QCD corrections to the electric dipole moment of the neutron in the MSSM

We consider the QCD corrections to the electric dipole moment of the neutron in the Minimal Supersymmetric Standard Model. We provide a master formula for the Wilson coefficients at the low energy scale including for the first time the mixing between the electric and chromoelectric operators and correcting widely used previous LO estimates. We show that, because of the mixing between the electric and chromoelectric operators, the neutralino contribution is always strongly suppressed. We find that, in general, the effect of the QCD corrections is to reduce the amount of CP violation generated at the high scale. We discuss the perturbative uncertainties of the LO computation, which are particularly large for the gluino-mediated contribution. This motivates our Next-to-Leading order analysis. We compute for the first time the order alpha_s corrections to the Wilson coefficients for the gluino contributions, and recompute the two-loop anomalous dimension for the dipole operators. We show that the large LO uncertainty disappears once NLO corrections are taken into account.Comment: 23 pages, 5 figures, added references, corrected typo

Mass Determination in SUSY-like Events with Missing Energy

We describe a kinematic method which is capable of determining the overall mass scale in SUSY-like events at a hadron collider with two missing (dark matter) particles. We focus on the kinematic topology in which a pair of identical particles is produced with each decaying to two leptons and an invisible particle (schematically, $pp\to YY+jets$ followed by each $Y$ decaying via $Y\to \ell X\to \ell\ell'N$ where $N$ is invisible). This topology arises in many SUSY processes such as squark and gluino production and decay, not to mention t\anti t di-lepton decays. In the example where the final state leptons are all muons, our errors on the masses of the particles $Y$, $X$ and $N$ in the decay chain range from 4 GeV for 2000 events after cuts to 13 GeV for 400 events after cuts. Errors for mass differences are much smaller. Our ability to determine masses comes from considering all the kinematic information in the event, including the missing momentum, in conjunction with the quadratic constraints that arise from the $Y$, $X$ and $N$ mass-shell conditions. Realistic missing momentum and lepton momenta uncertainties are included in the analysis.Comment: 41 pages, 14 figures, various clarifications and expanded discussion included in revised version that conforms to the version to be publishe

PYTHIA 6.4 Physics and Manual

The PYTHIA program can be used to generate high-energy-physics `events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, within and beyond the Standard Model, with emphasis on those where strong interactions play a role, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, underlying events and beam remnants, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.Comment: 576 pages, no figures, uses JHEP3.cls. The code and further information may be found on the PYTHIA web page: http://www.thep.lu.se/~torbjorn/Pythia.html Changes in version 2: Mistakenly deleted section heading for "Physics Processes" reinserted, affecting section numbering. Minor updates to take into account referee comments and new colour reconnection option