Signatures of α clustering in ultrarelativistic collisions with light nuclei

Abstract

We explore possible observable signatures of α clustering of light nuclei in ultra-relativistic nuclear collisions involving 7,9 Be, 12 C, and 16 O. The clustering leads to specific spatial correlations of the nucleon distributions in the ground state, which are manifest in the earliest stage of the ultra-high energy reaction. The formed initial state of the fireball is sensitive to these correlations, and the effect influences, after the collective evolution of the system, the hadron production in the final stage. Specifically, we study effects on the harmonic flow in collisions of light clustered nuclei with a heavy target ( 208 Pb), showing that measures of the elliptic flow are sensitive to clusterization in 7,9 Be, whereas triangular flow is sensitive to clusterization in 12 C and 16 O. Specific predictions are made for model collisions at the CERN SPS energies. In another exploratory development we also examine the proton-beryllium collisions, where the 3/2 − ground state of 7,9 Be nucleus is polarized by an external magnetic field. Clusterization leads to multiplicity distributions of participant nucleons which depend on the orientation of the polarization with respect to the collision axis, as well as on the magnetic number of the state. The obtained effects on multiplicities reach a factor of a few for collisions with a large number of participant nucleons.

Exploring new small system geometries in heavy ion collisions

“…Numerous studies have been carried out following the hypothesis that some light nuclei have structures dominated by α clustering [9][10][11]. For example, if a carbon nucleus was composed of three α clusters centered on the corners of a triangle, observable consequences might be seen in the measurement of enhanced triangular flow in collisions of carbon on a heavy nucleus, e.g., C+Au.…”

“…Most analyses have implemented very simple nuclear geometries, and we have implemented one such geometry following Ref. [9]. For carbon, one assumes that three α-like clusters are centered at the corners of a perfect equilateral triangle with the length of each side taken to be L = 2.8 fm.…”

“…Specific proposals for colliding deformed uranium nuclei [7] and comparing the collisions of different isobars [8] (Zr/Ru) have been implemented at RHIC to test predictions for the chiral magnetic effect and other magnetic field-correlated effects. There have even been proposals that posit that the hydrodynamic evolution is so well understood that one can test hypotheses about possible alpha clustering in small nuclei such as beryllium, carbon, and oxygen via their imprint in the initial geometry [9][10][11].…”

Elliptic flow in ultrarelativistic collisions with light polarized nuclei

“…where we include the explicit Clebsch-Gordan coefficients from Eq. (20). The formula holds for perfectly polarized light nuclei, central collisions with sufficiently large number of sources, and j ≥ 1.…”

“…Early studies of collectivity in small systems were carried out in [8][9][10][11][12], followed by investigations of triangularity in 3 He-A collisions [13][14][15], or studies of the α clusterization effects in 12 C-A collisions [16][17][18][19] and other light clustered nuclei [20][21][22].…”