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George Rupp

Publications and source records attributed to George Rupp.

At least 55 records · Page 3Linked to original sources
arXiv2011

Towards Meson Spectroscopy Instead of Bump Hunting

Mesonic resonances are generally observed in data as narrow, moderately broad, or wide peaks in scattering or production processes. In the eyes of nearly all experimentalists, any suchlike bump is a true resonance as soon as its statistical significance exceeds certain minimal values. However, this simple point of view ignores possible effects from competing hadronic channels and the opening of the corresponding thresholds. On the other hand, most theoretical hadron-model builders consider mesons merely bound states of a quark and an antiquark, or of more exotic combinations sometimes involving valence gluons as well. Also the latter description is much too naive, since considerable mass shifts or even the dynamical generation of extra states due to unquenching are equally ignored. In the present paper, a largely empirical yet very successful approach to meson spectroscopy is revisited, in which all the above phenomena can be accounted for non-perturbatively, with concrete examples of some enigmatic mesonic states described in detail. First, the X(4260) charmonium enhancement is argued to be a non-resonant structure resulting from depletion effects due to competing channels and resonances. Then, the X(3872) charmonium-like meson is described as a unitarised $J^{PC}=1^{++}$ $c\bar{c}$ state. Also, the unusual pattern of masses and widths of the open-charm axial-vector mesons $D_1(2420)$, $D_1(2430)$, $D_{s1}(2536)$, and $D_{s1}(2460)$ is shown to follow from highly non-perturbative coupled-channel and mixing effects. Finally, first indications of a very light scalar boson are presented, on the basis of published BABAR data.

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arXiv2011

Quasi-bound states in the continuum: a dynamical coupled-channel calculation of axial-vector charmed mesons

Masses and widths of the charmed axial-vector mesons $D_1(2420)$, $D_1(2430)$, $D_{s1}(2536)$, and $D_{s1}(2460)$ are calculated nonperturbatively in the Resonance-Spectrum-Expansion model, by coupling various open and closed meson-meson channels to the bare $J^P=1^+$ $c\bar{q}$ ($q=u,d$) and $c\bar{s}$ states. The coupling to two-meson channels dynamically mixes and lifts the mass degeneracy of the spectroscopic $^3P_1$ and $^1P_1$ states, as an alternative to the usual spin-orbit splitting. Of the two resulting $S$-matrix poles in either case, one stays very close to the energy of the bare state, as a quasi-bound state in the continuum, whereas the other shifts considerably. This is in agreement with the experimental observation that the $D_1(2420)$ and $D_{s1}(2536)$ have much smaller widths than one would naively expect. The whole pattern of masses and widths of the axial-vector charmed mesons can thus be quite well reproduced with only two free parameters, one of which being already strongly constrained by previous model calculations. Finally, predictions for pole positions of radially excited axial-vector charmed mesons are presented.

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arXiv2011

Delicate interplay between the D0-D*0, rho0-J/psi, and omega-J/psi channels in the X(3872) resonance

The nature of the X(3872) enhancement is analysed in the framework of the Resonance-Spectrum Expansion, by studying it as a regular $J^{PC}=1^{++}$ charmonium state, though strongly influenced and shifted by open-charm decay channels. The observed but Okubo-Zweig-Iizuka-forbidden $ρ^0 J/ψ$ and $ωJ/ψ$ channels are coupled as well, but effectively smeared out by using complex $ρ^0$ and $ω$ masses, in order to account for their physical widths, followed by a rigorous algebraic procedure to restore unitarity. A very delicate interplay between the $D^0 D^{*0}$, $ρ^0 J/ψ$, and $ωJ/ψ$ channels is observed. The data clearly suggest that the X(3872) is a very narrow axial-vector $c\bar{c}$ resonance, with a pole at or slightly below the $D^0D^{*0}$ threshold.

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arXiv2011

First indications of the existence of a 38 MeV light scalar boson

We present evidence for the existence of a light scalar particle that most probably couples exclusively to gluons and quarks. Theoretical and phenomenological arguments are presented to support the existence of a light scalar boson for confinement and quark-pair creation. Previously observed interference effects allow to set a narrow window for the scalar's mass and also for its flavor-mass-dependent coupling to quarks. Here, in order to find a direct signal indicating its production, we study published BABAR data on leptonic bottomonium decays. We observe a clear excess signal in the invariant-mass projections of electron-positron and muon-antimuon, which may be due to the emission of a so far unobserved scalar particle with a mass of about 38 MeV. In the process of our analysis, we also find an indication of the existence of a bottomonium-like hybrid state at about 10.061 GeV. Further signals might be interpreted as replicas of the light scalar, with masses roughly two and three times as large.

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arXiv2010

Exes and why Z? Some charming and beautiful observations

Threshold enhancements like the X(4660) and depletion effects as the X(4260) are listed as c-cbar resonances in the Particle Data Group tables. We will discuss these observations, and present a list of further c-cbar enhancements, which are more likely to represent true vector charmonium excitations. We will furthermore discuss the importance of the observed Z resonances, viz. Z(4050), Z(4250), and Z(4430), for the family of charm-strange mesons. Another piece of very important information that can be extracted from the present data is the universal, flavor independent frequency of 190 MeV for mesons, due to the quark-antiquark oscillations within the glue environment. Finally, we will show hints from the data at a further flavor-independent quantity, having a value of 76 +-2 MeV, the origin of which is not yet understood. Talk available at http://cft.fis.uc.pt/eef/Frascati2010start.htm

hep-ph↗
arXiv2010

Observation of the Upsilon(2 3D1) and indication of the Upsilon(1 3D1)

We present evidence, from published BABAR data, for the existence of further excitations in the b-bbar spectrum, namely the long-awaited Upsilon(1D) and Upsilon(2D) with central masses of 10098 pm 5 MeV and 10492 pm 5 MeV, respectively. The significance of the Upsilon(1 3D1) and Upsilon(2 3D1) signals is found to be 3.0 and 10.7 standard deviations, respectively.

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arXiv2010

Is Upsilon(10580) really Upsilon(4S)?

We analyse electron-positron data for b-bbar production published by the BABAR Collaboration, in the invariant-mass interval delimited by the B-Bbar and Lambda(b)-Lambda(b) thresholds. In particular, we describe the Upsilon(10580) enhancement, not as a b-bbar resonance, but rather as a threshold phenomenon due to the opening of the B-Bbar decay channel and enhanced by the Upsilon(2D) bound-state pole not far below this threshold. The same data provide evidence for the true Upsilon(4S) resonance, which we find at 10.735 GeV with a width of 38 MeV. At higher energies, two more known Upsilon resonances are observed by us in the data and classified. The vital role played in our analysis by the universal confinement frequency omega is again confirmed, via a comparison with the charmonium spectrum.

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arXiv2010

Drawbacks of applying perturbative schemes to meson spectroscopy

We study meson-meson scattering in a soluble model which describes asymptotically free mesons and confined quark-antiquark pairs via coupled channels. Concretely, the two scattered mesons are assumed to interact through s-channel meson-exchange diagrams. Furthermore, we develop a perturbative expansion of the model, and show that the thus found resonance pole positions, including contributions up to fourth order in perturbation theory, completely fail to reproduce the exact results. This shows that the resonance predictions based on perturbative approximations in quark models may be highly unreliable.

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arXiv2010

The quark-antiquark spectrum from upside down

We argue that the spectra of quark-antiquark systems should better be studied from higher radial excitations and, in particular, from configurations with well-defined quantum numbers, rather than from ground states and lower radial excitations, the most suitable system being charmonium.

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arXiv2010

Light and heavy at the end of the funnel

We show that, by taking a bare mass spectrum with constant spacings for the quark-antiquark propagators, which is subject to considerable mass shifts from meson loops, one adequately describes a large variety of mesonic resonances, from the light scalars to the b-bbar states. All our results indicate that a harmonic-oscilator spectrum with universal frequency, in combination with coupled-channel effects, does a much better job than the q-barq spectrum of the funnel potential.

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arXiv2010

Complex masses in the S-matrix

Most excited hadrons have multiparticle strong decay modes, which can often be described as resulting from intermediate states containing one or two resonances. In a theoretical approach, such a description in terms of quasi-two-particle initial and final states leads to unitarity violations, because of the complex masses of the involved resonances. In the present paper, an empirical algebraic procedure is presented to restore unitarity of the S-matrix while preserving its symmetry. Preliminary results are presented in a first application to S-wave pion-pion scattering, in the framework of the Resonance-Spectrum Expansion.

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arXiv2010

A very broad X(4260) and the resonance parameters of the 3D vector charmonium state

We argue that the X(4260) enhancement contains a wealth of information on vector c-cbar spectroscopy. We discuss the shape of the X(4260) observed in the OZI-forbidden process "electron-positron into J/psi and a pair of charged pions", in particular at and near vector charmonium resonances as well as open-charm threshold enhancements. The resulting very broad X(4260) structure does not seem to classify itself as a vector charmonium resonance, but its detailed shape allows to identify new vector c-cbar states. Here, we estimate the resonance parameters of the psi(3D) state.

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arXiv2010

Evidence for further charmonium vector resonances

We discuss the shape of threshold signals in production cross sections of the reaction e+ + e- --> D* + antiD*, at the opening of the D(s)* antiD(s)* and Lambda(c)+ Lambda(c)- channels. Furthermore, evidence for the 3D, 5S, 4D, 6S, 5D, 7S, 6D, and 8S charmonium vector resonances is presented, on the basis of data recently published by the BaBar Collaboration. Central masses and resonance widths are estimated. Confirmation of these resonances would be a huge step in lifting the precision level of hadron spectroscopy towards that of atomic spectroscopy, with far-reaching consequences for theory.

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arXiv2009

Multichannel calculation of excited vector $ϕ$ resonances and the $ϕ(2170)$

A multichannel calculation of excited $J^{PC}=1^{--}$ $ϕ$ states is carried out within a generalization of the Resonance-Spectrum Expansion, which may shed light on the classification of the $ϕ(2170)$ resonance, discovered by BABAR and originally denoted X(2175). In this framework, a complete spectrum of bare $s\bar{s}$ states is coupled to those OZI-allowed decay channels that should be most relevant for the considered energy range. The included $S$- and $P$-wave two-meson channels comprise the lowest pseudoscalar, vector, scalar, and axial-vector mesons, while in the $q\bar{q}$ sector both the $^{3}S_1$ and $^{3}D_1$ states are coupled. The only two free parameters are tuned so as to reproduce mass and width of the $ϕ(1020)$, but come out reasonably close to previously used values. Among the model's $T$-matrix poles, there are good candidates for observed resonances, as well other ones that should exist according to the quark model. Besides the expected resonances as unitarized confinement states, a dynamical resonance pole is found at $(2186-i246)$ MeV. The huge width makes its interpretation as the $ϕ(2170)$ somewhat dubious, but further improvements of the model may change this conclusion.

hep-ph↗
arXiv2009

Mass and width of the Upsilon(4S)

Recent data on e(-)+e(+)-->b+anti-b by the BABAR Collaboration [B. Aubert et al, Phys. Rev. Lett. 102, 012001 (2009), arXiv:0809.4120] in the energy range delimited by the B+anti-B and Lambda(b)(+)+Lambda(b)(-) thresholds are analyzed in a multichannel formalism that incorporates the usual Breit-Wigner resonances, but interfering with a background signal due to the opening of open-bottom thresholds. In particular, the Upsilon(4S) resonance is determined to have a mass of 10.735 GeV and a width of 38 MeV. Also two higher Upsilon resonances are identified, parametrized, and classified. Moreover, it is found that near the B+anti-B threshold open-bottom production in electron-positron annihilation is dominated by the reaction chain e(-)+e(+)-->n+anti-n-->B+anti-B (n=u/d) rather than e(-)+e(+)-->b+anti-b-->B+anti-B whereas near the B(s)+anti-B(s) threshold the reaction chain e(-)+e(+)-->s+anti-s-->B+anti-B dominates the production amplitude. The vital role played in this analysis by the universal confinement frequency, defined in 1980 [E. van Beveren, C. Dullemond, and G. Rupp, Phys. Rev. D21, 772 (1980)] and accurately determined in 1983 [E. van Beveren, G. Rupp, T.A. Rijken, and C. Dullemond, Phys. Rev. D27, 1527 (1983)], is further confirmed.

hep-ph↗
arXiv2009

Comment on "Study of D(sJ) decays to D(*)K in inclusive e(+)e(-) interactions"

We comment on the recent observation of the decay mode D(sJ)(*)(2860)-->D(*)K by the BABAR Collaboration [arXiv:0908.0806], and contest their peremptory conclusion that the data exclude a 0(+) assignment for the D(sJ)(*)(2860). In particular, we argue that the observed branching fraction B(D(sJ)(*)(2860)-->D(*)K)/B(D(sJ)(*)(2860)-->DK)=1.1 pm 0.15 pm 0.19 supports the existence of two largely overlapping resonances at about 2.86 GeV, namely a pair of radially excited tensor 2(+) and scalar 0(+) c-sbar states. This scenario is further justified by comparing with the corresponding excited charmonium states. Also other aspects of the charm-strange spectrum are discussed.

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