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Abstract
Heavy-quark jets are important in many of today's collider studies and searches, yet predictions for them are subject to much larger uncertainties than for light jets. This is because of strong enhancements in higher orders from large logarithms, ln(p_t/m_Q). We propose a new definition of heavy-quark jets, which is free of final-state logarithms to all orders and such that all initial-state collinear logarithms can be resummed into the heavy-quark parton distributions. Heavy-jet spectra can then be calculated in the massless approximation, which is simpler than a massive calculation ...
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(19 Nov 1999)
Abstract
Within an effective field theory framework we study heavy-quark--antiquark systems with a typical distance between the heavy quark and the antiquark smaller than $1/Λ_ QCD$. A suitable definition of the potential is given within this framework, while non-potential (retardation) effects are taken into account in a systematic way. We explore different physical systems. Model-independent results on the short distance behavior of the energies of the gluonic excitations between static quarks are obtained. Finally, we show how infrared renormalons affecting the static potential get cancelled in the effective theory. ...
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(14 Jan 2013)
Abstract
The announcement of the discovery of a Higgs boson-like particle at CERN will be remembered as one of the milestones of the scientific endeavor of the 21st century. In this paper we present a study of information spreading processes on Twitter before, during and after the announcement of the discovery of a new particle with the features of the elusive Higgs boson on 4th July 2012. We report evidence for non-trivial spatio-temporal patterns in user activities at individual and global level, such as tweeting, re-tweeting and replying ...
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(26 May 2006)
posted to hep pdf qcd
by andybuckley
on 2013-01-22 12:38:27
Abstract
Parton Density Functions (PDFs) and their uncertainties are extremely important topics for both the Tevatron and the LHC. Experiments at the Tevatron can enhance this knowledge not only by constraining the PDF fits, but also by developing and refining the available PDF tools through feed-back from the experiments that are currently analyzing the highest energy hadron collider data available. It is important that the community has standardized tools and methods at its disposal. In this note we summarize briefly the most recent developments of the The Les Houches ...
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(29 Dec 2012)
posted to hep higgs lhc parity physics
by andybuckley
on 2013-01-04 16:50:05
Abstract
A study is presented of the mass and spin-parity of the new boson recently observed at the LHC at a mass near 125 GeV. An integrated luminosity of 17.3 inverse femtobarns, collected by the CMS experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, is used. The measured mass in the ZZ channel, where both Z bosons decay to e or mu pairs, is 126.2 +/- 0.6 (stat.) +/- 0.2 (syst.) GeV. The angular distributions of the lepton pairs in this channel are sensitive ...
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(20 Jul 2012)
Abstract
We present a process-independent technique to consistently combine next-to-leading order parton-level calculations of varying jet multiplicity and parton showers. Double counting is avoided by means of a modified truncated shower scheme. This method preserves both the fixed-order accuracy of the parton-level result and the logarithmic accuracy of the parton shower. We discuss the renormalisation and factorisation scale dependence of the approach and present results from an automated implementation in the Sherpa event generator using the test case of W-boson production at the Large Hadron Collider. We observe a dramatic ...
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(20 Jul 2012)
Abstract
We present a new approach to combine multiple NLO parton-level calculations matched to parton showers into a single inclusive event sample. The method provides a description of hard multi-jet configurations at next-to leading order in the perturbative expansion of QCD, and it is supplemented with the all-orders resummed modelling of jet fragmentation provided by the parton shower. The formal accuracy of this technique is discussed in detail, invoking the example of electron-positron annihilation into hadrons. We focus on the effect of renormalisation scale variations in particular. Comparison with experimental ...
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(27 Sep 2012)
Abstract
The next-to-leading order accuracy for MC@NLO results exclusive in J light jets is achieved if the computation is based on matrix elements that feature J and J+1 QCD partons. The simultaneous prediction of observables which are exclusive in different light-jet multiplicities cannot simply be obtained by summing the above results over the relevant range in J; rather, a suitable merging procedure must be defined. We address the problem of such a merging, and propose a solution that can be easily incorporated into existing MC@NLO implementations. We use the ...
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posted to no-tag
by andybuckley
on 2012-12-11 13:51:52
Abstract
We present an alternative approach to identifying and characterizing jet substructure. An angular correlation function is introduced that can be used to extract angular and mass scales within a jet without reference to a clustering algorithm. This procedure gives rise to a number of useful jet observables. As an application, we construct a top quark tagging algorithm that is competitive with existing methods. ...
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Abstract
I present a definition of the cross section for the production of an isolated photon plus $n$ jets which only depends upon direct photon production, and it is independent of the parton-to-photon fragmentation contribution. This prescription, based on a modified cone approach which implements the isolation condition in a smooth way, treats in the same way quarks and gluons and can be directly applied to experimental data in hadron-hadron, photon-hadron and $\epem$ collisions. The case of several, isolated photons in the final state can also be dealt with ...
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(22 May 2012)
by K. Arnold, L. d'Errico, S. Gieseke, et al.D. Grellscheid, K. Hamilton, A. Papaefstathiou, S. Platzer, P. Richardson, C. Rohr, A. Schofield, A. Siodmok, M. Stoll, D. Winn
posted to generator hep herwig mc physics qcd
by andybuckley
on 2012-06-20 22:27:58
Abstract
A new release of the Monte Carlo event generator Herwig++ (version 2.6) is now available. This version comes with a number of improvements including: a new structure for the implementation of next-to-leading order matrix elements; an improved treatment of wide-angle gluon radiation; new hard-coded next-to-leading order matrix elements for deep inelastic scattering and weak vector boson fusion; additional models of physics beyond the Standard Model, including the production of colour sextet particles; a statistical colour reconnection model; automated energy scaling of underlying-event tunes. ...
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(19 Oct 2011)
posted to gluon jets lo nlo qcd quark tagging
by andybuckley
on 2012-06-14 12:33:16
Abstract
Being able to distinguish light-quark jets from gluon jets on an event-by-event basis could significantly enhance the reach for many new physics searches at the Large Hadron Collider. Through an exhaustive search of existing and novel jet substructure observables, we find that a multivariate approach can filter out over 95% of the gluon jets while keeping more than half of the light-quark jets. Moreover, a combination of two simple variables, the charge track multiplicity and the $p_T$-weighted linear radial moment (girth), can achieve similar results. While this pair ...
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(15 Dec 2010)
Abstract
We present an implementation of the next-to-leading order dijet production process in hadronic collisions in the framework of POWHEG, which is a method to implement NLO calculations within a shower Monte Carlo context. In constructing the simulation, we have made use of the POWHEG BOX toolkit, which makes light of many of the most technical steps. The majority of this article is concerned with the study of the predictions of the Monte Carlo simulation. In so doing, we validate our program for use in experimental analyses, elaborating ...
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(18 Aug 2010)
Abstract
We present updated predictions for the total cross section for Higgs boson production through gluon fusion at hadron colliders. In addition to renormalization-group improvement at next-to-next-to-next-to-leading logarithmic accuracy, we incorporate the two-loop electroweak corrections, which leads to the most precise predictions at present. Numerical results are given for Higgs masses between 115 GeV and 200 GeV at the Tevatron with \sqrts=1.96 TeV and the LHC with \sqrts=7-14 TeV. ...
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(2 Aug 2010)
posted to diffraction hep lhc physics qcd
by andybuckley
on 2010-08-08 14:00:57
Abstract
We note that the definition of diffractive events is a matter of convention. We discuss two possible `definitions': one based on unitarity and the other on Large Rapidity Gaps (LRG) or Pomeron exchange. LRG can also arise from fluctuations and we quantify this effect and some of the related uncertainties. We find care must be taken in extracting the Pomeron contribution from LRG events. We show that long-range correlations in multiplicities can arise from the same multi-Pomeron diagrams that are responsible for LRG events, and explain how early ...
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(21 May 2010)
posted to diffraction hep physics pythia qcd
by andybuckley
on 2010-08-08 13:58:13
Abstract
The PYTHIA program can be used to generate high-energy-physics 'events' with sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide a representation, as accurate as possible, of event properties in a wide range of reactions. One such reaction, that is not well understood is Diffraction. Among the several alternative approaches that have been proposed, in PYTHIA, we follow a fairly conventional Pomeron based one, but fully integrated to use the standard PYTHIA machinery for multiple interactions, parton showers and hadronization. ...
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(6 Jul 2010)
Abstract
A selection of the latest and most frequently used parton distribution functions (PDFs) is incorporated in Pythia8, including the Monte Carlo-adapted PDFs from the MSTW and CTEQ collaborations. This article examines the differences in PDFs as well as the effect they have on results of simulations and compare with data collected by the CDF experiment. Monte Carlo-adapted PDFs do a better job than leading- and next-to-leading order PDFs for many observables, but there is room for further improvements. ...
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Abstract
We study the mu<0 branch of the minimal supergravity ansatz of the minimal supersymmetric standard model. The extent to which mu<0 is disfavoured compared to mu>0 in global fits is calculated with Markov Chain Monte Carlo methods and bridge sampling. The fits include state-of-the-art two-loop MSSM contributions to the electroweak observables M_W and sin^2 theta_w^l, as well as the anomalous magnetic moment of the muon (g-2)_mu, the relic density of dark matter and other relevant indirect observables. mu<0 is only marginally disfavoured in global fits and should be ...
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Abstract
If new particles are discovered at the LHC, it will be important to determine their spins in as model-independent a way as possible. We consider the case, commonly encountered in models of physics beyond the Standard Model, of a new scalar or fermion $D$ decaying sequentially into other new particles $C,B,A$ via the decay chain $D\to C q$, $C\to B l^near$, $B\to A l^far$, $l^near$ and $l^far$ being opposite-sign same-flavour charged leptons and $A$ being invisible. We compute the observable 2- and 3-particle invariant mass distributions for all ...
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Abstract
If the cosmic dark matter consists of weakly-interacting massive particles, these particles should be produced in reactions at the next generation of high-energy accelerators. Measurements at these accelerators can then be used to determine the microscopic properties of the dark matter. From this, we can predict the cosmic density, the annihilation cross sections, and the cross sections relevant to direct detection. In this paper, we present studies in supersymmetry models with neutralino dark matter that give quantitative estimates of the accuracy that can be expected. We show that ...
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Abstract
We review constraints on the minimal supersymmetric extension of the Standard Model (MSSM) coming from direct searches at accelerators such as LEP, indirect measurements such as b -> s gamma decay and the anomalous magnetic moment of the muon. The recently corrected sign of pole light-by-light scattering contributions to the latter is taken into account. We combine these constraints with those due to the cosmological density of stable supersymmetric relic particles. The possible indications on the supersymmetric mass scale provided by fine-tuning arguments are reviewed critically. We discuss ...
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Abstract
SOFTSUSY is a program which accurately calculates the spectrum of superparticles in the CP-conserving Minimal Supersymmetric Standard Model (MSSM), with a full flavour mixing structure. The program solves the renormalisation group equations with theoretical constraints on soft supersymmetry breaking terms provided by the user. Weak-scale gauge coupling and fermion mass data (including one-loop finite MSSM corrections) are used as a boundary condition, as well as successful radiative electroweak symmetry breaking. The program can also calculate a measure of fine-tuning. The program structure has been designed to easily generalise to ...
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(4 Mar 2010)
Abstract
We give a brief introduction to theories with extra dimensions. We first introduce the basic formalism for studying extra-dimensional theories, including the Kaluza-Klein decomposition and the effective theory for 3-branes. We then focus on two types of scenarios: large extra dimensions as a solution to the hierarchy problem and TeV$^-1$-size extra dimensions with Standard Model fields propagating in them. We discuss the experimental tests and constraints on these scenarios, and also the questions in particle physics which may be addressed with the help of extra dimensions. This is ...
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Abstract
We propose a new higher-dimensional mechanism for solving the Hierarchy Problem. The Weak scale is generated from a large scale of order the Planck scale through an exponential hierarchy. However, this exponential arises not from gauge interactions but from the background metric (which is a slice of AdS_5 spacetime). This mechanism relies on the existence of only a single additional dimension. We demonstrate a simple explicit example of this mechanism with two three-branes, one of which contains the Standard Model fields. The experimental consequences of this scenario are ...
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by B. C. Allanach, M. Battaglia, G. A. Blair, et al.M. Carena, A. De Roeck, A. Dedes, A. Djouadi, D. Gerdes, N. Ghodbane, J. Gunion, H. E. Haber, T. Han, S. Heinemeyer, J. L. Hewett, I. Hinchliffe, J. Kalinowski, H. E. Logan, S. P. Martin, H. U. Martyn, K. T. Matchev, S. Moretti, F. Moortgat, G. Moortgat-Pick, S. Mrenna, U. Nauenberg, Y. Okada, K. A. Olive, W. Porod, M. Schmitt, S. Su, C. E. M. Wagner, G. Weiglein, J. Wells, G. W. Wilson, P. Zerwas
Abstract
The “Snowmass Points and Slopes” (SPS) are a set of benchmark points and parameter lines in the MSSM parameter space corresponding to different scenarios in the search for Supersymmetry at present and future experiments. This set of benchmarks was agreed upon at the 2001 “Snowmass Workshop on the Future of Particle Physics” as a consensus based on different existing proposals. ...
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by K. Aamodt, N. Abel, U. Abeysekara, et al.A. Abrahantes Quintana, A. Acero, D. Adamová, M. Aggarwal, G. Aglieri Rinella, A. Agocs, S. Aguilar Salazar, Z. Ahammed, A. Ahmad, N. Ahmad, S. Ahn, R. Akimoto, A. Akindinov, D. Aleksandrov, B. Alessandro, R. Alfaro Molina, A. Alici, E. Almaráz Aviña, J. Alme, T. Alt, V. Altini, S. Altinpinar, C. Andrei, A. Andronic, G. Anelli, V. Angelov, C. Anson, T. AntiÄiÄ, F. Antinori, S. Antinori, K. Antipin, D. AntoÃ…czyk, P. Antonioli, A. Anzo, L. Aphecetche, H. Appelshäuser, S. Arcelli, R. Arceo, A. Arend, N. Armesto, R. Arnaldi, T. Aronsson, I. Arsene, A. Asryan, A. Augustinus, R. Averbeck, T. Awes, J. Ãystã¶, M. Azmi, S. Bablok, M. Bach, A. BadalÃ, Y. Baek, S. Bagnasco, R. Bailhache, R. Bala, A. Baldisseri, A. Baldit, J. Bán, R. Barbera, G. Barnaföldi, L. Barnby, V. Barret, J. Bartke, F. Barile, M. Basile, V. Basmanov, N. Bastid, B. Bathen, G. Batigne, B. Batyunya, C. Baumann, I. Bearden, B. Becker, I. Belikov, R. Bellwied, E. Belmont-Moreno, A. Belogianni, L. Benhabib, S. Beole, I. Berceanu, A. Bercuci, E. Berdermann, Y. Berdnikov, L. Betev, A. Bhasin, A. Bhati, L. Bianchi, N. Bianchi, C. Bianchin, J. BielÄÃÂk, J. BielÄÃÂková, A. Bilandzic, L. Bimbot, E. Biolcati, A. Blanc, F. Blanco, F. Blanco, D. Blau, C. Blume, M. Boccioli, N. Bock, A. Bøgdanov, H. Bøggild, M. Bogolyubsky, J. Bohm, L. Boldizsár, M. Bombara, C. Bombonati, M. Bondila, H. Borel, V. Borshchov, C. Bortolin, S. Bose, L. Bosisio, F. Bossú, M. Botje, S. Böttger, G. Bourdaud, B. Boyer, M. Braun, P. Braun-Munzinger, L. Bravina, M. Bregant, T. Breitner, G. Bruckner, R. Brun, E. Bruna, G. Bruno, D. Budnikov, H. Buesching, K. Bugaev, P. Buncic, O. Busch, Z. Buthelezi, D. Caffarri, X. Cai, H. Caines, E. Camacho, P. Camerini, M. Campbell, V. Canoa Roman, G. Capitani, G. Cara Romeo, F. Carena, W. Carena, F. Carminati, A. Casanova DÃÂaz, M. Caselle, J. Castillo Castellanos, J. Castillo Hernandez, V. Catanescu, E. Cattaruzza, C. Cavicchioli, P. Cerello, V. Chambert, B. Chang, S. Chapeland, A. Charpy, J. Charvet, S. Chattopadhyay, S. Chattopadhyay, M. Cherney, C. Cheshkov, B. Cheynis, E. Chiavassa, V. Chibante Barroso, D. Chinellato, P. Chochula, K. Choi, M. Chojnacki, P. Christakoglou, C. Christensen, P. Christiansen, T. Chujo, F. Chuman, C. Cicalo, L. Cifarelli, F. Cindolo, J. Cleymans, O. Cobanoglu, J. P. Coffin, S. Coli, A. Colla, G. Conesa Balbastre, Z. Conesa del Valle, E. Conner, P. Constantin, G. Contin, J. Contreras, Y. Corrales Morales, T. Cormier, P. Cortese, I. Cortés Maldonado, M. Cosentino, F. Costa, M. Cotallo, E. Crescio, P. Crochet, E. Cuautle, L. Cunqueiro, J. Cussonneau, A. Dainese, H. Dalsgaard, A. Danu, I. Das, S. Das, A. Dash, S. Dash, G. de Barros, A. De Caro, G. de Cataldo, J. de Cuveland, A. De Falco, M. de Gaspari, J. de Groot, D. De Gruttola, A. de Haas, N. De Marco, R. de Rooij, S. De Pasquale, G. de Vaux, H. Delagrange, G. Dellacasa, A. Deloff, V. Demanov, E. Dénes, A. Deppman, G. DâErasmo, D. Derkach, A. Devaux, D. Di Bari, C. Di Giglio, S. Di Liberto, A. Di Mauro, P. Di Nezza, M. Dialinas, L. DÃÂaz, R. DÃÂaz, T. Dietel, H. Ding, R. DiviÃ, à Djuvsland, G. do Amaral Valdiviesso, V. Dobretsov, A. Dobrin, T. Dobrowolski, B. Dönigus, I. DomÃÂnguez, D. Don, O. Dordic, A. Dubey, J. Dubuisson, L. Ducroux, P. Dupieux, A. Dutta Majumdar, M. Dutta Majumdar, D. Elia, D. Emschermann, A. Enokizono, B. Espagnon, M. Estienne, D. Evans, S. Evrard, G. Eyyubova, C. Fabjan, D. Fabris, J. Faivre, D. Falchieri, A. Fantoni, M. Fasel, R. Fearick, A. Fedunov, D. Fehlker, V. Fekete, D. Felea, B. Fenton-Olsen, G. Feofilov, A. Fernández Téllez, E. Ferreiro, A. Ferretti, R. Ferretti, M. Figueredo, S. Filchagin, R. Fini, F. Fionda, E. Fiore, M. Floris, Z. Fodor, S. Foertsch, P. Foka, S. Fokin, F. Formenti, E. Fragiacomo, M. Fragkiadakis, U. Frankenfeld, A. Frolov, U. Fuchs, F. Furano, C. Furget, M. Fusco Girard, J. Gaardhøje, S. Gadrat, M. Gagliardi, A. Gago, M. Gallio, P. Ganoti, M. Ganti, C. Garabatos, C. Garc, J. Gebelein, R. Gemme, M. Germain, A. Gheata, M. Gheata, B. Ghidini, P. Ghosh, G. Giraudo, P. Giubellino, E. Gladysz-Dziadus, R. Glasow, P. Glässel, A. Glenn, R. Gomez, H. González Santos, L. González-Trueba, P. González-Zamora, S. Gorbunov, Y. Gorbunov, S. Gotovac, H. Gottschlag, V. Grabski, R. Grajcarek, A. Grelli, A. Grigoras, C. Grigoras, V. Grigoriev, A. Grigoryan, B. Grinyov, N. Grion, P. Gros, J. Grosse-Oetringhaus, J. Y. Grossiord, R. Grosso, C. Guarnaccia, F. Guber, R. Guernane, B. Guerzoni, K. Gulbrandsen, H. Gulkanyan, T. Gunji, A. Gupta, R. Gupta, H. A. Gustafsson, H. Gutbrod, à Haaland, C. Hadjidakis, M. Haiduc, H. Hamagaki, G. Hamar, J. Hamblen, B. Han, J. Harris, M. Hartig, A. Harutyunyan, D. Hasch, D. Hasegan, D. Hatzifotiadou, A. Hayrapetyan, M. Heide, M. Heinz, H. Helstrup, A. Herghelegiu, C. Hernández, G. Herrera Corral, N. Herrmann, K. Hetland, B. Hicks, A. Hiei, P. Hille, B. Hippolyte, T. Horaguchi, Y. Hori, P. Hristov, I. HÃ…ivnáÄová, S. Hu, S. Huber, T. Humanic, D. Hutter, D. Hwang, R. Ichou, R. Ilkaev, I. Ilkiv, P. Innocenti, M. Ippolitov, M. Irfan, C. Ivan, A. Ivanov, M. Ivanov, V. Ivanov, T. Iwasaki, A. JachoÃ…kowski, P. Jacobs, L. JanÄurová, S. Jangal, R. Janik, K. Jayananda, C. Jena, S. Jena, L. Jirden, G. Jones, P. Jones, P. Jovanovi, H. Jung, W. Jung, A. Jusko, A. Kaidalov, S. Kalcher, P. Kali, T. Kalliokoski, A. Kalweit, A. Kamal, R. Kamermans, K. Kanaki, E. Kang, J. Kang, J. Kapitan, V. Kaplin, S. Kapusta, T. Karavicheva, E. Karpechev, A. Kazantsev, U. Kebschull, R. Keidel, M. Khan, S. Khan, A. Khanzadeev, Y. Kharlov, D. Kikola, B. Kileng, D. Kim, D. Kim, D. Kim, H. Kim, J. Kim, J. Kim, J. Kim, M. Kim, M. Kim, S. Kim, S. Kim, Y. Kim, S. Kirsch, I. Kisel, S. Kiselev, A. Kisiel, J. Klay, J. Klein, C. Klein, M. Kliemant, A. Klovning, A. Kluge, S. Kniege, K. Koch, R. Kolevatov, A. Kolojvari, V. Kondratiev, N. Kondratyeva, A. Konevskih, E. KornaÃ…, R. Kour, M. Kowalski, S. Kox, K. Kozlov, J. Kral, I. Králik, F. Kramer, I. Kraus, A. KravÄáková, T. Krawutschke, M. Krivda, D. Krumbhorn, M. Krus, E. Kryshen, M. Krzewicki, Y. Kucheriaev, C. Kuhn, P. Kuijer, L. Kumar, N. Kumar, R. Kupczak, P. Kurashvili, A. Kurepin, A. Kurepin, A. Kuryakin, S. Kushpil, V. Kushpil, M. Kutouski, H. Kvaerno, M. Kweon, Y. Kwon, P. La Rocca, F. Lackner, P. Ladrón de Guevara, V. Lafage, C. Lal, C. Lara, D. Larsen, G. Laurenti, C. Lazzeroni, Y. Le Bornec, N. Le Bris, H. Lee, K. Lee, S. Lee, F. Lefèvre, M. Lenhardt, L. Leistam, J. Lehnert, V. Lenti, H. León, I. León Monzón, H. León Vargas, P. Lévai, Y. Li, R. Lietava, S. Lindal, V. Lindenstruth, C. Lippmann, M. Lisa, O. Listratenko, L. Liu, V. Loginov, S. Lohn, X. Lopez, M. López Noriega, R. López-RamÃÂrez, E. López Torres, G. Løvhøiden, A. Lozea Feijo Soares, S. Lu, M. Lunardon, G. Luparello, L. Luquin, J. R. Lutz, M. Luvisetto, K. Ma, R. Ma, D. Madagodahettige-Don, A. Maevskaya, M. Mager, A. Mahajan, D. Mahapatra, A. Maire, I. Makhlyueva, D. MalâKevich, M. Malaev, I. Maldonado Cervantes, M. Malek, T. Malkiewicz, P. Malzacher, A. Mamonov, L. Manceau, L. Mangotra, V. Manko, F. Manso, V. Manzari, Y. Mao, J. MareÅ¡, G. Margagliotti, A. Margotti, A. MarÃÂn, I. Martashvili, P. Martinengo, M. MartÃÂnez, A. MartÃÂnez Davalos, G. MartÃÂnez GarcÃÂa, Y. Maruyama, A. Marzari Chiesa, S. Masciocchi, M. Masera, M. Masetti, A. Masoni, L. Massacrier, M. Mastromarco, A. Mastroserio, Z. Matthews, B. Mattos Tavares, A. Matyja, D. Mayani, G. Mazza, M. Mazzoni, F. Meddi, A. Menchaca-Rocha, P. Mendez Lorenzo, M. Meoni, J. Mercado Pérez, P. Mereu, Y. Miake, A. Michalon, N. Miftakhov, J. Milosevic, F. Minafra, A. Mischke, D. MiÃ…kowiec, C. Mitu, K. Mizoguchi, J. Mlynarz, B. Mohanty, L. Molnar, M. Mondal, L. Montaño Zetina, M. Monteno, E. Montes, M. Morando, S. Moretto, A. Morsch, T. Moukhanova, V. Muccifora, E. Mudnic, S. Muhuri, H. Müller, M. Munhoz, J. Munoz, L. Musa, A. Musso, B. Nandi, R. Nania, E. Nappi, F. Navach, S. Navin, T. Nayak, S. Nazarenko, G. Nazarov, A. Nedosekin, F. Nendaz, J. Newby, A. Nianine, M. Nicassio, B. Nielsen, S. Nikolaev, V. Nikolic, S. Nikulin, V. Nikulin, B. Nilsen, M. Nilsson, F. Noferini, P. Nomokonov, G. Nooren, N. Novitzky, A. Nyatha, C. Nygaard, A. Nyiri, J. Nystrand, A. Ochirov, G. Odyniec, H. Oeschler, M. Oinonen, K. Okada, Y. Okada, M. Oldenburg, J. Oleniacz, C. Oppedisano, F. Orsini, A. OrtÃÂz Velázquez, G. Ortona, C. Oskamp, A. Oskarsson, F. Osmic, L. Ãsterman, P. Ostrowski, I. Otterlund, J. Otwinowski, G. Ãvrebekk, K. Oyama, K. Ozawa, Y. Pachmayer, M. Pachr, F. Padilla, P. Pagano, G. PaiÄ, F. Painke, C. Pajares, S. Pal, S. Pal, A. Palaha, A. Palmeri, R. Panse, G. Pappalardo, W. Park, B. PastirÄák, C. Pastore, V. Paticchio, A. Pavlinov, T. Pawlak, T. Peitzmann, A. Pepato, H. Pereira, D. Peressounko, C. Pérez, D. Perini, D. Perrino, W. Peryt, J. Peschek, A. Pesci, V. Peskov, Y. Pestov, A. Peters, V. PetráÄek, A. Petridis, M. Petris, P. Petrov, M. Petrovici, C. Petta, J. Peyré, S. Piano, A. Piccotti, M. Pikna, P. Pillot, L. Pinsky, N. Pitz, F. Piuz, R. Platt, M. PÃ…oskoÃ…, J. Pluta, T. Pocheptsov, S. Pochybova, P. Podesta Lerma, F. Poggio, M. Poghosyan, K. Polák, B. Polichtchouk, P. Polozov, V. Polyakov, B. Pommeresch, A. Pop, F. Posa, V. PospÃÂÅ¡il, B. Potukuchi, J. Pouthas, S. Prasad, R. Preghenella, F. Prino, C. Pruneau, I. Pshenichnov, G. Puddu, P. Pujahari, A. Pulvirenti, A. Punin, V. Punin, M. PutiÅ¡, J. Putschke, E. Quercigh, A. Rachevski, A. Rademakers, S. Radomski, T. Räihä, J. Rak, A. Rakotozafindrabe, L. Ramello, A. RamÃÂrez Reyes, M. Rammler, R. Raniwala, S. Raniwala, S. Räsänen, I. Rashevskaya, S. Rath, K. Read, J. Real, K. Redlich, R. Renfordt, A. Reolon, A. Reshetin, F. Rettig, J. P. Revol, K. Reygers, H. Ricaud, L. Riccati, R. Ricci, M. Richter, P. Riedler, W. Riegler, F. Riggi, A. Rivetti, M. Rodriguez Cahuantzi, K. Røed, D. Röhrich, S. Román López, R. Romita, F. Ronchetti, P. Rosinský, P. Rosnet, S. Rossegger, A. Rossi, F. Roukoutakis, S. Rousseau, C. Roy, P. Roy, A. Rubio-Montero, R. Rui, I. Rusanov, G. Russo, E. Ryabinkin, A. Rybicki, S. Sadovsky, AfaåãÂk, R. Sahoo, J. Saini, P. Saiz, D. Sakata, C. Salgado, R. Salgueiro Dominques da Silva, S. Salur, T. Samanta, S. Sambyal, V. Samsonov, ándor, A. Sandoval, M. Sano, S. Sano, R. Santo, R. Santoro, J. Sarkamo, P. Saturnini, E. Scapparone, F. Scarlassara, R. Scharenberg, C. Schiaua, R. Schicker, H. Schindler, C. Schmidt, H. Schmidt, S. Schreiner, S. Schuchmann, J. Schukraft, Y. Schutz, K. Schwarz, K. Schweda, G. Scioli, E. Scomparin, G. Segato, D. Semenov, S. Senyukov, J. Seo, S. Serci, L. Serkin, E. Serradilla, A. Sevcenco, I. Sgura, G. Shabratova, R. Shahoyan, G. Sharkov, N. Sharma, S. Sharma, K. Shigaki, M. Shimomura, K. Shtejer, Y. Sibiriak, M. Siciliano, E. Sicking, E. Siddi, T. Siemiarczuk, A. Silenzi, D. Silvermyr, E. Simili, G. Simonetti, R. Singaraju, R. Singh, V. Singhal, B. Sinha, T. Sinha, B. Sitar, M. Sitta, T. Skaali, K. Skjerdal, R. Smakal, N. Smirnov, R. Snellings, H. Snow, C. Søgaard, O. Sokolov, A. Soloviev, H. Soltveit, R. Soltz, W. Sommer, C. Son, H. Son, M. Song, C. Soos, F. Soramel, D. Soyk, M. Spyropoulou-Stassinaki, B. Srivastava, J. Stachel, F. Staley, I. Stan, G. Stefanek, G. Stefanini, T. Steinbeck, E. Stenlund, G. Steyn, D. Stocco, R. Stock, P. Stolpovsky, P. Strmen, A. Suaide, M. Subieta Vásquez, T. Sugitate, C. Suire, Umbera, T. Susa, D. Swoboda, T. Symons, A. Szanto de Toledo, I. Szarka, A. Szostak, M. Szuba, M. Tadel, C. Tagridis, A. Takahara, J. Takahashi, R. Tanabe, J. Tapia Takaki, H. Taureg, A. Tauro, M. Tavlet, G. Tejeda Muñoz, A. Telesca, C. Terrevoli, J. Thäder, R. Tieulent, D. Tlusty, A. Toia, T. Tolyhy, C. Torcato de Matos, H. Torii, G. Torralba, L. Toscano, F. Tosello, A. Tournaire, T. Traczyk, P. Tribedy, G. Tröger, D. Truesdale, W. Trzaska, G. Tsiledakis, E. Tsilis, T. Tsuji, A. Tumkin, R. Turrisi, A. Turvey, T. Tveter, H. Tydesjö, K. Tywoniuk, J. Ulery, K. Ullaland, A. Uras, J. Urbán, G. Urciuoli, G. Usai, A. Vacchi, M. Vala, L. Valencia Palomo, S. Vallero, A. van den Brink, N. van der Kolk, P. Vande Vyvre, M. van Leeuwen, L. Vannucci, A. Vargas, R. Varma, A. Vasiliev, I. Vassiliev, M. Vassiliou, V. Vechernin, M. Venaruzzo, E. Vercellin, S. Vergara, R. Vernet, M. Verweij, I. Vetlitskiy, L. Vickovic, G. Viesti, O. Vikhlyantsev, Z. Vilakazi, O. Villalobos Baillie, A. Vinogradov, L. Vinogradov, Y. Vinogradov, T. Virgili, Y. Viyogi, A. Vodopianov, K. Voloshin, S. Voloshin, G. Volpe, B. von Haller, D. Vranic, J. Vrláková, B. Vulpescu, B. Wagner, V. Wagner, L. Wallet, R. Wan, D. Wang, Y. Wang, Y. Wang, K. Watanabe, Q. Wen, J. Wessels, J. Wiechula, J. Wikne, A. Wilk, G. Wilk, M. Williams, N. Willis, B. Windelband, C. Xu, C. Yang, H. Yang, A. Yasnopolsky, F. Yermia, J. Yi, Z. Yin, H. Yokoyama, I. K. Yoo, X. Yuan, I. Yushmanov, E. Zabrodin, B. Zagreev, A. Zalite, C. Zampolli, Yu Zanevsky, S. Zaporozhets, A. Zarochentsev, P. Závada, H. Zbroszczyk, P. Zelnicek, A. Zenin, A. Zepeda, I. Zgura, M. Zhalov, X. Zhang, D. Zhou, S. Zhou, S. Zhou, J. Zhu, A. Zichichi, A. Zinchenko, G. Zinovjev, M. Zinovjev, Y. Zoccarato, V. ZycháÄek
Abstract
On 23rd November 2009, during the early commissioning of the CERN Large Hadron Collider (LHC), two counter-rotating proton bunches were circulated for the first time concurrently in the machine, at the LHC injection energy of 450 GeV per beam. Although the proton intensity was very low, with only one pilot bunch per beam, and no systematic attempt was made to optimize the collision optics, all LHC experiments reported a number of collision candidates. In the ALICE experiment, the collision region was centred ...
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(11 Oct 2010)
Abstract
We use the graphics processing unit (GPU) for fast calculations of helicity amplitudes of physics processes. As our first attempt, we compute $u\baru\to nγ$ ($n=2$ to 8) processes in $pp$ collisions at $\sqrts = 14$TeV by transferring the MadGraph generated HELAS amplitudes (FORTRAN) into newly developed HEGET ( HELAS Evaluation with GPU Enhanced Technology) codes written in CUDA, a C-platform developed by NVIDIA for general purpose computing on the GPU. Compared with the usual CPU programs, we obtain 40-150 times better performance on the ...
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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 595, No. 2. (20 Nov 2008), pp. 480-501, doi:10.1016/j.nima.2008.07.086
Abstract
Hypothesis tests for the presence of new sources of Poisson counts amidst background processes are frequently performed in high energy physics (HEP), gamma ray astronomy (GRA), and other branches of science. While there are conceptual issues already when the mean rate of background is precisely known, the issues are even more difficult when the mean background rate has non-negligible uncertainty. After describing a variety of methods to be found in the HEP and GRA literature, we consider in detail three classes of algorithms and evaluate them over a ...
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(28 May 2009)
Abstract
We describe the recent developments to extend the multi-parton interaction model of underlying events in Herwig++ into the soft, non-perturbative, regime. This allows the program to describe also minimum bias collisions in which there is no hard interaction, for the first time. It is publicly available from versions 2.3 onwards and describes the Tevatron underlying event and minimum bias data. The extrapolations to the LHC nevertheless suffer considerable ambiguity, as we discuss. ...
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Abstract
This article is a very basic introduction to supersymmetry. It introduces the two kinds of superfields needed for supersymmetric extensions of the Standard Model, the chiral superfield and the vector superfield, and discusses in detail how to construct supersymmetric, gauge invariant Lagrangians. The main ideas on how to break supersymmetry spontaneously are also covered. The article is meant to provide a platform for further reading. ...
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(9 Jun 2006)
Abstract
In this paper we describe a program (SOPHTY) implementing QED corrections to decays in the HERWIG++ event generator. In order to resum the dominant soft emissions to all orders, the program is based on the YFS formalism. In addition, universal large collinear logarithms are included and the approach can be systematically extended to incorporate exact, process specific, higher order corrections to decays. Due to the large number of possible decay modes the program is designed to operate, as far as possible, independently of the decay matrix elements. ...
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(25 Mar 2009)
Abstract
We study Matrix Element corrections as implemented in four popular event generators for hadron collisions. We compare PYTHIA, HERWIG, ALPGEN and SHERPA in the Z/gamma* inclusive production at LHC. PYTHIA and HERWIG are able to correct the first emission from the shower taking the Matrix Element calculation for one additional parton into account. SHERPA and ALPGEN are able to take into account Matrix Element corrections not only for one, but rather for several hard emissions from the incoming partons. This can be done at the price of introducing ...
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(5 Mar 2008)
by C. Buttar, J. D'Hondt, M. Kramer, et al.G. Salam, M. Wobisch, N. E. Adam, V. Adler, A. Arbuzov, D. Bardin, U. Baur, A. A. Bhatti, S. Bondarenko, V. Buge, J. M. Butterworth, M. Cacciari, M. Campanelli, Q. H. Cao, Carloni M. C. Calame, P. Christova, D. D'Enterria, J. D'Hondt, S. Ferrag, K. Geerlings, V. Halyo, M. Heinrich, J. Huston, J. Jackson, B. Jantzen, L. Kalinovskaya, D. Kcira, B. Klein, A. Kulesza, P. Loch, G. Montagna, S. Moretti, D. Newbold, O. Nicrosini, H. Nilsen, A. A. Penin, F. Piccinini, S. Pozzorini, K. Rabbertz, J. Rojo Chacon, R. Sadykov, M. Schulze, C. Shepherd-Themistocleous, A. Sherstnev, P. Z. Skands, L. Sonnenschein, G. Soyez, R. S. Thorne, M. Tytgat, P. Van Mulders, M. Vazquez Acosta, A. Vicini, I. Villella, D. Wackeroth, C. P. Yuan
Abstract
This report summarizes the activity on comparisons of existings tools for the standard model and on issues in jet physics by the SMHC working group during and subsequent to the Workshop "Physics at TeV Colliders", Les Houches, France, 11-29 June, 2007. ...
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(8 Apr 2002)
posted to hep lhc physics slhc upgrade
by andybuckley
on 2009-07-17 22:14:58
Abstract
We discuss the physics potential and the experimental challenges of an upgraded LHC running at an instantaneous luminosity of 10**35 cm-2s-1. The detector R&D needed to operate ATLAS and CMS in a very high radiation environment and the expected detector performance are discussed. A few examples of the increased physics potential are given, ranging from precise measurements within the Standard Model (in particular in the Higgs sector) to the discovery reach for several New Physics processes ...
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(19 Sep 2008)
Abstract
We present further development and the first public release of our multimodal nested sampling algorithm, called MultiNest. This Bayesian inference tool calculates the evidence, with an associated error estimate, and produces posterior samples from distributions that may contain multiple modes and pronounced (curving) degeneracies in high dimensions. The developments presented here lead to further substantial improvements in sampling efficiency and robustness, as compared to the original algorithm presented in Feroz & Hobson (2008), which itself significantly outperformed existing MCMC techniques in a wide range of astrophysical inference problems. The ...
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(23 Apr 2007)
Abstract
The quality of the narrow-width approximation is examined for partonic and convolved cross sections of sample processes. By comparison with accurate predictions significant limitations are revealed. ...
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(9 Jun 2009)
posted to hep jets lhc physics qcd
by andybuckley
on 2009-07-17 22:07:13
Abstract
Recent developments in jet clustering are reviewed. We present a list of fast and infrared and collinear safe algorithms, and also describe new tools like jet areas. We show how these techniques can be applied to the study of underlying event or, more generally, of any background which can be considered distributed in a sufficiently uniform way. ...
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(6 Apr 2010)
Abstract
As the LHC prepares to start taking data, this review is intended to provide a QCD theorist's understanding and views on jet finding at hadron colliders, including recent developments. My hope is that it will serve both as a primer for the newcomer to jets and as a quick reference for those with some experience of the subject. It is devoted to the questions of how one defines jets, how jets relate to partons, and to the emerging subject of how best to use jets at the ...
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Abstract
I summarize the arguments that strongly suggest that our universe is the product of inflation. The mechanisms that lead to eternal inflation in both new and chaotic models are described. Although the infinity of pocket universes produced by eternal inflation are unobservable, it is argued that eternal inflation has real consequences in terms of the way that predictions are extracted from theoretical models. The ambiguities in defining probabilities in eternally inflating spacetimes are reviewed, with emphasis on the youngness paradox that ...
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(5 Jun 2009)
Abstract
A strategy for calculating the color structure needed for soft gluon resummation for processes with any number of colored partons is introduced using a N_c --> infinity inspired basis. In this basis a general formalism can be found at the same time as the calculations are simplified. The advantages are illustrated by recalculating the soft anomalous dimension matrix for the processes gg --> gg, q\qbar --> q \qbar g and q\qbar --> ggg. ...
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(6 Mar 2009)
Abstract
We derive an improved prescription for the merging of matrix elements with parton showers, extending the CKKW approach. A flavour-dependent phase space separation criterion is proposed. We show that this new method preserves the logarithmic accuracy of the shower, and that the original proposal can be derived from it. One of the main requirements for the method is a truncated shower algorithm. We outline the corresponding Monte Carlo procedures and apply the new prescription to QCD jet production in e+e- collisions and Drell-Yan lepton pair production. Explicit colour ...
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(16 Jan 2009)
by M. Dittmar, S. Forte, A. Glazov, et al.S. Moch, G. Altarelli, J. Anderson, R. D. Ball, G. Beuf, M. Boonekamp, H. Burkhardt, F. Caola, M. Ciafaloni, D. Colferai, A. Cooper-Sarkar, A. de Roeck, L. Del Debbio, J. Feltesse, F. Gelis, J. Grebenyuk, A. Guffanti, V. Halyo, J. I. Latorre, V. Lendermann, Gang Li, L. Motyka, T. Petersen, A. Piccione, V. Radescu, M. Rogal, J. Rojo, C. Royon, G. P. Salam, D. Salek, A. M. Stasto, R. S. Thorne, M. Ubiali, J. A. M. Vermaseren, A. Vogt, G. Watt, C. D. White
Abstract
We provide an assessment of the state of the art in various issues related to experimental measurements, phenomenological methods and theoretical results relevant for the determination of parton distribution functions (PDFs) and their uncertainties, with the specific aim of providing benchmarks of different existing approaches and results in view of their application to physics at the LHC. We discuss higher order corrections, we review and compare different approaches to small x resummation, and we assess the possible relevance of parton saturation in the determination of PDFS at HERA ...
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(4 Jun 2008)
Abstract
We present a study of the results obtained combining LO partonic matrix elements with either LO or NLO partons distributions. These are compared to the best prediction using NLO for both matrix elements and parton distributions. The aim is to determine which parton distributions are most appropriate to use in those cases where only LO matrix elements are available, e.g. as in many Monte Carlo generators. Both LO and NLO parton distributions have flaws, sometimes serious, for some processes, so a modified optimal LO set is suggested. We ...
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(19 Nov 2007)
posted to pdfs qcd
by andybuckley
on 2009-03-26 14:20:51
Abstract
I consider the uncertainties in parton distributions and the consequences for hadronic cross-sections. There is ever-increasing sophistication in the relationship between the uncertainties of the distributions and the errors on the experimental data used to extract them. However, I demonstrate that this uncertainty is frequently subsumed by that due to the choice of data used in fits, and more surprisingly by the precise details of the theoretical framework used. Variations in heavy flavour prescriptions provide striking examples. ...
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(2 Dec 2008)
Abstract
A new release of the Monte Carlo program Herwig++ (version 2.3) is now available. This version includes a number of improvements including: the extension of the program to lepton-hadron collisions; the inclusion of several processes accurate at next-to-leading order in the POsitive Weight Hardest Emission Generator (POWHEG) scheme; the inclusion of three-body decays and finite-width effects in Beyond the Standard Model (BSM) physics processes; a new procedure for reconstructing the kinematics of the parton shower based on the colour structure of the hard scattering process; a new model ...
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Abstract
We give a classical confidence belt construction which unifies the treatment of upper confidence limits for null results and two-sided confidence intervals for non-null results. The unified treatment solves a problem (apparently not previously recognized) that the choice of upper limit or two-sided intervals leads to intervals which are not confidence intervals if the choice is based on the data. We apply the construction to two related problems which have recently been a battleground between classical and Bayesian statistics: Poisson processes ...
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(16 Jul 1999)
posted to dis hera montecarlo qcd rivet
by andybuckley
on 2009-02-19 11:18:05
Abstract
Measurements of transverse energy flow are presented for neutral current deep-inelastic scattering events produced in positron-proton collisions at HERA. The kinematic range covers squared momentum transfers Q^2 from 3.2 to 2,200 GeV^2, the Bjorken scaling variable x from 8.10^-5 to 0.11 and the hadronic mass W from 66 to 233 GeV. The transverse energy flow is measured in the hadronic centre of mass frame and is studied as a function of Q^2, x, W and pseudorapidity. A comparison is made with QCD based models. The behaviour of the ...
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(3 Nov 2000)
by U. Baur, E. L. Berger, H. T. Diehl, et al.D. Errede, D. Casey, T. Dorigo, J. Huston, J. Owens, J. Womersley, L. Apanasevich, M. Begel, Y. Gershtein, M. Kelly, S. Kuhlmann, S. Leone, D. Partos, D. Rainwater, W. Sakumoto, G. Steinbruck, M. Zielinski, V. Zutshi
posted to qcd tevatron
by andybuckley
on 2009-02-18 13:38:40
Abstract
This report discusses physics issues which can be addressed in photon and weak boson production in Run II at the Tevatron. The current understanding and the potential of Run II to expand our knowledge of direct photon production in hadronic collisions is discussed. We explore the prospects for using the W-boson cross section to measure the integrated luminosity, improving the measurement of the W and Z boson transverse momentum distributions, the Z -> b\bar b signal, and the lepton angular distribution in W decays. Finally, we consider the ...
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(14 Jul 2008)
posted to hep lhc montecarlo pdf physics qcd
by andybuckley
on 2009-01-27 15:34:46
Abstract
The goal of this study is to find a prescription for defining parton distributions (PDFs) which are most appropriate for use in those codes where only LO matrix elements (MEs) are used, as in many Monte Carlo generators. We describe a modification of LO PDFs, based on using alpha_S at NLO, a specific prescription of the coupling in the QCD evolution, and violation of the momentum sum rule. We compare results with the truth - the prediction using NLO for both MEs and PDFs, and the standard ...
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(13 Dec 2000)
posted to bfkl ccfm ep hera montecarlo pdf qcd
by andybuckley
on 2009-01-23 10:04:49
Abstract
We discuss a practical formulation of backward evolution for the CCFM small-$x$ evolution equation and show results from its implementation in the new Monte Carlo event-generator CASCADE. ...
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