# Multigap Resistive Plate Chambers for Time of Flight Applications
## 3 Applications in Large Experiments
### STAR Experiment in RHIC
#### 3.1.3 The PID Performance  
In the 200 GeV d + Au collisions, the average MRPC ToF timing resolution alone was measured to be 85 ps. The tracks of passing particles were reconstructed by the TPC, and their momentum and dE/dx were also recorded. Then the particle path can be calculated and extended to the ToF system. Figure 4a [57] shows the relationship between the inversed velocity (1/\(\beta\)) measured by the ToF system and the momentum (\(p\)) obtained from TPC. The ToF provides good PID capabilities with 1.6 GeV/c for \(\pi\)/K and 3 GeV/c for K/p separation. The embedded pad shows the distribution of the square of the mass for momentum in the range of 1.2 and 1.4 GeV/c. The pions, kaons and protons can be distinguished clearly. Furthermore, it makes the separation between electrons and hadrons possible with the help of velocity information from ToF and dE/dx obtained by TPC [58]. Figure 4b [59] shows the relation between dE/dx and momentum when setting \(|1/\beta-1|\leq 0.03\). Clear separation of electrons from hadrons can be seen.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Operation Condition**} & \multicolumn{3}{c}{**Time Resolution (ps)**} \\ \cline{3-5} \multicolumn{2}{c}{} & **Start Time** & **Overall** & **Stop Time** \\ \hline Run 3 & 200 GeV d + Au & \(\sim\)85 & \(\sim\)120 & \(\sim\)**85** \\  & 200 GeV p + p & \(\sim\)140 & \(\sim\)160 & \(\sim\)**80** \\ \hline Run 4 & 62 GeV Au + Au & \(\sim\)55 & \(\sim\)105 & \(\sim\)**89** \\ \cline{2-5} Run 4 & 200 GeV Au + Au & FF/RFF & \(\sim\)27 & \(\sim\)74 & \(\sim\)**70** \\ \hline Run 5 & 200 GeV Cu + Cu (ToT) & -50 & \(\sim\)92 & \(\sim\)**75** \\  & 64 GeV Cu + Cu (ToT) & \(\sim\)82 & \(\sim\)125 & \(\sim\)**94** \\ \hline Run 8 & 200 GeV p + p (ToT) & -83 & \(\sim\)112 & \(\sim\)**75** \\ \hline Run 9 & \multirow{2}{*}{500 GeV p + p (ToT)} & \multirow{2}{*}{-85} & \multirow{2}{*}{-117} & \multirow{2}{*}{\(\sim\)**78**} \\  & 86 trays & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: The time resolutions of the STAR MRPC during different physics runs. The stop times in bold text are provided by the ToF system.  
Figure 4: (**a**) 1/\(\beta\) vs. momentum for \(\pi^{\pm}\), K\({}^{\pm}\), and p(p) from 200 GeV d+Au collisions. Reproduced with permission from STAR Collaboration, Physics Letters B; published by Elsevier B.V., 2005 [57]. Insert: the distribution of the square of the mass for momentum in the range of 1.2 and 1.4 GeV/c. (**b**) dE/dx in the TPC vs. particle momentum (\(p\)) with a ToF cut of \(|1/\beta-1|\leq 0.03\). The figure is mapped low statistics bin to blue and high statistics bin to red. Reproduced with permission from [PERSON] et al., Phys. Rev. Lett.; published by the American Physical Society, 2005 [59]. Insert: projection on the dE/dx axis for particle momenta \(1<p<1.5\) GeV/c.  
Another example that shows the synergy between dE/dx and the ToF is illustrated with the observation of antimatter Helium-4 [60], as shown in Figure 5. The dE/dx of \(\rm\overline{{}^{3}He}\)/\(\rm\overline{{}^{4}He}\) and \(\rm\overline{{}^{3}He}\)/\(\rm\overline{{}^{4}He}\) versus mass derived from TPC and ToF are demonstrated separately on the top two views. The average masses of \(\rm 3^{\rm 3}He\) (\(\rm\overline{{}^{3}He}\)) and \(\rm\overline{{}^{4}He}\) (\(\rm\overline{{}^{4}He}\)) are around 2.8 and 3.7 \(\rm GeV/c^{2}\). The bottom view shows statistics about \(\rm 3^{\rm 3}He\) (\(\rm\overline{{}^{3}He}\)) and \(\rm\overline{{}^{4}He}\) (\(\rm\overline{{}^{4}He}\)). The mass peaks of \(\rm 3^{\rm 3}He\) and \(\rm{}^{4}He\) can be separated obviously, which reveals the importance of the ToF system.