Constraining double-parton correlations and interferences

In this paper, we address double parton scattering (DPS) in pA collisions. Within the Light-Front approach, we formally derive the two contributions to the nuclear double parton distribution (DPD), namely: DPS1, involving two partons from the same nucleon, and DPS2, where the two partons belong to different parent nucleons. We then generalize the sum rule for hadron DPDs to the nuclear case and analytically show how all contributions combine to give the expected results. In addition partial sum rules for the DPDs related to DPS1 and DPS2 mechanisms are discussed for the first time. The deuteron system is considered for the first calculation of the nuclear DPD by using a realistic wave function obtained from the very refined nucleon-nucleon AV18 potential, embedded in a rigorous Poincaré covariant formalism. Results are used to test sum rules and properly verify that DPS1 contribution compares with the DPS2 one, although smaller. We also introduce EMC-like ratios involving nuclear and free DPDs to address the potential role of DPS in understanding in depth the EMC effect.

We consider the production of W-boson plus dijet, W-boson plus b-jets and same sign WW via double parton scattering (DPS) in pA collisions at the LHC and evaluate the corresponding cross sections. The impact of a novel DPS contribution pertinent to pA collisions is quantified. Exploiting the experimental capability of performing measurements differential in the impact parameter in pA collisions, we discuss a method to single out this novel DPS contribution. The method allows the subtraction of the leading twist (LT) single parton scattering background and it gives access in a very clean way to double parton distribution functions in the proton. We calculate leading twist and DPS cross sections and study the dependence of the observables on the cuts in the jets phase space. In the Wjj channel the observation of DPS is possible with data already accumulated in pA runs and the situation will greatly improve for the next high luminosity runs. For the Wb{bar{b}} final state, the statistics within the current data is too low, but there is possibility to observe DPS in this channel in future runs, albeit with much reduced sensitivity than in Wjj final state. Finally the DPS observation in the same sign WW channel will require either significant increase of integrated luminosity beyond that foreseen in next pA runs or improved methods for W reconstruction, along with its charge, in hadronic decay channels.

The high gluon density in the initial state of hadronic collisions at LHC energies implies that the probability of multiple parton interactions within one proton-proton collision increases. In particular, this motivates one to investigate the importance of Double Parton Scattering (DPS) processes at the LHC. In a DPS process one can have, from one proton-proton collision, two interacting partons coming from each colliding hadron. In this context, the relation between the double parton distribution functions (dPDF) and the usual parton distribution functions (PDF) is discussed, and some formulae for the DPS cross section are compared. Our results focus on the production of different final states related to two heavy quark-antiquark pairs. Those include [Formula: see text], which is called the golden channel of DPS, [Formula: see text] and [Formula: see text].

We study parton distributions for two partons, a quark and a gluon, in the light-front dressed quark model, with focus on correlations between the two partons. The model calculation leads to sizable spin-spin and spin-kinematic correlations of interest for studies of double parton scattering (DPS) in high-energy collisions. In particular, we find that the transverse dependence of the double parton distributions (DPDs) does not factorize within the model. The results gives insight to the strengths of correlations in different kinematical regions, which can help in constructing input DPDs in cross section calculations.

We present the construction of unintegrated double parton distribution\nfunctions which include dependence on transverse momenta of partons. We extend\nthe formulation which was used to obtain the single unintegrated parton\ndistributions from the standard, integrated parton distribution functions.\nStarting from the homogeneous part of the evolution equations for the\nintegrated double parton distributions, we construct the unintegrated double\nparton distributions as the convolutions of the integrated double distributions\nand the splitting functions, multiplied by the Sudakov form factors. We show\nthat there exist three domains of external hard scales which require three\ndistinct forms of the unintegrated double distributions. The additional\ntransverse momentum dependence which arises through the Sudakov form factors\nleads to non-trivial correlations in the parton momenta. We also discuss the\nnon-homogeneous contribution to the unintegrated double parton distributions,\nwhich arises due to the splitting of a single parton into daughter partons with\nhigh transverse momenta. We analyze two cases, the unfolding of the transverse\nmomenta dependence from the last step of the evolution of two partons, and the\ncase where the transverse momenta are generated directly from the single parton\nsplitting.\n

A bstract Reconstructing Mellin moments of double parton distributions from calculations on a Euclidean lattice requires taking an integral over a variable that may be regarded as a Ioffe time. The Fourier conjugate of this variable plays the role of a kinematic skewness in the double parton distributions. We discuss the skewness dependence of the relevant hadronic correlation functions. Using several models, we study the impact of this dependence on extracting moments of double parton distributions from existing lattice data.

We show how the double parton distributions may be obtained consistently from the many-body light-cone wave functions. We illustrate the method on the example of the pion with two Fock components. The procedure, by construction, satisfies the Gaunt-Stirling sum rules. The resulting single parton distributions of valence quarks and gluons are consistent with a phenomenological parametrization at a low scale.

We discuss production of four jets pp → jjjjX with at least two jets with large rapidity separation in proton-proton collisions at the LHC through the mechanism of double-parton scattering (DPS). The cross section is calculated in a factorizaed approximation. Each hard subprocess is calculated in LO collinear approximation. The LO pQCD calculations are shown to give a reasonably good descritption of CMS and ATLAS data on inclusive jet production. It is shown that relative contribution of DPS is growing with increasing rapidity distance between the most remote jets, center-of-mass energy and with decreasing (mini)jet transverse momenta. We show also result for angular azimuthal dijet correlations calculated in the framework of kt -factorization approximation.

Recent results on double parton scattering (DPS) studies using data collected during Run 1 and Run 2 of the LHC with the CMS experiment are presented. Double parton scattering is investigated in several final states including vector bosons and multi-jets. Measurements of observables designed to highlight the DPS contribution are shown and compared to MC predictions from models based on multiple partonic interactions (MPIs) phenomenology.

We briefly discuss the status of double parton scattering (DPS) on both theoretical and experimental sides and summarize the state of the naive DPS model, where the scatterers are taken completely independent. We then elaborate on some of the effects which are neglected in such an approach, and often ignored in phenomenological studies, with focus on polarization - which arises from the correlation between the spin of two partons inside a proton. Polarization is of particular interest, thanks to its direct and calculable connections to the distribution of particles in the final state. Although the physics described is different, there are strong similarities between polarization in DPS and in single partons scattering with measured transverse momentum, and several of the techniques and results from studies of transverse momentum dependent parton distributions can be translated into the setting of double parton scattering.

Double parton scattering is sensitive to correlations between the two partons\nin the hadron, including correlations in flavor, spin, color, momentum\nfractions and transverse separation. We obtain a first estimate of the size of\nthese correlations by calculating the corresponding double parton distribution\nfunctions in a bag model of the proton. We find significant correlations\nbetween momentum fractions, spin and flavor, but negligible correlations with\ntransverse separation. The model estimates of the relative importance of these\ncorrelations will help experimental studies disentangle them.\n

Double parton scattering in proton-proton collisions includes kinematic regions in which two partons inside a proton originate from the perturbative splitting of a single parton. This leads to a double counting problem between single and double hard scattering. We present a solution to this problem, which allows for the definition of double parton distributions as operator matrix elements in a proton, and which can be used at higher orders in perturbation theory. We show how the evaluation of double hard scattering in this framework can provide a rough estimate for the size of the higher-order contributions to single hard scattering that are affected by double counting. In a numeric study, we identify situations in which these higher-order contributions must be explicitly calculated and included if one wants to attain an accuracy at which double hard scattering becomes relevant, and other situations where such contributions may be neglected.

Selected recent quantum chromodynamics (QCD) measurements are reviewed for Fermilab Run II Tevatron proton-antiproton collisions studied by the Collider Detector at Fermilab (CDF) and D0 Collaborations at a centre-of-mass energy of {radical}s = 1.96 TeV. Tantamount to Rutherford scattering studies at the TeV scale, inclusive jet and dijet production cross-section measurements are used to seek and constrain new particle physics phenomena, test perturbative QCD calculations, inform parton distribution function (PDF) determinations, and extract a precise value of the strong coupling constant, a{sub s}(m{sub Z}) = 0.1161{sub -0.0048}{sup +0.0041}. Inclusive photon production cross-section measurements reveal an inability of next-to-leading-order (NLO) perturbative QCD (pQCD) calculations to describe low-energy photons arising directly in the hard scatter. Events with {gamma} + 3-jet configurations are used to measure the increasingly important double parton scattering (DPS) phenomenon, with an obtained effective interaction cross section of {sigma}{sub eff} = 16.4 {+-} 2.3 mb. Observations of central exclusive particle production demonstrate the viability of observing the Standard Model Higgs boson using similar techniques at the Large Hadron Collider (LHC). Three areas of inquiry into lower energy QCD, crucial to understanding high-energy collider phenomena, are discussed: the examination of intra-jet track kinematics to infer that jet formation is dominatedmore » by pQCD, and not hadronization, effects; detailed studies of the underlying event and its universality; and inclusive minimum-bias charged-particle momentum and multiplicity measurements, which are shown to challenge the Monte Carlo generators.« less

Given the large parton luminosities, sizable rate of events, with several pairs of b-quarks produced contemporarily by multiple parton interactions, are foreseen in hadronic and nuclear collisions at very high energies. We compare the different contributions to \( b\bar bb\bar b \) production, due to single and double parton scatterings, in pp and in p A collisions at the CERN LHC within the acceptance of the ALICE and of the LHCb detectors.

The production of weak gauge bosons in association with heavy flavored mesons at the LHCb conditions is considered, and a detailed study of the different contributing processes is presented including single (SPS) and double (DPS) parton scattering mechanisms. We find that the usual DPS factorization formula needs to be corrected for the limited partonic phase space, and that including the relevant corrections reduces discrepancies in the associated $ZD$ production. We conclude finally that double parton scattering dominates the production of same-sign $W^\pm D^\pm$ states, as well as the production of $W^-$ bosons associated with $B$-mesons. The latter processes can thus be regarded as new useful DPS indicators.