Splash Events Plots

EE and EB

Average energy per crystal in ECAL seen during 800 “beam splash” events collected with beams coming from the negative side.

White regions are masked channels (0.9% of total) of which one quarter may be recovered.

For 0.75% trigger information allows a coarse energy reconstruction; only for 0.15% neither data nor trigger information are available.

Energy modulations are a combination of the energy flow traversing CMS and geometry effects.

In particular, the lower energy at large radii in the ECAL Endcap downstream to the beam direction is due to the ECAL barrel shield.

This is consistent with a muon flux reduction along the barrel of about 25%, corresponding to stopping muons. 

The average muon fluence is about 5 muons cm-2



Preshower

Preshower was the last component installed in CMS (Spring 09). It successfully operated during all “beam splash” events. 

Number of muons per sensor crossing the ECAL preshower in 1 “beam splash” event collected with the beam coming from the negative side.

Two white regions are excluded from readout. Work is ongoing to recover both. 

Flux modulations are consistent with the energy maps seen in the ECAL Endcaps. 

Isolated hot spots are attributed to muon radiation 

Sensors cover 37.1 cm2 each, thus the average muon fluence is about 5 muons cm-2.