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Register a new userSuperfluid effects in collision between systems with small particle number
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The interpretation of the new effect of the superfluidity in reactions with small number of particles is discussed in a simple model where the exact solution is accessible. It is find that the fluctuations of observable with the gauge angle reproduce well the exact fluctuations. Then a method of projection is proposed and tested to determine the transfer probabilities between two superfluid systems.
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We present a number conserving particle-hole RPA theory for collective excitations in the transition from normal to superfluid nuclei. The method derives from an RPA theory developed long ago in quantum chemistry using antisymmetric geminal powers, or equivalently number projected HFB states, as reference states. We show within a minimal model of pairing plus monopole interactions that the number conserving particle-hole RPA excitations evolve smoothly across the superfluid phase transition close to the exact results, contrary to particle-hole RPA in the normal phase and quasiparticle RPA in the superfluid phase that require a change of basis at the broken symmetry point. The new formalism can be applied in a straightforward manner to study particle-hole excitations on top of a number projected HFB state.
High statistics data sets from experiments at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) with small and large collision species have enabled a wealth of new flow measurements, including the event-by-event correlation between observables. One exciting such observable $rho(v^{2}_{n},[p_{T}])$ gauges the correlation between the mean transverse momentum of particles in an event and the various flow coefficients ($v_n$) in the same event [1]. Recently it has been proposed that very low multiplicity events may be sensitive to initial-state glasma correlations [2] rather than flow-related dynamics. We find utilizing the IP-JAZMA framework that the color domain explanation for the glasma results are incomplete. We then explore predictions from PYTHIA-8, and the version for including nuclear collisions called PYTHIA-ANGANTYR, which have only non-flow correlations and the AMPT model which has both non-flow and flow-type correlations. We find that PYTHIA-ANGANTYR has non-flow contributions to $rho(v^{2}_{n},[p_{T}])$ in p+O, p+Pb, O+O collisions that are positive at low multiplicity and comparable to the glasma correlations. It is striking that in PYTHIA-8 in p+p collisions there is actually a sign-change from positive to negative $rho(v^{2}_{n},[p_{T}])$ as a function of multiplicity. The AMPT results match the experimental data general trends in Pb+Pb collisions at the LHC, except at low multiplicity where AMPT has the opposite sign. In p+Pb collisions, AMPT has the opposite sign from experimental data and we explore this within the context of parton geometry. Predictions for p+O, O+O, and Xe+Xe are also presented.
Experimental measurements in collisions of small systems from p+p to p/d/3He+A at RHIC and the LHC reveal particle emission patterns that are strikingly similar to those observed in A+A collisions. One explanation of these patterns is the formation of small droplets of quark-gluon plasma followed by hydrodynamic evolution. A geometry engineering program was proposed [1] to investigate these emission patterns, and the experimental data from that program in p+Au, d+Au, 3He+Au collisions for elliptic and triangular anisotropy coefficients v2 and v3 follow the pattern predicted by hydrodynamic calculations [2]. One alternative approach, referred to as initial-state correlations, suggests that for small systems the patterns observed in the final-state hadrons are encoded at the earliest moments of the collision, and therefore require no final-state parton scattering or hydrodynamic evolution [3,4]. Recently, new calculations using only initial-state correlations, in the dilute-dense approximation of gluon saturation physics, reported striking agreement with the v2 patterns observed in p/d/3He+Au data at RHIC [5]. The reported results are counterintuitive and thus we aim here to reproduce some of the basic features of these calculations. In this first investigation, we provide a description of our model, IP-Jazma, and investigate its implications for saturation scales, multiplicity distributions and eccentricities, reserving for later work the analysis of momentum spectra and azimuthal anisotropies. We find that our implementation of the saturation physics model reproduces the results of the earlier calculation of the multiplicity distribution in d+Au collisions at RHIC. However, our investigations, together with existing data, call into question some of the essential elements reported in Ref. [5].
Results for high multiplicity pp and p-Pb collisions at the LHC have revealed that these small collision systems exhibit features of collectivity. To understand the origin of these unexpected phenomena, the relative transverse activity classifier ($R_{rm{T}}$) can be exploited as a tool to disentangle soft and hard particle production, by studying the yield of charged particles in different topological regions associated with transverse momentum trigger particles. This allows to study system size dependence of charged particle production of different origins and in particular search for jet-quenching effects. Here, results on the system size and $R_{rm{T}}$ dependence of charged particle production in pp, p-Pb and Pb-Pb collisions at $sqrt{s_{rm NN}}$ = 5.02 TeV are presented.
We discuss the effect of pairing on two-neutron space correlations in deformed nuclei. The spatial correlations are described by the pairing tensor in coordinate space calculated in the HFB approach. The calculations are done using the D1S Gogny force. We show that the pairing tensor has a rather small extension in the relative coordinate, a feature observed earlier in spherical nuclei. It is pointed out that in deformed nuclei the coherence length corresponding to the pairing tensor has a pattern similar to what we have found previously in spherical nuclei, i.e., it is maximal in the interior of the nucleus and then it is decreasing rather fast in the surface region where it reaches a minimal value of about 2 fm. This minimal value of the coherence length in the surface is essentially determined by the finite size properties of single-particle states in the vicinity of the chemical potential and has little to do with enhanced pairing correlations in the nuclear surface. It is shown that in nuclei the coherence length is not a good indicator of the intensity of pairing correlations. This feature is contrasted with the situation in infinite matter.
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