Abstract
We show that an event-shape engineering based on the mean transverse momentum of charged hadrons, [p_t], provides an optimal handle on the strength of the magnetic field created in central heavy-ion collisions at high energy. This is established through quantitative evaluations of the correlation existing between the event-by-event magnetic field produced by the spectator protons in 5.02 TeV Pb + Pb collisions and the event-by-event [p_t] at a given collision centrality. We argue that the event selection based on [p_t] provides a better handle on the magnetic field than the more traditional selection based on the event ellipticities. Advantages brought by this new method for the experimental search of the chiral magnetic effect are discussed.
Highlights
The interaction of two heavy nuclei at relativistic energy gives rise to a short-lived electromagnetic (EM) field of gigantic strength
We show that an event-shape engineering based on the mean transverse momentum of charged hadrons, [ pt ], provides an optimal handle on the strength of the magnetic field created in central heavy-ion collisions at high energy
The charge carried by the protons lying at the edges of the colliding ions, and that fly along the beam pipe without undergoing any interactions, engenders in particular a magnetic field over the transverse plane
Summary
The interaction of two heavy nuclei at relativistic energy gives rise to a short-lived electromagnetic (EM) field of gigantic strength. Nucleons are labeled as participants if they undergo at least one interaction with a nucleon from the other nucleus, and spectators, if they fly unscattered away from the interaction region along the beam direction These spectators are especially important in our analysis, as we shall evaluate the magnetic fields which they induce over the collision area. We denote the number of spectator nucleons in a collision event by Ns. In one nucleus, each participant nucleon is turned into a transverse density of participant matter by centering on top of its location a two-dimensional Gaussian profile of width w = 0.8 fm, and random normalization sampled from a gamma distribution of unit mean and unit variance.
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