From the Atkins diet to the Metabolism diet and the Russian Air Force diet, there’s no shortage of ideas on the correct way to understand the origins of human mass. When it comes to the deeper question of the masses of the elementary particles that make up the ordinary mass of the universe, things aren’t much different.
Most physicists agree that the stunning successes of the standard model of particle physics imply that particle masses must be due to their interactions with a new field known as the Higgs field. At currently accessible energies, it is thought that the Higgs field is a scalar field, and that elementary particles acquire mass because the universe is filled with a condensate of the Higgs field, through which all standard model particles are forced to wade.
One of the hints that the standard model may not be complete comes from the properties of the quantum theory of this Higgs field. For the Higgs field to perform properly, its mass must be around the weak scale (except for in an extremely narrow region of parameter space). However, the masses of scalar fields receive large corrections from quantum effects (so-called quadratic divergences) and, unless one fine-tunes the theory a truly ridiculous amount, the expected mass of the Higgs boson may be as high as the Planck scale – sixteen orders of magnitude higher than the weak scale. This tension, between the required low mass scale of the Higgs field and the ultra-high Planck scale to which it might be driven, is known as the hierarchy problem of the standard model.
Much of the motivation for the next generation of particle colliders – the Large Hadron Collider (LHC) at CERN, and the proposed International Linear Collider (ILC) – comes from the desire to identify the mechanism responsible for the generation of mass (finding the Higgs particle) and to understand the structure through which the hierarchy mentioned above is rendered stable. Other motivations come from the connections between colliders and cosmology.
In the most recent issue of Scientific American, Gordy Kane, a renowned particle theorist from the University of Michigan, discusses these issues in a nicely written article titled The Mysteries of Mass. One of the leading candidates to explain the hierarchy problem is supersymmetry, which tames the quadratic divergences by introducing a new set of particles into the model, related to the standard model particles by, well, supersymmetry. Gordy has been a major player in research into supersymmetry, and understandably this constitutes one focus of the article. It is worth pointing out, however, that there are a number of other ideas floating around (such as extra dimensions, on which JoAnne is an expert), not to mention the perennial favorite – none of the above. Whether you find the idea of supersymmetry compelling or not, the origin of mass is certainly one of the deepest questions facing physics today, and I think Gordy’s article provides an interesting summary of the main questions and challenges.
As we approach the turn on of the LHC, probably in 2007, serious attempts to figure out how to interpret its data to distinguish between the various ideas that theorists have generated have ramped up. To this end, in a few days, CERN will host the LHC Olympics – a sort of blind test of how well such a distinction might be made. They even have a pdf primer. When the results of all this are in, hopefully in a few months, I (or JoAnne if I can persuade her) will report on what happened.
July 19th, 2005 at 5:23 am
I would like to lay cold hard cash on “none of the above”, and a friend of mine favours “Higgs but no supersymmetry”.
Do you very excellent physicistes know of a bookie who would take such bets. (Restricted to the LHC turning these such somethings up, in the first instance.)
July 19th, 2005 at 5:44 am
[...] (3) SUSY 2005. This just started yesterday. This meeting is a natural complement to say, Strings 2005, in that it is focusing on phenomenological issues a hair’s breadth away from real experiments and observations, and it gets more exciting every year since we are closer to testing out some key ideas in big upcoming experiments at the LHC. (See Mark’s recent post by the way.) JoAnne, being one of the people (a “phenomenologist”) who can bridge the gap between the sometimes esoteric stringy constructions of my people and the actual signatures of those ideas in real experiments done in those marvelous machines, is here too, as I said above and is speaking at some point. I really should do a daily report to the world about what’s going on (such as Jacques Distler’s reports from Strings), but I’m really a tourist here, so I won’t. I don’t know enough of the language and the detailed issues to give a good report on most of the talks. I’m sitting and learning what I can here and there, and largely shutting up with the questions as is appropriate, since this is a large meeting of reports on work, not a chit-chat. Also, since I’m supposed to be working, I won’t be going to everything. Oh. I should mention one other excellent thing the organizers did. Their poster and website have a picture of the newest stained glass window in the cathedral. It is called the “Millennium Window”, from about five years ago when anything new in the UK had to have the word “Millennium” in the title. (Had I not stupidly left the cable for my camera in LA, I’d show you some of the other splendid windows, both old and new. There’s even a Marks and Spencer’s window, which I think has cabbages and a loaf of bread among other things. This never fails to crack me up. Oh. If you thought some of the palace interiors and windows were splendid in the movie “Elizabeth” some years ago, it might be because you were looking at some of the scenes shot in the Cathedral used as a stand – in. Also, the cloisters of the cathedral (tour here) are used as part of Hogwart’s in the Harry Potter movies. See here.) Where was I? Oh yes. The conference’s title has a subtitle, and so the full thing says “SUSY 2005, the Millennium Window to Particle Physics”. Nice. Would have been better if they’d done it for SUSY 1999, 2000 or 2001 maybe, but still nice. [...]
July 19th, 2005 at 6:23 am
Sorry des, I don’t know who’d be willing to take such a bet, although I would be stunned if Ladbrokes hadn’t at least considered it. I’d probably put my money on that something will be discovered, but that with the LHC alone, we’ll have a hard time attributing it to any particular theoretical framework. I am interested to see what the LHC olympics manage to do though.
Good luck.
July 19th, 2005 at 6:50 am
A missed charged scalar at 69 GeV; a neutral scalar at 115 GeV, another scalar or pseudoscalar at , ie, at 246 GeV. Interpretation of a 2 doublet singlet model and no elementary SUSY. Any takers?
July 19th, 2005 at 6:51 am
(I mean a doublet higgs model perhaps with a singlet too)
July 19th, 2005 at 9:28 am
I would also like to bet on “no new discovery” but I am afraid to do so because I would then be betting AGAINST billions of dollars of investment. And when you are talking about huge amount of money, the outcome MUST be politically correct. And if it can not be done above the table you bet it WILL be done below the table.
Just recently I discovered, quite surprisingly, that raw experimental data obtained on CERN, including those that CERN scientists base their paper on, are top secret and classified material that outsiders are prohibited to obtain. That’s by the confession of some one inside CERN. I always thought those experimental data are open for any member of the public to obtain and study, as long as one is willing to compensate for the cost of retriving and delivering those information. But that is not the case.
Quantoken
July 19th, 2005 at 11:20 am
Mark,
One semantic point about Higgs physics as the “origin of mass” as it is usually referred to. Firstly (and this is a point Wilczek likes to make) most of the mass around us, in the form of protons and neutrons, is largely insensitive to Higgs physics, and comes from QCD. Also, discovering the Higgs will probably leave the pattern of masses (flavor physics) mysterious. I think “origin of mass” is a bit of a misleading slogan, the “origin of symmetry breaking” is better, since it forces one to discuss symmetry breaking (as you have done) which is a fascinating concept.
best,
Moshe
July 19th, 2005 at 1:39 pm
I’m with Moshe on the irksomeness of “the origin of mass” as a rallying cry for searching for the Higgs. You finessed it in the post (the mass of “elementary particles,” which presumably would not include nucleons), but I think it usually tends to reflect a misguided desire to get non-experts excited about a subject that physicists are excited about for quite different reasons.
July 23rd, 2005 at 7:37 am
Quantoken said:
“Just recently I discovered, quite surprisingly, that raw experimental data obtained on CERN, including those that CERN scientists base their paper on, are top secret and classified material that outsiders are prohibited to obtain. ..”
So where did you discover that ? Ever heard about the Grid project ?
July 27th, 2005 at 11:08 am
Quantoken said:
“Just recently I discovered, quite surprisingly, that raw experimental data obtained on CERN, including those that CERN scientists base their paper on, are top secret and classified material that outsiders are prohibited to obtain. ..”
I should clarify the situation. The raw data is the property of the collaboration (ATLAS, CMS LHCb etc.) which obtained it. This is standard practice in all particle physics experiments. It is fair as it will have taken ~2000 physicists over 15 years of effort to build the experiment and it is crucial that they get the payback for that. So it is only these people who have the right to analyse the data and present distilled results as public papers authored by the whole collaboration (acknowledging everyone’s contributions) which can then be used by the theoretical community. This also avoids the kind of situation where non-experimentalists try to use the data without an understanding of the intricacies of the data-taking environment or a knowledge of the experiment performance (which typically cannot easily be factorised out) and hence draw incorrect conclusions. It is the job of the experimentalists doing the data analysis to use their detailed specialist knowledge of such factors to correct for them and present data in journals in a format which can be used more easily by theorists to test specific phenomenological models.
The Grid is a tool which will be used for data analysis, and if your institute is participating then it may well end up receiving a small subset of the data for processing (’reconstruction’). This is not the same as saying that you have the freedom to then analyse that data yourself and write independent papers on it however. The data is passed straight back to the central collaboration for merging with all the other data and analysis by experimentalists in physics analysis working groups.
August 4th, 2005 at 2:01 pm
So what happened?
August 4th, 2005 at 2:16 pm
I think we have to wait a few months until they’ve finished and release the results.
August 4th, 2005 at 3:06 pm
Well I can tell what happened, to the extent I was in the lectures.
At any rate I learned more than what I had expected. Two points I, an outsider in this business, found somewhat baffling are:
1) It won’t be easy to identify (once LHC is running) what kind of
supersymmetric standard model it is, if at all. There is a many-to-one
map, ie, one and the same set of given experimental data tends to
match many quite different discrete choices of parameters of the
supersymmetric standard model. This is partly because for a hadronic
collider, there are very many intermediate processes between the
original event and what you actually measure, to obscure the picture.
It seems to me that in order to do a thorough job, an enormous
effort plus luck will be necessary in order to meaningfully disentangle
the data.
2) It seems that most if not all of the analysis software is tuned
for the MSSM and variations thereof. On top of that, each of the
groups seem to have their own class of pet models they focus on. I
wonder how one could possibly find something unexpected in this
manner. I sensed a firm belief in “string inspired” MSSM’s (as if
there would be such a thing) and there was even the notion of
“scanning the M-theory parameter space”. I just hope that our
experimental collegues are independent enough such as not to be too
biased in favor what certain theoreticians tell them.
August 4th, 2005 at 4:20 pm
My understanding is that’s largely because there are so few independent “signals” that they can measure at the LHC. And we’re mapping a very high-dimensional parameter space into this low-dimensional signal space.
(This is also rather discontinuous map, as various channels open up, or shut off, as you twiddle the parameters of the theory.)
It’s not the biases in the analysis that I worry about; data can always be reanalyzed with different assumptions. It’s that something important might slip past the cuts that they need to make, and never get recorded.
August 4th, 2005 at 4:26 pm
Hadron colliders are great machines for discovering particles, and can certainly take you some way to nailing down a class of models. However, lepton machines, with their precision, are great machines for discovering specifically what the model is and how the new particles fit into our understanding of space and time (as in SUSY or extra dimensions).
Jacques last comment is important. It is one of the arguments (I think) that it is useful to have a future International Linear Collider and the LHC running concurrently for some period, so that one could go back and, in principle, go back and run in some parameter region.
August 5th, 2005 at 1:21 am
Hi Folks,
Hate to squash your enthusiasm, but don’t expect much from the LHC Olympics. Why, you ask? It is a good idea, but it’s not being implemented in a realistic manner. There are many flaws inherent in theorists pretending to do experimenter’s tasks. But there is a really, really BIG one associated with the LHC Olympics. Namely, the folks in charge have not given the background associated with the signals they report. (Presumably because it would take too much time and computer power.) This means that one literally cannot do anything meaningful with the data. For example, they give a signal which is obviously associated with neutralino production. Unless one knows better, one would not realize that the signal rate they report is statistically insignificant. In other words, it is swamped by background events. It would never be reported and thus cannot be used in the determination of the underlying physics. The physics reality of the LHC is much more complicated than what is being represented in the LHC Olympics. I wouldn’t expect any data-driven theorists to waste their time participating.
August 5th, 2005 at 5:48 am
Killjoy! Oh sure, it’s all fun and games until someone knows what they’re talking about
August 5th, 2005 at 1:20 pm
I joint to the vote for a linear collider somewhere.
As for the background, isn’t a theoretical calculation after all? I mean, perhaps the organisers of the Olympics expected it to be evaluated by the participants, from general collider parameters.
JD comment: It’s not the biases in the analysis that I worry about; data can always be reanalyzed with different assumptions. It’s that something important might slip past the cuts that they need to make, and never get recorded.
…reminders me of another thing: is someone out thare taking care of permanent backup of LEPI+LEPII data, just in case non MSSM analysis is needed? Same about tevatron, I hope.
January 4th, 2006 at 1:07 am
The BBC on the LHC
The BBC has a nice article about CERN’s Large Hadron Collider (LHC).
I’ve mentioned the LHC before, and what we expect will be its central role in providing insights into some of the biggest questions in particle physics and cosmology. Th…
March 31st, 2006 at 1:34 pm
[...] Physicists (like us) are, with good reason, eagerly anticipating results from the Large Hadron Collider at CERN, scheduled to turn on next year. The LHC will collide protons at much higher energies than ever before, giving us direct access to a regime that has been hidden from us up to now. But until then, a whole host of smaller experiments are interrogating particle physics from a variety of different angles, using clever techniques to get indirect information about new physics. Just a quick rundown of some recent results: [...]