Charge asymmetry ratio as a probe of quark flavour couplings of resonant particles at the LHC

We show how a precise knowledge of parton distribution functions, in particular those of the u and d quarks, can be used to constrain a certain class of New Physics models in which new heavy charged resonances couple to quarks and leptons. We illustrate the method by considering a left-right symmetric model with a W' from a SU(2)_R gauge sector produced in quark-antiquark annihilation and decaying into a charged lepton and a heavy Majorana neutrino. We discuss a number of quark and lepton mixing scenarios, and simulate both signals and backgrounds in order to determine the size of the expected charge asymmetry. We show that various quark-W' mixing scenarios can indeed be constrained by charge asymmetry measurements at the LHC, particularly at 14 TeV centre of mass energy.Comment: 14 pages, 3 figure

The γγ→J/ψJ/ψ\gamma \gamma \to J/\psi J/\psi reaction and the J/ψJ/ψJ/\psi J/\psi pair production in exclusive ultraperipheral ultrarelativistic heavy ion collisions

We calculate the cross section for the $\gamma \gamma \to J/\psi J/\psi$ process. Two mechanisms are considered: box (two-loop) diagrams of the order of $O(\alpha_{em}^2 \alpha_s^2)$ and two-gluon exchange of the order of $O(\alpha_{em}^2 \alpha_s^4)$. The first mechanism is calculated in the heavy-quark non-relativistic approximation while the second case we also include the effects of quantum motion of quarks in the bound state. The box contribution dominates at energies close to the threshold ($W <$ 15 GeV) while the two-gluon mechanism takes over at $W >$ 15 GeV. Including the bound-state wave function effects for the two-gluon exchange mechanism gives a cross section 0.1 - 0.4 pb, substantially smaller than that in the non-relativistic limit (0.4 - 1.6 pb). We also find a strong infrared sensitivity which manifests itself in a rather strong dependence on the mass for the $t$-channel gluons. The elementary cross section is then used in the Equivalent Photon Approximation (EPA) in the impact parameter space to calculate the cross section for $^{208}Pb+^{208}Pb \to ^{208}Pb + J/\psi J/\psi + ^{208}Pb$ reaction. Distributions in rapidity of the $J/\psi J/\psi$ pair and invariant mass of the pair are shown.Comment: 15 pages, 11 figure

Mass Spectrum in R-Parity Violating mSUGRA and Benchmark Points

We investigate in detail the low-energy spectrum of the R-parity violating mSUGRA model using the computer program \texttt{SOFTSUSY}. We impose the experimental constraints from the measurement of the anomalous magnetic moment of the muon, $(g-2)_\mu$, the decay b\ra s\gamma as well as the mass bounds from direct searches at colliders, in particular on the Higgs boson and the lightest chargino. We also include a new calculation for the R parity violating contribution to \Br(B_s\ra \mu^+\mu^-). We then focus on cases where the lightest neutralino is {\em not} the lightest supersymmetric particle (LSP). In this region of parameter space either the lightest scalar tau (stau) or the scalar tau neutrino (tau sneutrino) is the LSP. We suggest four benchmark points with typical spectra and novel collider signatures for detailed phenomenological analysis and simulation by the LHC collaborations.Comment: 19 pages, 11 figure

R-Parity violating minimal supergravity at the LHC

We consider the case where supersymmetry with broken R-parity is embedded in the minimal supergravity model (mSUGRA). This alters the standard mSUGRA spectrum and opens a wide range in parameter space, where the scalar tau is the lightest supersymmetric particle, instead of the lightest neutralino. We study the resulting LHC phenomenology. Promising signatures would be detached vertices from long-lived staus, multi lepton final states and multi-tau final states. We investigate in detail the corresponding cross sections and decay rates in characteristic benchmark scenarios.Comment: Submitted for the SUSY07 proceedings, 4 pages, LaTeX, 5 eps figure