arXiv subjects

Qin Qin

Publications and source records attributed to Qin Qin.

At least 37 records · Page 2Linked to original sources

arXiv2022

$D_s^{\ast} \to ϕ$ helicity form factors and the exclusive weak decays

The decay width of the $D_s^{\ast}$ meson is dominated by the electromagnetic mode $D_s^\ast \to D_s γ$, and it is thus the longest-lived charged vector meson. In light of this point, we perform the first QCD LCSRs calculation of $D_s^{\ast}\to ϕ$ helicity form factors and discuss the experiment potential of discovering exclusive $D_s^{\ast}$ weak decays. The main result is the partial decay widths, which read as $Γ_{D_s^\ast \to l ν} = 2.44 \times 10^{-12} \, {\rm GeV}$, $Γ_{D_s^\ast \to ϕl ν} = (3.28^{+0.82}_{-0.71}) \times 10^{-14} \, {\rm GeV}$, $Γ_{D_s^{\ast} \to ϕπ} = ( 3.81^{+1.52}_{-1.33} ) \times 10^{-14} \, {\rm GeV}$ and $Γ_{D_s^{\ast}\to ϕρ} = ( 1.16^{+0.42}_{-0.39} ) \times 10^{-13} \, {\rm GeV}$. We show that these channels are promising in the near future, serving as the first experimental observation of weak decays of a vector meson, and would open up a new playground for precision test of the standard model.

hep-ph↗

arXiv2022

Domain Shift-oriented Machine Anomalous Sound Detection Model Based on Self-Supervised Learning

Thanks to the development of deep learning, research on machine anomalous sound detection based on self-supervised learning has made remarkable achievements. However, there are differences in the acoustic characteristics of the test set and the training set under different operating conditions of the same machine (domain shifts). It is challenging for the existing detection methods to learn the domain shifts features stably with low computation overhead. To address these problems, we propose a domain shift-oriented machine anomalous sound detection model based on self-supervised learning (TranSelf-DyGCN) in this paper. Firstly, we design a time-frequency domain feature modeling network to capture global and local spatial and time-domain features, thus improving the stability of machine anomalous sound detection stability under domain shifts. Then, we adopt a Dynamic Graph Convolutional Network (DyGCN) to model the inter-dependence relationship between domain shifts features, enabling the model to perceive domain shifts features efficiently. Finally, we use a Domain Adaptive Network (DAN) to compensate for the performance decrease caused by domain shifts, making the model adapt to anomalous sound better in the self-supervised environment. The performance of the suggested model is validated on DCASE 2020 task 2 and DCASE 2022 task 2.

cs.SD↗

arXiv2022

Deciphering the long-distance penguin contribution to $\bar B_{d, s} \to γγ$ decays

We compute for the first time the long-distance penguin contribution to the double radiative $B$-meson decays due to the purely hadronic operators acting with the electromagnetic current in the background soft-gluon field from first field-theoretical principles by introducing a novel subleading $B$-meson distribution amplitude. The numerically dominant penguin amplitude arises from the soft-gluon radiation off the light up-quark loop rather than the counterpart charm-loop effect on account of the peculiar analytical behaviour of the short-distance hard-collinear function. Importantly the long-distance up-quark penguin contribution brings about the substantial cancellation of the known factorizable power correction possessing the same multiplication CKM parameters, thus enabling $B_{d, \, s} \to γγ$ to become new benchmark probes of physics beyond the Standard Model.

hep-ph↗

arXiv2022

Monojet search for heavy neutrinos at future $Z$-factories

The existence of heavy neutrinos is the most prominent feature of type-I seesaw-like mechanisms, which naturally explain tiny masses of observed neutrinos. Various experiments have been conducted to search for heavy neutrinos, with meson decays sensitive to heavy neutrinos lighter than $B$ mesons and high energy collider experiments sensitive to the ones with masses larger than $\mathcal{O}(0.1)$ TeV. In between, there is a mass gap uncovered by these two kinds of experiments, and by this work, we investigate the 3-15 GeV neutrino searches at future $Z$-factories via the process $e^{-}e^{+}\rightarrow Z \rightarrow νN \rightarrow ν\ell\bar{q}q'$ with $\ell=e,μ$. Based on the simulation of signal and background events, we find that the signals appear as monojet events owning to the large Lorentz boost of the heavy neutrinos. Furthermore, the substructures of such monojet are essential to reconstruct the signal and suppress the background. The upper bounds on the cross section of the signal process and the mixing parameter ${| V_{\ell N}|}^2$ are obtained. Compared with other experiments, the monojet method at future $Z$-factories will be able to fill the gap around this mass range.

hep-ph↗

arXiv2022

Inclusive approach to hunt for the beauty-charmed baryons $Ξ_{bc}$

With a distinctive internal structure from all established hadrons, the beauty-charmed baryons $Ξ_{bc}$ can provide us with new points of view to decipher the strong interaction. In this work, we point out that the inclusive $Ξ_{bc} \to Ξ_{cc}^{++}+X$ decay is a golden channel for the experimental discovery of $Ξ_{bc}$ at the LHC. A unique feature of this process is that the $Ξ_{cc}^{++}$ is displaced, which greatly reduces the combinatorial background. A feasibility analysis is performed on the $Ξ_{bc}^+$ search, which is expected to have a longer lifetime than $Ξ_{bc}^0$ and thus a better displacement resolution. The $Ξ_{bc}^+ \to Ξ_{cc}^{++}+X$ branching ratio is calculated within the heavy diquark effective theory. Combining the $Ξ_{bc}$ production rate and the $Ξ_{cc}^{++}$ detection efficiency, we anticipate that hundreds of signal events will be collected during LHCb Run 3.

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arXiv2021

The factorization-assisted topological-amplitude approach and its applications

Heavy meson decays provide an important platform for studies of both QCD and electroweak dynamics, which may contain some portals to understanding of nonperturbative QCD and physics beyond the Standard Model. The factorization-assisted topological-amplitude approach was proposed to study two-body non-leptonic $D$ meson decays, where a promising QCD inspired approach from first principles is still missing. It was also applied to $B$ meson decays whose subleading power contributions are difficult to calculate. By factorizing topological amplitudes into short distance Wilson coefficients and long distance hadronic matrix elements either to be calculated or to be parameterized, it provides an effective framework to extract information of nonperturbative dynamics involved. With important flavor SU(3) breaking effects taken into account, the data of the decay branching ratios (and also CP asymmetries in $B$ decays) can be fitted well. The extracted amplitudes were further applied to make predictions for other observables, such as CP asymmetries in $D$ decays, mixing parameters in the $D^0-\bar{D}^0$ system, and so on. By this review, we will describe the formulation of the factorization-assisted topological-amplitude approach and summarize its applications in $D$ and $B$ meson decays and highlight some of its achievements.

hep-ph↗

arXiv2021

Colour and baryon number fluctuation of preconfinement system in production process and T_cc structure

We suggest to study the production mechanism and some details of the production properties to probe the structure of the DDpi resonance T_cc^+ recently observed by the LHCb Collaboration. If the resonance is produced as a four-quark state, one can find the corresponding finger prints via measurements on some production properties that are the same as those of Xi_cc. The reason is that a special colour connection on the interface between the perturbative and non perturbative QCD is required for these doubly-charm hadron production. On the other hand, if T_cc^+ is produced as a hadron molecule, the measurement on the momentum correlation of DD^* can be a smoking gun to make the judgement. The present data favour a compact four-quark state production via the cc diquark fragmentation.

hep-ph↗

arXiv2021

Discovery potentials of double-charm tetraquarks

In this study, we investigate the discovery potential of double-charm tetraquarks $T^{\{cc\}}_{[\bar{q}\bar{q}']}$. We find that their production cross sections at the LHCb with $\sqrt{s} = 13$ TeV reach $\mathcal{O}(10^4)$ pb, which indicates that the LHCb has collected $\mathcal{O}(10^8)$ such particles. Through the decay channels of $T^{\{cc\}}_{[\bar{u}\bar{d}]}\to D^{+}K^{-}π^{+}$ or $D^0D^+γ$ (if stable) or $T^{\{cc\}}_{[\bar{u}\bar{d}]}\to D^0D^{*+}\to D^0D^0π^+$ (if unstable), it is highly expected that they get discovered at the LHCb in the near future. We also discuss the productions and decays of the double-charm tetraquarks at future Tera-$Z$ factories.

hep-ph↗

arXiv2020

Phenomenology of inclusive $\bar{B}\to X_s \ell^+ \ell^-$ for the Belle II era

With the first data being recorded at Belle II, we are at the brink of a new era in quark flavour physics. The many exciting new opportunities for Belle~II include a full angular analysis of inclusive ${\bar B \to X_{s} \, \ell^+\ell^-}$ which has the potential to reveal new physics, in particular by its interplay with the exclusive $b \to s \ell^+\ell^-$ counterparts studied extensively at LHCb. In this paper, we present fully updated Standard Model predictions for all angular observables necessary for this endeavour. These predictions are tailored to Belle II and include an elaborate study of the treatment of collinear photons which become crucial when aiming for the highest precision. In addition, we present a phenomenological study of the potential for Belle II to reveal possible new physics in the inclusive decay channel, both in an independent manner and in combination with exclusive modes.

hep-ph↗

arXiv2020

Signatures of a Flavor Changing $Z'$ Boson in $B_q \to γZ'$

Rare $B$ meson decays offer an opportunity to probe a light hidden $Z'$ boson. In this work we explore a new channel $B_q \to γZ'$ ($q = d, s$) followed by a cascade decay of $Z'$ into an invisible (neutrino or dark matter) or charged lepton pair $\ell^+ \ell^-$ ($\ell=e ,μ)$. The study is based on a simplified effective model where the down quark sector has tiny flavor-changing neutral current couplings with $Z'$. For the first time, we calculate ${\rm BR}(B_q \to γZ')$ at the leading power of $1/m_b$ and $1/E_γ$. Confronting with the strong constraints from semi-invisible decays of $B$ meson, we find that the branching ratio for $B_d \to {\rm invisible} + γ$ can be larger than its Standard Model prediction, leaving a large room for new physics, in particular for light dark matter. Additionally, the branching ratio for $B_d \to e^+ e^- γ$ can also be sizable when the corresponding flavor violating $Z'$ coupling to quarks is of the axial-vector type. On the other hand, the predicted branching ratios of $B_d \to μ^+ μ^- γ$ and $B_s \to \ell^+ \ell^- γ$ are severely constrained by the experimental measurements.

hep-ph↗

arXiv2019

Long distance effects in inclusive rare $B$ decays and phenomenology of $\bar{B}\to X_d \ell^+\ell^-$

Rare inclusive $B$ decays such as $\bar{B}\to X_{s(d)} \ell^+\ell^-$ are interesting probes for physics beyond the Standard Model. Due to the complementarity to their exclusive counterparts, they might shed light on the anomalies currently seen in exclusive $b \to s$ transitions. Distinguishing new-physics effects from the Standard Model requires precise predictions and necessitates the control of long distance effects. In the present work we revisit and improve the description of various long distance effects in inclusive decays such as charmonium and light-quark resonances, nonfactorisable power corrections, and cascade decays. We then apply these results to a state-of-the-art phenomenological study of $\bar{B}\to X_d \ell^+\ell^-$, including also logarithmically enhanced QED corrections and the recently calculated five-body contributions. To fully exploit the new-physics potential of inclusive flavour-changing neutral current decays, the $\bar{B}\to X_d \ell^+\ell^-$ observables should be measured in a dedicated Belle II analysis.

hep-ph↗

arXiv2019

Heavy neutrino searches at future $Z$-factories

We analyze the capacity of future $Z$-factories to search for heavy neutrinos with their mass from 10 to 85 GeV. The heavy neutrinos $N$ are considered to be produced via the process $e^+e^-\to Z\to νN$ and to decay into an electron or muon and two jets. By means of Monte Carlo simulation of such signal events and the Standard Model background events, we obtain the upper bounds on the cross sections $σ(e^+e^-\to νN\to ν\ell jj)$ given by the $Z$-factories with integrated luminosities of 0.1, 1 and 10 ab$^{-1}$ if no signal events are observed. Under the assumption of a minimal extension of the Standard Model in the neutrino sector, we also present the corresponding constraints on the mixing parameters of the heavy neutrinos with the Standard Model leptons, and find they are improved by at least one order compared to current experimental constraints.

hep-ph↗

arXiv2019

$Z \to π^+π^-, K^+K^-$: A touchstone of the PQCD approach

We study two rare decays, $Z \to π^+π^-$ and $K^+K^-$, in the perturbative QCD approach up to the next-to-leading order of the strong coupling and the leading power of $1/m_Z$, $m_Z$ being the $Z$ boson mass. The branching ratios $\mathcal{B}(Z\to π^+π^-) = (0.83 \pm 0.02 \pm 0.02 \pm 0.04)\times 10^{-12}$ and $\mathcal{B}(Z\to K^+K^-) = (1.74^{+0.03}_{-0.05} \pm 0.04 \pm 0.02)\times 10^{-12}$ are obtained and can be measured at a tera-$Z$ factory. Because the subleading-power contributions to the branching ratios are negligible, and the leading one does not depend on any free parameter, the two channels can serve as a touchstone for the applicability of the perturbative QCD approach.

hep-ph↗

arXiv2018

Charged lepton flavor violating Higgs decays at future $e^+e^-$ colliders

After the discovery of the Higgs boson, several future experiments have been proposed to study the Higgs boson properties, including two circular lepton colliders, the CEPC and the FCC-ee, and one linear lepton collider, the ILC. We evaluate the precision reach of these colliders in measuring the branching ratios of the charged lepton flavor violating Higgs decays $H\to e^\pmμ^\mp$, $e^\pmτ^\mp$ and $μ^\pmτ^\mp$. The expected upper bounds on the branching ratios given by the circular (linear) colliders are found to be $\mathcal{B}(H\to e^\pmμ^\mp) < 1.2\ (2.1) \times 10^{-5}$, $\mathcal{B}(H\to e^\pmτ^\mp) < 1.6\ (2.4) \times 10^{-4}$ and $\mathcal{B}(H\to μ^\pmτ^\mp) < 1.4\ (2.3) \times 10^{-4}$ at 95\% CL, which are improved by one to two orders compared to the current experimental bounds. We also discuss the constraints that these upper bounds set on certain theory parameters, including the charged lepton flavor violating Higgs couplings, the corresponding parameters in the type-III 2HDM, and the new physics cut-off scales in the SMEFT, in RS models and in models with heavy neutrinos.

hep-ph↗

arXiv2018

Five-particle contributions to the inclusive rare $\bar B \to X_{s(d)} \, \ell^+\ell^-$ decays

We calculate tree-level contributions to the inclusive rare $\bar B \to X_{s(d)} \, \ell^+\ell^-$ decays. At the partonic level they stem from the five-particle process $b \to s(d) \, q \bar q \, \ell^+\ell^-$, with $q \in \{u,d,s\}$. While for $b \to d$ transitions such five-body final states contribute at the same order in the Wolfenstein expansion compared to the three-body partonic decay, they are CKM suppressed in $b \to s$ decays. In the perturbative expansion, we include all leading-order contributions, as well as partial next-to-leading order QCD and QED effects. In the case of the differential branching ratio, we present all results completely analytically in terms of polylogarithmic functions of at most weight three. We also consider the differential forward-backward asymmetry, where all except one interference could be obtained analytically. From a phenomenological point of view the newly calculated contributions are at the percent level or below.

hep-ph↗

arXiv2018

Discovery potential of stable and near-threshold doubly heavy tetraquarks at the LHC

We study the LHC discovery potential of the double-bottom tetraquarks $bb \bar u \bar d$, $bb \bar u \bar s$ and $bb \bar d \bar s$, the lightest of which having $J^P=1^+$, called $T^{\{bb\}}_{[\bar u \bar d]}$, $T^{\{bb\}}_{[\bar u \bar s]}$ and $T^{\{bb\}}_{[\bar d \bar s]}$, are expected to be stable against strong decays. Employing the Monte Carlo generators MadGraph5$\_$aMC@NLO and Pythia6, we simulate the process $pp\to \bar b b\bar b b$ and calculate the $b b$-diquark jet configurations, specified by the invariant mass interval $m_{bb} < M_{T^{\{bb\}}_{[\bar q \bar q']}} + ΔM$. Estimates of $ΔM$ from the measured product $σ(pp \to B_c^+ +X){\cal B}(B_c^+\to J/ψπ^+)$ are presented and used to to get the $b b$-diquark jet cross sections in double-bottom hadrons $σ(pp \to H_{\{bb\}} +X)$, where $H_{\{bb\}} $ represent tetraquarks and baryons. This is combined with the LHCb data on the fragmentation $b \to Λ_b$ and $b \to B$ to obtain $σ(pp\to T^{\{bb\}}_{[\bar u\bar d]} +X) = (2.4 ^{+0.9}_{-0.6})\ \text{nb} $, and about a half of this for the $T^{\{bb\}}_{[\bar{u}\bar{s}]}$ and $T^{\{bb\}}_{[\bar d \bar s]}$. We also present estimates of the production cross sections for the mixed bottom-charm tetraquarks, $bc \bar u \bar d$, $bc \bar u \bar s$ and $bc \bar d \bar s$, obtaining $σ(pp\to T^{[bc]}_{[\bar u \bar d]} +X)= (48^{+19}_{-12})\ {\rm nb}$, and the related ones having $T^{[bc]}_{[\bar u \bar s]}$ and $T^{[bc]}_{[\bar d \bar s]}$. They have excellent discovery potential at the LHC, as their branching ratios in various charge combinations of $BD_{(s)} (γ)$ are anticipated to be large.

hep-ph↗

arXiv2018

Prospects of discovering stable double-heavy tetraquarks at a Tera-$Z$ factory

Motivated by a number of theoretical considerations, predicting the deeply bound double-heavy tetraquarks $T^{\{bb\}}_{[\bar u \bar d]}$, $T^{\{bb\}}_{[\bar u \bar s]}$ and $T^{\{bb\}}_{[\bar d \bar s]}$, we explore the potential of their discovery at Tera-$Z$ factories. Using the process $Z \to b \bar b b \bar b$, we calculate, employing the Monte Carlo generators MadGraph5$\_$aMC@NLO and Pythia6, the phase space configuration in which the~$b b$ pair is likely to fragment as a diquark. In a jet-cone, defined by an invariant mass interval $m_{bb} < M_{T^{\{bb\}}_{[\bar q \bar q']}} + ΔM$, the sought-after tetraquarks $T^{\{bb\}}_{[\bar q \bar q^\prime]}$ as well as the double-bottom baryons,~$Ξ_{bb}^{0,-}$, and $Ω_{bb}^-$, can be produced. Using the heavy quark--diquark symmetry, we estimate $\mathcal{B} (Z \to T^{\{bb\}}_{[\bar u \bar d]} + \; \bar b \bar b) = (1.4^{+1.1}_{-0.5}) \times 10^{-6}$, and about a half of this for the $T^{\{bb\}}_{[\bar{u}\bar{s}]}$ and $T^{\{bb\}}_{[\bar d \bar s]}$. We also present an estimate of their lifetimes using the heavy quark expansion, yielding $τ(T^{\{bb\}}_{[\bar q \bar q^\prime]}) \simeq 800$~fs. Measuring the tetraquark masses would require decays, such as $T^{\{bb\} -}_{[\bar u \bar d]} \to B^- D^- π^+$, $T^{\{bb\} -}_{[\bar u \bar d]} \to J/ψ\overline K^0 B^-$, $T^{\{bb\} -}_{[\bar u \bar d]} \to J/ψK^- \overline B^0$, $T^{\{bb\} -}_{[\bar u \bar s]} \to Ξ_{bc}^0 Σ^-$, and $T^{\{bb\} 0}_{[\bar d \bar s]} \to Ξ_{bc}^0 \barΣ^0$, with subsequent decay chains in exclusive non-leptonic final states. We estimate a couple of the decay widths and find that the product branching ratios do not exceed~$10^{-5}$. Hence, a good fraction of these modes will be required for a discovery of $T^{\{bb\}}_{[\bar q \bar q']}$ at a Tera-$Z$ factory.

hep-ph↗

arXiv2018

$D^0$-$\overline{D}^0$ mixing parameter $y$ in the factorization-assisted topological-amplitude approach

We calculate the $D^0$-$\overline{D}^0$ mixing parameter $y$ in the factorization-assisted topological-amplitude (FAT) approach, considering contributions from $D^{0}\to PP$, $PV$, and $VV$ modes, where $P$ ($V$) stands for a pseudoscalar (vector) meson. The $D^{0}\to PP$ and $PV$ decay amplitudes are extracted in the FAT approach, and the $D^{0}\to VV$ decay amplitudes with final states in the longitudinal polarization are estimated via the parameter set for $D^{0}\to PV$. It is found that the $VV$ contribution to $y$, being of order of $10^{-4}$, is negligible, and that the $PP$ and $PV$ contributions amount only up to $y_{PP+PV}=(0.21\pm0.07)\%$, a prediction more precise than those previously obtained in the literature, and much lower than the experimental data $y_{\rm exp}=(0.61\pm0.08)\%$. We conclude that $D^{0}$ meson decays into other two-body and multi-particle final states are relevant to the evaluation of $y$, so it is difficult to understand it fully in an exclusive approach.

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