Taking Stock: Where is the Higgs Search Now?

Today, we got new information at the Moriond conference on the search for the Higgs particle (in particular, Phase 1 of the search, which involves the search for the simplest possible Higgs particle, called the “Standard Model Higgs”) from the Tevatron and the Large Hadron Collider [LHC], the Tevatron’s successor.  With those results in hand, and having had a little time to mull them over, let me give you a short summary.  If you want more details, read today’s earlier post and yesterday’s preparatory post.

Before I do that, let me make a remark.  There is a big difference between healthy skepticism and political denialism.  I get the impression that some people who are writing or reading other blogs misinterpret my caution with regard to experimental results as being somehow a political and unreasonable bias against the Higgs particle being present, either at a mass of 125 GeV/c2 or at all.  That’s ridiculous.  All that is going on is that I simply am not convinced yet by the data.  I’m a careful scientist… period.  And you’ll see that I’m consistent; later in this post I will advise you not to over-react negatively to what ATLAS didn’t see.

What happened today at the Moriond conference?

What did we learn?

The Tevatron experiments see a combined 2.2 standard deviation [2.2 ``sigma''] excess in their search, consistent with a Standard Model Higgs particle with a mass anywhere in the range of 115 to 135 GeV/c2.  This is not inconsistent with the Higgs hints that we saw in December from the LHC experiments.  Here I am being perhaps overly careful in not saying, more positively, “it is consistent with the Higgs hints…” only because this measurement is intrinsically too crude to allow us to narrow in on 124-126 GeV, where ATLAS and CMS see their hints.  In short, the Tevatron measurement could, in the end, turn out to indicate a Higgs at a different mass than the one indicated by the current ATLAS and CMS hints.  Anyway, it’s a minor and mostly a semantic point.

The results from ATLAS were a bit of a shock.  In all three processes on which ATLAS reported, CMS has presented results already, and in each case CMS saw a small excess (1 standard deviation [1"sigma"], which is  small indeed.)  But ATLAS reported today that it sees essentially no excess in any of the three, and even a deficit in one of them for low mass.  This has a big effect.

  • First, it allows ATLAS to exclude a Standard Model Higgs all the way up to 122 GeV/c2 (except for a little window 1 GeV/c2 wide centered at 118) and down to 129 GeV/c2.  The only large window left for the Standard Model Higgs particle is 122-129, more or less centered around the hint at 126 GeV/c2 that they saw in December.
  • But second, the significance of the December hint, when combined with the new data that shows no excesses in these three new processes, drops by about a full standard deviation.  That’s a pretty big drop.

What does it all mean?

I think it basically means, roughly, status quo.  We got some positive information and some negative information today, and none of it is that easy to interpret.  So I think we are roughly where we were before, except that we probably no longer have to worry about any Standard Model Higgs below 122 GeV/c2.  Before today we had a decent hint of a Standard Model-like Higgs particle with a mass around 125 GeV/c2; we still have it.  Let me explain what I mean.

There are easy (relatively!) searches for the Higgs, and there are hard ones.  The easy searches are the ones where the backgrounds are relatively simple and the signal is a narrow peak on a plot.  There are two:

  1. Higgs decaying to  photons
  2. Higgs decaying to two lepton/anti-lepton pairs (often called “four leptons” for short)

Results on these were presented by both ATLAS and CMS back in December.  The hard searches are the ones where the backgrounds are rather complicated and the signal is quite broad, so that a mistake in estimating a background can either create a fake signal or hide a real one.    There are three (mainly) for a lightweight Higgs:

  1. Higgs decaying to a lepton, an anti-lepton, a neutrino and an anti-neutrino
  2. Higgs decaying to a tau lepton/anti-lepton pair
  3. Higgs decaying to a bottom quark/anti-quark pair

These are the three that ATLAS reported on today (where they saw no sign of a Higgs signal), and that CMS presented back in December (and saw a small excess in all three.)  [ATLAS presented a result on the first one in December, but only using part of their data; it showed a small excess at the time, but not now.]  The third process is the main one in which CDF and DZero reported an excess today, though the first one also plays a role in interpreting that excess.

In other words, everything we learned today had to do with the difficult searches — the ones that are hard to perform, hard to interpret, and hard to check.  And everything we learned was 1 or 2 sigma information; not very compelling even statistically.

For this reason,

  • I would not conclude that the new Tevatron results make the 125 GeV Higgs case much stronger
  • I would not conclude that the new ATLAS results make the 125 GeV Higgs case much weaker

For the same reason, when I explained why I was skeptical of the evidence back in December, I told you that in my view the CMS excesses in the difficult searches did not make the case for a 125 GeV Higgs much more compelling.  Since the easy searches at CMS do not show as large excesses as ATLAS’s do, I wasn’t really comfortable with the whole case from CMS.   Their case improved in January, when they added a bit more information from their easy search for two photons.

If, like me, you discount the difficult Higgs searches somewhat relative to the easy Higgs ones, then almost nothing has changed, as far as the current Higgs hints, after today’s up and down information.  The excess in the two easy searches at ATLAS is still there, and there are excesses at CMS at least in the two-photon search.  Even from the beginning, I gave you good reasons to think the ATLAS’s easy-search excesses were a bit larger than they should be, probably due to an upward statistical fluctuation in the background.    Conversely I think now that one should not overstate how bad today’s ATLAS news is for the Higgs hints.  It’s still quite reasonable to think there may be a Standard Model Higgs there at 125 GeV/c2.  There’s some evidence in its favor, and it’s certainly not ruled out at this point. (Whereas now, almost all other masses are.)

So as usual I advise patience and calm and no hyperventilating; the 2012 data will settle the issue.  Either there is a Standard Model Higgs with a mass within a few percent of 125 GeV/c2 , or we’ll soon be fanning out in Phase 2 of the Higgs search, looking for all the other types of Higgs particles that might be out there.

28 responses to “Taking Stock: Where is the Higgs Search Now?

  1. Matt: ” There is a big difference between healthy skepticism and political denialism.”

    There is tons of political denial about any negative news for the Higgs search among Higgs blogs. Your post is the only fair one, from your academic integrity, and it goes way beyond the healthy skepticism. Thanks Matt.

  2. It seems Science in dancing with the media is being caught up in the sensationalistic nature of the latter. One has to be careful because in trying to attract attention one may fall flat on ones face when something gets hyped only to be found otherwise.
    Ignore the true science and integrity of those involved for a bit but look at the neutrinos faster than light saga. Many non scientists I have spoken to joke it off as a dodgy cable issue and ‘poor’ science. Granted a hard call when to go public but one has to be careful especially given the sound bite scientists to whom fame comes through sensationalism.
    Will this new set of results be a case of ‘first you say nothing there, then we have some LHC results and now there is something there, we just hadn’t finished analysing the data’. It’s not to say this is not true but the public are can be a cynical bunch and one needs to be very savvy with how they are fed.

    Never let the truth get in the way of a good story as they say

  3. In the December seminar ATLAS presented the full amount of data for the diphoton and four lepton channels, plus 2.01 fb-1 of data for the H →WW(∗) channel.
    In the accompanying note ATLAS-CONF-2011-163 one can read that the combined local significance of the detected excess at 126 GeV is 3.4 sigma, taking into account the two high resolution channels, further increased to 3.6 sigma by the inclusion of the third channel.
    In the slide 26 of the Moriond ATLAS talk the same combination is updated graphically. The change of the situation is dramatic: the maximum of the joint local significance of the two high mass resolution channels (red line) now drops to 2.7 sigma (blu line) upon inclusion of the H →WW(∗) channel (4.7 fb-1 of data), and then further reduces to 2.5 sigma by adding the H → tau tau and H→bbar channels .
    Thus, even ignoring the two new H → tau tau and H→bbar channels , which anyhow contribute marginally, the simple inclusion of the full amount of data of the H →WW(∗) channel has reduced substantially the significance of the 126 GeV excess. And this channel is very important, as witnessed by its crucial role in driving most of the exclusion in the low mass region.
    So, statistically the ATLAS evidence is weaker than before.
    Unfortunately, low counting statistics is a field perfectly suited to generate surprises.
    For example, in the golden four lepton channel, on the basis of the predicted background, one could easily conclude a-priori from a probabilistic calculation that it is very unlikely that two independent experiments would observe the same quantitative excess of three events clustered in 1 GeV at two different energies. In practice, instead, this is what happened, three events custered within 1 GeV at 119 GeV for CMS, 3 events clustered at 124 GeV for ATLAS.
    Another example of a kind of statistical surprise is the premature appearance of the 126 GeV fluctuation in the ATLAS diphoton mass distribution, which was somehow already present in the distribution shown at the Grenoble EPS-HEP conference in July and based only on 1 fb-1 of data.

    • Now as i grasped –almost — your description of the micro-world consisting of fields and vibrations , no more no less ! are we living in a tremendous delusion ?? take ALL representations of molecules in biology with nice diagrams based on x-ray diffraction images ….. are all this a grand illusion ? if in reality we got ONLY vibrations interacting with vibrations am i right if i claim that ALL images of molecules with solid balls representing atoms are mere illusion ? your share of the answer is to show how can we imagine say a molecule of sugar C6H12O6 as mere field vibrations ……..AS virtual particle concept is so misleading , can we claim that ALL molecules representations are utterly misleading ? the world consists of molecules not atoms , how can we grasp that all is a mirage or almost a mirage OF UNSEEN VIBRATIONS??

    • TO MATT.
      I hate to stand on shaken ground , so i need your solid ,clear , explicit answer : According to latest revealation of physics are fields THE ontological reality or mere scientific relative time dependent reality ? are the G.R. metric the one which is configurated by distribution of mass / energy for our calculations or space-time itself is patterned according to that distribution?
      For me physics is not to calculate the evolution of some thing , for me physics should be a revealation of reality.
      thanks matt., you remind me of 2 great scientists who had the talent to make physics a topic of awe and mind stimulation…george gamow and isac asimov despite the hidden agenda behind asimov writings which you are totally clear of that……thanks again.

    • In addition , we understand that fields ARE the fundamental entities —ontological or scientific– then are we to take the fields intrinsic fluctuations as fundamental ? ie.it cannot be reduced or explained by simpler cause ? are the higgs field value being NOT zero an intrinsic fundamental property or it can in reality =zero? then what mechanism assign to it its non-intrinsic value of non zero ?
      Are we to expect from LHC a revealation concerning the nature of the higgs field ?
      Are LHC staff worried about elevating its energy to 14 instead of 8 ?

      • What do you meant by ontological? This word, ontological, is related to philosophy rather than physics and science. Are the three laws of Newton ontological? Is the euclidean geometry ontological? When we study physics we better don´t care about philosophical categories, we just study the facts of nature and from them build up hypothesis, theories and theorems. According to K. Popper a scientific theory is true or false until is replaced for a new theory. None of them are ontological, except that the new theory improved the old one.

        To say that space time is ontological seems to me a tautology. Before Newton and Copernicus got in the stage our point of view about space time has barely something to do with the present frame. Was Aristotle no ontological compared with Copernicus and Newton? Is Einstein ontological but Heisenberg is not ontological? In my opinion space time is an entity that is a priori neutral, only after the scientifics look into it and make theories that have to be validated through experiments we could say that something is true or close to a veritable fact. I would replace the concept of ontological for true (or close to true) and false when we study physical data.

        • Dear JEP : How can we ignore that the fundamental level of physics is ontological by its nature , when you study fundamental “” building blocks “” of the cosmos you cannot just stop at the equations and solutions and close your eyes to the MEANING of what you are doing , ……please do not take us back hundreds of years , we are in the era of the fundamentals.
          Keep in mind the meaning of the last word , …..FUNDAMENTAL = ONTOLOGICAL as you cannot reduce it to any further level.
          As for space-time cant you see the FUNDAMENTAL difference between configuration of the metric as a math.tool and patterning the essence / identity / substance/ you name it of space-time?
          Dear JEP ; Ontology gives the meaning , ignoring it transform humans to mere calculating machines……..WE ARE HUMANS NOT MACHINES.
          regards
          shami with respect.

  4. Meanwhile, back at the Asian nuclear reactors, electron neutrinos are disappearing….

    http://www.interactions.org/cms/?pid=1031513

  5. Bozart McMencken

    Just an etymological reminder. “Illusion” derives from the Latin /il/- (on, at) + /ludere/ (a play).

    To say that “reality is an illusion” really only says is that what we call reality is some sort of forces playing on the surface of other things. Like wind on water, to use a familiar metaphor.

    This tells us nothing about the actual physical realities of wind and water per se, nor how best to interact with them in our daily lives. If we want to sail across the oceanic winds and waters, metaphysics and philosophy may accompany a successful accidental crossing, and possibly well prepare the shipwrecked sailor for the likely failed experience…but celestial navigation or dead reckoning will probably serve more reliably to get from shore to shore.

    I have long had a concern about the general ignorance of scientific and quantitative research methods among the public. I have recently grown–mostly through readings in particle physics–a deeper concern: the ignorance of qualtitative and philosophical/humanities methods, and their limits, among people of a scientific bent, as well as among the science- and math-impaired.

    What I see very often in discussion of things like the hypothesized Higgs boson is people leaping between different realms of discourse, different methods, different constructs. (I saw the same thing in the “social” sciences, by the way, in the course of my career in research and policy communications over 30 years.)

    So, yes, the universe may well be a play on…something. Still, when you are hungry and go to make lunch, you generally reach for the culinary arts, not metaphysics. Prof. Matt’s glorious contribution is in retaining a truly skeptical, scientific mind on the topic of Higgs bosons. This is the highest form of public science, setting aside axes to grind and grants to secure in favor of the genuine, disciplined attempt to figure out “how things work,” and remaining open to the very real limits of what we know, or can. Thank you, Matt, for being a voice of clarity among a staggering amount of hoo-ha and woo.

  6. aa. ss.: Don´t worry about, I don´t ignore the fundamental level of physics neither the meaning of what scientifics study. Wich are the building blocks of the cosmos: gluons, electrons, quarks, flavours, atoms or molecules? I do not pretend to go back hundreds of years but to anchor at the present. I´m afraid that we aren´t in the era of fundamental, on the contrary we arrived to a point where the zoo of particles increases and the theory of unification is far away from us. My comment don´t pretend to negate the philosophical concept of ontological, what I say is that the ontological term barely relates to physics. To write down many times the word ontological don´t really ensure that we abandon the surface of anything. But anyway, I respect your point of view although I don´t share it.

    • TO JFP : Lets omit the word you dislike , lets say ; the real , the true , the thing as it is , whatever you like , O.K. , the point is : suppose we found that the REAL fundamental ultimate entity are vibrating fields with specified excitation mode for every thing in the macro , well , specification belongs to the formal realm ( ie. control , direction , patterning…..etc. ), and as a matter of fact the formal is above and beyond the physical— please read ( the law of physicodynamical incompleteness by Dr. david abel )—-so my final aim is to show / mention / give a hint to clarify that the stand JUST IS is the most absurd stand in all of science , we cannot stop at saying ; well our explanation for such phenomenon is complete if we say IT IS, we must go beyond mere existence of it to explanation of that existence even if we find it absolutely necessary to go beyond physics.
      You may claim that i have a religious agenda , not so , but if you read —-reflections on relativity , an ebook in 724 pages by kevin brown —-you can see how pure physics is completely absorbed in thinking about the real.
      You cannot separate the observation from the concept beyond it , and i doubt that you adopt the most unrealistic interpretation of Q.M. which is satisfied with ; observe and calculate and that is all .
      When i mention the real i am following the lead of the ontological “” i have to “” interpretations of Q.M…….is not the many worlds such one?
      I am not arguing , i just respect and admire this website and hope to give some reflective flavor.
      shami with respect.
      P.S.: to matt. : are we abusing you hospitality? if so , pardon us.

      • Let me look at it from other perspective. It seems that in your opinion the real/ontological aspect of matter is contained in the concept of determinism. Whatever is out of determinism gets in a delicate/uncertain territory. Irrespective of any philosophical or metaphysical approach to this issue we stand up with the epistemology that the science provides to us. As far as I know the modern physics studies the continuous/determined aspect of matter as well as the discontinuous/undetermined aspect of it. Using your terminology, shall we have two ontologies/realities? If it is so, there is no room to argue about only one ontology, a nuance that weakens your point of view. What is real or not (in the physical realm) has to be discovered trough the theory and experiments, I can´t see any other way.

        • Now the point of separation in world views is clear , i would never limit my world view in the real/ontological aspect of matter as you called it , yes i agree totally that our epistemology is contained in the ” landscape” of science but that landscape is ONLY for the material aspect of existence , we as conscious humans represent a totally transcendental aspect of the real , i do not mean that there are 2 realities , for me it is a grand reality in which the material / scientific/ epistemological aspect is a minor part , dont forget that all of our science depends on our power of understanding , our ability to think , our majestic consciousness , so human mind is the primary ingredient in reality while the physical is the secondary …….. here my friend its not science which is our source , it is our subjective indisputable unrefutable reality which is an ultimate fact even if science is utterly blind to its nature or identity.
          I would blame any scientist who insist on the material aspect only , i consider all scientists claiming that they work on any kind of T.O.E. and assuming that E. is the realm of mass/energy only no matter how they represent it in their speculations i consider them as missing the most higher aspect of reality.
          I advocate a world view in which not only the higgs would solve the mass problem , but which reflect on WHY this particular field was assigned to this role and what mechanism gave it its specifications and what formal patterning causal power specified and connected interaction strength to certain mass…….. here my friend we as humans MUST reflect , wonder , think even if this level of existence is far above and beyond empirical science.
          Knowledge is not ONLY what science presents , knowledge in its broad , vast reality is an ocean without a shore which must embrace all of existence including the searching , inquiring , wondering mind.

  7. With reference to the Tevatron’s 2.2 sigma excess, driven by H to b bbar: near the end of the CDF results page for WH to l nu b bbar, which of the vector + Higgs channels is the one where the Tevatron expected to get closest to the SM cross-section x branching ratio, they state that for the WZ control channel, which was used to test the new HOBIT b-tagger, the fit for the total WZ cross section distributions yields 5.63 +1.79 -1.76 pb, in comparison to the
    SM prediction of 3.2 \pm 0.2 pb. This ratio of about 5/3 for observed/expected in the control channel is about the same as the ratio of observed/expected in the signal channel for m_H = 125 GeV, from the table and graph a bit further up the web page.

    • To Matt. : If the basic structure of reality are quantum fields , how can we understand the discrete traces of PARTICLES in all experimental particle physics ? your world view is of basic fields then why this is not reflected in the PARTICLE traces ? we cannot imagine those tracings as ripples in a waving field.

    • MATT.:
      Would you please explain to the laypersons like me how we can understand the physical reality being a vast multilevel waving ocean —- all kinds of fields—-and in the same time every single waving have its persisting identity and every single waving/ripple is identical to the far away one –electrons for ex.–, how in the human body we got 10^28 atoms then in av. 10^30 ripples interacting in such huge harmony???
      Are physical reality as fields a reality indeed or just a figment of imaginations???? can we have ultimate– not empirical– proof for this????

  8. to “aa.sh” and “jfp” :

    Most readers come to this blog to hear what Matt has to say. Could you please take your lengthy exchange somewhere else?

  9. Matt,

    When you say the 2012 data will settle the issue – based on what I have read, won’t we also need some “luck” as the integrated luminosity (if all goes well) will just barely give us the significance for 95% CL?

  10. @aa.sh. POLONIUS: What do you read, my lord? HAMLET: Words, words, words…

  11. Matt, I really like your blog. You explain stuff, not just report, on many (obviously confused) experimental results. You are one of the best HEP bloggers. Please keep it as simple as possible.

    • Thank you; I always have to balance keeping things simple with getting them out quickly, but I always do my best to give a simplified (but not simplistic) summary of important results as soon as I can.

    • I wonder why you concentrate on the higgs as if LHC is only for it ??
      As now the balance is SHIFTING TOWARDS WARM DARK MATTER instead of the cdm then LHC is losing a great deal as it CANNOT find wdm particles.
      This is a greater matter!! than the higgs , why you ignore it ? this is cosmic matter!!

      • I think you are significantly overstating the case for warm dark matter.

        As for what I’m doing on the site; I do talk about dark matter when there’s something to say:

        http://profmattstrassler.com/2012/03/05/news-from-la-thuile-with-much-more-to-come/

        However, the LHC was built to help us understand the Higgs field. It is guaranteed to give us insights (indeed it already has given us many.)

        If the LHC helps us to understand dark matter, that will be fantastic news, as a bonus. But there’s no guarantee. Dark matter particles may not be of a type that can be produced at the LHC at all.

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