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S. Kraml

Publications and source records attributed to S. Kraml.

At least 73 records · Page 4Linked to original sources
arXiv2004

Reconstructing Supersymmetric Theories by Coherent LHC / LC Analyses

Supersymmetry analyses will potentially be a central area for experiments at the LHC and at a future e+ e- linear collider. Results from the two facilities will mutually complement and augment each other so that a comprehensive and precise picture of the supersymmetric world can be developed. We will demonstrate in this report how coherent analyses at LHC and LC experiments can be used to explore the breaking mechanism of supersymmetry and to reconstruct the fundamental theory at high energies, in particular at the grand unification scale. This will be exemplified for minimal supergravity in detailed experimental simulations performed for the Snowmass reference point SPS1a.

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arXiv2003

Physics Impact of a Precise Determination of the Top Quark Mass at an e+e- Linear Collider

At a prospective e+e- Linear Collider (LC) a very precise determination of the top quark mass with an accuracy of $δm_t <= 100 MeV$ will be possible. This is to be compared with the envisaged accuracy of $δm_t = 1-2 GeV$ at the Tevatron and the LHC. We discuss the physics impact of such a precise determination of m_t, focusing on the Standard Model (SM) and its minimal supersymmetric extension (MSSM). In particular, we show the importance of a precise knowledge of m_t for electroweak precision observables, and for Higgs physics and the scalar top sector of the MSSM. Taking the mSUGRA model as a specific example, we furthermore demonstrate the importance of a precise m_t value for the prediction of sparticle masses and for constraints on the parameter space allowed by the relic density. The uncertainty in m_t also significantly affects the reconstruction of the supersymmetric high scale theory. We find that going from hadron collider to LC accuracy in m_t leads to an improvement of the investigated quantities by up to an order of magnitude.

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arXiv2003

Theoretical uncertainties in sparticle mass predictions from computational tools

We estimate the current theoretical uncertainty in sparticle mass predictions by comparing several state-of-the-art computations within the minimal supersymmetric standard model (MSSM). We find that the theoretical uncertainty is comparable to the expected statistical errors from the Large Hadron Collider (LHC), and significantly larger than those expected from a future e+e- Linear Collider (LC). We quantify the theoretical uncertainty on relevant sparticle observables for both LHC and LC, and show that the value of the error is significantly dependent upon the supersymmetry (SUSY) breaking parameters. We also present the theoretical uncertainty induced in fundamental-scale SUSY breaking parameters when they are fitted from LHC measurements. Two regions of the SUSY parameter space where accurate predictions are particularly difficult are examined in detail: the large tan(beta) and focus point regimes.

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arXiv2002

CP violation in charged Higgs boson decays into tau and neutrino

We calculate the CP-violating rate asymmetry of H^\pm decays into tau and neutrino at one loop in the MSSM with complex parameters. We find that the asymmetry is typically of the order of 10^-3, depending mainly on the phases of the trilinear coupling A_τand of the gaugino mass M_1.

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arXiv2002

CP violation in charged Higgs boson decays in the MSSM with complex parameters

Supersymmetric loop contributions can lead to different decay rates of H+\to t\bar b and H-\to b\bar t. We calculate the decay rate asymmetry δ^CP = \frac{Γ(H+\to t\bar b)-Γ(H-\to b\bar t)}{{Γ(H+\to t\bar b)+Γ(H-\to b\bar t)} at next-to-leading order in the MSSM with complex parameters. We analyse the parameter dependence of δ^CP with emphasis on the phases of A_t and A_b. It turns out that the most important contribution comes from the loop with stop, sbottom, and gluino. If this contribution is present, δ^CP can go up to 10-15% for tan(beta)~10, and to ~5% for large values of tan(beta).

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arXiv2002

CP violation in charged Higgs boson decays in the MSSM with complex parameters

Supersymmetric loop contributions can lead to different decay rates of H+\to t\bar b and H-\to b\bar t. We calculate the decay rate asymmetry δ^CP = \frac{Γ(H+\to t\bar b)-Γ(H-\to b\bar t)}{{Γ(H+\to t\bar b)+Γ(H-\to b\bar t)} at next-to-leading order in the MSSM with complex parameters. We analyse the parameter dependence of δ^CP with emphasis on the phases of A_t and A_b. It turns out that the most important contribution comes from the loop with stop, sbottom, and gluino. If this contribution is present, δ^CP can go up to 10-15%.

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arXiv2002

Comparison of SUSY mass spectrum calculations

We provide a comparison of the results of four SUSY mass spectrum calculations in mSUGRA: Isajet, SuSpect, SoftSusy, and SPheno. In particular, we focus on the high tan(beta) and focus point regions, where the differences in the results are known to be large.

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arXiv2002

CP violating asymmetries in single top quark production at the Tevatron p pbar collider

Analytic expressions for the angular distributions of the $b$-quarks associated with single $t$-quark production in $p \bar p \to W^* \to t \bar b \to b \bar b W$ and of the leptons from the subsequent decay $W \to lν$ are obtained in the laboratory system. CP violation in the $t$-production vertex is assumed. Different angular and total cross section CP violating asymmetries are considered. Relations testing CP violation solely in the $t$-decay vertex are also obtained. A numerical analysis is performed in the MSSM with a CP violating phase of the trilinear coupling $A_{\tilde t}$. The asymmetries are typically of the order $10^{-3}$ - $10^{-4}$.

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arXiv2002

Physics Opportunities at mu+mu- Higgs Factories

We update theoretical studies of the physics opportunities presented by mu+mu- Higgs factories. Interesting measurements of the Standard Model Higgs decays into {\bar b}b, tau+tau- and WW* may be possible if the Higgs mass is less than about 160 GeV, as preferred by the precision electroweak data, the mass range being extended by varying appropriately the beam energy resolution. A suitable value of the beam energy resolution would also enable the uncertainty in the b-quark mass to be minimized, facilitating measurements of parameters in the MSSM at such a first mu+mu- Higgs factory. These measurements would be sensitive to radiative corrections to the Higgs-fermion-antifermion decay vertices, which may violate CP. Radiative corrections in the MSSM may also induce CP violation in Higgs-mass mixing, which can be probed via various asymmetries measurable using polarized mu+mu- beams. In addition, Higgs-chargino couplings may be probed at a second mu+mu- Higgs factory.

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arXiv2000

Improved SUSY QCD corrections to Higgs boson decays into quarks and squarks

The O(alpha_s) SUSY QCD corrections to the decays of the MSSM Higgs bosons into bottom quarks and squarks can be very large for large tan beta in the on--shell renormalization scheme. We improve the calculation by a careful choice of the tree-level Higgs boson couplings in terms of running parameters of quarks and squarks.

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arXiv2000

Phenomenology of stops, sbottoms, tau-sneutrinos, and staus at an e+e- Linear Collider

We discuss production and decays of stops, sbottoms, tau-sneutrinos, and staus in e+e- annihilation in the energy range \sqrt{s} = 0.5-1 TeV. We present numerical predictions within the Minimal Supersymmetric Standard Model for cross sections and decay rates, including one-loop radiative corrections as well as initial state radiation. We also study the importance of beam polarization for the determination of the underlying SUSY parameters. Moreover, we make a comparison of the potential to study squarks and sleptons of the 3rd generation between Tevatron, LHC, and Linear Collider.

hep-ph↗
arXiv2000

Summary of the SUSY Working Group of the 1999 Les Houches Workshop

The results obtained by the Working Group on Supersymmetry at the 1999 Les Houches Workshop on Collider Physics are summarized. Separate chapters treat "general" supersymmetry, R-parity violation, gauge mediated supersymmetry breaking, and anomaly mediated supersymmetry breaking.

hep-ph↗
arXiv2000

Improved SUSY QCD corrections to Higgs boson decays into quarks and squarks

We improve the calculation of the supersymmetric $O(α_s)$ QCD corrections to the decays of Higgs bosons into quarks and squarks in the Minimal Supersymmetric Standard Model. In the on-shell renormalization scheme these corrections can be very large, which makes the perturbative expansion unreliable. This is especially serious for decays into bottom quarks and squarks for large $\tanβ$. Their corrected widths can even become negative. We show that this problem can be solved by a careful choice of the tree-level Higgs boson couplings to quarks and squarks, in terms of the QCD and SUSY QCD running quark masses, running trilinear couplings $A_q$, and on-shell left-right mixing angles of squarks. We also present numerical results for the corrected partial decay widths for the large $\tanβ$ case.

hep-ph↗
arXiv1999

Production and decays of stops, sbottoms, and staus

We present a phenomenological analysis of production and decays of stops, sbottoms, and staus in e+e- collisions with sqrt(s) = 500 - 800 GeV. We include SUSY-QCD and Yukawa coupling corrections as well as initial state radiation. We show that e- beam polarization is a powerful tool for a determination of the underlying SUSY parameters. Using in addition a polarized e+ beam improves the precision of the parameter determination by about 25%.

hep-ph↗
arXiv1999

Impact of bosonic decays on the search for stau_2 and tau-sneutrino

We perform a detailed study of the decays of the heavier tau slepton (stau_2) and tau-sneutrino (snu_tau) in the Minimal Supersymmetric Standard Model (MSSM). We show that the decays into Higgs or gauge bosons, i.e. stau_2 -> stau_1 + (h^0, H^0, A^0 or Z^0), stau_2 -> snu_tau + (H^- or W^-), and snu_tau -> stau_1 + (H^+ or W^+), can be very important due to the sizable tau Yukawa coupling and large mixing parameters of stau. Compared to the decays into fermions, such as stau_2 -> tau + neutralino_i and stau_2 -> nu_tau + chargino_j^-, these bosonic decay modes can have significantly different decay distributions. This could have an important influence on the search for stau_2 and snu_tau and the determination of the MSSM parameters at future colliders.

hep-ph↗
arXiv1999

Yukawa coupling corrections to stop, sbottom, and stau production in e+ e- annihilation

We calculate within the MSSM the one-loop Yukawa coupling corrections to the processes e+ e- \to stops, sbottoms, and staus in order of Yukawa coupling squared. These corrections are due to the exchange of charginos, neutralinos, charged and neutral Higgs bosons, and charged and neutral Higgs ghosts. We give the complete analytical formulae. We also perform a detailed numerical analysis of the Yukawa coupling corrections, including also the SUSY-QCD corrections. It turns out that for stop and sbottom production the Yukawa coupling corrections are typically +/- 10% of the tree-level cross section. For stau production they are about +/- 5%.

hep-ph↗
arXiv1999

Stop and Sbottom Phenomenology in the MSSM

The first chapter serves as an introduction to the MSSM. I briefly review the model and explain why stops and sbottoms provide an interesting playground for exploring and testing this model. In the second chapter I discuss stop and sbottom production at lepton colliders. I give the analytical formulae for the production cross sections at e+e- and mu+mu- colliders including (general) beam polarization. A numerical analysis shows the cross sections that can be expected at LEP2, an e+e- Linear Collider, and a Muon Collider. In particular, I address the topics of what can be gained by using polarized beams and how one can determine the MSSM parameters by cross section measurements. The third chapter is devoted to stop and sbottom decays including 1-loop SUSY-QCD corrections. The calculations are done in the on-shell renormalization scheme using dimensional reduction. I present the analytical formulae for the \order(alpha_s) corrected decay widths and explain the subtleties that have to be taken into account in the calculations. Moreover, I perform a detailed numerical analysis of squark decay widths and branching ratios at tree level and \order(alpha_s).

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