分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-07-11
摘要: We study the decay of a Z' boson into two Z bosons by extending the Landau-Yang theorem to a parent particle decaying into two Z bosons. For a spin-1 parent the theorem predicts that (1) there are only two possible couplings and (2) the normalized differential cross section depends on kinematics only through a phase shift in the azimuthal angle between the two decay planes of the Z boson. When the parent is a Z' the two possible couplings are anomaly induced and CP violating, respectively. At the CERN Large Hadron Collider their effects could be disentangled when both Z bosons decay leptonically.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-07-08
摘要: We discuss general on-shell couplings of a scalar with two Z bosons using an operator analysis. In addition to the operator that originated from the Higgs mechanism, two dimension-five operators, one CP even and one CP odd, are generated only at the loop level. Simple formulas are derived for the differential decay distributions when the Z pair subsequently decays into four leptons by computing the helicity amplitudes, from which it is shown the CP-odd operator merely induces a phase shift in the azimuthal angular distribution between the two decay planes of the Z bosons. We also investigate new physics scenarios giving rise to loop-induced decays of a scalar into the ZZ pair, and argue that the total decay width of such a scalar would be an order-of-magnitude smaller than that of a Higgs boson, should such decays be observed in the early running of the LHC. Therefore, the total decay width alone is a strong indicator of the Higgs nature, or the lack thereof, of a scalar resonance in ZZ final states. In addition, we study the possibility of using the azimuthal angular distribution to disentangle effects among all three operators.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-16
摘要: We calculate the O(alpha(cw)M(t)(2)/M-W(2)) supersymmetric (SUSY) electroweak corrections to single top quark production via --> at the Fermilab Tevatron in the minimal supersymmetric model. The supersymmetric electroweak corrections to the cross section are at most a few percent for tan beta > 1, but can exceed 10% for tan beta < 1. The combined effects of SUSY electroweak corrections and the Yukawa corrections can exceed 10% for favorable parameter values, which might be observable at a high-luminosity Tevatron.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-16
摘要: We calculate the one-loop QCD corrections to t-->(t) over tilde(1)(0)(j) using the dimensional reduction scheme, including QCD and supersymmetric QCD corrections. The analytic expressions for the corrections to the decay width are given, which can easily be extended to t-->(+)(j)(b) over tilde(i). The numerical results show that the correction amounts to more than a 10% reduction in the partial width relative to the tree level result. We also compare the corrections in the no-mixing top squark case with those in the mixing top squark case.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-16
摘要: We evaluate the supersymmetric QCD corrections to single top quark production via q (q) over bar'-->t (b) over bar at the Fermilab Tevatron in the minimal supersymmetric model. We find that within the allowed range of squark and gluino masses the supersymmetric QCD corrections can enhance the cross section by a few percent. The combined effects of SUSY QCD, SUSY EW, and the Yukawa couplings can exceed 10% for the smallest allowed tan beta(similar or equal to 0.25) but are only a few percent for tan beta>1.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: If all the supersymmetry particles (sparticles) except a light Higgs boson are too heavy to be directly produced at the Large Hadron Collider and Tevatron, a possible way to reveal evidence for supersymmetry is through their virtual effects in other processes. We examine such supersymmetric QCD effects in bottom pair production associated with a light Higgs boson at the Large Hadron Collider and Tevatron. We find that if the relevant sparticles (gluinos and squarks) are well above the TeV scale, too heavy to be directly produced, they can still have sizable virtual effects in this process. For large tan beta, such residual effects can alter the production rate by as much as 40%, which should be observable in future measurements of this process.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: The Higgs boson production pp(p (p) over bar)-->bh+X via bg-->bh at hadron colliders, which may be an important channel for testing the bottom quark Yukawa coupling, is subject to large supersymmetric quantum corrections. In this work the one-loop supersymmetric (SUSY) QCD corrections to this process are evaluated and are found to be quite sizable in some parameter space. We also study the behavior of the corrections in the limit of heavy SUSY masses and find the remnant effects of SUSY QCD. These remnant effects, which are left over in the Higgs sector by the heavy sparticles, are found to be so sizable (for a light CP-odd Higgs boson and large tan beta) that they might be observable in future experiments. The exploration of such remnant effects is important for probing SUSY, especially in the case that the sparticles are too heavy (above TeV) to be directly discovered in future experiments.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: In the next-to-minimal supersymmetric model (NMSSM) a light CP-odd Higgs boson is so far allowed by current experiments, which, together with a large tan beta, may greatly enhance the rare dileptonic decays B -> X(s)l(+)l(-) and B(s)-> l(+)l(-)gamma. We examine these decays paying special attention to the new operator allowed by the light CP-odd Higgs boson. We find that in the parameter space allowed by current experiments like CERN LEP II and b -> s gamma, the branching ratios of these rare decays can be greatly enhanced, and thus the existing experimental data on B -> X(s)mu(+)mu(-) can further stringently constrain the parameter space (especially the region with a superlight CP-odd Higgs boson and large tan beta). In the surviving parameter space we give the predictions for other dileptonic decay branching ratios and also show the results for the forward-backward asymmetry.