Measurement of the Lb Lifetime in Lb

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Measurement of the Lb Lifetime in LbJ/yL0 in pp
Collisions at vs1.96 TeV
Konstantin Anikeev, Jonathan Lewis, Pat Lukens,
Robyn Madrak, Ting Miao, Rick Tesarek, Slawek
Tkaczyk Fermilab Luis Labarga Echeverria, Juan
Pablo Fernandez Universidad Autonoma de Madrid /
CIEMAT Elliot Lipeles, Mark Neubauer, Frank
Würthwein UC San Diego John Alison, Joe
Boudreau, Chunlei Liu University of Pittsburgh
CDF Paper Seminar August 31, 2006 PRL Final
Draft CDF 8281 Analysis documented in CDF
8248/8084/7867 B Physics Group Blessing May 11,
2006
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Lifetimes Why Do We Care?

• The total width (G) of a particle, inversely
  related to the lifetime (t), characterizes
• underlying dynamics govering its decay
• ? strong, electromagnetic, weak interactions
• Weak decay of hadrons depends upon fundamental
• parameters of the Standard Model we'd like to
  know
• ? CKM matrix elements, quark masses
• Our world is one of quarks (and gluons) confined
  
• inside hadrons rather than weakly-decaying free
  quarks
• ? Complicates theory interpretation of
  observations
• Lifetimes of weakly decaying hadrons of the same
  
• heavy flavor provide a quantitative connection
• between these two worlds

Vcb
You are here
t(D)/t(D0) ? 2.5 t(B)/t(B0) ? 1
increasing mQ
8 (spectator ansatz)
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Lifetimes of b-Flavored Hadrons

• Critical testbed for theoretical framework used
  to predict heavy quark quantities
• Qualitatively expect
• but one can do better than this...!
• b-hadron lifetime ratios can be calculated with
  reasonable precision
• using Heavy Quark Expansion (HQE) since
  mbLQCD ? large energy release in decay

t(Bc) t(Lb) ? t(Bs) ? t(B0) ? t(B)
2 for t(B)/t(B0), 1 for t(Bs)/t(B0), 6 for
t(Lb)/t(B0)
Weak Annihilation
Pauli Interference
Only charged B mesons
Same final state ? interference (destructive)
Weak Scattering/Exchange
Helicity suppressed in mesons, not baryons
Different final states ? no interference
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Heavy Quark Expansion
Inclusive decay width expressed as an operator
product expansion (OPE) in LQCD/mb and as(mb)
O(1/mb4)

• ci(n) contain short-distance
• physics from scales ? m O(mb)
• ? perturbatively calculable
• Matrix elements contain
• long-distance physics
• ? hard! especially for baryons
• Spectator contributions
• enter at 1/mb3 (5-10)

Experiment (world avg)
Theory
LO

• NLO QCD and sub-leading spectator
• corrections can be important!
• For t(Lb)/t(B0)
• NLO QCD -8
• (hep-ph/0203089)
• Sub-leading spectator -(2-3)
• (hep-ph/0407004)

NLO
Tarantino, et al. hep-ph/0203089
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Lb Lifetime Before Us
Experiment (world avg)
Theory
LO
Semi-leptonic modes (dominant)
Fully -reconstructed modes
NLO
For t (Lb)/t (B0), early theory predictions
(0.94) and experiment differed by more than 2s
? "Lb lifetime puzzle" Current NLO QCD 1/mb4
calculation t(Lb) / t(B0) 0.86
0.05 consistent w/ HFAG 2005 world avg t(Lb)
/ t(B0) 0.803 0.047
Tarantino, et al. hep-ph/0203089
The situation is far from resolved - need more
experimental input on t(Lb)!
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Lb Lifetime Analysis Strategy
clean trigger for decay
Measure t(Lb) in fully-reconstructed decay
channel Lb?J/yL0
Pros - Mass peak to distinguish signal
bkg - Event-by-event measure of bg (boost)
(Do not rely on MC to account for
unobserved n as in semi-leptonics) Con -
Smaller signal ? larger stat. error
relative to semi-leptonics
Use t(B0) measurement in B0?J/yKs as reference
mode
? similar decay J/y V0 (V0Ks0,L0) ? larger
sample 6 ? Lb
Check lifetime in fully reconstructed Bu,d?(J/y,
y')X decay modes
? validate lifetime analysis using J/y
vertex only for all decay modes
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b-Hadron Lifetimes We Measure
B0 ? J/y Ks, J/y ? mm, Ks ? pp
y(2S) Ks, y(2S) ? mm, Ks ? pp y(2S)
Ks, y(2S) ? J/ypp, J/y ? mm, Ks ? pp B0 ?
J/y K0, J/y ? mm, K0 ? Kp y(2S)
K0, y(2S) ? mm, K0 ? Kp y(2S) K0,
y(2S) ? J/ypp, J/y ? mm, K0 ? Kp B ? J/y K,
J/y ? mm y(2S) K, y(2S) ? mm
y(2S) K, y(2S) ? J/ypp, J/y ? mm B
? J/y K, J/y ? mm, K ? Ksp Lb ? J/y
L0, J/y ? mm, L0 ? pp
Full systematics
Statistical errors only (for cross-v)
Full systematics
Our primary goal
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Results Yield
B0?J/yKs
L0?J/yL0
N(Lb) 538 38
N(B0) 3376 88
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Fit Model Overview
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Fit Model Signal PDL
ct368 mm ss36 mm
log scale
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Fit Model Background PDL

zero lifetime (prompt)
"negative lifetime" (resolution tails)

long-lived background (b ? J/y X combined with
unrelated tracks)
prompt
log scale
long-lived background components
"negative lifetime" tail
Fits with different shape assumptions used to
constrain systematic
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Results Lifetime
B0?J/yKs
L0?J/yL0
PDG 2006 459 mm
PDG 2006 369 mm
ct(Lb) 477.625.0 mm
ct(B0) 456.89.0 mm
-8.9
-23.4
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b-Hadron Lifetime Summary
Combined B 494.3 ? 4.5 mm Combined B0
464.5 ? 5.3 mm Combined DPDG 4.3 ? 5.5 mm
These are not t(B0), t(B) measurements Statist
ical errors only! ? High-level validation
of analysis for well-established B0/B lifetimes
We use these results to cross-? our measurement
of lifetimes in fully-reconstructed decay using
J/y to determine B decay vertex
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Systematic Uncertainties
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Summary of Results
We measure in decay mode B0?J/yKs ct
(B0) 456.8 9.0 (stat.) 4.9 (syst.) mm
1.524 0.030 (stat.) 0.016
(syst.) ps consistent w/ PDG 2004 value of
1.530 0.009 ps We also measure in decay mode
Lb?J/yL0 ct (Lb) 477.6 25.0
(stat.) 9.9 (syst.) mm 1.593
0.083 (stat.) 0.033 (syst.) ps
-8.9
-23.4
-0.078
Three completely independent analysis
implementations within our group have confirmed
these results
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Conclusions
Using our Lb lifetime and the PDG 2004 B0
lifetime, we get t (Lb)/t (B0) 1.041 0.057
(stat.syst.) This result is inconsistent with
PDG 2004 world average t (Lb) _at_ 3.2s level
Our
t(Lb) measurement is the
world's
most precise measurement
? best by far
in a fully
reconstructed decay
channel
"Theory"
World Avg (w/o our result)
Our Result
and consistent with theory
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The New D0 1fb-1 Result
t(Lb) 1.298 0.137(stat.) 0.050(syst.) ps
(D0 1fb-1)
Note different x-axis scale!
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Outlook
Current experimental situation
t(Lb) in Lb?Lcp from CDF is the next step!
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Thanks from the Authors!

• Many thanks to our godparents
• Rick Field (chair), Farrukh Azfar, Fabrizio Scuri
• Comments from our reading institutions and
  others
• HEP Korea, MIT, Barcelona, Illinois, IPP-Canada,
• SPRG, Beate, Joe Kroll
• B physics group conveners
• Matthew Herndon and Kevin Pitts
• Lifetime and Mixing sub-group conveners
• Guillelmo Gomez-ceballos and Sinead Farrington

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Extras
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Theory / Exp Another Look
From talk by Alexey Petrov _at_ ICHEP 2006 (the
overlay of our result in black is mine)