soft-collinear-effective theory

Max-Planck-Institute for PhysicsWerner-Heisenberg-Institut

Munich

André H. Hoang

6th Vienna Central European Seminar, Nov 27 - 29, 2009

Soft-Collinear-Effective Theoryand

Jets at Colliders


Outline

• Jets physics and precision QCD

• Theoretical tools

• Soft–Collinear–Effective–Theory (SCET)

• Overview of achievements

• Isolated Drell-Yan

• Top mass from invariant reconstruction

• Conclusion

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LHC runs!

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Jet PhysicsUnderstanding of jets is essential in the search for the Higgs boson and for new physics at the LHC

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Not this kind of jets!



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Jet: cluster of energetic hadrons leaving tracks xxx and energy deposits in the detectors.



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QCD machineryQCD machinery


Jet PhysicsOur level of understanding of jets at the conceptual level is reflected in our ability to

do precision measurements of SM parameters:

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Jet PhysicsOur level of understanding of jets at the conceptual level is reflected in our ability to

describe standard processes:

ALEPH, DELPHI, L3, OPAL, SLD

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Theoretical Tools

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Theoretical Tools

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QCD Factorization:

Collins, Soper,Sterman; Bodwin

e.g. Drell-Yan

inclusive production

nonperturbative parton distributions

(process independent)

perturbative short-distance cross section

(process dependent)


Theoretical Tools

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QCD Factorization:


e.g. Drell-Yan


near threshold Sterman; Catani, Trentadue


Theoretical Tools

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QCD Factorization:


e.g. Drell-Yan


near threshold Sterman; Catani, Trentadue

• not directly measurable (selection cuts, beam remnant)

• very few events

• size of power corrections


Theoretical Tools

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Monte Carlo Event Generators:

Universal tool to describe/predict experimental distributions and rates depending on e.g. selection cuts.

parton shower

LL(+NLO)

perturbative

non-perturbative


Theoretical Tools

André H. Hoang

Monte Carlo Event Generators:

Universal tool to describe/predict experimental distributions and rates depending on e.g. selection cuts.

parton shower

LL(+NLO)

perturbative

• relies on LL (partly NLO) parton shower approximation

• shower cut represents an infrared regularization (factorization) scheme that is yet unspecified

non-perturbative


Monte Carlo GeneratorsStrong coupling from event shapes:

Almost all measurements from event shapes use the MC hadronization models to determine hadronization corrections to multiloop partonic computations.

Herwig 6.2

Pythia 6.1

parton-level prediction

hadron-level prediction

Q = 35 GeV

(JADE)Dissertori, et al.

Becher, Schwartz

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Monte Carlo GeneratorsTop mass measurements:

p pt

t-

W

W

b

b-

jetjetjet

jet

Invariant mass reconstruction:

scheme dependent

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Monte Carlo GeneratorsTop mass measurements:

p pt

t-

W

W

b

b-

jetjetjet

jet

Invariant mass reconstruction:

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Soft-Collinear-Effective Theory

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Doing jet physics using the concept of mode and scale separation at the Lagrangian and operator level

More transparent access to jet physics problems. SCET is an alternative approach to jet physics.

• Feynman rules

• systematic power counting

New proofs of factorization for processes not yet considered in the classic jet approach.

Easier (and field theoretic) access to power corrections and subleading twist terms.

IR-log resummation (soft+collinear) through renormalization.

Precision QCD at the LHC.



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Bauer, Fleming, Pirjol, Stewart

First developed for single jet problems in B-physics.

Light-cone coordinates:

2000-2001jet invariant mass



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jet invariant massBauer, Fleming, Pirjol, Stewart

First developed for single jet problems in B-physics.

2000-2001

Separation of modes:



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Lagrangian: similar to QCD Lagrangian

Collinear Lagrangian: small

large

Bauer, Fleming, Pirjol, Stewart



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Currents:

jet field

n-collinear Wilson line

Jet fields are gauge invariant under collinear gauge transformations.



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Factorization:

Soft field redefinition: soft-collinear decoupling



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Factorization:


soft-collinear decoupling at the operator level



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Factorization:


soft-collinear decoupling at the operator level

• applies to any number of final state jets

• can be generalized to initial state jets

(SCET-II)


SCET: Conceptual Work

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Subleading Power:

Bauer, Fleming, Pirjol, Stewart 0011336Bauer, Stewart 0107001Bauer, Pirjol, Stewart 0109045

Bauer, Pirjol, Stewart 0011336Pirjol, Stewart 0211251Beneke, Feldmann 0008255Beneke, Chapovsky, etal 0206152Chay, Kim 0205117

SCET with mass: Leibovich, Ligeti, Wise 0303099Boos, Feldmann, Mannel

0504005

0-bin subtraction: Manohar, Stewart 0605001Idilbi, Mehen 0707.1101

Glauber gluons:

Liu, Ma 0802.2973Idilbi, Majumder 0808.1087

Renormalons: Hoang, Stewart 0709.3519

All order infrared structure: Becher, Neubert 0903.1126

Becher, Neubert 0904.1021Feroglia, Neubert, etal 0908.3676

Feroglia, Neubert, etal 0908.3676

k factorization:

Chay 0711.4296

T

Nandi, Li 0704.3790

Parton shower: Bauer, Schwartz 0607296Bauer, Tackmann, Thaler

0705.1719Bauer, Tackmann 0801.4028Chiu, Fuhrer, Hoang etal 0901.1332


SCET: Collider Applications

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Manohar 0309176Chay, Kim 0511066Chen, Idilbi, Ji 0607003Becher, Neubert, Pejak 0607228Chay, Kim 0205117

Bauer, Lee, Manohar, etal

0309278Schwartz 0709.2866

Zu, Sheng, etal 0903.5047Ahrens, Becher, etal 0809.4298

Chiu, Kelley, Manohar 0709.2709

Leibovich, Liu 0705.3230

Idilbi, Ji 0501006Becher, Neubert, Xu 0710.0680Stewart, Tackmann, etal 0910.0467

Hoang, Stewart 0709.3519Bauer, Fleming,Lee etal 0801.4569Becher, Schwartz 0803.0342

Hoang, Kluth 0806.3852Hornig, Lee, Ovanesyan 0901.3780

Idilbi, Ji, Ma, Yuan 0509294

Mantry, Petriello 0911.4135

Chiu, Kelley, Manohar 0712.0396Chiu, Kelley, Manohar 0806.1240Chiu, Fuehrer, etal 0909.0947

Fleming, Leibovich,etal 0607121

Bauer, Lange 0905.4739Becher, Schwartz 0911.0681

Fleming, Hoang, etal 0703207Fleming, Hoang, etal 0711.2079Jain, Scimemi, Stewart 0801.0743


Isolated Drell-Yan

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Stewart, Tackmann, Waalewijn

0910.0467Drell-Yan with central jet veto.

Beam thrust:

• event-shape-like and suitable for analytic computations

• contribution of unmeasured beam remnant negligible

• cut on vetoes high p jetsT

beam functions

• factorization for

• related to initial state parton showerPDF


Top Reconstruction and Event Shapes .

Possibility to define reconstruction prescription such that non-perturbative effects can be extracted from event shapes.

Fleming, Mantry, Stewart, AHH

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Invariant mass distribution

Jet mass, thrust distribution

for thrust, jet masses

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Fleming, Mantry, Stewart, AHHTop Quark

Light quarks

universal !

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Invariant Mass Peak and Top Mass

Fleming, Mantry, Stewart, AHH

best mass scheme: jet mass

first moment of the soft function

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. Abbate, Fickinger, Mateu, Stewart, AHH

488 bins

NNNLL’ NNNLL NNLL’ NNLL NLL’

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Conclusions

• Approach to jet physics and high energy scattering processes using effective field theory.

• Alternative and compatible approach to classic jet physics.

• Modularity: SCET can be combined with HQET, NRQCD, Chiral p.th.

• Initiates novel applications (conceptual & computational).

• Aim: Precision QCD Physics at LHC

Soft-Collinear-Effective-Theory:

Stay tuned!

André H. Hoang

soft-collinear-effective theory

Documents

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new physics

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