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We discuss the elliptic flow dependence on pseudorapidity and number of participating nucleons in the framework of string percolation, and argue that the geometry of the initial overlap region of interaction, projected in the impact parameter plane, determines the experimentally measured azimuthal asymmetries. We found good agreement with data., Comment: 7 pages, 2 figures

We present a multiplicity distribution model with two components, soft (S) and semi-hard (SH), in the TeV region. The two components are supposed to have a common physical origin, as they result from the superposition of independent collisions, such that both can be represented by negative binomial distributions with parameters 〈n〉 and k satisfying kS/〈n〉S=kSH/〈n〉SH. We discuss the relation of our model to multicollision models (Dual Parton Model, unitarized eikonal models).

Cumulant oscillations, or $H_q$ moment oscillations, appear if the KNO multiparticle distribution decreases at large z, $z\equiv n/ $, faster than the exponential, $exp(-D z^\mu)$, with $\mu > 1$. In nucleus-nucleus interactions this behaviour is related to the limitation in the average number of elementary central collisions (or average number of strings centrally produced), due to the finite number of nucleons involved. Colour deconfinement, via percolating string fusion, will drastically decrease the fraction of centrally produced strings and increase the cut-off parameter $\mu$: Moment oscillations will be displaced to smaller q and the width of the KNO distribution and forward-backward particle correlations will become smaller., Comment: 11 pages, 2 Postscript figures

We discuss the discrete non-linear branching structure of the QCD evolution equations for multiparton production. Asymptotic consistency of the model with the large N c limit of QCD requires the inclusion of an effective 4-gluon vertex in the evolution tree. In contrast to previous calculations, this gives the possibility of having KNO gluon jet distributions wider than quark jet distributions.

High-resolution measurements for the 40 Ca ( γ , p ) 39 K reaction have been performed at E γ =60 MeV. Five groups of states in the residual nucleus were identified. The angular cross sections for the 2 s 1 2 and the 1 d 3 2 hole state are reasonably well predicted in an RPA model. Both the shape and the magnitude of the angular cross sections of the remaining groups of states suggest the excitation of two-hole-one-particle states evidencing a two-body photoabsorption mechanism.

One-dimensional Ising systems are used to simulate particle rapidity distributions. We show that in the one-dimensional Ising model intermittent-like behaviour occurs. We further show that with increasing multiplicities and factorial moments this behaviour tends to decrease.

We argue that if semihard QCD is in the origin of the increase of σ el / σ tot , then a softening of the leading particle spectrum, corresponding to an increase of the inelasticity, should occur. By establishing a simple relation between the inelasticity and the ratio σ el / σ tot , we are able to describe the energy dependence of the inelasticity, in agreement with cosmic-ray data.

It is shown that in a very good approximation the eikonal in hadron-hadron collisions at high energies has a universal dependence on the geometrical scaling variable β ≡ b2R2(s). This universality was checked for πp and K+p, at NAL and lower energies, and also for φp and ψp. The consequences of our results for the properties of the Pomeron and validity of Quark model calculations are discussed.

We calculate quark and gluon fragmentation functions at large Q 2 by means of perturbative QCD starting from “physical” thresholds. Our formalism provides a general framework to generate fragmentation functions (valence, sea and gluon) from threshold valence quark and gluon fragmentation functions. Thresholds of various flavours are taken into account and give rise to natural flavour dependence of fragmentation functions. We incorporate resonance production which has an important effect on the energy ( z ) spectrum of final hadrons. The inclusive hadron spectrum from quarkonium decay is also predicted.

It is shown that, as a consequence of the centrality of the semi-hard amplitude, it is possible to obtain an upper and a lower bound for the ratio 〈n〉 SH 〈n〉 of the minijet average multiplicity over the inelastic average multiplicity and an upper bound for the ratio C 2 SH C 2 of the corresponding normalized second moments of the particle distributions. In minijet events multiplicities are higher and the KNO distributions are narrower.

Universality of inclusive fragmentation density functions in lepton induced processes (ep, νp, e + e − ) and purely hadronic processes is discussed from the point of view of the Topological Expansion/Dual Unitarization Scheme. It is shown that planar, single jet dominated processes have universal inclusive distributions and average multiplicities. In multi-jet processes, treated in a simple approximation, 〈 x 〉 is inversely proportional to the number N of jets and the magnitude of the seagull effect increases as N 2 .

The relevance of the underlying SU(2) quark diagram structure of production amplitudes in understanding charge transfer and particle correlation data is pointed out.

By using the duality hypothesis of Freund and Harari, the high energy missing mass spectra of pp → pX were calculated from the relatively low energy missing mass data. The resonance contributions to the triple-Regge region was calculated from a finite energy sum rule which included all the diffractive N∗ resonances as well as the nucleon pole. The background contribution to the triple-Regge region was estimated from semi-local duality by averaging over the background of a particular resonance N∗ (1688). It was also found that the Pomeron treated as a simple pole couples much more weakly than the usual Reggeon to the inelastic processes in the triple-Regge region.

Applying the Harari-Freund duality hypothesis to the inclusive reaction pp → pX near the phase space boundary, we give a prediction on the small transverse momentum squared, ( p ⊥ c ) 2 , distribution of the ISR data. Also, using the Feynman scaling variable, x , we demonstrate explicitly the exponential ( p ⊥ c ) 2 dependence of the Lorentz invariant cross-sections E c d 3 σ d p c 3 from the triple-Regge formula.

In the spirit of the duality hypothesis of Freund and Harari a triple-Regge like formula is used to interpret and parameterize the data in photo and electroproduction of vector mesons in the presence, or not, of a background. The (missing mass) 2 , (photon mass) 2 and (p-p momentum transfer) 2 dependences of the e + p → e + p + X cross-section are given and compared with experiments. An explanation is proposed for the (apparently) conflicting existing data.

The use of a scaling variable z′ = (n−α) (〈n〉−α) with α being constant provides an extension of the KNO scaling to low energies. A generalized Wroblewski-formula to higher moments 〈(n−〈n〉) N 〉 N = K N 〈n〉−K N α is obtained. We tentatively connect α with the leading particle effect.

We argue that the intermittency exponents ƒ i , characteristic of the dependence of the normalised factorial moments Fi on the bin rapidity δy, are δy and overall rapidity Y dependent and that, approximately, they satisfy the scaling ƒ i (δy, Y) → ψ i (η≡ δyY) in the limits δy → 0, Y → ∞.

We compare string percolation phenomenology to Glasma results on particle rapidity densities, effective string or flux tube intrinsic correlations, the ridge phenomena and long range forward-backward correlations. Effective strings may be a tool to extend the Glasma to the low density QCD regime. A good example is given by the minimum of the negative binomial distribution parameter k expected to occur at low energy/centrality., Submitted to Phys. Lett B