sPHENIX HCal discussion

[Edward Kistenev <kistenev AT bnl.gov>]

Mickey,

I think you complicate the matters enormously. The system as I proposed to build it will have one tiny LED’s  (blue, ~420nm, light absorbed  by WLS fibers, very little power) pulsed simultaneously by  trigger pulse common to many LED's. One option is to pulse 48 LED’s (8x6 towers) by the same pulse making all kinds of correlation checks possible. The LED’s pulsed by a common pulse are ONE LED per TOWER, selecting address in 5 consecutive events you will send LED light to all five tiles in every tower and you have complete configuration control (test whatever trigger configuration you want - something you will never do if fibers are part of your design).

Please note that if single pixel signals are measurable in a 14 bits system with 5 SiPM ganged passively on a common preamp (need ~50mkV noise) - you will have the best in the world monitoring system - no need in photocells or any further complications. But you will still need ongoing calibration. In PHENIX we decided that pi0’s are the source of that calibration, in sPHENIX HCAl - it should be muons. There is no problem with taking low rate of muon events - trigger is nearly the same as for jets, all information for that trigger is available.

Here is what I wrote to JL about LED’s few days ago:

Couple words on LED choice. Going to 380 kills the purpose. In PbSc we went this way thinking that dust accumulation, aging, god knows what may produce something unknown and UV will help to disentangle it. That system happen to be rather useless and works ONLY because it is laser based. The amount of UV light you need to deliver to the object you are trying to excite requires a lot of power (multiple emission-absorption steps) and nothing except long fiber from the source (laser in case of PbSc) to detector allows you to decouple the two - pickup and signal of scintillation (we introduced a fiber in our setup at UTFSM to help with this interference problem even with our blue LED and low amplitude pulsing). Whoever insists on 380 should first show the actual benefits of it before the decision is made otherwise it is just a wishful thinking.

Edward

Edward Kistenev, PhD

PHENIX Physicist

On Dec 23, 2015, at 2:04 PM, Mickey Chiu <chiu AT bnl.gov> wrote:

Hi Edward,

Here’s an email I sent to John on a UV LED which might be able to excite the scintillator directly…  I’m not sure what kind of scintillator is used in the Uniplast tiles, but I thought you might be interested…

Mickey

Begin forwarded message:

From: Mickey Chiu <chiu AT bnl.gov>

Date: December 20, 2015 at 11:02:47 AM EST

To: John Haggerty <haggerty AT bnl.gov>

Subject: Re: UV LED?

Hi John,

For the LED calibration, if possible I’d get one LED for some cluster of towers, and use fibers to transport it out.  That would save on the cost of the LED, and also it actually reduces the fluctuations from having an independent LED for each tower.  Also, you should monitor that LED with a pin diode if possible, which is not going to be dependent on temperature and has gain of 1 by definition.  That’s what we’ve done for the MPC, based on what Terry suggested (and used for the PbGl).  It’s worked pretty well for us… We correct the time dependencies of the gain to ~1% just from the LED (we know based on our pi0 peak).  This is even with the crappy PbWO4 and APD which both have huge dependencies on temperature and radiation damage.

I think CMS seems to be even much better than us.  It should be worthwhile for someone to explore how they do their calibration.

Mickey

On Dec 19, 2015, at 3:46 PM, Mickey Chiu <chiu AT bnl.gov> wrote:

Begin forwarded message:

From: "Tsang, Thomas Y" <tsang AT bnl.gov>

Date: December 18, 2015 at 7:03:13 PM EST

To: "Chiu, Mickey" <chiu AT rcf.rhic.bnl.gov>

Subject: RE: UV LED?

~$300-$500 /ea

Sensor electronics, they probably can give you surface mount type.
http://www.s-et.com/uvtop.html


Now ThorLabs also carry their UVLEDs
http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=2814&pn=LED265W

__________________________
Thomas Tsang, Ph.D.
Instrumentation Division, 535B
Brookhaven National Laboratory
Upton, NY 11973
 
Phone: 631-344-2225
Fax: 631-344-5773
URL: http://www.inst.bnl.gov/programs/laseropt/lasers/


-----Original Message-----
From: Mickey Chiu [mailto:chiu AT bnl.gov]
Sent: Friday, December 18, 2015 5:25 PM
To: Tsang, Thomas Y
Subject: UV LED?

Hi Thomas,

We might be interested in UV LED’s for calibrations in sPHENIX.  I think you mentioned that you know a good source of them.  Can you point me to where to find them?  Also, how much are they, and do they have surface mount versions?

Thanks!

Mickey
--
Building 510C
Department of Physics
Brookhaven National Laboratory
Upton, NY 11973
Phone: 631-344-8428

-- 
Building 510C
Department of Physics
Brookhaven National Laboratory
Upton, NY 11973
Phone: 631-344-8428

-- 
Building 510C
Department of Physics
Brookhaven National Laboratory
Upton, NY 11973
Phone: 631-344-8428

-- 
Building 510C
Department of Physics
Brookhaven National Laboratory
Upton, NY 11973
Phone: 631-344-8428