Transcript Tagging methods - University of California, San Diego

Inclusive semileptonic B decays:
experimental
Elisabetta Barberio
University of Melbourne
FPCP: Vancouver April 2006
Standard Model Consistency Tests
Vub and Vcb provide a test of CP violation in the Standard
Model comparing the measurements on the (r, h) plane
The width of the green ring
need to be reduced to
match sin2b and other
measurements
The error on the ring width
is dominated by Vub
Vub
Vcb
Goal: Accurate determination of |Vub|
April 2006
E. Barberio
2
Semileptonic B decays
tree level, short distance:
Vcb ,Vub
decay properties depend
directly on |Vcb|, |Vub|,mb
perturbative regime (asn)
u
+ long distance:
,u
April 2006
But quarks are bound by soft
gluons: non-perturbative (LQCD)
long distance interactions of b
quark with light quark
E. Barberio
3
Inclusive semileptonic decays
Many theorists love inclusive semileptonic decays
Short distance is calculable
Long distance leading order and short distance contribution
are cleanly separated and probability to
hadronnize is 1
To compare Operator Product Expansion predictions
with experiments:
integration over neutrino and lepton phase space provides
smearing over the invariant hadronic mass of the final state
April 2006
E. Barberio
4
Inclusive semileptonic decays
Vcb
vs
Vub
Vcb: most accurate determination from the inclusive decays
2% precision limited by theory error
precise Heavy Quarks parameters, tests of OPE
Vub: 7.5% precision shared between experimental and
theoretical errors
small rate and large bcln background
space cuts to remove bcln background which introduce
O(1) dependence on non-preturbative b-quark distribution
function
April 2006
E. Barberio
5
Vcb from inclusive semileptonic decays
Gsl (b  c

2
n )   th Vcb 
BR(b  c

n)
b
exp.
D|Vcb|<1%
Gsl described by Heavy Quark Expansion in (1/mb)n and ask

G(B  Xcln) 
GF2 mb5




V
1
A
A
A
cb 
ew
nonpert
pert 


192 3
2
non perturbative parameters need to be measured

The expansion
depend on mb definition: non-perturbative terms
are expansion dependent
Theory error was dominated by 1/mb3 terms and above
April 2006
E. Barberio
6
Bc moments in semileptonic decays
Xn are relate to non-perturbative parameters
X
n

dG
dX
dX  f ' m ,m ,a 
OPE
b
c
s
dG

dX
dX
  X Xo 
n
moments evaluated on the full lepton spectrum or part of
it: p > pmin in the B rest frame
higher moments are sensitive to 1/mb3 terms  reduce
theory error on Vcb and HQ parameters
April 2006
E. Barberio
7
Inclusive SL decays
rate
|Vcb|
shape
mc, m2G,
mb, m2
shape
|Vcb|
shape
rate
Difficulty to go from measured shape to true shape: e.g. QED
corrections, accessible phase space, resolution, background
April 2006
E. Barberio
8
moments in semileptonic decays
E : lepton energy spectrum in BXc n (BaBar Belle CLEO Delphi)
MX 2: hadronic mass spectrum in BXc n (BaBar CDF CLEO Delphi)
Most recent measurements from Belle
mx (GeV)
Plmin =0.7 GeV
P*l (GeV)
Plmin =0.4 GeV
P*l (GeV)
from the moments of these distributions we get Vcb and HQ
parameters
April 2006
E. Barberio
9
Parameters Extraction
BABAR: up to 1/mb3: fit ~90 measurement to extract HQ parameter and
Vcb at the same time
BABAR
M1x
o= used, •= unused
in the nominal fit
MX moments
M2x
M3x
M4x
c 2/ndf =20/15
P.Gambino,
N.Uraltsev
M0l
M1l
hep-ph/0401063
hep-ph/0403166
April 2006
E. Barberio
M2l
M3l
Red line: HQE fit
Yellow band: theory 10
errors
Vcb and HQ parameters
Exp
Global fit Kinetic scheme
expansion (hep-ph/0507253)
HQ
Gsl
3
|Vcb |(41.960.23exp 0.35 HQE 0.59GSL )10
dVcb @ 2%
mb < 1%, mc @ 5%
U(1S) expansion scheme has
similar results
used measurements:
April 2006
E. Barberio
11
Vub inclusive determination
B Xuln rate tree level from OPE  corrected for
perturbative as and non-perturbative 1/mb terms
 L QCD 
dG(B Xul ) mb G F 

~

3 parton model  C n 
n
d(p.s.)
 mb 
192  
5
2
In principle main uncertainty
from mb5
BUT…..
BrBXuln)/BrBXcln) =1/50
April 2006
E. Barberio
12
Shape Function
Limited phase space to reduce the B  Xcln background:
OPE doesn’t work everywhere in the phase space  nonperturbative Shape Function F(K+) to extrapolate to the full
phase space
F(K+)
Detailed shape not constrained,
in particular the low tail
0
K+
L = MB -mb
Mean and r.m.s. are known
Shape Function need to be determined from experimental data
April 2006
E. Barberio
13
Inclusive B  Xuln
mu << mc  exploits different kinematics
B
B
l
El = lepton energy
nn
q2 = lepton-neutrino mass squared
Xuu
X
P+ = EX -|PX|
mX = hadron system mass
Not to scale!
Signal events have smaller MX and P+  Larger El and q2
bc
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
bu
April 2006
bc
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
bu
E. Barberio
bc
bc
QuickTi me™ and a
QuickT i me™ and a
T IFF (LZW) decompressor
T IFF (LZW) decom pressor
are needed to see this pi cture. are needed to see thi s pi cture.
bu
bu
mX
14
Lepton Endpoint
BABAR PRD 73:12006
Belle PLB 621:28
CLEO PRL 88:231803
First measurement from CLEO El>2.3 GeV
BaBar El>2.0 GeV
Belle El> 1.9 GeV
Crucial accurate subtraction of
background is crucial!
BaBar
S/B ~1/10 eff~ 40%
DB (10-4)
BABAR 80fb-1 5.72 ± 0.41stat ± 0.65sys
Belle 27fb-1
8.47 ± 0.37stat ± 1.53sys
CLEO 9fb-1
2.30 ± 0.15stat ± 0.35sys
April 2006
E. Barberio
15
Measuring mX q2 P+
BABAR hep-ex/0507017
Belle PRL 95:241801
Reconstruct all decay products to measure MX ,q2 or P+
fully-reconstructed B meson
flavor and momentum known
lepton in the recoil-B
mmiss consistent with a neutrino
lepton charge consistent with B flavor
left-over particles belong to X
equal mB on both sides; mmiss = 0
April 2006
E. Barberio
S/B ~ 2 Eff~ 0.1%
16
Measuring Partial Branching Fraction
P+ BLNP PRL93:221802
DB (10-4)
BABAR 211fb-1
Belle 253fb-1
first measurement
of P+ spectrum
April 2006
mX < 1.7, q2 > 8
mX < 1.7
mX < 1.7, q2 > 8
P+ < 0.66
8.7 ± 0.9stat ± 0.9sys
12.4 ± 1.1stat ± 1.0sys
8.4 ± 0.8stat ± 1.0sys
11.0 ± 1.0stat ± 1.6sys
E. Barberio
17
Turning DB into |Vub|
b → s
Inclusive b → clv
E
El
mX
SSFs
Shape
Function
HQE Fit
mb
El
Inclusive
b → ulv
|Vub|
q2
mX
duality
WA
HFAG main results:
HQ parameters form
b  Xcln and b  Xs
hep-ph/0507253
Dealing with Shape Function
easy to fit shape function
Belle
E>1.8 GeV
Better resolution  K* peak
(more difficult for SF)
E* (GeV)
Solution  use directly the  spectrum:

April 2006
cut
xi
E (GeV)
cut
dG(B Xul )
dG(B Xs )
dx
 dE W(xi, E )
dxi
dE

E. Barberio
theory
19
Inclusive |Vub|: BLNP framework
|Vub| world average as of Winter 06
Inputs:
mb(SF) = 4.60  0.04 GeV
m2(SF) = 0.20  0.04 GeV2
|Vub|BLNP=(4.45  0.20  0.26) 10-3
d|Vub| =  7.3%
April 2006
E. Barberio
Statistical
2.2%
Expt. syst.
2.7%
B  Xcln model
B  Xuln model
1.9%
Subleading SF
3.8%
other theory error
4.5%
2.1%
20
Theory Errors
Quark-hadron duality is not considered (cut dependent)
 b cln and b  s data fit well HQ predictions
b
Weak annihilation   1.9% error
 Expected to be <2% of the total rate B  B
 Gw.a./G(b  u) < 7.4 % from CLEO
u
l
b
n
u
g
q
HQ parameters   4.1% mainly mb; kinematics cuts depend
q
on mb,!
Sub-leading shape function   3.8% dominated by the
lepton endpoint measurements
April 2006
E. Barberio
21
n

Inclusive |Vub|: DGE framework
Dressed Gluon Exponentiation (DGE)
on-shell b-quark calculation converted into hadronic variables
used as approximation to the meson decay spectrum
|Vub|DGE = (4.41  0.20  0.20) 10-3
Still digesting the
method
DGE theory  2.9% matching scheme method and scale
mb(MS)   1.3% on event fraction mb(MS)=4.200.04 GeV
as
  1.0% on event fraction
total GSL
  3.0 %
April 2006
E. Barberio
22
Vub without Shape Function
V
dG(BXs )
GBXu lu ub 2  WE 
dE
dE
Vts
2
Vts ~ Vcb O(1)
Babar
Based on Leibovich, Low,
Rothstein, PLB 486:86
First proposal by Neubert
Weight function
Babar
Babar
mxcut
OPE mx<2.50 GeV
LLR mx<1.67 GeV
3
Vub  3.380.70stat 0.30sys 0.10theo 10
April 2006
3
Vub  4.430.30stat 0.25sys 0.29theo 10
E. Barberio
23
|Vub|: inclusive vs exclusive
|Vub| exclusive
|Vub| inclusive
W.A. Winter 06
April 2006
W.A. Winter 06
E. Barberio
24
|Vub|: CKM consistency
Most probable value of Vub from measurements of other
CKM parameters Standard Model predictions with
Dms measurement
(thank to Pierini)
Vub from exclusive
measurements
Vub from inclusive
measurements
April 2006
E. Barberio
25
Conclusions
b cln
Vcb 2% error dominated by theory, mb @1% (kinetic and U(1S) schemes),
mc @5% (kinetic scheme)
but how well do we know the B Xcln spectrum?
b uln
Vub ~7.4% error shared between theoretical and experimental
inclusive vs exclusive less than 1.4 s difference, depending on the
inclusive extracting method
We have now different methods to extract Vub
|Vub| @ 5% possible? Improve knowledge of B Xcln, B Xuln and more
work on the theoretical error
April 2006
E. Barberio
26
Inclusive |Vub|: comparisons
HQ parameters from cln and sg
April 2006
HQ parameters from sg only
E. Barberio
27
Mx unfolded spectrum for B  Xc l n
Belle
D*
D
D**
April 2006
E. Barberio
28
photon energy spectrum
E : photon energy spectrum in Bs
(BaBar Belle CLEO Delphi)
photon energy spectrum in B Xs not sensitive
to new physics and give information on B
structure
u, c, t
E   mb  ... var E   m 2 / 12 ...
Belle
E>1.8 GeV

 
1GeV 0.40
CLEO

mb 1GeV  4.62 GeV
m
April 2006
2

E>2 GeV
 
1GeV 0.477 0.052
mb 1GeV  4.66 0.067 GeV
GeV
2
m 2
E. Barberio
GeV2
29