Future Photon Colliders Research Articles

Photoproduction ofJ/ψin association with acc¯pair

Based on the color-singlet model, we investigate the photoproduction of $J/\psi$ associated with a $c \bar{c}$ pair with all subprocesses including the direct, single-resolved, and double-resolved channels. The amplitude squared of these subprocesses are obtained analytically. By choosing corresponding parameters, we give theoretical predictions for the $J/\psi$ transverse momentum distributions both at the LEPII and at the future photon colliders for these subprocesses. The numerical results show that at the LEPII these processes can not give enough contributions to account for the experimental data, and it indicates that the color-octet mechanism may still be needed. At the photon collider with the laser back scattering photons, the resolved photon channe will dominate over the direct one in small and moderate $p_t$ regions with large $\sqrt{s}$. By measuring the $J/\psi$ production associated with a $c\bar{c}$ pair, this process can be separated from the inclusive $J/\psi$ production and may provide a new chance to test the color-singlet contributions.

Unparticle Effects on Top Quark Pair Production at Photon Collider

The unparticle effects on tt̄ production at the future photon collider are investigated. Distributions of tt̄ invariant mass and that for transverse momentum of top quark with respect to Standard Model and unparticle production are predicted. An odd valley with scalar unparticle contribution appears for some values of du, which is due to the big cancellation between the contribution from SM and that from unparticle. This character may be used to study the properties of scalar unparticle. Our investigations also show that scalar unparticle may play a significant role in tt̄ production at the photon collider if it exists.

Dominant two-loop electroweak corrections to the hadroproduction of a pseudoscalar Higgs boson and its photonic decay

We present the dominant two-loop electroweak corrections to the partial decay widths to gluon jets and prompt photons of the neutral $CP$-odd Higgs boson ${A}^{0}$, with mass ${M}_{{A}^{0}}<2{M}_{W}$, in the two-Higgs-doublet model for low to intermediate values of the ratio $\mathrm{tan}\ensuremath{\beta}={v}_{2}/{v}_{1}$ of the vacuum expectation values. They apply as they stand to the production cross sections in hadronic and two-photon collisions, at the Tevatron, the LHC, and a future photon collider. The appearance of three ${\ensuremath{\gamma}}_{5}$ matrices in closed fermion loops requires special care in the dimensional regularization of ultraviolet divergences, and the finite electroweak renormalization of the pseudoscalar current restoring the anticommutativity of ${\ensuremath{\gamma}}_{5}$ is performed for the first time. The corrections are negative and amount to several percent, so that they fully compensate or partly screen the enhancement due to QCD corrections.

Design study of an optical cavity for a future photon collider at ILC

Hard photons well above 100 GeV have to be generated in a future photon collider which essentially will be based on the infrastructure of the planned International Linear Collider (ILC). The energy of near-infrared laser photons will be boosted by Compton backscattering against a high-energy relativistic electron beam. For high effectiveness, a very powerful laser system is required that exceeds today's state-of-the-art capabilities. In this paper a design of an auxiliary passive cavity is discussed that resonantly enhances the peak-power of the laser. The properties and prospects of such a cavity are addressed on the basis of the specifications for the European TeV Energy Superconducting Linear Accelerator (TESLA) proposal. Those of the ILC are expected to be similar.

Studies on chargino production and decay at a photon collider

A Monte-Carlo analysis on production and decay of supersymmetric charginos at a future photon-collider is presented. A photon collider offers the possibility of a direct branching-ratio measurement. In this study, the process gamma,gamma -> chi_1^+,chi_1^- -> W+W-chi_1^0chi_1^0 -> 4-jets,chi_1^0chi_1^0 has been considered for a specific mSUGRA scenario. Various backgrounds and parameterised detector simulation have been included. Depending on the centre-of-mass energy, a statistical error for the directly measurable branching ratio BR(chi}_1^+ ->chi}_1^0 W^+) of up to 3.5% can be reached.

Testing the noncommutative standard model at a future photon collider

Extensions of the Standard Model of elementary particle physics to noncommutative geometries have been proposed as a low-energy limit of string models. Independent of this motivation, one may consider such a model as an effective field theory with higher-dimensional operators containing an antisymmetric rank-two background field. We study the signals of such a Noncommutative Standard Model (NCSM) and analyze the discovery potential of a future photon collider, considering angular distributions in fermion pair production.

Hadronic cross-sections in two photon processes at a future linear collider

In this note we address the issue of measurability of the hadronic cross-sections at a future photon collider as well as for the two-photon processes at a future high energy linear $e^+e^-$ collider. We extend, to higher energy, our previous estimates of the accuracy with which the \gamgam\ cross-section needs to be measured, in order to distinguish between different theoretical models of energy dependence of the total cross-sections. We show that the necessary precision to discriminate among these models is indeed possible at future linear colliders in the Photon Collider option. Further we note that even in the $e^+e^-$ option a measurement of the hadron production cross-section via \gamgam processes, with an accuracy necessary to allow discrimination between different theoretical models, should be possible. We also comment briefly on the implications of these predictions for hadronic backgrounds at the future TeV energy $e^+e^-$ collider CLIC.

A model of F2γ at arbitrary Q2 and the total photon–photon cross-sections at high energies

A model of the real photon structure function F 2 γ which can be used in the low Q 2, low x region is formulated. It includes both the VMD and the QCD components, the latter based on arbitrary parton distributions in the photon and suitably extrapolated to the low Q 2 region. The model using the GRV and GRS’ parton densities describes reasonably well the existing high energy data on F 2 γ , σ γγ and the low Q 2 data on σ γ ∗ γ . Predictions for high energy cross-section for γγ scattering and γ ∗ γ relevant to future Photon Colliders are given.

Spin of Scattered Electrons in the Nonlinear Compton Effect

The polarization of the final electron for the nonlinear Compton effect in a field of a circularly polarized electromagnetic wave is considered. The complete set of formulas necessary for simulation of the e → γ conversion at future photon colliders is given. We note the possibility to transform the longitudinal polarization of the initial electron into transverse polarization of the final electron.

Gamma gamma -->Ze+e- and related processes using polarized photon beams.

The cross sections for processes with the production of $Z$ and pairs of leptons or quarks in the $\ensuremath{\gamma}\ensuremath{\gamma}$ collisions are calculated. They are large enough to give an important background for Higgs boson hunting at future photon colliders if the Higgs boson mass is about 100 GeV and they are small for the production of two $Z$. The equivalent electron approximation for the polarized photon beams is presented.

FEL based photon collider at SLC as a prototype of future photon colliders

FEL based photon collider at SLC as a prototype of future photon colliders