arXiv subjects

Joan Sola

Publications and source records attributed to Joan Sola.

135 records · Page 8Linked to original sources

arXiv1997

Top and Higgs decays: looking for quantum SUSY signatures in hadron colliders

I present an updated discussion of the one-loop corrections to the standard top quark decay, t-> W^+ b, and to the charged Higgs mode, t-> H^+ b, within the framework of the MSSM. These higher order contributions to the top width are compared with the direct top decays into 2 and 3 real SUSY particles. It turns out that whereas the SUSY effects on t-> W^+ b add up to those from standard QCD, they tend most likely to erase the conventional QCD corrections to t-> H+ b. However, in the latter case the full (strong plus electroweak) SUSY quantum effects are generally so large that the QCD corrections effectively come out with the ``wrong sign''. A qualitatively distinct, and quantitatively significant, ``quantum signature'' of that type might constitute a most sought-after imprint of ``virtual'' Supersymmetry, which remains sizeable enough even in the absence of any direct top decay into SUSY particles. Similar considerations are made for the hadronic partial widths of the Higgs bosons of the MSSM. While a first valuable test of these effects could possibly be performed at the upgraded Tevatron, a more precise verification would most probably be carried out in future experiments at the LHC.

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arXiv1996

Quantum effects on $t\to H^{+} b$ in the MSSM: a window to ``virtual'' supersymmetry?

We analyze the one-loop effects (strong and electroweak) on the unconventional top quark decay mode $t\rightarrow H^{+} b$ within the MSSM. The results are presented in the on-shell renormalization scheme with a physically well motivated definition of $\tanβ$. The study of this process at the quantum level is useful to unravel the potential supersymmetric nature of the charged Higgs emerging from that decay. As compared with the standard mode $t\rightarrow W^{+} b$, the corrections to $t\rightarrow H^{+} b$ are large, slowly decoupling and persist at a sizeable level even for all sparticle masses well above the LEP 200 discovery range. As a matter of fact, the potential size of the SUSY effects, which amount to corrections of several ten percent, could counterbalance the standard QCD corrections and even make them to appear with the ``wrong'' sign. Therefore, if the charged Higgs decay of the top quark is kinematically allowed -a possibility which is not excluded by the recent measurements of the branching ratio $BR(t\rightarrow W^{+} b)$ at the Tevatron - it could be an invaluable laboratory to search for ``virtual'' supersymmetry. While a first significant test of these effects could possibly be performed at the upgraded Tevatron, a more precise verification would most likely be carried out in future experiments at the LHC.

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arXiv1996

Supersymmetric QCD corrections to the top quark decay of a heavy charged higgs boson

The supersymmetric QCD corrections to the hadronic width of a heavy charged Higgs boson, basically dominated by the top-quark decay mode $H^{+}\rightarrow t \bar{b}$, are evaluated at ${\cal O}(α_s)$ within the MSSM and compared with the standard QCD corrections. The study of such quantum effects, which turn out to be rather large, is essential to understand the hypothetical supersymmetric nature of a heavy charged Higgs boson potentially produced in the near future at the Tevatron and/or at the LHC.

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arXiv1996

Strong effects on the hadronic widths of the neutral Higgs Bosons in the MSSM

We analyze the correlation of QCD one-loop effects on the partial widths of the three neutral Higgs bosons of the MSSM decaying into quark-antiquark pairs. The SUSY-QCD effects turn out to be comparable or even larger than the standard QCD effects and are slowly decoupling in a wide window of the parameter space. Our study is aimed at elucidating the possible supersymmetric nature of the neutral Higgs bosons that might be discovered in the near future at the Tevatron and/or at the LHC. In particular, we point out the presence of potentially large SUSY corrections to the various neutral Higgs production cross-sections.

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arXiv1996

MSSM and Z width: implications on top quark and Higgs physics

We discuss the one-loop quantum corrections to the top quark width and to the hadronic widths of the Higgs bosons of the MSSM, and emphasize the results obtained in particular regions of the MSSM parameter space which have been proposed to alleviate the anomalies observed in the decay modes of the $Z$ into $b\bar{b}$ and $c\bar{c}$. We find that the corrections can be large and should be visible through the measurement of the top quark production cross-sections in future experiments at the Tevatron and at the LHC.

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arXiv1996

Supersymmetric three-body decays of the Top Quark in the MSSM

We survey all possible supersymmetric three-body decays of the top quark in the framework of the MSSM and present detailed numerical analyses of the most relevant cases. Although the two-body channels are generally dominant, it is not inconceivable that some or all of our most favourite two-body SUSY candidates could be suppressed. In this event there is still the possibility that some of the available three-body SUSY modes might exhibit a substantial branching fraction and/or carry exotic signatures that would facilitate their identification. Furthermore, in view of the projected inclusive measurement of the top-quark width $Γ_t$ in future colliders, one should have at one's disposal the full second order correction (electroweak and strong) to the value of that parameter in the MSSM. Our analysis confirms that some supersymmetric three-body decays could be relevant and thus contribute to $Γ_t$ at a level comparable to the largest one loop supersymmetric effects on two-body modes recently computed in the literature.

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arXiv1995

The Top-Quark Width in the Light of $Z$-Boson Physics

We discuss possible non-standard contributions to the top-quark width, particularly the virtual effects on the standard decay $t\rightarrow W^+\,b$ within the context of the MSSM. We also place a renewed emphasis on the unconventional mode $t\rightarrow H^+\,b$ in the light of recent analyses of $Z$-boson observables. It turns out that in the region of parameter space highlighted by $Z$-boson physics, the charged Higgs mode should exhibite an appreciable branching fraction as compared to the standard decay of the top quark. Remarkably enough, the corresponding quantum effects in this region are also rather large, slowly decoupling, and most likely resolvable in the next generation of experiments at Tevatron and at LHC.

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arXiv1995

Matching the Low and High Energy Determinations of $α_s(M_z)$ in the MSSM

Recent calculations of supersymmetric corrections to the conflicting ratios $R_b$ and $R_c$ have shown that an alleged discrepancy between the SM predictions of these observables and the corresponding experimental values can be cured in the MSSM within a certain region of the parameter space. Here we show that, in this very same region, also a well-known discrepancy between the low and high energy determinations of $α_s(M_Z)$ can be disposed of. Specifically, we find that the lineshape determination of the strong coupling constant, which in the SM points towards the large central value $α_s(M_Z) \stackrel{\scriptstyle >}{{ }_{\sim}} 0.125$, can be matched up with the value suggested by the wealth of low-energy data, namely $α_s(M_Z) \simeq 0.11$, which is smaller and more in line with the traditional QCD expectations at low energy. Our approach differs from previous analyses in that we argue that the desired matching could originate to a large extent from a purely electroweak supersymmetric quantum effect.

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arXiv1995

THE QUANTUM CORRELATION R_b-R_c IN THE MSSM: MORE HINTS OF SUPERSYMMETRY?

We study the correlation of quantum effects on the ratios R_b and R_c within the framework of the MSSM. While in the SM the quantity R_b is in discrepancy with experiment at the 2 σlevel from below, and R_c differs from the experimental result at the 1.5 σlevel from above, the theoretical prediction for both observables could simultaneously improve in the MSSM, provided that \tanβis large enough (\tanβ\sim m_t/m_b) and there exists a light supersymmetric pseudoscalar Higgs, and also a light stop and a light chargino, all of them in the 50 GeV ballpark. In view of the masses predicted for these SUSY particles, persistence of the `R_b-R_c crisis' in the next run of experiments would not only suggest indirect evidence of SUSY, but should also encourage direct finding of SUSY at LEP 200. We also point out the consistency of this picture with other observables and the intriguing possibility that this Z-physics scenario might allow getting a hint of SUSY at Tevatron through the simple observation of t\to H^{+}b.

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