Gluino production in ultrarelativistic heavy ion collisions and nuclear shadowing

Abstract

In this article we investigate the influence of nuclear effects in the production of gluinos in nuclear collisions at the LHC, and estimate the transverse momentum dependence of the nuclear ratios RpA = dσ(pA) dyd 2 p T /A dσ(pp) dyd 2 p T and RAA = dσ(AA) dyd 2 p T /A 2 dσ(pp) dyd 2 p T . We demonstrate that depending on the magnitude of the nuclear effects, the production of gluinos could be enhanced, compared to protonproton collisions. The study of these observables can be useful to determine the magnitude of the shadowing and antishadowing effects in the nuclear gluon distribution. Moreover, we test different SPS scenarios, corresponding to different soft SUSY breaking mechanisms, and find that the nuclear ratios are strongly dependent on that choice. PACS numbers: 12.60.Jv; 14.80.Ly; 24.85.+p The main aim of the Large Hadron Collider (LHC), which is already running and soon will be in complete operation with 14 TeV, is to find the Higgs particle. That discovery may either confirm the Standard Model (SM) or open new windows towards new physics. Although the SM explain all experimental data except neutrino masses, there are many reasons to go beyond it. Some theoretical problems in the SM are: hierarchy problem, electroweak symmetry breaking, gauge coupling unification, etc [1]. The Minimal Supersymmetric Standard Model (MSSM) is the simplest supersymmetric extension of the SM, being a good candidate to Physics Beyond Standard Model [1,2]. In the MSSM, for each usual particle, one assigns a superpartner with oposite statistics: it means that for each boson there is a fermionic superpartner, and the reverse in the case of fermions. In the strong sector, one has the so called supersymmetric QCD (sQCD), where besides the gluon (boson) and quarks (fermions), there are the corresponding superpartners: gluinos (fermions) and squarks (bosons). On this model, the gluinos are the superpartners of gluons, they are color octet fermions and therefore they can not mix with other particles, as a result its mass is a parameter of soft SUSY breaking terms. Gluinos are Majorana fermions, expected to be one of the most massive MSSM sparticles, and therefore, their production is only feasible at very energetic machines such as the LHC. The gluino and squark masses are still unknown parameters, but they cannot be smaller than around a half TeV, as predicted by several models for SUSY breaking. The "Snowmass Points and Slopes"SPS) [3] are a set of benchmark points and parameter lines in the MSSM parameter space corresponding to different scenarios in the search for supersymmetry at present and future experiments (See [4] for a very nice review). The aim of this convention is reconstructing Scenario mg (GeV ) mq (GeV ) SPS1a 595.2 539.9 SPS1b 916.1 836.2 SPS2 784.4 1533.6 SPS3 914.3 818.3 SPS4 721.0 732.2 SPS5 710.3 643.9 SPS6 708.5 641.3 SPS7 926.0 861.3 SPS8 820.5 1081.6 SPS9 1275.2 1219.2TABLE I: The values of the masses of gluinos and squarks in the SPS scenarios.the fundamental supersymmetric theory, and its breaking mec...

Prompt doubleJ/ψproduction in proton-proton collisions at the LHC

“…It remains to be seen if full next-to-leading-order (NLO) corrections can fill such a large gap between LO results and the CMS data, see also Refs. [12][13][14][15]. Although the relative importance of the NLO corrections is process-dependent, we recall that the NLO corrections enhance the LO NRQCD cross-section for single inclusive J/Ψ production by a factor about 10 [49], see also Refs.…”

The Minimal Supersymmetric Standard Model (MSSM) and General Singlet Extensions of the MSSM (GSEMSSM), a short review

“…The gluinos are expected to be one of the most massive sparticles which constitute the MSSM and therefore their production is only feasible at a very energetic machine such as the Large Hadron Collider (LHC). The gluino production in nuclear collisions was presented at [35,74,76,98,99,100,101].Therefore one of the sources of CP violation in the MSSM arises from the gluinos sector. Some phenomenological studies about this case see [102].…”

Investigating the high-energy QCD approaches for prompt-photon production at the LHC

“…The influence of nonlinear gluon evolution in prompt photon production is estimated in Ref. [12], where we find an enhancement of the prompt photon cross section for LHC energies.…”

“…A LO QCD study of prompt photon production in pA and AA collisions including more recent nuclear pdf's is done in ref. [10], and it is shown that the amount of shadowing and antishadowing is very distinct for the various nuclear pdf's available, so these processes are usefull to discriminate among the different nuclear pdf's. Moreover, a precise knowledge of the gluon pdf's is crucial for a better understanding of the QCD evolution, mostly the possible nonlinear QCD evolution at small x and small Q 2 , where the gluon density in the nucleus becomes large and starts to saturate at momentum scales near Q sat (the so-called "saturation scale") [11].…”