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N. Matagne

Publications and source records attributed to N. Matagne.

At least 19 recordsLinked to original sources

Updated $1/N_c$ expansion analysis of $[{\bf 56, 2^+}]$ and $[{\bf 70, \ell^+}]$ baryon multiplets

The mass spectra of the $[{\bf 56, 2^+}]$ and $[{\bf 70, \ell+}]$ multiplets, both belonging to the $N$ = 2 band, is reviewed in the $1/N_c$ expansion method. Previous studies, separately made for each multiplet, are presently updated to the 2014 Particle Data Group. The mass formula including corrections up to $\mathcal{O}(1/N_c)$ and first order in SU(3) flavor symmetry breaking, has the same independent operator basis in both cases. A special emphasis is made on the role of the SU(3) symmetry breaking operators $B_i$ $(i = 1,2,3)$. This can allow for multiplet assignment of $Λ$ and $Σ$ hyperons, which generally is quite difficult to make. Tentative assignments of hyperons with two- and one-star resonances are made to the $[{\bf 70, \ell+}]$ multiplet. Another important aim is to find out whether or not a common value of the coefficient $c_1$ of the dominant operator in the mass formula, can well fit the present data in both multiplets. A negative answer, which is here the case, implies distinct Regge trajectories for symmetric and mixed symmetric states.

hep-ph

Baryon resonances in large $N_c$ QCD

We review the current status and present open challenges of large $N_c$ QCD baryon spectroscopy. After introducing the $1/N_c$ expansion method we first shortly revisit the latest achievements for the ground state properties. Next we discuss the applicability of this method to excited states, presenting two different approaches with their advantages and disadvantages. Selected results for the spectrum and strong and electromagnetic decays are described. We also show further developments supported by the qualitative compatibility between the quark excitation picture and the meson-nucleon scattering picture. We give a quantitative comparison between results obtained from the mass formula of the $1/N_c$ expansion method and quark models and shortly discuss the implications of different large $N_c$ limits.

hep-ph

$[{\bf 70, \ell^+}]$ baryons in large $N_c$ QCD revisited: The effect on Regge trajectories

A simple procedure within the $1/N_c$ expansion method where all the $N_c$ quarks are treated on the same footing has been found successful in describing mixed symmetric negative parity baryon states belonging to the $[{\bf 70},\ell^-]$ multiplets %with $\ell$ = 1, 2 or 3. of the $N$ = 1 and 3 bands. Presently it is applied to mixed symmetric positive parity $[{\bf 70},0^+]$ and $[{\bf 70},2^+]$ multiplets of the $N$ = 2 band. We search for the most dominant terms in the mass formula. The results are compared to those obtained in the procedure where the system is separated into a core and an excited quark. We find that both the spin and isospin operators of the entire system of $N_c$ quarks play dominant roles in describing the data, like for negative parity states. As a by-product we present the contribution of the leading spin-isospin singlet term as a function of the band number, which hints at distinct Regge trajectories for the symmetric and mixed symmetric states.

hep-ph

Upsilon production in p(d)A collisions at RHIC and the LHC

We study the effect of nuclear matter in Upsilon production in dAu collisions at RHIC and pPb collisions at the LHC. We find that the nuclear modification factor, R^Upsilon_dAu, measured at RHIC is not satisfactorily reproduced by the conventional effects used in the literature, namely the modification of the gluon distribution in bound nucleons and an --effective-- survival probability for a bound state to escape the nucleus. In particular, we argue that this probability should be close to 1 as opposed to the J/psi case. We note that, at backward rapidities, the unexpected suppression of R^Upsilon_dAu observed by PHENIX hints at the presence of a gluon EMC effect, analogous to the quark EMC effect -- but likely stronger. Further nuclear matter effects, such as saturation and fractional energy loss, are discussed, but none of them fit in a more global picture of quarkonium production. Predictions for Upsilon(nS) for the forthcoming pPb run at 5 TeV at the LHC are also presented.

hep-ph

Highly excited states of baryons in large $N_c$ QCD

The masses of highly excited negative parity baryons belonging to the $N$ = 3 band are calculated in the $1/N_c$ expansion method of QCD. We use a procedure which allows to write the mass formula by using a small number of linearly independent operators. The numerical fit of the dynamical coefficients in the mass formula show that the pure spin and pure flavor terms are dominant in the expansion, like for the $N$ = 1 band. We present the trend of some important dynamical coefficients as a function of the band number $N$ or alternatively of the excitation energy.

hep-ph

Negative parity baryons in the $1/N_c$ expansion: the three towers of states revisited

We discuss the compatibility between the quark-shell picture and the meson-nucleon scattering picture in large $N_c$ QCD for mixed symmetric $\ell$ = 1 states previously analyzed by using a simple Hamiltonian including operators up to order $\mathcal{O}(N^0_c)$ defined in the standard ground state symmetric core + excited quark procedure. Here we introduce a Hamiltonian of order $\mathcal{O}(N^0_c)$ defined in a new approach where the separation of the system into two parts is not required. Three degenerate sets of states (towers) with the same quantum numbers as in the scattering picture and in the standard procedure are obtained. Thus the 0 is equally achieved. The eigenvalues of the presently chosen Hamiltonian also have simple analytic expressions, depending linearly on the three dynamical coefficients entering the Hamiltonian. This reinforces the validity of the new approach which had already 0 described excited negative parity baryons in a large energy range.

hep-ph

Highly excited negative parity baryons in the $1/N_c$ expansion

The masses of experimentally known highly excited baryons of negative parity supposed to belong to the $[{\bf 70},\ell^-]$ multiplets ($\ell$ = 1,2,3) of the $N = 3$ band are calculated in the $1/N_c$ expansion method to order $1/N_c$ by using a procedure which allows to considerably reduce the number of linearly independent operators entering the mass formula. The numerical fits to present data show that the coefficients encoding the QCD dynamics have large, comparable values, for the flavor and spin operators. It implies that these operators contribute dominantly to the flavor-spin SU(6) symmetry breaking, like for the $[{\bf 70},1^-]$ multiplet of the $N = 1$ band.

hep-ph

Centrality, rapidity, and transverse-momentum dependence of gluon shadowing and antishadowing on $J/ψ$ production in $d$Au collisions at $\sqrt{s}$=200 GeV

We have carried out a wide study of shadowing and antishadowing effects on \jpsi\ production in \dAu\ collisions at $\sqrt{s_{NN}}=200$ GeV. We have studied the effects of three different gluon nPDF sets, using the exact kinematics for a $2\to 2$ process, namely $g+g\to J/ψ+g$ as expected from LO pQCD. We have computed the rapidity dependence of \RCP\ and $R_{d\rm Au}$ for the different centrality classes of the PHENIX data. For mid rapidities, we have also computed the transverse-momentum dependence of the nuclear modification factor, which cannot be predicted with the usual $2\to 1$ simplified kinematics. All these observables have been compared to the PHENIX data in \dAu\ collisions.

hep-ph

Negative parity baryons in the $1/N_c$ expansion: the quark excitation versus the meson-nucleon resonance picture

In order to better understand the fundamental issue regarding the compatibility between the quark-shell picture and that of resonances in meson-nucleon scattering in large $N_c$ QCD we extend the work of Cohen and Lebed on mixed symmetric $\ell $ = 1 baryons to analyze excited states with $\ell $ = 3. We give an explicit proof on the degeneracy of mass eigenvalues of a simple Hamiltonian including operators up to order $\mathcal{O}(N^0_c)$ \emph{i. e.} neglecting $1/N_c$ corrections in the quark-shell picture in the large $N_c$ limit. We obtain three degenerate multiplets formed of $\ell = 3$ states, as in the case of $\ell $ = 1 baryons. The compatibility between this picture and that of resonances in meson-nucleon scattering is discussed in the light of the present results.

hep-ph

Quarkonium as a tool: cold nuclear matter effects

We discuss the quarkonium production as a tool for the study of the Quark Gluon Plasma. In particular, we concentrate on the Cold Nuclear Matter effetcs. We show that quarkonium production is also useful for the study of Quantum Chromodynamics first principles and the nuclear Parton Distribution Functions.

hep-ph

Cold Nuclear Matter Effects on extrinsic J/psi production at sqrt{s_{NN}}=2.76 TeV at the LHC

We evaluate the Cold Nuclear Matter effects on J/psi production in pPb and PbPb collisions at the current LHC energy, taking into account the gluon shadowing and the nuclear absorption. We use the complete kinematics in the underlying 2 to 2 partonic process, namely $g+g \to \jpsi + g$ as expected from LO pQCD. The resulting shadowing is responsible for a large J/psi suppression in pPb and PbPb, and shows a strong rapidity dependence.

hep-ph

Cold Nuclear Matter Effects on jpsi Production with Extrinsic pT at $\sqrt{s_{NN}}=5.5\mathrm{~TeV}$ at the LHC

Taking into account the gluon shadowing and the $J/ψ$ nuclear absorption, we evaluate the Cold Nuclear Matter (CNM) effects on $J/ψ$ production in $p$Pb and PbPb collisions at the design LHC energy for PbPb collisions, $\sqrt{s_{NN}}=5.5$ TeV. In view of the good agreement between the yield prediction using the LO CSM and the ALICE data at 7 TeV, we employ the latter model to use a complete description of the kinematics of the underlying $2 \rightarrow 2$ partonic process, namely $g + g \rightarrow J/ψ+ g$. We observe a large $J/ψ$ suppression in $p$Pb and PbPb collisions due to the strong shadowing of the gluon distribution in the lead ion at the corresponding gluon momentum fractions. This suppression from CNM effects has a strong rapidity dependence which may compensate, partially or completely, that of of the predicted charm recombination in PbPb collisions.

hep-ph

SU(6) $[{\bf 70},1^-]$ baryon multiplet in the $1/N_c$ expansion

The masses of excited states of mixed orbital symmetry of nonstrange and strange baryons belonging to the lowest $[{\bf 70},1^-]$ multiplet are calculated in the $1/N_c$ expansion to order $1/N_c$ with a new method which allows to considerably reduce the number of linearly independent operators entering the mass formula. This study represents an extension to SU(6) of our work on nonstrange baryons, the framework of which was SU(4). The conclusion regarding the role of the flavor operator, neglected in previous SU(6) studies, is reinforced. Namely, both the flavor and spin operators contribute dominantly to the flavor-spin breaking.

hep-ph

Mixed symmetric baryon multiplets in large $N_c$ QCD: two and three flavours

We propose a new method to study mixed symmetric multiplets of baryons in the context of the $1/N_c$ expansion approach. The simplicity of the method allows to better understand the role of various operators acting on spin and flavour degrees of freedom. The method is tested on two and three flavours. It is shown that the spin and flavour operators proportional to the quadratic invariants of SU$_S$(2) and SU$_F$(3) respectively are dominant in the mass formula.

hep-ph

New look at the $[{\bf 70},1^-]$ nonstrange and strange baryons in the $1/N_c$ expansion

The masses of excited nonstrange and strange baryons belonging to the multiplet $[{\bf 70},1^-]$ are calculated in the $1/N_c$ expansion to order $1/N_c$ with a new method which allows to considerably reduce the number of linearly independent operators entering the mass formula. This study represents an extension to SU(6) of our work on nonstrange baryons, the framework of which was SU(4).

hep-ph

Group theoretical study of nonstrange and strange mixed symmetric baryon states $[N_c-1,1]$ in the $1/N_c$ expansion

Using group theory arguments we extend and complete our previous work by deriving all SU(6) exact wave functions associated to the spectrum of mixed symmetric baryon states $[N_c-1,1]$ in the $1/N_c$ expansion. The extension to SU(6) enables us to study the mass spectra of both strange and nonstrange baryons, while previous work was restricted to nonstrange baryons described by SU(4). The wave functions are specially written in a form to allow a comparison with the approximate, customarily used wave functions, where the system is separated into a ground state core and an excited quark. We show that the matrix elements of the flavor operator calculated with the exact wave functions acquire the same asymptotic form at large $N_c$, irrespective of the spin-flavor multiplet contained in $[N_c-1,1]$, while with the approximate wave function one cannot obtain a similar behaviour. The isoscalar factors of the permutation group of $N_c$ particles derived here can be used in any problem where a given fermion system is described by the partition $[N_c-1,1]$, and one fermion has to be separated from the rest.

hep-ph

Lowest negative parity baryons in the $1/N_c$ expansion

We review a recently proposed approach to study the lowest negative parity baryons within the $1/N_c$ expansion. The method is based on the derivation of the matrix elements of SU(2N$_f$) generators for mixed symmetric $[N_c-1,1]$ flavor-spin states. Presently it is applied to the N = 1 band and a comparison is made with a former method based on the decoupling of the system into a symmetric core of $N_c-1$ quarks and an excited one. We prove that the decoupling is not necessary and moreover, it misses some important physical consequences.

hep-ph