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    Is That A New Massive Particle ? Is That Some Kind Of Higgs ?
    By Tommaso Dorigo | April 6th 2011 02:52 AM | 66 comments | Print | E-mail | Track Comments
    About Tommaso

    I am an experimental particle physicist working with the CMS experiment at CERN. In my spare time I play chess, abuse the piano, and aim my dobson...

    View Tommaso's Profile
    UPDATE (4/7): I posted a link to a nice animated GIF which shows the (approximate) effect of scaling up the MC/data jet energy scale factor on the CDF new particle signal. See here.

    UPDATE (4/7):
    I added some considerations on the tentative CDF signal in a separate post today (4/7). You can find there a comparison with older semileptonic diboson searches at CDF and DZERO.

    UPDATE (4/6): Okay, I won't wait 5PM FNAL time after all, since I see that other online resources are already discussing it -including the New York Times online, which quotes the co- CDF spokesperson, Giovanni Punzi. I will let the previous post with the same title live below, but here I am attaching something on top.

    Introduction

    By means of introduction, let me first of all explain the process by means of which a unexpected discovery is made in high-energy physics.

    It so happens that when experimental particle physicists search for something known, they bump into something they do not understand about their data. Most of the times, it is just a bug in their code, so physicists are accustomed to not grow excited in any way, but rather get a big cup of coffee and sit (possibly during nighttime) in front of the computer, painstakingly checking their code. Then they run it again, and if the unknown feature persists, they return to the code once again. Only after three or four iterations do they venture to start speculating that something might be going on in the data.

    At that point, a more fun phase starts: the effect is studied systematically by using different simulations, by checking it with orthogonal samples of data which should not possess the same feature: so-called "control samples". Usually, in this phase one is able to spot a deficiency of the background simulations which one is comparing the data to.

    Sometimes, however, the feature is hard to explain away with bugs or with insufficiently trustable simulations. At that point, a physicist has better start thinking in terms of what new physics model could be producing the effect he or she is seeing in the data. Another obvious thing that the physicist needs to do at this stage is to search for the same signal in other datasets which might likely be sensitive to it.

    At the end of the lengthy process by means of which the physicists have tried to "kill" the signal they originally saw in the data, they will usually have grown confident enough to publish it. A statistical analysis should accompany the published signal, estimating how likely it is that it is a statistical effect. This is what is given in "sigma" units: a "3-sigma" signal is an evidence for a new effect, but might be produced by background fluctuations a few times in a thousand. A "5-sigma" effect is instead enough to grant the right of claiming the "observation" of the new effect.

    Some more background on dijet resonance searches

    The above process, in a nutshell, is more or less what has happened in CDF when a significant signal of jet pairs produced together with W bosons was first noticed. The authors of the analysis were looking for diboson production, a rare but well-known process occurring when protons and antiprotons create two W bosons together, or a W and a Z boson.

    These diboson processes can best be studied by searching for events with two, three, or four charged leptons (electrons or muons, that is, since tau leptons are much harder to collect due to their frequent decay into hadrons), because backgrounds are very small in that case. Indeed, CDF saw the first evidence of WW production as early as in 1998, that is before LEP II started to produce them in large numbers. In Run II, both CDF and DZERO studied WW, WZ, and ZZ production in detail by using the fully leptonic decay of the two bosons. However, one can use jets as well.

    If one requires one W boson to decay into an electron-neutrino or a lepton-neutrino pair, while the other W (or even a Z boson) to decay into a pair of quarks, the experimental signature is not in principle less striking than that of two leptons and missing energy: it presents a lepton, missing energy, and two hadronic jets. Alas, jets are however the most common product of high-energy proton-antiproton collisions at the Tevatron, and the WW signal, with its small production rate (only one WW pair is produced every 5 billion collisions, and one WZ every 20 billion collisions) is therefore buried in a large background of single W production events which feature two hadronic jets emitted by QCD radiation. This makes the search of "semileptonic" WW or WZ decays a nightmare.

    The authors of the CDF analysis, however, sought precisely that process, knowing that spotting it would be a very good starting point to searches for the Higgs boson. A light Higgs particle is in fact produced with a non negligible rate at the Tevatron together with a W boson, and it decays in a pair of hadronic jets. The same signature arises, with some important differences that I will discuss later. WH production is much rarer than the rare WW and WZ processes, so one does not expect to run into the former when searching for the latter; but one may always dream...

    The WW/WZ search (you cannot distinguish well the hadronic decay of a W from that of a Z, so the WW and WZ signals mix and are studied together in semileptonic diboson searches) was fruitful, and in fact two separate analyses were able to extract the semileptonic WW/WZ signal from the data in the last couple of years, after a sufficient statistics of collisions had been made available. I wrote about the searches in past articles, and I will place here a link as soon as I dig them out of my 2000+ posts... Let us however discuss the present signal here.

    What's that bump down there ?

    The authors saw that their background to WW/WZ events was not modeled very precisely, and investigated the high-mass region with more care. They were in for a surprise. The bump was not a ephemeral feature of the data, and simulations of the background could not explain it away. This started a much deeper investigation, which eventually led to the paper you can read on the preprint arxiv today.

    I will now describe the analysis in some detail, but experts are better advised to read the paper themselves. The analysis is not too hard in itself, although the interpretation of the result eventually is.

    The search starts with the so-called "high-pT lepton datasets": samples of events collected by requiring online that the detector sees a energetic electron or muon. These samples contain sizable fractions of W decays, and the signal can indeed be extracted with methods we learned from Carlo Rubbia almost 30 years ago: require that the lepton is energetic (rejecting some events where the electron or muon is faked by other particles) and isolated (to remove events where the lepton is due to the decay of a bottom or charmed hadron); and require that there is a significant amount of "missing transverse energy", an imbalance in the total energy flowing out of the collision in the plane transverse to the beam direction. In W decays missing energy is due to the escape of an energetic neutrino, while backgrounds produce missing energy only if the measurements of all particles in the calorimeter conspire to produce an asymmetry.

    After those standard selection cuts, the data is already quite pure in W decays. But what about the other one ? This is selected by enforcing the presence of two hadronic jets. The background, at this point, has the rather dull name of "W plus jets" production; some residual background from top quark pairs is also present, along with events where the leptonic signal is a fake and the event is actually a multijet one.

    To purify the sample, some additional inessential cuts are applied; the one to cite is perhaps the requirement that the missing energy points away from the jets in the transverse plane, a fact that removes multijet background where the missing energy is due to jet energy measurement errors. At this point, one can already compute the dijet invariant mass, and try to figure out what is the reason for its shape.

    The comparison is made with Monte Carlo simulations of the predicted background processes. Together with W+jets, ttbar, and multijet events, one sees a enhancement due to the presence of the original searched signal, namely WW/WZ semileptonic decays. You can well see them in the figure below.


    The red histogram is the diboson signal, which is evident in the data: it peaks at 80-90 GeV, where the hadronic W or Z decay contributes. Note also that the W+jets background totally dominates. Note further that there is a mismodeling of the data in the region above 120 GeV: it seems like all data points are displaced by one bin toward the right with respect to background predictions.

    So, the data overshoot the backgrounds in the region 120-160 GeV. First of all, we can ask ourselves a very basic question: is the effect statistical or systematic ? Of course it is systematic: the data points are all higher than the predicted background, and by a significant amount. But what systematic effect is the cause of this mismatch ? Different options are on the table.

    Sources of the mismatch

    The first thing a reasonable physicist might hypothesize is that there be an error in the jet energy scale which is set in the Monte Carlo. Imagine that when a 50-GeV parton from a real collision hits the detector it is reconstructed as a 50-GeV jet, but that when a simulated 50-GeV parton does the same, 45 GeV are estimated: this is a "energy scale" error, and it would cause the dijet invariant mass of the estimated backgrounds to peak and be displaced by 10% leftward, as is observed.

    It goes without saying that if this were still an option on the table, CDF would have not published the paper we are discussing. The jet energy scale is studied with excruciating detail at the Tevatron, and the uncertainty on it is below the percent level(at least for quark jets). Top quarks are by now a very good source of calibration for the variable, since they contain W->jj decays with which one can verify whether the jet reconstruction in the data and in the simulations agree. So jet energy scale does not seem a likely candidate for the mismatch.

    The second possibility is that one of the backgrounds is mismodeled, either in shape or in normalization. If you looked carefully in the figure above, you would see that the shape of the QCD background (the "multijet" processes, those that do not yield a real electron or muon) has a different shape from the W+jet background. So if one had underestimated the QCD background, maybe the total dijet mass would disagree with the data in the region where the background is falling...

    It is unlikely that the multijet shape has been so heavily underestimated, though. To make up for the observed excess in the 120-160 GeV region, one should hypothesize that the QCD multijet fraction has been underestimated by 100% or so: and since the QCD fraction is determined from the data -it is the only background component for which the experimenters did not trust the simulation, in fact- one can hardly believe that this is an option.

    The third possibility is that this is just a mismodeling of the main background, the W+jets "green" component above. This is unlikely, but it remains the most likely hypothesis. The authors did try to deform the W+jets dijet mass shape by changing parameters in the simulation, making different assumptions, reweighing events based on some other kinematical features of the jets; but systematics remain rather small.

    And what if ... ?

    So there is a fourth option on the table: there might be a new particle, a massive body with mass in the 140-150 GeV ballpark, which contributes to the data sample. This particle would be created in association with W bosons, and decay primarily into jets. The latter hypothesis is necessary because if one were to allow the particle to also decay into leptons one would find a logical inconsistency with the very precise measurements that CDF (and DZERO) have made in Run II of their fully leptonic datasets.

    So let us have a look at a fit of the dijet mass spectrum which includes the Gaussian signal from a narrow resonance at 140 GeV. Mind you, I say "narrow" because I am implying that the width of the excess seen in the data is roughly the same as the one observed for the W/Z peak at 80-90 GeV, once rescaled to account for the change in resolution in going up by 50 GeV. Those two bosons have natural widths of 2.1 and 2.5 GeV respectively, so that their mass shape is almost perfectly Gaussian (as opposed to a Breit-Wigner resonance shape): the jet energy resolution effects dominate over the natural width. What I call "narrow" is therefore something whose natural width is small with respect to jet resolution effects.

    This fit is much better than the previous one, of course -we added degrees of freedom! There are statistical estimators that allow one to draw a conclusion from the fact that a Signal+Background fit is much better than a Background-only one. The authors studied those estimators, and were able to determine that the statistical significance of the feature in the data corresponds to a deviation of 3.2 standard deviations, in Gaussian approximation. What that means is that it is very unlikely -one in a few thousandths- that the fluctuation is caused by statistical effects alone.

    But is it an observation ? Well, first of all, an observation of what. This particle is not called for by the most en vogue models -it cannot be a Higgs boson, because if a Higgs boson were sitting at 140 GeV with such a large production rate we would have seen it decay into WW pairs a long time ago. Furthermore, the Higgs would mostly decay into bottom quark jets, but these jets are not b-tagged -if they were, this would be similar to the analysis of WH production, which does not see any excess.

    So, no Higgs. But it might be another fancy beyond-the-standard-model particle, right ?

    Well, of course. There are so many models that extend the standard model beyond our current observations, that one can easily find a few that fit the extra particle. Take this paper, for instance. A light Z' boson with suppressed couplings to leptons might fit the bill.

    In the paper (which appeared five days ago in the arxiv), the Z' model is fit to the data of CDF, which were actually presented in the PhD thesis of Viviana Cavaliere a while ago. This is a theoretical paper of the class of "instant preprint" which we have seen flourish with the first LHC publications... It is a sign of the times. The figure on the right is not qualitatively different from the one in the CDF publication, but it is a real new physics model which produces the blue bump, and not just a Gaussian fit. So one needs to take it seriously.

    And there is, in principle, another reason for taking the Z' hypothesis seriously. The authors of the new theoretical paper claim that the Z', added to the standard model, produces a asymmetry in top production which is in the right direction, explaining away some of the discrepancy that top-antitop asymmetry analyses have seen in the recent past at the Tevatron. You can check that out in the figure on the left, where the Z' model produces the asymmetry prediction shown with a blue line. The CDF data are black points, and the SM prediction is the dashed line.


    All in all, this is very intriguing, of course. I however have my own ideas. One of the things that I am not convinced about is the quality of the agreement of the background shaoe with the data in regions away from that where the tentative new signal arises. If you look carefully, you will see that the peak of the mass distribution, where the WW/WZ signal resides, is not well modeled. I already mentioned that above, but here I stress it to explain that one might go wrong with the dijet mass shape not just if one commits an error in the estimate of the jet energy scale, but also if one simulates jets with different kinematical properties. The angle between the two jets influences the mass distribution, and in fact this is discussed in some detail in the CDF paper. I do not find the result of that investigation conclusive enough, however, so I must keep my idea that one of the most likely explanations for the observed 120-160 GeV discrepancy is that the W+jet background is not modeled well enough by the simulation.

    I add to that a consideration. The excess observed by the authors in the mass spectrum is mostly due to electrons (156+-42 events versus 97+-38 in the muon sample), and the electron sample is potentially richer with QCD background. While the two numbers are not inconsistent with one another, they leave one wondering...

    In conclusion

    I do not particularly like to play the die-hard sceptic -this is after all a paper I myself reviewed and signed!- but I believe this is nothing but the umpteenth would-be new physics signal, destined to be buried by the analysis of further data, by the crafting of more precise simulations, or by the better understanding of Standard Model sources. Nevertheless, it is quite interesting to see this paper coming out now. Both DZERO, and the LHC experiments ATLAS and CMS, have now a lead to investigate their own data! If they were to see a 3-sigma effect in the same mass range and in the same kind of events, it would be already time to put the champagne in the fridge....



    Older post:

    This post is for now just a placeholder of an article I am publishing after 5PM Fermilab time, to report about a new find by the CDF collaboration. Come back and reload in a few hours and you'll get more information... The reason is that I have promised I would wait to blog on this until a seminar takes place (at 4PM at Fermilab), but I wanted to let you know that the result is now public, such that I can even attach a plot below, one which is already available online.




    As you see in the background-subtracted plot above, besides the peak due to W and Z bosons in red, there seems to be a resonance at 150 GeV or so (fit by the blue histogram), one that decays into pairs of jets and that is produced in association with a W boson in proton-antiproton collisions. The quoted significance of the Gaussian bump is 3.2 standard deviations, once look-elsewhere effect and systematics are accounted for. Yes, I know, this smells of Higgs, but it cannot be... For reasons I will explain later today.

    And to give away what I think in world premiere: the answers to the questions I placed in the title of this post are "No. No."

    Further reading:

    Peter Woit discusses this shortly
    Lubos Motl with more links
    (apologies to both for having their names in the same paragraph)
    Resonaances discusses the latest news on the related topic of ttbar asymmetry
    He also talks about this signal now
    Michael Schmitt has a very in-depth discussion of the signal.
    Physics and Physicists
    Sean Carroll
    Flip Tanedo
    Philip Gibbs
    Arcadian Pseudofunctor
    Marco Frasca

    Also see:
    Physics World
    CBS (which quotes this post)
    New York Times online
    Science news
    20 minutes (in French)
    More coming... Write more links in the comments thread!

    Comments

    DON'T HOLD US IN SUSPENDERS MAN! OUT WITH IT!

    SynapticNulship
    Let this page be known as the historic site in which "don't keep us in suspense" was replaced with a new idiom, "don't hold us in suspenders."
    This is a very interesting analysis and I really need to read more from you. I have read the paper almost 5 times and tried to come up with an explanation(s). It cannot be a Higgs, because the two jets are not b-jets.
    I will read it again until you write about it.

    The Stand-Up Physicist
    I almost had to throw away a bunch of "No Stinkin' Higgs" t-shirts - no, give them away to Good Will. That was close.
    In arXiv 1104.0699 the CDF authors say:
    "... the invariant mass distribution of jet pairs produced in association with a
    W boson using data collected with the CDF detector which correspond to an integrated luminosity of 4.3 fb-1. The observed distribution has
    an excess in the 120-160 GeV/c2 mass range
    which is not described by current theoretical predictions within the statistical and systematic uncertainties. ...".

    As you say, Tommaso: "... This particle ... cannot be a Higgs boson ..."
    and
    "... the CDF analysis ... sought ... "semileptonic" WW or WZ decays ...these jets are not b-tagged ..."
    and
    "... the data overshoot the backgrounds in the region 120-160 GeV ...
    The ... significance ... is 3.2 standard deviations ... a 3-sigma effect ...".

    I would like to compare that 3-sigma effect with the results described in your old blog entry "Proofread my PASCOS 2006 proceedings" (5 September 2007), particularly comment 11 (by me) and comment 13 (your reply to 11):
    I said: "... With respect to the CDF figure shown (colored by me with blue for the peak around 174 GeV) at
    http://www.valdostamuseum.org/hamsmith/CDF94.gif
    ...[and]...
    With respect to the D0 figure shown (colored by me with blue for the peak around 174 GeV) at
    http://www.valdostamuseum.org/hamsmith/D097Mar.gif
    ...
    what are the odds of such large fluctuations showing up at the same energy level in two totally independent sets of data ? ...".
    You replied:
    "... It is of the order of 4-sigma.
    However, one would be entitled to claim a 4-sigma effect only if one observed the data after predicting the location of the excess beforehand. In other words, a 13-over-4.5 event excess is less significant if it is allowed to sit anywhere in a plot. But maybe you had predicted the top at 140 before the CDF plot of 1994 came out, so that is not a concern. ...".

    As you noted, I had predicted a Tquark state with mass in that range before 1994. One of my many web pages about that is a relatively brief summary at
    http://www.valdostamuseum.org/hamsmith/Triviality3states2009.html

    I would like to see the 3-sigma results of arXiv 1104.0699 to be interpreted in connection with the 4-sigma results of the earlier Fermilab semileptonic histograms (and other earlier Fermilab data as to which my interpretetations differ from the early Fermilab interpretations).

    Tony

    dorigo
    Tony, in 2007 I tried to explain it to you. I do not like to be quoted out of context. Please read back the full answer I gave you back then:

    As for the two plots you mention, they show single bin fluctuations at 140 GeV. I read 8 events in the CDF one, in the face of a background plus signal totalling probably 2.5, and 5 in the D0 one, with about 2 from bgr+”standard” ttbar. You ask what is the probability of such a fluctuation, and that I can answer. It is of the order of 4-sigma. However, one would be entitled to claim a 4-sigma effect only if one observed the data after predicting the location of the excess beforehand. In other words, a 13-over-4.5 event excess is less significant if it is allowed to sit anywhere in a plot. But maybe you had predicted the top at 140 before the CDF plot of 1994 came out, so that is not a concern.

    My own concern as an experimentalist is that such a spike is not physical, given the mass resolution of CDF and D0 on a top quark decay. The top has a resolution of about 25 GeV, so in any one 10 GeV bin there cannot be more than 20% or so of the total. That spike may be very unlikely as a fluctuation, but it is even more so as a signal.

    To be clear, there can be no effect that makes a signal significantly narrower than what it is expected. One would have to hypothesize that all jets in those events fluctuated to neutral pions (measured better), and still the resolution would be far, far larger than the 5-10 GeV necessary to at least hope that a significant portion of the signal falls in a single bin

    So Tony: those 1-bin fluctuations have no real physical meaning. And trying to sweep them together with the "signal" now published by CDF is a bad thing to do, because there is no reason to hypothesize that a particle may decay to both 2-jet final states and 3-jet final states.

    Cheers,

    T.


    Hank
    "One thing we know for sure -- it is not the Higgs-boson. That is the only thing we know for sure."
    But it's a good result for Tevatron because no one knows what it is.
    The Stand-Up Physicist
    I was REALLY impressed by a recent talk from someone working on the ATLAS detector (Dr. Valerie Perez Reale). Those folks are thorough. She was on a gamma-gamma detection team. There are apparently several teams working on different kinds of signals. No doubt there is a team working with jets. Another cool thing is that the CMS detector is competing with ATLAS using the same beam.

    Is it felt that the LHC will be able to confirm or deny this bump in a fairly short time frame? I have read about the LHC excluding all kinds of things, so this news strikes me as a bit odd, the old machine on the planet out-doing the new kind on the block.

    [Note added later: From the end of the NYTimes article:
    Joe Lykken, a Fermilab particle theorist, said Dr. Punzi’s group would have four times as much data in an analysis later this year. 
    More data is good, independent data is better.]
    Hank
    More data is good, independent data is better.
    What does that mean?  You think they will build a mirror of the Tevatron somewhere and duplicate this?   10 inverse femtobarns is a lot to sift through and it takes time but it is still Batavia people doing it.
    The Stand-Up Physicist
    Independent as in the LHC collecting similar data. I know they smash different things together, so my question might be moot, I don't know.
    Hank
    Maybe not.  Luminosity isn't everything.    Statistically speaking, if the Higgs exists, it has shown up somewhere in the Tevatron collisions.   Finding it is another matter and the LHC is supposed to make that easier.   But this other thing is....well, no one knows.
    Larry Arnold
    Well I simply would not know, but then again if it is, why was it not discovered yesterday, and then again perhaps it was.

    Can one really speak of discovery at all because either it is there or it is not, and if it wasn't there yesterday, then where was it?

    Language allows me to phrase questions like that, now let's see what science says .......... (the sound of nail's being bitten in a place where no-one can hear that)
    Ciao Tommaso,

    excellent post! As usual.

    I guess the next step for the collider community is to consider the MJJ spectra from the other experiments, D0, CMS and ATLAS. I am a little surprised that there is no concurrent statement from D0, since there used to be a courtesy agreement between the two collaborations concerning discoveries. Do you know anything about that?

    I agree with you that the ΔR reweighting test is inconclusive but the other tests are quite reasonable. Note that Buckley et alia missed the fact that the jets are not b-jets, so part of their model has to be discarded.

    Michael

    The courtesy rule as far as I know is not applied anymore, so it seems that D0 people didn't know anything about this until few days ago. In any case, during the W&C seminar D0 announced that they will come out with something in a few weeks timescale. So let's wait for them...

    Oh, this will be fun. Theorists will crank out all sorts of models of what causes that bump, and in so doing will predict all sorts of new particles just out of reach. After all, theories are a dime a dozen. And if this bump disappears like a zit treated with Clearasil, then the theorist feeding frenzy will stop as abruptly as it started. So it goes with 99.9% of all 3-sigma bumps.

    Well, unlike most signals, theorists appear to be forming a rough consensus: the signal is real, and due to some extra neutral current state which can also explain the ttbar forward backward asymmetry. The question, of course, is: if this is real (which I certainly believe) then are people more willing to call a fairy a fairy? After all, new physics at the EW scale makes the fairy hypothesis a little less compelling.

    WoW ! This is Great ! A real cliff hanger ! Or is it just a way to keep the Fermi National Accelerator Lab open until further notice.

    Perhaps the explanation is not a Leptophobic model but a chromophilic one. Something that could really disguise itself as a contribution to the background in a QCD experiment.

    Alejandro, some of us actually PREDICTED such an object.

    And another question is: why did Tommaso not tell us about the Cavaliere thesis, since it was already public? Was he not allowed to do that?

    dorigo
    Hey Kea, I did not know about the thesis. I have no time to try and know all the public material that comes out of CDF in one form or another...

    Cheers,
    T.
    Indeed, it is my conviction that our not so good understanding of QCD is playing us a
    bad joke as also happens for the asymmetry. It is difficult to understand why this matter is so underestimated and the effort of the community working on this is generally overlooked favoring more exotic explanations.

    Cheers,

    Marco

    QCD phase diagram is still unknown. Nobody knows the QCD equation of state. And I'm also asking the question, do we know well QCD when we run experiments with TeV energy? From the day N1, LHC saw "strange" QCD events even with pp collision (not with heavy ion).

    There is another big experiment at GSI FAIR (2015) that has to provide some experimental evidence about QCD equation of state. Until that moment, we can run Lattice QCD, Holographic QCD, and phenomenological QCD codes.

    Again we see something strange in terms of lepton versus quark coupling. Reminds me of CDF's multi-muon / lepton jets, the JACEE charged / photon ratio anti-centauros, and the centauro cosmic ray particles mentioned in hep-ph/0111163.

    And if this particle is to be true, why it is only created in association with a W? And if it is true, why it does not decay to a pair of b-jets? Why it does like to decay into "ligher" jets?
    This particle could a non-SM Higgs, but still, if turns to be, why it does not decay to b-jets?

    dorigo
    Hatim, two simple answers:
    - nobody could see such a particle if it were produced with jets, because 1) we do not trigger well on those events, and 2) we would be swamped by the QCD background.
    - nobody says this tentative state does not decay to b-jets. All that is observed (indirectly) is that it is not enhanced by requiring the jets to be from b-quarks.

    Cheers,
    T.
    Then one question remains:
    Why it is only created in association with W and not a Z? Am I missing something?

    dorigo
    Hatim, nobody searched for a jj resonance in Z + 2j data yet, so you cannot say that it is not produced together with a Z, nor can you say the opposite.

    In any case, there are 10 W bosons decaying leptonically per every Z boson decaying leptonically which are reconstructed in Tevatron data. This is due to the branching fractions and elpton efficiencies. So one expects that any particle produced equally with W and Z bosons would have a rate a factor of 10 smaller in ZX final states, other things being equal. Since the "excess" in W data is of the order of 250 events, one expects 25 events in Zjj data in a similarly sized dataset. This makes the search in Z+jets events less than conclusive -but to my knowledge it has not been tried yet. However, there is a search in missing energy plus jets which CDF published two years ago (and which I refereed internally). They saw the WW/WZ /ZZ signal in the dijet mass distribution, but I do not see any enhancement in the 145 GeV region there.

    Also DZERO searched for dibosons in semileptonic mode a while ago, the result shows no signal (actually a dip where the CDF signal is), see
    http://dorigo.wordpress.com/2008/10/24/d0-bags-evidence-for-semileptonic-dibosons/

    or just have a look at the figure below.




    Cheers,
    T.
    Beautiful! Thank you so much Tommaso. I am sure all other players in the field - D0, ATLAS and CMS - are doing their best to "confirm" this CDF "discovery"! HEP will be very exciting in the next couple of years.

    Thanks again

    "In order to account for the trial factor within our search window, 120-200 GeV/c2, in each pseudoexperiment we
    calculate the delta-chi-squared varying the position of the Gaussian component in steps of 4 GeV/c2."

    There's an old rule of thumb that you claim discovery at 4 sigma if you know what you're looking for, and 5 if you don't. Part of that rule of thumb is motivated by the trial factor. This seems to have been explicitly taken into account for the window, though there's an unconsidered trial factor of how many signatures one looked at besides W+jj. So should one consider the 3.2 sigma as being 0.8 sigma away from 4, or 1.8 away from being 5?

    Also, there seems to be some confusion--it's not that the data in this mass range are b-phobic, right? As far as one can tell, it contains the b's at the same rate as normal QCD W+jj background. ("We compare the fraction of events with at least one bjet in the excess region (120-160 GeV/c2) to that in the sideband regions (100-120 and 160-180 GeV/c2), and find them to be compatible with each other.") It's merely not-obviously-b-philic (as an SM Higgs would be.)

    dorigo
    Hi Andy,
    nice to see you here.

    Yes, the claim is not that the thing would not go into b's, only that it is not enhanced if one searches explicitly for b's. Which is a totally different thing. Of course, one can still note that even a Z boson would be enhanced wrt general QCD jets, because the B(bb) of the Z is 15% while a QCD jet is a b only 1% of the time in that energy range (rule of thumb). But certainly what the authors seem to imply is that the tentative object is not decaying "preferentially" into b's, like a Higgs would.

    About the look-elsewhere effect: they accounted for it as you describe, but the "derating" of the significance is not decoupled from the other systematical effects, because they account for all at once. So one does not know what the significance would be if one accounted for systematics but not for the look-elsewhere effect. They do say that if they extend the search window to 300 GeV the significance goes down by another 0.2 sigma though.
    I think these 3.2 sigma are quite solid as a statistical estimate, i.e. we are 0.8 sigma away from a "4-sigma observation". The problem here is that the reliance on MC for the main background, and the issues with energy scale and other detailed modelings, make these 3.2 sigma not at all convincing. At least to me.

    Take a look at a plot I have grabbed from another forum, which shows what happens if one takes the CDF data and scales the simulation up with a jet energy scale factor of 1.05 (I think):

    [Figure credit: TBA]
    As you see, there not only is a disappearance of the excess at 150 GeV, but also the low-mass points are in better agreement... Food for thought.

    Cheers,
    T.
    That's pretty striking! Although you said it was highly unlikely that CDF would have their jet energy scale wrong...
    Either way, I'm on your side for now Tommaso -- my gut says there will be a 'mundane' explanation for this anomaly, rather than new physics.

    dorigo
    Ok, I can give the proper credit for the above picture now that I received permission. It is from Tommaso Tabarelli de Fatis, who also provided me with a better version, which I paste below:


    This version of the scaling up is by 4% of the jet energy scale. Note the plots of residues on top. Left: original CDF version of the data/MC comparison; right: with JES up by 4%.

    Note also that I by no means imply that this is the reason for the CDF excess in the 150 GeV region. I think it is unlikely that the JES is wrong by such a large factor in the CDF analysis. However, one needs to take this into account when considering all other hypotheses.

    T.
    Hi Tommaso,

    I do not understand how these plots are produced. You say that the JES is scaled up by 4%. But if I understand correctly this would scale up the energy of the individual jets and then based on the new jet energies the new dijet invariant mass is computed. This would explain why the plots after the JES shape the shape from the original plots. But what I do not understand is how did Tommaso Tabarelli de Fatis have access to the individual jet energies and directions so that he can compute his new Mjj, given that he is not a collaborator of CDF. And even if he were, the internal rules would not have allowed for him to publish the plots. Therefore, I think that he had access only to the Mjj plot and only modified that plot, but all I can imagine he could do is multiply the shape by some value, or maybe move the bins to the right (but then what would happen to the first bin?). Could you please clarify this a bit?

    Thanks,
    Adrian

    dorigo
    Hi Adrian,

    of course no jet energy is available externally. In principle one could determine the distribution of jet energies that contribute to each bin of the invariant mass distribution, and work from there; but what Tommaso did was to just scale up the mass by the jES factor. The correlation between a shift in jet Et and the resulting shift in mass is almost 1.0.

    Cheers,
    T.
    Hi Tommaso!

    Since you put those plots there, maybe you can answer something I've been puzzling over. The JETP talk has a backup slide in which the jet energy scale is increased by 7%. (Page 52 of the pdf on the JETP page.) However, the underlying MC don't seem to have moved up in mass everywhere by 7%. (It looks to me as if the MC was shifted up by 7% rather than the data down by 7%.) By eye (as you observe above), 7% is about one bin and looks on page 21 like a one-bin shift ought to bring everything into good agreement. But it only brings the W/Z peak into good agreement. How could an overall jet scale shift move only the W/Z mass but not the rest of it?

    When I saw the title of the slide I expected it to look pretty much exactly like the plots you have above, and the fact that it doesn't confuzzles me.

    (That said, I agree 7% or even 5% is a lot to miss by.)

    dorigo
    Hi Andy,

    whether one shifts the data or the MC is a question of choice I guess. I do not know what the authors did - I should look in detail at their internal notes, and then I would know but I could not report about it here! What I know is that the plots I pasted above are made with a very simple recipe, which shifts up ALL backgrounds (including WW/WZ). . Actually, 4% appear to be enough, if you look at the latest plot pasted above.

    I have no further insight, I am afraid...
    Cheers,
    T.
    Very exciting, I have been waiting for these results for over 10 years. Please see equation 18 in my paper http://theoryofeverything.org/TOE/JGM/ToE.pdf which predicts a Higgs (or per Lisi, a Higgs sector boson) at 148 GeV.

    Tommaso,

    this is slightly off-topic, but allow me to ask nevertheless. Recently I read the slides of Harris' talk in Moriond on CMS results, at http://indico.in2p3.fr/conferenceOtherViews.py?view=standard&confId=4403 where he presented some measurements on polarized W bosons. Is there a chance to test the following, somewhat unusual conjecture at CMS:

    "The mass of longitudinal and transverse W bosons (and Z bosons) might differ by a small amount. The amount slowly increases with energy."

    To be clear, such a test is only useful if the Higgs is not found; in this case, such a mass difference is one way to maintain unitarity in the standard model while dispensing with the need for a Higgs boson. If you could comment, I'd be glad. In the meantime, all the best for your blog!

    dorigo
    Hi Frank,

    hmmm I have nothing quite meaningful to say, except that in principle the measurement is possible. We do distinguish W bosons polarization states in top production, for instance. But I guess it would take a lot of data to do such a measurement.

    Cheers,
    T.
    Regardless of being perceived as 'too soon' to pass judgement - Many have a dizzying sense of displacement after reading Matthew R. Buckley's paper, this Monday.

    Although not seminal, in posit, it is exceptional for the shape of an intuition surrounding recent experimental findings at Tevatron: http://arxiv.org/PS_cache/arxiv/pdf/1103/1103.6035v2.pdf

    I have a heightened expectation for another surprise, soon coming, that may imply a 'rewrite' of electroweak theory or greater.

    LHCb?

    Does that a bulge in your data mean you're happy to see us?

    Terms like "energetic"electron,"sizable"fractions,"charmed"hadron and "conspire" are not scientific terms.They may be alright for baking cakes,startreck or Harrypotter movies,but can you stand back and look at yourselves.I'm afraid that the king is in the altogether,the altogether he's altogether as naked as the day that he was born.Interesting in the imaginative sense though I wouldn't stake my life or the lives of others,or our livelihoods on it.

    dorigo
    Sorry, Don, if you had a point I missed it. What are you referring to ? This is not science, it is science blogging, or have you lost your sense of reality ?

    Cheers,
    T.
    dorigo
    ...Besides, I challenge you to find the expressions you mention (except "conspire", which is just a word) in a baking recipe. I can find dozens of instances in PRL and PRDs.

    Cheers,
    T.
    I've been following Greg Moxness' work in theoretical physics for years now. It will be very intriguing if his particle prediction of 148 GeV comes to pass, and if it does, then the academic community should look at his work to ascertain its validity.

    Intrepid, the Moxness prediction was 142 MeV, not 142 GeV. Wrong scale.

    Kea,

    Intrepid is correct - it is 148 GeV on eq. 18 of http://theoryofeverything.org/TOE/JGM/ToE.pdf
    (not sure where you got 142??)

    BTW - In my paper I do state this is the Higgs. While the discovery is clearly not the Higgs, the model I am using for determining this particle mass point does not rely on the specifics of the Higgs mechanism.

    Ah, I just glimpsed the m_0 on page 10. My apologies. It's the first time I have seen your paper. I must say, that with varying constants and twistors, you may well be on to something. No matter that you mistakenly called it a Higgs, because it will part of the replacement Higgs mechanism, even if fairy fields themselves do not exist.

    OK, I posted about your paper on my blog. Cool stuff.

    The very fact that this new particle and force were predicted theoretically by Sidharth (: arXiv:1103.1496; arXiv:1104.0116; New Adv.Phys.5(1)2011) lends credence to the discovery being real and not an artifact.

    birla, a 2011 paper does not constitute a prediction, since the thesis was available from Dec 2010.

    OK, so I looked at the Moxness paper, but it does not explain where the m_H comes from (and the numbers don't seem to work). The insights sound vaguely correct, but in the end it looks like a lucky numerological guess.

    Kea,
    My mass prediction for completing the link between the Standard Model (SM) and General Relativity (GR), that is a Theory of Everything (ToE), is based on a relationship between electron mas, Fine Structure, the Vacuum Expectation and W/Z bosons. Please detail your suggestion that the "numbers don't seem to work".

    JGM, I plugged the actual numbers into your formula on page 4 (for the 148 GeV) but I didn't get 148. If you could write out here how to input the correct parameters, I will look further into the matter. And BTW, naming it a TOE is fricking annoying, because there is much more to QG than that (and QG can never be a TOE, because there is no such thing).

    @ kea--- When I posted my suggestion that Moxness' research needed to be examined by the physics academic community, I meant by actual scientists who carry advanced degrees in theoretical physics, who currently teach and do research in the field.

    Um, IE, by your definition I am an actual scientist. Sorry to disappoint your prejudices. Of course, I do not currently have a university job, but you did use this criterion in your definition. Anonymous cowards should check their facts before making stupid remarks.

    BTW, IE, guess what topic my PhD thesis in Theoretical Physics was on? An emergent twistorial gravity with a varying constant cosmology. Sound familiar? I am the most qualified person on the planet to judge Moxness' ideas.

    The basic problem with Intrepid Explorer's comment: "When I posted my suggestion that Moxness' research needed to be examined by the physics academic community, I meant by actual scientists who carry advanced degrees in theoretical physics, who currently teach and do research in the field." is that actual scientists who have advanced degrees in theoretical physics, who currently teach and do research in the field are way,. way, way too busy to waste time looking at stuff like that. They're much too busy with (a) their own research, and (b) following the research of a few people who everybody follows.

    Carl,
    I agree, this seems to be one of several systemic issues with academia - causing "group think" or lemming like behavior. That is why it takes them so long to get out of the ruts with theories that have failed. It's unfortunate that it is only those elder academics (typically retired) that dare to question the establishment like those of us already on the outside.

    Kea,
    Please see my blog post with a simple explanation for the calculation for my new particle prediction of 10+ years ago. http://theoryofeverything.org/wordpress/?p=265

    Thank you, Gregory. That is a great help.

    Indian scientist questions authenticity of ‘god particle discovery ’
    (From Wires, April 26)An eminent Indian physicist Monday questioned the authenticity of the reports that speak of the discovery of the Higgs boson also known as god particle that is believed to bestow mass on other particles. A leaked internal memo contains unconfirmed reports that one of the detectors at the Large Hadron Colliders at CERN near Geneva picked up signals that could be a ‘Higgs boson’ says the Telegraph. B.G.Sidharth of the B.M.Birla Science Centre at Hyderabad said he was very skeptical about this claim.
    “This is unofficially leaked news – such a thing has happened before” Sidharth who has authored several books and published research papers on the subject said. He had come out with new theoretical findings recently that say that there is a new force of nature acting between particles and their anti-particle counterparts. This can be seen at very high energies and is very shortlived. A discovery matching this description has been announced by the CDF team at Fermilab’s Tevatron in Illinois. There is about a one in a thousand chance that this observation is a fluke. But given the theoretical background, the chances this is wrong is even less.
    “In fact the latest LHC news (that says Higgs boson has been detected) has to be first verified and authenticated by the team itself, before any conclusion whatsoever can be drawn” he said adding ‘at present it is no more than a rumour’.
    According to the Standard Model of particle physics the universe is composed of matter and anti matter. Besides there is an intermediary particle the ‘Higgs boson’ believed to bestow mass on matter and anti matter. The hypothetical elementary particle ‘Higgs boson’ predicted by the British physicist Peter Higgs some forty five years ago, has however not been directly discovered yet.
    The Large Hadron Collider (LHC) at CERN created three years ago is likely to confirm or reject the existence of these new particles Some physicists even feel that the discovey of the Higgs would merely confirm the Standard Model, but physics would be more interesting in the absence of Higgs.
    .

    Hey - the new particle bump (referred to by Kea as "the Moxness Bump" was spotted last night on the TV show "The Big Bang Theory". See my blog post on it.
    http://theoryofeverything.org/wordpress/?m=201105

    I am a journalist and I want to know more about Kind Of Higgs. I hope you will share information in future. Thanks.