Abstract
We demonstrate that the recent studies of J/ψ-pair production by CMS at the LHC and by D0 at the Tevatron reveal the presence of different production mechanisms in different kinematical regions. We find out that next-to-leading-order single parton scattering contributions at αs5 dominate the yield at large transverse momenta of the pair. Our analysis further emphasises the importance of double parton scatterings – which are expected to dominate the yield at large J/ψ-rapidity differences – at large invariant masses of the pair in the CMS acceptance, and thereby solve a large discrepancy between the theory and the CMS data. In addition, we provide the first exact – gauge-invariant and infrared-safe – evaluation of a class of leading-PT (PT−4) next-to-next-to-leading-order contributions at αs6, which can be relevant in the region of large values of PTmin=min(PT1,PT2). Finally, we derive simple relations for the feed-down fractions from the production of an excited charmonium state with a J/ψ in the case of the dominance of the double parton scatterings, which significantly deviate from those for single parton scatterings. Such relations can be used to discriminate these extreme scenarios, either DPS or SPS dominance.
Highlights
Heavy-quarkonium production has attracted considerable interest in the high-energy physics community since the J /ψ discovery, exactly forty years ago
), we find it is dominant only when the yields are out of reach for current experiments and we conclude that an evaluation up to αs5 accuracy is probably sufficient at present time
We claimed in a recent work [21] that there was no compelling reason to call for significant double parton scattering (DPS) contributions in order to describe the J /ψ -pair measurement by LHCb at 7 TeV in the forward rapidity region (2 < yψ < 4.5)
Summary
Heavy-quarkonium production has attracted considerable interest in the high-energy physics community since the J /ψ discovery, exactly forty years ago. The recent D0 [12] study could provide the very first separation of the DPSs from SPSs and a measurement of σψDψPS and σψSPψS by using the yield dependence on the (pseudo)rapidity difference between the J /ψ pair, as it was first proposed in [25] Such a separation relies on a good modelling of the DPS and SPS rapiditydifference spectra, this can reasonably be considered as the first observation of a DPS signal in quarkonium-pair production, even if SPSs contribute in a significant fraction of the D0 acceptance. ), we find it is dominant only when the yields are out of reach for current experiments and we conclude that an evaluation up to αs accuracy is probably sufficient at present time
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