Les Houches

(accessible to everyone, editing rights to conveners and organizers)

Techniques and calculations for SM phenomenology:

• Calculations/tools:
  • expected precision for fundamental Standard Model processes at 14 and 100 TeV; what calculations are needed to match this precision?
  • NNLO and N3LO; status/challenges/prospects
  • theory uncertainties; more rigorous estimates? correlations? In particular, theory uncertainty for EW corrections?
  • usage of NNLO results; grids seem to be a real bottleneck now for precision work
  • resummation in analytic and parton shower calculations
    • uncertainty for 'softly-vetoed' distributions
    • comparisons of jet veto calculations
    • tuned comparison of NLL parton showers; sub-leading power corrections

• PDFs:
  • followup on PDF4LHC21 benchmarking exercise; better understanding of tolerances, tensions
  • EW corrections/EW PDFs; how to provide consistent calculations (lepton definition with QED effects)
  • Electron-ion collider (EIC); what will EIC tell us? how do we prepare for that?
  • N3LO PDFS; how firm are changes to the gluon, and what should be done for benchmark Higgs cross sections; progress on splitting functions
  • PDF uncertainties, i.e. hopscotch vs Monte Carlo sampling
  • intrinsic charm
  • theory uncertainties/correlations in fit. Double counting?
  • quark-gluon discrimination for PDF determination

• Higgs:
  • understanding the SM for high Higgs pT; role of top mass corrections/scheme (MSbar vs on-shell); how to improve channel sensitivities;
  • VBF signal at high pT; gluon-fusion background in VBF phase-space
  • parton-shower uncertainties in VBF

• EW sector:
  • polarisation measurements (for diboson/VBS as well): theory/experiment interplay
  • prospects for tri-boson production. Are there any theoretical limitations for run III?
  • W mass:
    • (non-perturbative) modeling
    • new ideas/methods (asymmetry)
    • determination at e+e-
    • theory agnostic determination; how agnostic?
  • STXS for multiboson processes

• Top:
  • ttW tension; multi-jet merging and other modelling aspects (including treatment in experiments)
  • merging of off-shell ttW with parton shower
  • modelling of ttbb
  • tt+X: on-shell vs. off-shell. role of single-top contributions
  • tt+gamma: modeling, in particular regarding on-shell/off-shell
  • Additional jet activity in top-quark pair production and decay

• Jets:
  • flavor tagging of jets; matching what theorists can predict (IR safety) and what experimentalists can measure [overlap with Jet substructure techniques, see below]
  • use heavy flavor jets for W+c (→strange quark PDFs) and Z+c (→intrinsic charm)
  • further investigations/understanding of jet R-dependent scale uncertainties

• Miscellaneous
  • forward physics → FASER. Anything needed from SM point of view?

• Machine Learning
  • Matrix Element calculation using ML
  • Interpretable models
  • Fast surrogate models for physics simulations
  • Workflows and interoperability with experimental software
  • Incorporating uncertainties in the training of ML models
  • ML-based unfolding techniques
  • Enforcing properties to ML models: Lorentz invariance/equivariance, permutation invariance, IRC safety

Jet substructure techniques:

• detailed comparison between recently proposed jet flavour algorithms
• starting from state-of-the-art ML-taggers, estimate how much they are correlated to the physics in the measurements of substructure we already have. Discuss good procedures to best tune MC to describe ML-taggers. Discuss good procedures to estimate uncertainties on ML-taggers, given the physics understanding of various effects (an example is scale-variations, where our constraints from data are certainly stronger than the factor 2 variations in many cases, but sometimes the opposite).
• take stock of how well most recent generator developments have improved description of multiple new measurements of substructure. (Followup from a previous Les Houches 2015 on q/g-tagging)

Tools, Event Generators and Machine Learning:

Standard Model Higgs:

• ggF
  • N3LO PDFs: Seems that aN3LO PDFs have a large impact, beyond the previously assigned PDF-TH uncert. Do other groups agree with this and how robust are these conclusions? Do cuts affect the conclusion and are the changes localised in PS? What other reasonable approximations could we make for comparison? (Related lit: 2207.04739)
  • ggF+jj as a background for VBF
  • EW Corrections: Various approximations seem to agree well with each other and the full result. Impact on STXS bins? (Related lit: 2010.09451)

• B-quark issues
  • Backgrounds for Higgs processes (ttbb/ttH, V+HF/VH)
  • 4FS/5FS (bbH, t/H/Z+j, ttbb, fused Monte Carlos) (e.g. 2006.10086, 2109.15039, 2207.11264)

• Flavour algorithms (Overlap with Techniques and calculations for SM phenomenology group)
  • Potential for LH study regarding the various recent flavour jet algorithms comparison/review/benchmarking (Related lit: 2208.11138, 2205.01109, 2205.01117, 2205.11879, 2104.06920, 2202.05082)
  • Using new flavour jet algorithms in EXP vs new TH developments
  • Jet Lund planes, hadronisation models
  • Start with e+e- →bb+j? Sensible to think about the impact on Higgs sector yet (H→bb+j)?

• Off-shell measurements
  • Challenges of multi-leg processes, e.g. ggVVjj very challenging matrix element, can/should we approximate it with matching/merging? Are new techniques helpful (e.g. OTTER)?
  • Interpreting off-shell measurements in terms of EFTs, how does this impact interpretation of width measurements? (Related lit: 2203.02418)

• Jets
  • VH, VH+j, VBF @ NNLO with decay H→bb (ideally @ NNLO), identifying/tagging jets
  • q/g jet tagging

• HH
  • EFTs (SMEFT/HEFT)
  • Constraining the Higgs self-coupling using H + HH, are other processes or HH channels beyond ggHH useful?
  • Currently using STXS for H input for self-coupling, it was not optimised for this, is there something better we can do here (e.g. fiducial differential measurements optimised for kappa_lam)?

• Yukawa couplings
  • top: ttH/tttt
  • charm: VHcc (a la VHbb), indirect measurements via ptH

• Experiment/Theory efficient information exchange
  • Likelihoods, discriminators, fiducial cross sections, differential distributions
  • negative events and strategies to mitigate them
  • public codes, weighted vs unweighted events, making the best use of the latest fixed-order results
  • making use of new results appearing whilst analysis is ongoing and can TH help here? Can unbinned reweighting with machine learning be useful?

• Parton-shower Issues and Developments
  • The limiting systematic on VBF (and very significant for other Higgs processes), what can we do with this? What can new showers say on this right now?
  • New showers, subleading-color issues with parton showers, formal accuracy, and possible effects on Higgs physics (PanScales 2205.02237, 2207.09467; Forshaw, Plätzer et al 2003.06400, 2007.09648, 2011.15087, 2012.15215; Dire, VINCIA, …)

• New opportunities for Run3 (unexplored regions, != cuts etc)
  • Identifying processes that should be reexamined at higher precision, or which were too rare before
  • Boosted regions and how Run3 can change this picture (increased statistics, improvements in boosted tagging)

• STXS
  • v1.2 too aggressive binning (required merging bins upon analysis)
  • v1.3 binning less aggressive could be worth adding bins to highlight specific observables (e.g. CP-sensitive binning)
  • Integrating decays in STXS
  • Thinking about the HL-LHC and its sensitivity in combination with e+e- Higgs factory.

• Backgrounds
  • Predictions+uncertainty models for backgrounds to ttH production: tt+HF, ggH+HF, tt+V, previous proposal was to estimate ttV EW correction in different phase space regions
  • Identifying backgrounds needed for other Higgs channels/measurements and what we can do to address them (see e.g. H background to HH, H+2j, ggVVjj, ttbb topics)

• Precision
  • Requirements and goals for measuring Higgs processes and properties @ HL-LHC / 14 TeV, 100 TeV, and e+e- Higgs Factories

Higgs:

• “Precision”:
  • Trilinear and quadrilinear Higgs couplings
  • Lepton flavour violation in the Higgs sector
  • Constraining the CP structure of the Higgs couplings
  • Higgs and EFT
  • Characterizing Higgs boson production and decay
• “Novelties”:
  • Exotic decays of the 125 GeV Higgs boson
  • Additional Higgs bosons (low/high mass) - uncovered parameter space
  • Naturalness
    • Gaps in searches for traditional models (SUSY, compositness)
    • Searches for cosmological triggers (new Higgs bosons and v-like leptons)
    • Unexpected signatures of naturalness

Machine Learning and Tools:

• Reinterpretation: Tools like Rivet, Gambit, .., ML for reinterpretation, reinterpretation of model agnostic searches
• EFTs: Fits, PDF inclusion, SMEFT progress …
• Physics & ML: Injection of physics priors into classification and generative models; interpretable ML techniques; ML for optimal sensitivity for BSM searches and optimal observables and likelihood learning, opening the black box
• Anomalies: A unified view of different anomaly detection techniques,.pushing the boundaries of anomaly detection

Low-energy precision probes of BSM:

• New Electric Dipole Moment searches?
• Parity violation in new systems?
• Exotic atoms/ions to test exotic forces
  • muonic atoms
  • antiprotonic atoms
  • highly charged ions
  • Rydberg states