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

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$^{-1}$

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

MCPLOTS: a particle physics resource based on volunteer computing

The mcplots.cern.ch web site (MCPLOTS) provides a simple online repository of plots made with high-energy-physics event generators, comparing them to a wide variety of experimental data. The repository is based on the HEPDATA online database of experimental results and on the RIVET Monte Carlo analysis tool. The repository is continually updated and relies on computing power donated by volunteers, via the LHC@HOME platform.Comment: 30 page

K0s-K0s correlations in 7 TeV pp collisions from the ALICE experiment at the LHC

Identical neutral kaon pair correlations are measured in 7 TeV pp collisions in the ALICE experiment. K0s-K0s correlation functions are formed in 3 multiplicity X 4 kT bins. The femtoscopic kaon source parameters Rinv and lambda are extracted from these correlation functions by fitting a (femtoscopy) X (PYTHIA) model to them, PYTHIA accounting for the non-flat baseline found in pp collisions. Source parameters are obtained from a fit which includes quantum statistics and final-state interactions of the a0/f0 resonance. K0s-K0s correlations show a systematic increase in Rinv for increasing multiplicity bin and decreasing Rinv for increasing kT bin as seen in pi-pi correlations in the pp system, as well as seen in heavy-ion collisions. Also, K0s-K0s correlations are observed to smoothly extend this pi-pi Rinv behavior for the pp system up to about three times higher kT than the kT range measured in pi-pi correlations.Comment: Proceedings of the Quark Matter 2011 Conference, 4 pages, 5 figure

Some Interesting Min-Bias Distributions for Early LHC Runs

A few observable distributions in min-bias (inelastic, non-diffractive) events which could be well constrained with early LHC data are presented, with some comments on their significance for placing constraints on theoretical models. The effects of fiducial cuts (p{perpendicular} &gt; 0.5 GeV, |{eta}| &lt; 2.5) and extrapolation from the Tevatron are illustrated

Transverse-momentum-ordered showers and interleaved multiple interactions

Abstract We propose a sophisticated framework for high-energy hadronic collisions, wherein different QCD physics processes are interleaved in a common sequence of falling transverse-momentum values. Thereby phase-space competition is introduced between multiple parton-parton interactions and initialstate radiation. As a first step we develop new transverse-momentum-ordered showers for initial-and final-state radiation, which should be of use also beyond the scope of the current article. These showers are then applied in the context of multiple interactions, and a few tests of the new model are presented. The article concludes with an outlook on further aspects, such as the possibility of a shower branching giving partons participating in two different interactions

Diffraction dissociation in proton-proton collisions at s\sqrt{s} = 0.9 TeV, 2.76 TeV and 7 TeV with ALICE at the LHC

The relative rates of single- and double- diffractive processes were measured with the ALICE detector by studying properties of gaps in the pseudorapidity distribution of particles produced in proton-proton collisions at $\sqrt{s}$ = 0.9 TeV, 2.76 TeV and 7 TeV. ALICE triggering efficiencies are determined for various classes of events, using a detector simulation validated with data on inclusive particle production. Cross-sections are determined using van der Meer scans to measure beam properties and obtain a measurement of the luminosity

The SUSY-QCD coupling relation

In order to establish supersymmetry at future colliders, it is not sufficient to discover new particles, but the identity of gauge couplings and the corresponding Yukawa couplings between gauginos, sfermions and fermions needs to be verified. In detailed studies it was found that the SUSY-Yukawa couplings of the electroweak sector can be studied with great precision at the ILC, but a similar analysis for the Yukawa coupling of the SUSY-QCD sector proves to be far more challenging. Here a first phenomenological study for determining this coupling is presented, using a method which combines information from LHC and ILC