We study the coupling of a tetraquark system to an exchanged meson-meson channel, using a pure gluonic theory based four-quark potential {\em matrix} model which is known to fit well a large number of data points for lattice simulations of different geometries of a four-quark system. We find that if this minimal-area-based potential matrix replaces the earlier used simple Gaussian form for the gluon field overlap factor $f$ in its off-diagonal terms, the resulting $T$-matrix and phase shifts develop an angle dependence whose partial wave analysis reveals $D$ wave and higher angular momentum components in it. In addition to the obvious implications of this result for the meson-meson scattering, this new feature indicates the possibility of orbital excitations influencing properties of meson-meson molecules through a polarization potential. We have used a formalism of the resonating group method, treated kinetic energy and overlap matrices on model of the potential matrix, but decoupled the resulting complicated integral equations through the Born approximation. In this exploratory study we have used a quadratic confinement and not included the spin-dependence; we also used the approximation of equal constituent quark masses.
We report on state-of-the-art theoretical predictions for $pp\to t\bar{t}b\bar{b}$ including full off-shell effects in the di-lepton decay channel at NLO QCD accuracy. We briefly discuss the impact of NLO QCD corrections on differential distributions and also asses theoretical uncertainties from scale and PDF dependence. Furthermore, we propose a simple kinematic reconstruction in order to distinguish $b$ jets originating from top-quark decays from arising from gluon splittings.
Next-to-leading order QCD corrections to top quark spin correlations at hadron colliders: the reactions $g g \to t {\bar t} (g)$ and $g q ({\bar q}) \to t {\bar t} q ({\bar q})$
In this contribution we report on the latest theoretical predictions for $t\bar{t}b\bar{b}$. These results are obtained for the fully decayed final state $pp \rightarrow e^+ ν_e μ^- ν_μ b \bar{b} b \bar{b}$ at next-to-leading order accuracy in QCD. We present predictions with full off-shell effects and in the Narrow Width Approximation. Specifically, we report on the size of the NLO QCD corrections and the size of the full off-shell effects. Finally, we study the nature of the $b$-jets present in the final state.
We present a full off-shell NLO QCD calculation of $pp \rightarrow e^+ ν_e b μ^- \barν_μ\bar{b} b \bar{b} + X$. Results are obtained using the HELAC-NLO Monte Carlo framework. We discuss a comparison to previous results and to experimental measurements. We also investigate the contribution of the initial states involving $b$-quarks and we introduce two $b$-jet tagging schemes.
QCD corrections to t\bar t b \bar b productions via photon-photon collisions at linear colliders
在标准模型下，计算了在$γγ$对撞机上对$t\bar t b \bar b$产生过程的完全次主导阶（NLO）QCD修正.单圈QCD修正的计算包括六边形和五边形振幅的计算。我们研究了非线性光学QCD修正的总截面、末态顶夸克态和底夸克态的横动量分布以及截面与重整化标度$μ$的关系。结果表明，在所选的参数空间中，非线性光学QCD修正通常会增加LO截面，当碰撞能量从$400 GeV$增加到$2 TeV$时，K因子从1.70变化到1.14。结果表明，非线性光学QCD修正显著地改变了末态顶夸克和底夸克的横动量分布，并且显著地改善了重整化标度下$γγ\to t\bar t b\bar b$过程的横截面的独立性.
We investigate $J/ψ$ decays into octet baryon-antibaryons pairs. The decay amplitudes are computed within the collinear QCD factorisation framework. The subleading amplitude, which describes the decay of longitudinally polarised charmonium, is computed using twist-4 three-quark distribution amplitudes. The obtained results are used for a qualitative analysis of the experimental data. It is found that the polarisation parameter $α_B$ can be described with an accuracy $10-30\%$, which may indicate that the pQCD contribution dominates this observable.
Effects of charged Higgs boson and QCD corrections in $\bar B \to D τ\barν_τ$
我们研究了$\bar B \to D τ\barν_τ$中带电希格斯玻色子玻色子交换的效应。考虑了与MSSM具有相同Yukawa耦合的双Higgs偶重态模型Ⅱ的Yukawa耦合。我们评估的衰变率，包括次领先的QCD修正和估计的理论计算中的不确定性。我们的分析将有助于探测B工厂实验中的扩展Higgs扇区。
We present state-of-the-art predictions for off-shell $t\bar{t}b\bar{b}$ production with di-lepton decays at the LHC with $\sqrt{s}=13$ TeV. Results are accurate at NLO in QCD and include all resonant and non-resonant diagrams, interferences and finite-width effects for top quarks and $W$ bosons. We discuss the impact of QCD corrections and assess theoretical uncertainties from scale and PDF dependence at the integrated and differential level. Additionally we investigate the size of contributions induced by initial-state $b$ quarks to the NLO cross section.
In this article, we study the $J^{PC}=0^{++}$ and $2^{++}$ $QQ\bar{Q}\bar{Q}$ tetraquark states with the QCD sum rules, and obtain the predictions $M_{X(cc\bar{c}\bar{c},0^{++})} =5.99\pm0.08\,\rm{GeV}$, $M_{X(cc\bar{c}\bar{c},2^{++})} =6.09\pm0.08\,\rm{GeV}$, $M_{X(bb\bar{b}\bar{b},0^{++})} =18.84\pm0.09\,\rm{GeV}$ and $M_{X(bb\bar{b}\bar{b},2^{++})}=18.85\pm0.09\,\rm{GeV}$, which can be confronted to the experimental data in the future. Furthermore, we illustrate that the diquark-antidiquark type tetraquark state can be taken as a special superposition of a series of meson-meson pairs and em…
In this paper we present a short overview on the dynamical holographic QCD method for hadron physics and QCD matter. The 5-dimensional dynamical holographic QCD model is constructed in the graviton-dilaton-scalar framework with the dilaton background field $Φ$ and the scalar field $X$ dual to the gluon condensate and the chiral condensate operator thus can represent the gluodynamics (linear confinement) and chiral dynamics (chiral symmetry breaking), respectively. The dilaton background field and the scalar field are a function of the 5th dimension, which plays the role of the energy scale, in…
Decays $J/ψ\to B\bar B$ into octet baryon-antibaryons pairs are studied within the QCD factorisation framework. The next-to-leading power correction to the leading-order decay amplitude is calculated for the first time. The phenomenological analysis also includes the interference with the electromagnetic decay $J/ψ\to γ^*\to B\bar B$. The branching fractions and the angular coefficients $α_B$ are described with an accuracy of about $20\%$. The obtained results allow us to conclude that the calculated amplitudes provide a dominant contribution and therefore QCD factorisation provides a suitable…
Exclusive $B_c^\ast \rightarrow D_{s}~ν\barν$ decay is studied in the framework of the three--point QCD sum rules approach. The two gluon condensate contributions to the correlation function are calculated and the form factors of this transition are found. The decay width and total branching ratio for this decay is also calculated.
In this proceeding we present predictions for the complete NLO QCD corrections to the production of $t\bar{t}b\bar{b}$ in the dilepton decay channel of the top quark at the LHC with $\sqrt{s}=13$ TeV. The calculation is performed considering all the full off-shell effects. Moreover, the various sources of uncertainty for this process are studied in detail. We then compare these predictions to experimental measurements. We additionally investigate the impact of the $b$-quark initiated subprocesses.
QCD corrections to charged current processes at the Next Linear Collider: CC10, CC11 and CC20 at O(alpha_s)
计算了描述带电电流过程$e^+ e^- \to u \bar d μ\barν_μ$（CC 10）、$e^+ e^- \to u \bar d e^- \barν_e$（CC 20）和$e^+ e^- \to u \bar d s \bar c$（CC 11）的电弱图全规范不变集的单圈QCD修正。我们比较了精确的计算与“天真”的方法，已被广泛应用于文献中的强辐射校正，并讨论了唯象相关的QCD校正NLC物理。
Using light-front holography, we predict simultaneously the pion decay constant and the pion charge radius by taking into account (higher twist) dynamical spin effects whose relative importance is constrained by QCD.
We present the two-loop master integrals relevant to the ${\mathcal O}(αα_s)$-corrections to the decay $H \rightarrow b \bar{b}$ through a $H t \bar{t}$-coupling. We keep the full dependence on the heavy particle masses, but neglect the $b$-quark mass. The occurring square roots can be rationalised and the result is expressed in terms of multiple polylogarithms.
In this paper we review the hadroproduction mechanisms of double-charm baryons for the different experimental environments and reinterpret the SELEX and LHCb results.
The calculation of $t\bar{t}Z$ production including leptonic decays of both $Z$ boson and top quarks via a partially or fully off-shell calculation represents a definite step forward towards a more accurate description of events whose signatures originate from $t\bar{t}Z$ production. In this talk we review two studies that represent the state of the art of theoretical modeling of $t\bar{t}Z$ production by either performing the NLO QCD calculation of the fully decayed $pp\rightarrow e^+ν_eμ^-\barν_μb\bar{b}τ^+τ^-$ process (see Ref. [1]) or matching the NLO QCD calculation of $pp\rightarrow t\ba…
