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Yu-Jie Zhang

Publications and source records attributed to Yu-Jie Zhang.

At least 55 records · Page 3Linked to original sources

The Fourth Generation Quark and the 750 GeV Diphoton Excess

Recently, the CMS and ATLAS collaborations have reported a diphoton peak at 750 GeV in the RunII of LHC at 13 TeV. We assume that the heavy fourth generation quark doublet $z,~y$ with $380 $GeV mass, and the width of $z,t$ is much less $b$ quark. Then we show that the contributions of the $(z \bar z+y \bar y)/\sqrt{2}$ bound state $η_{zy}(1S)$ to the diphoton measurements through $σ(pp\to η_{zy}(1s)\to γγ) $ are $ 5.6^{+5.6}_{-2.8} {\rm fb}$ at $\sqrt S=13$ TeV. They are constant with the 750 GeV diphoton excess measured by the CMS ant ATLAS collaborations.

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Interference effects on Higgs mass measurement in $e^+e^-\to H(γγ) Z$ at CEPC

A high luminosity Circular Electron Positron Collider (CEPC) as a Higgs Factory will be helpful to the precision measurement of the Higgs mass. The signal-background interference effect is carefully studied for the Higgs diphoton decay mode in the associated Z boson production at the future $e^+e^-$ colliders at energy $246 {\rm GeV}$. The mass shifts go up from about $20 {\rm MeV}$ to $50 {\rm MeV}$ for the experimental mass resolution ranging from $0.8 {\rm GeV}$ to $2 {\rm GeV}$.

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Crossover of electron-electron interaction effect in Sn-doped indium oxide films

We systematically study the structures and electrical transport properties of a series of Sn-doped indium oxide (ITO) films with thickness $t$ ranging from $\sim$5 to $\sim$53\,nm. Scanning electron microscopy and x-ray diffraction results indicate that the $t\lesssim 16.8$\,nm films are polycrystalline, while those $t\gtrsim 26.7$\,nm films are epitaxially grown along [100] direction. For the epitaxial films, the Altshuler and Aronov electron-electron interaction (EEI) effect governs the temperature behaviors of the sheet conductance $σ_\square$ at low temperatures, and the ratios of relative change of Hall coefficient $ΔR_H/R_H$ to relative change of sheet resistance $ΔR_\square/R_\square$ are $\approx$2, which is quantitatively consistent with Altshuler and Aronov EEI theory and seldom observed in other systems. For those polycrystalline films, both the sheet conductance and Hall coefficient vary linearly with logarithm of temperature below several tens Kelvin, which can be well described by the current EEI theories in granular metals. We extract the intergranular tunneling conductance of each film by comparing the $σ_\square(T)$ data with the predication of EEI theories in granular metals. It is found that when the tunneling conductance is less than the conductance of a single indium tin oxide (ITO) grain, the ITO film reveals granular metal characteristics in transport properties, conversely, the film shows transport properties of homogeneous disordered conductors. Our results indicate that electrical transport measurement can not only reveal the underlying charge transport properties of the film but also be a powerful tool to detect the subtle homogeneity of the film.

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$α_sv^2$ corrections to $η_c$ and $χ_{cJ}$ production recoiled with a photon at $e^+e^-$ colliders

We consider the production of the $η_c$ and $χ_{cJ}$ states recoiled with a photon up to $\mathcal{O}(α_s v^2)$ at BESIII and B-factories within the frame of NRQCD factorization. With the corrections, we revisit the numerical calculations to the cross sections for the $η_c(nS)$ and the $χ_{cJ}(mP)$ states. We argue that the search for $XYZ$ states with even charge conjugation such as $X(3872)$, $X(3940)$, $X(4160)$, and $X(4350)$ recoiled with a photon at BESIII may help clarify the nature of these states. For completeness, the production of charmonium with even charge conjugation recoiled with a photon at B factories is also discussed.

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Search for $C=+$ charmonium and XYZ states in $e^+e^-\to γ+ H$ at BESIII

Within the framework of nonrelativistic quantum chromodynamics, we study the production of $C=+$ charmonium states $H$ in $e^+e^-\to γ~+~H$ at BESIII with $H=η_c(nS)$ (n=1, 2, 3, and 4), $χ_{cJ}(nP)$ (n=1, 2, and 3), and $^1D_2(nD)$ (n=1 and 2). The radiative and relativistic corrections are calculated to next-to-leading order for $S$ and $P$ wave states. We then argue that the search for $C=+$ $XYZ$ states such as $X(3872)$, $X(3940)$, $X(4160)$, and $X(4350)$ in $e^+e^-\to γ~+~H$ at BESIII may help clarify the nature of these states. BESIII can search $XYZ$ states through two body process $e^+e^-\to γH$, where $H$ decay to $J/ψπ^+π^-$, $J/ψϕ$, or $D \bar D$. This result may be useful in identifying the nature of $C=+$ $XYZ$ states. For completeness, the production of $C=+$ charmonium in $e^+e^-\to γ+~H$ at B factories is also discussed.

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Electron-electron scatttering in Sn-doped indium oxide thick films

We have measured the low-field magnetoresistances (MRs) of a series of Sn-doped indium oxide thick films in the temperature $T$ range 4--35 K. The electron dephasing rate $1/τ_φ$ as a function of $T$ for each film was extracted by comparing the MR data with the three-dimensional (3D) weak-localization theoretical predictions. We found that the extracted $1/τ_φ$ varies linearly with $T^{3/2}$. Furthermore, at a given $T$, $1/τ_φ$ varies linearly with $k_F^{-5/2}l^{-3/2}$, where $k_{F}$ is the Fermi wavenumber, and $l$ is the electron elastic mean free path. These features are well explained in terms of the small-energy-transfer electron-electron scattering time in 3D disordered conductors. This electron dephasing mechanism dominates over the electron-phonon ($e$-ph) scattering process because the carrier concentrations in our films are $\sim$ 3 orders of magnitude lower than those in typical metals, which resulted in a greatly suppressed $e$-ph relaxation rate.

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Relativistic Correction to J/psi and Upsilon Pair Production

The relativistic corrections to the productions of double J/psi, double Upsilon, and J/psi+Upsilon at the Tevatron and the LHC were investigated within the frame of nonrelativistic QCD. The ratios of short distance coefficients between relativistic correction and leading order result for color singlet and color octet states in large p_T limit are approximately -1,-11/3, respectively, for pair production. And for J/psi+Upsilon process the ratio is -11/6 for the CO channel. The K factors of relativistic corrections for color singlet and color octet double J/psi production are -0.23 and -0.84 with adopting v^2=0.23. The relativistic corrections significantly dilute the difference between the shape of color-singlet differential cross sections and the color-octet's at leading order. Also our results show that the single parton scattering model may be enough to explain the LHCb data for the J/psi pair production.

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Relativistic Correction to Color Octet J/psi Production at Hadron Colliders

The relativistic corrections to the color-octet $J/ψ$ hadroproduction at the Tevatron and LHC are calculated up to $\mathcal{O}(v^2)$ in nonrelativistic QCD factorization frame. The short distance coefficients are obtained by matching full QCD with NRQCD results for the partonic subprocess $g+g\to J/ψ({}^1S_0^{[8]},{}^3S_1^{[8]}, {}^3P_J^{[8]})+g$, $q+\bar{q}\to J/ψ({}^1S_0^{[8]},{}^3S_1^{[8]}, {}^3P_J^{[8]})+g$ and $g+q({\bar{q}})\to J/ψ({}^1S_0^{[8]},{}^3S_1^{[8]}, {}^3P_J^{[8]})+q({\bar{q}})$. The short distance coefficient ratios of relativistic correction to leading order for color-octet states ${^1}S_{0}^{[8]}$, ${^3}S_{1}^{[8]}$, and ${^3}P_{J}^{[8]}$ at large $p_T$ are approximately -5/6, -11/6, and -31/30, respectively, for each subprocess, and it is 1/6 for color-singlet state ${^3}S_{1}^{[1]}$. If the higher order long distance matrix elements are estimated through velocity scaling rule with adopting $v^2=0.23$ and the lower order long distance matrix elements are fixed, the leading order cross sections of color-octet states are reduced by about a factor of $20\sim40%$ at large $p_T$ at both the Tevatron and the LHC. Comparing with QCD radiative corrections to color-octet states, relativistic correction is ignored along with $p_T$ increasing. Using long distance matrix elements extracted from the fit to $J/ψ$ production at the Tevatron, we can find the unpolarization cross sections of $J/ψ$ production at the LHC taking into account both QCD and relativistic corrections are changed by about $20\sim50%$ of that considering only QCD corrections. These results indicate that relativistic corrections may play an important role in $J/ψ$ production at the Tevatron and the LHC.

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Feynman Rules for the Rational Part of One-loop QCD Corrections in the MSSM

The complete set of Feynman rules for the rational part R of QCD corrections in the MSSM are calculated at the one-loop level, which can be very useful in the next-to-leading order calculations in supersymmetric models. Our results are expressed in the 't Hooft-Veltman regularization scheme and in the Four Dimensional Helicity scheme with non-anticommutating and anticommutating $γ_5$ strategies.

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J/psi polarization at hadron colliders in nonrelativistic QCD

With nonrelativistic QCD factorization, we present a full next-to-leading order computation of the polarization observable for $J/psi$ production at hadron colliders including all important Fock states, i.e. $^3S_1[1,8]$, $^1S_0[8]$, and $^3P_J[8]$. We find the $^3P_J[8]$ channel contributes a positive longitudinal component and a negative transverse component. So the $J/psi$ polarization puzzle may be understood as the transverse components canceling between $^3S_1[8]$ and $^3P_J[8]$ channels, which results in mainly the unpolarized (even slightly longitudinally polarized) $J/psi$. This may give a possible solution to the long-standing $J/psi$ polarization puzzle. Predictions for $J/psi$ polarization at the LHC are also presented.

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Electron dephasing in homogeneous and inhomogeneous indium tin oxide thin films

The electron dephasing processes in two-dimensional homogeneous and inhomogeneous indium tin oxide thin films have been investigated in a wide temperature range 0.3--90 K. We found that the small-energy-transfer electron-electron ($e$-$e$) scattering process dominated the dephasing from a few K to several tens K. At higher temperatures, a crossover to the large-energy-transfer $e$-$e$ scattering process was observed. Below about 1--2 K, the dephasing time $τ_φ$ revealed a very weak temperature dependence, which intriguingly scaled approximately with the inverse of the electron diffusion constant $D$, i.e., $τ_φ(T \approx 0.3 \, {\rm K}) \propto 1/D$. Theoretical implications of our results are discussed. The reason why the electron-phonon relaxation rate is negligibly weak in this low-carrier-concentration material is presented.

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Reduction Schemes in Cutoff Regularization and Higgs Decay into Two Photons

We present a new systematic method to evaluate one-loop tensor integrals in conventional ultraviolet cutoff regularization. By deriving a new recursive relation that describes the momentum translation variance of ultraviolet integrals, we implement this relation in the Passarino-Veltman reduction method. With this method, we recalculated the Higgs boson decay into two photons process at one-loop level in the Standard Model. We reanalyze this process carefully and clarify some issues arisen recently in cutoff regularization.

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Dijet Invariant Mass Distribution in Top Quark Hadronic Decay with QCD Corrections

The dijet invariant mass distributions from the hadronic decay of unpolarized top quark ($t\to b W^+$ followed by $W^+\to u \bar{d}$) are calculated, including the next-to-leading order QCD radiative corrections. We treat the top decay in the complex mass scheme due to the existence of the intermediate state W boson. Our analytical expressions are also available in different dimensional regularization schemes and $γ_5$ strategies. Finally, in order to construct the jets, we use different jet algorithms to compare their influences on our results. The obtained dijet mass distributions from the top quark decay are useful to distinguish these dijets from those produced via other sources and to clarify the issue about the recent CDF Collaborations' $Wjj$ anomaly.

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Feynman Rules for the Rational Part of the Standard Model One-loop Amplitudes in the 't Hooft-Veltman $γ_5$ Scheme

We study Feynman rules for the rational part $R$ of the Standard Model amplitudes at one-loop level in the 't Hooft-Veltman $γ_5$ scheme. Comparing our results for quantum chromodynamics and electroweak 1-loop amplitudes with that obtained based on the Kreimer-Korner-Schilcher (KKS) $γ_5$ scheme, we find the latter result can be recovered when our $γ_5$ scheme becomes identical (by setting $g5s=1$ in our expressions) with the KKS scheme. As an independent check, we also calculate Feynman rules obtained in the KKS scheme, finding our results in complete agreement with formulae presented in the literature. Our results, which are studied in two different $γ_5$ schemes, may be useful for clarifying the $γ_5$ problem in dimensional regularization. They are helpful to eliminate or find ambiguities arising from different dimensional regularization schemes.

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Logarithmic temperature dependence of Hall transport in granular metals

We have measured the Hall coefficient $R_H$ and the electrical conductivity $σ$ of a series of ultrathin indium tin oxide films between 2 and 300 K. A robust $R_H$\,$\propto$\,ln$T$ law is observed in a considerably wide temperature range of 2 and $\sim$120 K. This ln$T$ dependence is explained as originated from the electron-electron interaction effect in the presence of granularity, as newly theoretically predicted. Furthermore, we observed a $σ$\,$\propto$\,ln$T$ law from 3 K up to several tens K, which also arose from the Coulomb interaction effect in inhomogeneous systems. These results provide strong experimental supports for the current theoretical concepts for charge transport in granular metals with intergrain tunneling conductivity $g_T$$\gg$1.

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Leptonic Decay of Upsilon, a Possible Signature of New Physics

We calculate the inclusive decay width of $Υ\to l^+ l^-$. Then we get the ratio $R_{τμ}=Γ[Υ\to τ^+τ^-]/ Γ[Υ\to μ^+μ^-]$ to ${\cal{O}}(α)$ and ${\cal{O}}(α_s^2)$ within the Standard Model(SM). Comparing with the recent Babar's data $R_{τμ}=1.005\pm0.013\pm 0.022$, we find that SM prediction $R_{τμ}$ is not consistent with the experimental data in the error bar. The discrepancy is about $1.25σ$. So leptonic decay of $Υ$ may be a possible signature of New Physics(NP). We present a better approach to test the Standard Model, $R_{τμ}(E_{soft})=.Γ[Υ\to τ^+τ^-+X]/ Γ[Υ\to μ^+μ^-+X]|_{E_X<E_{soft}}$. After resumming the large logarithms, we get $R_{τμ}(E_{soft})$ at the precision level of 0.1%. It can be compared with experimental data more precise. We also consider the impact of $R_{τμ}(E_{soft})$ and $R_{τμ}$ from light Higgs $h$ and pseudoscalar Higgs $A_0$.

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$J / ψ$ electromagnetic production associated with light hadrons at $B$ factories

The electromagnetic productions of $J ψ$ associated with light hadrons(LH) and leptonic pairs($μ^+μ^-$, $τ^+τ^-$) at $B$ factories are studied. We find that the direct electromagnetic production cross sections of $J / ψ$($ψ(2S)$) associated with light hadrons is about $0.10(0.04)$ pb. The direct production cross sections of $J / ψ$($ψ(2S)$) associated with $μ^+μ^-$ is about $0.056(0.020)$ pb. If we include the contributions from $ψ(2S)$ decay, we can get the prompt cross section $σ[e^+e^- \to J/ψ+μ^+μ^-]=(0.068 \pm 0.002)$ pb, about $(16 \pm 5) %$ of the Belle data $σ[e^+e^- \to J/ψ+X_{non-c\bar c}]=(0.43\pm 0.09\pm 0.09)$ pb, meanwhile the $e^+e^- \to J/ψ+τ^+τ^-$ process only contributes $2 %$. The prompt cross section $σ[e^+e^- \to J/ψ+Light Hadrons]=(0.121 \pm 0.005)$ pb is about $(28 \pm 8) %$ of the Belle data.

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QCD radiative correction to color-octet $J/ψ$ inclusive production at B Factories

In nonrelativistic Quantum Chromodynamics (NRQCD), we study the next-to-leading order (NLO) QCD radiative correction to the color-octet $J/ψ$ inclusive production at B Factories. Compared with the leading-order (LO) result, the NLO QCD corrections are found to enhance the short-distance coefficients in the color-octet $J/ψ$ production $ e^+ e^-\to c \bar c (^3P_0^{(8)} {\rm or} ^3P_0^{(8)})g$ by a factor of about 1.9. Moreover, the peak at the endpoint in the $J/ψ$ energy distribution predicted at LO can be smeared by the NLO corrections, but the major color-octet contribution still comes from the large energy region of $J/ψ$. By fitting the latest data of $σ(e^{+}e^{-}\to J/ψ+X_{\mathrm{non-c\bar{c}}})$ observed by Belle, we find that the values of color-octet matrix elements are much smaller than expected earlier by using the naive velocity scaling rules or extracted from fitting experimental data with LO calculations. As the most stringent constraint by setting the color-singlet contribution to be zero in $e^{+}e^{-}\to J/ψ+X_{\mathrm{non-c\bar{c}}}$, we get an upper limit of the color-octet matrix element, $<0| {\cal O}^{J/ψ}[{}^1S_0^{(8)}]|0> + 4.0 <0| {\cal O}^{J/ψ} [{}^3P_0^{(8)}]|0>/m_c^2 <(2.0 \pm 0.6)\times 10^{-2} {\rm GeV}^3$ at NLO in $α_s$.

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