Tuesday, October 08, 2013

CMS: second BEH boson near \(135\GeV\) gets an \(e^+e^-\) boost

The announcement of the Nobel prize for the Brout-Englert-Higgs mechanism (Weinberg just said that he was sorry that Guralnik, Hagen, and Kibble couldn't share this prize; Migdal and Polyakov independently found the mechanism while playing with trucks in a Soviet kindergarten: they were 19; hat tip: John Preskill) doesn't mean that everything has been settled about the God particle's sector. The boss of CMS, Joe Incandela, said that he wasn't sorry that he didn't share the Nobel prize. His prize and his colleagues' prize was the discovery itself.

This isn't just a proclamation to look nice and Feynman-like before the 2014 Nobel prize in physics that he may still receive. ;-) It's how many people actually feel. And the CMS might discover something more revolutionary than just a single Higgs boson which is cool but it's so 1960s, too. Sometimes I take the perspective that the experimenters and theorists should be evaluated together and Brout, Englert, Higgs and the three pals above were just 48 years faster than ATLAS and CMS. ATLAS and CMS should get a Nobel prize for something that they find before the theorists! ;-)



Click to zoom in.

Three months ago, I mentioned a bizarre 3-sigma excess in the search for the Higgs boson decaying to two photons. Aside from the Higgs boson of mass \(125.7\GeV\) that we have learned to know and love – and, in the case of two senior physicists, to use it as a credit card as well – there seemed to be an extra peak centered at \(136.5\GeV\). Moreover, it seems like the same excess appears in two disjoint channels.

If true, it's the second Higgs boson! Well, if the new particle will be indeed found and its spin is zero, I propose to call this particle the Brout-Englert boson and to reserve the term Higgs boson for the known boson of mass \(125.7\GeV\). ;-) Only Higgs fully realized that there was a new scalar excitation but Englert has been much more active in supersymmetry etc. so it wouldn't be a bad idea to call a SUSY-like particle related to the BEH mechanism after him (and Brout). There should be many more particles to be named after Georgi, Dimopoulos, Bill Gates, and a few others.

What I offer you today isn't equally strong (unlike the \(\gamma\gamma\) excess above, it isn't discussed as an excess in the paper) and I don't have a consistent interpretation but it's still interesting because a new peak sits at almost the same place.




I am talking about a freshly released preprint CMS PAS HIG-13-007,
Search for the Standard Model Higgs boson in the\(\mu^+\mu^-\) decay channel in \(pp\) collisions at \(\sqrt{s}=7\TeV\) and \(8\TeV\)
The title talks about the muon pairs but they actually show a result for the electron-positron pairs, too. And it's the latter graph that is somewhat intriguing.




The last Figure 16 looks like this:



Click to zoom in.

The left graph deals with the \(e^+ e^-\) final state, the right graph is about the \(\mu^+\mu^-\) final state. The absolute excess near \(135\GeV\) is less than 2 sigma in the left graph. However, relatively to the values of the curve near \(130\GeV\) and \(140\GeV\), the local increase is closer to 3 sigmas.

A much smaller peak appears for the same mass in the muon pair graph, too, although I would obviously never discuss such a small bump – smaller than other bumps – in isolation.

The tendency to produce the excesses near \(m_H=135\GeV\) surely seems interesting to me. However, I don't have a consistent enough story in the minimal supersymmetric standard model (MSSM). The coupling of all Higgs fields to the fermions is dictated by the Yukawa couplings which are determined from the fermion masses – in the MSSM case, it's done separately for the up-type quarks and for the down-type quarks along with the charged leptons.

In the MSSM, much like in the SM, the decay of the Higgs to electron pairs should be negligible. Well, the muon pair decays are "marginally" visible but the muon is 200+ times heavier than the electron. That means that the Yukawa coupling is 200+ times larger for the muon pair; and the decay probability (squared amplitude) is therefore about 40,000 times smaller for the electron pair final state than for the muon final state.

The ratio of the two doublets' Higgs vevs,\[

\tan\beta = \frac{v_u}{v_d},

\] would have to be huge for the electron pair channel to show up: that would allow \(v_u\) to be tiny which is needed to keep \(m_e=v_d \cdot y_e\) tiny despite a very high Yukawa coupling \(y_e\). But then the muon pair would show up 40,000 more clearly. This disagrees with the data. Moreover, \(\tan\beta\gg 1\) has already been constrained by observations involving the bottom quarks, a discipline in which the Tevatron was competitive even in the last papers.

However, some non-minimal model in which the Higgs doublets are numerous and couple selectively and very differently to quarks and leptons, and perhaps differently to different generations of leptons (models with six or more Higgs doublets are omnipresent in string phenomenology), could account for all the excesses near \(135\GeV\). More intelligent comments than this blog entry of mine will be cordially welcome.

11 comments:

  1. Leonard WeinsteinOct 8, 2013, 7:39:00 PM

    Lubos,
    This is off topic, but would you comment on the following:

    A Different
    Concept of the Nature of the Universe

    Leonard Weinstein
    October 8, 2013

    The need for large amounts of undetected dark matter was introduced to compensate
    for the calculated lack of adequate gravity expected from the normal matter
    observed to be present in space, that would be needed to make galaxies form
    properly, and also to explain the unexpected distortion of some observed astronomical
    images. The requirement for the need for dark matter makes the implicit
    assumption that we understand the nature of space and gravity, and that the
    metric of space-time varies
    smoothly over all scales, with variation determined only by the overall size
    and shape of the universe, and local gravity due to mass concentrations.

    An alternate possibility to how galaxies form and light ray paths could be distorted might be a
    consequence of large-scale non-uniformities in the local metric of space-time, but
    which have nothing to do with hypothetical dark mass, but just be due to the
    fact that the metric, even
    away from masses, is not as uniform as assumed. The assumption of a smoothly
    varying metric only dependent on matter concentration has no specific basis
    other than it seems reasonable. However, we simply do not know enough about the
    universe to be so sure. In fact the matter concentration that makes the
    galaxies group and form along specific web like lines may be due to the
    non-uniformity of the metric, with this non-uniform distribution resulting from a less that perfectly regular
    initial start of the universe.

    It is presently
    accepted that the initial start of our present universe (big bang) was not
    perfectly symmetrical and resulted in a slight energy and mass non-uniformity.
    This assumed non-uniformity caused the web like distribution of mass to cause
    galaxy formation along the web like distribution. It is then assumed that the
    dark matter was also concentrated along lines of this web of concentration, and
    its presence answers the question of why the galaxies appear to have more mass
    than seen by normal detection methods, and why light sometimes is distorted
    when it seems it should not be.

    If it is
    assumed the metric of space-time was not uniformly formed rather than the
    non-uniform spread of matter and dark matter (which formed after the universe cooled
    enough), the web of galaxies could be explained differently, and the need for
    dark matter goes away. The galaxies could be at locations where the metric is
    sufficiently different from average to account for presumed lack of matter. In
    addition, the locations of metric variation could also account for the image distortion
    of distant objects sometimes seen.

    An argument for the
    presence of a dark energy has also been
    introduced. This is used to explain the acceleration of expansion of the
    universe. Since we have no clue why there was inflation at the beginning of the
    formation of the universe, and why the universe expands at all, it should be
    clear that we are just making what seems to be a reasonable guess to explain
    present behavior by introducing the concept of dark energy. However, what
    appears to be dark energy may be just a variation in the speed of the
    stretching of space due to whatever causes space to expand at all. Expansion
    may be non-uniform and if the time scale is long enough, we would miss that
    altogether. Based on our limited understanding, there is no compelling reason
    for the need for DARK MATTER AND DARK ENERGY in space if we instead assume that
    space itself is non-uniform in structure, and unsteady in size variation.

    ReplyDelete
  2. Please don't think that your idea is original:
    http://en.wikipedia.org/wiki/Modified_Newtonian_dynamics

    Even so, it isn't a good one. MOND theories are contrived and misguided.

    ReplyDelete
  3. Leonard WeinsteinOct 8, 2013, 8:33:00 PM

    My idea is somewhat similar to MOND but not the same. MOND assumes variation in the response to gravity, depending on the magnitude, and specifically that small gravity variations are different than larger ones. My comment is that the space-time metric itself is not uniform. and at different locations the geodesics of space-time vary. All scale of gravity would be the same Newtonian like at a given location, but different scale at different locations.

    ReplyDelete
  4. Sorry Lumo,

    my comment is certainly not more intelligent than your nice intriguing article ... :-P.

    But I am curious if you have an idea what the broader bump below 150 GeV in the H -> mu mu channel could be, if anything not boring?


    Concerning the seemingly never complitely dying out 135 GeV excesses (maybe it is making fun of us poping out in different data playing catch me), a not so MSSM explanation would also provide more than the minimal (but by no means small!) amount of fun ... :-)


    Cheers

    ReplyDelete
  5. Well, that's a minor variation at best, and equally futile and misguided.

    ReplyDelete
  6. Leonard WeinsteinOct 9, 2013, 2:42:00 PM

    It is all very nice to make negative comments, but with no supporting basis. Inventing an unmeasurable dark matter to explain the observed galaxy motion, and distortions of light have no other supporting basis. My idea is that space is non-uniform in structure rather than an unseen mass is present. This is different and new, and does not require inventing unseen mass. Just how do you discount it?

    ReplyDelete
  7. You should read these papers:

    http://toebi.com/documents/ToEbi.pdf

    http://toebi.com/documents/AtomModelAndRelativity.pdf

    http://toebi.com/documents/Antimatter.pdf



    After those you'll know everything about dark energy, dark matter and antimatter. You are welcome ;-) Can you claim that your idea is better than mine?

    ReplyDelete
  8. Another light spin-0 Higgs? Just saw this paper in PRD today, BaBar "reported" 3 sigma excess in their light higgs search.

    http://prd.aps.org/abstract/PRD/v88/i7/e071102
    http://arxiv.org/pdf/1210.5669.pdf

    ReplyDelete
  9. An even simpler explanation (but I guess the CMS people did look at it) would be just an instrumental effect, where the same events are contributing both to the non-significant excess in gg and to the even smaller local mini-bump in ee. As you may not know, electrons and photons are identified using very correlated instrumental info, so such confusion may arise...

    ReplyDelete
  10. I am probably completely blind but I don't see the remark about a 3-sigma excess. Where do you see it in the BaBar paper?

    ReplyDelete
  11. Interesting. OK so you're saying that the channels may pollute each other. But the expectation has no bump around 135 GeV, has it?

    ReplyDelete