Heavy quark production at the TESLA collider and its sensitivity to the gluon content in the photon

Abstract

Heavy quark production is studied at the high energy linear e + e − collider (LC) TESLA both in its nominal and Photon Collider (PC) mode. Leading order cross-sections are calculated for the production of heavy quarks, e + e − → e + e − Q(Q)X, at high transverse momenta. The sensitivity of this process to the gluon content in the photon is studied. An e+ e − linear collider with a centre of mass system (CMS) energy in the range of 500 to 1000 GeV is the prime candidate for the next high energy accelerator project after the LHC. Recently TESLA [1] has completed a Technical Design Report for such a collider. For the study of a future electron-positron Linear Collider (LC) it is important to examine the physics potential of its main and possible additional options. Such an option is the Photon (or Compton) Collider (PC) in which high energy real photons can be obtained by backscattering photons from a laser beam on the electron or positron beam [2,3]. This way an excellent tool for the study of γγ collisions at high energies can be provided. In high energy e+ e − collisions the hadronic final state is predominantly produced in γ γ interactions where the virtual photons (γ ) are almost on mass shell. Their scattering can be effectively described with the interaction of real photons with energy spectra given by the Weizsäcker-Williams (WW) approximation [4]. Such a spectrum is generally quite soft, as shown in Fig. 1. In contrast, a Photon Collider, based on Compton scattering, provides beams of real photons which are much harder than those from a WW distribution (see Fig. 1). Furthermore these photons can be produced 1 in a definite polarization state. While the energy spectrum of the PC at the high energy end can be well calculated based on a few parameters of the laser and incident electron beam, the lower energy end depends much more on the details of machine and operation. Therefore we limit ourself to study only the high energy peak of 0.6 < y = E γ /E e < 0.83 [5]. The spectra used in this paper are described in the Appendix.The main goal of this study is to compare the LC and PC potential for probing the gluon distribution in the photon via heavy quark production. This analysis does not make use of polarization. The measurement of the process e + e − → e + e − Q(Q)X is an important test of QCD. It is well known that this process is promising for probing the structure of the photon, see e.g. [6,7] and [8], where a related topic is considered. Heavy quarks can be produced in γγ collisions through three mechanisms. Direct (DD) production occurs when both photons couple directly to a QQ pair. In single resolved photoproduction processes (DR) one of photons interacts via its partons with the second photon. When both photons split into a flux of quarks and gluons, the process is labelled a double resolved photon (RR) process.There are various schemes proposed for calculating cross-sections for processes involving heavy quarks, for the latest overview see ref [9]. Two standard schemes will be used in this a...

Higgs physics with a $\gamma \gamma$ collider based on CLIC 1

“…Although eγ scattering allows one to measure the quark distributions inside the photon, it constrains only weakly the gluon distribution, via the QCD evolution of the structure functions. Direct information on the gluon in the photon can, however, be obtained from measurements of jets [57], open charm [58] and J/ψ [59] production in γγ interactions at an eγ and γγ collider. Values of x down to a few ×10 −3 can be reached with charm and di-jet measurements [57,58], a region where predicted gluon distributions typically differ by a factor of two or more.…”

“…Direct information on the gluon in the photon can, however, be obtained from measurements of jets [57], open charm [58] and J/ψ [59] production in γγ interactions at an eγ and γγ collider. Values of x down to a few ×10 −3 can be reached with charm and di-jet measurements [57,58], a region where predicted gluon distributions typically differ by a factor of two or more.…”

Probe of the electromagnetic moments of the tau lepton in gamma-gamma collisions at the CLIC

“…The Compact Linear Collider (CLIC) is a proposed future e + e − collider, designed to fulfill e + e − collisions at energies from 0.5 to 3 TeV [32], and it is planned to be constructed with a three main stages research region [33]. The CLIC has been extensively studied for interactions beyond the SM [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50]. The CLIC enables to investigate the γγ and γe interactions by converting the original e − or e + beam into a photon beam through the laser backscattering procedure [51][52][53].…”