The role of spin degrees of freedom in high-energy hadron-hadron and lepton-hadron scattering is reviewed with emphasis on the dominant role of soft, diffractive, non-perturbative effects. Explicit models based on analyticity and Regge-pole theory, including the pomeron trajectory (gluon exchange in the $t$ channel) are discussed. We argue that there is a single, universal pomeron in Nature, manifest as relatively "soft" or "hard", depending on the kinematics considered. Regge trajectories are non-linear, complex functions, predicting a finite number of resonances. Explicit models and fits are presented that may be used in recovering generalized parton distributions from deeply virtual Compton scattering and electoproduction of vector mesons.
We investigate lepton-pair production in hard exclusive hadron-hadron collisions. We consider a double handbag (DH) mechanism in which the process amplitude factorizes in hard subprocesses, qq -> qq gamma* and qg -> qg gamma*, and in soft hadron matrix elements parameterized as generalized parton distributions (GPDs). Employing GPDs extracted from exclusive meson electroproduction, we present predictions for the lepton-pair cross section at kinematics typical for the LHC, NICA and FAIR. It turns out from our numerical studies that the quark-gluon subprocess dominates by far, the quark-quark (a…
Lepton polarization asymmetries in $B \to X_s τ^+ τ^-$ in MSSM
B介子的半轻子和轻子衰变是检验SM和超越SM的理论的重要探针，因为它们相对干净，理论不确定性小得多。在基于夸克能级跃迁$b \to s τ^+ τ^-$的半轻子衰变中，除了分支比之外，人们还可以研究与末态轻子相关的许多其他（可能的）可观测量，如轻子对前后不对称性，轻子极化不对称性等。但正如最近提出的，如果我们可以标记B介子，那么我们就可以测量两个轻子的极化不对称性。在这里，我们将研究SM中末态轻子及其最小超对称扩展（MSSM）的极化不对称性。
We study the flavor universality of the lepton couplings with the W and Z bosons. Currently, it is constrained by the electroweak precision observables. We focus on the leptonic decay of the pion. It is shown that the decay is expected to have a comparable or better sensitivity to the lepton-flavor universality in the near future. Furthermore, it provides a complementary information in determining the Wlnu couplings without assuming new physics models. This result is applied to a model of the extra lepton.
A spin-1 weakly interacting vector boson, Z', is predicted by many new physics theories. Searches at colliders for such a Z' resonance typically focus on lepton-antilepton or top-antitop events. Here we present a novel channel with a Z' resonance that decays to 4 leptons, but not to 2 leptons, and discuss its possible discovery at the Large Hadron Collider. This baryonic gauge boson is well motivated in a supersymmetry framework.
We first study the hadronic lepton flavor violating tau decays within the littlest Higgs model with T-parity (including one or two pseudoscalars, or a vector resonance). We consider the case where only T-odd particles and partner fermions contribute, and also its extension including Majorana neutrinos coming from an inverse seesaw. In both cases our mean values lie only one order of magnitude below current upper limits, strengthening the case of searching for these decays in the quest for new physics.
It has been pointed out recently that current low-energy constraints still allow for sizable flavor-changing decay rates of the 125 GeV boson into leptons, h -> tau ell (ell= e, mu). In this work we discuss the role of hadronic tau-lepton decays in probing lepton flavor violating couplings in the Higgs sector. At low energy, the effective Higgs coupling to gluons induced by heavy quarks contributes to hadronic tau decays, establishing a direct connection with the relevant process at the LHC, pp (gg)-> h -> tau ell. Semileptonic transitions like tau -> ell pi pi are sensitive to flavor-changing…
Hadron production in lepton-nucleus deep inelastic scattering is studied in a model including quark energy loss and nuclear absorption. The leading-order computations for hadron multiplicity ratios are presented and compared with the selected HERMES experimental data with the quark hadronization occurring inside the nucleus by means of the hadron formation time. It is shown that with increase of the energy fraction carried by the hadron, the nuclear suppression on hadron multiplicity ratio from nuclear absorption gets bigger. It is found that when hadronization occurs inside the nucleus, the n…
The polarization effects in the one-meson radiative decay of the polarized $τ$ lepton, $τ^-\toπ^-γν_τ$, are investigated. The inner bremsstrahlung and structural amplitudes are taken into account. The asymmetry of the differential decay width caused by the $τ$ lepton polarization and the Stokes parameters of the emitted photon itself, are calculated depending on the polarization of the decaying $τ$ lepton. The numerical estimation of these physical quantities was done for arbitrary direction of the $τ$ lepton polarization 3-vector in the rest frame. The vector and axial-vector form factors des…
Hadron production in lepton-nucleus deep inelastic scattering is studied in a quark energy loss model. The leading-order computations for hadron multiplicity ratios are presented and compared with the selected HERMES pions production data with the quark hadronization occurring outside the nucleus by means of the hadron formation time. It is found that the obtained energy loss per unit length is $0.440 \pm 0.013$ GeV/fm for an outgoing quark by the global fit. It is confirmed that the atomic mass number dependence of hadron attenuation is theoretically and experimentally in good agreement with …
We study the prospects for excluding or discovering vectorlike leptons using multilepton events at the LHC. We consider models in which the vectorlike leptons decay to tau leptons. If the vectorlike leptons are weak isosinglets, then discovery in multilepton states is found to be extremely challenging. For the case that the vectorlike leptons are weak isodoublet, we argue that there may be an opportunity for exclusion for masses up to about 275 GeV by direct searches with existing LHC data at sqrt{s}=8 TeV. We also discuss prospects for exclusion or discovery at the LHC with future sqrt{s}=13 …
Recently, CMS and ATLAS collaborations at LHC announced a Higgs like particle with mass near $125$GeV. Regarding this, to explore its intrinsic properties, different observables are needed to be measured precisely at the LHC for various decay channels of the Higgs. In this context, we calculate the final state lepton polarization asymmetries, namely, single lepton polarization asymmetries ($P_i$) and double lepton polarization asymmetries ($P_{ij}$) in the SM for radiative semileptonic Higgs decay $H\toγτ^+τ^-$. In the phenomenological analysis of these lepton polarization asymmetries both tre…
We study the single and double lepton polarization asymmetries in the semileptonic $B$ meson decays $B \to K_1 (1270) \ell^+ \ell^-$ $\ell \equiv e$, $μ$, $τ$), where the strange $P$-wave meson, $K_1(1270)$, is the mixtures of the $K_{1A}$ and $K_{1B}$, which are the $1^3P_1$ and $1^1P_1$ states, respectively. The lepton polarization asymmetries show relatively strong dependency in the various region of dileptonic invariant mass. The lepton polarization asymmetries can also be used for determining the $K_1(1270)$--$K_1(1400)$ mixing angle, $θ_{K_1}$ and new physics effects. Furthermore, it is …
Double-Lepton Polarization Asymmetries and Polarized Forward Backward Asymmetries in the Rare b \to s \ell^+ \ell^- Decays in a Single Universal Extra Dimension Scenario
研究了在标准模型和Appelquist-Cheng-Dobrescu模型中稀有b \to s \ell^+ \ell^-模式的双轻子极化不对称性和单、双轻子极化前后不对称性.特别地，我们研究了观测量对紧化额外维度半径R的敏感性，这是这个新物理模型中的新参数。
