# LHC Roundup

The first attempt to circulate a beam in the LHC is still set for next Wednesday, and the media is already full of LHC stories, with a lot more to come next week. Events are being organized all over the world to celebrate the day, including a 1:30 am pajama party at Fermilab (see here). Today’s Wall Street Journal carries a page one story about preparations at CERN that focus on improvisational comedy training for physicists to help them communicate.

For more serious news from the LHC, you can try following progress at CERN’s startup site for the public, or at the technical LHC commissioning site. Latest available minutes from the Installation and Commissioning Committee are here, including a timeline and objectives for the next few days and for September 10. The “also going on” column for September 10 lists just “chaos”.

Science magazine has some excellent LHC-related stories in this week’s issue. In this one, various people explain what the LHC is looking for and why it will take a while to get results. Gordy Kane is having none of that though, predicting discovery of supersymmetry next month:

“We predict a signature that they could see with five events,” says Michigan’s Kane. “They could see it in the first week of running in October.”

Another article, Researchers, Place Your Bets!, features bloggers Tommaso Dorigo and Jacques Distler. Tommaso has bet that the LHC will see no deviations from the standard model, although from what I remember, he did this just because if this happens it will be so depressing that at least some cash will cheer him up. Gordy Kane and Stuart Raby claim supersymmetry is such a sure thing that they can’t find anyone who will bet against it. Distler’s comment on this is:

I wonder how hard they tried.

The same article gives links to sites where you can bet on the Higgs boson discovery date.

Nature magazine is running an LHC-related editorial Cool Philosophies in this week’s issue. It is inspired by an interesting recent preprint by philosopher of science Alexei Grinbaum: On the eve of the LHC: conceptual questions in high-energy physics. Grinbaum gives an extensive discussion of the current state of particle theory and its societal context. He ends with a philosophical section on fine-tuning and currently popular anthropic arguments, arguing that these often invoke an invalid use of counterfactuals.

This entry was posted in Uncategorized. Bookmark the permalink.

### 21 Responses to LHC Roundup

1. T says:

Why does Gordy say this kind of thing? Such a respected theorist who shows absolutely zero understanding of experimental physics. They’ll be lucky if they can understand a single part of the detector in a month of running. Let’s just try to ease into calibration and hope nothing serious breaks.

2. GR says:

Well, I’m glad they’re doing improv, if anything it should help improve matters in the communication-to-outsiders department. I’m part of an improv group here, and physics majors seem to be disproportionately represented, for whatever reason, and it really does help. A lot more people in physics should give it a try. Not the string theory people, though, as it seems they’re already pretty good at spinning a yarn…

3. anon. says:

Never mind supersymmetry speculation. How long is it likely to take the LHC to check the electroweak symmetry breaking Higgs theories?

In one Higgs field theory, there is supposed to be a doublet of Higgs bosons, both having +1 weak hypercharge; but one of them has +1/2 weak isotopic charge and +1 electric charge, while the other has -1/2 weak isotopic charge and no electric charge. There are also other more complex versions of the Higgs field including versions with supersymmetry.

I’m wondering whether the LHC is really likely to check this part of the Standard Model, and identify the correct Higgs field (or if there is something else needed instead)? Is there any paper with assembled predictions from the landscape of different Higgs field theories. From my perspective, searching for supersymmetry (which doesn’t really make falsifiable predictions since the energy of the hypothetical partners can be higher than experiments can test), isn’t very exciting. It’s like looking for life on Mars; it may or may not exist.

But the Higgs field research is far more interesting because something has to give mass to the particles in the current Standard Model, and something has to break electroweak symmetry into electromagnetism and weak interactions at low energy.

4. Peter Woit says:

anon,

In the SM, there is just one observable Higgs field (the other components of the field can be gauged away). It has electromagnetic charge 0, and all its couplings are precisely known once one knows its mass. For the expected mass range, the LHC will produce lots of Higgs particles no matter what the mass, but the backgrounds are different for different masses. The low end of the mass range is the most difficult, and my understanding is that if the Higgs is there, it will take until at least 2010 to see a signal.

If you start adding in more Higgs fields, you will get much more complicated possibilities. In supersymmetric models these are more constrained, and also intensively studied. I don’t know of references off-hand, but they can’t be hard to find, this is an extremely intensively studied subject, and has been for decades now.

5. graviton383 says:

To answer anon’s question, it will take an integrated luminosity of ~10 fb^-1 or so
AFTER the detectors are well understood to start covering all of the mass range
for the Higgs favored by fits to electroweak data. Some masses may take longer,
some less. This sort of luminosity may take 2 years to accumulate & more to
analyze so think 2010-11 just to be safe. If the Higgs idea is wrong, discovering the
true nature of what replaces it may take somewhat longer requiring ~100 fb^-1 of
data.

6. anon. says:

Thanks for these answers. Is the Higgs field is supposed provide the charge for quantum gravity, since mass is gravitational charge?

E.g. could there be a gauge group for quantum gravity, like U(1) for electromagnetism, in which the charge is the Higgs boson and the gauge boson is the graviton?

7. Graviton,

while it is true that one first has to understand the data and only after can one look for a signal of a new particle, you gave the impression that the two phases are separate. Rather, it is a continuous improvement. The same data used to understand the detector response are also used for searches and measurements.

Indeed, what we will do first is to measure W and Z cross sections (which will be possible this fall, with thousands of them in the bag), top pair production (also easy with just 10 inverse picobarns, when about 8000 events per detector will be produced, let’s say a thousand good ones to study), and high-Et jet spectra.
Missing energy will be tough -probably the one variable which will take more time to tune. It depends on a good calibration of jets, cosmics, out of time stuff, everything basically.

What sucks, if we think at the SM Higgs, is that the 1.7 sigma excess found by LEP II (mostly ALEPH in truth) will be the very last thing we can study. I imagine that in one year or so we will start excluding masses above 135 GeV, those that are already improbable by EW fits, and in the meantime already partly excluded by the Tevatron (which, next year, should probably exclude down to 150 GeV or so).

Another note on the bet reported on Science Magazine: Peter is correct. The article does not mention it, but mine is an insurance bet, in the style of a blackjack addict such as I am. That, however, does not change one fact: I do not believe in SUSY.

Cheers,
T.

8. Victor says:

“That, however, does not change one fact: I do not believe in SUSY.”

This is not a particularly scientific attitude. Science isn’t about belief, it’s about facts. It concerns me that someone with obvious prejudice is involved in experiments which require an objective analysis.

9. Peter Woit says:

Victor,

I think Tommaso is just saying he thinks the probabilities are against SUSY. There’s significant circumstantial evidence against SUSY: basically if it is doing what it is supposed to (stabilizing the electroweak scale), it’s hard to understand why it hasn’t shown up at the Tevatron (where Tommaso has spent much of his career working hard looking for SUSY or anything like it).

I don’t think there’s any danger at all that he or others at the LHC will not look just as hard for SUSY there as they have done at the Tevatron. Theorists may allow their investment in certain speculative ideas to affect their work, but experimentalists don’t have that kind of investment in such ideas. One sad thing about the heavily ideological way in which theoretical particle physics has been pursued in recent years is that it gives people the wrong idea about how most scientists go about what they do. On the whole they’re much more interested in finding something new than worrying about whether or not it fits some particular theoretical prejudice.

10. Very well said Peter.

I can only add that personally, what I believe and what I do not has absolutely nothing to do with the way I perform an analysis.

My beliefs instead can (and should!) shape my decisions on what to work on – despite the fact that they are not, at least right now: my only Ph.D. student is working with me on something connected to SUSY. That, indeed, is the nice thing about being part of a large collaboration which will explore everything, with multiple teams in some instances assigned to the same topics.

When, however, decisions have to be taken concerning where to place the chips -say, in a trigger meeting where thresholds on physical objects are to be set on different data streams, to reduce the trigger accept rate facing an increase in the machine’s instantaneous luminosity, and thereby affecting the discovery reach of different experimental signatures- well, there a leadership is needed to sort individual opinions out. Usually one just relies on the experiment’s pre-defined goals. But, in principle, tough decisions may be required in some not-clear-cut cases, and then one’s beliefs might in theory end up having their weight. That is the only case when I can give it to you – my (mild) bias against SUSY being the correct theory might suggest I would be unfit to lead such a group. It would still be a stretch. So ultimately, your concern is ill-posed.

Cheers,
T.

11. Hi Peter, surprised to read “Gordy Kane and Stuart Raby claim supersymmetry is such a sure thing that they can’t find anyone who will bet against it.”

I thought Stephen Hawking had taken a bet that no physics beyond the Standard Model will be seen – have I got this wrong?
I personally would be happy to take a public bet that evidence of SUSY will be eventually be seen at the LHC – if only to publicise the theory, and to draw attention to the disgraceful fact that Ireland is not a member of CERN ..

12. Victor says:

Peter,
When you say that there is significant circumctantial evidence against SUSY, can you give a more detailed explanation of this statement? My understanding is that there is a lot of circumstantial evidence for SUSY as well, which is why there are many who expect to see it at LHC. As far as the hierarchy problem associated with the electroweak scale, I’ve been told that SUSY is still a viable solution for this, even if the supersymmetric particles are too heavy to have been seen at the Tevatron. What gives?

13. woit says:

Victor,

The fact that there were good arguments that supersymmetry should have shown up at the Tevatron and it didn’t is the circumstantial evidence I’m referring to. It was discussed in another posting, see

http://www.math.columbia.edu/~woit/wordpress/?p=710#comment-40040

This evidence is not conclusive, but it seems fairly strong to me. The facts typically given by SUSY proponents as circumstantial evidence in its favor seem to me much weaker. Anyway, we’ll see….

14. Peter Woit says:

Cormac,

If Hawking has bet against no physics beyond the SM, I hadn’t heard about that, and it seems surprising. I don’t know any reason why he would make such a bet. Perhaps you’re confusing him with Tommaso…

15. Hah, this would be the first time I get confused with a theoretician. And our accent is quite different also.

Cheers,
T.

16. Manel says:

The closest thing to what Cormac O’Raifeartaigh wrote that I know of is this:

http://img241.imageshack.us/img241/8962/susyzr5.png

17. Coin says:

Manel: I like ′t Hooft’s asterisk.

18. Manel says:

Yes, I agree. Sad but very plausible.

To what physics has sank into…

I still hope the LHC will have a positive and break the status quo and allow for real physics to be made.

19. Thanks Manel, fascinating sheet!
Tommaso, who have you taken the bet with? How about an inter-blog bet, that could be fun.

Apart from the two reasons above (to draw public attention to SUSY, and to the fact that Ireland is not a member of CERN), I do have another, slightly naive reason ..

If I understand right (as a humble experimentalist) SUSY, or something like it, is the only way around the comprehensive set of no-go theorems discovered in the 1960s – in other words, it is the last symmmetry left that could provide a unified framework that would include the strong force , and possibly gravity.

I find it hard to accept the unification of only 2 forces – and therefore plumb for SUSY, despite large uncertainties in the mechansim of SUSY breaking etc
Regards, Cormac

20. Peter Woit says:

Cormac,

Susy doesn’t help at all to unify electroweak and strong. They’re both internal symmetries. Attempts to unify these typically involve GUTs, but these have their problems, and the LHC will have nothing to say about the GUT issue.

21. Hi Cormac,

my bet is indeed an inter-blog one, since both challengers (Distler, 750$, and Watts, 250$) have their own site.

Cheers,
T.