We study the nonleptonic two-body weak decays of $Λ_b$ by modifying the MIT bag model without introducing new parameters to construct the momentum eigenstates of the baryons. We find that the branching ratios of $Λ_b^0 \to Λ_c^+ π^-$, $Λ_c^+ K^-$, $p π^-$ and $pK^-$ are $(4.5\pm0.2)\times 10^{-3}$, $(3.4\pm 0.1)\times 10^{-4}$, $(5.0\pm 0.5)\times 10^{-6}$ and $(6.0\pm 0.7) \times 10^{-6}$, which are all well consistent with the current experimental data, respectively. We also explore P and CP asymmetries for the decays of $Λ_b^0 \to p (π^-,K^-)$. In particular, we obtain that the direct CP-violating rate asymmetries in $Λ_b^0 \to p π^-$ and $Λ_b^0 \to p K^-$ are around $-4.4\%$ and $6.7\%$, in comparison with $(-2.5\pm2.9)\%$ and $(-2.5\pm2.2)\%$ from the Particle Data Group in 2020, respectively.
We calculate the radiative corrections to the nonleptonic inclusive B decay mode $b\to c ud$ taking into account the charm quark mass. The corrections increase the decay rate by (4--8)\%, depending on the renormalization point. Using these results, we obtain an improved theoretical prediction for the semileptonic branching ratio of B mesons. This talk relies on work done in collaboration with E. Bagan, V.M.\ Braun and P. Gosdzinsky.
We apply the MIT bag model to study the Boer-Mulders function of the pion, a $T$-odd function that describes the transverse polarization distribution of the quark inside the pion. We simulate the effect of the gauge link through the "one-gluon-exchange" approximation. We consider both the quark helicity nonflip and double-flip contributions. The result in the MIT bag model is compared with those in the spectator models.
Aiming on testing the $Ξ_c-Ξ_c'$ mixing, we study the decays of $Ξ_{cc}\to Ξ_c π$ with $Ξ_{cc} = (Ξ_{cc}^{++} , Ξ_{cc} ^+ )$, $Ξ_c = (Ξ_c^{(\prime)+},Ξ_c^{(\prime)0})$ and $π= (π^+ , π^0)$. The soft-meson limit is considered along with the pole model, and the baryon matrix elements are evaluated by the bag model with and without removing the center-of-mass motion (CMM). We find that the four-quark operator matrix elements are about twice larger once the unwanted CMM is removed. We obtain that ${\cal R} = {\cal B}(Ξ_{cc}^+ \to Ξ_c^{\prime +} π^+ )/ {\cal B}(Ξ_{cc}^+ \to Ξ_c^{ +} π^+ ) = 0.87^{+…
We utilize the MIT bag model and two different versions of the Color Dielectric Model in order to study the properties of strange matter, and to discuss the stability of strangelets. We also investigate the effect of the introduction of perturbative gluons. The MIT bag model and the Double Minimum version of the Color Dielectric Model allow the existence of strangelets, while the Single Minimum version excludes this possibility.
Using the MIT bag model, we study the contribution from the gluon vector potential due to the spectators to the orbital angular momentum of a quark in the bag model. For $α_s = {\cal O}(1)$, this spectator contribution to the quark orbital angular momentum in the gauge-covariant Ji decomposition is of the same order as the non gauge-covariant quark orbital angular momentum and its magnitude is larger for $d$ than for $u$ quarks and negative for both.
Cabibbo-allowed nonleptonic weak decays of charmed baryons $\lamc,~\xin,~\xip$ and $Ω_c^0$ into an octet baryon and a pseudoscalar meson are analyzed. The nonfactorizable contributions are evaluated under pole approximation, and it turns out that the $s$-wave amplitudes are dominated by the low-lying $\halfm$ resonances, while $p$-wave ones governed by the ground-state $\halfp$ poles. The MIT bag model is employed to calculate the coupling constants, form factors and baryon matrix elements. Our conclusions are: (i) $s$ waves are no longer dominated by commutator terms; the current-algebra meth…
The Sivers function, an asymmetric transverse-momentum distribution of the quarks in a transversely polarized nucleon, is calculated in the MIT bag model. The bag quark wave functions contain both $S$-wave and $P$-wave components, and their interference leads to nonvanishing Sivers function in the presence of the final state interactions. We approximate these interactions through one-gluon exchange. An estimate of another transverse momentum dependent distribution $h_1^\perp$ is also performed in the same model.
An alternative to introducing and subsequently renormalizing classical parameters in the expression for the vacuum energy of the MIT bag for quarks is proposed in the massless case by appealing to the QCD trace anomaly and scale separation due to asymptotic freedom. The explicit inclusion of gluons implies an unrealistically low separation scale.
Using the (modified) MIT bag model we calculated formfactors and decay widths for pseudoscalar - pseudoscalar and pseudoscalar - vector semileptonic decays of heavy to light mesons. We discuss the physical phenomena which are important in these processes and their influence on the measurable quantities. Our results are consistent with the available experimental data. A comparison with the results of other models is also given.
We calculate all twist-two, three and four parton distribution functions involving two quark correlations using the wavefunction of the MIT bag model. The distributions are evolved up to experimental scales and combined to give the various nucleon structure functions. Comparisons with recent experimental data on higher twist structure functions at moderate values of $Q^{2}$ give good agreement with the calculated structure functions.
The contribution of instanton-induced effective inter-quark interactions to the baryon mass splittings was considered in the bag model. It is found that results are different from those obtained in the constituent quark model where the instanton effects are like those from one-gluon exchange. This is because in the context of the bag model calculation the one-body instanton-induced interaction has to be included.
The electric and magnetic bag radiuses of the proton can be determined by MIT bag model based on electric and magnetic form factors of the proton. Also we determined electric and magnetic root mean squared radiuses of the proton, using of bag radius and compared with other results suggests a suitable compatibility.
The strong decays of the heavy baryons Σ^{(*)}_Q \to Λ_Q πare studied by combining the chiral dynamics and the MIT bag model. In charm sector, we calculate the decay widths Γ(Σ^{(*)}_c\to Λ_cπ) and compare with the experimental data and other theoretical estimations. In addition, we also predict the strong decay widths Γ(Σ^{(*)}_b\to Λ_bπ).
We discuss the properties of strange matter, in particular the minimum of the energy per baryon number as a function of the strangeness fraction. We utilize both the MIT bag model and the Color Dielectric Model and compare the energy per baryon with the masses of hyperons having the corresponding strangeness fraction, which are coherently calculated within both models. We also take into account the perturbative exchange of gluons. The results obtained in the two approaches allow to discuss the stability of strangelets. While the MIT bag model and the double minimum version of the Color Dielect…
Roles of instanton induced interactions (III) in the masses of pentaquark baryons, Theta^+ (J=1/2 and 3/2) and Xi^{--}, and a dibaryon, H, are discussed using the MIT bag model. It is shown that the two-body terms in III give a strong attraction mainly due to the increase of the number of pairs in multi-quark systems. In contrast, the three-body $u$-$d$-$s$ interaction is repulsive. It is found that III lowers the mass of negative-parity Theta^+ as much as 100 MeV from the mass predicted by the bag model without III.
The Isgur-Wise functions for the ground state to ground state semileptonic decays involving $b \rightarrow c$ transitions are calculated from the (modified) MIT bag model. It is checked that the results for the decays $\overline{B} \rightarrow D l \overlineν$ and $\overline{B} \rightarrow D^* l \overlineν$ agree well with experiment. Predictions for the decays $Λ_b \rightarrow Λ_c l \overlineν$, $\overline{B}_s \rightarrow D_s l \overlineν$ and $\overline{B}_s \rightarrow D^*_s l \overlineν$ are given and discussed.
We discuss contributions of chiral bosons to baryon spectra in the MIT bag model. It is believed that within hadrons, chiral bosons are degrees of freedom which are independent of gluons to provide strong interactions between quarks. In the original MIT bag model, only interaction mediated by gluon exchanges was considered, by contrast, in this work we take into account the interaction mediated by the exchanges of chiral bosons $σ$ and $π^{(\pm,0)}$. Then following the standard approach, we minimize the effective hamiltonian which includes both the contributions from gluon and chiral-boson exc…
The masses of the $D_{sj}^\ast$(2317)and $D_{sj}^\ast$(2463) were found in the MIT bag model in a reasonable agreement with the experimental values. The spectrum of ${0^\pm,1^\pm}$ for $D$ and $B$ mesons is presented. The equalities between the mass splittings $(1^+ - 1^-)(c\bar{q})\approx (1^+ - 1^-)(c\bar{s})$ and $(0^+ - 0^-)(c\bar{q})\approx (0^+ - 0^-)(c\bar{s})$, where $q=u, d$ are confirmed despite of the fact that $SU(3)_L\times SU(3)_R$ chiral symmetry is broken by the non-zero strange quark mass.
We present the results for the Generalized Transverse Momentum Distribution related to quark Orbital Angular Momentum, {\it i.e.} $F_{14}$, in the MIT bag model. This model has been modified to include the Peierls--Yoccoz projection to restore translational invariance. Such a modification allows to fulfill more satisfactorily basic sum rules, that would otherwise be less elegantly carried out with the original version. Using the same model, we have calculated the twist-$3$ GPD that corresponds to Orbital Angular Momentum à la Ji, through the Penttinen--Polyakov--Shuvaev--Strikman sum rule. Rec…
In this work we study different variations of the MIT bag model. We start with the so called non-ideal bag model and discuss it in detail. Then we implement a vector interaction in the MIT bag model that simulates a meson exchange interaction and fix the quark-meson coupling constants via symmetry group theory. At the end we propose an original model, inspired by the Boguta-Bodmer models, which allows us to control the repulsion interaction at high densities. For each version of the model we obtain a stability window as predicted by the Bodmer-Witten conjecture and discuss its thermodynamic co…
The modified quark-meson coupling model, which features a density dependent bag constant and bag radius in nuclear matter, is checked against the EMC effect within the framework of dynamical rescaling. Our emphasis is on the change in the average bag radius in nuclei, as evaluated in a local density approximation, and its implication for the rescaling parameter. We find that when the bag constant in nuclear matter is significantly reduced from its free-space value, the resulting rescaling parameter is in good agreement with that required to explain the observed depletion of the structure funct…
The stability of magnetized strange quark matter (MSQM) is studied in the MIT bag model with the density dependent bag pressure. In the consistent thermodynamic description of MSQM, the quark chemical potentials, the total thermodynamic potential and the anisotropic pressure acquire the corresponding additional term proportional to the density derivative of the bag pressure. The model parameter space is determined, for which MSQM is absolutely stable, i.e., its energy per baryon is less than that of the most stable $^{56}$Fe nucleus under the zero external pressure and vanishing temperature. I…
In this work we revisit the MIT bag model to describe quark matter within both the usual Fermi-Dirac and the Tsallis statistics. We verify the effects of the non-additivity of the latter by analysing two different pictures: the first order phase transition of the QCD phase diagram and stellar matter properties. While, the QCD phase diagram is visually affected by the Tsallis statistics, the resulting effects on quark star macroscopic properties are barely noticed.
At $ T = 0 $ the surface tension $ σ^{1/3} $ in the MIT bag model for a single hadron is known to be negligible as compared to the bag pressure $ B^{1/4}$. We show that at finite temperature it has a substantial value of 50 - 70 MeV which also differ from hadron to hadron. We also find that the dynamics of the Quark-Gluon Plasma is such that the creation of hybrids $(s\bar{s}g)$ with massive quarks will predominate over the creation of $ (s\bar{s}) $ mesons.
We study the hadron-quark phase transition in the interior of neutron stars (NS). For the hadronic sector, we use a microscopic equation of state (EOS) involving nucleons and hyperons derived within the Brueckner-Bethe-Goldstone many-body theory, with realistic two-body and three-body forces. For the description of quark matter, we employ both the MIT bag model with a density dependent bag constant, and the color dielectric model. We calculate the structure of NS interiors with the EOS comprising both phases, and we find that the NS maximum masses are never larger than 1.7 solar masses, no mat…
We study the effect of a very strong homogeneous magnetic field B on the thermal deconfinement transition within the simplest phenomenological approach: the MIT bag pressure for the quark- gluon plasma and a gas of pions for the hadronic sector. Even though the model is known to be crude in numerical precision and misses the correct nature of the (crossover) transition, it provides a simple setup for the discussion of some subtleties of vacuum and thermal contributions in each phase, and should provide a reasonable qualitative description of the critical temperature in the presence of B. We fi…
Recent observations of massive pulsars having masses of the order of two solar mass pose a new challenge for compact objects such as hybrid stars and neutron stars. Extensions of the bag model and the Nambu-Jona-Lasino model have been used to model these stars to get higher mass stars. Quark matter has been predicted in the cores of these massive stars. In this work we show that an extension of the bag model, with a chemical potential dependent bag parameter can lead to an isentropic phase transition in the core of the neutron star. Our model shows that an EoS having all three quarks $u$, $d$ …
In the present work we use the modified versions of the MIT bag model, on which both a vector field and a self-interacting term are introduced, to obtain hot quark matter and to investigate the QCD phase diagram. We first analyze two-flavored quark matter constrained to both the freeze-out and the liquid-gas phase transition at the hadronic phase. Later, three-flavored quark matter subject to $β$ equilibrium and charge neutrality is used to compute quark star macroscopic properties, which are confronted with recent observational massive and canonical star radius results. Finally, a comparison …
If instantons are introduced into the MIT bag model in such a way that bag radii are allowed to vary, the MIT bag interior can accommodate instanton density which is by an order of magnitude larger than in the case when the radii are fixed (although it is still significantly smaller than in the nonperturbative QCD vacuum). The instanton contribution to baryon mass shifts is also correspondingly larger. The instanton-induced part of the scalar strangeness of the nucleon MIT bag is an order of magnitude larger than found previously, within the linearized approximation. The decrease of the model …
We consider the prompt photon production in pp collisions using, within the framework of perturbative QCD, a non-Gaussian distribution for the transverse momentum distribution of the partons inside the proton. Our description adopts the widely used in the literature factorization of the partonic momentum distribution into longitudinal and transverse components. It is argued that the non-Gaussian distribution of the intrinsic transverse momenta of the partons is dictated by the asymptotic freedom as well as the 3D confinement of the partons in the proton. To make this association more transpare…
The typical transverse momentum of a quark in the proton is a basic property of any QCD based model of nucleon structure. However, calculations in phenomenological models typically give rather small values of transverse momenta, which are difficult to reconcile with the larger values observed in high energy experiments such as Drell-Yan reactions and Semi-inclusive deep inelastic scattering. In this letter we calculate the leading twist transverse momentum dependent distribution functions (TMDs) using a generalization of the Adelaide group's relativistic formalism that has previously given goo…
Neutron star due to their high interior matter density are expected to be composed of a quark core, a mixed quark-hadron matter, and a layer of hadronic matter. Thus, in this paper, we compute the equation of state of these parts of neutron star to evaluate its structure properties. We use two models for describing EOS of quark matter, NJL and MIT bag models, and employ three approaches in this work. A density dependent bag constant satisfy the quark confinement in the simple MIT bag model. We also study the interaction behavior of quarks, firstly one gluon exchange within MIT bag model and th…
In this work, we evaluate the energy spectra of baryons which consist of two heavy and one light quarks in the MIT bag model. The two heavy quarks constitute a heavy scalar or axial vector diquark. Concretely, we calculate the spectra of $|q(QQ')>_{1/2}$ and $|q(QQ')>_{3/2}$ where $Q$ and $Q'$ stand for $b$ and/or $c$ quarks. Especially, for $|q(bc)>_{1/2}$ there can be a mixing between $|q(bc)_0>_{1/2}$ and $|q(bc)_1>_{1/2}$ where the subscripts 0 and 1 refer to the spin state of the diquark (bc), the mixing is not calculable in the framework of quantum mechanics (QM) as the potential model i…
The quark-meson coupling model for nuclear matter, which describes nuclear matter as non-overlapping MIT bags bound by the self-consistent exchange of scalar and vector mesons, is modified by introducing medium modification of the bag constant. We model the density dependence of the bag constant in two different ways: one invokes a direct coupling of the bag constant to the scalar meson field, and the other relates the bag constant to the in-medium nucleon mass. Both models feature a decreasing bag constant with increasing density. We find that when the bag constant is significantly reduced in…
We calculate the two-body interaction of spherical hadronic bubbles immersed in a gluon plasma at temperatures above the phase transition. Modeling the bubbles with the MIT bag we find that the two body potential is repulsive for all bubble-bubble distances considered. This implies that a static configuration of spherical hadronic bubbles in a gluon background is consistent with the bag model of QCD.
The minimum energy per baryon number of strange quark matter is studied, as a function of the strangeness fraction, in the MIT bag model and in two different versions of the Color Dielectric Model: a comparison is made with the hyperon masses having the same strangeness fraction, and coherently calculated within both models. Calculations are carried out in mean field approximation, with one gluon exchange corrections. The results allow to discuss the model dependence of the stability of strangelets: they can be stable in the MIT bag model and in the double minimum version of the Color Dielectr…
Low-baryon number lumps of strange quark matter, strangelets, are presently searched for in ultra-relativistic heavy-ion experiments at CERN and Brookhaven. This paper gives an overview of the physical properties of strangelets with emphasis on experimental signatures such as mass and charge. Direct solutions of the Dirac equation with MIT bag model boundary conditions are applied and compared to calculations based on a smoothed density of states, as well as to simple mass-formulae based on the MIT bag. Most strangelet properties can be understood within an approximation including bulk, surfac…
Some odd characteristics are observed in the single particle distributions obtained from $ He + Li $ interactions at $ 4.5 AGeV/c $ momenta which are explained as the manifestation of a new mechanism of strangeness production via dibaryonic de-excitations. A signature of the formation of hadronic and baryonic clusters is also reported. The di-pionic signals of the dibaryonic orbital de-excitations are analyzed in the frame of the MIT - bag Model and a Monte Carlo simulation.The role played by the dibaryonic resonances in relativistic nuclear collisions could be a significant one. Key words: Re…
We perform an extensive analysis of neutrino diffusion in quark matter within the MIT bag model at arbitrary temperature and degeneracy. We examine in detail the contribution of each of the relevant weak interaction processes to the total neutrino opacity and evaluate the effect of the strange quark mass, the bag constant, and the QCD perturbative corrections to the MIT bag model. We also investigate the anisotropic contribution to the neutrino distribution function in scatterings, the mean energy transfer and the mean scattering angle. The density and temperature dependence of the diffusion c…
Roles of instanton induced interactions (III) in the masses of pentaquark baryons, Theta^+ (J=1/2 and 3/2) and Xi^{--}, and a dibaryon, H, are discussed using the MIT bag model in the negative parity case. It is shown that the two-body terms in III give a strong attraction mainly due to the increase of the number of pairs in multi-quark systems. In contrast, the three-body u-d-s interaction is repulsive. It is found that III lowers the mass of Theta^+ as much as 100 MeV from the mass predicted by the bag model without III.
