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Paper proposal in 200GeV p+p collisions

Updated on Thu, 2023-03-16 07:16. Originally created by nish on 2022-01-03 22:42.

 

 

 

 

Paper Proposal for 
Measurements of Charged Particle Multiplicity dependence of Higher-Order Net-proton Cumulants 
in 200 GeV p+p Collisions at √s = 200 GeV from RHIC

 

Risa Nishitani,  2023/03/16 Updated

https://drupal.star.bnl.gov/STAR/blog/nish/PWGC-meeting-20220318

https://drupal.star.bnl.gov/STAR/system/files/GPC_20220907.pdf

https://drupal.star.bnl.gov/STAR/system/files/GPCReply2ndRound.pdf 

 

Physics motivation

Goal: Search for the QCD critical point and first-order phase transition boundary

Critical point search

  • Observed net-proton κσ2 show non-monotonic energy dependence
  • It is consistent with theoretical prediction  
Crossover search
  • Observed C6/C2 systematically towards negative in peripheral to central collisions
  • LQCD, FRG: negative C5 and C6 for crossover phase transition 


Fluctuation measurement in p+p 

  • Precise determination of the physics baseline for fluctuation in Au+Au collisions
  • Check the possibility of phase transition in high multiplicity events in p+p collisions through the measurements of higher-order cumulants

    Run12 data have 70 times larger statistics than Run9 p+p results
    Multiplicity/Acceptance dependence would be newly available with high statistics dataset 
 
 

Abstract

 
We report on the charged-particle multiplicity dependence of net-proton cumulant ratios up to sixth-order from $\sqrt{s}$~=~200~GeV p+p collisions at the Relativistic Heavy Ion Collider (RHIC). The measured ratios, $C_{4}/C_{2}$, $C_{5}/C_{1}$, and $C_{6}/C_{2}$, decrease with increasing charged-particle multiplicity and rapidity acceptance. Neither the Skellam baselines nor PYTHIA8 calculations could account for the observed multiplicity dependence. In addition, the ratios of $C_{5}/C_{1}$ and $C_{6}/C_{2}$ decrease with multiplicity and approach negative values in the highest-multiplicity events. The negative ratios, as observed in central Au+Au collisions at 200 GeV hint at the formation of thermalized QCD matter in the most central p+p collisions at 200 GeV. Precise measurements at higher collision energies, in larger colliding systems and wider acceptance in rapidity will be important to further understanding of the observed multiplicity dependence.



Figures

FIG.1
 
   (a) Correlations between the energy loss, dE/dx, of charged tracks measured by the TPC and momentum divided by electric charge.  

   (b) Correlations between the mass squared, m2 GeV/c2, measured by the TOF and p/q. Contour bands represent the identified protons and antiprotons used in the analysis, while black dots are for other charged particles.

   (c) Charged particle multiplicity distribution.

   (d) Event-by-event net-proton multiplicity distributions within |y| < 0.5 and 0.4 < pT < 2.0 GeV/c for three ranges of charged particle multiplicity as indicated in the panel.  

 
FIG.2

 

Net-proton cumulant ratios, C2/C1, C3/C2, C4/C2, C5/C1, and C6/C2 as a function of charged-particle multiplicity from √s = 200 GeV p+p collisions. All protons and anti-protons are from |y| < 0.5 and 0.4 < pT < 2.0 GeV/c. Cyan points represent the event-averaged for 3 ≦ mch < 30, and they are plotted on the corresponding value of mchTPC.  The Skellam baselines are shown as dashed liens. The results of the PYTHIA8 calculations are shown as purple bands. Purple squares are results evet-averaged values from the model calculations.


Data: <mchTPC> = 6.25685 

PYTHIA 8 Average
 
Value
Statistic error
 
C2/C1
12.892
0.0428579
 
C3/C2
0.0746934
0.000224758
 
C4/C2
0.986126
0.000348293
 
C5/C1
0.828961
0.0146119
 
C6/C2
0.93979
0.0030201
 
FIG.3

Rapidity-acceptance depedece of the nnet-proton cumulant ratios shown as a function of the charged particle multiplicity from the √s = 200 GeV p+p collisions. Within |y| < 0.5, the mean multiplicity is found to be <mchTPC>=6.23 . The multiplicity averaged values from  |y| < 0.1 and  |y| < 0.5 are shown as  cyan square and circle, respectively. The Skellam baselines are shown in the dashed lines.



FIG.4


 

Net-proton cumulant ratios, C4/C2, C5/C1, and C6/C2 as a function of charged particle multiplicity for p+p collisions and Au+Au collisions at 200 GeV within |y| < 0.5 and 0.4 < pT < 2.0 GeV/c. 
Cyan points represent the event-average for 3 ≦ mchTPC < 30 from the  p+p collisions. Results from Au+Au collisions are shown in triangles for 0-40%, 40-50%, 50-60%, 60-70%, and 70-80% centralities. Red and orange bands show the systematic uncertaities for p+p collisions and Au+Au collisions, respectively. For both collinding system, the values of the charged particle multiplicity mchTPC were measured  within the same acceptance and nnno efficiency corrections were applied. The Skellam baselines are shown in long-dashed lines. The navy bands show corresponding susceptibility ratios of baryon number from lattice QCD calculations [Phys. Rev. D 101, 074502]. 

Data Table

  • CBWC for p+p

    		•  x y statistical error systematic error
    C4/C2 5.6519 0.87949 0.0006627 0.0079075
    C5/C1 5.6519 0.51666 0.0101024 0.0403578
    C6/C2 5.6519 0.46530 0.0046835 0.0388945

Conclusions
In summary,

we report the first measurements of higher-order cumulant ratios $C_{2}/C_{1}$, $C_{3}/C_{2}$, $C_{4}/C_{2}$, $C_{5}/C_{1}$ and $C_{6}/C_{2}$ of net-proton multiplicity distributions in $p$+$p$ collisions at $\sqrt{s}=$~200~GeV, as measured by the STAR detector at RHIC.
Both charged-particle multiplicity and rapidity-cut dependencies are reported.

It is found that the ratios are all below Skellam expectations. Calculations from PYTHIA8~\cite{Sjostrand:2014zea} failed to reproduce the multiplicity dependence and the hierarchy observed in net-proton ratios of $C_{4}/C_{2}$, $C_{5}/C_{1}$ and $C_{6}/C_{2}$.

Within uncertainties, the multiplicity dependence of these ratios is found to be smoothly connected to the results from Au+Au collisions at $\sqrt{s_{\rm NN}}=$~200~GeV. Overall, the net-proton cumulant ratios of $C_{4}/C_{2}$, $C_{5}/C_{1}$ and $C_{6}/C_{2}$ decrease progressively between the 200~GeV $p$+$p$ collisions and Au+Au central collisions. In the currently-measured highest-multiplicity bin, the ratios of $C_{5}/C_{1}$ and $C_{6}/C_{2}$ from $p$+$p$ collisions approach zero. While the multiplicity-averaged ratios from $p$+$p$ collisions remain positive, the results of Au+Au central collisions are negative and qualitatively consistent with lattice QCD calculations.

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