Measurement of η' meson in pp collisions at the LHC with ALICE

With a mass of nearly 1 GeV, the η' is the heaviest amongst the pseudoscalar mesons composed of the lightest quarks. This anomalously large mass is believed to be induced by the gluonic interactions and the axial U(1) anomaly of QCD. However, its exact production cross-section is still not well understood for heavy ion collisions, therefore the measurement of $\eta'$ can provide deeper insight into perturbative chromodynamics in this regime. Moreover, its measurements in proton-proton collisions at ultrarelativistic energies provide a baseline for heavy-ion collisions, where a large fraction of the mesons will decay within the produced quark-gluon plasma, which is anticipated to lead to the lowering of its mass with respect to its value in vacuum.

In this talk, the first results on the measurement of the η' production in the ALICE central barrel in pp collisions with a center of mass energy of $\sqrt{s} = 13 $ TeV will be presented. The $\eta'$ meson is reconstructed via its η' → π⁺ π^- η decay channel, where the η meson decays further into two photons. In ALICE, these photons can be measured in two different ways: either via their energy deposits in one of the electromagnetic calorimeters (EMCal, PHOS) or by tracking the e⁺e^- pairs from photon conversions in the Time Projection Chamber (TPC). In this analysis, the η' is reconstructed using both pure EMCal and PCM-EMCal combined data.