Multiple photon effects in pp scattering at SSC energies ∗

The Monte Carlo program SSCYFS2 is used in conjunction with available parton distribution functions to calculate the effects of multiple photon radiation on pp scattering at SSC energies. Effects relevant to precision SSC physics such as Higgs discovery and exploration are illustrated. Supported in part by the Texas National Research Laboratory Commission for the Superconducting Super Collider Laboratory via grant RCFY9201,by the US Department of Energy Contracts DE-FG05-91ER40627 and DE-AC03-76ER00515, and by the Polish Ministry of Education grants KBN 223729102 and KBN 203809101. Permanent address: Institute of Nuclear Physics, ul. Kawiory 26a, Krakow, Poland. Now that the SSC is under construction, it is important to prepare for the maximal exploration of its new energy frontier. Higher-order radiative corrections to its basic physics processes are then of large significance, for these corrections determine the precise level at which signals for new physics or Higgs physics can be separated from background as well as the precise level at which such signals can be measured. Accordingly, we have recently initiated [1] the development and implementation of the YFS Monte Carlo approach in Ref. [2] to higher-order radiative corrections to the SSC physics processes. In this Letter, we present our results for the multiple photon radiative effects in pp → qq() + n(γ) +X where q, q = u, d, s, and we require that the pp c.m.s. production angle of q(q), θq(q′), must satisfy the SDC acceptance cut (GEM would have a similar cut) |η| < 2.8 for definiteness. (We recall for completeness that the development in Ref. [2] is based on the original work of Yennie, Frautschi and Suura in Ref. [3].) Specifically, we use the Monte Carlo (MC) event generator SSCYFS2 which was developed in Ref. [1] for qq̄ ′ → q(q̄) + n(γ) (1) and the parton distributions of Refs. [4] to simulate, on an event-by-event basis, the multiple photon initial state radiative effects in pp → qq(′) + n(γ) +X , (2) where q, q = u, d, s. The basic master formula for the cross-section is then the usual parton distribution convolution σ = ∑ q,q ∫ Dq(x1)Dq′(x2)σYFS(x1x2s) dx1dx2 (3) where Dq(x1) is the usual parton distribution of quark q in p and σYFS is the YFS multiplephoton cross-section for (1) realized by MC methods in SSCYFS2 in Ref. [1]. We emphasize that the formula in (3) is new in that it combines the YFS amlpitude based higher order QED corrections to the reduced hard subprocess with the QCD evolved parton distributions. The theoretical basis for this is the well-known factorization theorem for hard hadron–hadron collisions [5]. Equivalently, since the distributions are strictly defined in the leading-log approximation framework, each emission of a gluon or a photon from an incoming parton is independent 1 in that framework so that all gluon emissions may be factorized away from the photon emissions,as we imply in (3), for the hard subprocess case.Note that this implies that the QED corrections to the low energy data from which the Dq are evolved have been done properly [6]. We emphasize that the entire cross-section in (3) is also now realized by MC methods by using such methods to choose x1 and x2 as well as to realize σYFS. The resulting program is called SSCYFSP and it will be described in detail elsewhere [7]. Here, we present results obtained with SSCYFSP and we comment on their implications for SSC physics objectives. More precisely, our complete trigger cuts for our sample MC data are as follows: Eγ > 3 GeV, Eparticleout > 80 GeV, θ > π/6 (4) so that we expect these data to be relevant to the GEM and the SDC acceptances. For this trigger, we show in turn in Figs. 1-5 the photon multiplicity, the total photon transverse momentum, the total photon mass, the final v-distribution of the outgoing qq ′) system, and the outgoing parton energy fraction distribution in the pp cms system. What we see in Fig.1 is that the mean value of nγ is .133 ±.369. Thus, multiple photon effects must be considered in detail in view of our cuts, where we require Eγ > 3 GeV. In Fig. 2, we show that the total photon transverse momentum has a mean value < p⊥,tot >= 4.1± 16.9 GeV. (5) The key issue regarding background to H → γγ in the intermediate regime is how often we get 40 GeV ∼ Eγ < ∼ 75 GeV in the transverse directions. We see from Fig. 2 that, even allowing for realistic parton distributions, which clearly degrade substantially the energy available in the reduced collisions in (3) on the average, we still will have to deal with this question in detail. Such discussion will appear elsewhere. In Fig. 3, we illustrate further the need to make a detailed study of the background from multiple photon effects to H → γγ via the total photon mass plot, where we find the mean value 〈Mnγ〉 = 〈(( ∑ i ki) ) 1 2 〉 = 37.2± 6.9 GeV. (6)