TWOGEN—a simple Monte Carlo generator for two-photon reactions (original) (raw)
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The European Physical Journal C, 2006
Recently, various cross sections of e + e − annihilation into hadrons were accurately measured in the energy range from 0.37 to 1.39 GeV with the CMD-2 detector at the VEPP-2M collider. In the π + π − channel a systematic uncertainty of 0.6% has been achieved. A Monte-Carlo Generator Photon Jets (MCGPJ) was developed to simulate events of the Bhabha scattering as well as production of two charged pions, kaons and muons. Based on the formalism of Structure Functions, the leading logarithmic contributions related to the emission of photon jets in the collinear region are incorporated into the MC generator. Radiative corrections (RC) in the first order of α are accounted for exactly. The theoretical precision of the cross sections with RC is estimated to be better than 0.2%. Numerous tests of the program as well as comparison with other MC generators and CMD-2 experimental data are presented.
Study ofη production in two-photon collisions
Zeitschrift für Physik C Particles and Fields, 1989
Production of the q~ meson in e + e-quasireal two photon collisions has been looked for in three channels. The data were obtained from an integrated luminosity of 189pb -~. An r/c signal is observed in two decay modes (K~ re+rc-n+re -) with a combined statistical significance of 3.5 standard deviations. Using the known r/c branching ratios to these channels and to K + K-re + re-, the combined partial r/c width to ~ is F~,(r/~) = 19.9 _+ 6.1 + 8.6 keV. The first error is statistical, and the second one includes the systematic and branching ratio errors. Calculated as an upper limit we obtain F~(qc)<36 keV (95% C.L., including the systematic error).
Two-Photon Processes at Intermediate Energies
2001
Exclusive hadron production processes in photon-photon collisions provide important tests of QCD at the amplitude level, particularly as measures of hadron distribution amplitudes and skewed parton distributions. The determination of the shape and normalization of the distribution amplitudes has become particularly important in view of their importance in the analysis of exclusive semi-leptonic and two-body hadronic B-decays. Interesting two-photon physics, including doubly-tagged γ * γ * reactions, will be accessible at low energy, high luminosity e + e − colliders, including measurements of channels important in the light-by-light contribution to the muon g-2 and the study of the transition between threshold production controlled by lowenergy effective chiral theories and the domain where leading-twist perturbative QCD becomes applicable. The threshold regime of hadron production in photon-photon and e + e − annihilation, where hadrons are formed at small relative velocity, is particularly interesting as a test of low energy theorems, soliton models, and new types of resonance production. Such studies will be particularly valuable in double-tagged reactions where polarization correlations, as well as the photon virtuality dependence, can be studied.
Inclusive production in two-photon collisions at LEP
Physics Letters B, 2002
Inclusive D * ± production in two-photon collisions is studied with the L3 detector at LEP, using 683 pb −1 of data collected at centre-of-mass energies from 183 to 208 GeV. Differential cross sections are determined as functions of the transverse momentum and pseudorapidity of the D * ± mesons in the kinematic region 1 GeV < P T < 12 GeV and |η| < 1.4. The cross sections σ(e + e − → e + e − D * ± X) in this kinematical region is measured and the σ(e + e − → e + e − ccX) cross section is derived. The measurements are compared with next-to-leading order perturbative QCD calculations.
WWGENPV 2.0 — A Monte Carlo event generator for four-fermion production at e+e− colliders
Computer Physics Communications, 1997
The Monte Carlo program WWGENPV, designed for computing distributions and generating events for four-fermion production in e + e − collisions, is described. The new version, 2.0, includes the full set of the electroweak (EW) tree-level matrix elements for double-and single-W production, initial-and final-state photonic radiation including p T /p L effects in the Structure Function formalism, all the relevant non-QED corrections (Coulomb correction, naive QCD, leading EW corrections). An hadronisation interface to JETSET is also provided. The program can be used in a three-fold way: as a Monte Carlo integrator for weighted events, providing predictions for several observables relevant for W physics; as an adaptive integrator, giving predictions for cross sections, energy and invariant mass losses with high numerical precision; as an event generator for unweighted events, both at partonic and hadronic level. In all the branches, the code can provide accurate and fast results.
Monte Carlo event generators for high energy particle physics event simulation
2019
Monte Carlo event generators (MCEGs) are the indispensable workhorses of particle physics, bridging the gap between theoretical ideas and first-principles calculations on the one hand, and the complex detector signatures and data of the experimental community on the other hand. All collider physics experiments are dependent on simulated events by MCEG codes such as Herwig, Pythia, Sherpa, POWHEG, and MG5_aMC@NLO to design and tune their detectors and analysis strategies. The development of MCEGs is overwhelmingly driven by a vibrant community of academics at European Universities, who also train the next generations of particle phenomenologists. The new challenges posed by possible future collider-based experiments and the fact that the first analyses at Run II of the LHC are now frequently limited by theory uncertainties urge the community to invest into further theoretical and technical improvements of these essential tools. In this short contribution to the European Strategy Upda...
Total cross section of two-photon production of hadrons
Zeitschrift für Physik C Particles and Fields, 1992
The total cross section for Y Y-+hadrons was measured as a function of the invariant mass W of the system (1.25 to 4.25 GeV) at the e + e-collider VEPP-4 with the detector MD-1. For the first time the data were obtained by detecting both scattered leptons with almost zero emission angles. The mean squared four momentum transfer (q2) is-0.005 GeV 2, the rms W resolution is 10~250 MeV. The data on the mean charged multiplicity (nc) are well described by the function (nc)=(1.62 _+ 0.37) + (1.83 _+ 0.45). In (W(GeV)). The W dependence of the total cross section is consistent with the theoretical prediction o-(nb) = 240 + 270/W(GeV).
Inclusive D∗±production in two-photon collisions at LEP
Physics Letters B, 2002
Inclusive D * ± production in two-photon collisions is studied with the L3 detector at LEP, using 683 pb −1 of data collected at centre-of-mass energies from 183 to 208 GeV. Differential cross sections are determined as functions of the transverse momentum and pseudorapidity of the D * ± mesons in the kinematic region 1 GeV < P T < 12 GeV and |η| < 1.4. The cross sections σ(e + e − → e + e − D * ± X) in this kinematical region is measured and the σ(e + e − → e + e − ccX) cross section is derived. The measurements are compared with next-to-leading order perturbative QCD calculations.