Inclusive hadron production in photon-photon collisions at next-to-leading order

Abstract

We study inclusive charged-hadron production in collisions of quasireal photons at next-to-leading order (NLO) in the QCD-improved parton model, using fragmentation functions recently extracted from PEP and LEP1 data of e + e − annihilation. We consistently superimpose the direct (DD), single-resolved (DR), and double-resolved (RR) γγ channels. We consider photon spectra generated by electromagnetic bremsstrahlung and/or beamstrahlung off colliding e + and e − beams as well as those which result from backscattering of laser light off such beams. First, we revisit existing single-tag data taken by TASSO at PETRA and by MARK II at PEP (with e + e − energy √ S ≈ 30 GeV) and confront them with our NLO calculations imposing the respective experimental cuts. We also make comparisons with the neutral-kaon to charged-hadron ratio measured by MARK II. Then, we present NLO predictions for LEP2, a next-generation e + e − linear collider (NLC) in the TESLA design with √ S = 500 GeV, and a Compton collider obtained by converting a 500-GeV NLC. We analyze transverse-momentum and rapidity spectra with regard to the scale dependence, the interplay of the DD, DR, and RR components, the sensitivity to the gluon density inside the resolved photon, and the influence of gluon fragmentation. It turns out that the inclusive measurement of small-p T hadrons at a Compton collider would greatly constrain the gluon density of the photon and the gluon fragmentation function.

Inclusive jet production in two-photon collisions at LEP

“…The GRV-HO parton density functions of Reference 23 are used and all elementary 2 → 2 and 2 → 3 processes are considered. The parameter Λ (5) is set to 130 MeV. The renormalization and factorisation scales are taken to be equal: µ = M = E t /2 [1].…”

“…The inclusive π 0 and π ± differential cross sections, measured as a function of transverse momentum, exhibit a clear excess over NLO QCD calculations [5] for large transverse momentum. In this Letter, inclusive jet production is studied, in similar two-photon interactions, for a centre-of-mass energy of the two interacting photons, W γγ , greater than 5 GeV.…”

A next-to-leading order study of photon-pion and pion pair hadro-production in the light of the Higgs boson search at the LHC

“…Therefore the erroneous treatment of the fragmentation process at small z will plague the estimates of inclusive dipion observables at colliders. This is the reason why the fits of independent fragmentation functions D i→π 0 (z, M 2 f ) to experimental data presented in the literature [16,27], and which we use in this work, start above some minimum value for z, e.g. z min ∼ 0.1.…”

“…This problem is visualised in Fig. 9 where we show the photon-pion invariant mass distribution calculated with both, the KKP [16] and the older BKK [27] fragmentation functions. The KKP parametrisation leads to a higher prediction than the BKK one.…”

Overview — Simulation of Sheet Metal Forming

“…Jets are reconstructed using the k ⊥ -clustering algorithm and analysed in the pseudorapidity range |η| < 1 for jet transverse momenta 3 < p t < 50 GeV. The remaining background from other processes after event selection increases In both cases the measurement are compared to a calculation in NLO QCD [13]. Figure taken from [14].…”