Event generators at BESⅢ

We present a brief remark and introduction to event generators for tau-charm physics currently used at BESⅢ, including KKMC, BesEvtGen, Bhlumi, Bhwide, Babayaga and inclusive Monte-Carlo event generators. This paper provides basic information on event generators for BESⅢ users.

Event generators for η/η' rare decays into π^+π^-1^+1^- and e^+e^-μ^+μ^-

Study of the rare and forbidden decays of η/η offers a sensitive probe to test fundamental symmetries of quantum chromodynamics and search for new physics beyond the Standard Model. To study the rare decays of η/η to π ＋ π - e ＋ e - , π ＋ π - μ ＋ μ - and e ＋ e - μ ＋ μ - at the BES detector, we developed several event generators based on the vector meson dominant model with finite-width corrections and the pseudoscalar mesons mixing theory. The various distributions from event generators are in good agreement with the theoretical predictions, which indicates that the event generators work very well after implemention in the BES Monte Carlo simulation package. In the BES physics analysis, the performance of the event generators will be improved in accordance with the distributions of different variables of η/η from data and the improvement on the theoretical calculations.

DJpsiFDC:an event generator for the process gg→J/ψJ/ψ at the LHC

DJpsiFDC is an event generator package for the process gg → J/ψJ/ψ. It generates events for primary leading-order 2 → 2 processes. The package could generate a Les Houches Event （LHE） document and this could easily be embedded into detector simulation software frameworks. The package is produced in Fortran code.

An exclusive event generator for e^+ e^- scan experiments

An exclusive event generator is designed for e＋e- scan experiments, including initial state radiation effects up to the second order correction. The generator is coded within the framework of BesEvtGen. There are seventy hadronic decay modes available, with effective center-of-mass energy coverage from the two pion mass threshold up to about 6 GeV. The accuracy achieved for the initial state radiation correction reaches the level achieved by the KKMC generator. The uncertainty associated with the calculation of the correction factor to the initial state radiation is dominated by the measurements of the energy-dependent Born cross section.

Tuning and validation of hadronic event generator for R value measurements in the tau-charm region

To measure the R value in an energy scan experiment with e＋e- collisions, precise calculation of initial state radiation is required in the event generators. We present an event generator for this consideration, which incorporates initial state radiation effects up to second order accuracy. The radiative correction factor is calculated using the totally hadronic Born cross section. The measured exclusive processes are generated according to their cross sections, while the unknown processes are generated using the LUND Area Law model, and its parameters are tuned with data collected at s = 3.65 GeV. The optimized values are validated with data in the range s = 2.2324--3.671 GeV. These optimized parameters are universally valid for event generation below the DIS threshold.

MONTE CARLO EVENT GENERATORS

Revised September 2013 by P. Nason （INFN, Milan） and P.Z. Skands （CERN） General-purpose Monte Carlo （GPMC） generators like HERWIG [1], HERWIG＋＋ [2], PYTHIA 6 [3], PYTHIA 8 [4], and SHERPA [5], provide fully exclusive simulations of high-energy collisions. They play an essential role in QCD modeling （in particular for aspects beyond fixed-order perturbative QCD）, in data analysis,

MONTE CARLO NEUTRINO EVENT GENERATORS

Written September 2013 by H. Gallagher （Tufts U.） and Y. Hayato （Tokyo U.） Monte Carlo neutrino generators are programs or libraries which simulate neutrino interactions with electrons, nucleons and nuclei. In this capacity their usual task is to take an input neutrino and nucleus and produce a set of 4-vectors for particles emerging from the interaction, which are then input to full detector simulations.

Event generators for η/η＇ decays at BESⅢ

The light unflavoured meson η/η＇ decays are valuable for testing non-perturbative quantum chromodynamics and exploring new physics beyond the Standard Model. This paper describes a series of event generators, including η/η＇→γl~＋l^-, η/η＇→γπ~＋π^-, η＇→ωe~＋e^-, η→π~＋π^-π~0, η/η＇→π~0π~0π~0, η＇→ηππ andη＇→π~＋π^-π~＋π^-/π~＋π^-π~0π~0, which have been developed for investigating η/ηdecay dynamics. For most of these generators, their usability has been validated in BESIII analyses for determining the detection efficiency, and background studies. The consistency between data and Monte Carlo shows that these generators work well in the BESⅢ simulation, and will also be useful for ongoing BESⅢ analyses and other experiments for studying η/η＇ physics.

Systematic studies on the nuclear parton distribution with photon and hadron productions in nuclear collisions at the LHC

A systematic study on the impact of widely-used nuclear-modified parton distribution function(nPDF)parameterizations on the production of direct photons and charged hadrons is performed by employing a next-toleading order Monte Carlo event generator JETPHOX in hadronic collisions at LHC energies.The nuclear modification factors of photon and charged hadron productions are studied in three types of collision systems,i.e.,small(p+p and p+Pb),medium(O+O),and large(Pb+Pb),in a wide rapidity acceptance.The results illustrate that the direct photon production process is a sensitive probe to decipher the difference of the nPDF parameterization implementations,which provides new insights for the experimental measurements to refine the nuclear modifications of the parton distributions.To provide a benchmark for searching for quark gluon plasma in the upcoming small system measurements at LHC energies,we carry out detailed studies on the cold nuclear matter effect in(O+O)collisions.Our outcomes show that the cold nuclear matter effects are negligible for the charged hadron production in(O+O)collisions,which can be used as a baseline to subtract the initial state contribution.