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Register a new userFinal State Radiative Effects for the Exact O(alpha) YFS Exponentiated (Un)Stable W+W- Production At and Beyond LEP2 Energies
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We present the LL final state radiative effects for the exact O(alpha) YFS exponentiated (un)stable WW pair production at LEP2/NLC energies using Monte Carlo event generator methods. The respective event generator, version 1.12 of the program YFSWW3, wherein both Standard Model and anomalous triple gauge boson couplings are allowed, generates n(gamma) radiation both from the initial state and from the intermediate W+ W- and generates the LL final state W decay radiative effects. Sample Monte Carlo data are illustrated.
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We present precision calculations of the processes e+e- -> 4-fermions in which the double resonant W+W- intermediate state occurs. Referring to this latter intermediate state as the signal process, we show that, by using the YFS Monte Carlo event generators YFSWW3-1.14 and KORALW1.42 in an appropriate combination, we achieve a physical precision on the signal process, as isolated with LEP2 MC Workshop cuts, below 0.5 per cent. We stress the full gauge invariance of our calculations and we compare our results with those of other authors where appropriate. In particular, sample Monte Carlo data are explicitly illustrated and compared with the results of the program RacoonWW of Dittmaier {it et al.}. In this way, we show that the total (physical plus technical) precision tag for the WW signal process cross section is 0.4 per cent for 200 GeV, for example. Results are also given for 500 GeV with an eye toward the LC.
In the energy region of LEP2 and above, four fermion final states in e+e- collisions can be produced by Feynman diagrams involving two, one or zero resonant bosons...
We present the exact O(alpha) correction to the process e+ e- -> f f-bar + gamma, f neq e, for ISR oplus FSR at and beyond LEP2 energies. We give explicit formulas for the completely differential cross section. As an important application, we compute the size of the respective sub-leading corrections of O(alpha L) to the f f-bar cross section, where L is the respective big logarithm in the renormalization group sense so that it is identifiable as L = ln |s|/m_e^2 when s is the squared e+e- cms energy. Comparisons are made with the available literature. We show explicitly that our results have the correct infrared limit, as a cross-check. Some comments are made about the implementation of our results in the framework of the Monte Carlo event generator KK MC.
We present the new Coherent Exclusive Exponentiation (CEEX), in comparison to the older Exclusive Exponentiation (EEX) and the semi-analytical Inclusive Exponentiation (IEX), for the process e+e- -> f-bar f + n(gamma), f=mu,tau,d,u,s,c,b, with validity for centre of mass energies from tau lepton threshold to 1 TeV. We analyse 2f numerical results at the Z-peak, 189 GeV and 500 GeV. We also present precision calculations of the signal processes e+e- -> 4f in which the double resonant W+W- intermediate state occurs using our YFSWW3-1.14 MC. Sample 4f Monte Carlo data are explicitly illustrated in comparison to the literature at LEP2 energies. These comparisons show that a TU for the signal process cross section of 0.4 percent is valid for the LEP2 200 GeV energy. LC energy results are also shown.
In a study of the reaction e-e+ -> W-W+ with the DELPHI detector, the probabilities of the two W particles occurring in the joint polarisation states transverse-transverse (TT), longitudinal-transverse plus transverse-longitudinal (LT) and longitudinal-longitudinal (LL) have been determined using the final states WW -> l nu q qbar (l = e, mu). The two-particle joint polarisation probabilities, i.e. the spin density matrix elements rho_TT, rho_LT, rho_LL, are measured as functions of the W- production angle, theta_W-, at an average reaction energy of 198.2 GeV. Averaged over all cos(theta_W-), the following joint probabilities are obtained: rho_TT = (67 +/- 8)%, rho_LT = (30 +/- 8)%, rho_LL = (3 +/- 7)% . These results are in agreement with the Standard Model predictions of 63.0%, 28.9% and 8.1%, respectively. The related polarisation cross-sections sigma_TT, sigma_LT and sigma_LL are also presented.
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