[Halld-cal] Assignment of "noisy" SiPMs

[George Lolos]

Hi Elton:

I would have made the exact same assignments for the more noisy SiPM's as you and with the same reasoning, so I'd say you are correct :-)

Cheers,

George
On 2012-12-06, at 4:56 PM, Elton Smith wrote:

> Dear collaborators,
> 
> At the Cal Working group meeting on Tuesday, Orlando showed spectra of 
> some SiPMs that had higher noise rate than typical. Yi checked that the 
> sensor we were looking at corresponded to a high dark rate by Hamamatsu 
> also, verifying the effect. These "noisy" units still fall within our 
> specification, having noise rates of perhaps 20-30% higher than average. 
> Note that once the sensors are irradiated, the dark rate due to 
> irradiation will dominate for all sensors. USM is continuing to re-check 
> the behavior of sensors that have been set aside based on initial 
> measurements. There was some discussion about placing some of these 
> units in regions of the detector where they would have the least impact.
> 
> There is now some urgency in making a decision regarding how to handle 
> these "noisy" units. The assignment of sensors to a particular board is 
> in process and we need to decide what to do with these units now so that 
> the jumper maps for the electronic boards can be finalized.
> 
> I suggest the following:
> 1) We need a list of all noisy SiPM identified by USM, and the criteria 
> for designating "noisy" SiPMs. This list will not be complete because 
> not all sensors have been tested. We can compare this list with noisy 
> SiPMs from Hamamatsu. If the USM list is verified, we can use the 
> Hamamatsu data to complete our list.
> 
> 2) I propose to assign the "noisy" SiPMs in the following way:
> a) Place all noisy SiPMs in the outer layers (sum of 4)
> b) Place all noisy SiPMs on the downstream boards
> c) Do not place two noisy SiPMs in the same sum.
> 
> My reasoning is as follows: a) the outer layer does not have TDCs, so is 
> not used as heavily as the other layers. Most of the energy is also 
> deposited in the inner layers, especially for the hits at low angles, 
> which constitute the majority of events. b) Use the downstream because 
> they will register the highest light output and the noise rate will be 
> relatively less important c) minimize the impact of noisy SiPMs by not 
> having more than one contribute to a single readout channel.
> 
> Thus, with this e-mail I am first requesting that USM provide the most 
> complete list of noisy channels they can at this time. Cross reference 
> to the Hamamatsu measurements can be done by USM or JLab. Second, if 
> anyone has any comments/suggestions/feedback to my proposal for 
> assignment of the SiPMs, please pass them on to the mailing list.
> 
> Thanks, Elton.
> 
> 
> 
> 
> -- 
> Elton Smith
> Jefferson Lab MS 12H5
> 12000 Jefferson Ave STE 16
> Newport News, VA 23606
> (757) 269-7625
> (757) 269-6331 fax
> 
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