SCET 2024

Apr 15, 2024, 8:40 AM → Apr 18, 2024, 4:00 PM Europe/Madrid

Salón de Actos (Salamanca, Colegio Arzobispo Fonseca)

Vicent Mateu (University of Salamanca), María Teresa Fernández Caramés (USAL), German Sborlini (USAL), Ignazio Scimemi (Universidad Complutense Madrid), Clara Peset (Madrid University), Miguel Benitez-Rathgeb (Universidad de Salamanca), Alberto Martín Clavero (University of Salamanca (USAL))

The XXI annual workshop on Soft-Collinear Effective Theory will take place in Salamanca (Spain), April 15-18, 2024 at Colegio Arzobispo Fonseca. The goal of the workshop is to bring together researchers interested in SCET, resummation and (non)perturbative QCD, to discuss the latest developments and their applications to particle and nuclear physics.

To ensure an informal atmosphere with plenty of time for discussion, attendance is limited to 80 participants. All talks will last 20 minutes, followed by 10 minutes of discussion.

For those interested in giving a talk, please submit an abstract through Indico. Be advised that talks are by invitation only, and submitting an abstract does not guarantee a slot for a talk. If you would like to suggest a talk, please email the organizers.

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The Conference will be held in April 15-18 2024 at Colegio Arzobispo Fonseca, belonging to the University of Salamanca. Lectures will take place at Salon de Actos.

Sponsors

               

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Reserva-English.pdf

Mon, April 15

8:40 AM Registration

9:00 AM Welcome

Session 1: heavy quarks

Chair: Vicent Mateu

1 Endpoint factorization for inclusive semileptonic top quark decays in off-shell boosted top quark production

In this talk we discuss a factorization for the $e^+e^-$ 2-jettiness distribution in the resonance region for boosted top quark pair production where the top quark descays semileptonically, and where we also measure leptonic distributions in the endpoint region where the bottom jet invariant mass is small. This multivariate distribution combines the known factorization theorems for inclusive dijet massive quark event-shapes in the resonance region and semileptonic heavy meson decays in the endpoint region. The novel ingredient in this factorization is an ultracollinear soft function that presents a differential generalization of the known bHQET inclusive jet function for the 2-jettiness factorization and, at the same time, a generalization of the known shape function for heavy meason decays, where the top quark state is defined through the jettiness measurement. Due to the finite top quark width the ultracollinear soft function can be computed in perturbation theory.

Speaker: Regner Christoph (University of Vienna)

SCET_2024_Regner.pdf

2 Progress in Understanding Heavy Quark Fragmentation in the Transverse Plane

I discuss ongoing progress in the understanding of heavy-quark transverse momentum-dependent (TMD) fragmentation functions (FFs). These advances include their explicit next-to-leading order calculation in massive SCET and bHQET, exposing a rich singularity structure that is also relevant for the extension of fixed-order subtraction schemes to quasi-collinear limits. I further present how many independent nonperturbative bHQET functions are needed to fully characterize heavy-quark fragmentation in the transverse plane, accounting -- for the first time -- for arbitrary heavy hadron polarization. This analysis exposes powerful spin symmetry relations across all possible (polarized) TMD FFs. I close by discussing prospects for interpreting these novel bHQET matrix elements in the context of quantum information theory as applied to hadronization.

Speaker: Johannes Michel (University of Amsterdam, Institute of Physics)

2024-04-15_SCET_heavy_quarks_Johannes_Michel.pdf

3 A Blueprint for Controlling the Monte-Carlo Top Quark Mass Scheme

To control the scheme of the Monte-Carlo (MC) top quark mass parameter several ingredients are mandatory, concerning the knowledge of the infrared dynamics of the top mass sensitive observable, the MC parton shower and the MC hadronization evolution. I discuss these ingredients and their interplay for the simple case of 2-jettiness for boosted top production in electron-positron annihilation, where these ingredients are now all known for the Herwig MC. Apart from having an at least NLL precise parton shower, which Herwig can provide for event-shapes, a crucial novel development is a SCET-QCD factorization compatible hadronization model, which I describe in some detail. The outcome is that for 2-jettiness the Herwig top mass mass parameter now represents a well defined and shower cut dependent renormalization scheme that can be quantified and controlled at NLO prediction. The approach I discuss represents a blueprint for controlling the scheme of the MC top mass parameter that can in principle be also applied to direct top quark mass measurements, even though there is still some way to get there.

Speaker: Andre Hoang (University of Vienna)

SCET-2024-Hoang-MCtopmass.pdf

11:00 AM Coffee Break

Session 2: heavy quark-glaubers

Chair: HuaXing Zhu

4 Factorization and resummation of the heavy quark pair angular decorrelation

We present a comprehensive theoretical investigation of the angular decorrelation of heavy quark pairs in electron-positron ($e^+e^-$) and electron-proton ($ep$) collisions. Emphasizing the back-to-back limit in $e^+e^-$ collisions, we highlight the necessity of a Transverse Momentum Dependent (TMD) factorization and resummation theorem for heavy quark pair production. Our study introduces a framework that extends beyond the traditional two-scale (hard scattering scale $Q$ and TMD scale $q_T$) approach of the Drell-Yan or Semi-Inclusive Deep Inelastic Scattering (SIDIS) processes, by incorporating a third scale - the heavy quark mass $m_\mQ$. We analyze three distinct scale hierarchies: $Q \gg m_\mQ \sim q_T$, $Q \gg m_\mQ \gg q_T$, and $Q \sim m_\mQ \gg q_T$, applying soft-collinear effective theory (SCET), boosted Heavy Quark Effective Theory (bHQET) and Heavy Quark Effective Theory (HQET) as appropriate. The theoretical framework is adapted to each scenario, considering the varying degrees of heavy quark boosting. The results are verified through asymptotic expansions in different scale regimes, aligning with theoretical expectations.

Speaker: Dingyu Shao (Fudan University)

scet_shao.pdf

5 Regge Amplitudes from Glauber SCET

The high energy (Regge) limit provides a playground for understanding all loop structures of scattering amplitudes, and plays an important role in the description of many phenomenologically relevant cross-sections. While well understood in the planar limit, the structure of non-planar corrections introduces many fascinating complexities, for which a general organizing principle is still lacking. In this talk, I discuss the structure of multi-reggeon exchanges in the context of the effective field theory for forward scattering (Glauber SCET), and their factorization into collinear operators and soft operators, providing a clear organization for non-planar terms. I then discuss the solutions of the rapidity RG evolutions in different color channels.

Speaker: Anjie Gao (MIT)

Anjie_SCET24.pdf

6 Towards NLO-BFKL from Glauber-SCET

The high energy limit of QCD is a storehouse of rich phenomenology. In this limit, perturbative series receive logarithmic (small-$x$) enhancements associated with wide-rapidity separations necessitating their all-order resummation. However, reliably and comprehensively incorporating the NLL corrections associated with this limit consistent with collinear resummation and PDF factorization has been a longstanding challenge. Existing approaches rely somewhat heavily on the simplifications that break down beyond leading logarithmic accuracy, making their higher-order extension challenging.

In this talk, I will describe recent progress in tackling this problem using the Glauber extension of SCET. In previous work [JHEP 09 (2023) 089], a factorization theorem for small-$x$ resummation in DIS was derived, that involved a universal process-independent collinear function and a process-dependent soft function. This work constitutes the first resummation in the high energy limit and has provided a promising approach for higher-order extension. In this talk, I will focus on the two-loop computation of the collinear function whose rapidity evolution is governed by the BFKL equation. The two-loop result thus gives direct access to the NLO BFKL kernel and provides a strong cross-check of the calculation by Fadin and Lipatov in 1998. Given the importance of keeping track of rapidity divergences, this result cannot be extracted reliably from a QCD process and necessitates automation of (Glauber) SCET Feynman rules and diagrams. I will further show how exploiting the Glauber Collapse Rule enables us to efficiently filter out a small subset of diagrams and master integrals, making an otherwise daunting calculation tractable.

Speaker: Aditya Pathak (DESY)

scet_24_pathak.pdf

1:00 PM Lunch

Session 3: glaubers

Chair: Alexey Vladimirov

7 RG-Improved Resummation of Super-Leading Logarithms

The higher-order behavior of logarithmically enhanced contributions in non-global observables is very intricate, in particular as double-logarithmic corrections arise first at high orders in perturbation theory. The resummation of these super-leading logarithms (SLLs) is extended by including the running of the strong coupling $\alpha_s(\mu)$, i.e. in RG-improved perturbation theory. This is done by using a new representation of the evolution operator, also allowing to show that higher order Glauber exchanges are parametrically suppressed. Working in the large-$N_c$ limit, it is possible to resum these higher-order Glauber exchanges to all orders for processes with quarks and/or gluons in the initial state.

Speaker: Michel Stillger (JGU Mainz)

SCET_2024_Stillger.pdf

8 Exclusive leptonic B decays at sub-leading power : factorization theorems for virtual structure-dependent QED effects and real corrections.

In this talk, I will present progress on the computation of the leptonic $B^- \rightarrow \ell^- \bar{\nu}_\ell$ decay in SCET. Above the confinement scale $\Lambda_{\rm QCD}$, we describe the virtual QED corrections of the decay with an EFT construction based on $\text{SCET}_{\rm I}\otimes \text{HQET}$ where both hard collinear and collinear modes are treated as independent degrees of freedom. Matching this theory to $\text{SCET}_{\rm II}\otimes \text{HQET}$, we refactorize the end-point divergent contribution and derive the order $\mathcal{O}(\alpha)$ contributions of the decay amplitude involving two- and three-particles Light-cone distribution amplitudes (LCDAs) of the B meson. We derive a factorization theorem for virtual corrections at the amplitude level and express virtual corrections in an effective Yukawa coupling. Below $\Lambda_{\rm QCD}$, we match the partonic picture to a low-energy EFT based on a combination of heavy meson EFT (HMET) and boosted heavy lepton EFT (bHELT). We demonstrate that, depending on the cut on final state radiation and on the lepton flavor, the real emission contribution from excited states of the B meson can become important and must be included in the low-energy EFT description.

Speaker: Max Ferré (JGU)

FERRE_SCET2024.pdf

4:00 PM Coffee Break

Session 4: B-physics

Chair: Guido Bell

9 $B_c \to \eta_c$ form factors at large recoil: interplay of soft-quark and soft-gluon double logarithms

At next-to-leading power, predictions in Soft-Collinear Effective Theory often suffer from a technical problem, known as endpoint-divergent convolution integrals. While this problem has recently been overcome for some processes, these methods are currently limited to examples with non-recursive refactorsation identities. As I will show in this talk, exclusive heavy-to-light transition form factors do not belong to this class. We therefore resort to diagrammatic resummation techniques to derive the double-logarithmic series of the so-called “soft-overlap” contribution to $B_c \to \eta_c$ form factors at large hadronic recoil (assuming the scale hierarchy $m_b \gg m_c\gg \Lambda_{\rm QCD}$). We find that the leading double logarithms arise from a peculiar interplay of soft-quark “endpoint logarithms” from ladder diagrams with energy-ordered spectator-quark propagators, as well as standard Sudakov-type soft-gluon corrections. We elucidate the all-order systematics, and show that their resummation proceeds via a novel type of integral equations.

Speaker: Dennis Horstmann (Siegen University)

SCET-2024-Horstmann.pdf

10 Factorization and Resummation for Sequential Recombination Jet Cross Section

We extend the class of factorization theorems for non-global observables from fixed angular constraints to cross sections defined in terms of sequential jet clustering. The associated hard and soft functions depend not only on the directions of the hard partons, but also on their energy fractions. We derive the one-loop anomalous dimension of the hard functions that drives the leading-logarithmic resummation. The anomalous dimension imposes energy ordering, which simplifies the clustering sequence. We perform resummations for gap-between-jet observables defined with different jet algorithms and explain the effects of the clustering on the importance of secondary emissions and on the effective gap size.

Speaker: Jürg Haag (UZH)

Haag_Jurg_Clustering_Logs.pdf

5:30 PM Free time

8:00 PM Welcome Cocktail

Tue, April 16

Session 5: alphaS determinations

Chair: Thomas Becher

11 Assessment of $\alpha_s(m_Z)$ fits from $e^+e^−$ Event Shapes accounting for 3-Jet Power Corrections

In recent articles, the discussion on the treatment of Power Corrections in the three-jet limit, along with its influence on precision $\alpha_s$ determinations from fits to event shape experimental data, has attracted a lot of attention. On the basis of a factorization formula for the $e^+e^-$ thrust distribution, derived within soft-collinear effective theory, we discuss the treatment of Power Corrections in the tail region of the spectrum and the problems connected to it. In addition, we review past studies on the strong coupling determination from event shapes carried out by some of us, and provide updated results produced with a new numerical code which incorporates recent theoretical developments. Furthermore, we show the mild effect caused by the tau-dependent power correction recently advocated for in the literature.

Speaker: Miguel Benitez-Rathgeb (Universidad de Salamanca)

Benitez_SCET-2024.pdf

12 Revisiting strong-coupling determinations from $e^+e^-$ event shapes

We explore systematic effects of renormalon cancellation schemes and perturbative scale choices on extractions of the strong coupling constant $\alpha_s(m_Z)$ and the leading non-perturbative shift parameter $\Omega_1$ from resummed predictions of hadronic event shapes in electron-positron collisions. Our analysis is based on thrust distributions to N$^3$LL$'$ accuracy in resummed perturbation theory using Soft Collinear Effective Theory, both matched to the most accurate available fixed-order predictions in QCD. We test the phenomenological impact sourced from varying amongst different renormalon cancellation schemes and sets of perturbative scale profile choices. We then perform a global fit to available data spanning center-of-mass energies between 35--207 GeV. Our results are consistent with prior SCET-based extractions of $\alpha_s(m_Z)$, but we are also led to a number of novel observations. Notably, we find that the combined effect of altering the renormalon cancellation scheme and profile parameters can lead to increased uncertainties on the extracted values in the $\alpha_s-\Omega_1$ plane. We also observe that fits performed over windows dominated by dijet events are typically of a higher quality than those that extend into the far tails of the distributions, motivating future fits focused more heavily in this region. We conclude with the potential of new strategies to mitigate these systematic effects and improve the precision of event-shape-based determinations of $\alpha_s(m_Z)$ and $\Omega_1$.

Speaker: Prof. Guido Bell (University of Siegen)

SCET24_Bell.pdf

13 Theory Uncertainties and Correlations from Theory Nuisance Parameters

The interpretation of precision measurements requires theory predictions with reliable and meaningful uncertainties and in particular correct correlations. Theory correlations are for example essential when fitting to differential spectra, but our default scale-variation-based methods, among their many shortcomings, are incapable of providing correct correlations. This is becoming a severe limitation in many precision studies.
Theory nuisance parameters (TNPs) overcome the limitations of scale variations.
After reviewing their basic idea (which was put forward some time ago), I will present as an example a concrete application of TNP-based uncertainty estimates for the resummed Drell-Yan $p_T$ spectrum, demonstrating how TNPs capture the correlations across the $p_T$ spectrum and between Z and W production. I will also show more generally that TNPs can provide statistically meaningful theory uncertainties.

Speaker: Frank Tackmann (DESY)

2024-04_16_SCET_TNPs.pdf

14 Extracting $\alpha_s$ from the Z $p_T$ spectrum

We study the extraction of $\alpha_s$ from the $Z$ boson $p_T$ spectrum at low $p_T$ using resummed predictions up to N$^4$LL.
Recently, the ATLAS collaboration presented a new extracted value for $\alpha_s$ which has been somewhat controversial due to its rather small theoretical uncertainties.
We study in detail the various sources of uncertainty, including the perturbative uncertainty, the one related to the nonperturbative model chosen, and the one associated with the parton distribution functions (PDF) considered.

Speaker: Giulia Marinelli (DESY)

marinelliscet.pdf

11:00 AM Coffee Break

Session 6: next-to-leading power

Chair: Gherardo Vita

15 Position-space renormalization of subleading-power soft-quark functions

The renormalization-group (RG) kernel for the next-to-leading power soft-quark function relevant to Higgs production in gluon-gluon fusion has up-to-now been inferred only from RG consistency of the factorization formula. In this talk the direct computation with position-space techniques is discussed, which reveals some subtleties related to incoming colour charges from "infinity". For the case of external photons, the kernel turns out to be essentially the "double copy" of the leading-twist static B-meson LCDA, to all orders in perturbation theory.

Speaker: Martin Beneke (TUM)

salamanca.pdf

16 Subleading power corrections to the color-singlet transverse momentum spectrum

One of the computational bottlenecks in state-of-the-art QCD NNLO calculations matched to resummation is the computation of the non-singular contributions to the spectrum of the given resolution variable (for example, the transverse momentum $q_T$ of the color singlet).

While we have a vast set of tools for computing and resumming the singular contributions, the non-singular ones are still typically obtained from the numerical difference between the full-QCD spectrum and the NNLO expansion of the singular contributions. In practice, this implies pushing the full-QCD NLO calculation for the process with one more jet up to very low $q_T$ values, where the cross section is logarithmically enhanced and the large cancellations between the two spectra leave us with large statistical errors.

The analytical knowledge of the expansion of the full-QCD spectrum beyond the $q_T$ leading power would allow us to approximate the non-singular contributions in the small $q_T$ limit, thus eliminating the need for a numerical subtraction up to such low values of the resolution variable. In this talk, I will present a systematic way to calculate such power corrections up to NNLO within the SCET formalism.

Speaker: Alessandro Gavardi (Deutsches Elektronen-Synchrotron DESY)

Gavardi_2024_SCET.pdf

17 Systematic one-loop matching at subleading power on SCET$_{\rm II}$

A crucial step in the investigation of subleading-power corrections is the process-dependent matching from QCD onto SCET$_{\rm II}$. In this matching, one often first performs the hard matching to SCET$_{\rm I}$ and in a second step matches onto SCET$_{\rm II}$.
However, the matching from SCET$_{\rm I}$ to SCET$_{\rm II}$ is process-independent, and thus lends itself to a systematic investigation. These universal matching relations then provide a basis for numerous applications to next-to-leading power SCET$_{\rm II}$ observables.

In this talk, I provide an overview of the one-loop matching at subleading power in SCET$_{\rm II}$.
To facilitate this matching, it proves useful to consider an effective Lagrangian encompassing both hard-collinear, collinear and soft modes. This Lagrangian can be constructed systematically to all-orders along the same lines as the usual SCET$_{\rm I}$ Lagrangian, but this time with a more involved gauge-symmetry. Additionally, I provide an overview of the novel structures appearing at the one-loop level, and discuss an example matching as a practical application of the Lagrangian.

Speaker: Patrick Hager (MITP, Johannes Gutenberg University Mainz)

SCET24Hager.pdf

1:00 PM Lunch

Session 7: Monte Carlos

Chair: Maximilian Stahlhofen

18 NNLO+PS event generation via jet veto resummation at NNLL'

Vetoes on energetic jets are common in experimental analyses and are used to reject backgrounds which have similar final states to signal processes of interest. In placing a jet veto, however, one introduces large logarithms of the veto scale over the hard scale of the process. I will discuss how the resummation of these logarithms in a SCET approach can be embedded into Monte Carlo event generators which match NNLO calculations to a parton shower algorithm via the GENEVA method. Taking the $W^+W^-$ production process as an example, I will present comparisons to ATLAS and CMS data which show excellent agreement between theory and measurement.

Speaker: Matthew Lim (University of Sussex)

SCET2024Lim.pdf

19 N$^3$LL resummation of one-jettiness for Z-boson plus jet production at the LHC

In this talk I will present the resummation of one-jettiness up to N$^3$LL accuracy for the Z+jet production process at the LHC. The resummed calculation is matched to the corresponding fixed-order predictions extending the validity of the results to regions of the phase space where further hard emissions are present. I will show numerical results and discuss the convergence of the different resummation orders.

Speaker: Alessandro Broggio (University of Vienna)

Broggio_SCET24.pdf

4:00 PM Coffee Break

Session 8: QCD and event shapes

Chair: German Sborlini

20 Collinear contributions to QCD resummations

Infrared singular factors originating from the QCD factorisation of scattering amplitudes in soft and collinear limits play an important role both in the organisation and in the calculation of the higher-order contributions to hard scattering cross sections. In this talk I will report on recent work for the evaluation of collinear contributions to QCD resummations of hard scattering observables. We start from the factorisation of squared amplitudes in the collinear limit and introduce fully differential collinear functions that have a process-independent structure. These collinear functions can then be integrated over the corresponding observable-dependent phase space to obtain the logarithmically-enhanced contributions to the observable of interest. For transverse-momentum dependent observables, we show how collinear functions can be defined without introducing what is known as rapidity divergences in the literature. We present analytical expressions for the collinear functions up to next-to-next-to-leading order in perturbation theory.

Speaker: Dr Prasanna K. Dhani (IFIC, University of Valencia - CSIC)

Dhani@SCET24.pdf

21 Towards NLL resummation of angularities with recoil

Jet angularities are a class of substructure observables whose sensitivity to angular distribution of radiation in a jet is controlled by a continuous parameter ‘$b$’ (with, $b > −1$ for IR safety). For $b$ close to $0$, the effect of recoil of collinear emissions due to soft radiations in the jet is a leading power effect while it gets power suppressed as $b$ approaches $1$. In a previous work, we utilized a broadening-like factorization theorem for the whole range of angularity exponents and showed that at the next-to-leading-order accuracy, it effectively reproduces the known results for broadening ($b = 0$) and thrust ($b = 1$). This framework then allows us to understand how recoil effects the distribution of jet angularities and provides, within the effective theory approach, new results for singular cross-sections of angularities between the exponents $0 < b < 1$. However, for a complete phenomenological relevance of these results, one needs to resum the large logarithms in the fixed order results to a next-to-leading-logarithmic (NLL) accuracy. In this talk, I will overview some of the recent developments towards obtaining a NLL resummed result for recoil-sensitive jet angularities.

Speaker: Ankita Budhraja (Nikhef)

Ankita_SCET_2024.pdf

22 Diffractive factorization using effective field theory

Diffractive processes are events with large rapidity gaps, which typically comprise a double-digit percent of events at colliders. Last year I discussed coherent diffraction with an intact scattered proton, whereas in this talk I focus on incoherent diffraction, where the proton is scattered into a jet. We derive the factorization of this process using Glauber SCET, showing that it splits apart into universal soft and hadronic functions. We compare and contrast this factorization to prevailing models in the literature. We further show that in diffractive $ep$ scattering, there are four nontrivial unpolarized (and four polarized) diffractive structure functions at leading order, including the conventionally studied $F_2$ and $F_L$, as well as two less-studied structures that in certain phase space regions comprise a large portion of the cross-section. Our work provides new observables and perturbative predictions for HERA and the EIC, and lays a path forward for studies of broader classes of diffractive processes, including at the LHC.

Speaker: Kyle Lee (MIT)

SCET_diffraction.pdf

6:00 PM Free time

8:30 PM Conference Dinner

Wed, April 17

Session 9: TMDs-I

Chair: Alessandro Broggio

23 Transverse Momentum Moments: The interplay between TMDs and PDFs

In this talk, I establish relations between Transverse Momentum Dependent distributions (TMDs) and collinear distributions (PDFs) by defining and analyzing Transverse Momentum Moments (TMMs), which are weighted integrals of TMDs. I discuss the zeroth, first, and second TMMs and present phenomenological results based on current TMD extractions. Furthermore, it is demonstrated that TMMs are equivalent to collinear distributions evaluated in a minimal subtraction scheme, with a calculable factor enabling conversion to the MS-bar scheme. Therefore, the presented framework offers promising prospects for simultaneous extractions of TMDs and PDFs in future studies.

Speaker: Óscar del Río García (Universidad Complutense Madrid)

Transverse Momentum Moments SCET24 Oscar.pdf

24 Factorization for $J/\psi$ lepto-production at small $p_T$

When the quarkonium is produced in the low-transverse momentum region, the contribution of soft and ultra-soft radiation between the heavy-quark pair becomes relevant. At this region, non-relativistic QCD breaks down and we need to promote the long-distance matrix elements to the TMD shape functions (TMDShFs). I am going to talk about the cross-section factorization for the $J/\psi$ lepto-production in terms of these TMDShFs. Additionally, I am going to discuss the evolution of the TMDShFs, the matching onto the LDMEs at high $p_T$ and the hard function of the process.

Speaker: Samuel F. Romera (University of the Basque Country)

SCET24-SFRomera.pdf

25 Kinematic power corrections in TMD factorization

I discuss the general structure of the power expansion in the transverse momentum dependent (TMD) factorization theorem. Different types of power corrections are important in different circumstances. Among them, kinematic power corrections (KPCs) are especially important since they restore charge conservation and frame invariance, which are violated at a fixed power order. I derive and sum a series of KPCs associated with the leading-power term of the TMD factorization theorem, and confirm the factorization properties explicitly at NLO. I also present first phenomenological results with inclusion of KPCs.

Speaker: Alexey Vladimirov (Universidad Complutense de Madrid)

Vladimirov.pdf

26 Semi-Inclusive Energy Correlators and Moment of TMDs

In this talk, I will introduce a novel category of observables known as the semi-inclusive energy correlators (SIECs), an extension of the recently proposed nucleon energy correlator to integrate a new element, the fragmenting energy correlation function. A few applications, including connection to moment of TMD distributions will be presented.

Speaker: HuaXing Zhu (Peking University)

EEC_visualization.mp4

SCET24_Zhu_PDF.pdf

SCET24_Zhu.pptx

11:00 AM Coffee Break

Session 10: TMDs-II

Chair: André Hoang

27 Illuminating Nucleon Gluon Interference via Calorimetric Asymmetry

We present an innovative approach to the linearly polarized gluons confined inside the unpolarized nucleon in lepton-nucleon scattering. Our method analyzes the correlation of energy flows at azimuthal separations $\phi$.The interference of the spinning gluon with both positive and negative helicities translates into a $\cos(2\phi)$ asymmetry imprinted on the detector. Unlike the conventional transverse momentum dependent probes, the $\cos(2\phi)$ asymmetry in this approach is preserved by rotational symmetry, holds to all orders, and is free of radiation contamination, and is thus expected provide the exquisite signature of the nucleon linearly polarized gluons.

Speaker: Xiaolin Li (Beijing Normal University)

SCET2024_xiaolin.pdf

28 Transverse Momentum Measurements with Jets at Next-to-Leading Power

In view of the increasing precision of theoretical calculations and experimental measurements, power corrections to transverse-momentum-dependent observables have become highly important. Power corrections for TMD observables are a rich and complex subject, and are difficult to grasp even in the most simple scenarios. Our goal is to understand TMD factorization at next-to-leading power for a relatively simple case: the semi-inclusive annihilation of an electron and a positron into two jets. By working with jets, everything is perturbatively calculable and there are substantial simplifications compared to the general next-to-leading power framework. We obtain a factorized expression for the cross section and identify the new jet functions that appear at next-to-leading power. As expected, we encounter special rapidity divergences and endpoint divergences. Importantly, our analysis with jets can be extended to semi-inclusive deep-inelastic scattering, with the future Electron-Ion Collider as key application.

Speaker: Max Jaarsma (University of Amsterdam)

SCET_Max_Jaarsma.pdf

29 TMD PDFs in Chiral Effective Theory

We develop a theoretical framework to match Transverse Momentum Dependent (TMD) PDFs onto chiral effective theory operators. A convolution formula is presented between TMD hadronic splitting functions and the high energy matching coefficients, which are identified to be the TMD PDFs of intermediate hadrons in the chiral limit. An operator product expansion is applied to the high energy TMD matching coefficients, allowing them to be written in terms of the collinear valence PDFs of intermediate hadrons. As an example, we calculate the isovector TMD splitting functions for the nucleon at leading order in the chiral expansion and present numerical results.

Speaker: Marston Copeland (Duke University)

TMDs in ChPT SCET.pdf

1:00 PM Lunch

Session 11: factorization

Chair: Johannes Michel

30 Identifying regions in wide-angle scattering and other QCD processes

The method of regions provides not only a systematic approach to computing Feynman integrals, but also useful information of formulating an EFT. For example, the SCET$_{\rm I}$ Lagrangian describing massless wide-angle scattering elegantly combines collinear and ultrasoft modes. This is grounded in the empirical observation that each loop in a pertinent region is either hard, collinear to an external momentum, or ultrasoft. It is then natural to ask the following questions. Are all regions confined to the prescribed types observed in processes like wide-angle scattering? Can other types of regions emerge in other scenarios, e.g., heavy-to-light decay?

This talk aims to answer these questions by drawing from a recent research, arXiv: 2312.14012. For the on-shell expansion and the soft expansion of generic wide-angle scattering, an all-order result is validated: each region involves only the hard mode, collinear modes, and ultrasoft mode, with their interactions following certain structures. For the heavy-to-light decay processes, in contrast, more modes are involved as the loop number increases. We will also discuss high-energy scattering regions, exploring the possibility of the Glauber mode.

Speaker: Dr Yao Ma (Institute of Theoretical Physics, ETH Zurich)

SCET24_YaoMa.pdf

31 Factorization and transverse phase-space parton distributions

In this talk, I would like to present a derivation of the factorization formula for the impact-parameter dependent cross section using Soft-Collinear Effective Theory. Especially, this talk focuses on inclusive hard processes with only colorless final-state products in hadron and nuclear collisions. To describe Such processes, one only needs to replace the beam functions with the Fourier transforms of transverse phase-space parton distribution functions, which are referred to thickness beam functions. The factorization formula is verified up to one loop in perturbative QCD for the inclusive Drell-Yan process in quark-antiquark collisions at a finite impact parameter. Besides, how this discussion could be extended to study jet cross sections in heavy-ion collisions will also be discussed briefly.

Speaker: Bin Wu (Universidade de Santiago de Compostela)

SECT2024_Wu.pdf

4:00 PM Coffee break

Session 12: hadronization

Chair: Ignazio Scimemi

32 Nonperturbative Corrections to Energy Correlators

SCET provides a rigorous framework to perform resummation to obtain high-precision perturbative results for energy correlators, motivating a comprehensive study of the corresponding nonperturbative effects. Furthermore, testing the universality of nonperturbative parameters among different event shape observables is of theoretical interest. Information on nonperturbative power corrections of the energy-energy correlator (EEC) can be extracted from a renormalon analysis. We study the nonperturbative power corrections to the EEC using operator based methods in the framework of SCET, which allow us to relate the nonperturbative correction of the two-point correlator to higher-point correlators.

Speaker: Zhiquan Sun (MIT)

scet24_zsun.pdf

33 Perturbative Evolution of Hadronization Effects in Energy Correlators

50 Years after the establishment of Quantum Chromodynamics (QCD), gaining first-principle comprehension of non-perturbative effects of QCD is still challenging. Lattice QCD methods have made huge progresses in this direction, including calculation of Parton Distribution Functions (PDF). However, the intricate Lorentzian dynamics underlying hadronization effects continue to elude a satisfactory explanation. Event shape observables in collider physics provide an excellent opportunity to investigate these phenomena. Despite the absence of first-principle calculations, enhanced theoretical understanding could offer a way to parameterize these non-perturbative effects.

In this talk, we will present how new theoretical concepts could guide us to parametrize hadronization effects in energy correlators, which are one of the most interesting observables for their universality and nice symmetry structures. In particular, we will focus on the collinear limit where the application of light-ray Operator Product Expansion (OPE) technique become viable. Similar to local operators' role in PDF evolution, light-ray operators govern the evolution of hadronization effects in energy correlators. We conclude by using Monte Carlo simulation data to validate this idea.

Speaker: Hao Chen (Zhejiang University)

SCET_2024_Hao_Chen.pdf

5:30 PM Free time

8:00 PM Visit to the the cathedral towers

Thu, April 18

Session 13: heavy ions and DIS

Chair: Christopher Lee

34 Anisotropic jet substructure observables for flowing matter

High-energy nuclear collisions offer a captivating glimpse into the creation and evolution of strongly coupled plasmas. Within these collisions, droplets of the quark-gluon plasma (QGP), a state of matter believed to have permeated the early universe, are generated. These droplets of the QGP quickly expand but their flow is azimuthal anisotropic and thus these processes offer insight into the dynamics interactions between the evolution of the plasma and the evolution of jets that probe the plasma. In this talk, I'll discuss the use of anisotropic jet substructure observables as a means of investigating anisotropically flowing matter. Using Soft-Collinear Effective Theory, we explicitly calculate the jet functions associated with these observables and apply them to p-p and A-A collisions. We demonstrate the fidelity of our formalism in p-p collisions by comparing each observable with experimental measurements at the LHC for the isotropic case. By introducing a model for the anisotropic flow, we demonstrate that each of these observables can serve as a novel probe of a strongly coupled flowing matter.

Speaker: John Terry (LANL)

Terry-SCET.pdf

35 QED nuclear medium effects in neutrino-nucleus and electron-nucleus scattering

The exchange of photons with nuclear medium modifies (anti)neutrino and electron scattering cross sections. We study the distortion of (anti)neutrino-nucleus and charged lepton-nucleus cross sections, medium-induced bremsstrahlung, and estimate the QED-medium effects on the final-state kinematics and scattering cross sections. We find new permille-to-percent level effects, which were never accounted for in either (anti)neutrino-nucleus or electron-nucleus scattering. We quantitatively compute the effects of Glauber photon-mediated multiple re-scattering within the nuclear medium and find that the relativistic charged lepton acquires a momentum of order 10 MeV transverse to its direction of propagation inside the nucleus. This broadening sizably deflects expected electron tracks and suppresses scattering cross sections. Precise extraction of the nucleon and nuclear structure by electron and muon probes should, thus, take the QED nuclear medium angular redistribution of particles into account.

Speaker: Dr Oleksandr Tomalak (Los Alamos National Laboratory)

Tomalak_talk_SCET_April_2024-2.pdf

36 Mass effects in the Higgs $q_T$ spectrum

We investigate finite b-mass effects arising from the bottom-loop in gluon-fusion Higgs production in the Higgs $q_T$ spectrum. In contrast to the cases of the $H \to\gamma\gamma$ decay or the $gg\to H$ form factor investigated previously at amplitude level, in this case the nontrivial b-mass effects are also resolved by real emissions and have to be considered within the context of $q_T$ factorization and resummation.
We consider the various hierarchies between $m_b$ and $q_T$ and $m_H$, leading to different factorization setups.

Speaker: Rebecca von Kuk

qqh-yb-yt.pdf

37 A DIS 1-jettiness event shape at N$^3$LL with power corrections

We present prediction for the DIS 1-jettiness event shape $\tau_1^b$ with next-to-next-to-next-to-leading-logarithmic (N$^3$LL) resummation. Our results include O($\alpha_s^2$) full QCD matched ingredients from a Monte Carlo generator, NLOJET++, and a rigorous treatment of hadronization corrections (power corrections) supplemented with the $R$-gap scheme to make the perturbative distributions free of $O(\Lambda_\textrm{QCD})$ renormalon ambiguities. We design profile scales so that our formulation works over a wide range of kinematic points $x$ and $Q$ which could cover the existing DIS experiment results at HERA as well as the new measurements from the upcoming Electron-Ion-Collider (EIC). Our predictions will serve as an important benchmark in the EIC experimental program and allow the precise determination of the QCD strong coupling and the universal nonperturbative parameter $\Omega_1$.

Speaker: June-Haak Ee (Los Alamos National Laboratory)

SCET2024-JHEE.pdf

11:00 AM Coffee break

Session 14: quark masses and renormalons

Chair: Aditya Pathak

38 Flavor thresholds and quark-mass effects in the Collins-Soper kernel (aka the rapidity anomalous dimension)

We discuss the treatment of finite charm and bottom quark mass effects in the Collins-Soper kernel or equivalently the rapidity anomalous dimension. In particular, we derive a consistent flavor matching relation with different numbers of active flavors. This allows us to properly separate the perturbative contributions due to heavy quarks from the remaining $n_F = 3$ massless contributions. Our results allow for the first time for a fully consistent comparison with the $n_F = 3$ lattice determinations of the Collins-Soper kernel in order to determine its non-perturbative contributions at large distances. We also discuss the corresponding impact of the mass effects and correct treatment of flavor thresholds in the evolution kernel at the level of the resummed $q_T$ spectrum.

Speaker: Peter Plößl (Deutsches Elektronen-Synchrotron DESY)

2024_04_18_SCET_Ploessl.pdf

39 The structure of quark mass corrections in double Higgs production amplitudes

The leading and next-to-leading order QCD predictions for Higgs boson pair production at hadron colliders suffer from a large mass renormalisation scheme uncertainty related to the choice of the top quark mass. In this talk, I will discuss how the Method of Regions and factorisation in SCET can be utilised to understand the dependence of the result on the value of the intermediate quark mass and gain control over the sizeable logarithmic mass corrections in the $gg \to HH$ amplitudes at leading and next-to-leading powers in the high-energy limit.

Speaker: Sebastian Jaskiewicz (University of Bern)

scet24_jaskiewiczs_talk.pdf

40 SCET and bHQET matching coefficients and jet functions in the large-$\beta_0$ limit

We present a systematic approach for computing and analyzing of non-cusp and cusp perutvative series. The approach facilitates the extraction of renormalon divergences, the corresponding series ambiguity and the relation to non-perturbative power corrections. We applied it to the matching coefficients of QCD onto SCET and of (massive) SCET onto bHQET, as well as to the jet functions in both effective theories. We find full agreement with the leading flavor power of the full theory results up to $\alpha_s^4$ and predict, both analytically and numerically, the leading flavor contributions of higher orders. We also discuss through these examples how the information on renormalon divergences may be used to improve the convergence of the corresponding series.

Speaker: Mr Néstor González Gracia (University of Valencia/IFIC)

SCET2024.pdf

1:00 PM End of the conference