Conveners
Collectivity in small systems: I
- Urs Wiedemann (CERN)
Collectivity in small systems: II
- James Lawrence Nagle (University of Colorado Boulder)
Collectivity in small systems: III
- Jun Takahashi (University of Campinas UNICAMP (BR))
Recent observations of long-range multi-particle azimuthal correlations in p-Pb and high multiplicity pp collisions provided new insights into collision dynamics and opened a possibility to study collective effects in these small systems.
In this talk, we present new measurements of $p_{\text{T}}$-differential elliptic flow coefficient $v_2$ for a variety of identified charged hadrons from pp...
Experimental evidence suggests that collectivity in asymmetric small systems ($p$, $d$, $^{3}$He+A) is directly related to the initial collision geometry. Therefore, a compelling question is whether the same argument can be extended to p+p, and even $e^+e^-$ collisions. We have modified A-Multiphase-Transport-Model (AMPT) to include the constituent quark structure of the proton. We find with...
Proton-nucleus collisions play an important role as a control system for
interpreting hot nuclear matter effects in $A+A$ collisions. Yet, there is a large amount of data from both RHIC and the LHC that indicate that collective effects are also present in such small systems. Understanding the origin of these effects is still incomplete, since a variety of models with very different underlying...
Measurements of long-range azimuthal correlations involving heavy-flavor quarks provide a powerful tool in unraveling the origin of collectivity observed in small collision systems. With data collected by the CMS experiment at the LHC in 2016, elliptic azimuthal anisotropy ($v_2$) of prompt $D^{0}$ meson at mid-rapidity in 8.16 TeV pPb collisions is presented from long-range two-particle...
The relevance of subnucleonic degrees of freedom and their fluctuations in the description of multiple experimental observations in small collision systems (flow harmonics, diffractive phenomena, hollowness effect...) has been recently established.
A representative example is the first measurement of symmetric cumulants, SC(n,m), performed by the CMS Collaboration in the three collision...
One of the key results of the LHC Run 1 was the observation of an enhanced production of strange particles in high multiplicity pp and p-Pb collisions at 7 and 5.02 TeV, respectively. A smooth increase of strange particles relative to the non-strange ones with event multiplicity has been observed in such systems. Results from Run 2 at the top LHC energy are extended exploiting a dedicated high...
Using the extraordinary versatility of RHIC in selecting different colliding
species, the PHENIX experiment has collected data in p+Al, p+Au, d+Au, and $^{3}$He$+$Au at 200 GeV center-of-mass energy and conducted a comprehensive set of anisotropic flow measurements. These geometry-controlled experiments provide a unique testing ground for theoretical models that produce azimuthal particle...
Recently, near-side azimuthal angular correlations across a large pesudorapidity gap, commonly called as long-range ridge-like correlations, have been observed in small collision systems. It opens up opportunities to explore the multiparton dynamics of QCD and the limitation of fluid dynamics description of the matter created in these collisions. We report the STAR measurement of azimuthal...
Measurements of four-particle flow cumulants $c_{n}\{4\}=\langle v_n^4\rangle -2\langle v_n^2\rangle^2$ for $n=2$ and 3, and symmetric cumulants $SC(n,m)=\langle v_n^2 v_m^2\rangle-\langle v_n^2\rangle\langle v_m^2\rangle$ for $(n,m)=(2,3)$ and $(2,4)$ are presented in $pp$, $p$+Pb and peripheral Pb+Pb collisions at various collision energies, aiming to probe the long-range collective nature...
First results on two-particle angular correlations for charged particles emitted in $e^+e^-$ collisions using 730 $pb^{-1}$ of data collected between 91 and 209 GeV with the ALEPH detector at LEP are presented. With the archived data, the correlation functions are studied over a broad range of pseudorapidity $\eta$ (rapidity $y$) and azimuthal angle $\phi$ with respect to the electron-positron...
Multi-particle correlations in hadronic colliding systems at both RHIC and the LHC are under detailed investigation in recent years. A wealth of experimental evidence suggests the presence of collective phenomena and the formation of a quark-gluon plasma (QGP) also in high-multiplicity pp and pPb collisions. In particular, multi-particle cumulant analyses have established the collective nature...
Many observables which are used as a signature of collective effects in heavy-ion collisions when measured in high multiplicity pp and pA interactions reveal a very similar behaviour. We present first measurements of different order flow coefficients and their magnitude correlations using the Symmetric Cumulants for data collected by ALICE during the LHC Run 2 operation. The data sample...
Recent observations at RHIC and the LHC of two- and multi-particle correlations
in high multiplicity relativistic proton-proton and proton-ion collisions and similarity of the results to those observed in central heavy-ion collisions are often interpreted as an evidence for collective particle production in small collision systems. These results motivate a study in even smaller systems, such...
We investigate the relative importance of initial and final state effects on azimuthal correlations in low and high multiplicity p+Pb collisions at LHC energies. By matching the classical Yang-Mills dynamics of pre-equilibrium gluon fields (IP-GLASMA) to a perturbative QCD based parton cascade for the final state evolution (BAMPS) on an event-by-event basis, we find that signatures of both the...
We report on recent progress in understanding multi-particle correlations in $pA$ collisions from the initial state. We consider a proof of principle model of eikonal quarks from the projectile proton multiple-scattering off of a dense nuclear target. With this model, we find that many of the features observed in light-heavy ion collisions at RHIC and the LHC which are often ascribed to...
Recent measurements of correlations between two particles separated in pseudorapidity and azimuthal angles have shown striking similarities between results obtained in $pp$, $p$+A and A+A collision systems. In the $pp$ collision system, unlike in $p$+A and A+A collisions, the strength of the correlations, quantified by the anisotropy parameter $v_2$, shows little dependence on the observed...
The observation of collective effects in small systems, such as strangeness enhancement and the appearance of a ridge, have posed a challenge to conventional models for multiparton interactions and hadronization underlying general purpose MC event generators.
In this talk I will present the microscopic model for collective effects recently implemented in the Pythia8 and DIPSY event...
Simulations of relativistic heavy-ion collisions based on viscous hydrodynamics provide an accurate description of the bulk observables measured at RHIC and LHC beam energies, including identified particle yields, mean $p_T$ and multiparticle correlations. The success of the hydrodynamic framework, however, is naturally expected to break down in the dilute limit where discrete particle degrees...
The multiplicity dependent results of identified particle production allowed the discovery of collective-like behavior in pp collisions at the LHC. Good understanding of the effects attributed to well-understood physics, like multiple hard scatterings, is required to establish the origin of the new phenomena. Experimentally, those effects can be controlled using event shapes, like transverse...
