Coherent exclusive exponentiation for precision Monte Carlo calculations

Abstract

We present the new coherent exclusive exponentiation ͑CEEX͒, the older exclusive exponentiation ͑EEX͒, and the semianalytical inclusive exponentiation ͑IEX͒ for the process e Ϫ e ϩ → f fϩn␥, where f ϭ , ,d,u,s,c,b, which are valid for center-of-mass energies from the lepton threshold to 1 TeV, that is, for CERN LEP1, LEP2, the SLC, future linear colliders, and b,c, factories, etc. The approaches are based on Yennie-Frautschi-Suura exponentiation. In CEEX, the effects due to photon emission from initial beams and outgoing fermions are calculated in QED up to second order, including all interference effects. Electroweak corrections are included to first order, at the amplitude level. Beams can be polarized longitudinally and transversely, and all spin correlations are incorporated in an exact manner. The EEX is more primitive, lacks initial-final interferences, but it is valuable for testing the newer CEEX. The IEX provides us with a set of sophisticated semianalytical formulas for the total cross section and selected inclusive distributions, which are mainly used for cross-checks of the Monte Carlo results. We analyze numerical results at the Z peak, 189 GeV and 500 GeV for simple kinematical cuts ͑comparisons with inclusive exponentiation͒ and for realistic experimental cuts. The physical precision and technical precision are determined for the total cross section and for the charge asymmetry.

Search forZc(3900)±→ωπ±Ablikim1, Ачасов2, Ai3 et al. 2015Phys. Rev. D181110View full textAdd to dashboardCite

“…[35], and equal to 1.06 for both energies; (1+δ) is the radiative correction factor, equal to 0.844 for √ s = 4.23 GeV and 0.848 for √ s = 4.26 GeV obtained using Ref. [29,30] by assuming the line shape of Born cross section σ(e + e − → Z c (3900) ± π ∓ ) to be a BW function with the parameters of the Y(4260) taken from PDG [31]; and B ω and B π 0 are the branching fractions of the decay ω → π + π − π 0 and π 0 → γγ [31], respectively. A conservative estimate of the upper limit of the Born cross section is determined by lowering the efficiency by one standard deviation of the systematic uncertainty.…”

“…The decays of ω → π + π − π 0 are generated with the OMEGA DALITZ model in evtgen [27,28]. Initial state radiation (ISR) is simulated with kkmc [29,30], where the Born cross section of e + e − → Z c (3900) ± π ∓ is assumed to follow a Y (4260) Breit-Wigner (BW) line shape with resonance parameters taken from the Particle Data Group (PDG) [31], in which listed as X(4260). Final state radiation (FSR) effects associated with charged particles are handled with PHOTOS [29].…”

“…The remaining events associated with charmonium decays are generated with lundcharm [32], while continuum hadronic events are generated with PYTHIA [33]. QED processes such as Bhabha scattering, dimuon and digamma events are generated with kkmc [29,30].…”

Determination of the LEP beam energy using radiative fermion-pair events

“…In this scheme, ISR is modelled with Coherent Exclusive Exponentiation (CEEX) [11] to O(α 2 ) precision. For the e + e − (nγ ) final-state process, BHWIDE [12] (v.1.00) is employed, in which ISR 25 OPAL uses a right-handed coordinate system in which the z axis is along the electron beam direction and the x axis is horizontal.…”

Search for associated production of massive states decaying into two photons in e+e− annihilations at =88–209 GeV

“…This process was simulated using the KK2f/CEEX [19] generator with hadronisation and fragmentation by PYTHIA 6.125 [20]. The CEEX modelling of ISR employs full second-order QED corrections to the matrix element, and applies coherent exponentiation of the QED corrections from interference between ISR and final-state radiation.…”