arXiv subjects

J. A. Leyva

Publications and source records attributed to J. A. Leyva.

5 recordsLinked to original sources

arXiv2014

$O(α_s)$ corrections to the polar angle dependence of the longitudinal spin-spin correlation asymmetry in $e^+e^-\to q\bar q$

We provide analytical results for the $O(α_s)$ corrections to the polar angle dependence of the longitudinal spin-spin correlation asymmetry in $e^+e^-\to q\bar q$. For top quark pair production the $O(α_s)$ corrections to the longitudinal spin-spin asymmetry are strongly polar angle dependent and can amount up to $4\%$ in the $q^2$-range from above $t\bar t$ threshold up to $\sqrt{q^2}=1000$ GeV. The $O(α_s)$ radiative corrections to the correlation asymmetry are below $1\%$ in the forward direction where the cross section is largest. In the $e^+e^-\to b\bar b$ case the $O(α_s)$ corrections reduce the asymmetry value from its $m_b=0$ value of $-100\%$ to approximately $-96\%$ for $q^2$-values around the $Z$ peak and are practically independent of the value of the polar angle theta. This reduction can be traced to finite anomalous contributions from residual mass effects which survive the $m_b\to 0$ limit. We discuss the role of the anomalous contributions and the pattern of how they contribute to spin-flip and non-flip terms.

hep-ph↗

arXiv1998

Gluon Polarization in e^+e^- -> t \bar t G: Polar Angle Dependence and Beam Polarization Effects

We calculate the linear and circular polarization of gluons produced in conjunction with massive quarks in the annihilation process $e^+e^-\to q \bar q G$. The linear polarization is calculated in the hadron event plane as well as in the gluon-beam plane. Beam polarization and polar orientation effects are included in our discussion. For typical top pair production energies at the Next-Linear-Collider (NLC) the degree of linear polarization in the hadron event plane remains close to its soft gluon value of 100% over most of the energy spectrum of the gluon. The linear polarization in the gluon-beam plane is generally smaller but peaks toward the hard end of the gluon spectrum. The dependence of the linear polarization on beam polarization and on the polar orientation of the gluon is small. The circular polarization is largest for maximal gluon energies and shows a strong dependence on the longitudinal beam polarization. The longitudinal polarization of the beam may therefore be used to tune the circular polarization of the gluon. The massive quark results are compared with the corresponding results for the massless quark case.

hep-ph↗

arXiv1998

On the rigidity of back-to-back top quark pairs in e^+e^- annihilation

We consider the effect of gluon radiation on the energy of top/antitop quarks and on the anticollinearity of top-antitop quark pairs produced in $e^+e^-$ annihilation. Our results are presented in terms of the $E_q$-dependence of the $t\bar tg$ cross section and the dependence on the cosine of the opening angle $θ_{12}$ between top and antitop for a center of mass energy of $\sqrt{q^2}=500 GeV$. We then go on to determine mean values for the top quark's energy as well as its longitudinal and transverse projections, and for the deviation of $\sinθ_{12}$ and $\cosθ_{12}$ from the anticollinearity limits $\sinθ_{12}=0$ and $\cosθ_{12}=-1$. For a center of mass energy of $500 GeV$ we obtain $ =248.22 GeV$, $ =247.24 GeV$ and $ =4.70 GeV$. Thus, at this energy gluon radiation causes a total average energy loss of 0.71% of the top quark's energy. The average energy loss in the longitudinal direction is 1.06% and the average energy gain in the transverse direction is 1.88%. These percentage figures go up to 3.77%, 5.19% and 6.06%, respectively, at $1000\GeV$. For the mean of the acollinearity angle $\barθ_{12}=180^0-θ_{12}$ we obtain $<\barθ_{12}>=1.25^0$ at $500 GeV$, the value of which goes up to $4.62^0$ at $1000 GeV$. From an analysis of the transverse momentum of the top we find that the mean transverse momentum of the top stays close to the mean total momentum of the gluon in the energy range from threshold to $1000 GeV$ showing that the gluon momentum has a large mean transverse component in this energy range.

hep-ph↗

arXiv1997

O(α_s) Corrections to Longitudinal Spin-Spin Correlations in e+e- -> q qbar

We calculate the $O(α_s)$ corrections to longitudinal spin-spin correlations in $e^+e^-\to q\bar q$. For top quark pair production the $O(α_s)$ corrections to the longitudinal spin-spin asymmetry amount to less than 1% in the $q^2$-range from above $t\bar t$-treshold up to $\sqrt{q^2}= 1000 GeV$. In the $e^+e^-\to b\bar b$ case the $O(α_s)$ corrections reduce the asymmetry value from its $m=0$ value of -1 to approximately -0.96 for $q^2$-values around the Z-peak. This reduction can be traced to finite anomalous contributions from residual mass effects which survive the $m\to 0$ limit. We discuss the role of the anomalous contributions and the pattern of how they contribute to spin-flip and no-flip terms.

hep-ph↗

arXiv1997

Gluon Polarization in $e^+e^-\to t\bar tG$

We calculate the linear polarization of gluons radiated off top quarks produced in e^+e^- annihilations. For typical top pair production energies at the Next-Linear-Collider (NLC) the degree of linear polarization remains close to its soft gluon value of 100% over almost the whole energy spectrum of the gluon. The massive quark results are compared with the corresponding results for the massless quark case.

hep-ph↗