Photon Linear Collider Research Articles

E + e − γ production at photon-photon colliders at complete electroweak NLO accuracy * *Supported in part by the National Natural Science Foundation of China (11775211, 12061141005) and the CAS Center for Excellence in Particle Physics (CCEPP)

We present the NLO electroweak radiative corrections to the production in γγ collision, which is an ideal channel for calibrating the beam luminosity of a Photon Linear Collider. We analyze the dependence of the total cross section on the beam colliding energy, and then investigate the kinematic distributions of final particles at various initial photon beam polarizations at EW NLO accuracy. The numerical results indicate that the EW relative corrections to the total cross section are non-negligible and become increasingly significant as the increase of the beam colliding energy, even can exceed –10% in the γγ collision at . Such EW corrections are very important and should be taken into consideration in precision theoretical and experimental studies at high-energy γγ colliders.

Pair production of doubly charged Higgs boson at photon linear collider in the Higgs triplet model

The characteristic feature of the Higgs Triplet Model (HTM) is the existence of the doubly charged Higgs bosons H±±. In this paper, we study the pair production of doubly charged Higgs bosons in γγ collisions at the International Linear Collider (ILC). We present the production cross-sections and the distributions of the various observables, i.e. the distributions of the transverse momenta, the rapidity distributions for doubly charged Higgs bosons and the production angle distributions of the charged Higgs boson pair. Our numerical results show that, the values of the unpolarized cross-sections can reach a few hundreds of fb. We also study the possible final state for the decay mode H±±→W±W± and relevant Standard Model (SM) background. Due to high produced rate and small SM background, the possible signals of H±± might be detected via this process in the future ILC experiments.

Triple Higgs boson production at the high-energy Photon Linear Collider in the Higgs triplet model

Besides the SM-like Higgs boson h, the Higgs triplet model (HTM) predicts the existence of charged and doubly charged Higgs bosons ( and ). In this letter, we focus on the study of the triple Higgs production in γγ collisions at the high-energy linear collider: and . We present the production cross-sections and the distributions of the various observables, i.e., the distributions of the energy and the transverse momenta of the SM-like Higgs boson and charged Higgs bosons. Our numerical results show that, with reasonable parameter values, the values of the cross-sections for two processes can reach the level of several tens of fb and hundreds of fb, respectively. Due to the small SM background, the possible signals of and might be detected via these processes in the future high-energy linear-collider experiments.

Feasibility study of the measurement of Higgs pair creation at a photon linear collider

We studied the feasibility of the measurement of Higgs pair creation at a Photon Linear Collider (PLC). From the sensitivity to the anomalous self-coupling of the Higgs boson, the optimum $\gamma \gamma$ collision energy was found to be around 270 GeV for a Higgs mass of 120 GeV/$c^2$. We found that large backgrounds such as $\gamma \gamma \rightarrow W^+W^-, ZZ,$ and $b\bar{b}b\bar{b}$, can be suppressed if correct assignment of tracks to parent partons is achieved and Higgs pair events can be observed with a statistical significance of $\sim 5 \sigma$ by operating the PLC for 5 years.

Meeting to discuss laser cavity design for photon linear collider — Daresbury, UK, 10 January 2006

The outcome of the meeting to discuss the proposed design for a laser cavity for the photon linear collider is presented.

Heavy neutral MSSM Higgs bosons at the photon linear collider — a comparison of two analyses

Measurement of the heavy neutral MSSM Higgs bosons H and A production in the process γγ → A/H → b\( \bar b \) at the Photon Linear Collider [1,2] has been considered in two independent analyses for the parameter range corresponding to the so-called ‘LHC wedge’. Significantly different conclusions were obtained; signal-to-background ratio 36 vs. 2. Here assumptions and results of these two analyses are compared. We have found that differences in the final results are mainly due to different assumptions on γγ-luminosity spectra, jet definitions and selection cuts.

Gamma gamma technology group

This report briefly describes the results presented at this conference on work to develop the technology required to build the proposed gamma gamma option, also known as the photon linear collider (PLC) [1]. Before describing the work presented at this conference I would like to put it in context. At the International Workshop on High Energy Photon Linear Colliders, 5–8 September 2005, Kazimierz Dolny, Poland, the first meeting of the Gamma Gamma Planners Group was held, chaired by David Miller. The purpose of the meeting was to form a group of people who would study the technical aspects of the photon linear collider. Various tasks were assigned, for example, A F Zarnecki agreed to look at the crossing angle and I agreed to study beam monitoring and feedback issues. A meeting was planned for October 2005 to study issues around the laser cavity design. Unfortunately one month after this David Miller suffered a major stroke which disrupted our efforts considerably. The organisation of the Laser Cavity meeting was taken over by myself and was postponed to 10 January 2006. I presented the outcome of this meeting at this conference [2]. I am happy to report that David continues to make a steady recovery and we look forward to seeing him again at future meetings.

Measuring Higgs CP properties through top quark production at a photon collider

We study resonant effects of heavy Higgs bosons on the top-pair production process at a photon linear collider. Observables which can be obtained by circular polarization of colliding photons and polarization measurement through the angular distribution of the top quark decays are useful not only for measuring the Higgs CP parity but also for resolving degeneracy of Higgs bosons.

Photon collider beam simulation with CAIN

The CAIN simulation program was used to study the outgoing beam profile for the photon collider at ILC. The main aim of the analysis was to verify the feasibility of the photon linear collider running with 20 mrad electron beam crossing angle. The main problem is the distorted electron beam, which has to be removed from the interaction region. It is shown that with a new design of the final dipole, it should be possible to avoid large energy losses at the face of the magnet.

PROBING HIGGS-SECTOR CP VIOLATION AT A PHOTON COLLIDER

In this review we demonstrate physics potential of a photon linear collider by studying the neutral Higgs–boson sector of the MSSM in which interesting CP-violating Higgs mixing could arise via radiative corrections.

New-Physics Search through γγ→tt¯→ℓX/bX

We probe optimal beam polarizations for new-physics search in top-quark and Higgs-boson sectors at Photon Linear Colliders (PLC). Expressing possible non-standard effects generated by SU(2)xU(1) gauge-invariant dimension-6 effective operators as anomalous top and Higgs couplings, we estimate expected statistical sensitivities of these couplings in gamma gamma -> t tbar -> lX/bX, using the optimal-observable method.

Probing the CP nature of the Higgs bosons by $t\overline{t}$ productionat photon linear colliders

We study effects of heavy Higgs bosons on the top-pair production process at photon linear colliders. The interference patterns between the resonant Higgs-production amplitudes and the continuum QED amplitudes are examined. The patterns tell us not only the CP nature of the Higgs bosons but also the phase of the $\gamma\gamma$--Higgs vertex which gives new information about the Higgs couplings to new charged particles. We point out that it is necessary to use circularly polarized photon beams to produce efficiently heavy Higgs bosons whose masses exceed the electron beam energy, and show that the above interference patterns of the production amplitudes can be studied by observing top decay angular distributions. Analytic expressions for the helicity amplitudes for the sequential process $\gamma\gamma \to t \bar{t} \to (bW^+) (\bar{b}W^-) \to (b f_1 \bar{f}_2) (\bar{b} f_3 \bar{f}_4)$ are presented in terms of the generic $\gamma\gamma \to t \bar{t}$ production amplitudes.

Author Index

In some supersymmetric extensions of the Standard Model fairly light superpartner of t-quark is predicted, which may form bound states (stoponiums) under certain conditions. We estimate potentials of TESLA linear collider in search for stoponium, considering the basic electron–positron option and the γγ option (Photon Linear Collider—PLC).It is found that PLC could be the best machine for discovery and study of these new narrow strong resonances. It can produce thousands stoponiums per 100fb−1 integrated γγ luminosity in the high energy peak. In the case of scenarios, when stoponium decays mainly into two gluons the signal/background ratio is about 14. In addition, the decay channel S→hh into two lightest Higgs bosons could be seen with high significance. Thus, several weeks run is sufficient for the discovery of stoponium, if its mass is approximately known (for example, from observation of direct stops production at LHC). Then, in MSSM scenarios with dominant S→hh decay PLC shows excellent possibilities to discover bound state of stops, practically immediately after beginning of operating. Thus, PLC has good possibilities to study strong interaction of top quark superpartners in nonperturbative regime.The e+e− option also has some prospects to observe stoponium but only in the case of scenarios with dominant decay into two lightest Higgs bosons, with tens of events per 100fb−1. Interesting possibility appears in the case when the resonance is seated on 0.1% width luminosity peak—one could resolve the stoponium exited states.

The High Energy γγ → γγ Scattering Cross Sections

Contributions of fermion loops, W-boson loops and their sum to the high energy γγ → γγ scattering total cross sections (|cosθ| < cos30°) are calculated by analytical expressions of γγ → γγ scattering amplitude. These contributions may be observed in the future photon linear collider and may be used to test standard model. The contribution of fermions' loops is a half of that in R.K. Arphlus and M. Neuuman's paper (Phys. Rev. 80 (1950) 380; 83 (1951) 776).

τ magnetic moment in a γγ collider

We analyze different observables to study the magnetic dipole moment of the tau pairs produced by photon linear colliders. We use the circular polarized photon beam and study distributions of polarized $\tau$ final pairs to define sensibly asymmetries to magnetic dipole moment.

Top quarks at photon colliders

A review of results on top quark physics expected at the photon linear colliders is presented.

TESLA: potentials of γγ and e +e − options in stoponium searches

In some supersymmetric extensions of the Standard Model fairly light superpartner of t-quark is predicted, which may form bound states ( stoponiums) under certain conditions. We estimate potentials of TESLA linear collider in search for stoponium, considering the basic electron–positron option and the γγ option (Photon Linear Collider—PLC). It is found that PLC could be the best machine for discovery and study of these new narrow strong resonances. It can produce thousands stoponiums per 100 fb −1 integrated γγ luminosity in the high energy peak. In the case of scenarios, when stoponium decays mainly into two gluons the signal/ background ratio is about 1 4 . In addition, the decay channel S→hh into two lightest Higgs bosons could be seen with high significance. Thus, several weeks run is sufficient for the discovery of stoponium, if its mass is approximately known (for example, from observation of direct stops production at LHC). Then, in MSSM scenarios with dominant S→hh decay PLC shows excellent possibilities to discover bound state of stops, practically immediately after beginning of operating. Thus, PLC has good possibilities to study strong interaction of top quark superpartners in nonperturbative regime. The e +e − option also has some prospects to observe stoponium but only in the case of scenarios with dominant decay into two lightest Higgs bosons, with tens of events per 100 fb −1 . Interesting possibility appears in the case when the resonance is seated on 0.1% width luminosity peak—one could resolve the stoponium exited states.

Stoponium search at photon linear collider

In some supersymmetric extensions of the Standard Model fairly light superpartner of t-quark is predicted, which may form bound states ({\it stoponiums}) under certain conditions. We study prospects of search for stoponium at the future Photon Linear Collider. It is found that this machine could be the best machine for discovery and study of these resonances at some scenarios of supersymmetric extension of the Standard Model. In particular, if the $hh$ decay channel is dominant stoponium could be observed at the beginning of PLC run with collision energy tuned at the stoponium mass. If this channel is kinematically closed stoponium could be discovered in $gg$, $\gamma\gamma$ and $ZZ$ decay channels but higher statistics are needed. Effects of the stoponium-Higgs mixing and degeneracy are briefly discussed.

Measuring the Higgs CP property through top quark pair production at photon linear colliders

We present a model-independent study of the effects of a neutral Higgs boson without definite $\mathrm{CP}$ parity in the process $\ensuremath{\gamma}\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}t\overline{t}$ around the mass pole of the Higgs boson. Near the resonance pole, the interference between the Higgs exchange and the continuum amplitudes can be sizable if the photon beams are polarized and helicities of the top quark and top antiquark are measured. The study of these interference effects enables one to determine the $\mathrm{CP}$ property of the Higgs boson completely. An example of the complete determination is demonstrated in the context of the minimal supersymmetric standard model.

CP-violating Zγγ and top-quark electric dipole couplings in [formula omitted

An effective anomalous CP-violating Zγγ coupling can give rise to observable CP-odd effects in γγ→t t . We study certain asymmetries in the decay lepton distributions in γγ→t t arising from top decay in the presence of a CP-violating Zγγ coupling as well as a top-quark electric dipole coupling. We find that a photon linear collider with geometric luminosity of 20 fb −1 can put limits of the order of 0.1 on the imaginary part of the CP-violating anomalous Zγγ coupling using these asymmetries.