Multiplicity studies and effective energy in ALICE at the LHC

Abstract

Abstract. In this work we explore the possibility to perform "effective energy" studies in very high energy collisions at the CERN Large Hadron Collider (LHC). In particular, we focus on the possibility to measure in pp collisions the average charged multiplicity as a function of the effective energy with the ALICE experiment, using its capability to measure the energy of the leading baryons with the Zero Degree Calorimeters. Analyses of this kind have been done at lower centre-of-mass energies and have shown that, once the appropriate kinematic variables are chosen, particle production is characterized by universal properties: no matter the nature of the interacting particles, the final states have identical features. Assuming that this universality picture can be extended to ion-ion collisions, as suggested by recent results from RHIC experiments, a novel approach based on the scaling hypothesis for limiting fragmentation has been used to derive the expected charged event multiplicity in AA interactions at LHC. This leads to scenarios where the multiplicity is significantly lower compared to most of the predictions from the models currently used to describe high energy AA collisions. A mean charged multiplicity of about 1000 − 2000 per rapidity unit (at η ∼ 0) is expected for the most central P b − P b collisions at √ s N N = 5.5 TeV. PACS. PACS-key discribing text of that key -PACS-key discribing text of that key

Prospects of Searching for (Un)particles From Hidden Sectors Using Rapidity Correlations in Multiparticle Production at the LHC

“…the height of the plateau) would be independent of √ s, and that the plateau would merely widen as the energy is increased, leading to a logarithmic growth of multiplicity [12], is clearly not in accord with data. It rather turns out that the total (charged) multiplicity grows as n = a 2 ln 2 √ s + a 1 ln √ s + a 0 [26] (see [27,28] for a discussion on the dissipating/effective energy in the collision). This fact can be seen as a phenomenological consequence of three concurrent features: a) The increase as ln √ s of the particle density at midrapidity, b) The almost trapezoidal shape (see Fig.1) of the (pseudo)rapidity distribution, and c) the growth of the width of the spectrum proportional to Y ∼ ln √ s. Let us note that the predicted density in the central region at LHC energies lies between 6 and 8 charged particles per rapidity unit, depending on the MC generator and model [29,30].…”

Investigating the origin of strangeness enhancement in small systems through multi-differential analyses

“…In pp collisions the effective energy is reduced with respect to the full centre-of-mass energy due to the leading effect, which consists of a high probability to emit forward baryons with large longitudinal momenta along the direction of the incident beams. More details can be found in [9] and references therein. The effective energy can be estimated by means of ALICE's ZDC by detecting the energy deposits of the forward leading baryons in each event hemisphere: E effective = √ s − E leading .…”

Universality of multiplicity distribution in proton-proton and electron-positron collisions

“…[30][31][32][33]. In this paper we argue that an event-by-event fluctuation of K can naturally connect the multiplicity distributions measured in e + e − and pp collisions and it would be interesting to investigate the full multiplicity distributions in proton-nucleus (pA) and nucleus-nucleus (AA) collisions [18,34].…”