W. J. Stirling - IPPP, Durham University, England

W. J. Stirling
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Name
W. J. Stirling
Affiliation
IPPP, Durham University, England
City
Durham
Country
United Kingdom

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High Energy Physics - Phenomenology (48)
 
High Energy Physics - Experiment (5)
 
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Publications Authored By W. J. Stirling

2016Nov
Authors: K. Akiba1, M. Akbiyik2, M. Albrow3, M. Arneodo4, V. Avati5, J. Baechler6, O. Villalobos Baillie7, P. Bartalini8, J. Bartels9, S. Baur10, C. Baus11, W. Beaumont12, U. Behrens13, D. Berge14, M. Berretti15, E. Bossini16, R. Boussarie17, S. Brodsky18, M. Broz19, M. Bruschi20, P. Bussey21, W. Byczynski22, J. C. Cabanillas Noris23, E. Calvo Villar24, A. Campbell25, F. Caporale26, W. Carvalho27, G. Chachamis28, E. Chapon29, C. Cheshkov30, J. Chwastowski31, R. Ciesielski32, D. Chinellato33, A. Cisek34, V. Coco35, P. Collins36, J. G. Contreras37, B. Cox38, D. de Jesus Damiao39, P. Davis40, M. Deile41, D. D'Enterria42, D. Druzhkin43, B. Ducloué44, R. Dumps45, R. Dzhelyadin46, P. Dziurdzia47, M. Eliachevitch48, P. Fassnacht49, F. Ferro50, S. Fichet51, D. Figueiredo52, B. Field53, D. Finogeev54, R. Fiore55, J. Forshaw56, A. Gago Medina57, M. Gallinaro58, A. Granik59, G. von Gersdorff60, S. Giani61, K. Golec-Biernat62, V. P. Goncalves63, P. Göttlicher64, K. Goulianos65, J. -Y. Grosslord66, L. A. Harland-Lang67, H. Van Haevermaet68, M. Hentschinski69, R. Engel70, G. Herrera Corral71, J. Hollar72, L. Huertas73, D. Johnson74, I. Katkov75, O. Kepka76, M. Khakzad77, L. Kheyn78, V. Khachatryan79, V. A. Khoze80, S. Klein81, M. van Klundert82, F. Krauss83, A. Kurepin84, N. Kurepin85, K. Kutak86, E. Kuznetsova87, G. Latino88, P. Lebiedowicz89, B. Lenzi90, E. Lewandowska91, S. Liu92, A. Luszczak93, M. Luszczak94, J. D. Madrigal95, M. Mangano96, Z. Marcone97, C. Marquet98, A. D. Martin99, T. Martin100, M. I. Martinez Hernandez101, C. Martins102, C. Mayer103, R. Mc Nulty104, P. Van Mechelen105, R. Macula106, E. Melo da Costa107, T. Mertzimekis108, C. Mesropian109, M. Mieskolainen110, N. Minafra111, I. L. Monzon112, L. Mundim113, B. Murdaca114, M. Murray115, H. Niewiadowski116, J. Nystrand117, E. G. de Oliveira118, R. Orava119, S. Ostapchenko120, K. Osterberg121, A. Panagiotou122, A. Papa123, R. Pasechnik124, T. Peitzmann125, L. A. Perez Moreno126, T. Pierog127, J. Pinfold128, M. Poghosyan129, M. E. Pol130, W. Prado131, V. Popov132, M. Rangel133, A. Reshetin134, J. -P. Revol135, M. Rijssenbeek136, M. Rodriguez137, B. Roland138, C. Royon139, M. Ruspa140, M. Ryskin141, A. Sabio Vera142, G. Safronov143, T. Sako144, H. Schindler145, D. Salek146, K. Safarik147, M. Saimpert148, A. Santoro149, R. Schicker150, J. Seger151, S. Sen152, A. Shabanov153, W. Schafer154, G. Gil Da Silveira155, P. Skands156, R. Soluk157, A. van Spilbeeck158, R. Staszewski159, S. Stevenson160, W. J. Stirling161, M. Strikman162, A. Szczurek163, L. Szymanowski164, J. D. Tapia Takaki165, M. Tasevsky166, K. Taesoo167, C. Thomas168, S. R. Torres169, A. Tricomi170, M. Trzebinski171, D. Tsybychev172, N. Turini173, R. Ulrich174, E. Usenko175, J. Varela176, M. Lo Vetere177, A. Villatoro Tello178, A. Vilela Pereira179, D. Volyanskyy180, S. Wallon181, G. Wilkinson182, H. Wöhrmann183, K. C. Zapp184, Y. Zoccarato185
Affiliations: 1LHC Forward Physics Working Group, 2LHC Forward Physics Working Group, 3LHC Forward Physics Working Group, 4LHC Forward Physics Working Group, 5LHC Forward Physics Working Group, 6LHC Forward Physics Working Group, 7LHC Forward Physics Working Group, 8LHC Forward Physics Working Group, 9LHC Forward Physics Working Group, 10LHC Forward Physics Working Group, 11LHC Forward Physics Working Group, 12LHC Forward Physics Working Group, 13LHC Forward Physics Working Group, 14LHC Forward Physics Working Group, 15LHC Forward Physics Working Group, 16LHC Forward Physics Working Group, 17LHC Forward Physics Working Group, 18LHC Forward Physics Working Group, 19LHC Forward Physics Working Group, 20LHC Forward Physics Working Group, 21LHC Forward Physics Working Group, 22LHC Forward Physics Working Group, 23LHC Forward Physics Working Group, 24LHC Forward Physics Working Group, 25LHC Forward Physics Working Group, 26LHC Forward Physics Working Group, 27LHC Forward Physics Working 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The goal of this report is to give a comprehensive overview of the rich field of forward physics, with a special attention to the topics that can be studied at the LHC. The report starts presenting a selection of the Monte Carlo simulation tools currently available, chapter 2, then enters the rich phenomenology of QCD at low, chapter 3, and high, chapter 4, momentum transfer, while the unique scattering conditions of central exclusive production are analyzed in chapter 5. The last two experimental topics, Cosmic Ray and Heavy Ion physics are presented in the chapter 6 and 7 respectively. Read More

We present high-resolution neutron Compton scattering measurements of liquid $^3$He below its renormalized Fermi temperature. Theoretical predictions are in excellent agreement with the experimental data when instrumental resolution and final state effects are accounted for. Our results resolve the long-standing inconsistency between theoretical and experimental estimates of the average atomic kinetic energy. Read More

We review recent results within the Durham model of central exclusive production. We discuss the theoretical aspects of this approach and consider the phenomenological implications in a variety of processes, comparing to existing collider data and addressing the possibilities for the future. Read More

We present the results of a recent novel application of the `hard exclusive' perturbative formalism to the process gg --> MMbar at large angles, where M (Mbar) is a light meson (anti-meson). As well as discussing the important theoretical features of the relevant leading-order gg --> qqbar(gg) qqbar(gg) 6-parton amplitudes, we also comment on their phenomenological implications. In particular, we consider the central exclusive production of meson pairs at comparatively large transverse momentum k_t, which is expected to proceed via this mechanism. Read More

Currently, the long-standing issue concerning the size of the gluonic content of the eta' and eta mesons remains unsettled. With this in mind we consider the central exclusive production (CEP) of eta', eta meson pairs in the perturbative regime, applying the Durham pQCD-based model of CEP and the `hard exclusive' formalism to evaluate the meson production subprocess. We calculate for the first time the relevant parton-level processes gg --> qqbar gg and gg --> gggg, where the final-state gg and qqbar pairs form a pseudoscalar flavour-singlet state. Read More

Selected new results in central exclusive production (CEP) processes within the pQCD-based Durham model are discussed. Topics covered include the CEP of SM and BSM Higgs-like particles, meson pair CEP and the gap survival probability. Read More

We consider the effect of next-to-leading order (NLO) electroweak corrections to Standard Model 2-to-2 processes, taking into account the potentially large double logarithms originating from both real and virtual corrections. A study of the leading Sudakov logarithms is presented and Bloch-Nordsieck (BN) violations are discussed for processes at the CERN Large Hadron Collider. In particular, we focus on the processes Z/photon+jet and also the ratio of Z to photon production. Read More

We investigate the effect of extending the standard MSTW parameterisation of input parton distribution functions (PDFs) using Chebyshev polynomials. We find evidence that four powers in the polynomial are sufficient for extremely high precision. Applying this to valence and sea quarks we find an improvement in the global fit, but a significant change only in the small-$x$ valence up-quark PDF, $u_V$. Read More

We study the polarisation of gauge bosons produced at the LHC. Polarisation effects for W bosons manifest themselves in the angular distributions of the lepton and in the distributions of lepton transverse momentum and missing transverse energy. The distributions also depend on the selection cuts, with kinematic effects competing with polarisation effects. Read More

Central exclusive production (CEP) processes in high-energy hadron-hadron collisions provide an especially clean environment in which to measure the nature and quantum numbers (in particular, the spin and parity) of new resonance states. Encouraged by the broad agreement between experimental measurements and theoretical predictions based on the Durham approach, we perform a detailed phenomenological analysis of diphoton and meson pair CEP final states, paying particular attention to the theoretical uncertainties in the predictions, including those from parton distribution functions, higher-order perturbative corrections, and non-perturbative and proton dissociation contributions. We present quantitative cross-section predictions for these CEP final states at the RHIC, Tevatron and LHC colliders. Read More

The production of charm quark jets in association with electroweak gauge bosons at the LHC can be used as a tool to constrain quark parton distribution functions (PDFs). Motivated by recent measurements at the Tevatron and LHC, we calculate cross sections for $W/Z+c$, comparing these to $W/Z+\textrm{jet}$, for various PDF sets. The cross-section differences can be understood in terms of the different underlying PDFs, with the strange quark distribution being particularly important for $W+c$ production. Read More

We discuss the role of two different types of diagram in the proton-proton double parton scattering (DPS) cross section - single and double perturbative splitting graphs. Using explicit calculations of simple graphs from these classes we show that the treatment of these graphs by the 'double PDF' framework for describing the DPS cross section, introduced a number of years ago by Snigirev and collaborators, is unsatisfactory. We suggest that a contribution from single perturbative splitting graphs should be included in the DPS cross section, albeit with a different geometrical prefactor to the contribution from 'zero perturbative splitting' graphs. Read More

Motivated by evidence for the existence of dark matter, many new physics models predict the pair production of new particles, followed by the decays into two invisible particles, leading to a momentum imbalance in the visible system. For the cases where all four components of the vector sum of the two `missing' momenta are measured from the momentum imbalance, we present analytic solutions of the final state system in terms of measureable momenta, with the mass shell constraints taken into account. We then introduce new variables which allow the masses involved in the new physics process, including that of the dark matter particles, to be extracted. Read More

2012Jan
Authors: LHC Higgs Cross Section Working Group, S. Dittmaier1, C. Mariotti2, G. Passarino3, R. Tanaka4, S. Alekhin, J. Alwall, E. A. Bagnaschi, A. Banfi, J. Blumlein, S. Bolognesi, N. Chanon, T. Cheng, L. Cieri, A. M. Cooper-Sarkar, M. Cutajar, S. Dawson, G. Davies, N. De Filippis, G. Degrassi, A. Denner, D. D'Enterria, S. Diglio, B. Di Micco, R. Di Nardo, R. K. Ellis, A. Farilla, S. Farrington, M. Felcini, G. Ferrera, M. Flechl, D. de Florian, S. Forte, S. Ganjour, M. V. Garzelli, S. Gascon-Shotkin, S. Glazov, S. Goria, M. Grazzini, J. -Ph. Guillet, C. Hackstein, K. Hamilton, R. Harlander, M. Hauru, S. Heinemeyer, S. Hoche, J. Huston, C. Jackson, P. Jimenez-Delgado, M. D. Jorgensen, M. Kado, S. Kallweit, A. Kardos, N. Kauer, H. Kim, M. Kovac, M. Kramer, F. Krauss, C. -M. Kuo, S. Lehti, Q. Li, N. Lorenzo, F. Maltoni, B. Mellado, S. O. Moch, A. Muck, M. Muhlleitner, P. Nadolsky, P. Nason, C. Neu, A. Nikitenko, C. Oleari, J. Olsen, S. Palmer, S. Paganis, C. G. Papadopoulos, T . C. Petersen, F. Petriello, F. Petrucci, G. Piacquadio, E. Pilon, C. T. Potter, J. Price, I. Puljak, W. Quayle, V. Radescu, D. Rebuzzi, L. Reina, J. Rojo, D. Rosco, G. P. Salam, A. Sapronov, J. Schaarschmidt, M. Schonherr, M. Schumacher, F. Siegert, P. Slavich, M. Spira, I. W. Stewart, W. J. Stirling, F. Stockli, C. Sturm, F. J. Tackmann, R. S. Thorne, D. Tommasini, P. Torrielli, F. Tramontano, Z. Trocsanyi, M. Ubiali, S. Uccirati, M. Vazquez Acosta, T. Vickey, A. Vicini, W. J. Waalewijn, D. Wackeroth, M. Warsinsky, M. Weber, M. Wiesemann, G. Weiglein, J. Yu, G. Zanderighi
Affiliations: 1eds., 2eds., 3eds., 4eds.

This Report summarises the results of the second year's activities of the LHC Higgs Cross Section Working Group. The main goal of the working group was to present the state of the art of Higgs Physics at the LHC, integrating all new results that have appeared in the last few years. The first working group report Handbook of LHC Higgs Cross Sections: 1. Read More

We review the recent progress in the theoretical description and experimental observation of multiple parton interactions. Subjects covered include experimental measurements of minimum bias interactions and of the underlying event, models of soft physics implemented in Monte Carlo generators, developments in the theoretical description of multiple parton interactions and phenomenological studies of double parton scattering. This article stems from contributions presented at the Helmholtz Alliance workshop on "Multi-Parton Interactions at the LHC", DESY Hamburg, 13-15 September 2010. Read More

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. Read More

A spin-3/2 top quark excitation originating in string realisations of the RS scenario has an effect on the production of top-antitop pairs in hadron-hadron collisions. We study the additional contribution of this state to the cross section for the LHC. We comment on the prospect of discovery or exclusion for a range of masses and couplings at both 7 and 14 TeV and show that the reach extends significantly with increasing centre-of-mass energy. Read More

We discuss the prospects of observing double parton scattering (DPS) processes with purely leptonic final states at the LHC. We first study same-sign W pair production, which is particularly suited for studying momentum and valence number conservation effects, followed by discussions on double Drell-Yan and production of J/psi pairs. The effects of initial state and intrinsic transverse momentum smearing on pair-wise transverse momentum balance characteristic to DPS are studied quantitatively. Read More

We study the prospects for observing double parton scattering through four-muon final states, forming two opposite-sign muon pairs, in the LHCb experiment in pp collisions at 14 TeV centre of mass energy. We consider two special cases, namely double Drell-Yan and J/psi-pair production. The kinematic properties and prospects for observing these processes are discussed. Read More

The irreducible background from Z(nunu)+jets, to beyond the Standard Model searches at the LHC, can be calibrated using gamma+jets data. The method utilises the fact that at high vector boson pT, the event kinematics are the same for the two processes and the cross sections differ mainly due to the boson-quark couplings. The method relies on a precise prediction from theory of the Z/gamma cross section ratio at high pT, which should be insensitive to effects from full event simulation. Read More

We present a study of the central exclusive production (CEP) of meson pairs, MMbar, at sufficiently high invariant mass that a perturbative QCD formalism is applicable. Within this framework, MMbar production proceeds via the gg --> MMbar hard scattering sub-process, which can be calculated within the hard exclusive formalism. We present explicit calculations for the gg --> MMbar helicity amplitudes for different meson states and, using these, show results for meson pair CEP in the perturbative regime. Read More

We argue that the recent LHCb observation of J/psi-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/psi mesons. Read More

The central exclusive production (CEP) of heavy resonance states that subsequently decay into meson pairs, MMbar, is an important signature for such processes at hadron colliders. However there is a potentially important background from the direct QCD production of meson pairs, as mediated for example by the exclusive gg --> MMbar hard scattering subprocess. This is in fact an interesting process in its own right, testing novel aspects of perturbative QCD technology. Read More

We consider Next-to-Leading-Order QCD corrections to ADD graviton exchange relevant for Deep Inelastic Scattering experiments. We calculate the relevant NLO structure functions by calculating the virtual and real corrections for a set of graviton interaction diagrams, demonstrating the expected cancellation of the UV and IR divergences. We compare the NLO and LO results at the centre-of-mass energy relevant to HERA experiments as well as for the proposed higher energy lepton-proton collider, LHeC, which has a higher fundamental scale reach. Read More

We present a detailed study of the double parton scattering (DPS) singularity, which is a specific type of Landau singularity that can occur in certain one-loop graphs in theories with massless particles. A simple formula for the DPS singular part of a four-point diagram with arbitrary internal/external particles is derived in terms of the transverse momentum integral of a product of light cone wavefunctions with tree-level matrix elements. This is used to reproduce and explain some results for DPS singularities in box integrals that have been obtained using traditional loop integration techniques. Read More

We compute transplanckian parton scattering in flat extra-dimensional theories at the LHC and at the recently discussed high-energy upgrade (HE LHC). We report new leading-order calculations of the QCD background. We apply appropriate cuts to satisfy the necessary conditions for the eikonal approximation to be valid while at the same time maximising the signal to background ratio at LHC energies. Read More

This document is intended as a study of benchmark cross sections at the LHC (at 7 TeV) at NLO using modern parton distribution functions currently available from the 6 PDF fitting groups that have participated in this exercise. It also contains a succinct user guide to the computation of PDFs, uncertainties and correlations using available PDF sets. A companion note, also submitted to the archive, provides an interim summary of the current recommendations of the PDF4LHC working group for the use of parton distribution functions and of PDF uncertainties at the LHC, for cross section and cross section uncertainty calculations. Read More

Central exclusive production (CEP) processes in high-energy hadron collisions offer a very promising framework for studying both novel aspects of QCD and new physics signals. We report on the results of a theoretical study of the CEP of heavy quarkonia (chi and eta) at the Tevatron, RHIC and LHC. These processes provide important information on the physics of bound states and can probe the current ideas and methods of QCD, such as effective field theories and lattice QCD. Read More

We study the Central Exclusive Production (CEP) of chi_cJ and eta_c mesons at RHIC in proton-proton collisions. We consider the chi_cJ --> J/psi + gamma decay channels and, recalling that the J_z=0 suppression of the J=1,2 states can be compensated by their larger branchings to J/psi + gamma, present predictions of rates and distributions for chi_c(0,1,2) production. Particular attention is paid to the impact of p_t cuts applied to the outgoing protons, which can influence the relative rates significantly. Read More

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. Read More

We study the sensitivity of our recent MSTW 2008 NLO and NNLO PDF analyses to the values of the charm- and bottom-quark masses, and we provide additional public PDF sets for a wide range of these heavy-quark masses. We quantify the impact of varying m_c and m_b on the cross sections for W, Z and Higgs production at the Tevatron and the LHC. We generate 3- and 4-flavour versions of the (5-flavour) MSTW 2008 PDFs by evolving the input PDFs and alpha_S determined from fits in the 5-flavour scheme, including the eigenvector PDF sets necessary for calculation of PDF uncertainties. Read More

We examine the effect of including the `combined' HERA structure function data in the MSTW global fit for parton distribution functions (PDFs). The combined neutral-current HERA data have a significant, if not dramatic, effect, of up to 2--3% at NLO for Z boson and Higgs production at the Tevatron and LHC, and a generally slightly smaller effect, particularly on LHC processes, at NNLO. This is an amount comparable, or less than, the typical PDF uncertainties, and hence we do not intend to release an imminent update to the MSTW 2008 fit. Read More

Central exclusive production (CEP) processes in high-energy proton -- (anti)proton collisions offer a very promising framework within which to study both novel aspects of QCD and new physics signals. Among the many interesting processes that can be studied in this way, those involving the production of heavy (c,b) quarkonia and gamma gamma states have sufficiently well understood theoretical properties and sufficiently large cross sections that they can serve as `standard candle' processes with which we can benchmark predictions for new physics CEP at the CERN Large Hadron Collider. Motivated by the broad agreement with theoretical predictions of recent CEP measurements at the Fermilab Tevatron, we perform a detailed quantitative study of heavy quarkonia (chi and eta) and gamma gamma production at the Tevatron, RHIC and LHC, paying particular attention to the various uncertainties in the calculations. Read More

The charge asymmetry in W + jets production at the LHC can serve to calibrate the presence of New Physics contributions. We study the ratio {\sigma}(W^+ + n jets)/{\sigma}(W^- + n jets) in the Standard Model for n <= 4, paying particular attention to the uncertainty in the prediction from higher-order perturbative corrections and uncertainties in parton distribution functions. We show that these uncertainties are generally of order a few percent, making the experimental measurement of the charge asymmetry ratio a particularly useful diagnostic tool for New Physics contributions. Read More

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 same-sign WWjj, di-boson and heavy flavour backgrounds, at 14 TeV centre-of-mass energy is then performed. Read More

It is anticipated that hard double parton scatterings will occur frequently in the collisions of the LHC, producing interesting signals and significant backgrounds to certain single scattering processes. For double scattering processes in which the same hard scale t = ln(Q^2) is involved in both collisions, we require the double parton distributions (dPDFs) D_h^{j_1j_2}(x_1,x_2;t) in order to make theoretical predictions of their rates and properties. We describe the development of a new set of leading order dPDFs that represents an improvement on approaches used previously. Read More

Motivated by the recent experimental observation of exclusive chi_c events at the Tevatron, we revisit earlier studies of central exclusive scalar chi_c0 meson production, before generalising the existing formalism to include chi_c1 and chi_c2 mesons. Although chi_c0 production was previously assumed to be dominant, we find that the chi_c1 and chi_c2 rates for the experimentally considered chi_c -> J/psi gamma -> mu+ mu- gamma decay process are in fact comparable to the chi_c0 rate. We have developed a new Monte Carlo event generator, SuperCHIC, which models the central exclusive production of the three chi_c states via this decay chain, and have explored possible ways of distinguishing them, given that their mass differences are not resolvable within the current experimental set-up. Read More

We outline the historical development of MRST/MSTW parton distribution functions (PDFs), and clarify how they should be regarded when compared to the most up-to-date 2008 MSTW sets, noting which sets are now obsolete and the reasons why. Read More

We determine the uncertainty on the strong coupling alpha_S due to the experimental errors on the data fitted in global analysis of hard-scattering data, within the standard framework of leading-twist fixed-order collinear factorisation in the MSbar scheme, finding that alpha_S(M_Z^2) = 0.1202^{+0.0012}_{-0. Read More

We present updated leading-order, next-to-leading order and next-to-next-to-leading order parton distribution functions ("MSTW 2008") determined from global analysis of hard-scattering data within the standard framework of leading-twist fixed-order collinear factorisation in the MSbar scheme. These parton distributions supersede the previously available "MRST" sets and should be used for the first LHC data-taking and for the associated theoretical calculations. New data sets fitted include CCFR/NuTeV dimuon cross sections, which constrain the strange quark and antiquark distributions, and Tevatron Run II data on inclusive jet production, the lepton charge asymmetry from W decays and the Z rapidity distribution. Read More

Parton distribution functions (pdfs) are an important ingredient for LHC phenomenology. Recent progress in determining pdfs from global analyses is reviewed, and some of the most important outstanding issues are highlighted. Particular attention is paid to the precision with which predictions for LHC `standard-candle' cross sections can be made, and also to new information that LHC can provide on pdfs. Read More

We consider the impact that can be made on our understanding of parton distributions (PDFs) and QCD from early measurements at the LHCb experiment. The high rapidity values make the experiment uniquely suited to a detailed study of small-x parton distributions and hence will make a significant contribution towards the clarification of both experimental and theoretical uncertainties on PDFs and their applications. Read More

We discuss selected topics in the forthcoming MSTW 2008 determination of parton distributions by global analysis. The tolerance parameter controlling the uncertainties on the parton distributions is now determined by a new dynamic procedure for each eigenvector of the covariance matrix. New data sets fitted include Tevatron Run II data on inclusive jet production, the lepton charge asymmetry from W decays and the Z rapidity distribution. Read More

We present the FP420 R&D project, which has been studying the key aspects of the development and installation of a silicon tracker and fast-timing detectors in the LHC tunnel at 420 m from the interaction points of the ATLAS and CMS experiments. These detectors would measure precisely very forward protons in conjunction with the corresponding central detectors as a means to study Standard Model (SM) physics, and to search for and characterise New Physics signals. This report includes a detailed description of the physics case for the detector and, in particular, for the measurement of Central Exclusive Production, pp --> p + phi + p, in which the outgoing protons remain intact and the central system phi may be a single particle such as a SM or MSSM Higgs boson. Read More

The prospects for central exclusive diffractive (CED) production of MSSM Higgs bosons at the LHC are reviewed. It is shown that the CED channels, making use of forward proton detectors at the LHC installed at 220 m and 420 m distance around ATLAS and / or CMS, can provide important information on the Higgs sector of the MSSM. In particular, CED production of the neutral CP-even Higgs bosons h and H and their decays into bottom quarks has the potential to probe interesting regions of the M_A--tan_beta parameter plane of the MSSM and may give access to the bottom Yukawa couplings of the Higgs bosons up to masses of M_H \approx 250 GeV. Read More

Combined analyses at the Large Hadron Collider and at the International Linear Collider are important to unravel a difficult region of supersymmetry that is characterized by scalar SUSY particles with masses around 2 TeV. Precision measurements of masses, cross sections and forward-backward asymmetries allow to determine the fundamental supersymmetric parameters even if only a small part of the spectrum is accessible. Mass constraints for the heavy particles can be derived. Read More

The physics potential of the Large Hadron Collider in combination with the planned International Linear Collider is discussed for a difficult region of supersymmetry that is characterized by scalar SUSY particles with masses around 2 TeV. Precision measurements of masses, cross sections and forward-backward asymmetries allow to determine the fundamental supersymmetric parameters even if only a small part of the spectrum is accessible. No assumptions on a specific SUSY-breaking mechanism are imposed. Read More

Recent calculations, concerning the magnetism of uranium in the U/Fe multilayer system have described the spatial dependence of the 5f polarization that might be expected. We have used the x-ray resonant magnetic reflectivity technique to obtain the profile of the induced uranium magnetic moment for selected U/Fe multilayer samples. This study extends the use of x-ray magnetic scattering for induced moment systems to the 5f actinide metals. Read More

We show that the use of forward proton detectors at the LHC installed at 220 m and 420 m distance around ATLAS and / or CMS can provide important information on the Higgs sector of the MSSM. We analyse central exclusive production of the neutral CP-even Higgs bosons h and H and their decays into bottom quarks, tau leptons and W bosons in different MSSM benchmark scenarios. Using plausible estimates for the achievable experimental efficiencies and the relevant background processes, we find that the prospective sensitivity of the diffractive Higgs production will allow to probe interesting regions of the M_A--tan_beta parameter plane of the MSSM. Read More

We present a new set of parton distributions obtained at NNLO. These differ from the previous sets available at NNLO due to improvements in the theoretical treatment. In particular we include a full treatment of heavy flavours in the region near the quark mass. Read More