Investigating local parity violation in heavy-ion collisions using $\mathrm{\Lambda }$ helicity

We propose the measurement of net $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ helicity, correlated event by event with the magnitude and sign of charge separation along the event's magnetic field direction, as a probe to investigate the chiral magnetic effect (CME) in heavy-ion collisions. With a simple simulation model of heavy-ion events that includes effects of local parity violation, we estimate the experimental correlation signal that could be expected at RHIC given the results of previous measurements that are sensitive to the CME.

Figure 1

Toy model calculation of the number of minimum-bias events required to see a correlation between event-by-event net $\mathrm{\Lambda }$ helicity and charge separation with respect to the first-order reaction plane. Blue squares represent the assumption that all the charged particle correlation signal is due to the CME and assumes both $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ are used, with the calculation given as a function of experimental efficiency for finding $\mathrm{\Lambda }\mathrm{s}$ varying from 3.5% to 30%. Green circles represent the number of events needed assuming only 1/2 of the measured charged particle correlation signal comes from CME. Statistical uncertainties from the simulations are shown on all points.