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Register a new userDe-Confinement in small systems: Clustering of color sources in high multiplicity $bar{p}$p collisions at $sqrt{s}$= 1.8 TeV
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It is shown that de-confinement can be achieved in high multiplicity non jet $bar{p}$p collisions at $sqrt{s}$= 1.8 TeV Fermi National Accelerator Laboratory(FNAL- E735) experiment. Previously the evidence for de-confinement was the demonstrated by the constant freeze out energy density in high multiplicity events. In this paper we use the same data but analyze the transverse momentum spectrum in the framework of the clustering of color sources. The charged particle pseudorapidities densities in the range 7.0 $leq langle dN_{c}/deta rangle leq$26.0 are considered. Results are presented for both thermodynamic and transport properties. The initial temperature and energy density are obtained and compared with the Lattice Quantum Chromo Dynamics(LQCD) simulations. The energy density ($varepsilon/T^{4}$) $sim$ 11.5 for $ langle dN_{c}/deta rangle sim $ 25.0 is close to the value for 0-10% central events in Au+Au collisions at $sqrt{s_{NN}}$= 200 GeV. The shear viscosity to entropy density ratio($eta/s$) is $sim$ 0.2 at the transition temperature. The result for the trace anomaly $Delta$ is in excellent agreement with LQCD simulations. These results confirm our earlier observation that the de-confined state of matter was created in high multiplicity events in $bar{p}$p collisions at $sqrt{s}$=1.8 TeV.
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We present strange particle spectra and yields measured at mid-rapidity in $sqrt{text{s}}=200$ GeV proton-proton ($p+p$) collisions at RHIC. We find that the previously observed universal transverse mass ($mathrm{m_{T}}equivsqrt{mathrm{p_{T}}^{2}+mathrm{m}^{2}}$) scaling of hadron production in $p+p$ collisions seems to break down at higher mt and that there is a difference in the shape of the mt spectrum between baryons and mesons. We observe mid-rapidity anti-baryon to baryon ratios near unity for $Lambda$ and $Xi$ baryons and no dependence of the ratio on transverse momentum, indicating that our data do not yet reach the quark-jet dominated region. We show the dependence of the mean transverse momentum (mpt) on measured charged particle multiplicity and on particle mass and infer that these trends are consistent with gluon-jet dominated particle production. The data are compared to previous measurements from CERN-SPS, ISR and FNAL experiments and to Leading Order (LO) and Next to Leading order (NLO) string fragmentation model predictions. We infer from these comparisons that the spectral shapes and particle yields from $p+p$ collisions at RHIC energies have large contributions from gluon jets rather than quark jets.
We have measured deconfined hadronic volumes, $4.4 < V < 13.0$ fm$^{3}$, produced by a one dimensional (1D) expansion. These volumes are directly proportional to the charged particle pseudorapidity densities $6.75 < dN_{c}/deta < 20.2$. The hadronization temperature is $T = 179.5 pm 5$ (syst) MeV. Using Bjorkens 1D model,the hadronization energy density is $epsilon_{F} = 1.10 pm 0.26$ (stat) GeV/fm$^{3}$ corresponding to an excitation of $24.8 pm 6.2$ (stat) quark-gluon degrees of freedom.
Particle production sensitive to non-factorizable and non-perturbative processes that contribute to the underlying event associated with a high transverse momentum ($p_{T}$) jet in proton+proton collisions at $sqrt{s}$=200 GeV is studied with the STAR detector. Each event is divided into three regions based on the azimuthal angle with respect to the highest-$p_{T}$ jet direction: in the leading jet direction (Toward), opposite to the leading jet (Away), and perpendicular to the leading jet (Transverse). In the Transverse region, the average charged particle density is found to be between 0.4 and 0.6 and the mean transverse momentum, $langle p_{T}rangle$, between 0.5-0.7 GeV/$c$ for particles with $p_{T}$$>$0.2 GeV/$c$ at mid-pseudorapidity ($|eta|$$<$1) and jet $p_{T}$$>$15 GeV/$c$. Both average particle density and $langle p_{T}rangle$ depend weakly on the leading jet $p_{T}$. Closer inspection of the Transverse region hints that contributions to the underlying event from initial- and final-state radiation are significantly smaller in these collisions than at the higher energies, up to 13 TeV, recorded at the LHC. Underlying event measurements associated with a high-$p_{T}$ jet will contribute to our understanding of QCD processes at hard and soft scales at RHIC energies, as well as provide constraints to modeling of underlying event dynamics.
A brief introduction of the relationship of string percolation to the Quantum Chromo Dynamics (QCD) phase diagram is presented. The behavior of the Polyakov loop close to the critical temperature is studied in terms of the color fields inside the clusters of overlapping strings, which are produced in high energy hadronic collisions. The non-Abelian nature of the color fields implies an enhancement of the transverse momentum and a suppression of the multiplicities relative to the non overlapping case. The prediction of this framework are compared with experimental results from the SPS, RHIC and LHC for $pp$ and AA collisions. Rapidity distributions, probability distributions of transverse momentum and multiplicities, Bose-Einstein correlations, elliptic flow and ridge structures are used to evaluate these comparison. The thermodynamical quantities, the temperature, and energy density derived from RHIC and LHC data and Color String Percolation Model (CSPM) are used to obtain the shear viscosity to entropy density ratio ($eta/s$). It was observed that the inverse of ($eta/s$) represents the trace anomaly $Delta =(varepsilon-3P)/T^{4}$. Thus the percolation approach within CSPM can be successfully used to describe the initial stages in high energy heavy ion collisions in the soft region in high energy heavy ion collisions. The thermodynamical quantities, temperature and the equation of state are in agreement with the lattice QCD calculations. Thus the clustering of color sources has a clear physical basis although it cannot be deduced directly from QCD.
In inelastic $p+p$ collisions, the interacting objects are quarks and gluons (partons). It is believed that there are multiple interactions between the partons in a single $p+p$ event. Recent studies of multiplicity dependence of particle production in $p+p$ collisions have gathered considerable interest in the scientific community. According to several theoretical calculations, multiple gluon participation in hadronic collisions is the cause of high-multiplicity events. If the interaction is hard enough (large $p_{rm T}$ transfer), the semi-hard processes of multiple interactions of partons might also lead to production of heavy particles like J/$psi$. At the LHC, an approximately linear increase of the relative J/$psi$ yield with charged particle multiplicity is observed in $p+p$ collisions. In the present work, we have studied the contribution of quarks and gluons to the multiplicity dependence of J/$psi$ production using pQCD inspired event generator, PYTHIA8 tune 4C, in $p+p$ collisions at $sqrt{s} =$13 TeV by investigating relative J/$psi$ yield and relative $langle p_{rm T} rangle$ of J/$psi$ as a function of charged particle multiplicity for different hard-QCD processes. We have estimated a newly defined ratio, $r_{pp} = {langle p_{rm T}^{2} rangle}_{i}/{langle p_{rm T}^{2} rangle}_{rm MB}$, to understand J/$psi$ production in high-multiplicity $p+p$ collisions. For the first time we attempt to study the nuclear modification factor like observables ($R_{rm pp}$ and $R_{rm cp}$) to understand the QCD medium formed in high-multiplicity $p+p$ collisions.
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