Title: Proton femtoscopy in Au+Au collisions at BES energies in RHIC

PA: Sebastian Siejka, Hanna Zbroszczyk, Paweł Szymański, Diana Pawłowska, Daniel Wielanek

Abstract:

The method of femtoscopy allows for determining the sizes of particle-emitting sources created in heavy-ion collisions at high energies. It uses Quantum Statistics effects and Final State Interactions to determine the space-time properties of the source. Extracting radii of the sources from two-baryon correlations and comparing them with those obtained from meson-baryon or two-meson correlations provides complementary information about source characteristics. This analysis is based on data collected by STAR for Au+Au collisions at Beam Energy Scan energies and studies femtoscopic correlations of protons and antiprotons. Correlations of protons have been studied for many years and the focus of this analysis is to apply corrections related to their production process.

Paper draft:

Analysis note:

Presentations:
Paper proposal [Aug. 28th, 2022]
Paper proposal update [Sep. 13th, 2022]

Results (proposed figures):

Figure 1


The ToF mass square versus momentum distribution (top) and a cross-section at p=2 GeV/c along with fitted Gaussian curves for pions, kaons and protons (bottom) for Au+Au collisions at √(s_NN )=39 GeV.

Figure 2


Proton-proton pair purity as a function of k^∗ for Au+Au collisions at √(s_NN )=39 GeV.

Figure 3


Fraction of primary pairs in experimental data as a function of collision energy estimated based on data generated by vHLLE-UrQMD model.

Figure 4


Residual correlation functions calculated using theoretical proton-lambda (left) and antiproton-lambda (right) correlation functions along with decay characteristics obtained using THERMINATOR 2 data.

Figure 5

Proton-proton, antiproton-antiproton and proton-antiproton correlation functions after applying all corrections for 3 Au+Au collision centralities at BES energies along with fits.

Figure 6

Extracted radii for various pair systems from correlation functions from central (top), mid-central (mid) and peripheral (bottom) collisions shown as a function of collision energy. Selected points have been gently shifted horizontally in order to improve readibility of the plot.

Figure 7

Comparison of extracted radii (coloured red, orange and yellow) with previous results for other energies and particle combinations. Points have been moved on the energy axis for better visibility of data.

Conclusions:

Despite corrections applied in order to account for contamination of experimental data with pairs containing protons and antiprotons originating from decays of other particles, we continue to observe discrepancies between radii obtained from correlation functions of identical and nonidentical baryons. One of the possible reasons for this might be the observed trend of growing fraction of primary proton-proton pairs at lower energies – further femtoscopic analysis of protons is warranted. Increased statistics should also have a positive impact on the analysis, allowing for lower errors.

Bibliography
[1] Nature 527 (2015) 345
[2] Phys. Rev. Lett. 114 (2015) 22301
[3] Phys. Rev. C 74 (2006) 54902
[4] Phys. Rev. C 74 (2006) 64906
[5] Phys. Rev. Lett. 87 (2001) 82301
[6] Phys. Rev. C 80 (2009) 24905
[7] Phys. Rev. C 103 (2021) 34908

Previous presentations:
Analysis update - residual correction [Jun. 2021]
Analysis update - fractions [Dec. 2020]
Quark Matter 2018
Analysis update [Apr. 2017]