Optimal spin basis in polarized photon linear colliders

Abstract

We analyze the spin correlations of the top quark pairs produced at Photon Linear Colliders. We employ the circular polarized photon beams and general spin basis for the top quark pair. We consider general spin bases to find a strong spin correlation between produced top quark and anti-top quark. We show the cross-section in these bases and discuss the characteristics of results.We have been progressing in our understanding of nature step by step. LEP and Tevatron experiments provided us with the precision measurement of the top quark mass [1,2], W boson mass, the bound for the Higgs boson mass and many other electro-weak parameters. With these numerous data, the standard electro-weak theory are enjoying the nature without any discrepancies at least in current experiments.In 1994, the last fundamental quark of the "Standard Model", the top was discovered at the Fermi-Lab Tevatron. The discovery of this very heavy fundamental particle is remarkable, which brought us some good chance to probe the electro-weak symmetry breaking mechanism. The top quark sector is not yet well established and many authors are discussing related problems. For instance, T or CP violation in the top quark sector and the possibility of the presence of anomalous couplings have been discussed in many papers [3]. A very heavy top quark arouse our interests in trying to understand the nature deeply and we expect to investigate the top quark sector of the Standard Model at the Next Linear Collider (NLC) [4,5] in the near future.The top quark physics at NLC is attractive and will give us some new information to understand the Standard Model and clue to physics beyond the Standard Model.On the other hand, the Photon Linear Colliders [6] may be the best alternatives to the electron positron colliders. Physics opportunities in the Photon Linear Colliders are as rich as those in the e + e − colliders and furthermore we have an unique opportunity in the case of the Photon Linear Colliders, namely, we can control the initial photon polarization by the inverse Compton scattering of the polarized laser by the electron/positron beams at NLC. Handling the polarized photon beams, we have the total angular momentum J = 0, 2, · · · states in the s-channel. Using these polarized high energy photon beams, we will have attractive channels for Higgs particle production [6], top quark pair production [7] and other interesting processes.It was discussed in the papers [8][9][10] that the spin of the top quark can be determined from the angular distribution of the electro-weak decay products of the top quark. So, it is interesting to investigate the spin correlations of the top quark pairs at the Photon Linear Colliders. We discuss in this paper the top quark pair production at the Photon Linear Colliders with the circular polarized photon beams and the general spin basis for the top and anti-top quarks.This paper is organized as follows. In Sec.II we explain our notation and convention to calculate the cross-section. We show the cross-section of the top quark pair...

Spin correlation effects in top quark pair production at the LHC

“…Both the like and unlike gluon helicity amplitudes agree with those found in the appendix of Ref. [13].…”

Lepton distribution as a probe of new physics in production and decay of thetquark and its polarization

“…[25,26,27,28,29,30]. Spin correlations in top pair production have been studied [31,32,33,34,35]. QCD corrections to such correlations have also been studied [36,37,38,39,40,41,42,43].…”

Non-universal gauge bosonZ′ and the spin correlation of top quark pair production at e−e+colliders

“…To obtain the differential cross section of the process e − e + → t t → b lν l bl ′ ν l ′ , the production and decay spin density matrixes are written as the usual approach. After integrating over the azimuthal angles of the charged leptons, one can obtain the following double differential distribution [9] 1 σ…”

“…Thus, studying the t t spin correlations provides an interesting possibility to test the SM and search for new physics. This fact has made that the spin correlation of the t t production at the ILC experiments has been extensively studied in the SM and new physics beyond the SM [8,9,10]. This paper is aimed at investigating the effects of the non-universal neutral gauge boson Z ′ predicted by the topcolor scenario on the top quark pair production via the process e − e + → t t, and seeing whether the possible signatures of Z ′ can be detected via measuring the t t spin correlation observable in the future ILC experiments.…”