Transcript hepweb.ucsd.edu

Measurement of the Lb Lifetime in
LbJ/yL0 in pp Collisions at √s=1.96 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
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
Vcb
 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
●
You are
here
Lifetimes of weakly decaying hadrons of the same
heavy flavor provide a quantitative connection
between these two worlds
 study of the interplay between the strong and weak interactions
 important testbed for understanding of non-perturbative effects in QCD
t(D+)/t(D0)  2.5
increasing mQ
t(B+)/t(B0)  1
∞ (spectator ansatz)
Lifetimes of b-Flavored Hadrons
Critical testbed for theoretical framework used to predict heavy quark quantities:
●
●
t(Bc) ≪ t(Lb)
Qualitatively expect:
but one can do better than this...!
t(Bs) 
t(B0)
t(B+)
b-hadron lifetime ratios can be calculated with reasonable precision:
2% for t(B+)/t(B0), 1% for t(Bs)/t(B0), 6% for t(Lb)/t(B0)
using Heavy Quark Expansion (HQE) since mb
LQCD  large energy release in decay
Pauli Interference
Weak Annihilation
Only charged
B mesons
Same final state
 interference
(destructive)
Weak Scattering/Exchange
Different final
states
 no
interference
Helicity
suppressed
in mesons,
not baryons
Heavy Quark Expansion
Inclusive decay width expressed as an operator product expansion (OPE) in LQCD/mb and as(mb)
●
Theory
Experiment
(world avg)
ci(n) contain short-distance
physics from scales  m = O(mb)
 perturbatively calculable
●
LO
Matrix elements contain
long-distance physics
 hard! especially for baryons
●
NLO
+O(1/mb4)
Spectator contributions
enter at 1/mb3 (~5-10%)
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)
Tarantino, et al.
hep-ph/0203089
Lb Lifetime: Before Us
LO
Experiment
(world avg)
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)!
Theory
Lb Lifetime: Analysis Strategy
Measure t(Lb) in fully-reconstructed
decay channel LbJ/yL0
clean trigger
for decay
relative to
semi-leptonics
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
Use t(B0) measurement in
B0J/yKs as reference mode
 similar decay: J/y + V0 (V0≡Ks0,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
b
ct=
L xy
b
b
T
= L xy c
Mb
pbt
b
, where L xy = x J /
− x PV ⋅ pT
b
b-Hadron Lifetimes We Measure
B0 
J/y Ks,
y(2S) Ks,
y(2S) Ks,
J/y  mm, Ks  pp
y(2S)  mm, Ks  pp
y(2S)  J/ypp, J/y  mm, Ks  pp
B0  J/y K*0,
J/y  mm, K*0  Kp
y(2S) K*0, y(2S)  mm, K*0  Kp
y(2S) K*0, y(2S)  J/ypp, J/y  mm, K*0 
B+ 
J/y K+,
y(2S) K+,
y(2S) K+,
J/y  mm
y(2S)  mm
y(2S)  J/ypp, J/y 
B+ 
J/y K*+,
J/y  mm, K*+  Ksp
Lb 
J/y L0,
J/y 
mm, L0 
mm
Full systematics
Kp
Statistical errors
only (for cross-√)
pp
Full systematics
Our primary goal
Results: Yield
B0 J/yKs
N(B0) = 3376 ± 88
L0
J/yL0
N(Lb) = 538 ± 38
Fit Model: Overview
Ove r a ll p r ob a b ilit y de n s it y fu n c t ion (PDF ) is a n or m a lize d s u m of
s ig n a l a n d b a c kg r ou n d c on t r ib u t ion s :
P
i,
∣
m
i
i , m i,
=
1 - f b P s ig
f b P bkg
wh ere:
i
i
mi
m
i
= P DL
P s ig , P b kg = s ig n a l, b a ck g r ou n d P DF
= P DL e r r or
= m ass
f b = b a ck g r ou n d fr a ct ion
= fit p a r a m e t e r s (in clu d in g f b )
= m a s s e r r or
P s ig , P b k g a r e p r od u c t s of P DL , P DL e r r or , a n d m a s s PDF s :
P s ig , b k g = P s ig , b k g
i∣
i
,
P s ig , b k g
i∣
P
m
s ig , b k g
m i∣
m
i
,
Un b in n e d m a xim u m like lih ood fit t o e xt r a c t
={ , , , }
( c on t a in s 1 8 p a r a m e t e r s , in c lu din g s ig n a l c )
Fit Model: Signal PDL
S ig n a l PDL m ode le d a s a n e xp on e n t ia l de c a y c on volu t e d wit h a Ga u s s ia n
r e s olu t ion fu n c t ion :
P s ig
i
,
i
∣
= E
s ig
i∣
c
∗ G
i
,
i
∣s
wh ere:
1
E
i∣c
= c
e
- i /c
0
, i≥ 0
,
0
i
-
G
i
,
i
∣s
=
1
2
s
log scale
= s ig n a l life t im e (t h e g oa l)
s = ove r a ll s ca le fa ct or on P DL e r r or s
e
i
2 s
2
i
2
i
ct=368 mm
ss=36 mm
Fit Model: Background PDL
Ba c kg r ou n d PDL m ode le d a s s u m of fou r c om p on e n t s :
P b kg
i
∣
i
, s , f -,
-
,f+ ,
+
,f++ ,
++
= G
i
,
i
∣s
*
{
1 -f -- f + -f + +
zero lifetime (prompt)
ff+
f+ +
"negative lifetime" (resolution tails)
log scale
long-lived background (b  J/y X
combined with unrelated tracks)
wh ere:
f-
f + (+ + )
+ (+ + )
= n e g a tive e xp on e n tia l fr a c tion
= n e g a tive e xp on e n tia l d e c a y le n g th
= 1 st ( 2 n d ) p os itive e xp on e n tia l fr a c tion
= 1 st ( 2 n d ) p os itive e xp on e n tia l d e c a y le n g th
Fits with different shape assumptions
used to constrain systematic
0
E - i∣ E i∣ +
E i∣ + +
prompt
"negative
lifetime"
tail
long-lived
background
components
}
Results: Lifetime
B0 J/yKs
PDG 2006: 459 mm
ct(B0) = 456.8+9.0
−8.9mm
L0
J/yL0
PDG 2006: 369 mm
ct(Lb) = 477.6+25.0
mm
−23.4
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:
Statistical
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
Systematic Uncertainties
Sou rce
Fit t er Bias
ct (B0 ) [mm ] ct(Lb ) [ mm ]
0.4
0.5
ct Resolu t ion
3 .1
5 .5
Mass Sign al
0.7
2 .3
Mass Backgrou n d
0.1
0.1
ct Backgrou n d
0.5
0.7
s ct Dist ribu t ion Modelin g
0.1
0.2
s m Dist ribu t ion Modelin g
0.6
0.2
Mass-ct Backgrou n d Correlat ion
1 .9
4.1
ct -s ct Backgrou n d Correlat ion
0.3
1 .3
Prim ary Vert ex Det erm in at ion
0.2
0.3
SVX In t ern al
2 .0
2 .0
SVX/COT Global
2 .2
3 .2
0.6
5 .4
4 .9
9 .9
Fit Model:
Align m en t :
V0 Poin t in g
Tot al
Summary of Results
We measure in decay mode B0 J/yKs :
ct (B0) = 456.8 +9.0−8.9
(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
−23.4
(stat.) ± 0.033 (syst.) ps
−0.078
Three completely independent analysis implementations
within our group have confirmed these results
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) @ 3.2s level
Our t(Lb) measurement is the
world's most precise measurement
 best by far in a fully
reconstructed decay channel
World Avg
(w/o our
result)
"Theory"
and consistent with theory
Our
Result
The New D0
-1
1fb
Result
t(Lb) = 1.298 ± 0.137(stat.) ± 0.050(syst.) ps (D0 1fb-1)
Note different x-axis scale!
Outlook
Current experimental
situation:
t(Lb) in Lb Lcp
from
CDF is the next step!
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
Extras
Theory / Exp: Another Look
From talk by Alexey Petrov @ ICHEP 2006
(the overlay of our result in black is mine)