arXiv subjects

Thomas Gutsche

Publications and source records attributed to Thomas Gutsche.

At least 37 records · Page 2Linked to original sources

arXiv2018

Effect of the $K\overline{K}$ and $ηη$ channels and interference phenomena in the two-pion and $K\overline{K}$ transitions of charmonia and bottomonia

It is shown that the basic shape of dipion and $K\overline{K}$ mass spectra in decays $J/ψ\toϕ(ππ,K\overline{K})$, $ψ(2S)\to J/ψ\,ππ$, $Y(4260)\to J/ϕ~ππ$ and in the two-pion transitions of bottomonia states are explained by an unified mechanism based on the contribution of the $ππ$, $K\overline{K}$ and $ηη$ coupled channels including their interference. The role of the individual $f_0$ resonances in making up the shape of the dipion mass distributions in the charmonia and bottomonia decays is considered.

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arXiv2018

Relating CP-violating decays to the neutron EDM

We use the present upper bound on the neutron electric dipole moment to give an estimate for the upper limit of the CP-violating couplings of the $η(η')$ meson to the neutron. Using this result, we derive constraints on the CP-violating two-pion decays of the $η(η')$. Our results are relevant for the running and planned GlueX and LHCb measurements of rare meson decays.

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arXiv2017

Electromagnetic structure of nucleon and Roper in soft-wall AdS/QCD

We present an improved study of the electromagnetic form factors of the nucleon and of the Roper-nucleon transition using an extended version of the effective action of soft-wall AdS/QCD. We include novel contribution from additional non-minimal terms, which do not renormalize the charge and do not change the normalization of the corresponding form factors, but the inclusion of these terms results in an important contribution to the momentum dependence of the form factors and helicity amplitudes.

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arXiv2017

Test of the multiquark structure of $a_1(1420)$ in strong two-body decays

We present an analysis of strong two-body decays of the $a_1(1420)$ with $J^{PC} = 1^{++}$ recently reported by the COMPASS Collaboration at CERN. Following the interpretation of the COMPASS Collaboration that the $a_1$ is an unusual state with a four-quark $q\bar q s \bar s$ structure we consider two possible configurations for this state --- hadronic molecular and color diquark-antidiquark structures. We find that the dominant decay mode of the $a_1$ is the decay into $K$ and $K^*$. In particular, we calculate that the four decay modes $a_1 \to VP$ with $VP = K^{*\pm}K^\mp$, $K^{*0}\bar K^0$, $\bar K^{*0}K^0$ together give a dominant contribution to the measured total width of about 150 MeV. The observational mode $a_1 \to f_0(980) + π^0$ is significantly suppressed by one order of magnitude.

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arXiv2017

Role of QCD compositeness in the production of scalar and tensor mesons through single-photon annihilation $e^+ e^- \to γ^* \to γS(T)$

We study the exclusive production of scalar $S = 0^{++}$ and tensor $T = 2^{++}$ mesons through single-photon annihilation $e^+ e^- \to γ^* \to γS(T)$. Using QCD compositeness of the involved hadrons considered as quark-antiquark systems, the prediction for the scaling of the differential cross sections of these processes is $dσ/dt \sim 1/s^3$ at large $s$. We further derive the scaling of the $γ^\ast \to γS$ and $γ^\ast \to γT$ transition form factors: $F_{γ^\astγS}(s) \sim 1/s$ and $F_{γ^\astγT}(s) \sim 1/s^2$. Results for the respective cross sections of the scalar and tensor meson production are presented. Note, when scalar and tensor mesons are considered as tetraquark systems of two tightly bound color diquarks, corresponding to them transition form factors and differential cross sections have the same falloffs as in case of quark-antiquark picture. For other tetraquark or two-hadron molecules configurations the transition form factors $F_{γ^\astγS(T)}(s)$ and the differential cross section $dσ/dt$ have additional $1/s$ and $1/s^2$ falloffs, respectively.

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arXiv2017

Selected strong decays of $η(2225)$ and $ϕ(2170)$ as $Λ\barΛ$ bound states

The strong decays of the two resonances $η(2225)$ and $ϕ(2170)$ are discussed for selected decay channels. The two resonances are considered as the $Λ\barΛ$ bound states in the molecular scenario. The phenomenological hadronic molecular approach is employed for the calculation of respective decay modes using effective Lagrangians. Our results show that the decay modes $η(2225)\to K^*K$ and $ϕ(2175) \to KK$ dominate over the partial decay widths of $η(2275)\to VV (ϕϕ, ωω, K^*K^*)$ and $ϕ(2175)\to VS (ωσ, K^*K^*_0(800), ϕf_0(980))$ due to phase space and couplings.

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arXiv2017

Role of scalar mesons in the beam asymmetry of $p \bar p$ and $Λ\bar Λ$ photoproduction at JLab

We suggest a description of the beam asymmetry in $p \bar p$ and $Λ\bar Λ$ photoproduction off the proton $\vecγ+ p \to p \bar p + p$ and $\vecγ+ p \to Λ\barΛ+ p$, takes into account the contribution of the scalar mesons $f_0(1370)$, $f_0(1500)$, and $f_0(1710)$. These scalars are considered as mixed states of a glueball and nonstrange and strange quarkonia in the framework based on the use of effective hadronic Lagrangians. Present results can be used to guide the possible search for this reaction by the GlueX Collaboration at JLab. Also, we did an estimate of contribution of heavier scalar meson states $f_0(2020)$, $f_0(2100)$, and $f_0(2200)$.

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arXiv2017

Decay chain information on the newly discovered double charm baryon state $Ξ_{cc}^{++}$

We interprete the new double charm baryon state found by the LHCb Collaboration in the invariant mass distribution of the set of final state particles $(Λ_c^+\,K^-\,π^+\,π^+)$ as being at the origin of the decay chain $Ξ_{cc}^{++} \to Σ_c^{++} (\to Λ_c^+ π^+) +\bar K^{*0} (\to K^- π^+)$. The nonleptonic decay $Ξ_{cc}^{++} \to Σ_c^{++} + \bar K^{*0}$ belongs to a class of decays where the quark flavor composition is such that the decay proceeds solely via the factorizing contribution precluding a contamination from internal $W$-exchange. We use the covariant confined quark model previously developed by us to calculate the four helicity amplitudes that describe the dynamics of the transition $Ξ_{cc}^{++} \to Σ_c^{++}$ induced by the effective $(c \to u)$ current. We then proceed to calculate the rate of the decay as well as the polarization of the $Σ_c^{++}$ and $Λ_c^+$ baryons and the longitudinal/transverse composition of the $\bar K^{*0}$. We estimate the decay $Ξ_{cc}^{++} \to Σ_c^{++} \bar K^{*0}$ to have a branching rate of $B(Ξ_{cc}^{++} \to Σ_c^{++} \bar K^{*0}) \sim 10.5 \%$. As a byproduct of our investigation we have also analyzed the decay $Ξ_{cc}^{++} \to Σ_c^{++} \bar K^{0}$ for which we find a branching ratio of $B(Ξ_{cc}^{++} \to Σ_c^{++} \bar K^0) \sim 2.5 \%$.

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arXiv2017

Theoretical description of the decays $Λ_b \to Λ^{(\ast)}(\frac12^\pm,\frac32^\pm) + J/ψ$

We calculate the invariant and helicity amplitudes for the transitions $Λ_b~\to~Λ^{(\ast)}(J^P)~+~J/ψ$ where the $Λ^{(\ast)}(J^P)$ are $Λ(sud)$-type ground and excited states with $J^P$ quantum numbers $J^P=\frac12^{\pm},\frac32^{\pm}$. The calculations are performed in the framework of a covariant confined quark model previously developed by us. We find that the values of the helicity amplitudes for the $Λ^\ast(1520,\,\frac32^-)$ and the $Λ^\ast(1890,\,\frac32^+)$ are suppressed compared with those for the ground state $Λ(1116,\,\frac12^+)$ and the excited state $Λ^\ast(1405,\,\frac12^-)$. This analysis is important for the identification of the hidden charm pentaquark states $P_c^+(4380)$ and $P_c^+(4450)$ which were discovered in the decay chain $Λ_b^0~\to~P_c^+(~\to~p~J/ψ)~+~K^- $ because the cascade decay chain $Λ_b~\to~Λ^\ast(\frac32^\pm)(~\to~pK^-)~+~J/ψ$ involves the same final state.

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arXiv2017

$Z_b(10610)$ and $Z_b'(10650)$ decays in a covariant quark model

We present a calculation of the strong decays of the exotic states $Z_b(10610)$ and $Z_b'(10650)$ using a covariant quark model. We use a molecular-type four-quark current for the coupling of the $Z_b(10610)$ and $Z_b'(10650)$ to the constituent heavy and light quarks.

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arXiv2017

Tetraquarks in holographic QCD

Using a soft-wall AdS/QCD approach we derive the Schrödinger-type equation of motion for the tetraquark wave function, which is dual to the dimension-4 AdS bulk profile. The latter coincides with the number of constituents in the leading Fock state of the tetraquark. The obtained equation of motion is solved analytically, providing predictions for both the tetraquark wave function and its mass. A low mass limit for possible tetraquark states is given by $M \ge 2 κ= 1$ GeV, where $κ= 0.5$ GeV is the typical value of the scale parameter in soft-wall AdS/QCD. We confirm results of the COMPASS Collaboration recently reported on the discovery of the $a_1(1414)$ state, interpreted as a tetraquark state composed of light quarks and having $J^{PC} = 1^{++}$. Our prediction for the mass of this state, $M_{a_1} = \sqrt{2}$ GeV $\simeq 1.414$ GeV, is in good agreement with the COMPASS result $M_{a_1} = 1.414^{+0.015}_{-0.013}$ GeV. Next we included finite quark mass effects, which are essential for the tetraquark states involving heavy quarks.

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arXiv2017

Nucleon parton distributions in a light-front quark model

Continuing with our analysis of parton distributions in the nucleon, we extend our light-front quark model in order to obtain both the helicity independent and helicity dependent parton distributions, analytically matching the results of global fits at the initial scale $μ\sim 1$ GeV, and which also contain the correct Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution. We also calculate the transverse parton, Wigner and Husimi distributions from a unified point of view, using our light-front wave functions and expressing them in terms of the parton distributions $q_v(x)$ and $δq_v(x)$. Our results are very relevant for the current and future program of the COMPASS experiment at SPS (CERN).

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arXiv2016

Nucleon tensor form factors in a relativistic confined quark model

We present results for the isotriplet and isosinglet tensor form factors of the nucleon in the relativistic confined quark model. The model allows us to calculate not only their normalizations at $Q^2=0$ and the related tensor charges, but also the full $Q^2$-dependence. Our results are compared to existing data and predictions of other theoretical approaches. We stress the importance of these form factors for the phenomenology of physics beyond the Standard Model.

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arXiv2016

CP-violating decays of the pseudoscalars eta and eta' and their connection to the electric dipole moment of the neutron

Using the present upper bound on the neutron electric dipole moment, we give an estimate for the upper limit of the CP-violating couplings of the eta(eta') to the nucleon. Using this result, we then derive constraints on the CP-violating eta(eta')-pi-pi couplings, which define the two-pion CP-violating decays of the eta and eta' mesons. Our results are relevant for the running and planned measurements of rare decays of the eta and eta' mesons by the GlueX Collaboration at JLab and the LHCb Collaboration at CERN.

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arXiv2016

Isospin-violating strong decays of scalar single-heavy tetraquarks

We present a study of the isospin-violating one-pion strong decays of single heavy tetraquarks $X_Q = X(s q \bar q \bar Q)$, $Q=c, b$, and $q=u, d$ with spin-parity $J^P = 0^+$. We assume that the tetraquarks have the configuration of a color diquark and a antidiquark. Three mechanisms of isospin violation can contribute to the decay rate: (1) mixing of the $X(s u \bar u \bar Q)$ and $X(s d \bar d \bar Q)$ tetraquark currents, (2) an explicit $m_d-m_u$ quark mass difference in the quark diagrams describing the corresponding decay transitions and (3) $π^0-η$ mixing in the final state. Our main results are: (1) It is quite likely that the investigated tetraquark states are isosinglet states with a small admixture of an isotriplet component; (2) The first isospin-breaking mechanism affects the decay rater more significantly than the others; (3) Our calculations contain a size parameter $Λ_{X_Q}$, characterizing the distribution of the quarks in the tetraquark state $X_Q$. Absolute decay rates depend very much on the choice of $Λ_{X_Q}$, varied from 1 to 2 GeV, reflecting the compactness of the multiquark system.

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arXiv2016

Four-quark structure of Zc(3900), Z(4430) and Xb(5568) states

We examine the four-quark structure of the recently discovered charged $Z_c(3900)$, $Z(4430)$, and $X_b(5568)$ states. We calculate the widths of the strong decays $Z_c^+ \to J/ψπ^+$ ($η_cρ^+$, $\bar D^0D^{\ast\,+}$, $\bar D^{\ast\,0}D^+$), $Z(4430)^+ \to J/ψπ^+$ ($ψ(2s) π^+$), and $X^+_b\to B_sπ^+$ within a covariant quark model previously developed by us. We find that the tetraquark-type current widely used in the literature for the $Z_c(3900)$ leads to a significant suppression of the $\bar D D^\ast$ and $\bar D^\ast D$ modes. Contrary to this a molecular-type current provides an enhancement by a factor of 6-7 for the $\bar D D^\ast$ modes compared with the $Z_c^+\to J/ψπ^+$, $η_cρ^+$ modes in agreement with recent experimental data from the BESIII Collaboration. In case of the $Z(4430)$ state we test a sensitivity of the ratio $R_Z$ of the $Z(4430)^+ \to ψ(2s) π^+$ and $Z(4430)^+ \to J/ψπ^+$ decay rates to a choice of the size parameter $Λ_{Z(4430)}$ of the $Z(4430)$. Using upper constraint for the sum of these two modes deduced from the LHCb Collaboration data we find that $R_Z$ varies from 4.64 to 4.08 when $Λ_{Z(4430)}$ changes from 2.2 to 3.2 GeV. Also we make the prediction for the $Z(4430)^+ \to D^{\ast\,+} \bar D^{\ast\,0}$ decay rate.

hep-ph↗

arXiv2016

Search for the glueball content of hadrons in gamma p interactions at GlueX

We suggest a theoretical framework for the description of double photon and proton-antiproton photoproduction off the proton gamma + p -> 2 gamma + p and gamma + p -> antip + p + p which takes into account the contribution of the scalar mesons f0(1370), f0(1500) and f0(1710). These scalars are considered as mixed states of a glueball and nonstrange and strange quarkonia. Our framework is based on the use of effective hadronic Lagrangians that phenomenologically take into account two-gluon exchange effects governing the gamma + p -> 2 gamma + p and gamma + p -> antip + p + p processes. Present results can be used to guide the possible search for these reactions by the GlueX Collaboration at JLab.

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arXiv2016

Deuteron electromagnetic structure functions and polarization properties in soft-wall AdS/QCD

We apply a soft-wall AdS/QCD approach to the description of deuteron structure functions and tensor polarized properties. Present work is a completion of our previous study on electromagnetic form factors. By the appropriate choice of two couplings in the effective action we are able to reproduce both the form factors and structure functions in full consistency with model-independent constraints set by perturbative QCD. Our framework is based on a five-dimensional action in AdS space formulated in terms of vector fields dual to the deuteron and the electromagnetic fields. The AdS fields depend on four Minkowski and one holographic coordinate $z$. The scale dependence of the form factors and structure functions is consistent with quark counting rules implying the $1/Q^{10}$ behavior of the charge form factor $G_C(Q^2)$, structure functions $A(Q^2)$ and $B(Q^2)$, and the $1/Q^{12}$ behavior of the magnetic $G_M(Q^2)$ and quadrupole $G_Q(Q^2)$ form factors.

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