How long until new physics?

The LHC is nearing the end of a long overnight run that started with a record luminosity of 3/ub/s. It is already the first run to collect over 100/nb (100 inverse nanobarns) in one go and it has another hour to run before they plan to terminate it. With luck they will be able to repeat this most days throughout August enabling them to collect 3/pb (3000 inverse nanobarns) this month which is about 10 times the data used for the ICHEP talks. After that they will start a rapid exponential growth of luminosity until the end of this year that should enable them to collect 1/fb (a million inverse nonabarns) by the end of 2011 when the LHC will shut down for further maintenance. Meanwhile the Tevatron continues to steadily collect data at a higher rate but lower energy and waits to hear how long it can continue.

That makes this a great time to play the game of guessing what will be discovered when and where. It is a game that anyone can play whether they are a humble independent blogger like myself or a full-time phenomenologist guru like John Ellis. Those who are insider members of one of the experimental collaborations will have to be careful not to reveal unpublished results but for the rest of us it is harmless fun.

Tommaso Dorigo looks to a 4th generation quark as the next discovery based on excesses above background for high mass events, now seen in both CDF and DZero at the Tevatron. In the end he cops out and says the signal is too weak and he thinks it will be a while before new physics is seen.

Lubos Motl has been excited about supersymmetry with the likelihood of a light Higgs and some excesses in channels where supersymmetry is supposed to live. The mass likelihoods for Higgs are represented by this plot from this presentation. Remember there could be more than one Higgs if supersymmetry is right.

Peter Woit reports a claim that early results from the LHC have already ruled out parts of the parameter space of supersymmetry and asks how long it will be before supersymmetry is ruled out. Nobody was expecting a high chance of seeing supersymmetry with so little data from the LHC so the impact on its parameter space so far must be very small. There is a small chance that evidence for new physics including supersymmetry could be seen this year in dijet or dimuon events at high mass if the right sort of particle exists. It is also even possible that Fermilab already have the evidence for a supersymmetry style Higgs and are going through a careful process of review and approval that could take several months.

To rule out supersymmetry if it is not there would take a little longer. Eliminating supersymmetry at the electroweak scale would require the full Higgs sector to be explored. If the Higgs is light as supersymmetry favours then it will take about 16 inverse femtobarns to cover the whole mass range looking for a 3-sigma signal. Fermilab could reach that point around 2013 if they are allowed to continue and their detectors withstand the potential radiation damage.

To convincingly rule out supersymmetry will however require the full force of the LHC. Taking Steve Meyers predictions for LHC luminosities as shown in this table, we can see that it should be around 2014 before they have enough data to rule out electroweak scale supersymmetry. Of course there may be another form of supersymmetry at much higher energies but that would be something very different that could not easily account for the effects that supersymmetry is meant to explain in the Higgs sector.

So if it is time for me to place my chips on the table I will bet on growing evidence for supersymmetry from now until end of 2011, but with the likelihood that we will have to wait until about 2014 for all the full details to emerge. If a fourth generation exists there is no reason to expect it at around this mass scale so I don’t expect to see it. Tommaso is probably right that the Tevatron excesses are due to something else.  

If anyone thinks something else will unfold, now is the time to say it.


16 Responses to How long until new physics?

  1. Chris Oakley says:

    Superstring theorists’ hope that supersymmetry will be found falls into the same category as the hope of a man buying a lottery ticket when he has gambling debts that he cannot repay. I tend to agree with Peter Woit, though – just because supersymmetry is theoretically possible, it does not mean that it is there. If you are not a superstringer the only reason for wanting it that makes any kind of sense is the putative cancellations in higher-order graphs – albeit in theories with no obvious connection with reality. However, in my book (although not anyone else’s that I can discern) this is is still infinity minus infinity, which makes the benefit of supersymmetry precisely zero.

  2. ervin goldfain says:

    Chris,

    I am not a superstring theorist but I have to say this: in all fairness, one cannot discard SUSY without mentioning that it brings to the table three purported benefits: gauge coupling unification, dark matter candidate(s) and a resolution to the hierarchy problem.

    Ervin

  3. Philip Gibbs says:

    There is obviously a strongly divided opinion about supersymmetry. I think it is because there is not one single thing that is strongly in its favour. It’s a collection is bits of evidence each of which on its own would be not totally convincing. It also depends on how far you buy the power of symmetry as a unifying idea. Personally I think it all adds up to a strong argument in favour of supersymmetry, but there is nothing that says it has to be right.

  4. Chris Oakley says:

    Excuse me, but the fact that the (e.g.) positron exists and has the same properties as the electron other than having opposite charge, is evidence for CPT symmetry. No-one can point to anything similar for supersymmetry. If present, it is inexact, and provided that each known fermion can matched up with a boson of adjacent spin – which it cannot at present – people will continue to say that it is in some sense there even though there is no supporting evidence. Why not just say that it isn’t? It is simpler, at least. As for gauge coupling unification and the heirarchy problem there is no benefit to me as I don’t buy into the renormalization group.

  5. Ervin Goldfain says:

    Chris,

    You say:

    “As for gauge coupling unification and the heirarchy problem there is no benefit to me as I don’t buy into the renormalization group.”

    The renormalization group is an invaluable tool for describing scaling behavior in quantum field theory and the dynamics of phase transitions in both statistical physics and condensed matter. How else can you explain the dependence of particle masses and gauge couplings to the probing energy scale?

  6. Chris Oakley says:

    Hi Ervin,

    Sorry, I should have been more precise. The renormalization group is ad hoc and not axiomatic (although it does annoy me when people claim that it is). As a result I have no interest in studying it. That is not quite the same as saying that I “don’t buy into it”.

  7. Luboš Motl says:

    Well, the statement that the LHC has already excluded a big portion of the supersymmetric parameter space is nothing else than a completely silly and pure misinformation. Obviously, one first has to reach the levels of integrated luminosity where you have the potential to discover something new (which the LHC has not yet reached), before you can reach the higher levels where you can become sure that you have looked and it’s not there.

    If you need a minute to have a big chance to find your keys, obviously, you can’t be sure that the keys are not there after 5 seconds.

    It’s preposterous to present the champions and opponents of SUSY as two equally motivated, educated, and working camps. The opponents build upon lies, misinformation, stupidity, and crackpotism – the kind of stuff written by Chris Oakley or Peter Void – while the champions focus on rational arguments such as rock solid equations of string theory, gauge coupling unification, observed existence of dark matter, or solutions to the hierarchy problem.

    I agree with Phil that the existence of SUSY is not settled yet but I think that even before things are settled, there must exist standards that distinguish good science from mass hysteria, hatred, and irrationality.

    Oakley: holy crap, the case of CPT or SUSY is completely analogous. SUSY is extremely constraining. It doesn’t just randomly pair random bosons and random fermions. It exactly forces their corresponding coupling constants to everything else to match, among many other things. It’s spontaneously broken in the real world, but so is the electroweak symmetry. Again, there’s no qualitative difference.

    The spontaneously broken symmetries are equally beautiful and equally constraining as the unbroken ones. The broken ones also imply massive gauge bosons (in the broken gauge symmetry case) or Nambu-Goldstone bosons (in the global symmetry case). Moreover, the high-energy scattering has to remain exactly symmetric, up to corrections that relatively go to zero for high E.

    It’s also ludicrous to attack the renormalization group. It’s the main conceptual fundament of what we know about quantum field theory – which is the state-of-the-art theory of almost everything. It’s an extremely deep insight that QFTs organize phenomena by the energy scales. And the renormalization group also explains why the seemingly “magic” earlier processes of renormalization – subtractions of infinities – work.

    What matters is that there exist physical regimes and limits that are pretty universal, independent of the way you get them. That’s why one can get them both by complicated treatments of “always regulated” theories with everything being cutoff, as well as by more creative and symmetric methods where infinities are reorganized and subtracted without their being regulated at every step.

  8. Philip Gibbs says:

    It’s good to see such strong yet diverse opinions over something that is likely to be resolved experimentally in a few years and possibly much quicker. That is a sign of how significant this is going to be. One way or another it is going to set the course of particle physics for the future and we have not seen anything like that from experiment for several decades.

    I feel as strongly as Lubos does about the prospects for supersymmetry. However, I am also accepting the possiblilty that I could be wrong just as he told me to with regard to another idea a few days ago 🙂 In fact that has always been the way I try to do things.

    The group of people who think supersymmetry will not be there is quite vocal, at least in the blogosphere. I think the evidence pointing to supersymmetry adds up to a very strong case, but it is still possible to imagine a different outcome. It would just mean we have to accept all the previous evidence as an amazing set of coincidences. It is much harder to imagine an outcome with no Higgs for example.

    In a court of law examining the evidence I’d expect the case for supersymmetry to be judged unproven, because law courts want at least one piece of decisive evidence. Higgs would probably already be found guilty of being correct 🙂 but sometimes there is a miscariage of justice even with such high standards.

    The experimental evidence will sort out the truth beyond any doubt very soon. This is science not law. In science we can always look for more evidence.

  9. Ulla says:

    In botany plants often show primitive charachters first, and as they grow they become differentated, and finally special treatures as flowers show up. All this is lying in the seed, implicitely. Everything follows the same symmetric plan. In my mind supersymmetry is not the answer, but some scaled-up variant of physic, that change a little for every time it is repeated. That is a fractal topology of the chromosomes? I wonder how that is shown in the supersymmetry?

    I am totally convinced biology is no exclusive part of the physics. It belongs there very much, and it can reveal many secrets and ad hoc hypotheses.

  10. PJ says:

    Thank you for this post. You have provided me with the first understandable explanation of the data coming out of the LHC since I posted my plea for help on July 27th. http://pjzen.wordpress.com/2010/07/27/lhc-results-not-just-the-same-old-thing/

  11. ervin goldfain says:

    Phil,

    You say:

    “The experimental evidence will sort out the truth beyond any doubt very soon. This is science not law. In science we can always look for more evidence.”

    Well written conclusion of this lively (and too often emotional) debate.

    Cheers,

    Ervin

  12. Kea says:

    We already have new physics with the new MINOS results (and other neutrino experiements) … but I guess you’re looking for 5 sigma. My money is on 5 sigma from MINOS before a true fairy field and SUSY exclusion from Fermilab or the LHC.

  13. ervin goldfain says:

    Kea,

    Interesting viewpoint on neutrinos where evidence for new physics may soon become compelling.

    But it is also possible that jets + missing energy searches at ATLAS will beat MINOS. Experiments under way there target a specific sector of the SUSY parameter space with a light 150-300 GeV gluino. According to RESONAANCES, this search requires only a limited amount of data (70 nb-1).

    Ervin

  14. Since Phil went to say something like “If anyone thinks something else will unfold, now is the time to say it” he can only blame himself for what follows;-).

    Concerning both fourth generation quark and supersymmetry, I am in a difficult position in which I cannot represent any emotionally loaded arguments.

    If generations correspond to the topologies labeled by the genus g of partonic two surface, then infinite number of them is in principle possible in case of fermions. For bosons states would be labeled by topologies of pairs of partonic two-surfaces defining the throats of wormhole contact and thus by (g1,g2): SU(N→ ∞) is the spectrum generating group.

    On the other hand, I have a nice argument saying that lowest genera (sphere, torus, sphere with two handles) are special since they are always hyper-elliptic that is allow discrete global conformal symmetry. The elementary particle vacuum functionals for higher genera vanish for hyper-ellliptic surfaces which would suggest that they are analogous to excited states and have higher mass. Bosons would would belong to 8+1 of the spectrum generating SU(3) meaning a prediction of exotic gluons and electroweak bosons belonging to octet and perhaps to be seen at LHC. Also both neutral and charged current processes in which genus is changed between say quarks and leptons would be possible.

    The higher genera would be “heavy”. But what it means: heavier than electroweak mass scale or nearly CP2 mass scale?

    I tend to believe on TGD counterpart of space-time supersymmetry for the brute reason that it follows from my own approach as approximate symmetry (I have been earlier emotional about the existence of even slightest indication for it!).

    Because M^4 spinors are replaced by 8-D spinors in TGD, the two Higgs doublets of SUSY are replaced by scalar 3+1 and pseudo-scalar 3+1 a as representations of vectorial SU(2)_w and one has 5 Higgses with same charges as in standard model but for of them are pseudo-scalars. For details see my blog and about other new physics predicted/suggested by TGD the posting At the Eve of LHC.

  15. Philip Gibbs says:

    Kea, neutrino physics is also exciting at the moment, but if I have to place my chips I would be betting that the CPT violating mass differences will fade away ome way or another.

    There is also hope for new physics in dark matter searches, cosmic ray observatorys, gravitational wave detectors and cosmological measurements, but I think the accelerators are going to have front stage for the next few years.

  16. Philip Gibbs says:

    ervin, the report on RESANAANCES is very good. He is duscussing the same paper that Woit mentioned. Accumulated luminosity is now 700/nb and rising so they have ten times as much data to play with. They have excluded very little with the 70/nb and there is definitely potential for new physics every time they increase the data collected by another order of magnitude.

    I thought the dijet events ATLAS reported at ICHEP were especially promising because they exceeded what was expected with so little data. Of course the stats were not at all significant, but it is easy to see how 10 times as much data could start to see something that is significant if it is there.

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