A new approach to modelling elastic and inelastic photon-initiated production at the LHC: SuperChic 4
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Regular Article - Theoretical Physics
A new approach to modelling elastic and inelastic photon-initiated production at the LHC: SuperChic 4 L. A. Harland-Lang1,a , M. Tasevsky2,b , V. A. Khoze3,4,c , M. G. Ryskin4,d 1
Rudolf Peierls Centre, Beecroft Building, Parks Road, Oxford OX1 3PU, UK Institute of Physics, Czech Academy of Sciences, 18221 Prague 8, Czech Republic 3 IPPP, Department of Physics, University of Durham, Durham DH1 3LE, UK 4 Petersburg Nuclear Physics Institute, NRC “Kurchatov Institute”, Gatchina, St. Petersburg 188300, Russia
2
Received: 4 August 2020 / Accepted: 8 September 2020 © The Author(s) 2020
Abstract We present the results of the new SuperChic 4 Monte Carlo implementation of photon-initiated production in proton–proton collisions, considering as a first example the case of lepton pair production. This is based on the structure function calculation of the underlying process, and focusses on a complete account of the various contributing channels, including the case where a rapidity gap veto is imposed. We provide a careful treatment of the contributions where either (single dissociation), both (double dissociation) or neither (elastic) proton interacts inelastically and dissociates, and interface our results to Pythia for showering and hadronization. The particle decay distribution from dissociation system, as well the survival probability for no additional proton–proton interactions, are both fully accounted for; these are essential for comparing to data where a rapidity gap veto is applied. We present detailed results for the impact of the veto requirement on the differential cross section, compare to and find good agreement with ATLAS 7 TeV data on semi-exclusive production, and provide a new precise evaluation of the background from semi-exclusive lepton pair production to SUSY particle production in compressed mass scenarios, which is found to be low.
1 Introduction Photon-initiated (PI) particle production is a key ingredient in the LHC physics programme, playing a role in precision predictions for inclusive electroweak particle production [1– 3], probes of Beyond the Standard Model (BSM) physics a e-mail: [email protected] (corresponding author) b e-mail:
[email protected]
c e-mail:
[email protected]
d e-mail:
[email protected]
[4–17], SM physics in the diffractive sector [6,7,18–21], and in ultraperipheral heavy ion collisions [22–26]. A unique feature of the PI channel in proton–proton collisions is that the colour singlet photon exchange naturally leads to exclusive events, where the photons are emitted elastically from the protons, which then remain intact. This is particularly relevant in the context of the dedicated forward proton detectors (FPDs) at the LHC, namely the AFP [27,28] and CT–PPS [29] FPDs which have been installed in association with both ATLAS and CMS, respectively. More generally, even if the initial-state photon is emitted inelastically, there is no colour flow as a result, and there is still a possibility for semi
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