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Paper proposal: Non-identical particle femtoscopy measurements in the STAR Beam Energy Scan program

Updated on Thu, 2024-05-02 10:11. Originally created by pawszy on 2022-09-13 07:47.

Title: Non-identical particle femtoscopy measurements in the STAR Beam Energy Scan program

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

Abstract: 

The femtoscopy method can probe the space-time structure and dynamics of strongly interacting nuclear matter created in high-energy collisions. The correlation of two non-identical particles allows one to extract information about asymmetry in the emission process between two kinds of particles. Such asymmetry arises in a system with a strong radial flow. In this work, femtoscopic analysis of three different systems (pion-kaon, pion-proton, and kaon-proton) in central (0-10\%) Au+Au collisions at $\sqrt{s_{NN}} = 39$ GeV is reported. Source sizes are consistent between different sign combinations and larger in the case of pion-kaon and pion-proton than for kaon-proton pairs. Obtained asymmetries show that lighter particles, on average, are emitted closer to the center of the source and/or later than heavier particles. Additionally, the pion-kaon correlations are analyzed in the centrality dependence in Au+Au collisions at $\sqrt{s_{NN}} = 39$ GeV and for three energies of the Beam Energy Scan program $\sqrt{s_{NN}} = 7.7$, $11.5$, and $39$ GeV. The sizes of pion-kaon sources increase with increasing centrality and energy. These results confirm that collective behavior exists in the lower energies of the BES-I program.

Paper draft:

Analysis Note:

Presentation: 
 
 

Results (Proposed figures):

Figure 6

 
a) The energy loss in the TPC detector as a function of particle momentum. b) Distribution of $1/\beta$ as a function of momentum. c) The $m^2$ as a function of momentum. Three regions representing $\pi$, $K$ and $p$ are marked. This example is from central (0-10\%) Au+Au collisions at $\sqrt{s_{NN}}$~= 39 GeV.

Figure 8

Spherical harmonics components $C^0_0$ (top panel) and $\Re C^1_1$ (bottom panel) of the $\pi K$ correlation function with fitted background polynomials (lines) for central (0-10\%) Au+Au collisions at $\sqrt{s_{NN}} = 39$ GeV. Zoomed on the y-axis to stress the background effect. Functions after corrections are presented in the top-right corner of both panels.

Figure 9

The purity of $\pi^+ K^+$, $\pi^+ p$, and $K^+ p$ pairs for Au+Au collisions at $\sqrt{s_{NN}} = 39$ GeV.

Figure 10

Impact of the momentum resolution on SH components.

Figure 11



Comparison of $C_0^0 (k^*)$ SH components of like-sign (bottom) and unlike-sign (top) $\pi K$ pairs for Au+Au collisions at $\sqrt{s_{NN}} = 39$ GeV in different (0-10\%, 10-30\% and 30-70\%) centrality classes. Uncertainties are statistical only.

Figure 12

Comparison of $\Re C_1^1 (k^*)$ SH components of like-sign (bottom) and unlike-sign (top) $\pi K$ pairs for Au+Au collisions at $\sqrt{s_{NN}} = 39$ GeV in different (0-10\%, 10-30\% and 30-70\%) centrality classes. Uncertainties are statistical only.

Figure 13

Centrality dependence of $\pi K$ source size (R) for Au+Au collisions at $\sqrt{s_{NN}} = 39$ GeV. Statistic uncertainties are represented by solid lines. Shades show systematic ones.

Figure 14

Centrality dependence of $\pi-K$ emission asymmetry ($\mu$) for Au+Au collisions at $\sqrt{s_{NN}} = 39$ GeV. Statistic uncertainties are represented by solid lines. Shades show systematic ones.


Figure 15



Comparison of $C_0^0 (k^*)$ SH components of like-sign (bottom) and unlike-sign (top) $\pi K$ pairs for central(0-10\%) Au+Au collisions at different energies $\sqrt{s_{NN}} = 7.7$, $11.5$ and $39$ GeV. Uncertainties are statistical only.

Figure 16



Comparison of $\Re C_1^1 (k^*)$ SH components of like-sign (bottom) and unlike-sign (top) $\pi K$ pairs for central(0-10\%) Au+Au collisions at different energies $\sqrt{s_{NN}} = 7.7$, $11.5$ and $39$ GeV. Uncertainties are statistical only.

Figure 17

Energy dependence of $\pi K$ source size (R) for 0-10\% most central Au+Au collisions at $\sqrt{s_{NN}} = 7.7$, $11.5$ and $39$ GeV. Statistic uncertainties are represented by solid lines. Shades show systematic ones.


Figure 18

Energy dependence of $\pi K$ emission asymmetry ($\mu$) for 0-10\% most central Au+Au collisions at $\sqrt{s_{NN}} = 7.7$, $11.5$ and $39$~GeV. Statistic uncertainties are represented by solid lines. Shades show systematic ones.

Figure 19

Comparison of $C_0^0 (k^*)$ SH components of like-sign (bottom) and unlike-sign (top) for $\pi K$, $\pi p$ and $Kp$ pairs for central (0-10\%) Au+Au collisions at $\sqrt{s_{NN}} = 39$ GeV. Uncertainties are statistical only.

Figure 20

Comparison of $\Re C_1^1 (k^*)$ SH components of like-sign (bottom) and unlike-sign (top) for $\pi K$, $\pi p$ and $Kp$ pairs for central (0-10\%) Au+Au collisions at $\sqrt{s_{NN}} = 39$ GeV. Uncertainties are statistical only.


Figure 21

  

Mean pair transverse mass dependence of source size for central (0-10\%) Au+Au collisions at $\sqrt{s_{NN}} = 39$ GeV for different charge combinations of $\pi K$, $\pi p$, and $Kp$ pairs.


Figure 22

Mean pair transverse mass dependence of emission asymmetry for central (0-10\%) Au+Au collisions at $\sqrt{s_{NN}} = 39$ GeV for different charge combinations of $\pi K$, $\pi p$, and $Kp$ pairs.

Figure 23


Comparison of the relation between emission asymmetry of $\pi K$, $\pi p$, and $K p$ pairs for different charge combinations for central (0-10\%) Au+Au collisions at $\sqrt{s_{NN}}$ = 39 GeV.

Figure 24


Model (Therminator 2 and UrQMD) predictions for $\pi^+K^+$ correlation functions. UrQMD and experimental functions correspond to 0-10\% and Therminator 2 to 0-5\% central Au+Au collisions at $\sqrt{s_{NN}}$= 39 GeV.

Figure 25


Model (Therminator 2 and UrQMD) predictions for $\pi^-K^+$ correlation functions. UrQMD and experimental functions correspond to 0-10\% and Therminator 2 to 0-5\% central Au+Au collisions at $\sqrt{s_{NN}}$= 39 GeV.

Figure 26

Comparison of correlation functions from Therminator 2 model for primary and all $\pi^+K^+$ pairs for Au+Au collisions at $\sqrt{s_{NN}}$ = 39 GeV in 0-10\% centrality class.

Figure 27

Comparison of correlation functions from UrQMD model for primary and all $\pi^+K^+$ pairs for Au+Au collisions at $\sqrt{s_{NN}}$ = 39 GeV in 0-10\% centrality class.

Conclusions:

  • Results indicate that the average space-time positions of pions and kaons (and also pions and protons) are not the same for Au+Au collisions at 7.7, 11.5, and 39 GeV.
  • Very small asymmetry is present in the case of kaon-proton pairs.
  • Measured asymmetry satisfies the predicted relationship:
     
  • Values of source parameters are consistent for all charge combinations.
  • Spherical harmonics components are well described using 3-dimensional Gauss distribution as the source function.
  • Strong interaction between kaons and protons needs investigation.




 

Previous presentations:

 

Bibliography:

[1] Kisiel, A., "CorrFit - A program to fit arbitrary two-particle correlation functions,", Nukleonika 49, 81-83 (2004).
 

 

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