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تسجيل مستخدم جديدGR@PPA 2.8: initial-state jet matching for weak boson production processes at hadron collisions
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The initial-state jet matching method introduced in our previous studies has been applied to the event generation of single $W$ and $Z$ production processes and diboson ($W^{+}W^{-}$, $WZ$ and $ZZ$) production processes at hadron collisions in the framework of the GR@PPA event generator. The generated events reproduce the transverse momentum spectra of weak bosons continuously in the entire kinematical region. The matrix elements (ME) for hard interactions are still at the tree level. As in previo
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We release an event generator package, GR@PPA 2.9, for simulating the direct (single) photon and diphoton (double photon) production in hadron collisions. The included programs were used in our previous studies, in which we have explicitly shown larg
e contributions from parton-associated processes. The programs consistently combine simulations based on matrix elements with parton-shower simulations that reproduce the multiple parton radiation and quark fragmentation to photons. The matrix elements include associated parton production processes up to two partons. We provide instructions for the installation and execution of the programs in this article. The practical performance is also presented.
GR@PPA 2.8 is a program package including event generators for single and double weak-boson production processes at hadron collisions, in which a jet matching method is implemented for simulating the weak-boson kinematics in the entire phase space. S
ince the initial release in November, 2010, several improvements have been applied to the program components. This report describes the improvements and changes applied so far, up to the 2.8.3 release.
The $phi_{eta}^{*}$ distribution of the $Z/gamma^{*} rightarrow ell^{+}ell^{-}$ production in hadron collisions is simulated using a leading-order event generator, GR@PPA. The initial-state parton shower, which simulates the multiple QCD-radiation ef
fects in the initial state, plays the dominant role in this simulation. The simulation in the default setting agrees with the high-statistics measurement by ATLAS at LHC with the precision at the level of 5%. The observed systematic deviation, which can be attributed to the effects of ignored higher-order contributions, can be reduced by adjusting the arbitrary energy scales in the simulation. The agreement at the level of 1% can be achieved over a very wide range without introducing any modification in the implemented naive leading-logarithmic parton shower.
Predictions from the GR@PPA event generator concerning the transverse-momentum ($p_{T}$) spectrum of $Z$ bosons are compared with recent measurements at LHC and Tevatron. The simulation results are in reasonable agreement with the measurements, altho
ugh marginal discrepancies are observed in high-$p_{T}$ regions. The principal agreements imply that the leading-order simulation with a primitive parton shower based on the leading-logarithmic approximation still provides a reasonable description of the transverse motion of the hard-interaction system in hadron collisions, without the need to introduce noble techniques to incorporate higher-order corrections.
The O(alpha) virtual weak radiative corrections to many hadron collider processes are known to become large and negative at high energies, due to the appearance of Sudakov-like logarithms. At the same order in perturbation theory, weak boson emission
diagrams contribute. Since the W and Z bosons are massive, the O(alpha) virtual weak radiative corrections and the contributions from weak boson emission are separately finite. Thus, unlike in QED or QCD calculations, there is no technical reason for including gauge boson emission diagrams in calculations of electroweak radiative corrections. In most calculations of the O(alpha) electroweak radiative corrections, weak boson emission diagrams are therefore not taken into account. Another reason for not including these diagrams is that they lead to final states which differ from that of the original process. However, in experiment, one usually considers partially inclusive final states. Weak boson emission diagrams thus should be included in calculations of electroweak radiative corrections. In this paper, I examine the role of weak boson emission in those processes at the Fermilab Tevatron and the CERN LHC for which the one-loop electroweak radiative corrections are known to become large at high energies (inclusive jet, isolated photon, Z+1 jet, Drell-Yan, di-boson, t-bar t, and single top production). In general, I find that the cross section for weak boson emission is substantial at high energies and that weak boson emission and the O(alpha) virtual weak radiative corrections partially cancel.
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