Matter-Antimatter Mass difference measurement of (Anti)Triton, (Anti)He3, and (Anti)He4
Abstract:
Figure 1: <dE/dx> plots of all tracks with a TOF mass2 measurement within 20% of expected mass value. The black lines correspond to fit lines for the expected <dE/dx> measurement for the studied nuclei. For all nuclei there is a clear grouping of tracks around the expected <dE/dx> measurement curve, indicating the presence of these nuclei in the final state of the collision.
Figure 2: Mass distributions of studied nuclei after the overlay procedure. Red data points are the positively charged nuclei. Black data are the negatively charged nuclei. The negatively charged mass distribution data was rescaled and shifted along the x axis to minimize the chi2 between it and the positively charged mass distribution data. This method of comparison removes the need for a precise mass function and also avoids the need for background estimation when fitting the distribution.
Figure 3: Measurements of ∆m/m of respective particles. For Clarity there is a y axis offset for the Neutron (+0.1 GeV/c2 offset), and both 3He and Triton measurements(±0.1 GeV/c2 offset) and ALICE HyperTriton (+0.1 GeV/c2 offset). Brackets represent systematic errors, bars represent statistical errors. The value and error of the mass difference for 4He is scaled down by a factor of 0.1. Note that reconstructed hyper-nuclei assume the decay 3He and anti-3He have equal mass.
Conclusion:
In this work we have measured the mass differences between Triton, Helium 3, and Alpha with their antimatter counterparts to be -0.26±0.60(stat.)±0.78(sys.), -0.16±0.60(stat.)±0.91(sys.), and -17.8±21.6(stat.)±25.1(sys.) MeV/c2 Respectively. These values are consistent with zero, as predicted by CPT symmetry. This is the first time the mass of anti-alpha has been measured after its first observation in 2011, and is the most massive antimatter state measured. The mass difference measurement of Helium 3 is over a 2 fold increase in precision over the previous result.
Target Journal: Physical Review Letters
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