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QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference on B Physics at Hadron Machines, Oct. 14-18 (Beauty 2003) Iain Stewart – p.1
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Page 1: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

QCD, Factorization,and the

Soft-Collinear Effective Theory

Iain W. StewartMIT

The 9th International Conference onB Physics at Hadron Machines, Oct. 14-18

(Beauty 2003)

Iain Stewart – p.1

Page 2: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Outline

� Motiviation, QCD, Expansion Parameters

Analogy with HQET

� What is the Soft-Collinear Effective Theory (SCET)?

Degrees of freedom, Physical picture, Symmetries

� �

-Physics Applications: ( ��� � ��� �� )

� � ��� , Color-Suppressed Decays (

� � � � � � � �

, � � � )

Heavy-to-Light Form factors

Status of

� � � �

decays (

� � � ��� � � � )

� Outlook and Issues

Summary from Beauty-SCET Workshop

Iain Stewart – p.2

Page 3: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Motivationb-Hadrons:

� Laboratory for EW, new physics, & QCD

� The lightest

’s decay weakly to many channnels

� � � � � � � �, � � � � � ���� � � �, � � � � �, � � � �,

� � ��� ,

� � � � � , � � � ,� �� �, � � � � �, � � � � � � �,� � ��� ,

� � � � ,

� � � ,

� � � �� �� ,� � ��� � �, � � ��� � ,

� � �� � � �,

� � �

(Repeat for

� � ,

��� , � � � )

� Need to understand (elliminate) hadronicuncertainties from QCD

Iain Stewart – p.3

Page 4: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Scalesquarks mass

u � � ���

d � � ��

s � ��� ��

c � � � � ��

b � �� � ��

t

� � � ��

} light

� �

} heavy

QCD

� � �� �

, resolution

� � � � �non-perturbative

� long distance� � � �� �perturbative

� short distance

In full QCD usually we can not predict amplitudes with smalluncertainties in a model independent way

Need Expansion Parameters

(If we use a model then we can not even estimate the uncertaintiesreliably)

Iain Stewart – p.4

Page 5: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Use Effective Field TheoriesUse Effective Field Theories: Separate physics at different

momentum scalesExpansion Parameters

(1) Electroweak Hamiltonian

�� � � � � �

(2) Heavy Quark Effective Theory (HQET)� � �� � �

(3) SU(3), Chiral Perturbation Theory

� � � �� �� � � �

(4) Soft-Collinear Effective Theory (SCET)� �� � �

,

� � ��� ��� �Depending on the observable one or more of these may be necessary

(5) Lattice QCD

�� � �

, � � � �

Iain Stewart – p.5

Page 6: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Electroweak Hamiltonian1) Integrating out the

�� �

( � �� ��� � �� ):b u

d

u

W

b u

u

d

u

u

b

W

d

g

db

uu

db

uu

u,c

db

bd

� � ���

� � � �� �� �� �

� � � ��� � ��� � � � ��� � � � � �

� � � ��� ��� ��� � � � ��� � ��� � �

� � � �� � ��� � ��

� ��� � � � � �

��� � �� � � �

� !�" � # $ � � �

� %& !�' ' ' � � � � � �

� ( � ) � � �� � ��� � � � �� � � � � �

� � �

Operators come with different CKM elements,

� � � � �� �, � � �

Iain Stewart – p.6

Page 7: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

HQET: � ���

Inclusive Decay: OPE in

� ��� �

� � � is free quark decay, �� � � � � corrections computable

No

� � � � corrections HQET gives 0 at this order

At

� � � � �� have dependence on��� ,� � defined in HQET

�� � ��

� �� � � ��� � �"! � � � � � #%$

� � � & & &

HQET is simpler than QCD Spin-Flavor Symmetry

Uncertainties suppressed by

� � � �

Iain Stewart – p.7

Page 8: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

HQET: � ���

Inclusive Decay: OPE in

� ��� �

Fit moments to simultaneously extract

� ��� � � , � � ( � �

),�� ,

� �

Example: CLEO

1 TotalExperimental

Ellipse

0th Moment ofLepton Energy

1st Hadronic Mass Moment

1st Moment of Lepton Energy

0

0.05

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0 0.80.70.60.50.40.30.20.1 (GeV)

I

1 (

Ge

V2)

II

II

II

II

II

1st Moment ofPhoton Energy

(b s )

0.50

1630802-010

� �� � � � �� � & � � � & � � � & � � � �� �

from S.Stone at EPS

Iain Stewart – p.7

Page 9: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Soft-Collinear Effective TheoryMany processes have energetic hadrons,

� � �

, where HQET doesnot apply

Iain Stewart – p.8

Page 10: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Soft-Collinear Effective TheoryC. Bauer, S. Fleming, M. Luke hep-ph/0005275 (PRD)

C. Bauer, S. Fleming, D. Pirjol, I.S. hep-ph/0011336 (PRD)

C. Bauer, I.S. hep-ph/0107001 (PLB)

C. Bauer, D. Pirjol, I.S. hep-ph/0109045 (PRD)

Builds on earlier work:Hard Exclusive: Brodsky, Lepage, � � �

Jet physics: Collins, Soper, Sterman, Korchemsky, � � �

B-physics Factorization: Dugan, Grinstein, Beneke, Buchalla, Neubert, Sachrajda, � � �

Iain Stewart – p.8

Page 11: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Soft-Collinear Effective Theory

Introduce fields for infrared degrees of freedom (in operators)

modes � � � �� �� � � � � fields

collinear

� � � �� ��

� � � � � � ��� ,

� ��

soft

� � ��

��

� � � � � � �� , � ��

usoft

� � � ��

� ��

� � � � � �� �� � , � �� �

Offshell modes with � � � � � � �

are integrated out (in coefficients)

Iain Stewart – p.8

Page 12: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Soft-Collinear Effective Theory

Introduce fields for infrared degrees of freedom (in operators)

modes � � � �� �� � � � � fields

collinear

� � � �� ��

� � � � � � ��� ,

� ��

soft

� � ��

��

� � � � � � �� , � ��

usoft

� � � ��

� ��

� � � � � �� �� � , � �� �

eg. B Dπ

Pion has: � ��

�� � �� � �� � ��

�� � � � � � � � ��� �

� � � �

pion in rest frame has constituent momenta:� � � � �� � � � � � ��

��

� �

boosting gives collinear constituents:

� � � � �� �� � � � � �

� ���

� � � � � � �� ��

� � � � �

Iain Stewart – p.8

Page 13: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Soft-Collinear Effective Theory

Introduce fields for infrared degrees of freedom (in operators)

modes � � � �� �� � � � � fields

collinear

� � � �� ��

� � � � � � ��� ,

� ��

soft

� � ��

��

� � � � � � �� , � ��

usoft

� � � ��

� ��

� � � � � �� �� � , � �� �

B D

π ��

are soft, � collinear

� � � � �� � � � � ��

Factorization if

� � � � � �

Iain Stewart – p.8

Page 14: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Soft-Collinear Effective Theory

Introduce fields for infrared degrees of freedom (in operators)

modes � � � �� �� � � � � fields

collinear

� � � �� ��

� � � � � � ��� ,

� ��

soft

� � ��

��

� � � � � � �� , � ��

usoft

� � � ��

� ��

� � � � � �� �� � , � �� �

Typically either:

SCET �

� � �� usoft � � � �

collinear � � � � � �

, jets

SCET � �

� � �� soft � � � �

collinear � � � � � �

, exclusive

Iain Stewart – p.8

Page 15: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Soft-Collinear Effective Theory

Introduce fields for infrared degrees of freedom (in operators)

modes � � � �� �� � � � � fields

collinear

� � � �� ��

� � � � � � ��� ,

� ��

soft

� � ��

��

� � � � � � �� , � ��

usoft

� � � ��

� ��

� � � � � �� �� � , � �� �

Symmetries

1) Gauge Symmetry, Collinear, Soft, Usoft2) Helicity, Spinor Reduction, �

� �� �

3) Reparameterization Invariance, �,� �

4) C,P,T in different sectors

Iain Stewart – p.8

Page 16: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

SCET

� gives a systematic expansion in

� � �

QCD

��

� model independent description of power corrections

can estimate uncertainties

� make symmetries explicit, understand factorization in a universal way

Determine quantities that are short and long distance,calculate short distance coefficients

Proof of Factorization means Known to be Model Independent oncehadronic parameters are determined

� � �� �� has hard coefficients

� � ���� �

with � � � �

, Wilsonlines W,

� � �� �� � has jet coefficients

with � � � �

, Wilson lines

,

Iain Stewart – p.9

Page 17: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Hadronic ParametersDefine universal hadronic parameters, exploit symmetries

Process Degrees of Freedom ( � � ) Non-Pert. functions��� � � � � � �� � � c (

� �

), s (

� �

)

� ��� �,

���

��� � � � � ��� � � c (

� �

), s (

� �

), c (

� �

)

� �� ��� � , ��

� � � �� "! #$ %, c (

� �

), us (

� �

)& �� � �

� � � �� "! #' (*)

� � ( ) �� � � c (

� �

), s (

� �

), c (� �

)

�,+ �� � �

,

�� ��- �

,

.� �/ �

� � % (*) c (

� �

), us (

� �)

�0+

� � c (

� �

), s (� �

), c (

� �

)

�,+ ,

�� ,

.� �/ �

� � 1 2 % c (

� �), s (

� �), c (

� �

)

�0+ ,

�03 ,

. 435 �/ �

6 � � � 6 � �

c (� �

)

&7 8 ! � � �

,

&:9 8 ! � � �

6 � % � 6 � �

c (� �

), s (

� �

)

�;�

% 2 < � < =

c (

� �

), s (

� �

)

�0> ,

�> ?

Iain Stewart – p.10

Page 18: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Hadronic ParametersSCET Authors (in no particular order):

S.Mantry, C.Bauer, D.Pirjol, I.S., S.Fleming, M.Luke, I.Rothstein,M.Beneke, T.Feldmann, M.Diehl, A.Chapovsky, Descotes-Genon,J.Chay, C.Kim, G.Buchalla, C.Sachrajda, E.Lunghi, D.Wyler, S.Bosch,R.Hill, B.Lange, M.Neubert, T.Becher, M.Wise, A.Manohar, T.Mehen,A.Leibovich, Z.Ligeti, � � �

Iain Stewart – p.10

Page 19: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Hadronic Parameters

Example:

� � � � � � � , � � � � � � �

� ��� � ��� � �� � � � � � � ��� � � � � ��

� � � � � ��

� � �

where

� ��� �� � � ���� ! ? � � � �� � � ��� � � � � � �� � � � ��� ! ��� � � ��

� &� / � �- � � / � � � - ! " �# �� �- �

$ �&% ? ' �)( % ? *,+ ( % ' � % - � � �/.10 . = �

LO =

� �

graphs

� ��� � ��

��

� �

, corrections will be

� � � � � � 2

Example 2:

� � � � �shape function

3 �4 � � � � �6587 9 �: � �

� � 4 � 587 � � �

Iain Stewart – p.10

Page 20: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

� � �

phenomenology

Type Decay Br

� �� � � �

Decay Br� �� � � �

I

� � � � � � � � � �� �� � � �� � � � � � � � � � � � � �� � � �

III

� � � � � � � �� � � �� � � � � � � � � � � � �� � �� �

II

� � � � � � � � � � � �� �� �� � � � � � � � � � � � � � � � � � �� �� �

I

� � � � � � �� � � � � � � � � � � � � �� � � � �� �

III

� � � � � � � �� � � � � � � � � � � � � �� � � � � � �

II

� � � � � � � � � � � �� � � � � � � � � � � � � �� � � �

PDG or a,b,c,d=CLEO, b=BELLE

New BaBar numbers (hep-ex/0310028 , yesterday):� � � � � � � � � � � � �� �� � �� ��

� � � � � � � � � � � � � �� �� � �� �� �

Iain Stewart – p.11

Page 21: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

� � �

phenomenology

Type Decay Br

� �� � � �

Decay Br� �� � � �

I

� � � � � � � � � �� �� � � �� � � � � � � � � � � � � �� � � �

III

� � � � � � � �� � � �� � � � � � � � � � � � �� � �� �

II

� � � � � � � � � � � �� �� �� � � � � � � � � � � � � � � � � � �� �� �

I

� � � � � � �� � � � � � � � � � � � � �� � � � �� �

III

� � � � � � � �� � � � � � � � � � � � � �� � � � � � �

II

� � � � � � � � � � � �� � � � � � � � � � � � � �� � � �

� � � � � � � � � � � decays agree within errors

� � � � � � � � � � � �

,

� � � � � � � � � � , small as expected (0 at LO)

� � 20-30% power corrections for

� � � � � � � � � )/

� � � � � � � � � )Nonzero strong phase,

9 � � �

Iain Stewart – p.11

Page 22: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

� � � ��� � ��� � � � �� � � � � �

� # � ��� � � � ��� � � � ��� � � � ��� � �

"Tree" "Color suppressed" "Exchange"

B D

b c

u , d

du

π

π

DB

b c

u

d , u d B

D

b

d

c

u

u ,d

u, d

π

��� � � � � � � � � � � � � � � � � � � �

� � � � � � � � � � � � � � � � � � � � � � �

Large

� �- not very predictive:

� � �� � � � � � � � � �

Iain Stewart – p.12

Page 23: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

� � � ��� � ��� � � � �� � � � � �

� # � ��� � � � ��� � � � ��� � � � ��� � �

"Tree" "Color suppressed" "Exchange"

B D

b c

u , d

du

π

π

DB

b c

u

d , u d B

D

b

d

c

u

u ,d

u, d

π

��� � � � � � � � � � � � � � � � � � � �

� � � � � � � � � � � � � � � � � � � � � � �

Naive Factorization - too small:

� � � � � � � � � � � � � � � � � � �� � � � � � � � � � � � � � � � � �� �

Iain Stewart – p.12

Page 24: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

� � � ��� � ��� � � � �� � � � � �

� # � ��� � � � ��� � � � ��� � � � ��� � �

"Tree" "Color suppressed" "Exchange"

B D

b c

u , d

du

π

π

DB

b c

u

d , u d B

D

b

d

c

u

u ,d

u, d

π

��� � � � � � � � � � � � � � � � � � � �

� � � � � � � � � � � � � � � � � � � � � � �

QCDF -

� � � �

is non-factorizable channel BBNS

pQCD - predicted with expansion in � �� ��

Keum et.al.

Iain Stewart – p.12

Page 25: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Factorization for Color-Suppressed Decays

Mantry, Pirjol, I.S.

� � � � � � � � � � �

� SCET factorization mechanism for color suppressed channels

still predictive

Iain Stewart – p.13

Page 26: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Factorization for Color-Suppressed Decays

Mantry, Pirjol, I.S."Tree" "Color suppressed" "Exchange"

B D

b c

u , d

du

π

π

DB

b c

u

d , u d B

D

b

d

c

u

u ,d

u, d

π

��� � � � � � � � � � � � � � � � � � � �

� � � � � � � � � � � � � � � � � � � � � � �

� � �� � � � � � � �

"��

��� 8 � �

��

��� 8 � � � � /

� � � � � � � � � � �� � � 8 � � � � �

� � �� � � � � � � �

��

� � 8 � !"

��

��� 8 � �"

� ��� ! / � � �

Iain Stewart – p.13

Page 27: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Take �

Mediated by a single class of

� �� �� operators

� � � � � ��

� � � ��� �

� � � ��� �

b

d

c

u

du,

d u,

(a)

bd

c

u

u,

d u,d

(b)

When matched onto

� �� �� � we find a factorization formula

(

� �� ):

� � �5 �� � � � � �� � ��� �� � �� � � � �� � � � � � � � �� � � �� � � � � � � � � �� � � � � � � �

two new non-perturbative soft functions

� : � � � �

� � �� # � � � 5 � ��7 ? � �� � � ��� �� � � � � 5 � � �7 � � � � ��� ��� � � � ��� �� � � � � � ��� ���

�� ��� �� � � ��! # � � #" � � $ � ��! # �&% � ')( � � ')* + same for

and

� �

Iain Stewart – p.14

Page 28: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Results and Predictions

� Find both

and

suppressed by

� ��

relative to

� �% � ' + is complex, gives non-perturbative strong phase which isindependent of

and choice of

vs.

� �Predictequal strong phases

� �� � �

equal amplitudes

� � � � ��

corrections to this are ��� % �� +

,

� ��

Expt (pdg average):

"�� % � " � $ � ��� � +�� %��� ! "��� � # +%$ &� ' ( ,

� *) � +� , ' - .' ( / ."�� % � " � $ � � ��� � + � %��� # "��� � 0 +%$ &� ' ( , � � ) � +� , " 1 ,

Iain Stewart – p.15

Page 29: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Test and Predictions

0 0.2 0.4 0.6 0.8 1

0

0.2

0.4

0.6

0.8

= D*= D

δ φ

RI2

A003

A0_

ππ

��� �

� ( � *� � ( � *

� � arg

% � ( � * �� ( � * +

Also predict (not post-dict):

� �� � �% �#" � $ � � � �� +

�% �" � $ � � � � + � &

Iain Stewart – p.16

Page 30: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Test and Predictions

0 0.2 0.4 0.6 0.8 1

0

0.2

0.4

0.6

0.8

= D*= D

δ φ

RI2

A003

A0_

ππ

��� �

� ( � *� � ( � *

� � arg

% � ( � * �� ( � * +

Also predict (not post-dict):

� ���� �

� � � � � � �� �� �

� � �� � � � � ��� � � ��� � � � ���� �

� � �� � � � � � ��� �

� � � � � � � � ��� � � ���

� � �� �

� � �� � � � � � � � �

� � �� � � � � � � � � � �� � � � ��� �

� � �� � � � � � � �� �

� � �� � � � � � � �� � � �

Iain Stewart – p.16

Page 31: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

More PredictionsMore predictions can be made if we expand

in �� % � *�� � � +

At tree level

� � �

=

� � �

= constant, � � ��

�� % � � +

� '( � '*so get

�� � � � � � � � �% � '( � '* +� '( � '*

�) % + � � � � � � +� ' �� )

Iain Stewart – p.17

Page 32: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

More PredictionsMore predictions can be made if we expand

in �� � ��� � � �

At tree level

� � �

=

� � �

= constant, � � ��

�� � � �

� �

� ��so get

�� � � � � � � � � � �

� �� �

� �

� ��

�) � � � � � � � �� ' �� )

� If

� ' � ) �� ' �� then

�� ) � � �� � �

�� *) � � � � ��� � � � �� ' � �

� � � ' � � �� ' � � � ��� 0 0 "� � � #

�� � � � � � � "��� � !

�� � ) ) ) ) � � ��� ! "��� 0

� Also would predict that� �� �)

� If we fit the complex � �

=

" " &� � � � � � �� �� , " 0 , � �

ie natural size, � � � ��� �� from dim. analysis

Iain Stewart – p.17

Page 33: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

More Predictions

naive factorization for colorsuppressed decays

?

Iain Stewart – p.18

Page 34: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Heavy-to-Light Decays

� Large � � accessible on the Lattice (

� �� � �, � � � & # � � � �)

� For small � � , � � � � �� and large energy factorization applies

� � � � �

q2 (GeV2/c4)

Eve

nts

/ (1

GeV

2 /c4 ) 20

10

0 5 10 15 20

CLEO

0

100

200

300

0 15 20

q2 (GeV 2/c4 )

Eve

nts/

2.2

GeV

2 /c4 BABAR

5 10

Why is it interesting?

� Important ingredient for

� �� � � � � � (CP violation)

� Phenomenology:�� � �

,

� � � ,

� � �� � �� ' ,� � �

Iain Stewart – p.19

Page 35: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Heavy-to-Light Form Factorspseudoscalar:

� � , �� ,

��� , vector:

,

�� ,

� ,

� � , � , � � , � (“Soft part” “Hard part”

Iain Stewart – p.20

Page 36: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Form Factor ResultsBauer, Pirjol, I.S.

Beneke, Feldmann

Our result

� � � � � � � � � � � � � �

� � � � � ��� ��� � �

� �

� �

��

��

�� � � � � �� � � �

$ � � � � � � � � � � �� � � �

� � � � � �� � �� � � � �

� � ��

B M

Λ~p 22 Λ~p 22Λ~p2 Q

~p2 Q2

result at LO in

, allorders in �� , where� � � �� � � �

Iain Stewart – p.21

Page 37: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

ResultsPirjol, I.S.�

to pseudoscalar

��� � � ����� � � � � � � ���� � � ��� � � � � � � ����� ��� � � � ��� � � � � � � �� ��� � � ��� � � � � �

� �� � � � � � � �� � � � � � � � �� � � ��� � � � � � � � �� ��� � � � � � � � � � � � � � �� � � ��� � � � � �

�! � � �#"$� � � � � � � �"%� � � �� � � � � � � �#"%� ��� � � � � � � � � � � � �� �� � � ��� � � � ��

Iain Stewart – p.22

Page 38: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

ResultsPirjol, I.S.�

to vector

� � � �� ��� � � � � � � �� � �� ��� � � � � � � �� ��� � � �� � � � � � � � � � � ��� � � � �� �� ��� � �

� � � � � �� �� � � � � � � � �� � � �� � � � � � � � �� ��� � � � � � � � � � � � �� ��� � � � �� �� ��� � �

� �� � ��� � � ���� ��� � � � � � � ��� � �� ��� � � � � � � ���� ��� � � �� ��� � � � � � � �� ��� � � � �� �� �� �

�� �� �

� � ��� � � �� � ����� �� � � �� � � � � � ����� � � �� � � � �

� � ����� � � � � � � � � � � �� �� � � �� �� �� � �

�� � � �� ��� � � � � � � �� � �� ��� � � � � � � �� ��� � � �� ��� � � � � � � �� ��� � � �� �� ��� � �

� �� � � � � �� � ��� � � � � � � �� � � �� ��� � � � � � � �� � ��� � � �� ��� � � � � � � �� ��� � � �� �� ��� � �

��� �� �

� � � � � �� � �� �� �� � � � � �� � � � �� �� � � �� � � � �

� � �� �� � � � � � ��� � � � � � � � � ��� � � �� �� ��� � �

Iain Stewart – p.22

Page 39: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Implications

� � � � � � � � �

and

� � � � � � � � �

by helicity symmetryBurdman, Hiller

� certain

� �� � and

� �� � combinations are � � � �

suppressed

� goal is to identify processes besides

� �� � � that depend onsame non-perturbative parameters, egs.

� �� � ,

� �� � � � ' ,� � � �

� If lattice can get points in the low � �

region they can read offimportant hadronic moments by fitting certain linear combinations

eg.

�� ��� �

� � � � �

� � � �� ' � �� � ' � � �

� �

� For

� �� � SCET reduces the lattice problem to(

� �� )$ (

� �� )

Maybe in the future we can get to(

� �� )$ (� �� )$ (

� �� )

Iain Stewart – p.23

Page 40: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Form Factor ResultMore comments

� � � � � ��� ���� �

� �

��

��

�� � � � � � � �

$ � � � � � � � � � � � � � � �� � � � �

� � � � � � � � � � � �

� � � ��

� No suppression of

� � � � � �

by an �� � � � is observed, mightexpect

� � � � � � � � � � � � � �) � ( � � ���� �

� In

� �� � BBNS use

� � � � � �Keum, Li, Sanda use “

� � � � � �” (with a different definition)

� Fit with f.f. models gives,� � � � � ��� + "��� �

Luo, Rosner

� Data for

� � � �� � �,

� � �� � �

,

� � �� � �

,� � � , will eventually tellus how

� �

compares with

� � �

� Theory Corrections are

� � �) � � � +� �

to this factorization,growing as

�) gets smaller

Iain Stewart – p.24

Page 41: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

eg. Measure � � � � � with

� � � � �� �� ' , �� � � � �� �� '

��� � � � � � �) ) � � � � � � � � � ) ) � � � � � �

�) ) � � � �

& � � � � � ) ) �& � � � � �

& � � � � � �� � � �� & �� �� � � �

& �� ' �� � � �

T = tree,

P = penguin

P/T

�� �

, need information from QCD (or isospin analysis)

Iain Stewart – p.25

Page 42: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

In “QCD Factorization” Beneke, Buchalla, Neubert, Sachrajda

B

π

π B π

π

� � �)

,

�) � � � � �

�) �

�) � �

In SCET Chay, Kim

Bauer, Pirjol, Rothstein, I.S. (in progress)

B π

Λ~p 22 Λ~p 22Λ~p2 Q

~p2 Q2

πΛ~p 22

involves ) ,

� � ,

�) �

Iain Stewart – p.26

Page 43: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Issues in1) Factorization/Exponentiation of gluons beyond

� � � �

Chay, Kim

2) Result if �� � � � &� & � &� 1 � � � �

is not perturbative?

3) New Soft-Collinear messenger modes Becher,Hill,Neubert

Could spoil factorization in

� �� � ,� � � , etc.

4) Glauber Gluons beyond

� �� �

(like Coulombic exchange)

5) Numerical stability and convergence, chirally enhanced terms?

6) Error estimates, could power corrections dominate

� � �� �� �

?(since BBNS and pQCD disagree with new Belle and BaBar data)or is something else going on� � � ?

Iain Stewart – p.27

Page 44: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Workshop Issues

� Is it always true that the vacuum factorizes? Manohar

�� � � �� � � � �� � �

� Can SCET help to explain the cross section for��� ' � � �� �

,

� �� ' �� � � � � ��

? Fleming

� Could singularities forbid factorization below the

� �

scale?Feldmann

� Claim of a non-zero time ordered product in

�� �� for

-decays.Pirjol

� Claim soft-Collinear modes exist and spoil factorization in somecases.

Neubert

� A proposal for a new choice of fields for

�� �� , and doubts aboutsoft-collinear modes.

Chay

Iain Stewart – p.28

Page 45: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Outlook

� SCET gives operator definitions to universal hadronic

parameters � need to measure these with experiment

� Subfields: Jet Physics,

Physics,

� � �

Physics

� Allows power corrections to be addressed in a model

independent way (even when we lack a rigorous OPE)

� Need to carefully examine expansion for each process and

improve our understanding of power corrections to go

beyond 20-30% accuracy for

’s

� SCET applies to many inclusive/exclusive processes

A lot of theory and phenomenology left to study � � �

Iain Stewart – p.29

Page 46: QCD, Factorization, and the Soft-Collinear Effective Theory€¦ · QCD, Factorization, and the Soft-Collinear Effective Theory Iain W. Stewart MIT The 9th International Conference

Colors

This is blue

This is red

This is brown

This is magenta

This is Dark Green

This is Dark Blue

This is Green

This is Cyan

Test how this color looks

Test how this color looks

Test how this color looks

Test how this color looks

Test how this color looks

Iain Stewart – p.30


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