Single hit resolution of CMS Drift Tube chambers in 2015

The Drift Tube (DT) single hit resolution was measured using 2015 data and applying the same method described here

Phi and Theta Super Layers (SL) were kept apart because their geometrical differences determine intrinsically different performances.

We recall here the main features of these plots:

1) Within every station, both Theta and Phi Super Layers show a symmetric behaviour w.r.t. to the z=0 plane, as expected from the detector symmetry.

2)  In Wheel 0, where tracks from the interaction region are mostly normal to all layers, the resolution is the same for Theta and Phi SL's.

3) Going from z=0 towards the forward regions, tracks from the interaction region have increasing values of pseudorapidity: this feature affects Phi and Theta SL's in opposite ways. In fact the theta angle lies on the measurement plane of Theta layers, while it is orthogonal to it for Phi layers. The result is that in Theta SL's the increasing inclination angle, by spoiling the cell linearity, also worsen the resolution. Instead, in Phi SL's the inclination angle increases the track path within the tube (along the wire direction), thus increasing the ionization charge and improving the resolution.

4) The poorer resolution of the Phi SL's in MB4, compared to MB1-MB3, is because in MB4 no corrections are applied to the hit position in order to take into account the muon time-of-flight and the signal propagation time along the wire. In fact in the MB4's no position information is available in the direction parallel to the wires.

DT measured resolution for Phi and Theta Super Layers, shown chamber by chamber.

DT measured resolution for Phi and Theta Super Layers, shown station by station

Apart from Theta SL's in MB1 stations of external wheels (where in any case the track inclination and the transverse component of magnetic field bias the residual distributions and make the gaussian fit unstable), the resolution observed this year is compatible or slightly better than the one obtained with 2012 data.

-- FrancescaCavallo - 2015-12-14