Nobel Anticipation

October 7, 2013

This is Nobel week and prize handouts start today with Medicine. Tomorrow is Physics, and Chemistry is on Wednesday. All others are political prizes of no interest here.

The physics prize should be awarded for the Higgs Boson and most likely Higgs himself and Englert will get it, but a third share may go to some other wildcard person or organisation. This will be decided by a vote at TRF but I can also remind you that a similar vote has been running for some time on viXra which has already been used to elect two winners of the much larger Fundamental Physics Prize.

Update 8-Oct-2013:  Congratulations to James E. Rothman, Randy W. Schekman and Thomas C. Südhof who won the Physiology or Medicine prize “for their discoveries of machinery regulating vesicle traffic, a major transport system in our cells”.

Today will be the turn of the physics prize and it this point it may be worth hedging bets by noting that this might not even be given for the Higgs. Each year the Nobel committee has a big pile of worthy nominations and they may just decide that one of them fits better. However the chances for Higgs seem slightly better than even.

Some people are suggesting that the third share for the Higgs could go to CERN. The committee have hinted that an organisation is not ruled out even though they have never used that option before, but I think CERN would be a mistake. This is because many people in the CMS and ATLAS collaborations are not strictly speaking part of CERN. You could justify that CERN played a deserving role but to then leave out the physicists who actually made the discovery would be a new kind of mistake for the Nobel committee to make. Lumping CMS and ATLAS together as one also seems a bit forced but they could give it to Higgs, CMS and ATLAS leaving out Englert. That is more like the kind of mistake they have made before. I favour the option of reserving the prize for the theorists. If they start giving it to big organisations then they will also have to look at many other big collaborations in the future and they probably dont want to set a precedent that could radically change the nature of the award.


Oh My God Particle!

March 19, 2013

It would be amiss of me not to jump into the debate about what Michio Kaku said on CBS about the Higgs boson. If you don’t know what I am talking about see the blogs of Sean Carroll, Matt Strassler, Peter Woit, Lubos Motl etc.

The initial case for the prosecution was that Kaku had said incorrectly that the Higgs Boson caused the big bang. If you listen more carefully to the details, he is saying that the Higgs boson could be part of a family of scalars that includes the inflaton responsible for inflation. This justifies that the Higgs boson put the bang into the big bang. It is perfectly true that this could be how it works and despite accusations to the contrary Kaku used the words “think” and “could” to indicate that this was a speculative hypothesis, not settled fact. If you missed those caveats it’s your fault not his.

He rightly stresses that physicists dont like the term God particle used by the reporters but he is not making a great deal out of it. The term sticks because people remember it and it tells them that the Higgs boson is considered important. I think it has been explained enough times that it was a joke and was not intended to be taken literally. If the public still don’t get that then there is no hope for their understanding. Ina any case Kaku is not the one guilty of promoting the usage in this interview.

Motl has covered this in the blog post and I agree with what he says. There is just one thing that I think is worth adding. Kaku says that the Higgs boson could be the trigger that sets the big bang off. This is the part that has led to so much criticism  In the original inflation theory the era of rapid expansion does not start right away when the universe is created. If that is the case then it might be true to say that the Higgs boson puts the bang into the big bang but it would not be right to say that it triggered the big bang. So what is he referring to? The answer I think is a genre of big bang theory in which there is a time before the big bang when it was in a steady meta-stable state. According to these theories our universe was triggered by a transition to another vacuum in which the inflaton is responsible for its rapid growth right from the first instant of the new phase. The theory of eternal inflation is one sub-variety of this type of cosmological hypothesis. Personally I do not favour such theories because they seem to be inspired by a philosophical desire to explain the universe in terms of temporal causality and as I discussed at length in my most recent FQXi essay, that is not my philosophy. Nevertheless it has become a popular class of theory with cosmologists. Ironically Sean Carroll who sparked off this attack on Kaku seems to be one of its biggest supporters.

Matt Strassler criticises Kaku above all for not making it clear which parts of what he was saying were speculative. I invite you to listen to what he said again (see the links to the video on the other blogs). He actually stresses very clearly that “we do not know how or why” the big bang started, but “we think” the Higgs boson may be a key piece of the answer. I don’t think he could have made it any clearer that these are just possibilities.

kAKUcbs

If you are concerned that Kaku seems to think that the Higgs boson is responsible for inflation then be aware that this might actually be the case. Sean Carroll denies that this can be the case and Matt Strassler says that it is unlikely. Motl explains exactly why it could be the case and I remember hearing about this in a webcast talk at Moriond on the same day as some of the new results were being aired. The theory requires an extra coupling between the Higgs boson and the curvature tensor and it has its problems, but then so does every other theory of inflation. The model does at least have the virtue of not requiring other unknown fields. When Strassler says that this version of inflation is “unlikely” he is expressing his own opinion. He claims in a comment that he does not express his own personal opinion without indicating as much, yet here he does exactly that.

Kaku is an eloquent speaker and he knows his subject. He is very careful with his words and knows the kind of angle on a physics story that will get the general public interested. Most people do not have the time to digest the kind of details that are explained at length on some of the blogs, yet Kaku can convey a feeling of our excitement that ordinary people can appreciate immediately. Yes, the basic known facts about the Higgs boson are interesting and exciting too but the more speculative ideas that people are working on are what really gets people to sit up and listen. If some physicists fear that people cannot distinguish between known and unknown facts when words like “could” and “think” are used then they are simply not giving people enough credit.

Science reporting needs to cover the full range of news from the latest experimental results to the wildest new theories being discussed by physicists. If it does not do so then it will not inspire new young scientists to take up research. People like Kaku may not please everyone but they are getting the message across. I am sure he will not be discouraged by boring physicists who simply don’t get it.


Higgs Spin (Is It really a Higgs then, finally?)

March 14, 2013

CERN have a new press release out today while latest results are being presented at the QCD part of the Moriond conference. There are further updates since last week including the long awaited CMS results for the diphoton decay channel. The diphoton rate relative to standard model is now 0.8 +- 0.3, much lower than before and a huge disappointment for hopes of beyond-standard-model physics.

MgamgamCMS

In the press release the CMS and ATLAS spokespeople are quoted as follows

The preliminary results with the full 2012 data set are magnificent and to me it is clear that we are dealing with a Higgs boson though we still have a long way to go to know what kind of Higgs boson it is.” said CMS spokesperson Joe Incandela.

“The beautiful new results represent a huge effort by many dedicated people. They point to the new particle having the spin-parity of a Higgs boson as in the Standard Model. We are now well started on the measurement programme in the Higgs sector,” said ATLAS spokesperson Dave Charlton.

So does this mean that they have officially conceded that it really is the Higgs boson and not some HHiggs-like imposter? The official line is now that “they find that the new particle is looking more and more like a Higgs boson, the particle linked to the mechanism that gives mass to elementary particles. It remains an open question, however, whether this is the Higgs boson of the Standard Model of particle physics, or possibly the lightest of several bosons predicted in some theories that go beyond the Standard Model.”

It’s a bit meally mouthed but nevertheless, most c0mmentators are interpreting this to mean that they have agreed that it is a Higgs boson of some sort.

The crux was the spin measurements which both teams agree disfavours spin 2 with positive parity at a 2 to 3 sigma level. The real Higgs boson has spin zero with positive parity and all other spin possibilities are directly ruled out by the fact that  it decays to two spin-one photons. Negative spin zero is not quite so strongly ruled out but this is not being billed as such an important observation.

particle propertty Can it be determined with LHC run 1 data? Does CERN think it is deterministic for a Higgs boson? current status
Decay modes YES YES WW,γγ,ZZ,ττ observed, bb,Zγ,μμ etc ongoing
Other Production modes NO NO gluon fusion OK, VBF, VH and ttH ongoing
no exotic decay modes NO NO preliminary results from ATLAS
Spin = 0 YES YES spin zero verified to about 2 or 3 sigma in each experiment
Parity = positive NO NO negative parity is disfavoured but not ruled out
W fusion NO NO nothing yet reported
Higgs self-coupling NO NO nothing yet reported

In summary, the things that CERN has decided are crucial for determining that this is a Higgs boson are thankfully exactly the things that can be determined from run 1 but there are plenty of other observations to keep them busy for run 2 and beyond.


CMS diphoton result approved

March 13, 2013

Todays LHCC meeting is currently being webcast and slides are going online here. Colin Bernet presenting the CMS update has confirmed that the crucial diphoton results have now been approved. He said they will be presented at Moriond today but the schedule suggests that it will be tomorrow. This part of the Moriond meeting is not being webcast so we will have to wait for slides to come online for the results.

 


Animated Higgs from ATLAS

March 7, 2013

ATLAS have provided some animated gifs showing the accumulation of Higgs events over time in the diphoton and four-lepton channels. Enjoy.

These dont seem to work in situ on the blog. You need to click on the images to get them to work.

Hgg-FloatingScale-Short2

4l-FixedScale-NoMuProf2

At what date do the Higgs bumps start to look real?

Youtube version:

https://www.youtube.com/watch?v=Ub1gcQW6rMc

 


Moriond Higgs Update

March 6, 2013

The latest Higgs updates are now being presented at Moriond. CMS have kicked off this morning with a presentation of bosonic decays including WW and ZZ but still not including the important diphoton channel. The full LHC run 1 dataset is now being used including 19.6/fb at 8 TeV

In ZZ they get a very clear signal on the event plot

MZZCMS1

Higgs Mass from ZZ is 125.8 +- 0.5(stat) +- 0.2(Syst)

The cross section relative to standard model is 0.91 +- 0.27

ATLAS also updated ZZ with 20.7/fb at 8 TeV to produce a similarly impressive plot

MZZATLAS1Higgs mass for ZZ from ATLAS is 124.3 +- 0.6(stat) +- 0.4(syst)

cross-section 1.7 +- 0.5

Unlike CMS, ATLAS have presented their diphoton results giving a mass estimate of 126.8 +- 0.2(stat) +- 0.7(stat)

MGGATLAS

diphoton cross-section is 1.65 +- 0.24(stat) +- 0.21(syst)

Rumour puts the CMS diphoton excess at 1.0 +- 0.2, to be shown at Moriond QCD next week perhaps (via Jester on twitter)

The excess over the standard model remains high but its significance has not increased because the value has gone down as more data has been added. When we first saw this excess a year ago we were excited that it may be real physics and we hoped that by this time we would have a truely significant effect. This has not happened. We still need to wait for CMS to show their diphoton results before we can draw any conclusion but rumours are that their overexcess has fallen even more dramatically. This means that expectations of significant BSM effects from run 1 are now lower.

CMS also gave us a plot of excesses in the WW channel over the standard model with Higgs at 125 GeV. In other words this plot should only show any excesses attributed to any other Higgs like particles. They said they are now doing this analysis for all the high mass searches which is a good move.

The WW cross-section from CMS is 0.76 +- 0.21

MWWCMS1

This shows that there are not yet any signs of higher mass Higgs particles as would be expected in Higgs multiplet models. If they exist then they must be quite well decoupled from the observed Higgs boson. The usual combined ZZ channel plot tells a similar story with no significant excesses beyond the known Higgs.

MZZCMS2

By the way, we are still waiting for the AMS-02 results due out soon. They had hoped to reveal them yesterday at Moriond but approval was not ready in time. Next oportunity could be the Moriond Cosmology conference next week


Looking Forward to Moriond

February 15, 2013

The LHC has ended its three-year long physics run this week and is now finishing off with some quench tests. Tomorrow (Saturday) morning the beams will be dumped for the last time for nearly two years while the collider is upgraded so that it can work at a higher energy of 12.5 – 13 TeV.

1302027_01-A4-at-144-dpi

But the fun is not quite all over yet. In just over two weeks time we should start to see the first of the final results from proton physics run that ended in December 2012. The event to watch is the Electro-Weak section of the Moriond Meeting that opens on the 2nd March. The schedule has not yet been published but when it is you should see it at this link. The following week they will hold the Moriond QCD meeting whose schedule is now available at this link. There will be a quick summary of the Higgs searches which I presume will have already been revealed the week before.

What we expect to see is an update for all the Higgs decay channels from both ATLAS and CMS. Remember that we have seen all the results for 5/fb @ 7TeV + 13/fb @ 8TeV, except that CMS choose not to publish the diphoton result because it was smaller than expected. This means that the public values for the diphoton cross-section are currently subject to a selection bias that needs to be put right. The hope is that we will get full results at something like 5/fb @ 7TeV + 20/fb @ 8TeV, In other words we will have 40% more data for most channels and about 75% more for the diphoton channel. We know that all channels other than diphoton are perfectly in line with the standard model Higgs while the diphoton channel cross-section is a bit too large. However, we need to remove the CMS selection bias before we can get excited about it.

In addition to the cross-sections we can hope for an update to the tests of spin parity on the Higgs boson. This is the final step required before CERN will be happy to declare that the Higgs-Very-Like-Boson is indeed the Higgs-Boson so that Nobel prizes can be handed out. It is unlikely that the individual results from CMS and ATLAS will be quite sufficient. These tests do not need a 5-sigma significance because they are property measurements rather than discoveries. I think they will settle for 3 or 4 sigmas but this will require the combination of CMS and ATLAS data.

The ATLAS and CMS collaborations have had plenty of time to analyse their results and have kept them under wraps with no rumours leaking out yet. This may mean that they are keeping them “blind” until the last-minute. If that is the case it will probably mean that there is not time to do an ATLAS+CMS official combination for Moriond. Unofficial combinations of the channel cross-sections can be done quickly by hand but the spin-parity is more subtle so there will be one final Higgs cliff-hanger until the summer.

Normally the biggest HEP conference of the year is either the European EPS-HEP conference or the ICHEP conference. These normally alternate in a two-year cycle but this year an extra ICHEP conference in Switzerland has been laid on. (UPDATE: It turns out that this is not an official ICHEP conference. Same committee appears to be organising over 1000 conferences this year. Do not register, ) The EPS-HEP conference looks legit and will be in Stockholm. Please always check before paying conference fees.

Update: 16-Feb-2013

nobeam2

See Mike Lamont’s final “run 1″ report in the CERN bulletin


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