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Sadly, no more gossip June 24, 2008

Posted by dorigo in Blogroll, games, physics, politics.

These days my honest yet slightly anarchical style of blogging is becoming harder and harder to maintain. I am curiously receiving a synchronous input from the two opposing sides of the Atlantic Ocean: a true coincidence, because the origins of these inputs are totally uncorrelated. And yet the push goes in the same direction. Worse still: since the input is coming from authoritative sources, it would be idiotic to ignore it.

Good science works by encouraging an open exchange of information only in fairy tales. In reality, the human factor weighs in to modify that optimal picture. Man is ambitious, selfish, vain. And hundreds, or even thousands, such individuals gathered together in the same project make a sociological bomb that is only begging to be set off. Handling such a bomb is not an easy matter: therefore, I do understand the concerns of these giant collaborations.

Time and again I am told by readers that one of the things that make this blog interesting to read is the cut-away view I occasionally provide of the inner workings of the scientific collaborations I work in. Well, that feature of this site is bound to be slightly dampened. Posts such as this one, or even this one, might be considered a diffusion of internally exchanged information, and as such they would create trouble (the first one did, in fact).

I decided I will unwillingly oblige. Not so much because of the harm that my own scientific career might be exposed to if I were unreasonable: I am not ambitious -I have a good life, my job satisfies me fully, and I do not depend for my living on my ridiculous salary. Rather, I will oblige because I fully understand that keeping a blog with some audience requires a good dose of responsibility. One of the things that makes me proud is to have belonged and still belong to CDF, the longest-lasting and one of the most successful physics experiments ever; and nowadays, I am spending most of my time to earn the right to be proud of belonging to CMS too. I certainly want to help these experiments!

What this all boils down to is, I think, only that I will not post any more about the humorous sides of internal meetings -the rest has never made it to this blog anyway- and that I will compensate by writing a bit more about the physics. Not such a terrible deal after all. I will have to save my irony for other matters.



1. DB - June 24, 2008

Hmm, I’ve been expecting a tightening up as we gear up for LHC switch on.

Illegitimi non carborundum nil desperandum

In the meantime, there is always Italian politics, so if I may paraphrase Schubert: Wer ist Silvio?

2. Guess Who - June 24, 2008

TD: “Man is ambitious”
TD: “I am not ambitious”
GW: Aha, TD is not a man! 😉

Really, it’s beyond me how this could reasonably have caused trouble.

3. Fred - June 24, 2008

Smart move, Tommaso. To expound on what DB wrote: when the lying-in-wait black hole finally sucks us all away as they throw the switch on at LHC, they’ll only have the thin skins of the naked king and the green frog to blame.
ps. How much are front row seats going for to witness the doomsayers’ “Assumption of the Virgin Collision”?

Mark Twain:
“Always acknowledge a fault. This will throw those in authority off their guard and give you an opportunity to commit more.”

4. cecil kirksey - June 24, 2008

Hi dorigo:
Having been reading your blog for several months now. Most interested in the search for the “God particle”, Higgs. But I have curious about some fundemental aspects of HE collisions. First if we collide an electron and positron they will be converted to pure energy which will then be converted to particles.

Now my basic question is: Can you provide a basic 101 review of what physical principles will control the decay of the pure energy into particles? I have read that the energy width is inversely proportional to the lifetime of a particle. Certain things have to be conserved like charge, etc. But from this pure energy state almost any particle could exist given enough energy. But basically what determines the probabilities of each potential particle?

As part of the analysis of collision decay events can you indicate how accurately the total energy of the dacy products can be determined? Thanks alot.

5. dorigo - June 24, 2008

Hi DB,

sure – I should talk about the new law by Berlusconi, which will wreak havoc in the italian judiciary system (and save him from a lawsuit that would otherwise end in a conviction).

Hello GW, well, the post you mention resulted in somebody complaining with somebody high up about this blog.

Hi Fred,

great saying from Mark Twain. I will tell you when to harness yourself to a park bench on the geneva lakefront, with eyeglasses on. It is for free.


6. dorigo - June 24, 2008

Dear Cecil,

thank you for visiting this blog.

Let us take a electron-positron collision at 91 GeV. They create a Z boson when they collide. The energy they possessed goes in the mass of the Z. At lower energy, the Z would be virtual, and overimposed with a photon, and things would be more complicated. But at 91 GeV, it is not hard to explain how that energy chooses to materialize into particles, in a millionth of a billionth of a billionth of a second.

The Z “couples” to matter fields (quarks and leptons) with a strength which is about half for “up-type” fermions (u,c,t quarks, e,mu, tau leptons) than it is to “down-type” fermions (d,s,b quarks, and the three neutrinos). This is due to some complicated math in the Standard Model lagrangian, and I will not go into that.

Since the decay Z->top antitop is forbidden by energy conservation (the top is heavier than half the Z mass), there remain 2 up-type quark-antiquark pairs, and three down-type quark-antiquark pairs. These, however, get multiplied by three, because quarks exist in three different colours.

Now if you call x the probability for Z->ee decay, you have 3x for charged leptons, plus a bit less than 6x for neutral leptons, plus three times a bit less than 6x for down-type quark pairs, plus three times 3x for up-type quarks.
All in all this makes about 33x (less than 36x since I was carrying on an initial approximation in the slightly less than double chance of down-type decay). Since the total accounts for all possible Z decays (there are others, but they are much less frequent and we will ignore them here), then 33x=1, or x=3%.

This explains the 3% chance of Z->ee decay, the 20% chance of Z-> neutrinos decay (six times 3%), and the 70% overall chance of quark decays.

Does that help ?


7. Guess Who - June 25, 2008

Clearly unreasonable. Plenty of frail egos and delusions of I-dont-know-what in physics.

Sometimes I just don’t understand people. I even went back to check when your infamous Lisa Randall post was, to see if it could have been what really ticked off some PC cop, but that was much later. Weird.

8. forrest noble - June 25, 2008

Tommaso, Guess Who

I believe that “I-don’t-know-what” physics would be a good attitude for many practitioners to investigate. With that perspective and a driving ambition to find out “what”, some great new experiments could be designed. The problem with we-think-we-know “what” attitude, nearly all of the available money is often spent while chasing a completely wrong theory. Even worse, while looking in the wrong direction, many observations are often completely misinterpreted. Of course this is true for science in general, not just physics.

your friend forrest

9. cecil kirksey - June 25, 2008

Thanks. What about the energy measurement accuracy? The reason I ask is that if some particle is not observed like a WIMP how much energy has to be missing before a particle is declared to exist but undedected? Of course this assumes conservation of energy-mass, right?

10. Tony Smith - June 25, 2008

Tommaso, when you “talk about the new law by Berlusconi, which will … save him from a lawsuit that would otherwise end in a conviction …”,

don’t forget that the same law

will allow Berslusconi to use the army to invade Naples

(a safer invasion than the possible USA invasion of Iran).

According to a 24 June 2008 Telegraph article by Malcolm Moore:
“… Soldiers could be sent into Italy’s cities, illegal immigrants will be imprisoned and all non-serious court cases will be frozen for a year under new measures approved by Italy’s senate. …
The senate voted 166 to 123 to approve a wide-ranging package of measures which will allow Silvio Berlusconi to govern Italy with an iron fist.
Mr Berlusconi, 71, will now be able to use as many as 3,000 soldiers for up to six months in order to fight crime.
Previously, the use of the army had to be agreed by the parliament beforehand.
The first destination for the troops is likely to be Naples,
where Mr Berlusconi faces violent opposition to his plans for dealing with the city’s rubbish crisis. …”.

I see parallels between iron-hand governmental ruling
iron-handed actions by physics collaborations.
Both can be rationalized,
and neither can be ignored by the vast bulk of constituents, most of whom just want to “have a good life”,
so both are likely to be very effective in the immediate future.

Tony Smith

11. Andrea Giammanco - June 25, 2008

Just a suggestion: maybe the same post(s) which caused trouble would not have triggered any action by the protagonists if any detail were removed, like names, time and title of the meeting.
For example:

Well into the second afternoon of an otherwise boring series of meetings, I had a moment of real hilarity during a colleague’s talk.

He had just started his talk, and he had slide three on the wide screen. No less than eighty collaborators were sitting in front of him, plus maybe thirty more connected via VRVS.


Of course it’s less funny if it’s not personal, but if adding personal details makes you run into trouble, maybe you should consider this compromise.
(Of course I will then ask you the names of the protagonists via private mail after every post 😉 )

12. nige - June 25, 2008

‘This explains the 3% chance of Z->ee decay, the 20% chance of Z-> neutrinos decay (six times 3%), and the 70% overall chance of quark decays.’

It is fascinating to see the physics involved in the calculations for probabilities of different decay branches in in comment 6 in response to Cecil.

13. dorigo - June 25, 2008

Hi all,

GW, I think the two instances I linked in the post have no potential of harming the experiment, but indeed the person involved in the first one could feel he did not have a chance to reply in kind.

Cecil, yes – a undetected particle leaving the detector with high energy -such as a neutrino or a WIMP- must have a certain energy to be detected. That, however, depends on the visible energy. Typically, the resolution on missing transverse energy (we measure only that component, unfortunately) grows with the square root of the visible transverse energy. So, for instance, if you see 300 GeV of Et you may say that 30 GeV of missing Et are significant; while if you see 1200 GeV, the same significance of missing Et is only achieved above 60 GeV: 30 \times \sqrt(1200/300) = 60.

Hi Tony,
thank you for bringing up the obscene manouvers Berlusconi has started just after being appointed premier again. I want to write a post about it, but have been swamped with other obligations… I will use your notes for inspiration.

Andrea, one learns to blog little by little. I agree with you; however, I like to be open in my blog so I often fall in this sort of trap of disclosing stuff that is harmful. I will be more careful in the future.

Nige, see above for some missing Et calculations 😉

Cheers all,


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