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Physics World on the Higgs affair May 2, 2007

Posted by dorigo in Blogroll, internet, news, personal, physics, politics, science.
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Martin Griffiths, a science writer on Physics World, has written for the May issue of his magazine a good account of the story of the news spread last March by the New Scientist and the Economist on the possible discovery of a Higgs boson at the Tevatron.

In the well-written piece, I got to learn a few details of the story which had escaped my insider visual at the time. For instance the fact that my actions (see also here for a summary) were defended by the CDF spokesperson Rob Roser, who does not think I and John Conway “crossed the lines” in reporting about the small excess of events seen by the Higgs search analysis in our blogs.

That bit matches my impressions of the events following the publishing of the two articles last March on NS and Economist, which I can now summarize roughly as follows (but beware, these are only my extrapolations): a few collaborators of my experiment (I know some of the actors, but not all of them) complained to the CDF Spokespersons about John and I leaking information to the media, and asked them to take action one way or another – from changing the internal bylaws to make it impossible for a collaborator to blog on public CDF results, to publically blaming our actions, to who knows what.

But Roser and Konigsberg apparently did not yield to the pressure, and they rather put together a set of “guidelines” which, while not mandatory, would drive collaborators’ behavior with respect to blogging matters as a sort of moral obligation – call it a Gentlemen’s agreement if you wish. I also know from Gordon Watts that D0 put together an almost exactly equal list of guidelines.

I find Roser and Konigsberg’s decision rather wise. Indeed, one of them once taught me that “you have to pick your battles”: meaning both that you cannot fight them all, and that you better avoid fighting those you are sure you would lose. And, despite the peer pressure that my friend Gordon thinks would be mounting against blogs, I believe a uncompromising position by CDF and D0 or whatever other large collaboration would only cause a backfire. That, at least, seems to be the regular outcome when somebody walks in the internet scene and tries to tell people what to do. 

Comments

1. gordonwatts - May 2, 2007

The problem is that we don’t live in the “internet scene” – we live in a much much smaller community: the HEP scene. So if it was generally decided that blogging was going to be frowned upon… it would be. As both of us have noted, it has not been.

I think peer pressure is by far the strongest thing that keeps us “in line.” We depend on the collaboration of others to get our work done. If we piss people off, they won’t work with us, we won’t get work done, and then where would our careers be?

2. dorigo - May 2, 2007

Gordon,

the thing is to avoid being too enamoured of one’s own career. Honesty is more important, and so is to live according to one’s own beliefs. If they had formally prevented me from blogging about CDF, I would have seriously considered leaving the collaboration and continue doing it, or I would have opened an anonymous site to do it regardless.

Cheers,
T.

3. Kea - May 2, 2007

From the article: “The spreading of scientific information through blogs cannot be ignored by those involved in large experiments,” says Dorigo. Indeed, the CDF collaboration is currently discussing whether to set up guidelines for blogging researchers.

This is a cheerful story, Tommaso. It is always comforting to see wisdom in the halls of power.

4. Quantoken - May 3, 2007

Quote from the link you provided:
http://cosmicvariance.com/2007/01/26/bump-hunting-part-1/
“We call it a boson as opposed to a fermion… because it is thought to have NO SPIN, no intrinsic angular momentum.”

Wow that’s a new low in today’s science community. I guess some one work day in and day out in the field should know better than making that elementary mistake. Quantum Mechanics, please! It’s impossible for any particle to have zero spin. Even three year kids know it!

5. Quantoken - May 3, 2007

It’s even lower consider that there were 45 follow up messages there, and numerous ping backs. Not a single person pointed out that mistake that was so obvious to me within a split second.

Hello, particles can have no zero spin. It is because of uncertainty principle of the QM. I learned QM more than a quarter century ago and have not used it for a long time. But I still remember that. You guys in the field do not get it? Incredible. I feel my tax payer dollars are a waste.

6. jeff - May 3, 2007

Hi quantoken. Can you explain to us why you believe zero-spin particles are not allowed? Lets be concrete and suggest we leave undiscoved particles out of the picture. How does the pion manage to do it?

7. dorigo - May 3, 2007

This reminds me of a sentence by Groucho Marx:
“A child of five could understand this. Go fetch a child of five!”.

Quantoken, doing outreach is not easy, it is time consuming, and it requires a significant effort in trying to simplify matters to make them readable. Mistakes are common. But… John is a quite accurate person and he seldom makes any. And in fact, he did not.

The Higgs -if it exists- is a scalar particle. It has zero spin. It still belongs to the category of “bosons”, because bosons have integer spins, and 0 is an integer.

Please explain what you remember about quantum mechanics preventing zero spin particles – which do occur, as Jeff points out, even in well-known particles. And leave taxpayers money alone, it’s a trembling little sum anyway.

Cheers,
T.

8. Quantoken - May 3, 2007

Jeff:
It’s QM uncertainty principle. The angular position and angular momentum are a pair of conjugate quantities so you can not determine both precisely. Same as you can not determine both the position and momentum precisely. If you fix the velocity of a particle to zero, then it’s position becomes completely undeterminable and it could spread out to infinity. In the case of angular momentum and angular position, however, the uncertainty of angular position can not be infinity, so the other uncertainty, the uncertainty of the angular momentum, can NOT be zero. The uncertainty of angular position is finite because we know the angle MUST be between 0 and 2*PI (0 to 4PI, i.e., 2 turns, for fermions). So the minimum angular momentum an elementary particle has must be at least 1 or 1/2 for fermions. It can not be zero.

Pion is not an elementary particle. Pion is a combinary of two quarks. Each quark has a none zero spin. The spin of two quarks happen to cancel each other resulting in a zero spin. But it’s OK for a composite, i.e., none-elementary particle like pion.

Higgs boson, as far as I know, if it exists, is NOT a composite particle and is truely a fundamental particle, so it can not have zero spin. If it has zero spin, you break the quantum uncertainty principle right here. The spin must be one. But then, if Higgs particle does not exist, then there is no point arguing whether its spin is zero or one. So let’s stop the argument right here and wait until you show me that Higgs boson is discovered, then we can discuss.

9. Francesco - May 3, 2007

Not a comment my apologize to everybody, only a reminder for an old friend, using the the top argument for mayor visibility. Hello Tom, now you have my mail second time! Bye

10. jeff - May 3, 2007

Hi quantoken. But for many years the pion was not known to be composite! It was dicovered in late forties and the spin was soon determined. Composite models showed up gradually and none of them, to my knowledge, argued the compositness of the pion on the basis of its spin being ZERO. Many of the fathers of quantum mechanics were still alive then and schools of brilliant physcicts were active. Why is it that noboby noticed this?

The argument that uses Heisenberg’s uncertainty principle must be used and interpreted with some caution. There is a significant difference between angular momentum and linear momentum. As you know, the conjugate variable of linear momentum is linear position, whereas the conjugate variable of angular momentum is angular position. But while linear position is defined over the whole axies of real numbers, angular position is PERIODIC. You too pointed out that for bosons the angle is restricted between 0 and 2PI. You are right in saying that Heisenberg’s relation forces us to conclude that IF spin (intrinsic angular momentum) is precisely known then the angle is completely uncertain. But that simply means that all angles between 0 and 2PI are equally probable. I don’t see any infinities!

ciao for now

11. jeff - May 3, 2007

The second part of my last comment to quantoken is the real answer I propose to his spin-zero “provocation”.

The first part is a warning. Modern science is based on the ethic that fame, prestige and sheer numbers alone do not garantee truth. Simply because schools of famous people say somehting doesn’t make it right. But this doesn’t mean that we should turn the ethic around. When some brave person stands up to say something unsual, challanging the famous, the powerful and the masses, then what he says is NOT more likely to be true simply because he is “original”. Originality is not a sufficient condition to jump to any conclusion, in particular that the masses are wrong. The ethics of modern science is based on the quality of argument, not in the numbers of people or the fame, power, money, looks, race, religion, sex, age, politcal party, of who is arguing.

12. dorigo - May 3, 2007

Hi all,

the question posed by quantoken is not totally silly. Indeed, while for the conjugate pairs linear momentum-position and energy-time the uncertainty principle applies strictly and there are no grey areas, for angular momentum and angular position things are more complicated – basically due to the quantization of L.

My short answer to how is it possible that a particle has intrinsic angular momentum equal to zero is that the uncertainty principle applies to quantities for which the pairs of conjugate variables are defined, which is not the case for the spin of spin zero particles. In other words, there is no direction around which to define a angular coordinate.

I understand Quantoken’s confusion, though: by thinking at the quantum harmonic oscillator, where the zero-point energy has a nonzero value (hbar/2 times the natural frequency), one may be led to believe the same applies to a quantized quantity as intrinsic spin. That is not the case.

By the way, by digging in the internet I found a paper where the uncertainty relation of angular momentum and angular position is indeed measured, with photon beams. It is http://www.iop.org/EJ/article/1367-2630/6/1/103/njp4_1_103.html , (New J. Phys. 6 (2004) 103).

In it, I read that indeed, the product DL*Dphi can assume values smaller than h/(2*pi). It is an interesting reading…

Cheers,
T.

13. DB - May 3, 2007

Quantoken (#4), how would you explain that the lowest electron orbital in a hydrogen atom has L=0? (Note that, as a spherical cloud, its angular position is completely indeterminate.)

14. Andrea Giammanco - May 4, 2007

The quantum indeterminacy is EXACTLY the reason why a scalar field has spin=0.
Being a scalar field means that the field is isotropic (like in the example of the spherical electronic cloud, said in comment #13).
A magnetic field, for example, is a vector. A vector points in a direction; once you determine the orientation of the vector in a specific point in space(/time), in that place this orientation is special (in fact, a magnet in that point feels an attraction which depends on its orientation). In quantum mechanics, this corresponds to spin=1.
For a scalar field (for example, the distribution of temperatures in a room) the direction is not special: in any place, the temperature that you feel is irrespective of how you are oriented. In quantum mechanics this means spin=0.

15. Andrea Giammanco - May 4, 2007

And this is also the reason why any conceivable Higgs field has to be a spin=0 boson (of course it could be composite, or a condensate of other particles, but the most economical starting point is to assume it elementary, and go to more complicated scenarios only if really necessary, as Ockham suggested):
– in order to give masses to elementary particles, you need symmetry breaking
– to have a spontaneous symmetry breaking, you need a field which assumes a “vacuum expectation value” (the ground state of the field) different from zero
– if this field where a vector, you would break the assumption of isotropy of the universe: the universe would have a special orientation (the direction of the vector in this ground state, which would be the same all over the known universe since all over the known universe the particle masses are the same), and this is not only estetically disappeling: it would also have observable consequences, since all the massive particles interact with this field.

So, any Higgs or Higgs-like particle has to have spin=0. If you don’t agree, first you have to invent a mechanism for particle masses which doesn’t involve any symmetry breaking.

16. dorigo - May 4, 2007

Hi Andrea,

thank you for your explanation, which I had failed to give, on why the Higgs has to be a scalar. It is a useful didactical contribution to this discussion.

Cheers,
T.

17. Not Even Wrong » Blog Archive » All Sorts of Stuff - May 5, 2007

[…] also has a posting about a new Physics World article discussing the recent blog-centered discussion of […]

18. Professor - May 6, 2007

Spin is an internal degree of freedom — it commutes with angular position — please stop this embarrassing discussion…

19. jeff - May 6, 2007

professor.
What is the conjugate variable of spin?
Isn’t spin, like angular(orbital) momentum, a fundamental operator for describing (generating) rotations in “external” space?
Internal? I might agree if it didn’t sound to me that you seem to be annoyed that there is an attemp to answer quantoken’s questions that addresses rotations in space.
Rather than “internal” I would use the expression that I was taught: spin does not have a classical analog; it is new, but like angular momentum it encodes the properties of rotations in space. A good exmaple of an INTERNAL operator (historically the first one introduced) is ISOSPIN.

Embarasment is in the eyes of the beholder.
cheers

20. Professor - May 7, 2007

jeff, spin is “self-conjugate”. Its components S_x, S_y, S_z form SU(2) algebra, and commute with all spatial (orbital) coordinates and momenta. For your and Quantoken reading, I suggest some undergraduate textbooks like Griffiths or Liboff. I assume that you know what complex numbers are and you know how to multiply matrices and perform basic integrations.
You will see that quantum spin is quite different from “rotations in space”.
Good luck!

21. dorigo - May 7, 2007

Professor, that reminds me that I have never really thought about discussing group representation theory at a sports magazine level here. I will give it a try.

Cheers,
T.

PS: please do not put anonymous commenters like quantoken (or yourself for that matter) at the same level as esteemed scientists like Jeff, who may have forgotten group theory but give a daily contribution to the advancement of Physics. The books you advise are good but Jeff has read scores of those.

T.

22. jeff - May 7, 2007

That spin commutes with space and normal angular momenta is of course true and had I thought more I would have realized myself that asking what the conjugate variable of spin was was a useless if not lame question. Spin has no classical analog. But the point I was trying to make is that spin is not “internal” as ISOSPIN is. Instead SPIN is necessary to represent rotations in usual space. Indeed SPIN can be addesed vectorially to orbital spin to get total angular moment. By that I stand. They do represent the same property of space.

Tommaso I do not need you to defend me. I will humbly suggest that professor reread the very same books he listed.

23. Professor - May 7, 2007

jeff — actually, you are bringing an interesting point. It is not uncommon to combine various “internal” and “external” operators (symmetries). For example, the spin-flavor SU(6) classification of baryons combines spin with isospin. Anyway, thanks Tomasso for your update on Higgs — the first “elementary” spin 0 particle, if it exists. If it does not exist, then nature really dislikes fundamental scalars…

24. dorigo - May 7, 2007

Hi all,

just to make it clear what I mean:

I do not mind anonymous comments here. However, anonymity comes at a price. As a non-disclosed person, you do not have all the rights of persons with a name and an email – you may be anyone, so you are effectively nobody. Of course, I still respect everybody’s (and nobody’s) opinions here…

Cheers,
T.

25. jeff - May 7, 2007

Hi professor
I guess I am stuck/spinning on the word “internal”. Interesting what you pointed out that internal and external operators can be combined as in spin-flavor SU(6). Ciao


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