LHC TOP WG meeting

24 Apr 2024, 14:00 → 26 Apr 2024, 13:15 Europe/Zurich

4/3-006 - TH Conference Room (CERN)

Fabio Maltoni (Universite Catholique de Louvain (UCL) (BE) and Università di Bologna), Jose Enrique Palencia Cortezon (Universidad de Oviedo (ES)), Maria Aldaya Martin (DESY), Wolfgang Wagner (Bergische Universitaet Wuppertal (DE))

This periodic open meeting of the LHC TOP Working Group takes place twice a year at CERN. The meeting provides a forum for discussion between experimentalists and theorists on the latest developments in top quark physics. Everybody is welcome to attend; please register using the link below. 

The meeting will take place at CERN and also via zoom. 

Recordings of the sessions will be available below once the meeting is over.

Link to the recordings

Wednesday, 24 April

14:00 → 15:30 Joint session of the LHC EFT and Top Working Groups: Experimental talks

14:00 Measurements of inclusive and differential cross-sections of tt_bar+γ production in pp collisions at Sqrt(s)=13 TeV with the ATLAS detector

Based on https://arxiv.org/abs/2403.09452.

The absolute and normalised differential cross-sections are measured for several variables characterising the photon, lepton and jet kinematics as well as the angular separation between those objects. The observables are found to be in good agreement with the Monte Carlo predictions. The photon transverse momentum differential distribution is used to set limits on effective field theory parameters related to the electroweak dipole moments of the top quark. The combined limits using the photon and the Z boson transverse momentum measured in tt_bar production in associations with a Z boson are also set.

Speakers: Jan Hahn (Universitaet Siegen), Jan Joachim Hahn (Universitaet Siegen (DE))

TalkLHCtop2024Hahn.pdf

14:20 Discussion

14:30 Search for charged-lepton-flavour violating μτqt interactions in top-quark production and decay in pp collisions at √s = 13 TeV with the ATLAS detector at the LHC

Based on https://arxiv.org/abs/2403.06742.

The analysis targets events containing two muons with the same electric charge, a hadronically decaying τ-lepton and at least one jet, with exactly one b-tagged jet, produced by a μτqt interaction. Agreement with the Standard Model expectation within 1.6σ is observed, and limits are set at the 95% CL on the charged-lepton-flavour violation branching ratio of B(t→μτq) < 8.7×10−7. An Effective Field Theory interpretation is performed yielding 95% CL limits on Wilson coefficients, dependent on the flavour of the associated light quark and the Lorentz structure of the coupling.

Speaker: Jacob Julian Kempster (University of Sussex (GB))

JKempster_TopCLFV_LHCEFTWG_240424.pdf

14:50 Discussion

15:00 Search for baryon number violation in top quark production and decay using proton-proton collisions at √ s = 13 TeV

Reference: https://arxiv.org/abs/2402.18461 (TOP-22-003)

A search is presented for baryon number violating interactions in top quark production and decay. Upper limits are placed on the strength of baryon number violating couplings. For the first time the production of single top quarks via baryon number violating interactions is studied. This allows the search to set the most stringent constraints to date on the branching fraction of the top quark decay to a lepton, an up-type quark (u or c), and a down-type quark (d, s, or b). The results improve the previous bounds by three to six orders of magnitude based on the fermion flavor combination of the baryon number violating interactions.

Speaker: Reza Goldouzian (University of Notre Dame (US))

2024_LHCTOPWG_Reza.pdf

15:20 Discussion

15:30 → 16:00 Coffee break

16:00 → 18:00 Joint session of the LHC EFT and Top Working Groups: Presentations from theory

16:00 Collider sensitivity to SMEFT heavy-quark operators at one-loop in top-quark processes

Based on https://arxiv.org/abs/2402.06528

We study the effects of four-heavy-quark operators in the production of top quarks in the framework of the Standard Model Effective Field Theory (SMEFT) at the LHC. In particular, we compute for the first time the total contribution of the four-top-quark operator which enters only at the one-loop level in the top-quark pair production process. Analytical results at one-loop are presented for the gluon- and quark-initiated sub-processes, which allowed a first complete validation of the SMEFT@NLO in Madgraph5_aMC@NLO. The 95% CL bounds on four-heavy-quark operators from the available top-quark pair and four-top-quark production data are provided, which are complementary to other bounds found in the literature. We focus on the comparison of the sensitivities of the top-quark pair and the four-top-quark production processes, where in the latter case the four-top-quark operator contributes at tree-level. We conclude that the sensitivities of the two processes to four-heavy-quark operators are comparable. The projected sensitivities of both processes at HL-LHC are also presented.

Speaker: Mr Andrés Felipe Vásquez Tocora (IFT - Universidade Estadual Paulista - Julio de Mesquita Filho)

ttbar_4heavy.pdf

16:20 Discussion

16:30 Renormalisation group running effects in p p → tt_bar h pp → tt_bar h in the Standard Model Effective Field Theory

Speaker: Stefano Di Noi (Università di Padova and INFN, Sezione di Padova)

DiNoi_EFT_TOP.pdf

16:50 Discussion

17:00 Indirect constraints on top quark operators from a global SMEFT analysis

Speaker: Alfredo Stanzione

Talk_Alfredo_Stanzione.pdf

17:20 Discussion

17:30 Quantum Top Entanglement in SMEFT

Speakers: Claudio Severi (University of Manchester), Claudio Severi (Universita e INFN, Bologna (IT))

claudio_smeft.pdf

17:50 Discussion

18:00 → 20:00 Joint drink in salle de pas perdu

Thursday, 25 April

09:00 → 11:00 LHC top WG Open Meeting: Introduction and top-quark mass

Conveners: Prof. Fabio Maltoni (Universite Catholique de Louvain (UCL) (BE) and Università di Bologna), Jose Enrique Palencia Cortezon (Universidad de Oviedo (ES)), Maria Aldaya Martin (DESY), Wolfgang Wagner (Bergische Universitaet Wuppertal (DE))

09:00 Introduction

Speakers: Prof. Fabio Maltoni (Universite Catholique de Louvain (UCL) (BE) and Università di Bologna), Jose Enrique Palencia Cortezon (Universidad de Oviedo (ES)), Maria Aldaya Martin (DESY), Wolfgang Wagner (Bergische Universitaet Wuppertal (DE))

Intro_Open_Meeting_April_25_2024.pdf

09:20 Discussion

09:30 Combination of measurements of the top quark mass from data collected by the ATLAS and CMS experiments at √s = 7 and 8 TeV

Reference: https://arxiv.org/abs/2402.08713
A combination of fifteen top quark mass measurements performed by the ATLAS and CMS experiments at the LHC is presented. The data sets used correspond to an integrated luminosity of up to 5 and 20−1 of proton-proton collisions at center-of-mass energies of 7 and 8 TeV, respectively.

Speakers: Mark Andrew Owen (University of Glasgow (GB)), Martijn Mulders (CERN), Matteo Defranchis (CERN)

LHCTopMassApril2024.pdf

09:50 Discussion

10:00 Top-quark pole mass extraction at NNLO accuracy, from total, single- and double-differential cross sections for ttˉ+X production at the LHC

Reference: https://arxiv.org/abs/2311.05509

We extract the top-quark mass value in the on-shell renormalization scheme from the comparison of theoretical predictions for pp→tt_bar+X at next-to-next-to-leading order (NNLO) QCD accuracy with experimental data collected by the ATLAS and CMS collaborations for absolute total, normalized single-differential and double-differential cross-sections during Run 1, Run 2 and the ongoing Run 3 at the Large Hadron Collider (LHC). For the theory computations of heavy-quark pair-production we use the MATRIX framework, interfaced to PineAPPL for the generation of grids of theory predictions, which can be efficiently used a-posteriori during the fit, performed within xFitter. We take several state-of-the-art parton distribution functions (PDFs) as input for the fit and evaluate their associated uncertainties, as well as the uncertainties arising from renormalization and factorization scale variation. Fit uncertainties related to the datasets are also part of the extracted uncertainty of the top-quark mass and turn out to be of similar size as the combined scale and PDF uncertainty.

Speakers: Oleksandr Zenaiev, Oleksandr Zenaiev (Hamburg University)

Zenaiev-LHCtopWG-Apr25-ttbar.pdf

10:20 Discussion

10:30 A blueprint for understanding the Monte-Carlo top quark mass parameter

Reference: https://arxiv.org/abs/2404.09856

To control the scheme of the Monte-Carlo (MC) top quark mass parameter several ingredients are mandatory, concerning the knowledge of the IR 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 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 may eventually be also applied to direct-type top quark mass measurements.

Speakers: Andre Hoang, Andre Hoang (Austrian Academy of Sciences (AT))

LHC-topWG-Hoang-MCtopmass.pdf

Matching Hadronization and Perturbative Evolution: The Cluster Model in Light of Infrared Shower Cutoff Dependence

Reference: https://arxiv.org/abs/2404.09856

10:50 Discussion

11:00 → 11:30 Coffee break

11:30 → 13:00 LHC top WG Open Meeting: Flavour changing neutral currents / lepton flavour violation

11:30 ATLAS-CMS comparison: Search for flavour-changing neutral-current couplings between the top quark and Higgs boson in multi-lepton final states

A search for flavour-changing neutral-current interactions involving the top quark, the Higgs boson and an up-type quark (q = u,c) with the ATLAS detector at the Large Hadron Collider is presented. The analysis considers leptonic decays of the top quark along with Higgs-boson decays into two W bosons, two Z bosons or a τ+τ− pair. It focuses on final states containing either two leptons (electrons or muons) of the same charge or three leptons, of which exactly two have an identical charge. The considered processes are tt_bar production with one top quark decaying via t → Hq and pp → Ht production. The proton-proton collision data set analysed amounts to 140 fb−1 at √s = 13 TeV.

Speaker: Marvin Emin Geyik (Bergische Universitaet Wuppertal (DE))

LHCTopWG_tHq_FCNC_ML_Marvin_Geyik.pdf

11:50 Discussion

12:00 ATLAS-Highlight-1: Precise test of lepton flavour universality in W-boson decays into muons and electrons in pp collisions at √s = 13 TeV with the ATLAS detector

Reference: https://arxiv.org/abs/2403.02133

The ratio of branching ratios of the W boson to muons and electrons, Rμ/eW = B(W→μν)/B(W→eν), has been measured using 140 fb−1 of pp collision data at s√=13 TeV collected with the ATLAS detector at the LHC, probing the universality of lepton couplings.

Speaker: Richard Hawkings (CERN)

TopLHC_20240425_v1.pdf

12:20 Discussion

12:30 Dark matter as the trigger of flavor changing neutral current decays of the top quark

Reference: https://arxiv.org/abs/2402.08652

In this talk, I will discuss a possible between dark matter (DM) and one-loop induced top quark FCNC decays. In a simplified t-channel DM model that extends the SM with one colored scalar mediator and one right-handed fermion both odd under an ad-hoc Z_2 symmetry, I will show that that moderate to large rates of the top quark FCNC decays are
possible while respecting the existing constraints. Then I will discuss the phenomenological implications at hadron colliders (HL-LHC and FCC-hh) of four phenomenologically viable scenarios.

Speaker: Dr Adil Jueid (Institute for Basic Science)

talk_LHCTopWG_2024_AJ.pdf

12:50 Discussion

13:00 → 14:30 Lunch Break

14:30 → 16:30 LHC top WG Open Meeting: Interference effects in Top+X processes

14:30 Theory predictions for tZj production

Speaker: Davide Pagani (Universita e INFN, Bologna (IT))

tZj_TopWG.pdf

14:50 Discussion

15:00 CMS-Highlight-1: Measurement of inclusive and differential cross sections for single top quark production in association with a W boson in proton-proton collisions at 13.6 TeV

Reference: CMS-PAS-TOP-23-008 (https://cds.cern.ch/record/2893766)

Speaker: Alejandro Soto Rodriguez (Universidad de Oviedo (ES))

LHCtopWG_tWRun3.pdf

15:20 Discussion

15:30 CMS-Highlight-2: Inclusive and differential measurement of top quark cross sections in association with a Z boson

Reference: CMS-PAS-TOP-23-004 (https://cds.cern.ch/record/2893862)

Speaker: Federica Colombina (Deutsches Elektronen-Synchrotron (DE))

TOP-23-004.pdf

15:50 Discussion

16:00 Top-Quark Decay at Next-to-Next-to-Next-to-Leading Order in QCD

Reference: https://arxiv.org/abs/2309.01937

We present the first complete high-precision QCD corrections to the inclusive decay width Γ_t, the W-helicity fractions f_{L,R,0} and semi-inclusive distributions for the top-quark decay process t → b + W+ + X_QCD at NNNLO in the strong coupling constant α_s.

Speaker: Xiang Chen (Peking University)

XiangChen20240425.pdf

16:20 Discussion

16:30 → 17:00 Coffee break

17:00 → 18:00 LHC top WG Open Meeting

17:00 CMS-Highlight-3: Measurement of the inclusive tt cross section in final states with one lepton and additional jets and combination with the final states with two leptons at 5.02 TeV with 2017 data

Reference: CMS-PAS-TOP-23-005 (https://cds.cern.ch/record/2895219)

Speaker: Javier Del Riego Badas (Universidad de Oviedo (ES))

LHCTopWG_ttbar5TeV.pdf

17:20 Discussion

17:30 The rise and fall of light stops in the LHC top quark sample

Reference: https://arxiv.org/abs/2312.09794

We discuss the possibility that light new physics in the top quark sample at the LHC can be found by investigating with greater care well known kinematic distributions, such as the invariant mass m_bℓ of the b-jet and the charged lepton in fully leptonic tt_bar events. We demonstrate that new physics can be probed in the rising part of the already measured m_bℓ distribution. To this end we analyze a concrete supersymmetric scenario with light right-handed stop quark, chargino and neutralino.

Speaker: Roberto Franceschini (Rome 3 U.)

topLHCwg - April 25 2024 - The rise and fall of the light stops - Roberto Franceschini .pdf

17:50 Discussion

19:00 → 21:00 Dinner (Cafe de La Place)

Friday, 26 April

09:30 → 11:00 LHC top WG Open Meeting: Four-top-quark production

09:30 3t vs 4t calculation at C-NLO

Speaker: Hesham El Faham (The University of Manchester)

ElFaham_3t_vs_4t_TOPWG_2024.pdf

09:50 Discussion

10:00 Plans for 4-top-quark LHCtopWG combination

Speakers: Baptiste Ravina (Georg August Universitaet Goettingen (DE)), Kirill Skovpen (Ghent University (BE))

kskovpen4Tops.pdf

10:20 Discussion

10:30 Four top final states with NLO accuracy in perturbative QCD: 4 lepton channel

Reference: https://arxiv.org/abs/2401.10678

Triggered by the observation of four top-quark production at the LHC by the ATLAS and CMS collaboration we report on the calculation of the next-to-leading order QCD corrections to the Standard Model process pp→tt¯tt¯ in the 4ℓ top-quark decay channel. We take into account higher-order QCD effects in both the production and decays of the four top quarks. The latter effects are treated in the narrow width approximation, which preserves top-quark spin correlations throughout the calculation. We present results for two selected renormalisation and factorisation scale settings and three different PDF sets.

Speakers: Malgorzata Maria Worek (Rheinisch Westfaelische Tech. Hoch. (DE)), Nikolaos Dimitrakopoulos

LHC_top_wg_talk.pdf

10:50 Discussion

11:00 → 11:30 Coffee break

11:30 → 13:00 LHC top WG Open Meeting: Observation of entanglement in top-quark-antiquark pair production

11:30 Probing entanglement in top quark production with the CMS detector

Reference: CMS-PAS-TOP-23-001 (https://cds.cern.ch/record/2893854)

Entanglement is an intrinsic property of quantum mechanics and its measurement probes the current understanding of the underlying quantum nature of elementary particles at a fundamental level. A measurement of the extent of entanglement in top quark-antiquark events produced in proton-proton collisions at a center-of-mass energy of 13 TeV is performed on the data recorded by the CMS experiment at the CERN LHC in 2016, corresponding to an integrated luminosity of 35.9 fb−1.

Speakers: Andreas Werner Jung (Purdue University (US)), Giulia Negro (Purdue University (US))

entanglement_LHCtopWG_25Apr2024_Negro.pdf

11:50 Discussion

12:00 Comparison of the ATLAS and CMS measurements of entanglement in top-quark-antiquark pair production

Speaker: Yoav Afik (University of Chicago (US))

ATLAS_and_CMS_Top_Entanglement___LHC_Top_WG.pdf

12:20 Discussion

12:30 Threshold and bound state effects in tt

Speakers: Claudio Severi (Universita e INFN, Bologna (IT)), Claudio Severi (University of Manchester)

claudio_threshold.pdf

12:50 Discussion