arXiv subjects

H. Bahtiyar

Publications and source records attributed to H. Bahtiyar.

6 recordsLinked to original sources

arXiv2023

Electromagnetic Structure of Spin-$\frac12$ Doubly Charmed Baryons in Lattice QCD

We compute the electromagnetic properties of spin-$\frac12$ doubly charmed baryons on 2+1 flavor lattices that have a pion mass of $\sim$ 156 MeV. The Tsukuba action is employed for the charm quark in addition to the standard isotropic Clover action to quantify the $\mathcal{O}(m_q a)$ effects. We calculate the electric and magnetic Sachs form factors and extract the magnetic moments and electric and magnetic charge radii. We also investigate the individual quark sector contributions to the charge radii and the magnetic moments. The results provide vital information to understand the size and shape of the doubly charmed baryons. We find that the two heavy charm quarks drive the charge radii and the magnetic moments to smaller values than that of light baryons. The central values of the observables that are obtained using the relativistic action for the charm quark are $5$ to $10\%$ larger than those obtained using the Clover action. Utilizing the available lattice data, we reexamine the quark mass dependence of the observables.

hep-lat↗

arXiv2021

Zb tetraquark channel and $B\bar B^*$ interaction from lattice QCD

Two tetraquark candidates $Z_b(10610)$ and $Z_b(10650)$ with flavor structure $\bar bb\bar du$ were discovered by Belle experiment in 2011. We present a preliminary $N_f=2$ lattice study of the $\bar bb\bar du$ system in the approximation of static $b$ quarks, where the total spin of heavy quarks is fixed to one. The ground and the excited eigen-energies are determined as a function of separation $r$ between $b$ and $\bar b$. The lower eigenstates are related to a bottomonium and a pion. One of the higher eigenstates is dominated by $B\bar B^*$: its energy is significantly below $m_B+m_{B*}$ for r=[0.1,0.4] fm, which suggests sizable attraction. The attractive potential $V(r)$ between $B$ and $\bar B^*$ is extracted assuming that this eigenstate is related exclusively to $B\bar B^*$. Assuming a certain form of the potential and solving non-relativistic Schrodinger equation, we find a bound state pole below $B\bar B^*$ threshold. For certain parametrizations, the bound state is very close to the $B\bar B^*$ threshold - this feature could be related to $Z_b(10610)$ in the experiment.

hep-lat↗

arXiv2021

Zb tetraquark channel from lattice QCD and Born-Oppenheimer approximation

Two $Z_b$ hadrons with exotic quark structure $\bar bb\bar du$ were discovered by Belle experiment. We present a lattice QCD study of the $\bar bb\bar du$ system in the approximation of static $b$ quarks, where the total spin of heavy quarks is fixed to one. The energies of eigenstates are determined as a function of the separation $r$ between $b$ and $\bar b$. The lower eigenstates are related to a bottomonium and a pion. The eigenstate dominated by $B\bar B^*$ has energy significantly below $m_B+m_{B^*}$, which points to a sizable attraction for small $r$. The attractive potential $V(r)$ between $B$ and $\bar B^*$ is extracted assuming that this eigenstate is related exclusively to $B\bar B^*$. The Schrödinger equation for $B\bar B^*$ within the extracted potential leads to one bound state below $B\bar B^*$ threshold, whose mass depends on the parametrization of the lattice potential. For certain parametrizations, the bound state is very close to the $B\bar B^*$ threshold and renders a narrow peak in the $B\bar B^*$ rate above threshold - these features could be related to $Z_b(10610)$ in the experiment.

hep-lat↗

arXiv2018

Radiative transitions of doubly charmed baryons in lattice QCD

We evaluate the spin-$3/2 \to$ spin-$1/2$ electromagnetic transitions of the doubly charmed baryons on 2+1 flavor, $32^3 \times 64$ PACS-CS lattices with a pion mass of $156(9)$ MeV/c$^2$. A relativistic heavy quark action is employed to minimize the associated systematic errors on charm-quark observables. We extract the magnetic dipole, $M1$, and the electric quadrupole, $E2$, transition form factors. In order to make a reliable estimate of the $M1$ form factor, we carry out an analysis by including the effect of excited-state contributions. We find that the $M1$ transition is dominant and light degrees of freedom ($u/d$- or $s$-quark) play the leading role. $E2$ form factors, on the other hand, are found to be negligibly small, which in turn, have minimal effect on the helicity and transition amplitudes. We predict the decay widths and lifetimes of $Ξ_{cc}^{\ast +,++}$ and $Ω_{cc}^{\ast +}$ based on our results. Finite size effects on these ensembles are expected to be around 1\%. Differences in kinematical and dynamical factors with respect to the $Nγ\toΔ$ transition are discussed and compared to non-lattice determinations as well keeping possible systematic artifacts in mind. A comparison to $Ω_c γ\rightarrow Ω_c^\ast$ transition and a discussion on systematic errors related to the choice of heavy quark action are also given. Results we present here are particularly suggestive for experimental facilities such as LHCb, PANDA, Belle II and BESIII to search for further states.

hep-lat↗

arXiv2017

$Ξ_c γ\rightarrowΞ^\prime_c$ transition in lattice QCD

We evaluate the electromagnetic $Ξ_c γ\rightarrowΞ_c^\prime$ transition on 2+1 flavor lattices corresponding to a pion mass of $\sim 156$ MeV. We extract the magnetic Sachs and Pauli form factors which give the $Ξ_c$-$Ξ_c^\prime$ transition magnetic moment and the decay rates of $Ξ_c^\prime$ baryons. We did not find a signal for the magnetic form factor of the neutral transition $Ξ_c^0 γ\rightarrowΞ_c^{\prime 0}$, which is suppressed by the U-spin flavor symmetry. As a byproduct, we extract the magnetic form factors and the magnetic moments of $Ξ_c$ and $Ξ_c^\prime$ baryons, which give an insight to the dynamics of $u/d$, $s$ and $c$ quarks having masses at different scales.

hep-lat↗

arXiv2015

$Ω_c γ\rightarrowΩ_c^\ast$ transition in lattice QCD

We study the electromagnetic $Ω_c γ\rightarrowΩ_c^\ast$ transition in 2+1 flavor lattice QCD, which gives access to the dominant decay mode of $Ω_c^\ast$ baryon. The magnetic dipole and the electric quadrupole transition form factors are computed. The magnetic dipole form factor is found to be mainly determined by the strange quark and the electric quadrupole form factor to be negligibly small, in consistency with the quark model. We also evaluate the helicity amplitudes and the decay rate.

hep-lat↗