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Thomas Gutsche

Publications and source records attributed to Thomas Gutsche.

At least 73 records · Page 4Linked to original sources
arXiv2014

Selected strong decay modes of Y(4260)

In present work the Y(4260) resonance is considered as a weakly bound state of a pseudoscalar D and an axial D1 charm meson. We consider the two-body decay Y(4260) -> Zc(3900) + pi where Zc(3900) is treated as hadron molecule as well. Moreover we compute the Y(4260) decay modes J/psi pi(+) pi(-), recently observed by the BESIII Collaboration, and psi(2S) pi(+) pi(-). In the last process both the contact diagram with D D1 -> psi(nS) pi(+) pi(-) and the resonance diagram with D D1 -> Zc(3900) + pi -> psi(nS) pi(+) pi(-) are taken into account.

hep-ph↗
arXiv2014

Electromagnetic structure of the nucleon and the Roper resonance in a light-front quark approach

A relativistic light-front quark model is used to describe both the elastic nucleon and nucleon-Roper transition form factors in a large Q2 range, up to 35 GeV2 for the elastic and up to 12 GeV2 for the resonance case. Relativistic three-quark configurations satisfying the Pauli exclusion principle on the light-front are used for the derivation of the current matrix elements. The Roper resonance is considered as a mixed state of a three-quark core configuration and a molecular N+sigma hadron component. Based on this ansatz we obtain a realistic description of both processes, elastic and inelastic, and show that existing experimental data are indicative of a composite structure of the Roper resonance.

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arXiv2013

The scalar mesons in multi-channel $ππ$ scattering and decays of the $ψ$ and $Υ$ families

The $f_0$ mesons are studied in a combined analysis of data on the isoscalar S-wave processes $ππ\toππ,K\overline{K},ηη$ and on decays $J/ψ\toϕ(ππ, K\overline{K})$, $ψ(2S)\to J/ψ(ππ)$, and $Υ(2S)\toΥ(1S)ππ$ from the Argus, Crystal Ball, CLEO, CUSB, DM2, Mark II, Mark III, and BES II collaborations. The method of analysis, based on analyticity and unitarity and using an uniformization procedure, is set forth with some details. Some spectroscopic implications from results of the analysis are discussed.

hep-ph↗
arXiv2013

Polarization effects in the cascade decay Lambda_b -> Lambda(-> p pi-) + J/psi(-> l+ l-) in the covariant confined quark model

We calculate the invariant and helicity amplitudes for the nonleptonic decay Lambda_b -> Lambda + J/psi, psi(2S) in the covariant confined quark model. We discuss joint angular decay distributions in the cascade decay Lambda_b -> Lambda(-> p pi-) + J/psi, psi(2S) (-> l+ l-) and calculate some of the asymmetry parameters that characterize the joint angular decay distribution. We confirm expectations from the naive quark model that the transitions into the lambda_Lambda=1/2 helicity states of the daughter baryon Lambda are strongly suppressed leading to a near maximal negative polarization of the Lambda. For the same reason the azimuthal correlation between the two decay planes spanned by (p pi-) and (l+ l-) is negligibly small. We provide form factor results for the whole accessible q2-range. Our results are close to lattice results at minimum recoil and light-cone sum rule results at maximum recoil. A new feature of our analysis is that we include lepton mass effects in the calculation which allows us to also describe the cascade decay Lambda_b -> Lambda(-> p pi-) + psi(2S)(-> tau+ tau-).

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arXiv2013

Strong decays of molecular states Zc(+) and Zc'(+)

The two newly observed hidden-charm mesons Zc(+)[3900] and a possible partner state Zc'(+)[3950] with quantum numbers J(P) = 1(+) are considered as hadronic molecules composed of bar(D)D* and bar(D)* D*, respectively. We give predictions for the decay widths of the strong two-body transitions Zc(+) -> H + pi(+) and Zc' -> H + pi(+) with H = Psi(nS), hc(mP) in a phenomenological Lagrangian approach.

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arXiv2013

Light-front quark model consistent with Drell-Yan-West duality and quark counting rules

We propose a phenomenological light-front wave function for hadrons with arbitrary twist-dimension (mesons, baryons and multiquark states), which gives the correct scaling behavior of structure functions (parton distributions) and form factors for pions and nucleons. For other hadronic states the proposed wave function produces form factors consistent with quark counting rules, and gives predictions for structure functions (parton distributions). As an application we build a light-front quark model for nucleons based on the proposed wave function.

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arXiv2013

Rare baryon decays Lambda_b -> Lambda l+ l- (l=e, mu, tau) and Lambda_b -> Lambda gamma : Differential and total rates, lepton- and hadron-side forward-backward asymmetries

Using the covariant constituent quark model previously developed by us we calculate the differential rate and the forward-backward asymmetries on the lepton and hadron side for the rare baryon decays Lambda_b -> Lambda l+ l- (l=e, mu, tau) and Lambda_b -> Lambda gamma. We use helicity methods to write down a three-fold joint angular decay distribution for the cascade decay Lambda_b -> Lambda (-> p pi-) + J_eff (-> l+ l-). Through appropriate angular integrations we obtain expressions for the rates, the lepton-side forward-backward (FB) asymmetry and the polarization of the daughter baryon Lambda leading to a hadron-side forward-backward asymmetry. We present numerical results on these observables using the covariant quark model and compare our results to the results of other calculations that have appeared in the literature.

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arXiv2013

Limits on Lepton Flavor Violation from μ-e-conversion

We revisit the status of Lepton Flavor Violating (LFV) μe qq contact interactions from the view point of μ- e -conversion in nuclei. We consider their contribution to this LFV process via the two mechanisms on the hadronic level: direct nucleon and meson exchange ones. In the former case the quarks are embedded directly into the nucleons while in the latter in mesons which then interact with nucleons in a nucleus. We revise and in some cases reevaluate the hadronic parameters relevant for both mechanisms and calculate the contribution of the above mentioned contact interactions in coherent μ- e -conversion in various nuclei. Then we update the existing upper bounds and also derive new ones for the scales of the μe qq contact interactions from the experimental limits on the capture rates of μ- e -conversion. We compare these limits with the ones derived in the literature from other LFV processes and comment on the prospects of LHC searches related to the contact μe qq interactions.

hep-ph↗
arXiv2013

Nucleon resonances in AdS/QCD

We describe the electroproduction of the N(1440) Roper resonance in soft-wall AdS/QCD. The Roper resonance is identified as the first radially excited state of the nucleon, where higher-Fock states in addition to the three-quark component are included. The main conclusion is that the leading 3q component plays the dominant role in the description of electroproduction properties of this resonance: form factors, helicity amplitudes and charge densities. The obtained results are in good agreement with the recent results of the CLAS Collaboration at JLab.

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arXiv2013

Chiral Symmetry Breaking and Meson Wave Functions in Soft-Wall AdS/QCD

We consider mesons composed of light and heavy quarks and discuss the construction of the corresponding meson wave functions in soft-wall AdS/QCD. We specifically take care that constraints imposed by chiral symmetry breaking and by the heavy quark limit are fulfilled. The main results are: i) the wave functions of light mesons have a nontrivial dependence on the current quark mass, which gives rise to a mass spectrum consistent with the one including explicit breaking of chiral symmetry; ii) the wave functions of heavy-light mesons generate their correct mass spectrum, the mass splittings of vector and pseudoscalar states, and the correct scaling of leptonic decay constants f(Q \bar q) \sim 1/sqrt(mQ); iii) the wave functions of heavy quarkonia produce their correct mass spectrum and lead to a scaling behaviour of the leptonic decay constants f(Q \bar Q) \sim sqrt(mQ) and f(c \bar b) \sim mc/sqrt(mb) at mc << mb, consistent with potential models and QCD sum rules.

hep-ph↗
arXiv2012

Decays of Zb(+) and Zb'(+) as hadronic molecules

The two newly observed hidden-bottom mesons Zb(10610) and Zb'(10650) with quantum numbers J(P) = 1(+) are considered as hadronic molecules composed of BB(*) and B(*)B(*), respectively. We give predictions for the widths of the strong two-body decays Zb(+) to Upsilon(nS) + pi(+) and Zb'(+) to Upsilon(nS) + pi(+) in a phenomenological Lagrangian approach.

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arXiv2012

Nucleon structure including high Fock states in AdS/QCD

We present a detailed analysis of nucleon electromagnetic and axial form factors in a holographic soft-wall model. This approach is based on an action which describes hadrons with broken conformal invariance and incorporates confinement through the presence of a background dilaton field.For Nc=3 we describe the nucleon structure in a superposition of a three valence quark state with high Fock states including an adjustable number of partons (quarks, antiquarks and gluons) via studying the dynamics of 5D fermion fields of different scaling dimension in anti-de Sitter (ADS) space. According to the gauge/gravity duality the 5D fermion fields of different scaling dimension correspond to the Fock state components with a specific number of partons. In the present application we restrict to the contribution of 3, 4 and 5 parton components in the nucleon Fock state. With a minimal number of free parameters (dilaton scale parameter, mixing parameters of partial contributions of Fock states, coupling constants in the effective Lagrangian) we achieve a reasonable agreement with data for the nucleon form factors.

hep-ph↗
arXiv2012

Light baryons and their electromagnetic interactions in the covariant constituent quark model

We extend the confined covariant constituent quark model that was previously developed by us for mesons to the baryon sector. In our numerical calculation we use the same values for the constituent quark masses and the infrared cutoff as have been previously used in the meson sector. In a first application we describe the static properties of the proton and neutron, and the $Λ$-hyperon (magnetic moments and charge radii) and the behavior of the nucleon form factors at low momentum transfers. We discuss in some detail the conservation of gauge invariance of the electromagnetic transition matrix elements in the presence of a nonlocal coupling of the baryons to the three constituent quark fields.

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arXiv2012

Generalized parton distributions in an AdS/QCD hard-wall model

We use a matching procedure of sum rules relating the electromagnetic form factors to generalized parton distributions (GPDs) and AdS modes. In this way, in the framework of an AdS/QCD hard-wall model, the helicity-independent GPDs of quarks for the nucleon in the zero skewness case are calculated.

hep-ph↗
arXiv2012

Dilaton in a soft-wall holographic approach to mesons and baryons

We discuss a holographic soft-wall model developed for the description of mesons and baryons with adjustable quantum numbers n, J, L, S. This approach is based on an action which describes hadrons with broken conformal invariance and which incorporates confinement through the presence of a background dilaton field. We show that in the case of the bound-state problem (hadronic mass spectrum) two versions of the model with a positive and negative dilaton profile are equivalent to each other by a special transformation of the bulk field. We also comment on recent works which discuss the dilaton sign in the context of soft-wall approaches.

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arXiv2011

Hadron properties in AdS/QCD

We discuss a holographic soft-wall model developed for the description of mesons and baryons with adjustable quantum numbers n, J, L, S. This approach is based on an action which describes hadrons with broken conformal invariance and which incorporates confinement through the presence of a background dilaton field. Results obtained for heavy-light meson masses and decay constants are consistent with predictions of HQET. In the baryon sector applications to the baryon masses, nucleon electromagnetic form factors and generalized parton distributions are discussed.

hep-ph↗
arXiv2011

Hyperon forward spin polarizabilty gamma0

We present the results of a systematic leading order calculation of hyperon Compton scattering and extract the forward spin polarizability gamma0 of hyperons within the framework of SU(3) heavy baryon chiral perturbation theory (HBChPT). The results obtained for gamma0 in the case of nucleons agree with that of the known results of SU(2) HBChPT when kaon loops are not considered.

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