Tuesday, June 14, 2011 ... Deutsch/Español/Related posts from blogosphere

D0 rejects CDF's claim on top-antitop mass difference, too

First: major LHC detectors reach one inverse femtobarn!

By 21:10 Prague Summer Time tonight, the CMS and ATLAS at CERN have collected 1/fb of data each: see viXra blog.

This was the original plan for the whole year 2011 - and it's reached in mid June! The figure includes 47/pb from 2010, but 47/pb is collected in 36 hours in average these days, so on Wednesday, the 2011 run will probably reach a femtobarn, too. About 95% of the data have been recorded, so in a few more days, one also surpasses 1 recorded femtobarn of the data.

The LHC could collect 4/fb by the end of 2011 and, because of expected luminosity increases, 15/fb by the end of 2012 which should be enough to discover the Higgs boson even at the most inaccessible places. In fact, if the Higgs boson isn't in the data that have already been collected by now, then it's probably lighter than 135 GeV. It follows that the vacuum of the Standard Model is unstable and needs new, SUSY-like particles to be saved.

Now, let's look at the opposite side of the Atlantic

A Japanese translation of the text below is available.

In March, Tommaso Dorigo hyped a preprint by the CDF Collaboration,

Measurement of the mass difference between top and antitop quarks
As far as I remember, I hadn't discussed that paper on this blog because I considered it and still consider it a very bad, offensive piece of work. At any rate, they claimed that the top quark was much lighter than the antitop antiquark:
M(top) - M(antitop) = -3.3 +- 1.4(stat) +- 1.0(syst)
Using this lousy measurement, they wrote a paper phrased in such a way that they offered a 2-sigma evidence that the CPT "hypothesis" (which, of course, implies that antiparticles have to have exactly the same masses as particles) was wrong.

CDF, a pretty detector that has produced lots of rubbish lately (and maybe it's the people behind it who did it)

This is just offensive. It's the kind of shoddy research with the most sensationalist claims supported by the weakest possible (and, independently of that, flawed) evidence that belongs to the climate "science" but surely not to particle physics.

Today, the CDF's competitors at D0 have released their paper on the very same question:
Direct measurement of the mass difference between top and antitop quarks
There is no sign of the mass difference, of course. In the previous D0 paper, the very same mass difference was +3.8 +- 3.4 (stat) +- 1.2 (syst) - yes, the mass difference was going in the opposite direction than the CDF claim! The newest D0 paper says it is
M(top) - M(antitop) = +0.8 +- 1.8(stat) +- 0.5(syst)
Again, it's the opposite sign than the CDF claim but the mass difference is as zero as you could hope. The accuracy of the measurement remains disappointing but the preposterous idea suggested by the CDF paper that the experiments would begin to uncover a huge, multi-GeV mass difference between the top and the antitop has clearly been debunked.

Something is really wrong with the CDF detector and/or the CDF Collaboration and/or their methods.

Newsy Science: this is actually a fair and clear popular report on the Wjj 150 GeV events

In March, I had some exchanges with an experimenter on Dorigo's blog. The first thing I wrote was:
I think that the interpretation chosen by this [CDF] paper is shameful sensationalism. Paying attention to 2-sigma deviations is bad enough, but using 2-sigma deviations to "disprove" one of the most important principles of the discipline is a really bad taste.

Whoever had the idea to interpret their inability to measure the masses of tops and antitops more accurately in this far-reaching way should be ashamed.
Sean agreed with me. Andrea Giammanco, an experimenter who is not even a CDF member, tried to defend their work:
Hi Lubos,

I suspect you didn't actually read the paper.
I didn't find a single sentence of the paper where they claim that this result "disproves" anything. If I missed it, please point me to the exact line.

The most bold sentence that I found is that it deviates at 2 sigma level from the CPT-symmetry expectation. What is your criticism, exactly? That they should have written "it agrees at 2 sigma level with the CPT-symmetry expectation"? Whomever is able to read until that point in the paper also knows that the two statements are the same.

I must also add that I can't understand the criticism in some of the comments above for looking for an effect that "cannot" be there.

I find healthy to look for deviations even when you have no reason whatsoever to expect a deviation; I understand in general the criticism that, with finite resources, these must be prioritized, but this is a particularly uncontroversial case because data are anyway available as a by-product of all the rest of the Tevatron program, and performing this study doesn't require any other cost than a few months of salary of just two people (*).

There are several instructive historical examples of important effects that could have been observed before, because the data for their discovery were already available or easy to produce, but none of the "owners" of the data had considered to look for that particular effect (or, even worse, had actually stumbled into a 2-3 sigma deviation and paid no attention, remodelling the background or inflating the systematic uncertainty to take it into account and therefore unwittingly hiding it under the carpet.)

(*) their number and identity can be seen here:
So I gave him a longer explanation:
Dear Andrea, what I find offensive is their arrogant suggestion - included to the very title, and much of the abstract as well as the paper - that they have measured a nonzero difference between top and antitop masses.

To deduce what are the masses of the particles from their measurements, you effectively have to use some quantum field theory at one level or another. Quantum field theory implies that the mass difference is zero. So the most accurate measurement is to do nothing and to conclude that the difference is exactly zero.

In this sense, the most outrageous sentence about that paper is the last sentence, one that the measurement of the top-antitop mass difference - which is a whopping 3.3 GeV according to the CDF paper - is the "most accurate" measurement of the quantity.

This is just bullshit.

The most accurate measurement of the mass difference, done with a clever definition of the mass, is 0.000000 +- 0.000000 GeV, and neither they nor you have presented any real evidence that this is not the case. The CDF result is a striking sign of the immense inaccuracy with which they measure the mass of the heaviest quark, so it's really disingenious for them to claim that they've just produced the most accurate result.

They have produced one of the most *inaccurate* results for this quantity ever written down.

It is healthy to look for whatever effects but it is totally unhealthy to publish papers claiming to have measured effects that almost certainly don't exist, without having any real evidence for such claims.

CDF should have verified that they don't have any 5-sigma deviation, and because they don't, they should use the obvious identity mass(top) = mass(antitop) as a method to make their other measurements more accurate. In other words, they should have used the top-antitop average mass, 172.5 GeV, as the actual input to use for other measurements. They failed to do all such things which really indicates that most of the mass measurements depending on the matter-antimatter difference are likely to have similar 3.4-GeV-like errors, too.

They have surely nothing to boast about in this context, so it is irritating that they apparently do.

Obviously, they just don't feel that way. They produced the worst (largest) bullshit number ever describing the top-antitop difference - over 3.3 GeV even though it is obviously 0.000 GeV and many others have come really close to it - and they don't see any problem about claiming that the 3.3 GeV result for the mass difference is the "most accurate measurement". Holy crap.

Obviously, the conversations were completely unproductive. Maybe it's because the experimenters don't actually understand the laws of physics. Maybe they're being honest but they just don't know that to suggest that they have measured a nonzero mass difference of a particle and its antiparticle because of a 2-sigma bump is just idiotic. It's like claiming that the rectangular triangle with legs 3 and 4 has hypotenuse of 5.05 plus minus 0.02 meters which deviates from the Pythagorean "hypothesis" by 2 sigma.

Hopefully, they at least understand the experiments, so they should be able to understand that the D0 has just confirmed that I have always been right and that the CDF paper had actually made the most inaccurate measurement of the m(top)-m(antitop) mass difference ever, it should be ashamed of that paper, and it had absolutely no moral right to suggest far-reaching interpretations of their shoddy measurement.

Claims about the CPT violation (or, equivalently, about the nonzero matter-antimatter mass difference) are extraordinary claims and if you're a serious person, you simply shouldn't make them based on some illusions or 2-sigma signals.

I think that the CPT-symmetry is exact, a direct consequence of the Lorentz symmetry and analyticity. Just Wick-rotate your scattering problem to the Euclidean spacetime, rotate the "tz" plane by 180 degrees, and Wick-rotate back to the Minkowski space. You will get the CPT image of the original process. Because the analytic continuation and the "tz" rotation - which is a kind of the Lorentz boost - were the only operations and they're symmetries, it follows that CPT has to hold.

(You may be confused why the reversal of the "tz" plane gives you CPT rather than PT. While the obvious geometric transformation induced by this operation is PT, the particles also start to move backwards in time after this PT, and a particle moving backwards in time has to be interpreted as an antiparticle. So the full transformation is CPT, not PT, and one has to be sensitive to properly derive that the non-geometric "C" factor is included there as well.)

But even if you had doubts whether the CPT symmetry would be exact forever, it's just exact according to all measurements that had been done so far. So a claim that it doesn't hold - and that it's even violated by 2 percent by ordinary top quarks - is just an extraordinary claim and 2-sigma deviations are surely not good enough to claim to support the claim.

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snail feedback (2) :

reader Ervin Goldfain said...

Dear Lubos,

I am watching in disbelief what’s going on with dubious claims promoted by CDF…as I am also watching in disbelief how millions of dollars are awarded to Verlinde for his misguided research on entropic gravity …truly pathetic!

reader Luboš Motl said...

It is amazing, too. But the Spinoza prize is an internal Dutch affair. Maybe the Dutch science hasn't produced anything better recently than this piece of quite manifestly incorrect pop-science entropic nonsense.

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