
• Signal shape with neutrino effect correction
• Fit J/y-e data to extract Bc lifetime

52
Fit input value and neutrino effect correction

• ct proper decay length
• X pseudo-proper decay length
• K correction factor

K-distributions for 4 M(J/ye) bins
Input value for the lifetime fitting
53
Background estimates (w/o decay length cut)

• Background events are estimated using same way as
  s?B ratio measurement
• Prompt background and Bc signal are from the
  lifetime fitting directly

systematic uncertainties are included
54
Background distributions
Fake J/y
Photon conversion
Fake electron
55
J/ye data fit result

• ct142 22/-20 mm
• N(Bc)?237 events (N(prompt bkg) ?127)

56
Systematic uncertainties on ct(Bc)
Total systematic uncertainty is order of 7
(10mm)
57
Bc lifetime result

• CDF Run2 (360pb-1, J/ye)
• ct 142 22/-20 10 mm
• ? t 0.474 0.073/-0.066
  0.033 ps

Recent theoretical calculations in which 3 major
decay diagrams play important roles
58
Experimental results of the Bc meson lifetime
measurement
This analysis
59
Summary of the Bc analysis

• Have established the Bc signal in J/yen final
  state with 5.9s significance
• Measurements with good precision (worlds best)
• s(Bc)B(Bc?J/yen) / s(Bu)B(BugJ/yK)
• 0.282 ? 0.038(stat.) ? 0.035(yield) ?
  0.065(acc.)
• Lifetime
• t 0.4740.073/-0.066(stat.) ?0.033(syst.)
  ps
• The results are consistent with CDF Run I
  measurements
• Lifetime result agrees with theoretical models in
  which all the three major decay diagrams play
  important roles in the Bc decays

60
FIN Thank you

• This lifetime result with minor update was
  accepted for publication in Physical Review
  Letters PRL 97, 012002 (2006)

61
Backup slides
62
Introduction

• Three major decay diagrams
• Lifetime should be t(Bc) ? 1/(0.61.20.1) ? 0.5
  ps if all the three diagrams contribute
  to the decay

Others G(Pauli interference) G(penguin)
63
PDF and likelihood function

• Signal PDF
• Background PDF for fake J/y,fake e, conv. e, bb
• Event PDF
• Log likelihood

signal term
backgrounds term
Background shapes and the numbers are constrained
64
Fitter check before J/ye data fitting
BugJ/yK data
CDF Preliminary
ct504.1 9.3(stat.) mm ?good agreement with CDF
Run II result 498.8 8(stat.) 4(syst.) mm
Toy MC
Fitter returns reasonable lifetime result and
error
65
Cross check J/ye mass distribution

• Normalization 46 GeV/c2 using lifetime fit
  result
• Prompt shape Assume to be J/ytrack with Lxy lt
  3s
• Good agreement

66
Determination of the angle g from nonleptonic
Bc?DsD0 decays
67

• CP-even factors

CP-eigenstates for the oscillation D0?D0
68
(No Transcript)
69
Branching ratio of Bc?DD
Several billion Bc events are expected at LHC ?
104105 decays of Bc
70
CDF Run-II
Pub.
Pub.
M(J/y p?)
ct(J/y e?)
6287?5GeV
0.46?0.08 ps
Pub.
Pre.
M(J/y m?)
M(J/y e?)
71
D0 Run-II
Pre.
Pre.
72
Bc mass measurement
Latest

• CDF Run-II
• 1.1pb-1
• Bc?J/yp
• 50 signals
• gt7.5sigma

Close up
6276.5 4.0 2.7 MeV/c2