Revealing the source of the radial flow patterns in proton--proton collisions using hard probes
Antonio Ortiz, Gyula Bencédi, Héctor Bello
备注：
16 pages, 6 figures. The text was significantly modified and extended. One figure was removed whereas some were slightly modified. References were corrected and updated. The final version of this paper appears in Journal of Physics G (Nuclear and Particle Physics)
In this work, we propose a tool to reveal the origin of the collective-like phenomena observed in proton--proton collisions. We exploit the fundamental difference between the underlying mechanisms, color reconnection (CR) and hydrodynamics, which produce radial flow patterns in \textsc{Pythia}~8 and \textsc{Epos}~3, respectively. Specifically, we proceed by examining the strength of the coupling between the soft and hard components which, by construction, is larger in \textsc{Pythia}~8 than in \textsc{Epos}~3.
We study the transverse momentum ($p_{\rm T}$) distributions of charged pions, kaons and (anti)protons in inelastic pp collisions at $\sqrt{s}=$ 7\,TeV produced at mid-rapidity. Specific selections are made on an event-by-event basis as a function of the charged particle multiplicity and the transverse momentum of the leading jet ($p_{\rm T}^{\rm jet}$) reconstructed using the \textsc{FastJet} algorithm at mid-pseudorapidity ($|η|<1$). From our studies, quantitative and qualitative differences between \textsc{Pythia}~8 and \textsc{Epos}~3 are found in the $p_{\rm T}$ spectra when (for a given multiplicity class) the leading jet $p_{\rm T}$ is increased. In addition, we show that for low-multiplicity events the presence of jets can produce radial flow-like behavior. Motivated by our findings, we propose to perform a similar analysis using experimental data from RHIC and LHC.
We present the first quantum field theory calculation of the pointwise behaviour of the leading-twist parton distribution amplitudes (PDAs) of the proton and its lightest radial excitation. The proton's PDA is a broad, concave function, whose maximum is shifted relative to the peak in QCD's conformal limit expression for this PDA; an effect which signals the presence of both scalar and pseudovector diquark correlations in the nucleon, with the scalar generating around 60% of the proton's normalisation. The radial-excitation is constituted similarly, and the pointwise form of its PDA, which is …
One of the main challenges hampering an accurate measurement of the double parton scattering (DPS) cross sections is the difficulty in separating the DPS from the leading twist (LT) contributions. We argue that such a separation can be achieved, and cross section of DPS measured, by exploiting the different centrality dependence of DPS and LT processes in proton-nucleus scattering. We developed a Monte Carlo implementation of the DPS processes which includes realistic nucleon-nucleon (NN) correlations in nuclei, an accurate description of transverse geometry of both hard and soft NN collisions…
Revealing a deep connection between factorization and saturation: New insight into modeling high-energy proton-proton and nucleus-nucleus scattering in the EPOS4 framework
We analyse the transverse momentum ($p_{\rm T}$)-spectra as a function of charged-particle multiplicity at midrapidity ($|y| < 0.5$) for various identified particles such as $π^{\pm}$, $K^{\pm}$, $K_S^0$, $p+\overline{p}$, $ϕ$, $K^{*0} + \overline {K^{*0}}$, and $Λ$ + $\barΛ$ in proton-proton collisions at $\sqrt{s}$ = 7 TeV using Boltzmann-Gibbs Blast Wave (BGBW) model and thermodynamically consistent Tsallis distribution function. We obtain the multiplicity dependent kinetic freeze-out temperature ($T_{\rm kin}$) and radial flow ($β$) of various particles after fitting the $p_{\rm T}$-distri…
In this paper, one discusses the effects of the Tsallis entropy on the radial pressure distribution in the proton. Using a damped confinement potential the pressure distribution is obtained from the Tsallis entropy approach, being the entropic-index $ω$ connected with the proton temperature concerning some transition temperature. Then, the approach allows the study of the proton thermal evolution up to the Quark-Gluon Plasma regime. The von Laue stability condition, arising from the pressure distribution results in positive and negative energy regions. An analogy between the results for the ra…
The ridge signal, which is long-ranged in rapidity, in the di-hadron correlations in high-multiplicity p-p and p-A collisions opened up a whole new research area in high-energy QCD. Although the ridge had been observed in A-A collisions and interpreted as a result of the radial flow of quark-gluon plasma, it had not appeared until recently in the data of small collision systems such as p-p and p-A, nor had it been predicted theoretically or seen in the event generators. There are two competing approaches that attempt to explain the systematics of the di-hadron ridge signal; hydrodynamics and g…
The striking resemblance of high multiplicity proton-proton (pp) collisions at the LHC to heavy ion collisions challenges our conventional wisdom on the formation of the Quark-Gluon Plasma (QGP). A consistent explanation of the collectivity phenomena in pp will help us to understand the mechanism that leads to the QGP-like signals in small systems. In this study, we introduce a transport model approach connecting the initial conditions provided by PYTHIA8 with subsequent AMPT rescatterings to study the collective behavior in high energy pp collisions. The multiplicity dependence of light hadro…
The transverse, spatial structure of protons is an area revealing fundamental properties of matter, and provides key input for deeper understanding of emerging collective phenomena in high energy collisions of protons, as well as collisions of heavy ions. In this paper eccentricities and eccentricity fluctuations are predicted using the dipole formulation of BFKL evolution. Furthermore, first steps are taken towards generation of fully exclusive final states of $γ^*$A collisions, by assessing the importance of colour fluctuations in the initial state. Such steps are crucial for the preparation…
Comments on "Observation of Long-Range, Near-Side Angular Correlations in Proton-Proton Collisions at the LHC" by the CMS collaboration(arXiv:1009.4122v1 [hep-ex])"
Azimuthal distributions of radial velocities of charged hadrons produced in nucleus-nucleus $(AB)$ collisions are compared with the corresponding azimuthal distribution of charged hadron multiplicity in the framework of a multiphase transport (AMPT) model at two different collision energies. The mean radial velocity seems to be a good probe for studying radial expansion. While the anisotropic part of the distributions indicates a kind of collective nature of radial expansion, the isotropic part characterizes a thermal motion. The present investigation is carried out keeping the upcoming Compre…
An inclusive baryon to meson enhancement with increase in multiplicity has been observed in pp collisions at $\sqrt{s}$= 7 TeV. Such a striking feature of the data can be explained by approaches based on hydrodynamics and multi-parton interactions (MPI) coupled with color reconnection (CR) mechanism. In this paper, we investigate the multiplicity evolution of the charged particle yields associated with pions and protons selected from the intermediate $p_{T}$ region where the inclusive baryon to meson enhancement has been observed. The study has been peformed using EPOS 3 (hydrodynamics) and PY…
Results from the two-particle correlation between identified triggers (pions ($π^{\pm}$) , protons (p/$\bar{p}$))) and un-identified charged particles at intermediate transverse momentum ($p_{T}$) in p-Pb collisions at $\sqrt{s_{NN}} = $ 5.02 TeV have been presented. The events generated from a hybrid Monte-Carlo event generator, EPOS 3.107 that implements a flux-tube initial conditions followed by event by event 3+1D viscous hydrodynamical evolution, have been analysed to calculate two-dimensional correlation functions in $Δη$-$Δϕ$. The strength of angular correlations at small relative angle…
Inspired by the event accumulation around 2.6 GeV in the $η^\primeπ^+π^-$ invariant mass spectrum of $J/ψ\to γη^\primeπ^+π^-$, which was reported by the BESIII Collaboration, we carry out the study of the mass spectrum and decay behavior of four radial excitations in the pseudoscalar meson family, which include $η^{(\prime)}(6S)$ and $η^{(\prime)}(7S)$. Combining with these analysis, we present the calculation of the reactions induced by a pion or kaon on the proton target which are relevant to these four discussed states. According to this information, we give concrete experimental suggestion…
The multiplicity percentile dependence of cumulants, of net-proton number distributions in Au$-$Au collisions at $\sqrt{s_{NN}} = $ 200 GeV and Pb$-$Pb collisions at $\sqrt{s_{NN}} = $ 2.76 TeV has been investigated using the Angantyr model (the heavy-ion extension of the \textsc{Pythia 8} model). The effects of finite transverse momentum ($p_{\mathrm T}$) and pseudorapidity ($η$) acceptance on the net-proton cumulants have also been studied. Furthermore, the effects of the hydrodynamic expansion and feed down from weak decays were explored. It was found that radial flow has substantial impact…
