Comparison of SANC with KORALZ and PHOTOS

Using the SANC system we study the one-loop electroweak standard model prediction, including virtual and real photon emissions, for the decays of on-shell vector and scalar bosons B --> f anti-f (gamma), where B is a vector boson, Z or W, or a Standard Model Higgs. The complete one-loop corrections and exact photon emission matrix element are taken into account. For the phase-space integration, the Monte Carlo technique is used. For Z decay the QED part of the calculation is first cross-checked with the exact one-loop QED prediction of KORALZ. For Higgs boson and W decays, a comparison is made with the approximate QED calculation of PHOTOS Monte Carlo. This provides a useful element for the evaluation of the theoretical uncertainty of PHOTOS, very interesting for its application in ongoing LEP2 and future LC and LHC phenomenology.Comment: Submitted to Acta Physica Polonica. 9 pages, 6 figure

Matching NLO parton shower matrix element with exact phase space: case of W -> l nu (gamma) and gamma^* -> pi^+pi^-(gamma)

The PHOTOS Monte Carlo is often used for simulation of QED effects in decay of intermediate particles and resonances. Momenta are generated in such a way that samples of events cover the whole bremsstrahlung phase space. With the help of selection cuts, experimental acceptance can be then taken into account. The program is based on an exact multiphoton phase space. Crude matrix element is obtained by iteration of a universal multidimensional kernel. It ensures exact distribution in the soft photon region. Algorithm is compatible with exclusive exponentiation. To evaluate the program's precision, it is necessary to control the kernel with the help of perturbative results. If available, kernel is constructed from the exact first order matrix element. This ensures that all terms necessary for non-leading logarithms are taken into account. In the present paper we will focus on the W -> l nu and gamma^* -> pi^+ pi^- decays. The Born level cross sections for both processes approach zero in some points of the phase space. A process dependent compensating weight is constructed to incorporate the exact matrix element, but is recommended for use in tests only. In the hard photon region, where scalar QED is not expected to be reliable, the compensating weight for gamma^* decay can be large. With respect to the total rate, the effect remains at the permille level. It is nonetheless of interest. The terms leading to the effect are analogous to some terms appearing in QCD. The present paper can be understood either as a contribution to discussion on how to match two collinear emission chains resulting from charged sources in a way compatible with the exact and complete phase space, exclusive exponentiation and the first order matrix element of QED (scalar QED), or as the practical study of predictions for accelerator experiments.Comment: 24 page

Isochronal annealing effects on local structure, crystalline fraction, and undamaged region size of radiation damage in Ga-stabilized δ\delta-Pu

The effects on the local structure due to self-irradiation damage of Ga stabilized $\delta$-Pu stored at cryogenic temperatures have been examined using extended x-ray absorption fine structure (EXAFS) experiments. Extensive damage, seen as a loss of local order, was evident after 72 days of storage below 15 K. The effect was observed from both the Pu and Ga sites, although less pronounced around Ga. Isochronal annealing was performed on this sample to study the annealing processes that occur between cryogenic and room temperature storage conditions, where damage is mostly reversed. Damage fractions at various points along the annealing curve have been determined using an amplitude-ratio method, standard EXAFS fitting, and a spherical crystallite model, and provide information complementary to previous electrical resistivity- and susceptibility-based isochronal annealing studies. The use of a spherical crystallite model accounts for the changes in EXAFS spectra using just two parameters, namely, the crystalline fraction and the particle radius. Together, these results are discussed in terms of changes to the local structure around Ga and Pu throughout the annealing process and highlight the unusual role of Ga in the behavior of the lowest temperature anneals.Comment: 13 pages, 10 figure

One-Loop QCD Mass Effects in the Production of Polarized Bottom and Top Quarks

The analytic expressions for the production cross sections of polarized bottom and top quarks in $e^+e^-$ annihilation are explicitly derived at the one-loop order of strong interactions. Chirality-violating mass effects will reduce the longitudinal spin polarization for the light quark pairs by an amount of $3\%$, when one properly considers the massless limit for the final quarks. Numerical estimates of longitudinal spin polarization effects in the processes $e^+e^-\to b\bar{b}(g)$ and $e^+e^- \to t\bar{t}(g)$ are presented.Comment: 17 p. (5 figs available upon request), LaTeX, MZ-TH/93-30, RAL/93-81, FTUV/93-4

Top quark associated production of the neutral top-pion at high energy e+e−e^{+}e^{-} colliders

In the context of topcolor-assisted technicolor (TC2) models, we calculate the associated production of the neutral top-pion $\pi_{t}^{0}$ with a pair of top quarks via the process $e^{+}e^{-}\longrightarrow t\bar{t}\pi_{t}^{0}$. We find that the production cross section is larger than that of the process $e^{+}e^{-}\longrightarrow t\bar{t}H$ both in the standard model (SM) and in the minimal supersymmetric SM. With reasonable values of the parameters in TC2 models, the cross section can reach $20fb$. The neutral top-pion $\pi_{t}^{0}$ may be direct observed via this process.Comment: Latex files, 10 pages and 3 figure

A hybrid method for determining particle masses at the Large Hadron Collider with fully identified cascade decays

A new technique for improving the precision of measurements of SUSY particle masses at the LHC is introduced. The technique involves kinematic fitting of events with two fully identified decay chains. We incorporate both event ETmiss constraints and independent constraints provided by kinematic end-points in experiment invariant mass distributions of SUSY decay products. Incorporation of the event specific information maximises the information used in the fit and is shown to reduce the mass measurement uncertainites by ~30% compared to conventional fitting of experiment end-point constraints for the SPS1a benchmark model.Comment: 10 pages, 2 .eps figures, JHEP3 styl

Bremsstrahlung simulation in K to pi l^pm nu_l (gamma) decays

In physics simulation chains, the PHOTOS Monte Carlo program is often used to simulate QED effects in decays of intermediate particles and resonances. The program is based on an exact multiphoton phase space. In general, the matrix element is obtained from iterations of a universal kernel and approximations are involved. To evaluate the program precision, it is necessary to formulate and implement within the generator the exact matrix element, which depends on the decay channel. Then, all terms necessary for non-leading logarithms are taken into account. In the present letter we focus on the decay K to pi l^pm nu_l and tests of the PHOTOS Monte Carlo program. We conclude a 0.2% relative precision in the implementation of the hard photon matrix element into the emission kernel, including the case where approximations are used.Comment: 1+20 pages, 8 figure

A Clean Slepton Mixing Signal at the LHC

In supersymmetric scenarios where the scalar tau lepton is stable or long-lived, a search for a decay mode chi0 --> stau + mu at the LHC has a good sensitivity to the flavor mixing in the scalar lepton sector. We demonstrate that the sensitivities to the mixing angle at the level of sin(theta)=0.15 are possible with an integrated luminosity of 100fb^{-1} if the total production cross section of supersymmetric particles is of the order of 1pb. The sensitivity to the mixing parameter can be better than the experimental bound from the tau --> mu + gamma decay depending on model parameters.Comment: 7 pages, 2 figures, 1 table, the stau resolution corrected. version to appear in JHE

The ATLAS discovery potential for MSSM neutral Higgs bosons decaying to a mu+mu- pair in the mass range up to 130 GeV

Results are presented on the discovery potential for MSSM neutral Higgs bosons in the Mh-{max}scenario. The region of large tan beta, between 15 and 50, and mass between ~ 95 and 130 GeV is considered in the framework of the ATLAS experiment at the Large Hadron Collider (LHC), for a centre-of-mass energy = 14 TeV. This parameter region is not fully covered by the present data either from LEP or from Tevatron. The h/A bosons, supposed to be very close in mass in that region, are studied in the channel h/A -> mu+mu- accompanied by two b-jets. The study includes a method to control the most copious background, Zo -> mu+mu- accompanied by two b-jets. A possible contribution of the H boson to the signal is also considered