Another look at Run 17 days 105 and 106

In light of recent concern for the TPC calibrations of Run 17 pp510 by looking at the ratio of +/- charged particles as a function of pT and seeing it vary as a function of time period, I went back to take another look at how SpaceCharge looks in day 105 vs. day 106, which initially seemed to show large differences from each other.

I ran the code that measures SpaceCharge seen in the data on 39 runs sampling days 105 and 106. Here is a plot of the findings of how much SpaceCharge appears to be needed (day 105 in blue, day 106 in red) and the SpaceCharge correction that was used (in black), which was the result of the original calibration used in the P18ib physics production. That calibration used zdcenk (ZDC east singles, no-killer) as its luminosity scaler, so I plotted versus that.


Clearly the existing calibration underestimates the SpaceCharge at higher luminosity. Here is the fraction of additional SpaceCharge desired vs. zdcenk, same coloring:


The fraction needed grows faster than zdcenk, which implies that to get this correct, a calibration that grows faster than the first power of zdcenk will be needed (e.g. zdcenk^x where x>1.0, like maybe 1.2).

Also, there's no clear difference in what's needed on days 105 and 106 other than day 106 is recorded at a higher luminosity, but that might be enough to explain why the +/- ratio differs notably between the two days.

Lastly, I've plotted the above fraction of additional SpaceCharge desired (in blue, and scaled by 2e7) on the same plot as zdcenk vs. a proxy for time on days 105 and 106. For zdcenk, I've alternated colors (red and black) for different fills of the collider. This helps to see the mid-fill step in luminosity due to the beta squeeze that was performed that Run year.



By eye, it appears that there's nothing particularly different about the behavior before and after the beta squeeze: the fraction of additional SpaceCharge desired follows zdcenk similarly regardless of time.

My conclusions at this point are that the beta squeeze has no first order effect on the SpaceCharge, and that the original SpaceCharge calibration is too low at high luminosity by an amount that indicates we likely need to use a non-linear formula from the scalers.

-Gene