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Measurement of Measurement of |V|Vubub||
at BABARat BABAR
Rolf DubitzkyUniversity of Heidelberg
2Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
Measurements of |Vub| provide
stringent and redundantconsistency tests of the unitarity triangle (UT)
|Vub| is complementary to sin2b
MotivationMotivation
3Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
MotivationMotivation
Measurements of |Vub| provide
stringent and redundantconsistency tests of the unitarity triangle (UT)
|Vub| together with g canconstrain UT from tree levelprocesses alone
4Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
|V|Vubub| from semileptonic B-decays| from semileptonic B-decays● parton level inclusive rates depend only on
CKM matrix element and quark mass
Problem: is 50 times larger! Need to reduce
Option 2: exclusive
exclusive reconstruction of Xu final state
Problem: need formfactor
Option 1: inclusive
inclusive reconstruction + kinematic cut
Problem: need shape function
● hadron level easy to calculate in OPE (<5% error)
|Vub|
5Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
exp. resolution not includedbu scaled up!
Inclusive decaysInclusive decays
Use kinematic cuts to separate buln from bcln decays:
2qEl Xm
q2
El
mX
● only look at fraction of phase space● here OPE breaks down● need shape function to resum
non-perturbative corrections
6Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
Non-perturbative Effects (aka. Shape Function)Non-perturbative Effects (aka. Shape Function)
● Problems:● need to parameterize SF
...expenential, gausian, Roman...● need to measure parameters
mb, mp2
● subleading shape functions???● parameters can be measured from
the moments of the photon energy spectrum in b sg decays
● or in b cln moments of lepton energy andhadronic mass
7Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
Exclusive decaysExclusive decays
● measure exclusive final state p, r, w, h etc...
● good supression of bc decays, high signal-to-background● small branching fractions O(10-4) need high statistic
● need unknown Formfactor to extract |Vub|
● need to measure q2, i.e. either 4-momentum of n or B:
● Need theory to calculate f +(q 2)● Ball-Zwicky (q2 < 16 GeV2) Phys. Rev. D71, 014015● HPQCD (q2 > 16 GeV2) E. Gulez et al., Phys. Rev. D73, 074502● FNAL (q2 > 16 GeV2) M. Okamoto et al., heplat/0409116● APE (q2 > 16 GeV2) A. Abada et al., Nucl. Phys. B619, 565
8Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
New Results from BABARNew Results from BABARin
clus
ive
excl
usiv
euntagged tagged
1) enpoint of lepton energy 2) mX with weighted
3) mX with large acceptance
4)5)
6)
in
presented
here
published
2006
e+
e-
B
notreco’ d B
n lepton
hadron e+
e-
Bfullyreco’ d
B
n lepton
hadron
D*p
9Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
|V|Vubub|| - - Lepton endpointLepton endpoint
● Electrons in energy range: 2.0 < El <2.6GeV● event shapes, missing momentum● subtract continuum using
● offpeak data● onpeak for El>2.8GeV
● Fit El spectrum with BB backgroundsfrom charm (Den, D*en, D**en, D(*)pen, nonresonant, and Xuen)
88 fb -1
PRD73, 012006 (2006)
10Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
BaBar, PRD72:052004 (2005)
mmXX + weighted + weighted PRL96, 221801 (2006)
Instead of● assume ad-hoc model for SF and● get model parameters from bc and bsg
➔ directly use measured photon energy spectrumin bsg
➔ residual SF dependence via signal MC
i0 and i+: “ weight functions”
up to o (aS2) o (LmB/zmb)
Leibovich, Low and Rothstein: PRD61:053006 (2000), PRD62:014010 (2001),
Phys. Lett. B513:83 (2001)
11Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
mmXX + weighted + weighted PRL96, 221801 (2006)
1.67
82 fb -1
experimentaluncertainties
theory uncertainties
choose mXmax:
+ increase stat. error - increase theoretical error
Instead of● assume ad-hoc model for SF and● get model parameters from bc and bsg
➔ directly use measured photon energy spectrumin bsg
BaBar, PRD72:052004 (2005)
Leibovich, Low and Rothstein: PRD61:053006 (2000), PRD62:014010 (2001),
Phys. Lett. B513:83 (2001)
mXmax = 1.67:
Acceptance ~78%
12Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
mmXX with large acceptance with large acceptance PRL96, 221801 (2006)
OPE allows to extract |Vub| with ~5% error
measure entire mX spectrum up to mX = 2.5 GeV
no shape function in |Vub| extraction
● residual SF dependence via signal MCsystematic: 5.0%
● need to subtract b c backgroundsystematic: 3.8%increased statistical uncertainty
Acceptance ~97%
13Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
Exclusive MeasurementsExclusive Measurementspu
rity
purit
y
effic
ienc
yef
ficie
ncy
untagged + tight untagged + tight don’ t reconstruct “ other” B
tight cuts to “ reconstruct”
tagged tagged reconstruct “ other” B-meson
combine hadronic and semileptonic tags
untagged + loose untagged + loose don’ t reconstruct “ other” B
loose cuts to “ reconstruct”
PR
D72
:051
102
(200
5)
14Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
with had + sl tags combined with had + sl tags combined BABARPUB 06/040
hadr
onic
● reconstruct “ other” B: B D(*)Y(Y = n1p + n2K + n3p
0 + n4K0S with n1+n2<6, n3<3, n4<3)
● require one additional lepton, right charge● require one extra pion, flavor correlated to B● no additional track● no (small) additional neutral energy● require missing mass -0.3 < mmiss
2 < 0.3 Gev2/c4
sem
ilept
onic ● reconstruct “ other” B: B D(*) l
● require one additional lepton, right charge● require one extra pion, flavor correlated to B● no additional track● no (small) additional neutral energy● use unbinned max-likelihood fit to cos2B
cos2B = angle between Btag and Bsl
15Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
with had + sl tags combined with had + sl tags combined BABARPUB 06/040
Need to combine 4 measurements: 2 B-flavors:
B+ (p0 l+ n) and B0 (p+ l+ n) 2 tagging methods:
hadronic and semileptonic
minimize total error in each bin of q2
● statistical errors are uncorrelated
● systematics are correlated, except:● f+- and f00● tagging & fitting methods
215 fb -1
B+ sl tagB+ had tag
B0 sl tagB0 had tag
16Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
measure other semileptonic modes to constrain theoretical models
1) reconstruct “ other” B-meson:
B -> D(*)Y (“ hadronic tag” )
2) require electron (muon) with
p* > 0.5GeV (0.8GeV)
3) select etas in five decay modes:
4) |mmiss2| < 0.5GeV
5) zero additional tracks in event
tagged tagged
h h’
limited by statistic
316 fb -1
BABARCONF06/026
measure theratio
17Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
untaggeduntaggedBABARCONF06/015
hepex/0607060
What is new compared to the published untagged analysis (PRD72;051102)?
use much looser reconstruction to improve signal efficiency
e.g. no harsh cut on |mmiss2/2Emiss|
calculate q2 from B momentum in “ average” B-frame + unfolding
q2 resolution still good (~400MeV)
more parameters for backgrounds reduced systematics
5 times the signal yield: 25/fb-1
12 bins in q2
#1: 0 < q2 < 2GeV2 #7: 12 < q2 < 14GeV2#4: 6 < q2 < 8GeV2
18Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
extract |Vub|: compare shape with predictions:
untaggeduntaggedBABARCONF06/015
hepex/0607060
● ISGW2 does not fit well
● LQCD & LCSR coherent with our data
● covariance matrices in the conference paper
allowing theorist to use our data
● Using BK parameteriziation for f+(q2,a)
19Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
SummarySummary
Large datasets allow new analysis to reduce systematic error and study theoretical predictions in both, inclusive and exclusive, measurements
● inclusive measurements with direct input from
reduce dependence on shape function
● exclusive measurements with new final states and
larger number of bins in q2 help to constrain theoretical models
20Rolf Dubitzky – University of Heidelberg – BABAR – ICHEP06 Moscow
