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Reassessing the importance of the colour-singlet contributions to direct $J/ + W$ production at the LHC and the Tevatron Lansberg, Jean-Philippe ; Lorce, Cédric in Physics Letters B (2013), B726 We show that the colour-singlet contributions to the hadroproduction of $J/\Psi$ in association with a W boson are sizable, if not dominant over the colour-octet contributions. They are of two kinds, $sg ... [more ▼] We show that the colour-singlet contributions to the hadroproduction of $J/\Psi$ in association with a W boson are sizable, if not dominant over the colour-octet contributions. They are of two kinds, $sg\toJ/\Psi+c+W$ at $\alpha^3s\alpja$ and $q\overline q' \to\gamma^\star /Z ^\star W\to J/\Psi W$ at order $\alpha^3$. These have not been considered in the literature until now. Our conclusion is that the hadroproduction of a $J/\Psi$ in association with a W boson cannot be claimed as a clean probe of the colour-octet mechanism. The rate are small even at the LHC and it will be very delicate to disentangle the colour-octet contributions from the sizable colour-singlet ones and from the possibly large double-parton-scattering contributions. During this analysis, we have also noted that, for reactions such as the production of a $J/\Psi$ by light quark–antiquark fusion, the colour-singlet contribution via an off-shell photon is of the order of the expectation from the colour-octet contribution via an off-shell gluon. This is relevant for inclusive production at low energies close to the threshold. Such an observation also likely extends to other processes naturally involving light-quark annihilation. [less ▲] Detailed reference viewed: 21 (4 ULg)Next-to-leading-order QCD corrections to the yields and polarisations of J/Psi and Upsilon directly produced in association with a Z boson at the LHC ; Lansberg, Jean-Philippe ; Lorce, Cédric et al in Journal of High Energy Physics [=JHEP] (2013), 1303 We update the study of the production of direct $J/\Psi$ in association with a $Z$ boson at the Next-to-Leading Order (NLO) in $\alpha_S$ by evaluating both the yield differential in $P_T$ and the $J/\Psi ... [more ▼] We update the study of the production of direct $J/\Psi$ in association with a $Z$ boson at the Next-to-Leading Order (NLO) in $\alpha_S$ by evaluating both the yield differential in $P_T$ and the $J/\Psi$ polarisation in the QCD-based Colour-Singlet Model (CSM). Contrary to an earlier claim, QCD corrections at small and mid $P_T$ are small if one assumes that the factorisation and the renormalisation scales are commensurate with the $Z$ boson mass. As it can be anticipated, the t-channel gluon-exchange (t−CGE) topologies start to be dominant only for $P_T > m_Z/2$. The polarisation pattern is not altered by the QCD corrections. This is thus far the first quarkonium-production process where this is observed in the CSM. Along the same lines, our predictions for direct $\Upsilon + Z$ are also given. [less ▲] Detailed reference viewed: 10 (2 ULg)Accessing baryon to meson transition distribution amplitudes in meson production in association with a high invariant mass lepton pair at GSI-FAIR with P̅ ANDA Lansberg, Jean-Philippe ; ; Semenov-Tyan-Shanskiy, Kirill et al in Physical Review. D : Particles and Fields (2012), 86 Nucleon-antinucleon annihilation into a near backward- (or forward-) produced meson and a high invariant mass lepton pair admits a factorized description in terms of antinucleon (or nucleon) distribution ... [more ▼] Nucleon-antinucleon annihilation into a near backward- (or forward-) produced meson and a high invariant mass lepton pair admits a factorized description in terms of antinucleon (or nucleon) distribution amplitudes (DAs) and nucleon to meson (or antinucleon to meson) transition distribution amplitudes (TDAs). We estimate the cross section of backward (and forward) pion and eta-meson production in association with a high invariant mass lepton pair for the kinematical conditions of GSI-FAIR. The cross sections are found to be large enough to be measured with the PANDA detector. Interesting phenomenological applications of the approach are thus expected. [less ▲] Detailed reference viewed: 7 (0 ULg)30 Years of Strong Interactions: a Three-Day Meeting in Honour of Joseph Cugnon and Hans-Jürgen Pirner Cudell, Jean-René ; Lansberg, Jean-Philippe ; Book published by Springer (2012) Detailed reference viewed: 13 (2 ULg)Consistent model for \pi N transition distribution amplitudes and backward pion electroproduction Lansberg, Jean-Philippe ; ; Semenov-Tian-Chanski, Kirill et al in Physical Review. D : Particles and Fields (2012), 85 The extension of the concept of generalized parton distributions leads to the introduction of baryon to meson transition distribution amplitudes (TDAs), nondiagonal matrix elements of the nonlocal three ... [more ▼] The extension of the concept of generalized parton distributions leads to the introduction of baryon to meson transition distribution amplitudes (TDAs), nondiagonal matrix elements of the nonlocal three quark operator between a nucleon and a meson state. We present a general framework for modeling nucleon to pion (\pi N) TDAs. Our main tool is the spectral representation for \pi N TDAs in terms of quadruple distributions. We propose a factorized Ansatz for quadruple distributions with input from the soft-pion theorem for \pi N TDAs. The spectral representation is complemented with a D-term like contribution from the nucleon exchange in the cross channel. We then study backward pion electroproduction in the QCD collinear factorization approach in which the nonperturbative part of the amplitude involves N TDAs. Within our two component model for N TDAs, we update previous leading-twist estimates of the unpolarized cross section. Finally, we compute the transverse target single spin asymmetry as a function of skewness. We find it to be sizable in the valence region and sensitive to the phenomenological input of our \pi N TDA model. [less ▲] Detailed reference viewed: 14 (0 ULg)New contributions to heavy-quarkonium production Lansberg, Jean-Philippe ; Cudell, Jean-René ; in Physics Letters B (2006), 633(2-3), 301-308 We reconsider quarkonium production in a field-theoretical setting and we show that the lowest-order mechanism for heavy-quarkonium production receives in general contributions from two different cuts ... [more ▼] We reconsider quarkonium production in a field-theoretical setting and we show that the lowest-order mechanism for heavy-quarkonium production receives in general contributions from two different cuts. The first one corresponds to the usual colour-singlet mechanism. The second one has not been considered so far. We treat it in a gauge-invariant manner, and introduce new 4-point vertices, suggestive of the colour-octet mechanism. These new objects enable us to go beyond the static approximation. We show that the contribution of the new cut can be as large as the usual colour-singlet mechanism at high P-T for J/psi. In the psi' case, theoretical uncertainties are shown to be large and agreement with data is possible. (c) 2005 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 18 (6 ULg)HLPR 2004: Hadronic Physics: Joint meeting Heidelberg- Liege-Paris-Rostock Lansberg, Jean-Philippe ; Cudell, Jean-René ; Cugnon, Joseph Book published by American Institute of Physics - AIP Conference Proceedings (2005) Detailed reference viewed: 17 (5 ULg)A toy model for generalised parton distributions Cudell, Jean-René ; ; Cugnon, Joseph et al in AIP Conference Proceedings (2005), 775 Detailed reference viewed: 34 (3 ULg)Random matrix models for chiral and diquark condensation Vanderheyden, Benoît ; ; Lansberg, Jean-Philippe et al in AIP Conference Proceedings (2005), 775 We consider random matrix models for the thermodynamic competition between chiral symmetry breaking and diquark condensation in QCD at finite temperature and finite baryon density. The models produce mean ... [more ▼] We consider random matrix models for the thermodynamic competition between chiral symmetry breaking and diquark condensation in QCD at finite temperature and finite baryon density. The models produce mean field phase diagrams whose topology depends solely on the global symmetries of the theory. We discuss the block structure of the interactions that is imposed by chiral, spin, and color degrees of freedom and comment on the treatment of density and temperature effects. Extension of the coupling parameters to a larger class of theories allows us to investigate the robustness of the phase topology with respect to variations in the dynamics of the interactions. We briefly study the phase structure as a function of coupling parameters and the number of colors. [less ▲] Detailed reference viewed: 29 (10 ULg)A model for the generalized parton distribution of the pion Stassart, Pierre ; ; Cudell, Jean-René et al in AIP Conference Proceedings (2005), 756 Detailed reference viewed: 19 (3 ULg)Generalized parton distributions of the pion ; Cudell, Jean-René ; Cugnon, Joseph et al in Nuclear Physics B-Proceedings Supplements (2004, July), 133 Off-forward structure functions of the pion are investigated in twist-two and twist-three approximation. A simple model is used for the pion, which allows to introduce finite size effects, while ... [more ▼] Off-forward structure functions of the pion are investigated in twist-two and twist-three approximation. A simple model is used for the pion, which allows to introduce finite size effects, while preserving gauge invariance. Results for the imaginary parts of the gamma*pi --> gamma*pi off-forward amplitude and of the structure functions are presented. Generalized Callan-Gross relations are obtained. [less ▲] Detailed reference viewed: 21 (8 ULg)A model for the off-forward structure functions of the pion ; Cudell, Jean-René ; Cugnon, Joseph et al in Physics Letters B (2004), 587(3-4), 189-200 We extend our model for the pion, which we used previously to calculate its diagonal structure function, to the off-forward case. The imaginary part of the off-forward y*pi -->. gamma*pi scattering ... [more ▼] We extend our model for the pion, which we used previously to calculate its diagonal structure function, to the off-forward case. The imaginary part of the off-forward y*pi -->. gamma*pi scattering amplitude is evaluated in the chiral limit (m(pi) = 0) and related to the twist-two and twist-three generalised parton distributions H, H-3, (H) over tilde (3). Non-perturbative effects, linked to the size of the pion and still preserving gauge invariance, are included. Remarkable new relations between H, H3 and (H) over tilde (3) are obtained and discussed. (C) 2004 Published by Elsevier B.V. [less ▲] Detailed reference viewed: 17 (3 ULg)A simple model for generalised parton distributions of the pion Lansberg, Jean-Philippe ; ; Cudell, Jean-René et al in Bruncko, D.; Ferencei, J.; Strizenec, P. (Eds.) 12th International Workshop On Deep Inelastic Scattering (DIS 2004) (2004) Detailed reference viewed: 13 (1 ULg)Pion Structure Function and violation of the Momentum Sum Rule Lansberg, Jean-Philippe ; ; Cudell, Jean-René et al in Blin, A. H.; Hiller, B.; Ruivo, M. C. (Eds.) et al Hadron Physics: Effective Theories of Low Energy QCD N°2 (2003) We present a method to evaluate the pion structure functions from a box diagram calculation. Pion and constituent quark fields are coupled through the simplest pseudoscalar coupling. The gamma^* pi -> q ... [more ▼] We present a method to evaluate the pion structure functions from a box diagram calculation. Pion and constituent quark fields are coupled through the simplest pseudoscalar coupling. The gamma^* pi -> q \bar q cross-section is evaluated and related to the structure functions. We then show that the introduction of non-perturbative effects, related to the pion size and preserving gauge invariance, provides us with a straighforward relation with the quark distribution. It is predicted that higher-twist terms become negligible for Q^2 larger than about 2 GeV^2 and that quarks in the pion have a momentum fraction smaller than in the proton. We enlarge the discussion concerning this violation of the momentum sum rule, emphasizing that the sum rule is recovered in the chiral limit and also when the finite size condition is not imposed. [less ▲] Detailed reference viewed: 61 (3 ULg)Confinement and cut-off: A model for the Pion Quark Distribution Function Stassart, Pierre ; ; Cudell, Jean-René et al (2003) The pion structure function is investigated in a simple pseudo-scalar coupling model of pion and constituent quark fields. The imaginary part of the forward Compton scattering amplitude is evaluated. We ... [more ▼] The pion structure function is investigated in a simple pseudo-scalar coupling model of pion and constituent quark fields. The imaginary part of the forward Compton scattering amplitude is evaluated. We show that the introduction of non-perturbative effects, linked through a cut-off to the size of the pion, allows the reproduction of important features of the pion quark distribution function. [less ▲] Detailed reference viewed: 24 (14 ULg)A model for the pion structure function ; Cudell, Jean-René ; Cugnon, Joseph et al in Physics Letters B (2002), 547(3-4), 210-218 The pion structure function is investigated in a simple model, where pion and constituent quark fields are coupled through the simplest pseudoscalar coupling. The imaginary part of the forward gamma*pi ... [more ▼] The pion structure function is investigated in a simple model, where pion and constituent quark fields are coupled through the simplest pseudoscalar coupling. The imaginary part of the forward gamma*pi --> gamma*pi evaluated and related to the structure functions. It is shown that the introduction of non-perturbative effects linked to the size of the pion and preserving gauge invariance, allows a connection with the quark distribution. It is predicted that higher-twist terms become negligible for Q(2) larger than similar to 2 GeV2 and that quarks in the pion have a momentum fraction smaller than in the proton case. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲] Detailed reference viewed: 37 (14 ULg)The Valence Quark Distribution of the Pion Lansberg, Jean-Philippe ; ; Cudell, Jean-René et al in Dong Su; Burchat, Patricia (Eds.) XXII Physics in Collision Conference (PIC02) (2002) Detailed reference viewed: 32 (5 ULg)Neutral Pion Structure Function Cudell, Jean-René ; Cugnon, Joseph ; Jaminon, Martine et al Conference (2001) Detailed reference viewed: 17 (6 ULg) |
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