SCET2014: XIth Annual Workshop on Soft-Collinear Effective Theory

26 Mar 2014, 08:00 → 28 Mar 2014, 18:00 Europe/Berlin

Auditorium (Institute for Advanced Study of the Technische Universität München)

Grigory Kirilin, Martin Beneke, Michael Benzke, Miguel A. Escobedo, Nora Brambilla

This workshop is the eleventh in a series of annual meetings bringing together researchers working on topics in Soft-Collinear Effective Theory (SCET). SCET has been applied to various problems in heavy flavor physics, collider physics, heavy ion physics, and even quantum gravity. The aim of this workshop is to discuss recent developments in the field.
The workshop is hosted by the Technische Universität München and supported by the DFG Cluster of Excellence "Origin and Structure of the Universe".
There will be a self-hosted conference dinner on the evening of Thursday the 27th.
The registration deadline is February the 28th. There is no registration fee.
Abstract submission is now closed. If you still wish to submit an abstract, please contact the organisers using the contact button on the left.

Wednesday 26 March

09:00 → 10:35 Session 1

Convener: Prof. Andre Hoang (University of Vienna)

09:00 Welcome

Speaker: Prof. Martin Beneke (TUM)

09:05 Factorization and resummation of the gg—>H cross section with a jet veto

TBA

Speaker: Matthias Neubert (Johannes Gutenberg-Universität Mainz)

Slides neubert_new.pdf

09:35 Jet Vetos and Off-Shell Effects in H->WW

We study the effect of an exclusive jet veto on off-shell particle production using SCET to resum large logarithms of the ratio of the jet veto scale to the partonic centre of mass energy. Using gg->H->WW as an example, we calculate the resumed off-shell cross section, including signal-background interference, to NLL. We discuss the implications for extractions of the Higgs width.

Speaker: Ian Moult (MIT)

Slides IanMoult_SCET.pdf

10:05 Unstable particle EFT and mixed QCD-EW corrections to Drell-Yan processes

The mixed QCD-EW corrections are currently one of the main missing ingredients to improve theoretical predictions for W an Z-boson production at hadron colliders. Near the vector-boson resonances, a suitable framework for their calculation is given by the pole expansion that allows a consistent seperation of the radiative corrections into factorizable corrections to vector boson production and decay, and into non-factorizable corrections. This method can also be implemented using the method of unstable-particle effective theory. I discuss the application of this framework to the mixed QCD-EW corrections to Drell-Yan processes and present results for the non-factorizable corrections that exhibit interesting analytical and numerical cancellations.

Speaker: Christian Schwinn (University of Freiburg)

Slides dy_talk.pdf

10:35 → 11:00 Coffee break

11:00 → 12:40 Session 2

Convener: Michal Czakon (RWTH Aachen)

11:00 Comparing Direct and Effective Methods of Resummation

We compare methods "directly" in QCD and "effectively" in SCET to resum logs in momentum-space cross sections such as event shape distributions. We put expressions in both formalisms into a common form that demonstrates their precise equivalence. In this process we endow the traditional QCD formulas with proper dependence on separated hard, collinear, and soft scales, and also find some novel forms in which to write the SCET resummed cross sections. One of these ways allows us to truncate differential distributions in SCET so they retain correct accuracy even at "unprimed" NkLL order, and also match more closely the total integrated cross section.

Speaker: Christopher Lee (LANL)

Slides S2-CLeeNotes.pdf SCET_2014_Backup.pdf

11:40 Parton Luminosity Shapes and Threshold Resummation in SCET and Direct QCD

It was pointed out long ago that in hadronic collisions, the steep decline of the parton luminosity function gives rise to potentially large logarithms that can be resummed to all orders. Several SCET-based studies in threshold resummation have organized these logarithms by the determination of a soft scale. We further explore this issue for electroweak annihilations, and identify an expansion for the parton luminosity function in terms of its logarithmic derivatives. The first logarithmic derivative fixes threshold logarithms at LL, while higher logarithmic derivatives generate corrections starting at NLL. Numerical studies indicate that this expansion is highly convergent in almost all cases. The soft scale determined by this method coincides, at the percent level, with the soft scale found by minimizing the one-loop soft correction. In addition, this expansion enables us to write down a clean formula for the difference between resummed cross sections in direct QCD (dQCD) and SCET, and confirm that the difference is subleading for most collider scenarios. Besides the topic of parton luminosity shapes, we also derive some formal relations between resummation coefficients used in the dQCD and SCET.

Speaker: Mr Mao Zeng (Stony Brook University)

Slides S2-Mao_Zeng.pdf

12:10 Transverse-momentum spectra of electroweak bosons near threshold at NNLO

We obtain the next-to-next-to-leading order corrections to transverse-momentum spectra of W, Z and Higgs bosons near the partonic threshold. In the threshold limit, the electroweak boson recoils against a low-mass jet and all radiation is either soft, or collinear to the jet or the beam directions. We extract the virtual corrections from known results for the relevant two-loop four-point amplitudes and combine them with the soft and collinear two-loop functions. We have implemented these results in a public code PeTeR and present numerical results for the threshold resummed cross section of W, Z and Higgs bosons at next-to-next-to-next-to-leading logarithmic accuracy, matched to next-to-leading fixed-order perturbation theory.

Speaker: Thomas Becher (Bern University)

Slides becher_SCET14.pdf

12:40 → 14:00 Lunch break

14:00 → 16:00 Session 3

Convener: Matthias Neubert (Johannes Gutenberg-Universität Mainz)

14:00 An EFT approach to initial-state heavy quarks

We revisit the systematic inclusion of mass effects for heavy-quark initiated processes using an EFT setup. Via a series of matching steps our approach resums to all orders initial-state collinear logarithms whilst maintaining mass dependence in all matching coefficients. The result can be interpreted as a variable flavor number scheme, and reduces to the well known ACOT or FONLL schemes in particular limits. Our EFT approach also provides a systematic way to assess the uncertainties in the matching procedure, which is usually ignored in previous approaches.

Speaker: Dr Marco Bonvini (DESY)

Slides bonvini_SCET2014.pdf

14:30 Variable flavor number scheme for final state jets

We discuss a variable flavor number scheme for final state jets which can account for the effects of arbitrary finite quark masses for inclusive jet observables. The scheme is a generalization of the ACOT variable flavor number scheme for PDFs. It is based on a consistent description of massive collinear and soft modes allowing also for a treatment of rapidity divergences. We emphasize general properties, the calculations of threshold corrections, consistency conditions and relations to mass singularities found in fixed-order massive calculations. Specific examples covered are massive quark effects in event shapes and DIS.

Speaker: Piotr Pietrulewicz (University of Vienna)

Slides SCET2014.pdf

15:00 The two-loop beam function

In differential measurements at a hadron collider, collinear initial-state-radiation (ISR) is described by process-independent beam functions. We present our recent NNLO calculation of the inclusive virtuality-dependent beam function, which is relevant for any observables probing the virtuality of the colliding partons, e.g. N-jettiness and beam thrust. For such observables our results are the last important ingredient to account for all collinear ISR effects through N3LL order.

Speaker: Maximilian Stahlhofen (DESY)

Slides S3-Max_Stahlhofen.pdf

15:30 1-jettiness in DIS at NNLL+O(a_s)

We compute structure functions and cross sections for two-jet production in DIS, with one jet from initial state radiation (ISR) and the other from final state radiation, with a summation of large logarithms up to NNLL accuracy and with a correction at O(a_s) in fixed order accuracy. Use of the DIS event shape 1-jettiness ensures that events have two well-collimated jets. We choose one of three versions of 1-jettiness that may be easily measured in experiments and present analytic and numerical results for this version with parameters for the HERA collider.

Speaker: Daekyoung Kang (MIT)

Slides SCET2014-kang.pptx SCET2014-kang.pptx.pdf

16:00 → 16:30 Coffee break

16:30 → 18:00 Session 4

Convener: Prof. Matthew Schwartz (Harvard)

16:30 Dissecting Soft ISR, Underlying Event, and Hadronization with Factorization

An essential part of high-energy hadronic collisions is the soft hadronic activity and underlying event which occur in addition to energetic radiation from the primary hard interaction, and in the same proton-proton collision. In principle, there are three sources of such soft hadronic activity: soft radiation from the primary hard partons, secondary multiple parton interactions (MPI), and factorization violating effects (such as nonfactorizable effects from spectator interactions or beam remnants). The invariant mass spectrum of the leading jet in Z+jet and H+jet events has a direct sensitivity to these effects. We use a QCD factorization theorem to predict properties of both the perturbative and hadronization components of soft radiation and show how to distinguish soft initial state radiation (ISR) from MPI models using the jet radius, jet pT, and different channels.

Speaker: Wouter Waalewijn (Nikhef/UvA)

Slides scet14_waalewijn.pdf

17:00 Toward Multi-Differential Cross Sections: Measuring Two Angularities on a Single Jet

We present a first study of the double differential cross section of two angularities measured on a single jet. We show that the cross section factorizes on the boundaries of phase space, but can not be factorized into soft and collinear modes in the bulk of the phase space. Nevertheless, we are able to interpolate between the boundaries of the phase space to next-to-leading logarithmic accuracy subject to numerous constraints on the cross section and show that it is unique to order alpha_s^4. We compare to Monte Carlo and find qualitative agreement.

Speaker: Andrew Larkoski (MIT)

Slides SCET_Larkoski.pdf

17:30 Factorization and resummation for transverse thrust

A large class of event shape variables for hadron colliders has been defined and studied in a series of papers by Banfi, Salam, and Zanderighi. Those are analogous to the ones in leptonic collisions, but involve only the components of the momenta in the plane transverse to the beam direction. We analyze the simplest of those variables: transverse thrust, within SCET for the first time. We start by discussing transverse thrust in leptonic collisions, as an initial simplified case, and then move to hadronic collisions. We put forward a factorization theorem, compute the relevant soft and jet functions at one loop, and discuss resummation. We can compare, and check, our results for the leptonic case with fixed-order results obtained with EVENT2, and extract two-loop anomalous dimensions which are needed in the hadronic case.

Speaker: Xavier Garcia Tormo (Universität Bern)

Slides SCET14_tormo.pdf

Thursday 27 March

09:00 → 10:40 Session 5

Convener: Christian Bauer (LBNL)

09:00 Non-global logs to 3, 4, 5 and maybe 6 loops

I'll discuss the structure of leading non-global logarithms to all orders, and describe simplifications which allow the coefficients to be computed analytically.

Speaker: Prof. Matthew Schwartz (Harvard)

Slides https://www.youtube.com/watch?v=JX3VmDgiFnY SCET-NGLs-Schwartz.pdf

09:40 Resumming Phase Space Logarithms in Jet Shape

Distinguishing quark-initiated and gluon-initiated jets at the LHC has been one of the most important problems in jet physics studies. Jet shape probes the energy distribution inside a jet and is a useful observable in quark-gluon discrimination. The theoretical calculation of jet shape suffers from large logarithms of phase space cuts, in particular, log r/R where r and R are two hierarchical angular scales in the jet shape definition. We resum these global logarithms to next-to-leading logarithmic order accuracy (NLL_p) using soft-collinear effective theory. We also compare with the recent CMS differential jet shape measurement and get nice agreement.

Speaker: Dr Yang-Ting Chien (LANL)

Slides SCET2014.pdf

10:10 Recoil Free Observables

The effects of soft recoil not only complicate the form of a factorization theorem for a jet observable, but can also make effect various observables discrimination power for physics signals. Several observables that are inherently soft recoil free will be presented, regardless the virtuality of the soft radiation, and a precise operator definition of recoil freedom will be given. These observables come with a tunable parameter, allowing one to sweep through a range hierarchies of invariant mass scales between the jet and soft sectors. This allows one to connect rapidity divergences and resummation with traditional SCETI style resummation, and explore a kinematic regime where the jets have virtuality less than the soft radiation, hitherto unexplored in SCET factorization.

Speaker: Dr Duff Neill (MIT)

Slides SCET_2014_Recoil_Free.pdf

10:40 → 11:10 Coffee break

11:10 → 12:40 Session 6

Convener: Christopher Lee (LANL)

11:10 Soft-Collinear Factorization to All Orders

We provide a precise statement and proof of soft-collinear factorization to all orders in perturbation theory. Factorization is formulated as the equivalence at leading power of an amplitude in QCD and another amplitude in QCD computed from the product of independent operator matrix elements. The equivalence is regulator-independent and gauge-independent. This formulation relates any amplitude in QCD to the same amplitude with additional soft of collinear particles. Although the proof is self-contained, it combines techniques developed for the study of pinch surfaces, scattering amplitudes, and effective field theory. The factorization formula includes an operator definition of the zero-bin subtraction and unifies elements of SCET_I and SCET_II.

Speaker: Ilya Feige (Harvard University)

Slides SCET2014_Ilya.pdf

11:40 Anomalous power corrections

arXiv:1312.5327 [hep-ph]

Speaker: Guido Bell (University of Oxford)

Slides SCET14.pdf

12:10 Using the SCET framework for analysis of subleading power corrections in hard exclusive processes

We consider application of the SCET framework for analysis of the subleading power contributions for large angle exclusive production of pion pairs in the photon photon scattering. The cross sections for this process for sufficiently large values of energy and momentum transfer were measured by BELLE collaboration few years ago. The obtained data show a substantial deviation from the theoretical predictions based on the leading twist factorization formula. The possible explanation of this discrepancy is related with the large contribution of the so-called soft-overlap contribution. We used the SCET framework in order to perform an analysis of the corresponding subleading power corrections. In my presentation I want to focus attention on some problems which arises on this way and discuss their possible solutions. The phenomenological results will be also presented.

Speaker: Dr Nikolay Kivel (Helmholtz Institute Mainz)

Slides Kivel_SCET2014.pdf

12:40 → 14:00 Lunch break

14:00 → 16:00 Session 7

Convener: Frank Tackmann (DESY)

14:00 Phenomenological results for TMDs using SCET

In this talk I will report on latest results on Transverse Momentum Distributions using SCET. The discussion will include phenomenological analysis of Drell-Yan, Z-boson production and fragmentation. Future new lines of research will be also pointed out.

Speaker: Ignazio Scimemi (Universidad Complutense Madrid)

Slides SCET2014.1.pdf

14:30 Transverse Parton Distribution Functions at Next-To-Next-To-Leading-Order

I present a perturbative calculation of the transverse parton distribution functions for all partonic channels up to next-to-next-to-leading-order. Their gauge invariant operator definition proposed in SCET is supplemented by an analytic regulator on top of the dimensional one to control rapidity singularities. Demonstrating the cancellation of these divergences in physical observables at next-to-next-to-leading-order, I explicitly verify that the definition of transverse parton distribution functions is applicable beyond the first non-trivial order. I extract the coefficient functions relevant for a next-to-next-to-next-to-leading logarithmic transverse momentum resummation in a large class of processes at hadron colliders.

Speaker: Thomas Luebbert (University of Hamburg)

Slides Talk_Scet2014_TPDFsAtNNLO_ThomasLuebbert.pdf

15:00 Numerical SCET computations with Madgraph

SCET is a powerful tool, but complete analytic calculations using it are difficult. Jet mass has been computed, but 2- and 3-jet final states are nearly prohibitively difficult due to the complicated phase space integrals involved. But we observe that Monte Carlo generators already exist to do exactly these integrals numerically. We can use current parton-level generators (e.g. Madgraph) to sample the phase space integrals. We hope to use Madgraph to extend the practical reach of SCET by calculating LHC distributions for various 2-jet final states, and potentially extend it to 3 jets and more.

Speaker: David Farhi (Harvard University)

Slides S7-SCET_Farhi.pdf S7-SCET_Farhi.pptx

15:30 Fully massive thrust distribution

Results for the full quark mass dependence of the thrust distribution at NNLL order are presented. They apply for arbitrary quark masses, c.m. energies and the entire thrust distribution including the peak and tail region. The approach is based on the combination of five different field theoretic setups concerning the singular contributions, accounts for the summation of all logarithmic terms (all possible hierarchies concerning the hard, collinear and soft scale as well as the quark mass) and also deals with using a properly defined scale-dependent short-distance quark mass and gap scheme. The results represent a nontrivial strongly mass-dependent jet observable that can be used to measure heavy quark masses without replying on MC generators. There is an overlap to another proposed talk concerning the top mass from the MIT group, which focuses on the peak region, that represents one of the field theory set ups discussed here. The two talks are however, orthogonal, as this presentation focuses on aspects that are relevant for describing all kinematic situations in a coherent way.

Speaker: Prof. Andre Hoang (University of Vienna)

Slides Hoang_MassiveThrust.pdf

16:00 → 16:30 Coffee break

16:30 → 18:10 Session 8

Convener: Dr Thomas Mehen (Duke University)

16:30 Reggeization from Renormalization

In this talk I will study a basis of SCET operators which describe forward scattering and explain how, among other things, the renormalization of these operators yields the reggeization of the gluon.

Speaker: Prof. Iain Stewart (MIT)

17:10 The Regge limit of gauge amplitudes at two loops and beyond

The high-energy factorization of gauge theory scattering amplitudes in terms of universal impact factors and a Reggeized exchange in the t-channel, corresponding to a Regge pole in the angular momentum plane, is know to conflict with the structure of soft anomalous dimensions starting at the two-loop level. We explore the implications of this violation of factorization for two- and three-loop QCD amplitudes: first we propose criteria to organize the amplitudes into factorizing and non-factorizing terms, then we test them by recovering a known result for non-logarithmic terms at two loops. Finally we predict the precise value of the leading non-factorizing energy logarithms at three loops, and we uncover a set of all-order identities constraining infrared finite terms in quark and gluon amplitudes.

Speaker: Dr Leonardo Vernazza (INFN and Turin University)

Slides SCET2014-b.pdf

17:40 Theory of Double Parton Scattering

Double parton scattering (DPS) is the process in which two distinct pairs of partons hard scatter in an individual proton-proton collision. It can be an important background to single scattering processes suppressed by small or multiple coupling constants (e.g. new physics signals), and can reveal novel information about the proton structure. I review recent developments in the endeavour to describe this process theoretically using a 'hard scattering factorisation' framework, including my own work in the field.

Speaker: Dr Jonathan Gaunt (DESY)

Slides SCET2014_talkGaunt.pdf

19:30 → 22:00 Conference Dinner

Friday 28 March

09:00 → 10:40 Session 9

Convener: Zoltan Ligeti (LBL)

09:00 Effective field theory formalism and applications for dark matter

Employing induced representations of the Lorentz group (Wigner's little group construction), formalism for constructing heavy particle effective Lagrangians is developed, and Lagrangian constraints enforcing Lorentz invariance of the S matrix are derived. The relationship between Lorentz invariance and reparameterization invariance is established and it is shown why a standard ansatz for implementing reparameterization invariance in heavy fermion effective Lagrangians breaks down at order 1/M^4. Formalism for fields of arbitrary spin and for self-conjugate fields is presented, and the extension to effective theories of massless fields is discussed. We present formalism necessary to determine weak-scale matching coefficients in the computation of scattering cross sections for putative dark matter candidates interacting with the Standard Model. Particular attention is paid to the heavy-particle limit. A consistent renormalization scheme in the presence of nontrivial residual masses is implemented. Two-loop diagrams appearing in the matching to gluon operators are evaluated. Details are given for the computation of matching coefficients in the universal limit of WIMP-nucleon scattering for pure states of arbitrary quantum numbers, and for singlet-doublet and doublet-triplet mixed states. Based on 1208.0601, 1309.4092 and 1401.3339, with Solon and Heinonen

Speaker: Prof. Richard Hill (University of Chicago)

Slides SCET_hill.pdf

09:40 RG-improved fully differential predictions for top-pair production at hadron colliders

We present the combination of approximate-NNLO predictions for top-pair production with a fully-differential parton-level Monte Carlo describing the production and semi-leptonic decay of top quarks at NLO. Differences between our Monte Carlo implementation and results available in the literature will be discussed and comparisons will be made, both for inclusive cross-sections as well as distributions.

Speaker: Dr Andrew Papanastasiou (DESY)

Slides papanastasiou.pdf

10:10 The Complete Two-Loop Soft Function For Top Anti-Top Production At Electron Positron Colliders

In this talk, we describe in a detail a recent calculation of the two-loop soft function for top anti-top production at electron positron colliders. Our calculation allowed us to identify two important, previously unknown properties of squared matrix elements of pairs of massive soft Wilson lines. In particular, we demonstrate the applicability of Henn auxiliary systems to the calculation of the relevant phase space integrals and show that there exists a remarkably simple relation between the soft function considered in this talk in the limit that beta goes to one and the analogous soft function with massless Wilson lines.

Speaker: Dr Robert Schabinger (Johannes Gutenberg Universitaet)

Slides SCET2014talk.pdf

10:40 → 11:10 Coffee break

11:10 → 12:40 Session 10

Convener: Prof. Iain Stewart (MIT)

11:10 Qjets in SCET

Speaker: Andrew Hornig (LANL)

Slides SCET2014.key.zip SCET2014.pdf

11:40 SCET for boosted top production

In this talk we review an effective-theory approach for factorization and resummation of QCD effects in differential cross sections for top-quark pair production at hadron colliders in the double soft and small-mass limits.

Speaker: Pecjak Ben (IPPP Durham)

Slides SCET_14.pdf

12:10 Precision measurement of the top quark mass

We show how a precision result for the top quark mass can be obtained by measurement of the single top jet mass in collider situations. Using the factorization theorm for the double differential jet mass distribution in electron positron to top and antitop I compute the cross sectionat NNLL' order, which includes O(\alpha_s^2) Hard, Jet, and, Soft functions, as well as renormalon subtractions. I will also talk about extensions of the problem to the proton proton collider case.

Speaker: Aditya Pathak (Massachusetts Institute of Technology)

Slides SCET14_v2.pdf

12:40 → 14:00 Lunch break

14:00 → 15:30 Session 11

Convener: Thomas Becher (Bern University)

14:00 Asymptotics and Perturbative Constraints of the B-Meson LCDA

The description of the B-meson light-cone distribution amplitude (LCDA) based on the recently found eigenfunctions of the evolution kernel allows for several new and interesting findings. Small and large momenta no longer mix in this framework, and therefore perturbative constraints from a short-distance expansion of moments by Lee and Neubert can be implemented independently from modelling of long-distance effects. The tail of the distribution can be resummed, which corrects the previous orthodoxy. I will discuss the generic construction of LCDA models and the implication for the first inverse moment -- and logarithmic modulations thereof -- that enter factorization theorems of B decays.

Speaker: Dr Bjorn O. Lange (Siegen University)

Slides S11-lange.pdf

14:30 Fragmentation functions in Quarkonium Production

At the highest possible transverse momenta at the LHC, quarkonia production should be dominated by fragmentation. I review recent developments in the calculation of quarkonium fragmentation functions using Non-Relativistic QCD (NRQCD) and SCET, including both single and double parton fragmentation functions. I also apply the newly developed fragmenting jet functions to quarkonium to assess whether the measurement of the momentum fraction of quarkonia within jets can distinguish between color-singlet and color-octet production mechanisms.

Speaker: Dr Thomas Mehen (Duke University)

Slides SCET2014.key SCET2014.pdf

15:00 SCET_G-based leading particle and jet phenomenology in heavy-ion collisions at the LHC

In the past several decades, advances in the theory of strong interactions can be traced through theoretical and experimental developments in understanding particle and jet production in high-energy collider experiments. More recently, the strong suppression of the cross sections for these processes in heavy ion collisions at RHIC and the LHC energetic particle and jet production in has been used to extract the properties of the QGP. In this talk I will describe the connection between the traditional energy loss approach to jet quenching and the evolution approach, based upon the medium-induced splitting kernels derived in an effective theory of jet propagation in matter, SCET_G. I will further show how the study of the internal structure of the medium-induced parton showers allows to predict and interpret the modification of jet observables in nucleus-nucleus collisions at the LHC.

Speaker: Dr Ivan Vitev (LANL)

Slides SCET_Vitev_2014.pdf

15:30 → 16:00 Coffee