Parton Model Calculation of Inclusive Charm Production by a Low-energy Antiproton Beam

The cross section for inclusive charm production by a low-energy antiproton beam is calculated using the parton model and next-to-leading order perturbative QCD. For an antiproton beam with a momentum of 15 GeV, the charm cross section at next-to-leading order in the QCD coupling constant changes by more than an order of magnitude as the charm quark mass is varied from 1.3 to 1.7 GeV. The variations can be reduced by demanding that the same value of the charm quark mass give the measured charm cross sections for fixed-target experiments with a proton beam. The resulting estimate for the charm cross section from a low-energy antiproton beam is large enough to allow the study of charm meson mixing.Comment: 9 pages, 4 figure

J/psi production at sqrt(s)=1.96 and 7 TeV: Color-Singlet Model, NNLO* and polarisation

We study J/psi production in pp collisions at sqrt(s)=1.96 and 7 TeV using the Colour-Singlet Model (CSM), including next-to-leading order (NLO) corrections and dominant alphaS^5 contributions (NNLO*). We find that the CSM reproduces the existing data if the upper range of the NNLO* is near the actual --but presently unknown-- NNLO. The direct yield polarisation for the NLO and NNLO* is increasingly longitudinal in the helicity frame when P_T gets larger. Contrary to what is sometimes claimed in the literature, the prompt J/psi yield polarisation in the CSM is compatible with the experimental data from the CDF collaboration, when one combines the direct yield with a data-driven range for the polarisation of J/psi from chi(c).Comment: Contributed to the 22nd International Conference On Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2011), Annecy, France, May 23 - 28, 2011. 4 pages, 4 figures, uses iopams.sty, iopart12.clo, iopart.cls (included

Automation of the matrix element reweighting method

Matrix element reweighting is a powerful experimental technique widely employed to maximize the amount of information that can be extracted from a collider data set. We present a procedure that allows to automatically evaluate the weights for any process of interest in the standard model and beyond. Given the initial, intermediate and final state particles, and the transfer functions for the final physics objects, such as leptons, jets, missing transverse energy, our algorithm creates a phase-space mapping designed to efficiently perform the integration of the squared matrix element and the transfer functions. The implementation builds up on MadGraph, it is completely automatized and publicly available. A few sample applications are presented that show the capabilities of the code and illustrate the possibilities for new studies that such an approach opens up.Comment: 41 pages, 21 figure

Hadroproduction of J/psi and Upsilon in association with a heavy-quark pair

We calculate the cross sections for the direct hadroproduction of J/psi and Upsilon associated with a heavy-quark pair of the same flavour at leading order in alpha_S and v in NRQCD. These processes provide an interesting signature that could be studied at the Tevatron and the LHC and also constitute a gauge-invariant subset of the NLO corrections to the inclusive hadroproduction of J/psi and Upsilon. We find that the fragmentation approximation commonly used to evaluate the contribution of these processes to the inclusive quarkonium production sizeably underestimates the exact calculation in the kinematical region accessible at the Tevatron. Both J/psi and Upsilon are predicted to be unpolarised, independently of their transverse momentum.Comment: 13 pages, 5 figure

New Developments in MadGraph/MadEvent

We here present some recent developments of MadGraph/MadEvent since the latest published version, 4.0. These developments include: Jet matching with Pythia parton showers for both Standard Model and Beyond the Standard Model processes, decay chain functionality, decay width calculation and decay simulation, process generation for the Grid, a package for calculation of quarkonium amplitudes, calculation of Matrix Element weights for experimental events, automatic dipole subtraction for next-to-leading order calculations, and an interface to FeynRules, a package for automatic calculation of Feynman rules and model files from the Lagrangian of any New Physics model.Comment: 6 pages, 3 figures. Plenary talk given at SUSY08, Seoul, South Korea, June 2008. To appear in the proceeding

Survival before annihilation in Psi-prime decays

We extend the simple scenario for $\Psi'$ decays suggested a few years ago. The $c\bar c$ pair in the $\Psi'$ does not annihilate directly into three gluons but rather survives before annihilating. An interesting prediction is that a large fraction of all $\Psi'$ decays could originate from the $\Psi' \to \eta_{c} (3\pi)$ channel which we urge experimentalists to identify. Our model solves the problem of the apparent hadronic excess in $\Psi'$ decays as well as the $\rho\pi$ puzzle since, in our view, the two-body decays of the $\Psi'$ are naturally of electromagnetic origin. Further tests of this picture are proposed, e.g. $J/\Psi \to b_{1}\eta$.Comment: 6 pages, no figur

Upsilon production at the Tevatron and the LHC

We update the theoretical predictions for direct Y(nS) hadroproduction in the framework of NRQCD. We show that the next-to-leading order corrections in alpha_s to the color-singlet transition significantly raise the differential cross section at high pT and substantially affect the polarization of the Upsilon. Motivated by the remaining gap between the NLO yield and the cross section measurements at the Tevatron, we evaluate the leading part of the alpha_s^5 contributions, namely those coming from Y(nS) associated with three light partons. The differential color-singlet cross section at alpha_s^5 is in substantial agreement with the data, so that there is no evidence for the need of color-octet contributions. Furthermore, we find that the polarization of the Y(nS) is longitudinal. We also present our predictions for Y(nS) production at the LHC.Comment: 4 pages, 5 figure

Photoproduction of J/ψJ/\psi in association with a ccˉc\bar{c} pair

Based on the color-singlet model, we investigate the photoproduction of $J/\psi$ associated with a $c \bar{c}$ pair with all subprocesses including the direct, single-resolved, and double-resolved channels. The amplitude squared of these subprocesses are obtained analytically. By choosing corresponding parameters, we give theoretical predictions for the $J/\psi$ transverse momentum distributions both at the LEPII and at the future photon colliders for these subprocesses. The numerical results show that at the LEPII these processes can not give enough contributions to account for the experimental data, and it indicates that the color-octet mechanism may still be needed. At the photon collider with the laser back scattering photons, the resolved photon channe will dominate over the direct one in small and moderate $p_t$ regions with large $\sqrt{s}$. By measuring the $J/\psi$ production associated with a $c\bar{c}$ pair, this process can be separated from the inclusive $J/\psi$ production and may provide a new chance to test the color-singlet contributions.Comment: 16 pages, 7 figure

QED contribution to the production of J/\psi+c\bar{c}+X at the Tevatron and LHC

We calculate \alpha^{2}\alpha_{s}^{2} order QED contribution to J/\psi production in pp(\bar{p})\to J/\psi+c\bar{c} color-singlet process at the Tevatron and LHC in the framework of non-relativistic QCD. The contribution of the interference between the \alpha^{2}\alpha_{s}^{2} QED and \alpha_{s}^{4} QCD is also taken into account. The J/\psi production associated with a charm quark pair could be a measurable signal at hadron collider experiment. Our calculations show that by including the QED contribution, the p_{t} distribution is enhanced by a factor of 1.5 (1.9) at the Tevatron (LHC) at p_{t}=50 (100) GeV. In addition, the polarization of J/\psi turns from unpolarized in all region to increasingly transverse when p_{t} becomes larger.Comment: 14 pages, 6 figures, version accepted for publication in Phys Rev