Using the 1/N c expansion of QCD we analyze the spectrum of positive parity resonances with strangeness S = 0, −1, −2 and -3 in the 2-3 GeV mass region, supposed to belong to the [56, 4 + ] multiplet. The mass operator is similar to that of [56, 2 + ], previously studied in the literature.The analysis of the latter is revisited. In the [56, 4 + ] multiplet we find that the spin-spin term brings the dominant contribution and that the spin-orbit term is entirely negligible in the hyperfine interaction, in agreement with constituent quark model results. More data are strongly desirable, especially in the strange sector in order to fully exploit the power of this approach. * e-mail address: nmatagne@ulg.ac.be † e-mail address: fstancu@ulg.ac.be 1 I. INTRODUCTIONThe 1/N c expansion of QCD [1,2,3,4] has been proved a useful approach to study baryon spectroscopy. It has been applied to the ground state baryons [5,6,7,8,9,10,11] as well as to excited states, in particular to the negative parity spin-flavor [70, 1 − ] multiplet (N = 1 band) [12,13,14,15,16,17], to the positive parity Roper resonance belonging to [56', 0 + ] (N = 2 band) [18] and to the [56, 2 + ] multiplet (N = 2 band) [19]. In this approach the main features of the constituent quark model emerge naturally and in addition, new information is provided, as for example, on the spin-orbit problem.In this study we explore its applicability to the [56, 4 + ] multiplet (N = 4 band) for the first time. The number of experimentally known resonances in the 2-3 GeV region [20], expected to belong to this multiplet is quite restricted. Among the five possible candidates there are two four-star resonances, N(2220)9/2 + and ∆(2420)11/2 + , one three-star resonance Λ(2350)9/2 + , one two-star resonance ∆(2300)9/2 + and one one-star resonance ∆(2390)7/2 + . This is an exploratory study which will allow us to make some predictions.In constituent quark models the N = 4 band has been studied so far either in a large harmonic oscillator basis [21] or in a variational basis [22]. We shall show that the present approach reinforces the conclusion that the spin-orbit contribution to the hyperfine interaction can safely be neglected in constituent quark model calculations.The properties of low energy hadrons are interpreted to be a consequence of the spontaneous breaking of chiral symmetry [23]. For highly excited hadrons, as the ones considered here, there are phenomenological arguments to believe that the chiral symmetry is restored.This would imply a weakening (up to a cancellation) of the spin-orbit and tensor interactions [24]. Then the main contribution to the hyperfine interaction remains the spin-spin term. II. THE WAVE FUNCTIONSThe N = 4 band contains 17 multiples having symmetries (56), (70) with ℓ = 4 (see Table 2 of Ref. [22]) to a spin-flavor symmetric wave function. This giveswhere S, S z are the spin and its projection, d labels an SU(3) representation (here 8 and 10), Y, I, I z stand for the hypercharge, isospin and its projection and J, J z for ...

We study the effect of nuclear matter in Υ production in dAu collisions at RHIC and pPb collisions at the LHC. We find that the nuclear modification factor, R Υ 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 -effectivesurvival 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/ψ case. We note that, at backward rapidities, the unexpected suppression of R Υ 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 Υ(nS ) for the forthcoming pPb run at 5 TeV at the LHC are also presented.

The masses of positive [70, 0 + ] and [70, 2 + ] nonstrange and strange baryons are calculated in the 1/N c expansion. The approach is based on the separation of a system of N c quarks into an excited core and an excited quark. The previous work for two flavor baryons is now extended to include strange baryons, to first order in SU(3)-flavor breaking. We show that the extension to N f = 3 maintains the regularities previously observed in the behaviour of the linear term in N c , of the spin-spin and of the spin-orbit terms. In particular the contribution of the spin-dependent terms decrease with the excitation energy, the dominant term remaining the spin-spin term.

A connection is establisehd between the results of a potential quark model with dynamical masses and the 1/N c expansion mass formula used in the description of baryon resonances. It is shown that a remarkable compatibility exists between the two methods.

No abstract