Giulia Ricciardi Aug 1st, 2018 - PowerPoint Presentation

Slide1

Giulia Ricciardi

Aug

1st, 2018

|

Vxb| determination: an updated theoretical prospective

Maynooth

University, Ireland, August 1-6, 2018 

1

Slide2

Overview

Inclusive-exclusive determinations of |Vcb

| & |Vub| and related tension

normalize

the UT;

SM input

e.g

 

constrain

directly

the UT

 

Theoretical

uncertainties

2

Slide3

From 1995 to 2018: more

than

twenty years of CKM refinement

3

Slide4

Semileptonic

B decays

b →c l

ν

b →u l ν

Exclusive

B → D

(*)

ℓ

ν

,

I

nclusive

B →

X

c ℓνc

V

bc

b

V

bu

u

b

Exclusive

B →

π

(…)ℓ

ν

,

I

nclusive

B →

X

u

ℓ

ν

Most

precise

determination

of |V

ub| |Vcb|Assumed largely free of BSM

Inclusive/Exclusive: Different theoretical techniques Long standing tension between inclusive and exclusive determinations

Chen,Nam,Crivellin,Buras,Gemmler, Isidori, Mannel,...

lepton pair

lepton pair

4

Slide5

Heavy

Quark Expansion

for sufficiently

inclusive quantities (total width, moments of kinematical distributions) away from perturbative singularitiesHQE

separates short & long distance physics

double

series in αs

& 1/m

Inclusive decays

B



X

c

l

ν

are

short

distance coefficients, calculable in perturbation theory as a series in α

s

denote

local

operators of (scale)

dimension d:

same

set for all b

→

q

decays

n

on perturbative matrix

elements

parameterized in terms of HQE parameters

, whose

number grows

with powers

 

5

Slide6

Completed

perturbative

corrections

to leading term (parton model) Trott 04,

Aquila et al 05, Pak et al 08, Biswas et al 10 …

to power suppressed coefficients

Becher

et al 07, Alberti

et al

13-14,

Mannel

et al…

Power corrections (neglecting

perturbative corrections, i.e. working at tree

level)

computed and estimated up order

Gremm et al 96, Dassinger et

al 06,

Mannel

et al

10,

Heinonen

et al

14,

Gambino et al. 16…

 

HQE status

Starting

at

order

also intrinsic charm

contributions

and

inverse powers

  Bigi et al 05,09, 0911.3322, Breidenbachet al 08…

6

Slide7

7

|

Vcb

| inclusive extraction

Requires precise knowledge of b-quark, c-quark mass and HQE parametersrates

and

spectra very sensitive to

physical

pole mass

→

problems

in the

convergence

of

perturbative series for

the decay rates

→ use of “short-distance” mass definitions, kinetic, subtracted schemes 

HFLAV 2016 global fit (kinetic

scheme, mc constraint)

global fit (

HQE parameters, quark masses and |

Vcb

|) measuring

spectra plus all available moments

Lattice HQE

parameters

determination

First

steps

toward

transition

rates

from lattice

Gambino et al. 17, FNAL 18

Hashimoto

,

Meyer

18

First

steps

on lattice

Slide8

8

Exclusive

Decays

Lattice, QCD sum

rules

…

Lattice

a << 1/m

m

b

~ 1/a

effective

theories (HQET, NRQCD) that

eliminate

high degrees of freedom (systematic expansion in 1/mb )

(HQE, NRQCD…)

QCD sum rules

Analytical

approach

which

connects QCD Green functions

, in particular their Operator Product Expansion (

OPE),

and

their exp measurable hadronic counterparts

Slide9

Exclusive |

V

cb| determination

B

→ D(*)ℓν

Massless leptons limit

Zero

recoil

Heavy quark symmetry

F

 

Non perturbative

corrections

)

 

Phase

space

v

anishing

at

the no-

recoil

point

extrapolation

of the

exp

points

to

no-

recoil

point

 

Non-

z

ero

recoil

9

Slide10

CLN

B →

D ℓ

ν

Two lattice Nf=2+1 calculations at non-zero recoil with massive leptons

Fermilab

/MILC 1503.07237

→

form factors calculated for

a range of

recoil

momenta

z

-expansion

BGL

hep-ph

/9412324

2) HPQCD

1505.03925

CLN

parametrization

hep-ph

/9712417

10

Slide11

Global

fit

Bigi et al. 1606.08030

11

Slide12

12

Lattice

Two statistically

independent

analysis FNAL/MILC

PRD

14, 1403.0635 Total uncertainly about 2%

HPQCD

1711.11013

Preliminary

FNAL/MILC

at

non-zero

recoil 1710.09817 QCD sum

rulesMore

recent zero-recoil SR calculations include an estimate for the contribution of the excited states Gambino et al., 1206.2296

second error for excited states; lower values, much larger th

error

B → D

*

ℓ

ν

Form

Factors

Slide13

13

Extrapolation

to zero recoil point

since decay rates vanish at zero-recoil, one needs to extrapolate

the experimental points to zero recoil, using a parameterization of the dependence

 

preliminary

Belle

analysis

1702.01521

CLN

parameterization

Using Belle data,

switching from the

CLN

to

the BGL shifts the determination of |Vcb| Reliability of CLN questioned Bigi et al. 1703.06124, Grinstein et al. 1703.08170

Gambino

Portoroz 2017

Slide14

|

V

cb| summary

Most

precisebelow 2%

Still

excl incl

tension

3

σ

Within

larger

errors

no tension

14

Slide15

Traditionally extracted by the decay

B → π ℓ ν

(only a single form factor in massless limit)

Since the u-quark is not heavy, HQ symmetries are not as binding as in b →

cNon-pert th predictions for

usually confined to

regions of q2

Complementarity

Light Cone Sum Rules LCSR

low q

2

regions

GeV

(OPE near the light-cone)

Khodjamirian.Boyd, Grinstein, Lebed, …Lattice large q2

GeV (to avoid large discretization errors)Better fit with data HPQCD FNAL/MILC 09, ALPHA, HPQCD

, FNAL/MILC, RBC/UKQCD

 

|

V

ub

|

exclusive

detemination

FLAG 2017

HFLAV 2016

 

15

Slide16

16

b

→ u

decays into vector mesons

2015 LCSR

ff

computation

available-at

q

2

<12

GeV

+2013Belle(2012 Babar) data

B → ω

ℓ ν, B → ρ ℓ

ν

Results

compatible

,

but

consistently

lower

,

order

10

%

Theoretical

error

2-3

times

larger

than

exp

one

 

Slide17

17

Baryonic decays

Ratio of

relevant

form

factors

lattice

2+1 flavors of

dynamical domain-wall

fermions, RBC &

UKQCD

Configurations

Detmond

,

Lehner, Meinel

1503.01421

HFLAV 2016 (LHCb+BESIII)

Combined

fit

Meson+baryon

HFLAV

Slide18

18

Exclusive

|Vub

| summary

Uncertainties halfed last

few

years, around

4%

→

Large

th

error

→

Slide19

19

Prospects for

at Belle II

 

M.

Lubej

1705.05289

No

extensive

studies

for

vector

channels

Slide20

large b → c background

(

≈100 )

Need experimental phase space cuts to reduce background;

 

X

u

Inclusive

|

V

ub

|

20

Slide21

Phase space regions where OPE fails become dominant; new unwelcome effects (with respect to

semileptonic

b → c):

Final gluon radiation strongly inhibited: soft and collinear singularities

perturbative expansion of spectra affected by large logarithms a

sn

log2n(2 E

X

/

m

X

)

(

E

X

<<

mX) to be resummed at all orders in PT non–perturbative effects related to a small vibration of the b quark in the B meson (Fermi motion) enhanced

Inclusive

|Vub|21

Slide22

E

xperimental progress

Belle & Babar results access more than 90% data, latest Babar exp error < 4% 1611.05624

Theoretical approaches

predictions based on parameterizations of shape function, and OPE constraintsseveral cuts Bosch, Lange, Neubert , Paz (BLNP),

Gambino, Giordano, Ossola,

Uraltsev (GGOU) neural network fit (

Gambino,Healey,Mondino

)

m

X

-q

2

cut

Bauer, Ligeti, Luke (BLL)Lepton momentum spectrum Leibovich, Low, Rothstein (LLR

), Lange, Neubert, Paz (LNP)

global fit Ligeti, Stewart, Tackmann

predictions based on

resummed pQCD

Andersen,

Gardi

(DGE),

Aglietti

, Di

Lodovico

,

Ferrera

, GR (ADFR)

22

Slide23

23

New Babar 2016

measurement electron spectrum

show partial

BFs depend on the model Care in extrapolation

to full BF

Consistency

with

previous

measurements

only

in some

approaches

, e.g. BNLP

Babar 1611.05624Inclusive |Vub|

Still

tension inclusive-exclusive

about 2-3 σ

Slide24

Charged

Leptonic decays

Sensitive to BSM

physics

Only

measured error



20%

Babar 1207.0698

Belle 1503.05613

Simple and

clean

decay

in the SM

HPQCD

1302.2644

 

MeV

 

MeV

 

Fermilab

/MILC 1712.09262

Fermilab

/MILC 1712.09262

10%

uncertainty

from

decay

width

Agrees

with

both

excl

and

incl

Goldenzweig

La

Thuile

2017

 

24