ECAL response variations due to LHC irradiation

Abstract: Plots of the ECAL response to laser monitoring light in CMS during 2011 and 2012. The dependence vs time, eta and crystal radiation hardness are shown

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Figure Caption
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laser history 2011-12.png
Relative response to laser light (440 nm) measured by the ECAL laser monitoring system, averaged over all crystals in bins of pseudorapidity, for the 2011 and 2012 data taking periods

The response change observed in the ECAL channels is of the order of a few percent in the barrel, while it reaches up to 25% in the most forward endcap regions used for electron and photon reconstruction. The response change is up to 60% in channels closest to the beam pipe. These measurements are used to correct the physics data.

This is an update of the plots appearing in CMS-DP-2012/007 and CMS-DP-2012/015, and includes measurements taken up to October 2012. The bottom plot shows the instantaneous LHC luminosity delivered during this time period.

Out of date: this plot has been superceded by this plot
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loss vs mustd.png
Correlation between relative change of response from ECAL monitoring data, and the absorption coefficient, μstd, induced in crystals by a standard γ irradiation

The relative change of response is computed between 6-­September-­2011 and 4-­October‐2011. The parameter μstd is measured from a standard γ irradiation, performed during crystal quality control measurements, prior to their installation in CMS. Crystals produced by Shanghai Institute of Ceramics (SIC), and installed in CMS in the eta range 2.4 < η < 2.6, are plotted.

The presence of a correlation proves that a fraction of the signal loss is due to a change in crystal transmission from ionizing radiation damage.

The positive intercept of the correlation hints at the presence of a fraction of signal loss, uncorrelated with μstd, which could be caused by other sources, like losses in VPT response or cumulative losses from hadron‐specific changes in crystal transmission.
Topic attachments
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PDFpdf laser_history_2011-12.pdf r1 manage 2050.8 K 2013-07-11 - 17:28 ToyokoOrimoto  
PNGpng laser_history_2011-12.png r1 manage 123.8 K 2013-07-11 - 17:28 ToyokoOrimoto  
PDFpdf loss_vs_mustd.pdf r1 manage 47.0 K 2013-07-11 - 17:29 ToyokoOrimoto  
PNGpng loss_vs_mustd.png r1 manage 19.9 K 2013-07-11 - 17:29 ToyokoOrimoto  
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Topic revision: r2 - 2013-08-09 - ToyokoOrimoto
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