J/ψ production at the LHC

Abstract

We firstly examine hadroproduction of prompt J/ψ's at the Fermilab Tevatron in a Monte Carlo framework by means of the event generator PYTHIA 5.7 in which those colour-octet processes relevant for charmonium production have been implemented accordingly. We find that colour-octet matrix elements presented in literature from pp collider data are systematically overestimated due to overlooking of the effective primordial transverse momentum of partons (i.e. including higher-order QCD effects). We estimate the size of these effects using different parton distribution functions. Finally, after normalization to Tevatron data, we extrapolate up to LHC energies making a prediction on the expected pt differential cross-section for charmonium.

New extraction of color-octet NRQCD matrix elements from charmonium hadroproduction

“…On the other hand, once implemented Altarelli-Parisi evolution in our framework, the new extracted values of the color-octet ME < O 8 ( 3 S 1 ) > increase (table 1), recovering a similar result as in previous extractions [9]. On the other hand, the numerical values obtained for M 3 even decrease slightly, reinforcing the conclusions reported in our former work [1][2][3][4].…”

“…Nevertheless, in order to assess the significance of the cut-off on the values of the long-distance parameters we performed new fits to Tevatron data by changing p min t . We found that, by varying p min t in the [1,2] GeV range, the 3 S (8) 1 ME showed almost no appreciable change, whereas the 1 S…”

“…Production cross sections which are singular at p t = 0 are automatically regularized in running PYTHIA by setting a p t lower cut-off at 1 GeV [6]. Consistently with our aim of using by-default options whenever possible in the generation, we kept this value in all our previous analysis [1,4].…”

“…In a series of previous papers [1][2][3][4] we analyzed charmonium hadroproduction in the light of the color-octet model [5]. We employed a Monte Carlo generator (PYTHIA 5.7) [6] to assess the importance of some higher-order QCD effects.…”

Bottomonium production at the Tevatron and the LHC

“…In a series of previous papers [2,3,4,5] we examined charmonium hadroproduction in a Monte Carlo framework, using PYTHIA 5.7 [6] event generator with the colour-octet model (COM) [7] implemented in. Basically, such a production mechanism is based on the formation of an intermediate coloured state during the hard partonic interaction, evolving non-perturbatively into physical heavy resonances in the final state with certain probabilities governed by NRQCD [8].…”