arXiv subjects

Thomas Mehen

Publications and source records attributed to Thomas Mehen.

95 records · Page 6Linked to original sources

arXiv1997

Summing $O(β_0^n α_s^{n+1})$ Corrections to Top Quark Decays

Order $β_0^n α_s^{n+1}$ QCD corrections to top quark decays into $W^+$ and $H^+$ bosons are computed to all orders in perturbation theory. Predictions for the radiative corrections to the top quark width are compared with the estimates from BLM scale setting procedures. The results of the summation are shown to greatly improve understanding of higher order corrections in the limit $m_W,~m_H \to m_t$, where the BLM scale setting method is known to fail. Attempts to reduce nonperturbative error by substituting the running mass for the pole mass in the expression for the decay are shown to fail in the limit $m_W,~m_H \to m_t$ because of subtleties in the treatment of phase space.

hep-ph↗

arXiv1997

Leptoproduction of J/psi

We study leptoproduction of $J/ψ$ at large $Q^2$ within the nonrelativistic QCD (NRQCD) factorization formalism. The cross section is dominated by color-octet terms that are of order $α_s$. The color-singlet term, which is of order $α^2_s$, is shown to be a small contribution to the total cross section. We also calculate the tree diagrams for color-octet production at order $α^2_s$ in a region of phase space where there is no leading color-octet contribution. We find that in this regime the color-singlet contribution dominates. We argue that non-perturbative corrections arising from diffractive leptoproduction, higher twist effects, and higher order terms in the NRQCD velocity expansion should be suppressed as $Q^2$ is increased. Therefore, the color-octet matrix elements $< {\cal O}_8^ψ(^1S_0)>$ and $<{\cal O}_8^ψ(^3P_0)>$ can be reliably extracted from this process. Finally, we point out that an experimental measurement of the polarization of leptoproduced $J/ψ$ will provide an excellent test of the NRQCD factorization formalism.

hep-ph↗

arXiv1997

Testing Quarkonium Production with Photoproduced $J/ψ+ γ$

I compute the leading color-octet contributions to the process $γ+ p \to J/ψ+ γ(+ X)$ within the non-relativistic QCD (NRQCD) factorization formalism. In the color-singlet model, $J/ψ+ γ$ can only be produced when the photon interacts through its structure function, while the color-octet mechanism allows for production of $J/ψ+ γ$ via direct photon-gluon fusion. Resolved photon processes can be easily be distinguished from direct photon processes by examining the fraction of the incident photon energy carried away by the $J/ψ$ in the event. Therefore, this process provides a conclusive test of the color-octet mechanism. $J/ψ+ γ$ production is particularly sensitive to the NRQCD matrix element which figures prominently in the fragmentation production of $J/ψ$ at large $p_{\perp}$ in hadron colliders. I also examine the predictions of the color evaporation model (CEM) of quarkonium production and find that this process can easily discriminate between the NRQCD factorization formalism and the CEM.

hep-ph↗

arXiv1996

Scale Setting in Top Quark Decays

We compute the $O(β_0 α_s^2)$ QCD corrections to the Standard Model decay $t\rightarrow W^+ b$ as well as the non standard decay $t\rightarrow H^+ b$. We then use our results to compute the BLM scale for these decays, and study the dependence of the BLM scale on the mass of the boson in the decay. We find that the BLM procedure gives extremely small scales when top decays into heavy bosons. When we try to improve the BLM scale by reexpressing rates as a functions of the top quark running mass, we find the BLM scale exhibits unnatural dependence on the boson mass, casting doubts on the applicability of the BLM procedure to these processes.

hep-ph↗

arXiv1995

Excited Heavy Mesons Beyond Leading Order in the Heavy Quark Expansion

We examine the decays of excited heavy mesons, including the leading power corrections to the heavy quark limit. We find a new and natural explanation for the large deviation of the width of the $D_1(2420)$ from the heavy quark symmetry prediction. Our formalism leads to detailed predictions for the properties of the excited bottom mesons, some of which recently have been observed. Finally, we present a detailed analysis of the effect of power corrections and finite meson widths on the angular distributions which may be measured in heavy meson decays.

hep-ph↗