View
36
Download
0
Category
Tags:
Preview:
DESCRIPTION
Exclusive Semileptonic B Decays and |V ub |: Experimental. 4 th Flavor and CP Violation Conference Vancouver, BC 9 th – 12 th April 2006 Kevin Varvell University of Sydney. Significance of |V ub | Measurement. Precision measurement of SM parameter, size not theoretically predicted - PowerPoint PPT Presentation
Citation preview
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|
K. Varvell 3FPCP06 11-Apr-2006
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
K. Varvell 4FPCP06 11-Apr-2006
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
K. Varvell 6FPCP06 11-Apr-2006
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
K. Varvell 7FPCP06 11-Apr-2006
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)
K. Varvell 8FPCP06 11-Apr-2006
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
K. Varvell 9FPCP06 11-Apr-2006
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)
K. Varvell 10FPCP06 11-Apr-2006
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
K. Varvell 11FPCP06 11-Apr-2006
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
Yield 156 -lν, 69 0lν
253fb-1 (275M BB)
K. Varvell 12FPCP06 11-Apr-2006
|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
K. Varvell 13FPCP06 11-Apr-2006
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)
K. Varvell 14FPCP06 11-Apr-2006
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
K. Varvell 15FPCP06 11-Apr-2006
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
K. Varvell 16FPCP06 11-Apr-2006
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
Yield 36 -lν, 34 0lν
mγγ
211fb-1 (233M BB)
K. Varvell 17FPCP06 11-Apr-2006
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
K. Varvell 18FPCP06 11-Apr-2006
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
K. Varvell 19FPCP06 11-Apr-2006
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)
K. Varvell 20FPCP06 11-Apr-2006
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
K. Varvell 21FPCP06 11-Apr-2006
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
K. Varvell 22FPCP06 11-Apr-2006
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
K. Varvell 23FPCP06 11-Apr-2006
Summary of Exclusive |Vcb| Measurements
HFAG Winter 2006
Note: Does not include latest BaBar result from hep-ex/0602023
K. Varvell 24FPCP06 11-Apr-2006
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.
Recommended