Gluon induced contributions toZγproduction at hadron colliders

Abstract

We study the contribution of gluon induced partonic subprocesses to Zγ pair production at hadron colliders. These processes contribute only at next-to-next-to-leading order but are potentially enhanced by two factors of the gluon parton densities. However, we find that their contribution is modest and that next-to-leading order calculations give reliable predictions.

Vector boson pair production at the LHC

“…Although formally in perturbation theory they enter at NNLO the large flux of gluons at LHC center of mass energies can overcome the formal O(α 2 s ) suppression. Consequently we have included the gluon initiated processes gg → {γγ, Zγ, ZZ, W W } whose contributions have been studied in the past [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. We have also included higher order corrections to the gg → γγ process [13,14], which are formally at the level of N 3 LO in perturbation theory.…”

“…The allowed processes are gg → {γγ, Zγ, W + W − , ZZ}, each of which has been studied in some format in the past [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. We refer the reader to the appropriate section for details of each calculation.…”

“…[15,16]. More recently this process has been computed including the leptonic decay of the Z boson and other higher order contributions [17].…”

The two-loop helicity amplitudes for gg → V 1 V 2 → 4 leptons

“…This implies that it formally contributes only at NNLO in the perturbative expansion of the hadronic process, but numerical enhancements may be expected due to the large gluon luminosities at typical energies for diboson production at the LHC. For the gluon-induced processes, the oneloop amplitudes and the corresponding one-loop squared interference terms have been computed long ago [6][7][8][9][10][11][12]. Their impact on the total cross section was found to range approximately from 5% to more than 10% for different final states at the LHC, and to rise with increasing collider energy [1][2][3][4].…”

Interference effects in the decays of spin-zero resonances into γγ and t t ¯ $$ t\overline{t} $$

“…Here again, the sum in the first term runs over the Φ = H, A states and the second term describes the box diagram contribution of the gg → Zγ QCD background which is given by an amplitude similar to that of eq. (3.5) [74][75][76] A ggγZ = 2α s α q e q v q A q . (3.12) where the sum that runs over the six standard quark flavors, q = u, d, s, c, b, t and the amplitude A q is given in eq.…”