torsdag 7 april 2011

The fifth force found?

There are maybe a fifth force, that is either strong color or electroweak flavour, today the picture is not at all clear. Contrarily, most dimmy.

Lubos: A new Z prime boson The real question is: Why? There's no excessively good reason for the Z' boson to exist and no reason for it to not exist. We just usually prefer to believe in the non-existence unless we have a reason to do otherwise - unless we see a role that such a new particle could play. We don't know of such a role.

Such a new fifth force would remain a fifth wheel for some time. Imagine - people would say that there are five basic forces. One of them holds galaxies together and keeps us on the Earth; the other is responsible for all of chemistry, biology, and material science, not to speak about electromagnetic communication; the third force keeps atomic nuclei together; the fourth force causes some nuclei to beta-decay; and the fifth force adds 100 bizarre events at the Tevatron. ;-)

They could solve the mu problem in supersymmetric model building; mediate SUSY breaking; and add interesting yet dangerous predictions of flavor changing processes and new interactions with dark matter. The string-derived (beyond ordinary GUT) Z' bosons have also been claimed to be essential for light neutrino masses and proton stability.

Resonaances: The simplest explanation, proposed in this April Fools' paper, involves a 150 GeV Z' boson. A light Zprime with significant couplings to leptons are excluded by LEP and the Tevatron, but if the coupling to leptons is small then the limits are surprisingly weak. In particular, 150 GeV Z' with electroweak size couplings to quarks is perfectly allowed, and would have the right cross section to produce a bump observed by CDF. One should note that Z' with the mass of that order could generate a large forward backward asymmetry of the top production, as observed in another CDF analysis. But one should also note that generating the asymmetry requires a large flavor violating coupling u t Z' which in principle is not related to the coupling to the light quarks.

Washparkprophet: seems to solve problems that is isn't clear that we had in the first place. I'm skeptical, as are most physics bloggers looking at the announcement. Like Motl, I just don't see where the theoretical motivation for a fifth force comes from unless you have something like composite quarks or leptons out there that need to be held together and sometimes decay in high energy environments.

TGD: identification of the new particle would be as an exotic weak boson. The TGD based explanation of family replication phenomenon predicts that gauge bosons come in singlets and octets of a dynamical SU(3) symmetry associated with three fermion generations (fermion families correspond to topologies of partonic wormhole throats characterized by the number of handles attached to sphere). Exotic Z or W boson could be in question. If the symmetry breaking between octet and singlet is due to different value of p-adic prime alone then the mass would come as an multiple of half-octave of the mass of Z or W.
An entirely new interaction. Actually I have talked about entire hierarchy of scaled up variants of hadron physics (Aaaarrrrgggghhh!; do not get scared: it was an expression of extreme irritation by some colleague who believes that physics proceeds by infinitesimal steps) associated with Mersenne primes and strongly suggested by p-adic length scale hypothesis! The natural explanation for preference of quark pairs would be that strong interactions are somehow involved. This suggests a state analogous to a charged pion decaying to W boson and gluon creating the quark pair. This kind of proposal is indeed made in Technicolor at the Tevatron and has as its analog second fundamental prediction of TGD that p-adically scaled up variants of hadron physics should exist.

Resonaances: the new particle should not be too heavy and should couple strongly enough to both the 1st generation quarks and to the top quarks. Otherwise the effect would not show up on top of the QCD top pair production.should couple chirally, that is to say, with a different strength to left- and right-handed quarks. Otherwise it would not generate a forward-backward asymmetry.
A strong force for chirality?? (my comment)
the new particle has to have a large flavor violating coupling to the 1st and the 3rd generation, whereas similar couplings to the 1st and 2nd or to the 2nd and 3rd generations appear to be severely constrained by experiment. If any of these models corresponds to reality then some unexpected flavor structure is being revealed. Flavour = weak force
a new color triplet scalar decays to a top quark plus a light invisible fermion. Sounds much like stop → top + neutralino, although the required couplings do not fit SUSY. As the new particle production cannot of course interfere with the QCD top production, this possibility is somewhat disfavored by the top cross section measurements. On the other hand, such a new particle can be very well disguised, especially when its mass is close to the top mass, and is currently poorly constrained by new physics searches. Strong force again, with dark matter.

Twistor scattering theory for color say Kea.

NY Times: They found that in about 250 more cases than they expected, what came out of the collision were two jets of lightweight particles, like electrons, and a heavy-force-carrying particle called the W boson were produced. The team found that in about 250 times more cases than expected, the total energy of the jets clustered around a value of about 144 billion electron volts, as if they were the decay products of a hitherto unsuspected particle with that mass-energy. For comparison, a proton weighs about one billion electron volts.

This could not be the Standard Model Higgs, Dr. Punzi and his colleagues concluded, because the Higgs is predicted to decay into much heavier particles, namely quarks.


The result does not come from a search for new physics (take note of this please) but rather from an attempt to measure the cross section for di-boson production in which one W decays leptonically (e or μ) and the other boson decays to a pair of jets. The invariant mass distribution includes a peak near the W and Z masses – the red peak in the plot above – as it should. The mass resolution is about 12 GeV and hence not good enough to resolve individual W and Z peaks; the W peak dominates anyway.

There is a huge continuum background from W bosons produced with two jets.

So we have a nice, statistically-significant bump in this mass spectrum. Some theorists already posted their hypothesis (Buckley, Hooper, Kopp and Niel, arXiv:1103.6035, 31-Mar-2011) — even before the CDF Collaboration released their results! (I agree completely with Gordon Watts’ comments about this.) You can also read a report in the New York Times. I’ll not comment on that.

Of course, the observation requires confirmation. I am very sure that physicists at both ATLAS and CMS are studying their data carefully. Most probably, the D0 Collaboration will try to say something soon about it, too. So let’s pay attention and keep an open mind. Speculation is fun, but fluctuations do come and go….

(Disclosure: I am in inactive member of the CDF Collaboration but played no part in this analysis. I devote all of my research time to CMS.)

Other bloggers have already commented, ahead of me: See Physics and Physicists, Not Even Wrong, The Reference Frame, A Quantum Diaries Survivor and Cosmic Variance. I’m sure there will be lots of discussions on these blogs – and if I am lucky, a little bit here, too. ;)

12 kommentarer:

  1. What a DAY yesterday was, huh Ulla? The Z-prime announcement at Tevatron, more Multiverse madness, LISA cancelled (at least the USA contribution, not ESA's, but can ESA do it by itself?), AND Glenn Beck of the US's Tea Party was fired by uber-Conservative FOX News! I'm not sure I can take too many day days like that. Hopefully today will be quieter. :-)

    Yes, but this was the big one. 3.3 sigma confidence level, yes? That's fine, a bit better than 3, but I'm sad to see so many 3-sigma things rushed to announcement in the past year.

    What will it take to achieve 5-sigma? Results from ATLAS? How soon would you expect that to happen?

    Thanks you very much for your great overview at this post. Another good (and funny!) link is by Professor and Theoretical Astrophysicist Ethan Siegel at his weblog, Starts With A Bang, here.

  2. Thanks.

    They try the best to explain it away (Lubos, Sean). But this 'bump' has been seen earlier too, so there are good chances it will stay. This has been known for months they say, and that would mean it has been checked quite thoroughly, I guess, before it was published.

    Shelton has talked of this

    What would the new force be? Strong chirality? Dark matter coupling?

  3. Minimal Walking Technicolor? I have no idea.

    The whole mess with Tevatron is painful to me. I've worked for the US Government, briefly, and I can assure you that as an operation comes to a close, the employees, including and especially management, go out of their way to keep everyone fully employed for as long as possible. If it seems I am saying that this is politically motivated, I am not because I simply do not know, and that's the painful part. I want to know, and ignorance hurts my brain. Especially my own.

    Rather that gather a headache, I will go forward and assume something new has been found, the worst then would be simple disappointment rather than disgust.

    All I can say then is that if this IS technicolor, which competes with the Higgs, then hoo boy oh boy will there be a ton of new physics calculations to be done, so these soon to be out-of-work fine Fermilab scientists should find good employment in many places, even if that means they have to move to Europe and CERN. Or England. The Brits seem willing to believe just about anything, bless their hearts. You can't say they're not open-minded.

  4. This all begins to sound like non-commutative geometry a lot. Kea has maybe a clue what it is about? It was polarizing, someone said.

    If there is a fifth force, and it is not Higgs, then maybe there are six forces all together, one more to be found?

    I wonder what Nima think of this? 'Slicing' could point to manysheeted spacetime, or phase space.

    It is quite hard to think this would be about fundings. It is a too big news. If anything such is revealed the credibility will suffer very much. Can they take the risk?

  5. Physics Without Ideology – Bite by Bite

    A satirical blog about the ideologies and fixed ideas found in fundamental physics.

    8 April 2011
    Czech communist dreams up a proof of string theory against evidence
    A communist is a person that values his ideology more than the facts, and uses violence to spread it. A well-known czech communist - and sadly also physicist, once researcher at Harvard - has now transformed the recent Fermilab error in their data evaluation first into a new force, then into a invented Z' particle and finally into a proof of string theory. These are not lies any more, but fraud.

    So we see that in Czechia, at least one string theorist is so deranged that he needs to deceive others for a living. If belief in supersymmetry is only a delusion, belief in string theory is now definitely proven to be a mental condition.
    Posted by Nemo at 10:31

    Another post on the same blog:
    3 April 2011
    Fun about Motl
    True, one should not waste energy about Motl. But he is so smart, rude and unreasonable that I cannot resist making fun of him. One of my male friends – yes, they do exist – has the right description for what guys like him are doing in physics research: mental masturbation.

    It must be said that we speak about Motl's past: he is not a physicist any more. At present he converted to being a frustrated anti-global-warming activist. In his research past, the conjectures he explored – supersymmetry and strings – were only for his own enjoyment. Nobody else cares about these conjectures, because they do not agree with experiment. But a few rare people do share the same hobby.

    The best is that Motl recently told in his blog why he doesn't want to explain his past research to the general public: "it is like throwing pearls to swines." I had never seen this expression, which is from the bible, applied to this specific hobby.

  6. Have you read this article by Sean Carroll? It's only been 2 days and already the skeptics are coming out of the woodwork.

  7. "You see the extra little bump around 150 GeV, that’s what’s getting everyone so excited. It’s unlikely that the data are a good fit to the prediction; the “KS (Kolmogorov-Smirnov) probability” is given as 5×10-5, which means that it’s not bloody likely."

    I suppose they have looked at that before publishing.

    If 3-sigma results in particle physics usually go away, then why has this latest result gotten so much attention?

    Ye, why? Because it has been there so long already, and is not fading away? It would be ironic if the hunt for Higgs would have made this one overseen. But the sample is small.

  8. New scientist: But if technicolour is correct, it would not be able to resolve all the questions left unanswered by the standard model. For example, physicists believe that at the high energies found in the early universe, the fundamental forces of nature were unified into a single superforce. Supersymmetry, physicists' leading contender for a theory beyond the standard model, paves a way for the forces to unite at high energies, but technicolour does not.

    Figuring out which theory – if either – is right means combing through more heaps of data to determine if the new signal is real. Budget constraints mean the Tevatron will shut down this year, but fortunately the CDF team, which made the find, is already "sitting on almost twice the data that went into this analysis", says Roser. "Over the coming months we will redo the analysis with double the data."

    But the GUT scenario may not be true at all. It is too just a fancypicture? The forces may be dichotomous.

  9. Not Even Wrong in 30 oct 2008:
    This is not a signature characteristic of supersymmetry or any of the other known heavily-studied classes of models. If real, as far as I’m aware it’s something genuinely unexpected. Perhaps phenomenology experts can point to some less well-known models with this kind of signature. The only such thing I’m aware of is a very recent paper from three weeks ago by Arkani-Hamed and Weiner, entitled LHC Signals for a SuperUnified Theory of Dark Matter. They discuss a theory of dark matter involving a new hidden gauge symmetry, broken near the GeV scale, saying that this is “motivated directly by striking Data from the PAMELA and ATIC collaborations”. In these models there can be Gev-scale Higgs and gauge particles decaying to an anomalously large number of leptons. They discuss the question of whether the parameters of such models can be adjusted to give large decay lengths, and predict the observation of events that “contain at least two “lepton jets”: collections of n > 2 leptons, with small angular separations and GeV scale invariant masses”, pretty much just what CDF sees . Since the CDF paper undoubtedly has been the topic of intense discussion among the 450 or so physicists in the collaboration for many months now...

    And the preprint: In this short note we point out the consequences of the most straightforward embedding of this simple picture within low-energy SUSY, in which G_Dark breaking at the GeV scale arises naturally through radiative corrections, or Planck-suppressed operators. The theory predicts major additions to SUSY signals at the LHC. A completely generic prediction is that G_Dark particles can be produced in cascade decays of MSSM superpartners, since these end with pairs of MSSM LSP's that in turn decay into the true LSP and other particles in the dark sector. In turn, the lightest GeV-scale dark Higgses and gauge bosons eventually decay back into light SM states, and dominantly into leptons. Therefore, a large fraction of all SUSY events will contain at least two ``lepton jets'': collections of n>= 2 leptons, with small angular separations and GeV scale invariant masses. Furthermore, if the Dark Matter sector is directly charged under the Standard Model, the success of gauge coupling unification implies the presence of new long-lived colored particles that can be copiously produced at the LHC.


  11. Gregory Moxnes

    M Theory and/or Loop Quantum Gravity hold the promise of resolving the conflict between general relativity and quantum mechanics but lack experimental connections to predictability in physics. A connection is made to these and other theories vying for the title of a “Theory of Everything” by questioning the value of the traditional Planck unit reference point for the scales at which they operate. It also suggests a cosmological model which has acceleration as being fundamental. It provides for an intuitive understanding of the Standard Model and its relationship to particle masses and the structure of the atom. The prediction of particle mass and lifetimes is a good indicator for its validity.