A Quantum Diaries Survivor

Just a link to a post by Gianandrea Giacoma on the site of the sci.bzaar.net workshop, an event about which I wrote here, here and here.

In the post, Gian uses very kind words to introduce a video on my thoughts on the need of horizontality in scientific blogs. I already posted a link to my video yesterday (beware, it is in Italian - I will try to find the time for an English version though, or at least provide a transcript in English), but the one on the sci.bzaar.net site does not need to be downloaded before playing - a huge bonus since you might get bored halfway through (oh well, damned if you do. It’s just 7 minutes).

On Saturday, May 15th, a conference called “sci.bzaar.net” will take place in Milano. It will bring together a restricted group of researchers, psychologists, bloggers, designers, physicists, writers, philosophers, computer scientists and web experts, who will discuss scientific divulgation, production of knowledge, and open culture in the academic world.

I will not be there in person, but a video I produced for the event will be shown - and I will connect with skype or some other means to take questions. You can see the agenda of the workshop here.

In addition, I produced for the web site of the event another short video where I discuss the importance of horizontality in a blog aimed at scientific divulgation. Unfortunately, I only have a version in Italian so far (the event is aimed at an italian public). I will paste below a writeup as I have the time, but if you are interested you can see me in the 7-minutes video here (beware though, it is kind of heavy - 500 Mbytes!).

Yesterday I had a dinner I would not have missed for anything in the world. After a lot of work with internet searches and email exchanges, we were able to organize a rendez-vous with my colleagues of high school, some of which I had never ever seen again after the day of the last written test for the final exam, which in Italy is called “Maturità”, maturity exam.

We were able to get together only two-thirds of the class. 13 people willing to meet after so long time was already a result to be proud of and to look forward to. Italy is not a place where people tend to move away for travel: we tend to remain anchored to the places where we have our parents, and where we lived our childhood. Indeed, of the 13 people who met, only two were coming from outside the area (Antonino, from Mantova, and Gianluca, from Milano).

It was an immense pleasure to see some of them after 25 full years, and being able to take on the puns and the jokes where we had left them, as if time had not passed. Funnily, a bunch of 42- and 43-year-old men and women looked to me like a bunch of teenagers. It is still difficult for me to shake that impression, as I look at the pictures of the evening.

Here is my class 25 years ago, in front of our school:

Can you locate me ? Not too easy, but you should manage.

And here is the bunch who met yesterday, in Piazza Ferretto (Mestre):

Time passes for everybody, but we had a great time. We already agreed we will meet again in September, on a hopefully sunny Sunday on the beach of Lido di Venezia, for a lunch and a game of soccer, hoping that a few of the nine who missed the dinner yesterday will show up…

I stumbled today into two old booklets advertising a concert. One in Conegliano, on Friday, March 13th 1981; the other in Udine on Wednesday, May 28th, 1980. These were times when I toured north-eastern Italy with the orchestra of the Venice Conservatory, directed by m. Fabio Pirona. I was a teenager, but I could already play the recorder (straight flute) rather well.

I remember that already back then I did not really think that a career in music would suit my taste nor my talents -my interest was not focused on Physics yet but I had a pretty good idea I liked science already- but I nevertheless enjoyed playing the part of the musician. Probably this has been some sort of constant in my life: I have been an amateur musician, an amateur astronomer, an amateur chessplayer, an amateur reporter and photographer, but then I decided to become a professional physicist. In other words I seem to have applied to arts, sports, and intellectual activities what is commonplace to do with sentimental relationships: women and men flirt with the most attractive counterparts, but end up marrying the one which promises more stability.

So what were we playing back then, in Conegliano and Udine (but also in Venice, Mirano, and other places I can’t even recall) ? The offer was a trio of concerts by Johann Sebastian Bach: the Brandemburg Concerts number V, IV, and III. I was the second flutist in the fourth concert, as you can see in the scans I paste below.

Above, the front page of the booklet of Concert season in Conegliano, 1981

…and the page with the three concerts, and a few signatures from my colleagues.

The one above is instead the leaflet advertising the concert in Udine…

…and the back, with the program of the afternoon.

I have warm memories of those concerts. In the one in Conegliano, we performed excellently the fourth concert (I remember I was really pleased of the outcome and by my own performance) until -at the very end of the third movement- my instrument had become soaked with condensed breath, and it literally dripped. The condensed moisture flowed down the hole at the end and, what’s worse, down the hole on the back, which is closed by the left thumb to play bass tones and only closed halfways -by using the fingernail- to play high pitches. And one of those high pitches was needed towards the end of the Presto, when in the culmination of a forte I had to play a high mi. The thumb was unable to close the hole the way it should have, and my instrument let out a broken note which was probably heard even by the ticket seller outside the hall. That evening was spent on a pleasant restaurant on the hills of Conegliano, with the whole orchestra having fun of me -but it was cheerful and I did not resent it.

In the concert in Udine another incident happened. I was rather tense (I think it was the first time we performed the concert outside the walls of our Conservatory) and when the fifth concert was over, the solists came backstage, and I went on stage with my buddy Francesco and the first violin Andrea. As we were about to sit down, I realized I had left my scoresheet backstage! A better player would have acted nonchalantly and played by heart, but I was too nervous -so I rushed back and grabbed it, re-entering on stage with the eyes of the public on me but, what’s worse, those of my director following me like a missile approaches a plane to be taken down.

Ah, memories… I wish I had a recording of those concerts! I remember the one in Conegliano was indeed recorded, and I was promised a copy of the tape which never came.

Here is a selected list of interesting links from blogs I read:

• Bee at Backreaction has the most complete list of reasons why you should not be bothered by the LHC destroying the Earth. Instructive, entertaining, to the point. With useful furthering of the matter in the comments thread.
• Peter at Not Even Wrong has two interesting posts out. In one he reports about Witten’s take on dark energy. In the other the question on what string theorists would do if their pet theory was proven wrong is discussed. Don’t miss the comments thread.
• Carl at Mass explains in detail why the current cosmology does not explain the angular correlations in the fluctuations of cosmic microwave background for large angles, while a changing speed of light would fit the data better. Controversial!
• Lubos at the Reference Frame discusses whether a theory that makes no predictions is to be preferred or disfavored, in relation to one that is more predictive. He also has a poll. Let’s all ask him to add a bullet, “A and B are equally unlikely because they are both favored by Lubos”,
• Jester at Resonaances has a short but poignant post on how to be a good crackpot. Recommended.
• Kea at Arcadian Functor has reached lesson 182 in category theory. Her explanations make you believe you know those things, and there are a bunch of graphs you cannot miss. Esthetically pleasing.
• Chad at Uncertain Principles has one of his imperdible dog dialogues out. Highly recommended.

Although ten short meaningless posts won’t outvalue a longer thoughtful one, for today I stick with the former. So let me just paste here a link to a post about me at sci.bzaar.net, the site of a workshop I will attend virtually next week.

In a few days I plan to provide the site owner, Gianandrea Giacoma, with a couple of short videos where I discuss some limits of blogs in the context of scientific outreach. If I am not too lazy I will produce an English version of those (the event is for an italian audience).

Since I am temporarily hampered in my typing ability because of a bulky bandage on my left hand, this morning I thought I’d post a few pictures from last weekend’s vacation on Achensee, a pleasant alpine lake in Austria.

Here Filippo (left) and Ilaria (right) are pirates relaxing on their ship with their colleagues Achille and Olga.

A closeup of Ilaria.

And to be democratic, a picture of Filippo.

What is the name of these funny, beautiful flowers ?

The indoor pool of our hotel, where we spent the better part of our afternoon -kids loved it.

Ilaria in the pool.

A bit of the lake towards Maurach.

Filippo studying the dynamics of stones bouncing on the water.

Everybody loved the big jacuzzi.

I am writing this single-handedly because of a stupid mistake. I am  spending this long week-end (1st of May is a holiday in Italy) in a nice mountain place in the austrian alps with family and friends, and I found a way to make things interesting…

I was carving a small wooden ship for Ilaria this afternoon, on the terrace of our hotel room, and I forgot that the blade should be always aimed in the opposite direction of your flesh. So as a hard piece of wood gave in all of a sudden, I found myself shocked, looking at a wide cut on the second finger of my left hand. The skin layer was parted, allowing a entertaining view of the bone, partly attacked by the violent blow. Blood was copious but fortunately not threatening.

After some initial trouble - arranging for a trip to an emergency room isn’t straightforward with two kids, one of them sleeping - things were straightened out. The tendon was not damaged, and four stitches did the job. I am still shocked, though, by how stupid I have been. In cases such as this, however, I tend to feel happy for the fact that things are easily repaired - bad luck could see me impaired in my playing the piano or typing for what’s left to live… And since I intend to live for a long while more, it would have really been disappointing!

Upon coming back from a shor vacation on the Alps, I rushed to connect my laptop to the internet. And one of the first things I did was to check for recent results by CDF. The experiment has been producing new beautiful results at an impressive pace during the last few months: it is as if the work of years of preparations, refining algorithms, tools, thinking hard at new methods, and a parallel strong push for the collection and processing of data had converged to a singularity, and now results are popping up like flowers in a garden.

My interest in the new analyses is boosted by the fact that in less than a month I will be describing them at PPC2008, a conference in Albuquerque where I am going to give a talk on new CDF results. So it is about time for me to start thinking about the organization of my talk.

As I browsed the recent talks in the Higgs Discovery Group, I found a new blessed (i.e., internally approved for public consumption) result that warmed my heart. It is the first Run II limit on associated Higgs boson production based on the 4-jet signature of WH or ZH decay. This signature arises when the Higgs boson is produced by the process called “higgs-strahlung” off a virtual W or Z boson, and both bosons then decay in a pair of hadronic jets (see picture). The Higgs, if it is lighter than 135 GeV, most of the times decays to a pair of b-quarks (in red), while W and Z bosons decay to all available quarks (in blue) more democratically.

Hadronic decays of vector bosons are the most common ones: W bosons decay to two quark jets 66% of the time, and Z bosons 70% of the time. So, with a large fraction of Higgs bosons also materializing into two jets, looking for four-jet final states to see a WH or ZH signal might look like a no-brainer. Quite the contrary!

Indeed, the 4-jet final state has always been considered absolutely hopeless. 4-jet events are among the most common final states of a proton-antiproton collision, and the kinematic handles one can use to try and discriminate associated WH or ZH production from generic QCD 4-jet production are absolutely insufficient. One can consider the invariant mass of pairs of jets, in the knowledge that W, Z, H all have a well-defined mass, while QCD produces jet pairs without any constraint on their common mass.

Hopeless, in particle physics, is a very attractive word for some of us. Out-smarting our colleagues is one of the highest forms of satisfaction in a scientific workplace… So, after my group demonstrated against all odds the possibility to see top pair decays in their 6-jet final state (one that arises when both W bosons emitted in the chain decay to jet pairs), in 1996, we started thinking at what would be the best way to exploit the experience we had formed in reconstructing high-mass states with jets.

One branch had already born fruit: my PhD was already in full swing, and I would show a first signal of decays soon thereafter. But that is another long story. Instead, in 1998 we started working at the idea of reconstructing the WH or ZH signal in events with four hadronic jets. In Run I the analysis had already been undertaken by Juan Valls and Jorge Troconiz, and they had indeed produced a fine piece of physics, with a limit on Higgs production which challenged those in the “golden” leptonic channels.

We aimed at Run II, and started working at the most critical issue: the one of triggering on 4-jet events with b-quarks. The multijet trigger which had been the basis of both the and the analyses was very inefficient on the latter signal, because of inefficiencies in the online jet reconstruction.

Enter the SVT (silicon vertex tracker), a fantastic device which measures online the impact parameter of tracks, allowing the collection of B-decays with high efficiency. SVT had been designed for B-physics purposes and was thus aimed at low-energy events, so we needed to verify it would work fine for 4-jet events too. This implied determining that those complicated, high-track-multiplicity events were reconstructable in the 20 microseconds available for a trigger decision at Level 2; and then designing a set of selection cuts that would allow the maximum efficiency on signal events while keeping the data acquisition rate at an acceptable level. In parallel, we also studied alternative strategies involving the semileptonic decay of B-hadrons, by combining jet signatures with soft lepton detection.

This job kept us busy for three years, and fruited a graduation to Giorgio Cortiana, a PhD to Luca Scodellaro and Mario Paolo Giordani (and I am certainly forgetting some other students). But as Run II started for real, and multijet events started being collected with high efficiency, we gradually lost interest: Luca Scodellaro’s analysis had shown that the signal was really, really hopeless. Too hopeless even for us - or maybe we were already growing old and disillusioned ?

The recent analysis by Song-Ming Wang, Rong-Shyang Lu, and Ankush Mitra (Academia Sinica), Daniel Whiteson (UC Irvine), and Aart Heijboer and Joe Kroll (University of Pennsylvania) shows otherwise. Sure, they do not reach a sensitivity sufficient to exclude Standard Model production of WH and ZH events in any region of Higgs masses, but they nevertheless extract an excellent result which will be successfully combined with the other searches, improving the global Tevatron limits on Higgs production. Since this post has become much longer than I wanted, I will only describe it shortly, and jump to the results.

The analysis selects events with four jets, two of which have to contain a signal of B-hadron decay, and then uses a Matrix-Element approach to determine the probability that the observed final state is the result of the decay of a WH or ZH pair, and the probability that it is instead due to background processes. The information is merged in a discriminant which separates the processes on a statistical basis. One thus ends up fitting the distribution of the discriminant as a sum of background and signal, as in the plot below.

To put in evidence the small contribution from top pair production (in blue), diboson and single top (in green), and WH/ZH processes (in red), a logarithmic plot is appropriate:

As you see, the signal would contribute mainly in the right part of the distribution, but with a tiny fraction of the events: Standard Model predicts a contribution of less than 10 events in a sample of more than 20,000.

The maximum amount of signal allowed by the fit determines a limit on the production cross-section of Higgs and vector bosons. The limit on the cross-section depends on the Higgs boson mass for two reasons: one is the increase in collection efficiency as the Higgs mass grows, and the other is the decrease in Higgs branching fraction to b-jet pairs. In the end, one obtains a limit on the ratio between cross section and SM expected cross section, as a function of Higgs mass. The limit is always larger than 1 -it actually is higher than 30- so no Higgs mass is excluded by this search. It is shown below with a red line; the limit the analysis would predict to set, based on pseudo-experiments, is shown by the hatched black line and 1-sigma and 2-sigma yellow and green bands.

This result really makes me feel that the work we did eight years ago was not wasted!

If you just visited this blog (that is as I post this message, between 11.40 and 11.50PM on May 1st), you have a 10% chance of having generated its 500,000th view. Sorry, no red carpet, band with trumpets, or prize.

I believe about a third of the visitors are colleagues with some degree of parenthood -meaning they work in the same field I do, or similar ones. The rest are a 50-50 mix of non-physicists who are just interested in science, and occasional visitors who are not likely to hang around.

While I do enjoy the increased interaction I obtained in these years with fellow physicists, particularly theorists and people from whom I have a chance of learning something new, the class of readers that are dearest to me are the non-physicists who try to understand physics. It is to them that this blog is mostly aimed at.
Of course, I not always manage to write something that is both at the right level and interesting enough for them, but I do try to.

In any case, I thank all of you who visit this blog occasionally or regularly for giving me the encouragement and the stimulus to make this site worth the time I spend making it better and keeping it -hopefully- interesting and informative. I also use this occasion to encourage any of you who has something potentially worth a post, to submit it to me. You can get a feeling of what guest posts here may be by looking at the “guest post” page up here.