Multiple Interactions and Beam Remnants

Open issues on the structure of multiple interactions are outlined. An improved model is summarized, with a new approach to correlated parton densities in flavour, colour, longitudinal and transverse momenta, for both hard-scattering partons and beam-remnant ones.Comment: LaTeX, 5 pages, submitted to the proceedings of the Workshop on Physics at TeV Colliders, Les Houches, France, 26 May - 6 June 200

Searching for L-Violating Supersymmetry at the LHC

The possibility to simulate lepton number violating supersymmetric models has been introduced into the recently updated PYTHIA event generator, now containing 1278 decay channels of SUSY particles into SM particles via lepton number violating interactions. This generator has been used in combination with the ATLFAST detector simulation to study the impact of lepton number violation (LV) on event topologies in the ATLAS detector, and trigger menus designed for LV-SUSY are proposed based on very general considerations. In addition, a rather preliminary analysis is presented on the possibility for ATLAS to observe a signal above the background in several mSUGRA scenarios, using a combination of primitive cuts and neural networks to optimize the discriminating power between signal and background events over regions of parameter space rather than at individual points. It is found that a 5 sigma discovery is possible roughly for m_{1/2} < 1TeV and m_0 < 2TeV with an integrated luminosity of 30fb^{-1}, corresponding to one year of data taking with the LHC running at ``mid-luminosity'', L = 3*10^{33}s^{-1}cm^{-2}.Comment: 12 page

Progress on Multiple Interactions

We report on the development of a new model for the underlying event in hadron-hadron collisions. The model includes parton showers for all interactions, as well as non-trivial flavour, momentum, and colour correlations between interaction initiators and beam remnant partons.Comment: To appear in the proceedings of HEP 2003, 3p

Antenna Showers with Hadronic Initial States

We present an antenna shower formalism including contributions from initial-state partons and corresponding backwards evolution. We give a set of phase-space maps and antenna functions for massless partons which define a complete shower formalism suitable for computing observables with hadronic initial states. We focus on the initial-state components: initial-initial and initial-final antenna configurations. The formalism includes comprehensive possibilities for uncertainty estimates. We report on some preliminary results obtained with an implementation in the Vincia antenna-shower framework.Comment: 9 pages, 5 figure

One Universal Extra Dimension in Pythia

The Universal Extra Dimensions model has been implemented in the Pythia generator from version 6.4.18 onwards, in its minimal formulation with one inverse-TeV-sized extra dimension. The additional possibility of gravity-mediated decays, through a variable number of inverse-eV-sized extra dimensions into which only gravity extends, is also available. The implementation covers the lowest-lying Kaluza-Klein (KK) excitations of Standard Model particles, except for the excitations of the Higgs fields, with the mass spectrum calculated at one loop. 2 -> 2 tree-level production cross sections and KK number conserving 2-body decays are included. Mixing between iso-doublet and -singlet KK excitations is neglected thus far, and is expected to be negligible for all but the top sector.Comment: 11 page

Studies of isolated photon production in simulated proton-proton collisions with ALICE-EMCal

The production of prompt photons at high transverse momentum in proton-proton collisions (p-p) is a useful tool to study perturbative Quantum-Chromo-Dynamics (pQCD). In particular, they yield valuable information about parton distribution functions in the proton. The experimental measurement of prompt photons is a difficult task due to the large background of decay photons from neutral mesons, mainly pi0. We present a full simulation and reconstruction study of prompt photons identification in p-p at sqrt(s) = 14 TeV in the ALICE electromagnetic calorimeter EMCal, giving details on the methods developed to separate them from decay photons with the help of shower-shape and isolation cuts. We present Monte Carlo predictions for signal and background. The method used to extract the final isolated corrected cross-section is presented and the calculation of various experimental corrections is outlined.Comment: 4 pages, 6 figures. Proceedings Hot Quarks 2010 La-Londe-les-Maures (France), JPG submitte

L-Violating Supersymmetry: Implementation in PYTHIA and study of LHC discovery potential

In the Minimal Supersymmetric Standard Model (MSSM), the simultaneous appearance of lepton and baryon number violation causes the proton to decay much faster than the experimental bound allows. Customarily, a discrete symmetry known as R-parity is imposed to forbid these dangerous interactions. This work begins by arguing that there is no deep theoretical motivation for preferring R-parity over other discrete symmetries and continues by adopting the MSSM with baryon number conservation replacing R-parity conservation. For the purpose of studying the influence of the consequent lepton number violating interactions, 1278 new decay channels of supersymmetric particles into Standard Model particles have been included in the PYTHIA event generator. The augmented event generator is then used in combination with the atlfast detector simulation to study the impact of lepton number violation on event topologies in the ATLAS detector, and trigger menus designed for LV-SUSY are proposed based on very general conclusions. The subsequent analysis uses a combination of primitive cuts and neural networks to optimize the discriminating power between signal and background events. In all scenarios studied, it is found that a $5\sigma$ discovery is possible for cross sections down to $10^{-10}$ mb with an integrated luminosity of 30 fb$^{-1}$