arXiv subjects

Xin-Heng Guo

Publications and source records attributed to Xin-Heng Guo.

At least 73 records · Page 4Linked to original sources

arXiv2014

Effects of Shock Waves on Neutrino Oscillations in Three Supernova Models

It has been realized that the shock wave effects play an important role in neutrino oscillations during the supernova explosion. In recent years, with the development of simulations about supernova explosion, we have a better understanding about the density profiles and the shock waves in supernovae than before. It has been shown that the appearance of shock waves not only varies with time, but is also affected by the mass of the supernova. When the mass of the supernova happens to be in a certain range (e.g. it equals 10.8 times the mass of the sun), there might be a reverse shock wave, another sudden change of density except the forward shock wave, emerging in the supernova. In addition, there are some other time-dependent changes of density profiles in different supernova models. Because of these complex density profiles, the expression of the crossing probability at the high resonance, $P_H$, which we used previously would be no longer applicable. In order to get more accurate and reasonable results, we use the data of density profiles in three different supernova models obtained from simulations to study the variations of $P_s$ (the survival probability of $ν_e\rightarrowν_e$), as well as $P_c$ (the conversion probability of $ν_x\rightarrowν_e$). It is found that the mass of the supernova does make a difference on the behavior of $P_s$, and affects $P_c$ at the same time. With the results of $P_s$ and $P_c$, we can estimate the number of $ν_e$ remained after they go through the matter in the supernova.

hep-ph↗

arXiv2014

Direct CP violation in $τ^\pm\rightarrow K^\pm ρ^0 (ω)ν_τ\rightarrow K^\pm π^+π^-ν_τ$

We study the direct CP violation in the $τ^\pm\rightarrow K^\pm ρ^0 (ω)ν_τ\rightarrow K^\pm π^+π^-ν_τ$ decay process in the Standard Model. An interesting mechanism involving the charge symmetry violating mixing between $ρ^0$ and $ω$ is applied to enlarge the CP asymmetry. With this mechanism, the maximum differential and localized integrated CP asymmetries can reach $-(5.6^{+2.9}_{-1.7})\times10^{-12}$ and $6.3^{+2.4}_{-3.3}\times 10^{-11}$, respectively, which still leave plenty room for CP-violating New Physics to be discovered through this process.

hep-ph↗

arXiv2014

$CP$ violation for $B^{0}\rightarrow ρ^{0}(ω)ρ^{0}(ω) \rightarrow π^+π^-π^+π^-$ in QCD factorization

In the QCD factorization (QCDF) approach we study the direct $CP$ violation in $\bar{B}^{0}\rightarrowρ^0(ω)ρ^0(ω)\rightarrowπ^+π^-π^+π^-$ via the $ρ-ω$ mixing mechanism. We find that the $CP$ violation can be enhanced by double $ρ-ω$ mixing when the masses of the $π^+π^-$ pairs are in the vicinity of the $ω$ resonance, and the maximum $CP$ violation can reach 28{\%}. We also compare the results from the naive factorization and the QCD factorization.

hep-ph↗

arXiv2013

CP violation induced by the interference of scalar and vector resonances in three-body decays of bottom mesons

Large CP violation is an interesting phenomenon both theoretically and experimentally. Last year, LHCb Collaboration found in some three-body decays of bottom mesons that large CP violations appear in regions of the Dalitz plots that are not dominated by contributions from narrow resonances. In this paper, we present a mechanism which can induce such kind of large CP violations. In this mechanism, large localized CP asymmetries in phase space can be induced by the interference of two intermediate resonances with different spins. We also apply this mechanism to the decay channel $B^\pm\to K^\pm π^+π^-$.

hep-ph↗

arXiv2013

CP violation in $B^{\pm} \rightarrow π^{\pm}π^{+}π^{-}$ in the region with low invariant mass of one $π^{+}π^{-}$ pair

Recently, the large CP asymmetries in $B^\pm\toπ^\pmπ^+π^-$ decays were found by the LHCb Collaboration to localize in the region $m_{π^+π^-}^2<0.4 \text{GeV}^2$. We find such large localized CP asymmetries may be due to the interference between a light scalar and $ρ^0(770)$ intermediate resonances. Consequently, we argue that the distribution of CP asymmetries in the Dalitz plots of three-body B decays could be very helpful for identifying the presence of the scalar resonance.

hep-ph↗

arXiv2013

Detection of supernova neutrinos on the Earth for large theta13

Supernova (SN) neutrinos detected on the Earth are subject to the shock wave effects, the Mikheyev-Smirnov-Wolfenstein (MSW) effects, the neutrino collective effects and the Earth matter effects. Considering the recent experimental result about the large mixing angle $θ_{13}$ ($\backsimeq8.8^{\circ}$) provided by the Daya Bay Collaboration and applying the available knowledge for the neutrino conversion probability in the high resonance of SN, $P_{H}$, which is in the form of hypergeometric function in the case of large $θ_{13}$, we deduce the expression of $P_{H}$ taking into account the shock wave effects. It is found that $P_{H}$ is not zero in a certain range of time due to the shock wave effects. After considering all the four physical effects and scanning relevant parameters, we calculate the event numbers of SN neutrinos detected at the Daya Bay experiment. From the numerical results, it is found that the behaviors of neutrino event numbers detected on the Earth depend on the neutrino mass hierarchy and neutrino spectrum parameters including the temperature $T_α$, the dimensionless pinching parameter $η_α$ or $β_α$ (where $α$ refers to neutrino flavor), the average energy $< E_α>$, and the SN neutrino luminosities $L_α$. We also compare the results of two parametrization methods for the neutrino energy distributions and give the ranges of SN neutrino event numbers that will be detected at the Daya Bay experiment.

hep-ph↗

arXiv2013

Production of charged $ρ$ meson in bottom hadron charmed decays and the effect of the finite width correction of the $ρ$ meson

We calculate the branching ratio of a bottom hadron decaying into a charmed hadron and a charged $ρ$ meson within the QCD factorization approach. We consider the effect of the finite width correction of the $ρ$ meson. Our numerical calculation shows an obvious correction because of this effect. We find that the finite width effect of the $ρ$ meson reduces the branching ratios by about 9% to 11% for bottom meson decay channels: $B^+\to\bar{D^0}ρ^+$, $B^0\to D^-ρ^+$, and $B^0_s\to D^-_sρ^+$, and increases the branching ratio by about 10% for $Λ_b^0\toΛ_c^+ρ^-$.

hep-ph↗

arXiv2012

Perturbative and nonperturbative contributions to the strange quark asymmetry in the nucleon

There are two mechanisms for the generation of an asymmetry between the strange and anti-strange quark distributions in the nucleon: nonperturbative contributions originating from nucleons fluctuating into virtual baryon-meson pairs such as $ΛK$ and $ΣK$, and perturbative contributions arising from gluons splitting into strange and anti-strange quark pairs. While the nonperturbative contributions are dominant in the large-$x$ region, the perturbative contributions are more significant in the small-$x$ region. We calculate this asymmetry taking into account both nonperturbative and perturbative contributions, thus giving a more accurate evaluation of this asymmetry over the whole domain of $x$. We find that the perturbative contributions are generally a few times larger in magnitude than the nonperturbative contributions, which suggests that the best region to detect this asymmetry experimentally is in the region $0.02 < x < 0.03$. We find that the asymmetry may have more than one node, which is an effect that should be taken into account, e.g. for parameterizations of the strange and anti-strange quark distributions used in global analysis of parton distributions.

hep-ph↗

arXiv2012

Electron-positron pair production in an arbitrary polarized ultrastrong laser field

Electron-positron pair production in an arbitrary polarized ultrastrong laser field is investigated in the first order perturbation approximation in which the Volkov states are used for convenient calculation of scattering amplitude and cross section. It is found surprisingly that the optimal pair production depends strongly on the polarization. For some cases of field parameters, the optimal field is elliptically polarized or evenly circularly polarized one, rather than the usual linear polarization as indicated by previous works. Some insights into pair generation are given and some interesting unexpected features are also discussed briefly.

hep-ph↗

arXiv2011

QCD factorization for $Λ_b^0\toΛ_c^+π^-$

We prove that in the limit $m_b, m_c\to\infty$ with $m_c/m_b$ fixed, factorization holds at order $α_s$ for the decay $Λ_b^0\toΛ_c^+π^-$. This proof is done in the infinite-momentum frame in which the momenta of $π$, $Λ_c$, and $Λ_b$ go to infinity. Our result is renormalization scale and scheme independent at $\mathcal{O}(α_s)$. This is the same as QCD factorization for $B \to D π$.

hep-ph↗

arXiv2010

Acquire information about neutrino parameters by detecting supernova neutrinos

We consider the supernova shock effects, the Mikheyev-Smirnov-Wolfenstein (MSW) effects, the collective effects, and the Earth matter effects in the detection of type II supernova neutrinos on the Earth. It is found that the event number of supernova neutrinos depends on the neutrino mass hierarchy, the neutrino mixing angle $θ_{13}$, and neutrino masses. Therefore, we propose possible methods to identify the mass hierarchy and acquire information about $θ_{13}$ and neutrino masses by detecting supernova neutrinos. We apply these methods to some current neutrino experiments.

astro-ph.HE↗

arXiv2009

Supernova Neutrinos Detection On Earth

In this paper, we first discuss the detection of supernova neutrino on Earth. Then we propose a possible method to acquire information about $θ_{13}$ smaller than $1.5^\circ$ by detecting the ratio of the event numbers of different flavor supernova neutrinos. Such an sensitivity cannot yet be achieved by the Daya Bay reactor neutrino experiment.

hep-ph↗

arXiv2009

Realistic Earth matter effects and a method to acquire information about small θ_{13} in the detection of supernova neutrinos

In this paper, we first calculate the realistic Earth matter effects in the detection of type II supernova neutrinos at the Daya Bay reactor neutrino experiment which is currently under construction. It is found that the Earth matter effects depend on the neutrino incident angle $θ$, the neutrino mass hierarchy $Δm_{31}^{2}$, the crossing probability at the high resonance region inside the supernova, $P_{H}$, the neutrino temperature, $T_α$, and the pinching parameter in the neutrino spectrum, $η_α$. We also take into account the collective effects due to neutrino-neutrino interactions inside the supernova. With the expression for the dependence of $P_H$ on the neutrino mixing angle $θ_{13}$, we obtain the relations between $θ_{13}$ and the event numbers for various reaction channels of supernova neutrinos. Using these relations, we propose a possible method to acquire information about $θ_{13}$ smaller than $1.5^\circ$. Such a sensitivity cannot yet be achieved by the Daya Bay reactor neutrino experiment which has a sensitivity of the order of $θ_{13}\sim 3^\circ$. Furthermore, we apply this method to other neutrino experiments, i.e. Super-K, SNO, KamLAND, LVD, MinBooNE, Borexino, and Double-Chooz. We also study the energy spectra of the differential event numbers, ${\rm d}N/{\rm d}E$.

hep-ph↗

arXiv2008

Some mass relations for mesons and baryons in Regge phenomenology

In the quasilinear Regge trajectory ansatz, some useful linear mass inequalities, quadratic mass inequalities and quadratic mass equalities are derived for mesons and baryons. Based on these relations, mass ranges of some mesons and baryons are given. The masses of bc-bar and ss-bar belonging to the pseudoscalar, vector and tensor meson multiplets are also extracted. The J^P of the baryon Xi_cc(3520) is assigned to be 1/2^+. The numerical values for Regge slopes and intercepts of the 1/2^+ and 3/2^+ SU(4) baryon trajectories are extracted and the masses of the orbital excited baryons lying on the 1/2^+ and 3/2^+ trajectories are estimated. The J^P assignments of baryons Xi_c(2980), Xi_c(3055), Xi_c(3077) and Xi_c(3123) are discussed. The predictions are in reasonable agreement with the existing experimental data and those suggested in many other different approaches. The mass relations and the predictions may be useful for the discovery of the unobserved meson and baryon states and the J^P assignment of these states.

hep-ph↗

arXiv2008

Double heavy-quarkonium production from electron-positron annihilation in the Bethe-Salpeter formalism

In this work we evaluate the cross section of the process $e^+e^-\to J/ψη_c$ at energy $\sqrt{s}\approx 10.6$ GeV in the Bethe-Salpeter formalism. To simplify our calculation, the heavy quark limit is employed. Without taking the beyond-leading-order contribution(s) into account, the cross section calculated in this scenario is comparable with the experimental data. We also present our prediction for the cross section of double bottomonium production $e^+e^-\to Υ(1S)η_b$ for the energy range of $\sqrt{s}\approx (25 \hbox{-} 30)$ GeV which may be experimentally tested, even though there is no facility of this range available at present yet.

hep-ph↗

arXiv2008

Strong decays of heavy baryons in Bethe-Salpeter formalism

In this paper we study the properties of diquarks (composed of $u$ and/or $d$ quarks) in the Bethe-Salpeter formalism under the covariant instantaneous approximation. We calculate their BS wave functions and study their effective interaction with the pion. Using the effective coupling constant among the diquarks and the pion, in the heavy quark limit $m_Q\to\infty$, we calculate the decay widths of $Σ_Q^{(*)}$ ($Q=c,b$) in the BS formalism under the covariant instantaneous approximation and then give predictions of the decay widths $Γ(Σ_b^{(*)}\toΛ_b+π)$.

hep-ph↗

arXiv2007

Studying the scalar bound states of the $K\bar K$ system in the Bethe-Salpeter formalism

We study the possible bound states of the $K\bar K$ system in the Bethe-Salpeter formalism in the ladder and instantaneous approximations. We find that the bound states exist. However, these bound states have very small decay widths. Therefore, besides the possible $K\bar K$ component, there may be some other structures in the observed $f_0(980)$ and $a_0(980)$ .

hep-ph↗

arXiv2007

The Average Kinetic Energy of the Heavy Quark in $Λ_b$ in the Bethe-Salpeter Equation Approach

In the previous paper, based on the $SU(2)_{f}\times SU(2)_{s}$ heavy quark symmetries of the QCD Lagrangian in the heavy quark limit, the Bethe-Salpeter equation for the heavy baryon $Λ_b$ was established with the picture that $Λ_b$ is composed of a heavy quark and a scalar light diquark. In the present work, we apply this model to calculate $μ_π^2$ for $Λ_b$, the average kinetic energy of the heavy quark inside $Λ_{b}$. This quantity is particularly interesting since it can be measured in experiments and since it contributes to the inclusive semileptonic decays of $Λ_b$ when contributions from higher order terms in $1/M_b$ expansions are taken into account and consequently influences the determination of the Cabibbo-Kobayashi-Maskawa matrix elements $V_{ub}$ and $V_{cb}$. We find that $μ_π^2$ for $Λ_b$ is $0.25GeV^2$ $\sim$ $0.95GeV^2$, depending on the parameters in the model including the light diquark mass and the interaction strength between the heavy quark and the light diquark in the kernel of the BS equation. We also find that this result is consistent with the value of $μ_π^2$ for $Λ_b$ which is derived from the experimental value of $μ_π^2$ for the $B$ meson with the aid of the heavy quark effective theory.

hep-ph↗