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Register a new userA Precision Event Generator for EW Corrections in Hadron Scattering: ${cal KK}$MC-hh
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B.F.L. Ward
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${cal KK}$MC-hh is a precision event-generator for Z production and decay in hadronic collisions, which applies amplitude-level resummation to both initial and final state photon radiation, including perturbative residuals exact through ${cal O}(alpha^2L)$, together with exact ${cal O}(alpha)$ EW matrix element corrections. We present some comparisons to other programs and results showing the effect of multi-photon radiation for cuts motivated by a recent ATLAS W mass analysis. We also show preliminary untuned comparisons of the electroweak corrections of ${cal KK}$MC-hh to those of HORACE, which includes exact ${cal O}(alpha)$ corrections with resummed final-state photon radiation.
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We present an improvement of the MC event generator Herwiri2, where we recall the latter MC was a prototype for the inclusion of CEEX resummed EW corrections in hadron-hadron scattering at high cms energies. In this improvement the new exact ${cal O}(alpha^2L)$ resummed EW generator ${cal{KK}}$ MC 4.22, featuring as it does the CEEX realization of resummation in the EW sector, is put in union with the Herwig parton shower environment. The {rm LHE} format of the attendant output event file means that all other conventional parton shower environments are available to the would-be user of the resulting new MC. For this reason (and others -- see the text) we henceforth refer to the new improvement of the Herwiri2 MC as ${cal{KK}}text{MC-hh}$. Since this new MC features exact ${cal O}(alpha)$ pure weak corrections from the DIZET EW library and features the CEEX and the EEX YFS-style resummation of large multiple photon effects, it provides already the concrete path to 0.05% precision on such effects if we focus on the EW effects themselves. We therefore show predictions for observable distributions and comparisons with other approaches in the literature. This MC represents an important step in the realization of the exact amplitude-based $QEDotimes QCD$ resummation paradigm. Independently of this latter observation, the MC rigorously quantifies important EW effects in the current LHC experiments.
Continuing with our investigations of the expected sizes of multiple photon radiative effects in heavy gauge boson production with decay to charged lepton pairs in the context of the precision physics of the LHC, using KK{MC}-hh 4.22 we consider IFI and ISR effects for specific Z/$gamma^*$ Drell-Yan observables measured by the ATLAS and CMS Collaborations. With this version of KK{MC}-hh, we have coherent exclusive exponentiation (CEEX) electroweak (EW) exact ${cal O}(alpha^2 L)$ corrections in a hadronic MC and control over the corresponding EW initial-final interference (IFI) effects as well. Specifically, we illustrate the interplay between cuts of the type used in the measurement of $A_{FB}$ and $A_4$ at the LHC and the sizes of the expected responses of the attendant higher order corrections. We find that there are per cent to per mille level effects in the initial-state radiation, fractional per mille level effects in the IFI and per mille level effects in the over-all ${cal O}(alpha^2 L)$ corrections that any treatment of EW corrections at the per mille level should consider. Our results are applicable to current LHC experimental data analyses.
With an eye toward the precision physics of the LHC, such as the recent measurement of $M_W$ by the ATLAS Collaboration, we present here systematic studies relevant to the assessment of the expected size of multiple photon radiative effects in heavy gauge boson production with decay to charged lepton pairs. We use the new version 4.22 of ${cal KK}$MC-hh so that we have CEEX EW exact ${cal O}(alpha^2 L)$ corrections in a hadronic MC and control over the corresponding EW initial-final interference (IFI) effects as well. In this way, we illustrate the interplay between cuts of the type used in the measurement of $M_W$ at the LHC and the sizes of the expected responses of the attendant higher order corrections. We find that there are per cent to per mille level effects in the initial-state radiation, fractional per mille level effects in the IFI and per mille level effects in the over-all ${cal O}(alpha^2 L)$ corrections that any treatment of EW corrections at the per mille level should consider. Our results have direct applicability to current LHC experimental data analyses.
We present the upgrade of the coherent exclusive (CEEX) exponentiation realization of the Yennie-Frautschi-Suura (YFS) theory used in our Monte Carlo ({cal KK} MC) to the processes fbar{f}rightarrow fbar{f}, f=mu,tau,q, u_ell, f=e,mu,tau,q, u_ell, q=u,d,s,c,b,t, ell=e,mu,tau with f e f, with an eye toward the precision physics of the LHC and possible high energy muon colliders. We give a brief summary of the CEEX theory in comparison to the older (EEX) exclusive exponentiation theory and illustrate theoretical results relevant to the LHC and possible muon collider physics programs.
With an eye toward the precision physics of the LHC, FCC-ee and possible high energy muon colliders, we present the extension of the CEEX (coherent exclusive exponentiation) realization of the YFS approach to resummation in our KK MC to include the processes fbar{f}rightarrow fbar{f}, f=mu,tau, q, u_ell, f=e, mu,tau, q, u_ell, q=u,d,s,c,b,t, ell =e,mu,tau with f e f. After giving a brief summary of the CEEX theory with reference to the older EEX (exclusive exponentiation) theory, we illustrate theoretical results relevant to the LHC, FCC-ee, and possible muon collider physics programs.
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