From: Brown, RM (Bob) - PPD [R.M.Brown@rl.ac.uk]
Sent: 23 January 2008 10:56
To: Cockerill, DJA (David)
Subject: FW: Hadron damage to PWO

Attachments: arXiv-0709.4409.pdf

As promised...



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From: Brown, RM (Bob) - PPD 
Sent: 17 January 2008 14:45
To: 'Egidio Longo'; 'Quentin Ingram'; 'Philippe Bloch ((E-mail))'
Cc: 'Tejinder Virdee (E-mail)'
Subject: RE: Hadron damage to PWO

 
However, it turns out that the results presented in this paper have quite serious implications for CMS.

The results from the original proton irradiations were interpreted in the context of CMS in CMS Note 2005/10.
There it was noted that a 20 GeV proton fluence of 10^13 p/cm2 produced an induced absorption of
 2.0 m-1 (to be compared with the limit of 1.5 m-1, we have set for the gamma-induced absorption).

For comparison, the same degree of lattice damage (measured in terms of star density)  will be reached after
10 years of full luminosity operation at eta = 2.1 in the endcaps, and after 3 years of full luminosity
at eta = 2.6.

However, it was argued in Note 2005/10 that the absorption would scale not only with star density, but
also with the total track length per star.  This introduced a further factor of 4 in the extrapolation 
from 20 GeV protons to CMS pions.  In that scenario, the induced absorption would reach only 1.5 m-1 at
eta = 2.6, after ten years of operation.  This led to the (albeit tentative) conclusion that the 
EE performance would be maintained for a full ten years out to eta = 2.6.

The PSI results show that the damage does scale with star density, but does NOT scale
with star track length, implying that the ECAL performance will start to degrade progressively
inwards from eta = 2.6 after only 3 years of full luminosity running.

Bob.