Comments on: Billion Dollar Baby (The CMS Silicon Tracker)

By: Rando M

Rando M — Tue, 11 Aug 2009 01:34:42 +0000

Not quite. That’s the energy per particle, and the beam has several of these particles. 600 megajoules worth.

By: five 0h

five 0h — Thu, 09 Aug 2007 19:16:55 +0000

please corrrect me if im wrong but 1 tev is about 1.6 x 10 ^ -7 joules, making 7 of them (LHC design beam energy) 1.12 x 10 ^ -12 joules. now assuming that a mouse weighs 200 grams and can sprint at a rate of 1 m a second (running from kitty) its kinetic energy would equal ~ 10 ^ -1 joules.

what we have here is kinetic energy of the proton beam being ~11 orders of magnitude less than a sprinting mouse.

my point : the tracker will be fine.

the silicon however, that will need to be replaced eventually since the radiation will damage the lattice over time.

if the beam were to spill into the silicon, this process would be shortened dramatically

By: Mike Saelim

Mike Saelim — Mon, 30 Jul 2007 18:34:47 +0000

Hey! I’m in the University of Michigan REU at CERN this summer, and one of the people in our program is working at the TIF. Look around for a girl named Teesa from MIT!

By: Ellipsis

Ellipsis — Mon, 30 Jul 2007 05:57:26 +0000

Alexey — green and orange are the most widely-available colors of the shielding of commercial fiber optic cable. They are chosen to be very easily visible, because fiber optic is less happy about being stepped on, for example, than regular copper cable.

I’m not sure which lines the CMS tracker has chosen to be green and which to be orange. (I’m actually on Atlas — of course that doesn’t make me any less anonymous than the name “Ellipsis” — same is of course true for CMS.) Possibly they are using orange for trigger info and green for the event info that has passed the level-2 trigger. Or it could be green for TIB and orange for TOB? A CMS tracker person would have to answer.

Anyway, it is often interesting to note (you know this, but the average member of the public doesn’t) that in most modern tracking detectors, the _vast_ majority of the data coming out of the detector is actually for the trigger decisions and is subsequently thrown away, as compared with the much smaller amount of data that actually is saved (for the events that pass the trigger). (About 10 Terabytes / s, vs. 1 GB / s for both Atlas and CMS, at the nominal beam luminosity.)

By: Alexey Petrov

Alexey Petrov — Sun, 29 Jul 2007 02:33:33 +0000

Is there a reason for some wires being green and some – orange? Or someone is just a fan of the University of Miami?

By: Ellipsis

Ellipsis — Sat, 28 Jul 2007 23:45:35 +0000

Joanne (since John apparently is too busy to answer his questions…):
If there are problems like that, they tend to be (at least one hopes) structural rather than active elements (the head of a bolt, say, or a cable connector) that could be refitted without disturbing the silicon itself. It would have to be a pretty big error if the pixels themselves actually overlapped with the strips (if the latter were the case, I think the Japanese refer to what would result as “seppuku”). :/

Most of the time these sorts of things do fit without any problems, though.

But note that just a couple years ago, the beryllium inner cylinder of the Babar tracker was scraped by an errant bolt head on the insertion of the silicon detector (very luckily the damage was patchable)!

By: Coin

Coin — Sat, 28 Jul 2007 21:18:02 +0000

Aaron, when he says “robotics”, he means “bronze sphere rolling down an inclined plane”.

Very simple robotics, basically.

By: Aaron F.

Aaron F. — Sat, 28 Jul 2007 15:18:47 +0000

Hey, wait! Galileo couldn’t have done robotics in high school! That comment must be from an imposter!!! I’m sure the last comment this blog recieved from Galileo was real, though. Because… yeah. *Shifty eyes.*

By: Galileo

Galileo — Sat, 28 Jul 2007 15:16:01 +0000

What if it doesn’t fit inside the tracker? It’s not like you can just shave off a few pixels…

Well, when I was in high school robotics, all we needed to meet the size requirement was a file and some hammers…

By: eugene

eugene — Fri, 27 Jul 2007 21:04:43 +0000

great cable management

By: JoAnne

JoAnne — Fri, 27 Jul 2007 20:26:56 +0000

What if it doesn’t fit inside the tracker? It’s not like you can just shave off a few pixels…

By: a cornellian

a cornellian — Fri, 27 Jul 2007 15:58:33 +0000

I assume they are using depleted Si diodes. By reverse biasing the diodes you can fully deplete the bulk. When something, like a high energy particles (or x-rays or photons or electrons), fly through it interacts with the valence band electrons and promotes some to the conduction band. Due to the electric field in the depleted region the electron-hole pairs are swept apart. One or the other (I would guess the holes) is the charge collected by the pixel front end.

john:
Is it really fair to say that it is digitized in an adjacent cavern? From what I could find poking around the nets the PSI chip (PSI46) puts out the addresses of pixels that have been triggered by particle paths. Any analog information is squashed by the comparator in the pixel front end.

Is there a connection between this detector group, the MediPix detector group and the Pilatus group?

By: perturbed

perturbed — Fri, 27 Jul 2007 13:36:15 +0000

Wow. And we thought *we* had a cabling problem…
- Your friendly ATLAS neighbors

By: astromcnaught

astromcnaught — Fri, 27 Jul 2007 08:43:14 +0000

Nice post.
Given 14 TeV collisions, won’t all the materials surrounding that disintegrate within seconds?

By: Coin

Coin — Fri, 27 Jul 2007 07:36:27 +0000

So does this mean once the thing’s running it will be generating neat bubble-chamber looking images, only in 3D?

By: aquariid

aquariid — Fri, 27 Jul 2007 07:12:12 +0000

Once built my own cloud chamber, and it worked. I only needed to buy a chunk of dry ice which cost a couple of bucks. A billion dollars- sheesh!
But seriously, what are these pixel sensors? Are they light detectors like a ccd?

By: Ellipsis

Ellipsis — Fri, 27 Jul 2007 05:37:36 +0000

Yvette -- see, e.g., http://www.caen.it for a variety of nice and expensive choices for how to plug an expensive detector in.

By: Yvette

Yvette — Fri, 27 Jul 2007 04:07:08 +0000

Ok, I have a silly question but I’ve been wondering for a little while: how do you plug this stuff in? I’m guessing a bit more than a three-prong chord is required. Thanks!

By: Lab Lemming

Lab Lemming — Fri, 27 Jul 2007 02:55:15 +0000

Cool!

How do the pixels convert the passage of a single charged particle into a signal that your electronics can detect?

By: Myhatma Gander

Myhatma Gander — Fri, 27 Jul 2007 00:21:11 +0000

WHAT! They let you go into that room alone?! What if the Higgs had taken over your brain, and caused you to cut some wires, see http://arxiv.org/abs/0707.1919 ? Of course you will deny it. What lax security…or have *they* already taken over the CERN security people?!