A Quantum Diaries Survivor

Rome is a very nice city, which attracts millions of tourists every year. Its monuments, its history, the museums, the pope… All this is well known, but from now on Rome features a brand new tourist attraction: its air.

A very serious study performed by researchers of the italian CNR involved the analysis of samples of air in Rome, Taranto, and Algeri. The results ? In the air of Rome there is consistently a significant, although quite small, amount of cocaine - 0.1 nanograms per cubic meter.

The study has revealed the presence of other drugs in the air, and several carcinogenic substances as well. However, the CNR scientists say that overall the air in Rome has improved in the last few years. In all the three cities significant amounts of nicotine, cannabinol, and caffeine have also been detected, but only in Rome is cocaine significant.

Interesting to know, the highest concentrations of cocaine have been seen in the air around the Rome University “La Sapienza”… Enough to draw conclusions on the practice of sniffing cocaine by university professors ? I doubt it - their salary is too low for the prohibitive cost of the substance. Instead, I wonder if the CNR researchers took samples of air inside the various palaces of power, like the Ministeri, the Camera dei Deputati, the Senato. Results could be shocking.

Today’s Higgs boson session of the CDF week started with a very nice talk by Sven Heinemeyer on Higgs physics, which after a brief overview of the Standard Model Higgs, focused mostly on its cousins in the framework of the Minimal SUperSYmmetric models.

I must warn readers that this post cannot be at the level I usually keep these discussions, because of the complexity of some of the issues and the impending talks I am trying to follow with a small part of my brain today. Maybe later I will summarize it here!  

Anyway, after a brief but comprehensive introduction to the theoretical framework of electroweak symmetry breaking, Sven showed some details of the way the indirect limits on the Higgs mass have been cooked up by global fits to electroweak observables.  This is relevant for the famous “blue band plot” (check the latest version in the LEP electroweak working group pages), which shows what values of the Higgs mass are consistent with the measurement of electroweak processes that are influenced by it. It turns out that there are a few results pulling the most favored Higgs mass in the fit down, and only one pulling it up strongly enough. The point was made that if the forward-backward asymmetry measurement made by LEP with b-quarks from Z decay was taken out of the global fit, the Higgs mass would become really incompatible with the direct lower limit set by LEP II.

You can see it in the plot above (not exactly the one showed in Sven’s talk, but one containing similar information), where each individual SM observable provides an error bar showing which Higgs mass it favors, given the correctness of the standard model. The grey vertical band marks the preferred region, and each observable provides an independent (how much so I am not totally sure) range for M(h). I think Sven’s point is valid, but one could well single out other results (such as the one for the left-right asymmetry, A_LR) which pull down strongly, and the favored M(h) would move up quite a bit - the plot has a logarithmic x axis, and so points on the left appear to have large error bars while they are in fact more precise!

Then the famous Higgs reach plot (see below) was mentioned, to drive home the point that we “promised” exclusion limits tighter than LEP II by 2008 and some sensitivity up to 135 GeV with the full Run II statistics.  \begin(rant) … I was surprised and somewhat saddened to see that plot being made fun of, and not by the speaker! It looked like the audience did not give a lot of credibility to those predictions any more, despite many of them being the very authors of the underlying studies. Well, I still do.

[The plot above has been discussed in length elsewhere on this site. In short, it shows the integrated luminosity per each of the two Tevatron experiments (y axis) which is needed to exclude or discover the Higgs boson as a function of the Higgs mass.]

In my view, people tend to forget that CDF and D0 have consistently shown in the past that results reach and exceed expectations if we give them time. Nowadays, the Tevatron experiments are doing worse than what the plot implies for low values of the Higgs mass, but many of the improvements on the relative analyses (those looking for a light Higgs boson decaying to b-quark pairs)  have not been implemented yet! I think the pessimism that seemed to hide behind the slight amusement of the audience fights openly with the fact that our collaboration is strongly pursuing the Higgs boson in all the available channels, and is investing 70% of its resources into those analyses. \end(rant).   

After a rant, let me come back to Heinemayer’s talk. He asked himself: what is the preferred Higgs mass in the MSSM when electroweak measurements are all taken into account ? This is a nice exercise which for some reason I have not seen done before. Sven showed the result of these computations. It looks like the best fits all point to a preferred mass of about 110 GeV, for several choices of the MSSM parameters, and tan(beta) values of 10 or 50. So, if one were to compare this result with the preferred Higgs boson mass value in the Standard Model, which is now at 76 GeV, one would conclude that the MSSM seems favored with respect to the SM… But this means missing a crucial point! In fact, the price one pays in delta chi^2 is very high in the MSSM fits, as shown by the steepness of the family of curves in the graphs  he showed. In contrast, despite the fact that the preferred mass in the SM is lower, it is still giving a good fit with masses up to 140 GeV or so. That is to say, it is not so important what is the preferred value of your fits, as much as how wide is the region which still has a reasonable probability.

Now, to get to another important point made in the talk: Sven explained that the so-called “benchmark scenarios” for MSSM models (discussed, for instance, in http://xxx.lanl.gov/abs/hep-ph/0202167), which pick some reference values for many of the model parameters and only allow a variation of  M(A) and tan(beta), are all ignoring the “bounds”  from cold dark matter models. Now what this all means is the following. Standard cosmology, which has shown several successes in the recent past and which “fits” a very precise amount of dark matter in the matter-energy mix, is compatible with the presence in the universe of supersymmetric particles, which would provide the missing mass while not producing unwanted effects that would have been detected by past or curent experiments. The amount of dark matter is actually convertible -if one buys the extrapolation- in a mass and a typical cross section for these candidate superparticles. The point is then that the “benchmark scenarios” have MSSM parameters which do not agree well with the hints from the amount of cold dark matter cosmologists favor.

To mend that inconsistency, Sven discussed a scenario called NUHM - for “Non-unified Higgs model”, which implies non-unified scalar fermion and scalar Higgs parameters. I am not in the position of discussing the details of this scenario, because it is based on work that Sven has not published yet. Anyway, the choice of parameters of NUHM provides a better match to the amount of cold dark matter, while still being in fair agreement with electroweak and B physics measurements performed by particle accelerators.

Below I would have like to show the plots contained in Sven’s talk, which have a color code showing which regions of M(A) and tan(beta) in the NUHM benchmark scenario are fitting better with all data. In the plots, one notices that the best fits are in a region which will be hard to reach by the Tevatron experiments in their direct Higgs searches. I could not attach the plots to this post, because - as I discovered by talking to Sven during the coffee break - also theorists have restricted information at times. He has not published this work yet, and quite naturally I have to wait until he does to adobe this site with them…

Finally, Sven mentioned that the NUHM scenario is compatible with M(A)=160 GeV and tan(beta)>45 -the values that the CDF H->tau tau tentative signal (which, remember, is most likely only a 2-sigma fluctuation) points to. This also has some important consequences. If the A particles have a mass of 160 GeV, then the lightest neutral higgs boson, h, should be just around the corner for direct searches at low mass: the favored value for its mass would then be about 115 GeV, just above the LEP II limit, and at reach of CDF and D0. Also, another observable which is influenced by SUSY effects, the branching fraction of Bs mesons to muon pairs, would be larger than 2×10^-8, and so possibly at the reach of the Tevatron experiments with an extended running of the machine.

If you read the post down to this last line, you are probably a physicist, and you could be interested in exploring the information on the Higgs boson which has been made available on the FeynHiggs web page: http://www.feynhiggs.de .

Christopher Neu, a colleague in CDF where he co-leads the High-Pt b-tagging working group, announced yesterday the birth of her daughter Madeline Jane. Chris has worked with me in the group that recently produced a new measurement of the b-jet energy scale from a fit of the peak of Z decays to b-quark pairs. He gave an important contribution to our work by taking care of the trigger collecting our events, which has required constant care in the last few years due to its large cross section, which showed a quadratic rise with instantaneous luminosity - something which often plagues track and calorimeter-based triggers at the Tevatron.

Here is a nice picture of the new father and daughter together:

Just a quick picture of the auditorium here at IN2P3 where the second day of the 2007 CDF week is starting with a summary talk on the exotics group activities:

The cartoon on the slide shows two explorers looking at a tiny pyramid emerging from the sand, one of them saying “This could be the discovery of the century, depending, of course, on how deep down it goes.”

“Those who can remember the past may still be condemned to repeat it“

Chris Hays (after Santayana), speaking on the past history of discoveries and ensuing understanding of fundamental physics.

A anonymous physicist left a comment to a recent post here mentioning that the Dzero experiment is allegedly observing an excess of multi-b-quark events, asking me whether I have more details on the matter. Since I am not a member of the Dzero collaboration, it is too bad that the simple answer is NO. Too bad since I would not fear of being crucified if I did leak restricted information, as it would happen if it came from the CDF experiment.

However, I have friends. And they have friends too… You certainly know that the internet is less than a couple dozen links “thick”. Well, by the same token the high energy particle physics community is certainly less than five “friendship links” thick in turn: so it should be easy to gather information by milking your closest contacts - a fact that underlines how silly it is to pretend that individual experiments keep their result secret for half-year-long periods of time, waiting for all sorts of checks before diffusing preliminary results (which still have a non-zero chance of being wrong anyways).  I have been asking friends about the Dzero signal, and hopefully I will get some hints from them…

In the meantime, being in the dark is nice in a sense. I have zero information on what is the exact channel where Dzero has allegedly seen an excess of events. I only know it seems significant (4-sigma ? 5-sigma ?), and that it implies some narrow new state at about 180 GeV of mass. So I am free to speculate wildly: let me do it.

A supersymmetric Higgs boson ? That is certainly possible, although such a state would not be narrow if it had to show a production rate large enough to allow significant detection with a few inverse femtobarns of data. A supersymmetric b-quark ? Hmm, that hypothesis does not seem to fly too much either. A fourth generation b-quark with that mass would decay to a top quark - unless flavor-changing neutral currents were also playing a trick there. What else ? A gluino ? Also a possibility - it may decay to b-quarks.

I would favor the hypothesis of the SUSY Higgs boson: it would be great if Dzero were seeing a signal at 160-170 GeV - it could turn out to be compatible with the excess seen by the Higgs to tau-pairs search performed by CDF recently: the plot would thicken considerably if a tentative signal of a b-quark pair resonance were seen at that mass. John Conway, who is working on the tau-pairs search, tells me CDF will have a new 2-inverse-femtobarn result out for summer conferences. So the scenario of a joint SUSY Higgs discovery by CDF and Dzero in a few months is pretty much open!

In any case, with the low level of information we have available this far, practically anything is possible. We need more leaks. Dzero folks, please do not leave us in the dark! Anonymity for commenters here will be for once respected…

UPDATE: I think the analysis is an update of the one reported  here, with twice as much luminosity. I might be wrong though… Still gathering information. That work was a search for SUSY Higgs in events with three b-jets in the final state, selected by multiple secondary vertex tagging. In the paper, there is a cross section exclusion plot which shows they did obtain an observed limit worse than the expected one, for 170 GeV…

UPDATE: Ok, below you can see the plot I am referring to above. You see that with the multijet search D0 excluded MSSM Susy models implying a light higgs boson of 170 GeV for tan(beta) values above 121, when they expected to be able to exclude down to tan(beta)=104. The discrepancy is due to the small excess seen, 6748 events observed with three b-tagged jets versus 6687 predicted, in 900 inverse picobarns of data: in particular, those 6748 events had more of them with a mass of the two leading jets around 170 GeV than their model predicted. Now they are analyzing twice as much data, but I do not know whether they have improved their technique.

In the plot above, (let me stress it, it is the published old result by D0 in the same channel discussed in this post) the red line marks the lower limit of the region in the M(A):tan(beta) plane which is excluded by the multijet Susy Higgs search by D0 with 0.9/fb of data. It means that all pairs of values corresponding to coordinates above the red line are excluded at 95% confidence level or more. The black line, instead, shows what limit D0 expected to set. The expected and observed limits roughly coincide for M(A) lower than 150 GeV, and then divide, due to the slight excess observed in their analysis.

Today is the first day of the CDF week in Paris. A full week of discussion on the status of the experiment and the challenges awaiting us, and a detailed insight in the scores of analyses being brought forward by a thinning but still powerful group of highly experienced and focused physicists.

It’s good to be in CDF. An experiment that has run for very nearly a quarter of a century, and a collaboration which by trial and error has reached a wonderful equilibrium between its many souls - conservativeness defenders, bold seekers of the unexpected, precision measurement guys. All supported and intermingled with a backbone of detector fixers, electronic geniuses, bright thinkers. A bunch of extraordinary people, if you ask me. And the results are for everybody to see, although I will avoid listing them here.

This week, we will have more time to interact and entertain in relaxed discussions than what normally happens during the two-day CDF collaboration meetings held at Fermilab. And we will have invited talks by a few distinguished theorists and experimentalists to stimulate our brainstorming. Here is a list:

• I.Antoniadis will discusss “Physics and signatures of extra dimensions“
• D.Boutigny will talk about the “French computing center and perspectives“
• C.Grojean will tell us of “Electroweak theory beyond the Standard Model“
• S.Heinemeyer is on “Higgs & Susy at CDF II before LHC takes over“
• M.Mangano will give a “Workshop summary and further thoughts“
• L.Rolandi will have a “Perspective of an outsider on Higgs hunting at CDF“
• G.Salam will discuss “Jets, higher order & interplay between them“.

 As you see, a nice list of interesting topics, which I look forward to hear about. If you have a particular interest in any of these topics, drop me a line and I will try to cover them here. 

Got to Paris with a quite disturbed flight from Munich yesteday afternoon, with Germany and France struck by heavy thunderstorms. It all boiled down to some bumps on the road and a 1.5 hours delay.

Filippo is a good kid. He stood the long journey very merrily. This morning I paid him back with a visit to the Tour Eiffel, which he longed to see. We climbed it using the stairs (up to the second floor - the third can only be reached by elevator). He loved the view from the top, and I myself did enjoy it - the last time for me up there had been 30 years ago, with my father.

In the afternoon, we visited the Centre Pompidou, where a art exhibit for kids was set up on the bottom floor. I used some of his patience by bringing him to the modern art gallery, but his attention span only lasted some 20 minutes. Better than nothing.

Tomorrow the CDF week will start, and he will have other occasions to show his good manners and education by sitting quietly in the back while I follow the works.

[NB update: this post has been linked for a comment it contains. Readers coming from those links are probably more interested in other posts here about the recent rumors from Higgs searches, say for instance  this one or  this other one. ]

In a few hours I will leave Chicago with a Lufthansa flight to Munich. Tomorrow morning at 7AM I have a flight Munich-Venice which will allow me to arrive home at 9ish, unpack, pack another time, pick Filippo up, give a kiss to Mariarosa and Ilaria, and head to the airport again. There, another flight to Munich awaits us at 3PM, alas… And then from Munich to Paris, where I wil attend to the CDF week from Monday to Friday in the unusual company of my son.

I did try to convince Filippo that he could travel by himself to Munich if we asked for help from the Lufthansa check-in crew in Venice (I however do not know the details: did anybody here have to fly underage relatives alone?), so that I could leisurely wait for him in Munich and avoid two useless flights… But it did not work: he almost started crying when he saw I was tentatively serious. Filippo is 8, and although he is a quite smart kid, he is… well, still a kid. So I reassured we will be together for the full week in Paris. He will of course bring his game-boy and a lot of other things, to keep quiet during the talks…

Yesterday I visited Vincent and Jadwiga, two old friends of mine who live in a very nice flat on top of a tall building facing the shore of north Chicago.  Vincent is a retired physician and he has a wonderful collection of ancient central-american sculptures , dating a thousand to two thousand years ago. But he also likes to sculpt himself, and I really like what he does.

During my visit, he gave me the opportunity to experiment with clay. He had asked me to come prepared, to draw some sketches beforehand. I had something in a piece of paper and he liked my idea, so he gave me his tools and watched me while I molded the clay, giving me only sparse important advices on techincal issues.

Below you can see my first creation, which I called “Hadron Decay 01″. I must say I loved to play with that wonderful material, and I look forward to doing more of it with my children in the future…

Below is another view of the same piece: