Exclusive Semileptonic B Decays and |V ub |: Experimental

Exclusive Semileptonic B Decays and |Vub|:

Experimental

4th Flavor and CP Violation ConferenceVancouver, BC

9th – 12th April 2006

Kevin VarvellUniversity of Sydney

K. Varvell 2FPCP06 11-Apr-2006

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

sin21 (sin2β)

Current precision sin21 ~ 4% |Vcb| ~ 2% (one recent update mentioned here) |Vub| ~ 7% inclusive (talk this afternoon, E. Barberio) >10% exclusive (main subject of this talk) Aim is for ‹ 5% precision for |Vub|excl, compare with |Vub|incl

This side determinedBy |Vub|/|Vcb|


From Exclusive Semileptonic B decay to |Vub|

Measurements made in

Ideally want to measure rateof tree level process Γ(b x l )

Complicated by strong interaction effects – form factors needed

Channel B π l is the most promising for |Vub|

- one dominant form factor

q2 shape and normalization needed

f+(q2)

e+e-→Υ(4S) → BB


Earlier predictions made with quark models, e.g. ISGW2

Lattice QCD makes predictions at high q2 (q2 > ~16 GeV2) unquenched calculations have become available in recent

times e.g. HPQCD

FNAL Light Cone Sum Rules

makes predictions at low q2 (q2 < ~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)

Determining the Form Factor f+(q2)

hep-lat-0601201

hep-lat-0409116

PRD 71 (2005) 014015

hep-ph/0509090

5

Approaches to Measuring B(B π l )

Untagged initial 4-momentum known missing 4-momentum = ν Reconstruct B π l using mB (beam-constrained)

and ΔE = EB-Ebeam

Pros High efficiency

Cons ν resolution problematic Rel. high backgrounds (rel. low purity)

Semileptonic (SL) Tag One B reconstructed in a selection of D(*) l modes Two missing ν 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 ν resolution

Very low backgrounds

Cons Very low efficiency

Signal

ExampleTag

side

Rest used to reconstruct

Signal

Signal

ExampleTag

side


Range of Applicability of Methods

Scenario

Untagged

D(*) l tag

Full recon tag

140 250 500 1000fb-1

•Boundaries indicative only•Full recon tag will ultimately become method of choice.

Currently Belle Lint ~ 500 fb-1

BaBar Lint ~ 300 fb-1


CLEO Untagged B π l

Search (and fit for yields) across anumber of exclusive Xu l ν modes

+,0,+,0,ω,η

Isospin constraints imposed in fit

Extract partial BF in 3 q2 binsfor + and +

Phys. Rev. D 68 (2003) 072003

mBC ΔE

- result

(9.7M BB)


CLEO Untagged B π l (cont.)

FF models enter extractionof BF through Signal efficiency from MC b → u crossfeed and b → c

background modelling in MC

Phys. Rev. D 68 (2003) 072003

B(B0 π- l+ ) = (1.33 ± 0.18 ± 0.11 ± 0.01 ± 0.07) x 10-4

|Vub| = (3.17 ± 0.17 ± 0.03) x 10-3+0.16 +0.53

-0.17 -0.39( and mode combined)LCSR + LQCD (unq)

- result

(9.7M BB)

stat

stat

syst FF sig FF crossfeed

syst theoFF shape ρ

Different FFmodels


BaBar Untagged B0 π- l+

Simultaneous extraction of modes +,0,+,0

ΔE

mBC

Phys .Rev. D72 (2005) 051102

- result

Yield 396 -lν, 137 0lν

79fb-1 (86M BB)


BaBar Untagged B0 π- l+ (cont)

Isospin constraints imposed

Extract partial BF in 5 q2 bins 3 q2 bins ρ

“Marginal” agreement with ISGW2

Phys .Rev. D72 (2005) 051102

B(B0 π- l+ ) = (1.38 ± 0.10 ± 0.16 ± 0.08) x 10-4

|Vub| = (3.82 ± 0.14 ± 0.22 ± 0.11 ) x 10-

3

+0.88-0.52

- result

79fb-1 (86M BB)

stat

stat

syst

syst

FF shape

FF shape FF norm

FNAL LQCD


Simultaneous extraction of modes +,0,+,0

xB2 must lie in range [0,1]

for signal events

Belle SL Tag B π l+

hep-ex/0604024 Submitted to

PLB

Submitted to PLB

Mx

Mx xB2

xB2


253fb-1 (275M BB)


|Vub| = (3.60 ± 0.41 ± 0.20 ) x 10-

3

+0.62-0.41

Belle SL Tag B π l+ (cont)

Extract partial BF in 3 q2 bins

hep-ex/0604024

B(B0 π- l+ ) = (1.38 ± 0.19 ± 0.14 ± 0.03) x 10-4

B(B+ π0 l+ ) = (0.77 ± 0.14 ± 0.09 ± 0.00) x 10-4

|Vub| = (4.03 ± 0.46 ± 0.22 ) x 10-

3

+0.59-0.41

+ + 0, q2 ≥ 16 GeV2, FNAL

+ + 0, q2 ≥ 16 GeV2, HPQCD

stat

stat

stat

stat

syst

syst

syst

syst

FF shape

FF shape

theo

theo


BaBar SL Tag B0 π- l+

Single mode - studied

cos [0,1] for signal events

hep-ex/0506064

Yield 61 -lν

211fb-1 (232M BB)


BaBar SL Tag B0 π- l+ (cont)

Extract partial BF in 3 q2 bins

hep-ex/0506064

B(B0 π- l+ ) = (1.03 ± 0.25 ± 0.13) x 10-

4

+0.8

|Vub| = (3.3 ± 0.4 ± 0.2 ) x 10-3

-0.4+0.8

HPQCD04

211fb-1 (232M BB)

stat

stat

syst

syst FF norm


BaBar SL Tag B+ π0 l+

Single mode 0 studied

cosθB0l [-1, 1] for signal events

hep-ex/0506065

B(B+ π0 l+ ) = (1.80 ± 0.37 ± 0.23) x 10-

4

Yield 45 0lν

81fb-1 (88M BB)

stat syst


BaBar Full Recon Tag B π l+

Tag : Fully reconstructed B D decays (“Breco” tag)Select using ΔE, mES (beam constrained B candidate mass)

mmiss2 distribution : peaks at zero for signal (single missing

neutrino)

hep-ex/0507085


mγγ

211fb-1 (233M BB)


BaBar Full Recon Tag B π l+

Extract partial

BF in 3 q2 bins

hep-ex/0507085

|Vub| = (3.7 ± 0.3 ± 0.2 ) x 10-3

-0.5+0.8

+ + 0, HPQCD

B(B0 π- l+ ) = (1.14 ± 0.27 ± 0.17) x 10-

4

B(B+ π0 l+ ) = (0.86 ± 0.22 ± 0.11) x 10-4

B(B π l+ ) = (1.28 ± 0.23 ± 0.16) x 10-

4

Combined + + 0

stat

stat

stat

stat

syst

syst

syst

syst FF norm


HFAG Winter 2006

Note: Updated Belle SL tag result not yet incorporated in plot

Untagged analyses currently themost precise

Summary of B(B π l ) Exclusive

Average B(B0 π- l+ ):

(1.34 ± 0.08 ± 0.08) x 10-4


Summary of |Vub| from Exclusive B π l

HFAG Winter 2006

Using FF calculated in region of applicability

Using FF extrapolated to full q2 range

Experimental q2 shape input not used (yet)


Expt Mode BF [10-4] Reference

CLEO B0 ρ- l 2.17±0.34 ±0.41

CLEO B0 ρ- l 2.69±0.41 ±0.50

BaBar B0 ρ- l 2.57±0.52±0.59

BaBar B0 ρ- e 3.29±0.42±0.47±0.60

BaBar B0 ρ- l 2.14±0.21±0.51±0.28

Belle B0 ρ- l 2.17±0.54±0.31±0.08

CLEO B+ η l 0.84±0.31±0.16±0.09

Belle B+ ρ0 l 1.33±0.23±0.17±0.05

Belle B+ ω l 1.3±0.4±0.2±0.3

+0.47-0.54

Other B Xu l Exclusive Modes

PRD 68 (2003) 072003

PRD 61 (2000) 052001

hep-ex/0408068

PRL 90 (2003) 181801

PRD 72 (2005) 051102

PRD 68 (2003) 072003

hep-ex/0604024

hep-ex/06xxxxx

PRL 93 (2004) 131803

+0.35-0.47

HFAG Compilation, except with updated Belle SL result included

Untagged

Untagged

Untagged

SL

SL

Untagged

Full

Untagged

Untagged

Tag


BaBar Exclusive |Vcb| Measurement

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

hep-ex/0602023

w = vB· vD*

79fb-1 (86M BB)

Update to PRD 71 (2005)

051502 submitted to PRD

Update to PRD 71 (2005)

051502 submitted to PRD


Improvement in FF uncertainty

Reduces |Vcb| systematic error

Useful for understanding b → c background in b → u

BaBar Exclusive |Vcb| Measurement (cont)

hep-ex/0602023

w

χcosθV

cosθl

R1 = 1.396 ± 0.060 ± 0.035 ± 0.027

R2 = 0.885 ± 0.040 ± 0.022 ± 0.013

ρ2 = 1.145 ± 0.059 ± 0.030 ± 0.035

|Vcb| = (37.6 ± 0.3 ± 1.3 ) x 10-3+1.5-1.3

theostat syst


Summary of Exclusive |Vcb| Measurements

HFAG Winter 2006

Note: Does not include latest BaBar result from hep-ex/0602023


Summary and Future : Exclusive |Vub| Measurements

CLEO, BaBar and Belle ⇒ Xu BF measurements using several channels and several techniques

Xu : +,0,+,0,ω,η

⇒ |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.

Documents

Exclusive Semileptonic B Decays and |V ub |: Experimental