Abstract
Medipix and Timepix devices, installed in the ATLAS cavern, have provided valuable complementary luminosity information. Results are presented from measurements with the Timepix3 (TPX3) detectors. In contrast with previously employed frame-based data acquisition, the TPX3 detector remains active continuously, sending information on the pixel hits as they occur. The hit- and cluster-counting methods were used for the luminosity determination of the Large Hadron Collider (LHC) proton–proton collisions. The LHC luminosity versus time is determined using these two methods and fits to a simple model, which incorporates luminosity reduction from the single bunch and beam–beam interactions. The precision of the luminosity determination could be improved by counting the number of clusters, instead of just pixel hits. The internal precision and long-term stability of the TPX3 luminosity measurements are below 0.5%. TPX3, owing to its 1.56-ns time-tagging, is able to resolve the time structure of the luminosity due to the collisions of the individual proton bunches when integrated over an LHC fill.
Highlights
Precision luminosity measurements are of particular importance for many analyses in high-energy physics
A double-layer TPX3 device installed in the ATLAS detector cavern has successfully taken data at the LHC during Run-2 13 TeV proton-proton collisions
The relative internal short-term precision of the TPX3 luminosity measurements was determined from the LHC luminosity curve to be less than 0.5% for 60 s time intervals
Summary
Precision luminosity measurements are of particular importance for many analyses in high-energy physics. 2) An improved cluster separation: In the previous MPX and TPX luminosity analyses, no cluster (particle) counting with high statistics was possible. Owing to the precise pixel time-stamping of TPX3, cluster identification and separation could be done in high flux conditions. This leads to a higher precision of the luminosity measurements. An important innovation is that the TPX3 device allows for cluster counting up to high particle rates, since pixel data are digitized and read out as a stream rather than accumulated on-pixel until a full frame is transmitted. The two-layer structure of the TPX3 device doubles the measurement statistics and, in this analysis, allows one to determine the internal precision and long-term time stability of individual TPX3 devices.
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