Scale and isolation sensitivity of diphoton distributions at the LHC

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With current high precision collider data, the reliable estimation of theoretical uncertainties due to missing higher orders (MHOs) in perturbation theory has become a pressing issue for collider phenomenology. Traditionally, the size of the MHOs is estimated through scale variation, a simple but ad hoc method without probabilistic interpretation. Bayesian approaches provide a compelling alternative to estimate the size of the MHOs, but it is not clear how to interpret the perturbative scales, like the factorisation and renormalisation scales, in a Bayesian framework. Recently, it was proposed that the scales can be incorporated as hidden parameters into a Bayesian model. In this paper, we thoroughly scrutinise Bayesian approaches to MHO estimation and systematically study the performance of different models on an extensive set of high-order calculations. We extend the framework in two significant ways. First, we define a new model that allows for asymmetric probability distributions. Second, we introduce a prescription to incorporate information on perturbative scales without interpreting them as hidden model parameters. We clarify how the two scale prescriptions bias the result towards specific scale choice, and we discuss and compare different Bayesian MHO estimates among themselves and to the traditional scale variation approach. Finally, we provide a practical prescription of how existing perturbative results at the standard scale variation points can be converted to 68%/95% credibility intervals in the Bayesian approach using the new public code MiHO.

Section: Di-photon Productionmentioning

confidence: 99%

An analysis of Bayesian estimates for missing higher orders in perturbative calculations

Duhr

Huss

Mazeliauskas

et al. 2021

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“…For this reason a lot of theoretical effort has been invested in their evaluation and in the development of ever-more efficient methods for their calculation. A number of gauge theories are being studied, starting from string and supersymmetric theories [1][2][3][4][5][6][7][8][9][10][11][12][13], to gravity [14][15][16], to Yang-Mills [17,18], to QED [19] and QCD [20][21][22][23][24][25][26][27][28][29][30][31][32] and ultimately to the full Standard Model [33][34][35][36][37][38][39][40][41][42]. Research on generic methods for solving multi-loop integrals is also ongoing [43][44][45][46][47][48]…”

Section: Introductionmentioning

confidence: 99%

Two-loop leading-color helicity amplitudes for three-photon production at the LHC

Chawdhry

Czakon

Mitov

et al. 2021

We calculate all planar contributions to the two-loop massless helicity amplitudes for the process $$ q\overline{q} $$ q q ¯ → γγγ. The results are presented in fully analytic form in terms of the functional basis proposed recently by Chicherin and Sotnikov. With this publication we provide the two-loop contributions already used by us in the NNLO QCD calculation of the LHC process pp → γγγ [Chawdhry et al. (2019)]. Our results agree with a recent calculation of the same amplitude [Abreu et al. (2020)] which was performed using different techniques. We combine several modern computational techniques, notably, analytic solutions for the IBP identities, finite-field reconstruction techniques as well as the recent approach [Chen (2019)] for efficiently projecting helicity amplitudes. Our framework appears well-suited for the calculation of two-loop multileg amplitudes for which complete sets of master integrals exist.

“…More recently, an independent NNLO analysis using the antenna subtraction method [27][28][29] was presented in ref. [30], highlighting the importance of the choice of the isolation criterion and of the scales in estimating the theoretical uncertainties. Electroweak (EW) corrections for the diphoton production process at the LHC were computed in refs.…”

Section: Introductionmentioning

confidence: 99%

Precise predictions for photon pair production matched to parton showers in GENEVA

Alioli

Broggio

Gavardi

et al. 2021

We present a new calculation for the production of isolated photon pairs at the LHC with $$ {\mathrm{NNLL}}_{{\mathcal{T}}_0}^{\prime } $$ NNLL T 0 ′ +NNLO accuracy. This is the first implementation within the Geneva Monte Carlo framework of a process with a nontrivial Born-level definition which suffers from QED singularities. Throughout the computation we use a smooth-cone isolation algorithm to remove such divergences. The higher-order resummation of the 0-jettiness resolution variable $$ {\mathcal{T}}_0 $$ T 0 is based on a factorisation formula derived within Soft-Collinear Effective Theory which predicts all of the singular, virtual and real NNLO corrections. Starting from this precise parton-level prediction and by employing the Geneva method, we provide fully showered and hadronised events using Pythia8, while retaining the NNLO QCD accuracy for observables which are inclusive over the additional radiation. We compare our final predictions to LHC data at 7 TeV and find good agreement.