Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userIFI and ISR Effects for Z/$gamma^*$ Drell-Yan Observables using ${cal KK}$MC-hh
325
0
0.0
(
0
)
Authors
S. Jadach
Ask ChatGPT about the research
No Arabic abstract
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.
rate research
Read More
KKMC-hh is a hadronic event generator for Z boson production and decays, which includes exponentiated multi-photon radiation and first-order electroweak corrections. We have used KKMC-hh to investigate the role of initial sate radiation (ISR) and initial-final interference (IFI) in precision electroweak analyses at the LHC. We compare the effect of this radiation on angular distributions and forward-backward asymmetry, which are particularly important for the measurement of the weak mixing angle. We discuss the relation of the ISR implementation in KKMC-hh to ISR from parton distribution functions with QED corrections.
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.
${cal KK}$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.
We present a comparison of data of lepton angular distributions of Drell-Yan/$Z$ production with the fixed-order pQCD calculations by which the baseline of pQCD effects is illustrated. As for the $Z$ production, we predict that $A_0$ and $A_2$ for $Z$ plus single gluon-jet events are very different from that of $Z$ plus single quark-jet events, allowing a new experimental tool for checking various algorithms which attempt to discriminate quark jets from gluon jets. Using an intuitive geometric approach, we show that the violation of the Lam-Tung relation, appearing at large transverse-momentum region, is attributed to the presence of a non-coplanarity effect. This interpretation is consistent with the appearance of violation beyond LO-QCD effect.
Many extension of the standard model contain an extra U(1) gauge group with a heavy Z gauge boson. Perhaps the most clear signal for such a Z would be a resonance in the invariant mass spectrum of the lepton pairs to which it decays. In the absence of such a signal, experiments can set limits on the couplings of such a Z, using a standard formula from theory. We repeat its derivation and find that, unfortunately, the standard formula in the literature is a factor of 8 too small. We briefly explore the implication for existing experimental searches and encourage the high energy physics community to re-examine analyses that have used this formula.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
