The fully differential angular distribution for the rare flavor-changing neutral current decay {\bar B}_d^0 -> {\bar K}^{*0} (-> K^- π^+) e+ e- is studied. The emphasis is placed on accurate treatment of the contribution from the processes \bar{B}_d^0 -> \bar{K}^{*0} (-> K^- pi^+) V with intermediate vector resonances V = ρ(770), ω(782), ϕ(1020), J/ψ, ψ(2S), ... decaying into the e+ e- pair. The two versions of the vector-meson-dominance model for the transition V γare used and tested. The present method of including vector resonances is also compared with the existing in the literature method. The electron-positron invariant mass dependence of the branching ratio and various asymmetries is calculated. The branching ratio, longitudinal polarization fraction of the {\bar K}^{*0} meson, transverse asymmetry A_T^{(2)} and forward-backward asymmetry are compared with data from Belle and CDF, and predictions for experiments at LHCb are made.
We study the impact of future measurements of lepton-charge and forward-backward asymmetries in Drell-Yan processes in regions of transverse and invariant masses near the Standard Model gauge bosons peaks to improve the Parton Distribution Functions uncertainties. We study the implications on $W^{'}$ and $Z^{'}$ searches following the reduction of these uncertainties. We find that the sensitivity to the Beyond the Standard Model states is greatly increased with respect to the case of base Parton Distribution Functions sets, thereby enabling one to set more stringent limits on (or indeed discov…
We consider the forward-backward pion charge asymmetry for the e^{+}e^{-}\toπ^{+}π^{-}γprocess. At tree level we consider bremsstrahlung and double resonance contributions. Although the latter contribution is formally sub-leading, it is enhanced at low dipion invariant mass due to $ρ$ resonant effects. We consider also four alternative models to describe the final state radiation at the loop level: Resonance Chiral Perturbation Theory, Unitarized Chiral Perturbation Theory, Kaon Loop Model and Linear Sigma Model. The last three models yield results compatible with experimental data. The Kaon L…
Recently observed increase of direct CP asymmetry in charm meson nonleptonic decays is difficult to explain within the SM. If this effect is induced by new physics, this might be investigated in other charm processes. We propose to investigate new CP violating effects in rare decays $D \to P \ell^+ \ell^-$, which arise due to the interference of resonant part of the long distance contribution and the new physics affected short distance contribution. Performing a model independent analysis, we identify as appropriate observables the differential direct CP asymmetry and partial decay width CP as…
With the first evidence of direct CP violation in $D^0 \to K^+K^-/π^+π^-$ there is a strong reason to probe CP asymmetries in charm baryons in three-body final states $Λ_c \to pπ^+π^-/pK^+K^-$ & $Λ_c \to pK^+π^-$ with $Λ_c \to pK^-π^+$ to calibrate them. Analyzing the Dalitz plots carefully allows to find the 'existence' of New Dynamics (ND) and its `features'. One can test different methods to probe CP asymmetries. Final data from CDF and D0 experiments have advantage by comparing $Λ_c $ with $\bar Λ_c $ directly from $p \bar p $ collisions. LHCb will need more data with $\bar Λ_c$ transition…
In this work we will study the longitudinal polarisations of both leptons in the decay process ${\bar B} \to {\bar K}_2(1430)\, \ell^+ \, \ell^-$. This process has all the features of the related and well investigated process ${\bar B} \to {\bar K}^*(890) \, \ell^+ \, \ell^-$, with theoretically comparable branching ratios. The polarised differential decay rates as well as the single and double polarisation asymmetries are worked out, where the sensitivity of these to possible right-handed couplings for the related $b \to s$ radiative decay (and other generic BSM parameters) are also investiga…
The effects of "quark sea" in determining the flavor structure of the octet baryons have been investigated in the chiral constituent quark model (\chiCQM). The \chiCQM is able to qualitatively generate the requisite amount of quark sea and is also known to provide a satisfactory explanation of the proton spin and related issues in the nonperturbative regime. The Bjorken scaling variable x has been included phenomenologically in the sea quark distribution functions to understand its implications on the quark sea asymmetries like \bar d(x)-\bar (x), \bar d(x)/\bar u(x) and Gottfried integral for…
We study beam-transverse and normal single-spin asymmetry for electron-proton inelastic scattering in the resonance region for the case where a pion is observed in the final state. There is no beam single-spin asymmetry if the observed particle has single-photon exchange as its only interaction, but this is naturally circumvented when one observes a strongly interacting final state particle. The asymmetries are not large as there is an electron mass divided by momentum transfer suppression. We present results for the cases where the final electron and a pion are both observed, with asymmetries…
Angular distribution of the final particles in the decay $Λ_c^+\to K^- \, Δ(1232)^{++} \to K^- \, p \, π^+$ of the polarized charmed baryon is discussed. Asymmetries are proposed which allow for determination of the components of the $Λ_c^+$ polarization vector. The precession angle of the polarization in the process of baryon channeling in a bent crystal is directly related to these asymmetries. The decay rate and asymmetry parameter for the $Λ_c^+\to K^- \, Δ(1232)^{++}$ decay are calculated in the pole model and compared with experiment.
Using the Bethe-Salpeter equation (BSE) we investigate the forward-backward asymmetries $( A_{FB}) $ in $Λ_b \rightarrow Λl^+ l^-(l=e,μ,τ)$ in the quark-diquark model. This approach provides precise form factors that are different from those of QCD sum rules. We calculate the rare decay form factors for $Λ_b \rightarrow Λl^+ l^-$ and investigate the (integrated) forward-backward asymmetries in these decay channels. We find that the integrated $A^l_{FB}$, $\bar{A}^l_{FB}(Λ_b \rightarrow Λe^+ e^-) \simeq -0.1371 $, $\bar{A}^l_{FB}(Λ_b \rightarrow Λμ^+ μ^- ) \simeq -0.1376 $, $\bar{A}^l_{FB}(Λ_b …
We consider charmless weak decays of beauty-baryons into decuplet baryons and pseudoscalar mesons in a general framework based on $SU(3)$-flavor decomposition of the decay amplitudes. The dynamical assumption independent $SU(3)$ analysis accounts for the effects of an arbitrarily broken $SU(3)$ symmetry in these decays. An alternative approach in terms of quark diagrams is also provided and compared with the $SU(3)$ decomposition in the limit of exact $SU(3)$-flavor symmetry. Furthermore, the symmetries of the effective Hamiltonian is used to relate or neglect reduced $SU(3)$ amplitudes to der…
With the next start of LHC, a huge production of top quarks is expected. There are several models that predict the existence of heavy colored resonances decaying to top quarks in the TeV energy range. A peak in the differential cross section could reveal the existence of such a resonance, but this is experimentally challenging, because it requires selecting data samples where top and antitop quarks are highly boosted. Nonetheless, the production of such resonances might generate a sizable charge asymmetry of top versus antitop quarks. We consider a toy model with general flavour independent co…
We discuss lepton charge asymmetries in $t \bar t$ and $t \bar t γ$ production at the LHC, which can be measured in the semileptonic decay channel $t \bar t \to W^+ b \, W^- \bar b \to \ell^+ νb \, q \bar q' \bar b$ (or the charge conjugate). Considering several variants of a new physics scenario with a light colour octet, it is seen that for $t \bar t$ these asymmetries may have a sensitivity competitive with the dilepton asymmetry already measured. For $t \bar t γ$ the new leptonic asymmetries, as well as the $t \bar t$ charge asymmetry, will reach their full potential with the high luminosi…
Double Transverse-Spin Asymmetries for Drell-Yan Process in pp and p\bar{p} Collisions: Role of Nonleading QCD Corrections at Small Transverse Momentum
In this paper, we study the significance of the U$_\textrm{Y}$(1) Chern-Simons term in general, and its baryonic contribution in particular, for the evolution of the matter asymmetries and the hypermagnetic field in the temperature range $100$GeV$\leq T \leq 10$TeV. We show that an initial helical hypermagnetic field, denoted by $B_Y^{(0)}$, can grow matter asymmetries from zero initial value. However, the growth which is initially quadratic with respect to $B_Y^{(0)}$, saturates for values larger than a critical value. The inclusion of the baryonic contribution reduces this critical value, le…
Flavor asymmetry of polarized antiquark distributions and semi-inclusive DIS
QCD的$1/N_c$ -展开式表明核子中极化反夸克分布的大味不对称性。这是证实了在大$N_c$极限（手征夸克孤子模型），这给出了相当大的结果$Δ\bar u (x) - Δ\bar d (x)$和$Δ\bar u (x) + Δ\bar d (x) - 2 Δ\bar s (x)$模型计算。我们计算了这些味不对称性的贡献，在强子生产的自旋不对称性在半包容的深度非弹性散射。我们表明，大味不对称性预测的手征夸克孤子模型是一致的，与最近的HERMES数据的自旋不对称性带电强子生产。
The effects of nonperturbatively generated ``quark sea'' have been investigated to determine the flavor structure of the octet baryons. The chiral constituent quark model ($χ$CQM), which is known to provide a satisfactory explanation of the proton spin and related issues in the nonperturbative regime, is able to explain the qualitative generation of the requisite amount of quark sea. The importance of quark sea has been studied at different values of the Bjorken scaling variable $x$ by including it phenomenologically in the sea quark distribution functions. The results for the quark sea asymme…
CP violating asymmetries of b quarks and leptons in e^+e^- \to t\bar t and supersymmetry (review)
本文讨论了在CP破坏假设下，e^+e^- \to t \bar t中单衰变b夸克和轻子的分布.定义了不同的不对称性，它们对产生和衰变中的CP破坏独立敏感，对d^γ和d^Z的实部和虚部敏感。该解析表达式具有一般性，且与CP破坏模型无关.在他们中的大多数都是解析地完成相空间积分。给出了具有复杂耦合的MSSM的数值结果。
We study the $K^0_S-K^0_L$ asymmetries and $CP$ violations in charm-baryon decays with neutral kaons in the final state. The $K^0_S-K^0_L$ asymmetry can be used to search for two-body doubly Cabibbo-suppressed amplitudes of charm-baryon decays, with the one in $Λ^+_c\to pK^0_{S,L}$ as a promising observable. Besides, it is studied for a new $CP$-violation effect in these processes, induced by the interference between the Cabibbo-favored and doubly Cabibbo-suppressed amplitudes with the neutral kaon mixing. Once the new CP-violation effect is determined by experiments, the direct $CP$ asymmetry…
R-parity violation and CP-violating and CP-conserving spin asymmetries in l^+ l^- -> sneutrino -> tau^+ tau^-: probing sneutrino mixing at LEP2, NLC and mu^+mu^- colliders
We consider a class of baryogenesis models where the Lagrangian in the visible sector is Charge-Parity (CP) invariant and a baryon asymmetry is produced only when quantum statistics is taken into account. The CP symmetry is broken by matter effects, namely the assumption that the primordial plasma contains another asymmetric species, such as dark matter. Out-of-equilibrium baryon number violating decays can then generate an asymmetry through Bose enhancement and/or Pauli blocking of certain decay channels.
Using the covariant constituent quark model previously developed by us we calculate the differential rate and the forward-backward asymmetries on the lepton and hadron side for the rare baryon decays Lambda_b -> Lambda l+ l- (l=e, mu, tau) and Lambda_b -> Lambda gamma. We use helicity methods to write down a three-fold joint angular decay distribution for the cascade decay Lambda_b -> Lambda (-> p pi-) + J_eff (-> l+ l-). Through appropriate angular integrations we obtain expressions for the rates, the lepton-side forward-backward (FB) asymmetry and the polarization of the daughter baryon Lamb…
Quantum field theory, which is the basis for all of particle physics, requires that all processes respect $CPT$ invariance. It is therefore of paramount importance to test the validity of $CPT$ conservation. In this Letter, we show that the time-dependent, indirect $CP$ asymmetries involving $B$ decays to a $CP$ eigenstate contain enough information to measure $T$ and $CPT$ violation in $B^0$-${\bar B}^0$ mixing, in addition to the standard $CP$-violating weak phases. Entangled $B^0{\bar B}^0$ states are not required (so that this analysis can be carried out at LHCb, as well as at the $B$ fact…
CP violating asymmetries in single top quark production at the Tevatron p pbar collider
在实验室系统中得到了与$p \bar p \to W^* \to t \bar b \to b \bar b W$中的单$t$-夸克产生有关的$b$ -夸克角分布的解析表达式以及由随后的衰变$W \to lν$产生的轻子角分布的解析表达式。假设在$t$ -生产顶点中存在CP破坏。不同的角度和总的截面CP违反不对称性被认为是。还得到了仅在$t$ -衰变顶点中检验CP破坏的关系。数值分析了三线性耦合$A_{\tilde t}$的CP破坏相位对MSSM的影响。不对称性通常为$10^{-3}$ - $10^{-4}$的量级。
Motivated by the recent LHCb observation of $CP$ violation in charm, we study $CP$ violation in the charmed baryon decays. A simple method to search for the $CP$ violation relations in the flavor $SU(3)$ limit, which is associated with a complete interchange of $d$ and $s$ quarks, is proposed. With this method, hundreds of $CP$ violation sum rules in the doubly and singly charmed baryon decays can be found. As examples, the $CP$ violation sum rules in two-body charmed baryon decays are presented. Some of the $CP$ violation sum rules could help the experiment to find better observables. As bypr…
Triggered by a recent LHCb measurement and prospects for Belle II, we derive U-spin symmetry relations between integrated CP asymmetries of three-body $Λ_c^+$ and $Ξ_c^+$ decays. The sum rules read $A_{CP}(Λ_c^+\rightarrow p K^- K^+) + A_{CP}(Ξ_c^+\rightarrow Σ^+ π^- π^+) = 0$, $A_{CP}(Λ_c^+\rightarrow p π^- π^+) + A_{CP}(Ξ_c^+\rightarrow Σ^+ K^- K^+) = 0$, and $A_{CP}(Λ_c^+\rightarrow Σ^+ π^- K^+) + A_{CP}(Ξ_c^+\rightarrow pK^-π^+) = 0$. No such U-spin sum rule exists between $A_{CP}(Λ_c^+\rightarrow p K^- K^+)$ and $A_{CP}(Λ_c^+\rightarrow p π^- π^+)$. All of these sum rules are associated w…
Motivated by the recent LHCb collaboration measurements of charmless three-body decays of $\bar B_s^0$ meson, we calculate the branching fractions of $\bar B_s ^0 \to K^0 π^+π^-$, $\bar B_s ^0 \to K^0 K^+K^-$, $\bar B_s ^0 \to K^0 π^+K^-$ and $\bar B_s ^0 \to \bar K^0 K^+π^-$ decay modes using the factorization approach. Both the resonant and nonresonant contributions are studied in detail. For the decays $\bar B_s ^0 \to K^0 π^+π^-$ and $\bar B_s ^0 \to K^0 K^+K^-$, our results agree well with experimental data, and the former is dominated by the $K^*$, while the latter one is dominated by th…
We compute, for $t \bar t$ production at the LHC and at the Tevatron, several charge asymmetries to NLO QCD, including also the electromagnetic and weak-interaction corrections. We calculate these asymmetries both inclusively and with additional kinematic cuts and compare our results, where possible, with recent experimental results and with SM predictions. The $t \bar t$ asymmetries induce also corresponding asymmetries for the charged leptons from semileptonic top-quark decay. Although these asymmetries are, in the SM, smaller than the corresponding ones for top quarks, they are expected to …
We introduce a set of observables representing angular distribution asymmetries, which can be viewed as a generalization of the forward-backward asymmetry of angular distributions, and can be used as an effective tool to search for $C\!P$ violation in three-body decays of bottom and charmed baryons. We propose to search for such $C\!P$ asymmetries (1) in decays with $Λ^0$, $Σ^\pm$, or $Λ_c^+$ involved, such as $Λ_b\to Λ^0 D$ and $Λ_b\toΛ^0ρ(770)^0$; and (2) in three-body decays of bottom baryons with opposite parity intermediate resonances involved. Typical examples include $Ξ_b^-\to p K^- K^-…
