Photoproduction of top quarks in peripheral heavy ion collisions

Abstract

In relativistic heavy ion collisions, top quarks can be produced by photongluon fusion when a photon from the Weizsäcker-Williams virtual photon field of one nucleus interacts with a gluon in the other nucleus. Photoproduction with heavy ions at the Large Hadron Collider (LHC) will be the first accessible non-hadronic top production channel. We calculate the tt photoproduction cross sections, pair mass and top quark rapidity distributions in peripheral lead-lead and oxygen-oxygen collisions. The cross sections are sensitive to the top quark charge and the large-Q 2 gluon distribution in the nucleus. We find a cross section of 15 pb in oxygen-oxygen collisions, leading to 210 pairs in a one month (10 6 s) LHC run. In pA collisions, the rate is higher, 1100 pairs per month for pO. A comparison of the AA and pA data might allow for a study of gluon shadowing at high Q 2 .

The physics of ultraperipheral collisions at the LHC

“…The top rates, particularly for the lighter nuclei, are lower than those in Ref. [177], due to a revision in the expected LHC light ion luminosities. Thus using top quarks to measure the nuclear gluon distribution at high Q 2 seems unlikely.…”

“…Single W bosons will be produced at high p T in γ A and γ p interactions with much higher statistics, similar to previous studies at HERA [298,299]. In addition, photoproduction of tt pairs could provide a measure of the top quark charge [177]. In all these examples, measuring the forward proton improves background suppression as well as reconstruction of the event kinematics.…”

“…The maximum center-of-mass energy, √ s γ N ≈ 2E max m p , for singlephoton interactions with protons, γ p → Q Q [176], at the LHC is given in Table 1. At the LHC, the energies are high enough for tt photoproduction [177]. The total photon flux striking the target nucleus must be calculated numerically.…”

Physics of Ultra-Peripheral Nuclear Collisions

“…Considerably more interest has been devoted to direct photon interactions, in particular the production of heavy qq-pairs [6,89,90,91]. Recently, the cross section for photoproduction of heavy quark pairs in pp collisions has been calculated [92].…”

The coherent cross section of vector mesons in ultraperipheral PbPb collisions at the LHC

“…Recently, the ALICE collaboration have measured vector meson production in PbPb ultraperipheral collisions [4][5][6][7][8]. On the theoretical front, the photon production of vector mesons has been studied through various approaches, including perturbative quantum chromodynamics (pQCD), k T -factorization, and the color dipole model (CDM) [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. In this work, we use the dipole model to predict the vector meson production in PbPb ultraperipheral collisions at √ s NN = 2.76 TeV.…”