We study the production of same-sign W boson pairs at the LHC in double parton interactions. Compared with simple factorised double parton distributions (dPDFs), we show that the recently developed dPDFs, GS09, lead to non-trivial kinematic correlations between the W bosons. A numerical study of the prospects for observing this process using same-sign dilepton signatures, including W ± W ± jj, di-boson and heavy flavour backgrounds, at 14 TeV centre-of-mass energy is then performed. It is shown that a small excess of same-sign dilepton events from double parton scattering over a background dominated by single scattering W ± Z(γ * ) production could be observed at the LHC.

We argue that the recent LHCb observation of J/ψ-pair production indicates a significant contribution from double parton scattering, in addition to the standard single parton scattering component. We propose a method to measure the double parton scattering at LHCb using leptonic final states from the decay of two prompt J/ψ mesons.PACS numbers: 12.20. Ds, 13.85.Ni, 14.40.Lb Introduction. The Large Hadron Collider (LHC) provides a unique environment for precise measurements of hitherto poorly understood phenomena. Since the flux of incoming partons increases with the collision energy, there is a high probability at the LHC of multiparton scattering, i.e. scattering of more than one pair of partons in the same hadron-hadron collision. The partonparton correlations and distributions of multiple partons within a proton are difficult to address within the framework of perturbative QCD. Therefore detailed experimental studies of multi-parton interactions are of great importance. In particular, it is widely expected that measurements of double parton scattering (DPS) processes with final states carrying relatively large transverse momentum (p T ) will provide relevant information on the nature of multiple scattering. Probing DPS processes using leptonic final states has been discussed in [1]. In this Letter, we discuss how observing four-muon final states from pair production of J/ψ could provide additional experimental input.

We investigate in detail the low-energy spectrum of the R-parity violating minimal supergravity model using the computer program SOFTSUSY. We impose the experimental constraints from the measurement of the anomalous magnetic moment of the muon, (g − 2)µ, the decay b → sγ 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(Bs → µ + µ − ). We then focus on cases where the lightest neutralino is 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.

We study the splitting functions for the evolution of fragmentation distributions and the coefficient functions for single-hadron production in semi-inclusive e + e − annihilation in massless perturbative QCD for small values of the momentum fraction and scaling variable x, where their fixed-order approximations are completely destabilized by huge double logarithms of the form α n s x −1 ln 2n−a x. Complete analytic all-order expressions in Mellin-N space are presented for the resummation of these terms at the next-to-next-to-leading logarithmic accuracy. The poles for the first moments, related to the evolution of hadron multiplicities, and the small-x instabilities of the next-to-leading order splitting and coefficient functions are removed by this resummation, which leads to an oscillatory small-x behaviour and functions that can be used at N = 1 and down to extremely small values of x. First steps are presented towards extending these results to the higher accuracy required for an all-x combination with the state-of-the-art next-to-next-to-leading order large-x results.If the constants up to F (m) n,ℓ are known for all n and ℓ, then the splitting functions and coefficient functions can be determined at N m LL accuracy at all orders of the strong coupling. As observed in Ref. [19], the n th order small-x contributions to F T, φ are built up from n terms of the form(2.4)Since the terms with ε −2n+1 , . . . , ε −n−1 have to cancel in sum (2.1), there are n−1 relations between the LL coefficients A n,k which lead to the constants F (0) n,ℓ in Eq. (2.3), n−2 relations between the NLL coefficients B n,k etc. As discussed above, a N m LO calculation fixes the (nonvanishing) coefficients of ε −n , . . . , ε −n+m at all orders n, adding m + 1 more relations between the coefficients in Eq. (2.4). Consequently the highest m+1 double logarithms, i.e., the N m LL approximation, can be determined order by order from the N m LO results. Finally the resulting series, here calculated to order α 18 s using FORM and TFORM [24], can be employed to find their generating functions via over-constrained systems of linear equations. The whole procedure is analogous to, if computationally more involved than, the large-x resummation in Ref. [25].

1 The capital 'LARGE' emphasises that the volume is enormously large compared to the string scale. 2 Unless otherwise specified, throughout this paper numerical values of lengths and volumes will all be in units of the fundamental (string) scale, ls = 2π √ α ′ .

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In the minimal supersymmetric extension to the standard model, a nonzero lepton number violating coupling lambda(111);(') predicts both neutrinoless double-beta-decay and resonant single slepton production at the LHC. We show that, in this case, if neutrinoless double beta decay is discovered in the next generation of experiments, there exist good prospects to observe single slepton production at the LHC. Neutrinoless double beta decay could otherwise result from a different source (such as a nonzero Majorana neutrino mass). Resonant single slepton production at the LHC can therefore discriminate between the lambda(111);(') neutrinoless double-beta-decay mechanism and others.

We discuss how the mass of new physics particles involved in a pair of short decay chains leading to two invisible particles, for example slepton pair production, followed by the decay into two leptons and two neutralinos, may be measured in central exclusive production (CEP) with forward proton tagging. We show how the existing mass measurement strategies in CEP may be improved by making full use of the mass-shell constraints, and demonstrate that, with around 30 signal events, the masses of the slepton and neutralino can be measured with an accuracy of a few GeV.2 In the present context, there are 6 (= 8 − 2) unknowns: the four momenta of the twoχ 0 1 (8), minus the measured missing transverse momenta (2).