Latest results on bspectroscopy from CDF

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Latest results on b-spectroscopy from CDF

• Elena Vataga (Univ. of New Mexico, USA)
• On behalf of the CDF Collaboration
• CERN - October 31, 2006

2
Why B spectroscopy?

• We are not looking for New Physics (but may find
  subtle discrepancy)
• Standard Model is extraordinary. Deserves
  thorough elucidation.
• B-quark discovered in 1977. Wealth of b-mesons is
  found. Only one b-baryon well established so far.
• Effective theories derived from QCD needed for
  dynamical understanding HQET
• mc,mb,mt ?gt LQCD gtgt mu, md, ms ? Heavy Quark
  Symmetry
• HQET extensively tested for Qq systems
  interesting to check predictions for Qqq systems

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Whats new?

• Observation of orbitally excited Bs mesons
• Observation and mass measurement of Bc ? J/? ?
• Search for ?b ? J/? J/?
• Observation of new beauty baryons ?b?()

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Tools
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Tevatron
today results first fb-1

• Excellent performance of Tevatron in last years
• Record Instantaneous luminosity gt 2x1032 cm-2
  s-1
• Now delivered ?Ldt1.8 fb-1
• Good for b-physics on tape ?Ldt1.3 fb-1

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The CDF II detector
? coverage ? 1 84 in ?
96 layer drift chamber 44lt r lt132
cm, zlt155 cm ? 1.0, 30k channels
silicon layers 90 cm long, ? 2.0 r00
1.3?1.6 cm
Trigger 3 levels 25000 / 300 / 100 Hz L1 COT
tracks L2 silicon tracks dead time lt 5
Resolution pT0.15 pT vertex r-? 30 µm r-z
80 µm J/? mass 14 MeV/c2
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B physics _at_ Tevatron

• Compared to ee- experiments on U(4S) or Z0
• Pro
• pp ? bb x-section is gt1000 times larger (10 mb
  )
• All species of b-hadrons not just B?/B0, also
  Bs0, Bc, Lb0
• Contro
• QCD background 103 larger than ?(bb)
• multiple interactions, large combinatorics.
• Collision rate 1.7 MHz ? tape writing limit 100
  Hz

b
b
g
g
g
q
b
b
b
b
g
g
q
b
g
b
q
q
Flavor creation (annihilation)
Flavor creation (gluon fusion)
Flavor excitation
Gluon splitting
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B physics _at_ CDF triggers are crucial
BR10-5 visible with just trigger confirmation !
B?hh

• Trigger configurations
• Di-muon
• Lepton plus displaced track
• 2 displaced tracks

42 TB in BCHARM trigger!
Secondary Vertex Trigger (SVT) is unique to
CDF! First of its kind to trigger on fully
hadronic b/c decays
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Bs and Lb mass measurements
220 pb -1
PRL 96, 202001 2006
better precision than the current world overage!
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Lb Lifetime
1fb -1

• Measured with fully reconstructed Lb g J/y L0
  decay
• 542 Lb candidates
• World best t(Lb) measurement !

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Lb Lifetime vs theory
As precise as previous world average 3.1 ?
different though!
World Average (without this result)
NLO (C.Tarantino et al., hep-ph/0203089)
CDF New Result
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Observation of orbitally excited (L1) Bs
mesons
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Orbitally Excited BsJ Mesons

• B?B?, where ? is undetected
• Shift of possible Bs2, Bs1 peaks by ?M(B -
  B) 45.78 MeV/c2 (see PDG)
• Two channels B?J/?K, B?D?

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B sample 58 000!
Use Neural Network to optimize both B and Bs
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Orbitally Excited Bs-mesons
Bs2
Bs1

• Two signals
• Bs2 already seen by OPAL, DELPHI and DØ
• Bs1 ? first observation!

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Discovery of Bs1

• N (Bs2) 94.8 ? 23.4(stat)
• N (Bs1) 36.4 ? 9.0(stat)

P-value from Toy MC 2?10-7 Greater than 5 s !
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Observation of Bc ? J/y p and mass measurement
of Bc
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Bc ? J/? ?
u d
p
b c
c c

• Bc is not produced at B factories
• Observed in semileptonic mode
• Full reconstruction allows
• for precise mass measurement
• New analysis
• Tune selection on B? J/y K
• After approval, open box.
• Wait for significant excess
• Measure properties of the Bc

Bc
J/y
Bc change K to a p
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Bc ? J/? ?
Challenges theoretical predictions
theories
N(Bc) 45.2?9.4, S/?B 7.5
m(Bc) 6276.5 ? 4.0 (stat) ? 2.7(syst) MeV/c2
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Search for ?b ? J/? J/?
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Introduction
_
The Bottomonium system

• Spin-singlet bb bound state
• s(pp ? hbX ) mb level at Tevatron energy scale
• Large uncertainty on decay branching fraction
• BR(hb?J/?J/??mmmm) 10-7 ? -5

_
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Search for ?b?J/?J/?

• Exclusive search from CDF RunI and LEP
• Inclusive search from CLEO
  ( ?(nS)-gt hbg hb-gt hbg)
• No significant evidence yet.

• Run I history (80 pb-1)
• 7 events observed/ 1.8 backgr. (2.2 s)
• Upper limit 18 pb

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Results

• Expected 3.6 bkg events observe 3 events
• Set upper limit for production cross section

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Observation of new beauty baryons ?b?()
http//www.fnal.gov/pub/presspass/press_releases/s
igma-b-baryon.html
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Bottom Baryon States with B1,C0,JP 1/2, 3/2
Mass predictions from hep-ph/9406359
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Predictions on ?b-()/?b() properties

• NRQCD, HQET
• Potential models
• 1/Nc expansions
• Lattice QCD calculations

Strong decay with ? emission ?b?
?b ?
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Methodology
Decay chain ?b -(?)??b0 ?- ?b0?
?c?- ?c? p K -?
Trigger tracks
?? soft track from Primary Vertex
1-trk vertex
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Strategy
Optimize Lb yield
Blind Sb signal region
Check for possible reflections from other B decays
Optimize Sb selection (MC)
Evaluate different background contributions
Estimate detector resolution for Sb (MC)
Understanding of background is crucial!
OPEN THE BOX
Measure ?b yields and Masses
Set the limit
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Discriminating variable

• Search for narrow resonances in
• Q m(?b?)- m(?b)- m(?)
• Blinded region 0.03ltQlt0.10 GeV/c2
• Work with 2 distributions
• ( expect m(?b- )gt m(?b) )
• Same Charge (SC)
• ?b-(?) ??b0 ?- ? ?c?- ?- ( c.c )
• Opposite charge (OC)
• ?b(?) ??b0 ? ? ?c?- ? ( c.c )

Remove ?b resolution

• 5.787ltm(?b)lt5.857 GeV/c2

?b-(bdd) and anti-?b-
?b(buu) and anti-?b
Two ? have same/opposite charge
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Expected background
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?b sample
Largest in the World!
Reflections
Combinatorial background
Signal region 5.565, 5.670
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?b optimization

• Cut are optimized with signal region blinded.
• Signal is taken from PYTHIA
• Background is taken from the sidebands.
• Optimization is done maximizing FOM ?(S)/?B
• No cut on pT (??)

cross-check on D?D0?, included in systematic
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Background Composition
replaced
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Corrections to MC samples

• PYTHIA ?b??b?
• Do not expect perfect description for b-baryons
  experimental data are limited
• Needs reweighting
• PT(?b)
• PT(soft ?)
• Included in systematic

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Fitting background
Combinatorial
B mesons
?b HAUE
alternative fit shapes in systematics
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Detector resolution and signal width

• Estimated detector resolution from MC generating
  signal with 0 natural width 2 MeV/c2
• Cross-check on D ?D0? (MC)
• ?(?b) is predicted by HQET
• Dominated by natural width

Width grows with Q
hep-ph/9406359
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Sum of Background Fits

• Smooth background shape in signal window
• Fixed fit parameters before opening the box

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Unblinded Q distribution
Significant excess in both distributions!

• Naïve S/?(SB) 9 s

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Fitting the signal

• Simultaneous unbinned NLL fit for both
  ?b-()/?b() distributions
• Background frozen
• 4 peaks Breit-Wigner ?
  Gaussians
• ?(?b) function (Q)
• 7 Floating parameters
• Num of events in 4 peaks N (?b)
• Q(?b-) and Q (?b)
• Common parameter Q(?b)-Q(?b)

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Fit values and errors
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Signal significance

• Naïve 9s
• P-value calculation gt 5s (not enough Toy MC)
• Evaluate Likelihood Ratio for different
  hypothesis

4 peaks are 2.6 ?1019 more likely then no peak at
all

• Background fluctuation is statistically excluded
• Hypothesis with 4 peaks in the most favorable

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Summary

• We observe four ?b? resonant states 240 events
  in total
• The significance of the signal gt 5?
• The signal is consistent with the lowest lying
  ?b?(?) states
• We measure Q values

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Plans

• Increase statistics by
• ?b0? ?c?- from different triggers (1000)
• ?b0? J/? L0 ( 500)
• ?b0? ?c 3?
• Measure ?m M(?b) M(?b) for and
  separately
• Measure widths

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Conclusions

• CDF makes fundamental contributions in
  b-spectroscopy
• Performing the world most precise measurements of
  ?b Bc Bs B B0 masses
• Discovering new particles
• ?b?(?) ??b?
• Bs1 ? BK
• Bc ? J/? ?
• Setting new limits
• ?b ? J/? J/?
• And all these with only THE FIRST fb-1 !

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BACKUP
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?b?(?) masses

• Using m(?b) 5619.71.2(stat) 1.2(syst)

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Systematic Errors
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Sb Motivation

• Lb only established B baryon
• Enough statistics at Tevatron to probe other
  heavy baryons
• Next accessible baryons
• Sb bqq, q u,d

3/2(Sb )
JP SQ sqq
1/2 (Sb )

• HQET extensively tested for Qq systems
  interesting to check predictions for Qqq systems
• Baryon spectroscopy also tests Lattice QCD and
  potential quark models

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Fit correlation coeff.
?b peak is small relies on ?b- ?b to
determine its mean value
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?b N-1 scan
signal
background
PT (?b) gt 9.5 GeV/c
d0/?(d0) lt 3.
cos ?? gt -0.35
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Why b baryons?

• B-quark discovered in 1977
• Wealth of b-mesons is found
• Only one b-baryon well established so far
• Finding and studying b-baryons
• completes tests of SM
• Systematic expansion of QCD Heavy Quark Eff.
  Theory
• mc,mb,mt ?gt LQCD gtgt mu, md, ms ? Heavy Quark
  Symmetry
• Masses and decay rates test HQET
• HQET extensively tested for Qq systems
  interesting to check predictions for Qqq systems

54
Bs mass measurement
better precision than the current world overage!
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Lb mass measurements

• Observed Lb decays
• ?b0? J/? L0
• ?b0? ?c?-
• ?b0? ?cm-nm

?
?
?-
p
?
?b
better precision than the current world overage!
PRL 96, 202001 2006