Exclusive Semileptonic B Decays and |Vub|: Experimental

1
Exclusive Semileptonic B Decays and Vub
Experimental

• 4th Flavor and CP Violation Conference
• Vancouver, BC
• 9th 12th April 2006
• Kevin Varvell
• University of Sydney

2
Significance of Vub Measurement

• Precision measurement of SM parameter, size not
  theoretically predicted
• Constrain one side of the
• Unitarity Triangle
• Test consistency of SM
• picture, particularly
• between Vub/Vcb and
• sin2?1 (sin2ß)
• Current precision
• sin2?1 4
• Vcb 2 (one recent update
  mentioned here)
• Vub 7 inclusive (talk this afternoon, E.
  Barberio)
• gt10 exclusive (main subject of this
  talk)
• Aim is for 5 precision for Vubexcl, compare
  with Vubincl

This side determined By Vub/Vcb
3
From Exclusive Semileptonic B decay to Vub

• Measurements made in
• Ideally want to measure rate
• of tree level process G(b ? x l ?)
• Complicated by strong interaction
• effects form factors needed
• Channel B ? p l ? is the most
• promising for Vub
• - one dominant form factor
• q2 shape and normalization needed

f(q2)
4
Determining the Form Factor f(q2)

• Earlier predictions made with quark models, e.g.
  ISGW2
• Lattice QCD
• makes predictions at high q2 (q2 gt 16 GeV2)
• unquenched calculations have become available in
  recent times
• e.g. HPQCD
• FNAL
• Light Cone Sum Rules
• makes predictions at low q2 (q2 lt 14 GeV2)
• e.g. Ball Zwicky
• Parametrization has traditionally been used to
  extend LQCD or LCSR to full q2 range
• FF normalization main issue when extracting Vub
• How much theory input needed for Vub
  measurement?
• 
  (R. Hill talk)

hep-lat-0601201
hep-lat-0409116
PRD 71 (2005) 014015
hep-ph/0509090
5
Approaches to Measuring B(B ? p l ?)
Untagged initial 4-momentum known missing 4-momentum ? Reconstruct B ? p l ? using mB (beam-constrained) and ?E EB-Ebeam Pros High efficiency Cons ? resolution problematic Rel. high backgrounds (rel. low purity)
Semileptonic (SL) Tag One B reconstructed in a selection of D() l ? modes Two missing ? in event Use kinematic constraints Pros Lower backgrounds (higher purity) Cons Rel. low efficiency
Full Recon Tag One B reconstructed completely in known b ? c mode. Many modes used. Pros Very good ? resolution Very low backgrounds Cons Very low efficiency
6
Range of Applicability of Methods

• Boundaries indicative only
• Full recon tag will ultimately become method of
  choice.
• Currently
• Belle Lint 500 fb-1
• BaBar Lint 300 fb-1

7
CLEO Untagged B ? p l ?
Phys. Rev. D 68 (2003) 072003

• Search (and fit for yields) across a
• number of exclusive Xu l ? modes
• ?,?0,?,?0,?,?
• Isospin constraints imposed in fit
• Extract partial BF in 3 q2 bins
• for ? and ?

?- result
8
CLEO Untagged B ? p l ? (cont.)
Phys. Rev. D 68 (2003) 072003

• FF models enter extraction
• of BF through
• Signal efficiency from MC
• b ? u crossfeed and b ? c
• background modelling in MC

Different FF models
?- result
B(B0 ? p- l ?) (1.33 0.18 0.11 0.01
0.07) x 10-4
syst
FF sig
stat
FF crossfeed
(? and ? mode combined) LCSR LQCD (unq)
FF shape ?
stat
syst
theo
9
BaBar Untagged B0 ? p- l ?

• Simultaneous extraction of modes ?,?0,?,?0

Phys .Rev. D72 (2005) 051102
?- result
Yield 396 ?-l?, 137 ?0l?
10
BaBar Untagged B0 ? p- l ? (cont)

• Isospin constraints imposed
• Extract partial BF in
• 5 q2 bins ?
• 3 q2 bins ?
• Marginal agreement with ISGW2

Phys .Rev. D72 (2005) 051102
?- result
B(B0 ? p- l ?) (1.38 0.10 0.16 0.08) x
10-4
syst
stat
FF shape
FNAL LQCD
syst
stat
FF shape
FF norm
11
Belle SL Tag B ? p l ?
hep-ex/0604024

• Simultaneous extraction of modes ?,?0,?,?0
• xB2 must lie in range 0,1
• for signal events

Submitted to PLB
Yield 156 ?-l?, 69 ?0l?
12
Belle SL Tag B ? p l ? (cont)
hep-ex/0604024

• Extract partial BF in
• 3 q2 bins

B(B0 ? p- l ?) (1.38 0.19 0.14 0.03) x
10-4
stat
syst
FF shape
B(B ? p0 l ?) (0.77 0.14 0.09 0.00) x
10-4
syst
stat
FF shape
? ?0, q2 16 GeV2, FNAL
stat
syst
theo
? ?0, q2 16 GeV2, HPQCD
syst
stat
theo
13
BaBar SL Tag B0 ? p- l ?
hep-ex/0506064

• Single mode ?- studied
• cos2fB ? 0,1 for signal events

Yield 61 ?-l?
14
BaBar SL Tag B0 ? p- l ? (cont)
hep-ex/0506064

• Extract partial BF in
• 3 q2 bins

B(B0 ? p- l ?) (1.03 0.25 0.13) x 10-4
stat
syst
0.8
HPQCD04
syst
FF norm
stat
15
BaBar SL Tag B ? p0 l ?
hep-ex/0506065

• Single mode ?0 studied
• cos?B?0l ? -1, 1 for signal events

Yield 45 ?0l?
B(B ? p0 l ?) (1.80 0.37 0.23) x 10-4
stat
syst
16
BaBar Full Recon Tag B ? p l ?
hep-ex/0507085

• Tag Fully reconstructed B ? D decays (Breco
  tag)
• Select using ?E, mES (beam constrained B
  candidate mass)
• mmiss2 distribution peaks at zero for signal
  (single missing neutrino)

m??
Yield 36 ?-l?, 34 ?0l?
17
BaBar Full Recon Tag B ? p l ?
hep-ex/0507085

• Extract partial
• BF in 3 q2 bins

p0
p-
B(B0 ? p- l ?) (1.14 0.27 0.17) x 10-4
stat
syst
B(B ? p0 l ?) (0.86 0.22 0.11) x 10-4
stat
syst
Combined ? ?0
B(B ? p l ?) (1.28 0.23 0.16) x 10-4
syst
stat
? ?0, HPQCD
syst
stat
FF norm
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Summary of B(B ? p l ?) Exclusive
HFAG Winter 2006 Note Updated Belle SL
tag result not yet incorporated in
plot Untagged analyses currently the most precise
Average B(B0 ? p- l ?) (1.34 0.08 0.08) x
10-4
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Summary of Vub from Exclusive B ? p l ?
HFAG Winter 2006
Experimental q2 shape input not used (yet)
Using FF calculated in region of applicability
Using FF extrapolated to full q2 range
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Other B ? Xu l ? Exclusive Modes
Expt Mode BF 10-4 Reference
CLEO B0 ? ?- l ? 2.170.34 0.41
CLEO B0 ? ?- l ? 2.690.41 0.50
BaBar B0 ? ?- l ? 2.570.520.59
BaBar B0 ? ?- e ? 3.290.420.470.60
BaBar B0 ? ?- l ? 2.140.210.510.28
Belle B0 ? ?- l ? 2.170.540.310.08
CLEO B ? ? l ? 0.840.310.160.09
Belle B ? ?0 l ? 1.330.230.170.05
Belle B ? ? l ? 1.30.40.20.3
Tag
PRD 68 (2003) 072003
Untagged
Untagged
PRD 61 (2000) 052001
Full
hep-ex/0408068
PRL 90 (2003) 181801
Untagged
PRD 72 (2005) 051102
Untagged
SL
hep-ex/0604024
PRD 68 (2003) 072003
Untagged
SL
hep-ex/06xxxxx
PRL 93 (2004) 131803
Untagged
HFAG Compilation, except with updated Belle SL
result included
21
BaBar Exclusive Vcb Measurement
Update to PRD 71 (2005) 051502 submitted to PRD
hep-ex/0602023

• Multi-Dimensional fit to helicity amplitudes for
  ?2 (slope parameter) and R1, R2 (FF ratios), all
  functions of H,-,0(w).

w vB vD

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BaBar Exclusive Vcb Measurement (cont)
hep-ex/0602023

• Improvement in FF uncertainty
• Reduces Vcb systematic error
• Useful for understanding b ? c
• background in b ? u

R1 1.396 0.060 0.035 0.027 R2 0.885
0.040 0.022 0.013 ?2 1.145 0.059
0.030 0.035
w
cos?l
?
cos?V
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Summary of Exclusive Vcb Measurements

• HFAG Winter 2006
• Note
• Does not include latest BaBar result from
• hep-ex/0602023

24
Summary and Future Exclusive Vub Measurements

• CLEO, BaBar and Belle
• ? Xu BF measurements using several channels and
  several techniques
• Xu ?,?0,?,?0,?,?
• ? Vub extracted using ?,?0 modes Exptl
  error approaches 5
• - FF normalization error dominates
• ? Xc BF measurements and Vcb continue to be
  important
• ? future precision Xu measurements using Full
  Recon tagging
• ? FF shape measurements from experiment now
  possible
• Theory progress important (and happening) as well
  (R. Hill talk)
• 
  (P. Mackenzie talk)
• Vub to better than 5 precision overall from
  exclusive semileptonic B-factory
  measurements? ? Feasible.