Comments on: 3/fb reached!

By: A particle mass from its production rate « A Quantum Diaries Survivor

A particle mass from its production rate « A Quantum Diaries Survivor — Tue, 26 Jun 2007 10:23:30 +0000

[...] of the quarks and gluons inside the proton, we can compute the probability of a collision - the cross section for a given process. Now, it so happens that PDF functions are very large at low values of x, [...]

By: Luminosity Profile « Life as a Physicist

Luminosity Profile « Life as a Physicist — Tue, 19 Jun 2007 14:27:48 +0000

[...] person, showed this plot. I like this plot because it really made me rethink what is going on with our experiments luminosity. I like plots that jar me out of some preconceived notion I [...]

By: dorigo

dorigo — Sun, 17 Jun 2007 20:13:39 +0000

You are welcome Jeffrey. Always glad to explain particle physics jargon away…

Cheers,
T.

By: Jeffrey Scofield

Jeffrey Scofield — Sat, 16 Jun 2007 18:42:46 +0000

Thanks for the explanation of 1/fb. I have been wondering
what this means for a couple of months after seeing it in
Peter Woit’s blog.

(Hmm, I just found a definition by googling for“inverse barn.”
But yours is far superior.)

Obeisances and regards,
Jeff S.

By: dorigo

dorigo — Fri, 15 Jun 2007 18:42:31 +0000

Ana, I made the change today. Your feed should now include my posts in all their glory

Cheers,
T.

By: ana

ana — Fri, 15 Jun 2007 12:36:13 +0000

As for the full content feeds, I have the same feelings with Gordon.
Here,I recommended you to a good article that listed the reasons and comparison for abastract and full content feed:

For the Love of the Web, Please Use Full Content Feeds!
link here:http://www.devlounge.net/articles/for-the-love-of-the-web-please-use-full-content-feeds

By: gordonwatts

gordonwatts — Fri, 15 Jun 2007 12:13:24 +0000

Thanks! I appreciate that; makes it much easier to read your blog (along with others).

By: Fred

Fred — Fri, 15 Jun 2007 03:16:59 +0000

Good and swift move T. concerning the RSS suggestions by Ana and Gordon. Blogs and inter-corporate communications are the 2 lucky stiffs of this developed tool so far. Strangely, many but not all, news services appear to use web feeds as a slight-of-hand tactic. An interesting study can be found at: http://www.icmpa.umd.edu/pages/studies/rss_study_details/rss_study.html Of course, this is probably distorted in it’s own way. It’s simply a matter of filtered trust. Oh, congrats to you and your cronies for being dedicated workers. You should be proud of that nice curve, but don’t forget to count your blessings.

By: dorigo

dorigo — Thu, 14 Jun 2007 21:36:08 +0000

Gordon, thanks for the information – I think now I remember having been told that once (the beam optics).

And I will modify the feed.

Cheers,
T.

By: gordonwatts

gordonwatts — Thu, 14 Jun 2007 21:16:08 +0000

I agree with Ana, btw. I read almost all my blogs in a feed reader, going out of the reader means starting a web browser — so I don’t read your blog nearly as often as I do others that give the full feed. If you weren’t a blog about physics, I would have removed you from my blog reader already. -G.

By: gordonwatts

gordonwatts — Thu, 14 Jun 2007 21:04:52 +0000

BTW — if you want to see D0’s collected lumiosity as a function of time — you can here: http://d0server1.fnal.gov/projects/operations/D0RunII_DataTaking_files/image006.png — that is a public plot and it is updated about once a week (give or take). We have 3.04 at the moment. You’ll notice there are two numbers: the 3.04 and a 2.58. The larger number is what we think the Tevatron has delivered, and the 2.58 is what we have managed to write to tape (due to problems and other things).

By: gordonwatts

gordonwatts — Thu, 14 Jun 2007 21:02:20 +0000

T – The beam optics are definately not the same at the center of both CDF and D0. -Gordon.

By: gordonwatts

gordonwatts — Thu, 14 Jun 2007 21:00:53 +0000

Another thing that takes a long time: we are always upgrading our detector. For example, D0 added a new layer of silicon. Getting that tuned up takes a lot of work!

By: dorigo

dorigo — Thu, 14 Jun 2007 09:00:36 +0000

Hi Questioner,

it is 3/fb per experiment.

Actually, a sordid detail is that CDF and D0 measure the instantaneous luminosity each with their own devices, and D0’s luminosity appears to always be smaller by a few percents, despite the fact that the beam optics are the same in the center of the two experiments. As far as I know the Tevatron believes more in the CDF number and uses that one, so when 3/fb are delivered, D0 is probably seeing 2.95/fb or so…

Cheers,
T.

By: questioner

questioner — Thu, 14 Jun 2007 08:54:02 +0000

Can I ask a dumb theorist’s question? The 3 fb^-1, is this 3 fb^-1 per experiment or 3fb^-1 in total? So does this mean CDF now has 1.5 fb^-1 of run II data to analyse, or 3 fb^-1? Thanks.

By: dorigo

dorigo — Thu, 14 Jun 2007 06:53:00 +0000

Hi Ana,

how would my blog be better if syndication feeds received the full text rather than a summary ? I tend to think that by broadcasting only a summary, I encourage those who read the feeds and are interested by the topic to visit my site.

Cheers,
T.

By: ana

ana — Thu, 14 Jun 2007 06:44:59 +0000

Could you please output full text in RSS feed? It will make your blog more great!

By: dorigo

dorigo — Wed, 13 Jun 2007 18:00:40 +0000

Yes, in some sense the detector needs constant calibration if one wants to obtain the best resolutions, despite the fact that in general, these things are quite stable (some parts of CDF are 25 years old, and still going strong!).

The silicon sensors of CDF and D0 are expected to withstand well the radiation dose from 8/fb of data. The degradation thereafter is minor, and these machines are quite redundant in design, so that they can outlive some of their parts without jeopardizing the performance appreciably. I believe we would be able to do a very good use of twice as much luminosity as the amount we can collect until 2009.

About the silicon, I am more worried by the intrinsic dangers of high luminosity running. Beam aborts may cook our microstrip detectors, as can high losses! For that reason, in fact, after a new beam has been injected in the Tevatron, we turn on the silicon in CDF only after the beam has stabilized (following a phase called “scraping”).

In the end, you never know… A few years ago we killed quite a few sensors because the wire bonds went in resonance with the L1 data taking frequency above 30 kHz, and broke. This was due to the hall effect!

By: Peter Woit

Peter Woit — Wed, 13 Jun 2007 15:48:38 +0000

I see, basically the problem is that the behavior of the detector keeps changing.

Related to this, I remember reading a few years ago that sooner or later radiation damage would seriously degrade the performance of the inner parts of D0 and CDF. Is this still a problem and will it put a limit on how long the Tevatron can keep running?

By: dorigo

dorigo — Wed, 13 Jun 2007 15:12:52 +0000

Hello Peter,

good question. The time it takes to produce results with new data seems excruciatingly long from the outside, but it is even more so from the inside!

The problem is that there are several things that need to happen in series, before one can “turn the crank” of an already well oiled machinery.

The following applies to CDF, but D0 is probably very similar in all phases:

1) as collisions are delivered to CDF, the data is stored on tape.

2) Once store, the data needs to be reconstructed by software algorithms and then “Produced” by using calibration data which follows every few chunks of data taking. The steps leading to final production events are multiple and it may take up to four-five months to get from the moment of collection to the moment when the data can be used for analyses.

3) Then another problem starts: the data has to be validated – every analysis wants to check that the newly collected events are no different than the former ones. Here one also may encounter the problem of different running conditions: the instantaneous luminosity with which the data was taken in the first 1/fb was on average lower, and many (bad) things happen to data reconstruction as L increases. So analysis cuts may have to be retuned, cleanup revisited, etc. Moreover, the trigger collecting the data of interest of one particular analysis may (and often will) have been modified – it too for problems connected to changing luminosity. Many triggers, in fact, get changed frequently. And modeling the changes takes time.

4) Much more on a longer timescale is the issue of obtaining new jet energy corrections, new lepton efficiency numbers, new determinations of the b-tagging scale factor and other things: sets of numbers that depend on the data, and which are only partly obtained by turning a crank – the methods are there, but tweaks are always necessary. Also, during this phase a suitable amount of Monte Carlo events needs to be compared to the data, and producing large amounts of Monte Carlo takes time. Given that the Monte Carlo simulation in CDF reflects the details of data taking conditions, it needs to be produced fresh.

5) Finally, one can add the new data to the old data, and redo the whole analysis. More data means more CPU time for things such as optimization, running pseudoexperiments, etcetera.

6) Then the result needs to be blessed anew. And this also requires a repeated scrutiny by the collaboration, given that things are not so trivial when one redoes the analysis (as per points 1,2,3,4,5).

All in all, it may take one year from collisions to blessing… Alas, experiments in particle physics are not a trivial matter!

Cheers,
T.