A Quantum Diaries Survivor

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.

“The probability that there’s a bomb on your flight is really small, and yet still non negligible for anxious people like me. But the probability that there are two bombs is really ridiculously tiny! That’s why I always take one with me in my carry-on“.

Anonymous

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.

This blog has been on air for more than two years, and it is time (one reason will be clear in the next post) to have a look at some of the information wordpress offers to its members concerning incoming traffic. I am not so interested in the volume of visitors as much as in what they are looking for when they come by, and I have thus always found very useful the yardstick provided by the “Search engine terms”: what people typed in the google search box to be directed to my site.

Let us first of all look at the all-time data, before attempting to provide warnings for caveats and the like.

1. “tommaso dorigo”, 5857 searches
2. “placenta”, 2089 searches
3. “azores”, 1907 searches
4. “quantum diaries”,  1672 searches
5. “bubble chamber”, 1563 searches
6. “steven hawking”, 1408 searches
7. “funny road signs”, 1314 searches
8. “lisa randall”, 1062 searches
9. “bed”, 959 searches
10. “quantum diaries survivor”, 949 searches
11. “dorigo blog”, 880 searches
12. “vegetable porn”,  743 searches
13. “barmaid”,  739 searches
14. “funny street signs”,  578 searches

and then we later also find

21. “how to do a tracheotomy”, 434 searches

23. “particle collision”, 412 searches

30. “pegah emambakhsh”, 315 searches

36. “fellatios”, 235 searches

43. “top mass”, 195 searches

44. “michel platini”, 195 searches

and

50. “tomasso dorigo”, 175 searches.

Now, let me try to make a few points about the naked and outrageous data I displayed above.

First of all, by reading the above list one might be tempted to believe that the blog is not about physics. Wrong. The conclusion is based on a biased trial function, if you pass me the french. People in the web search for a lot of different things, and only a tiny minority looks for physics: so, as embarassing as it is, I get more people looking for fellatios than for top mass measurements.

Another thing to note is the fact that by posting pictures a blog does increase its traffic. This is a slightly concealed datum in the list above, but it becomes clear if you find out that people looking for “placenta” were drawn to my site because I did post a picture of one -and I think there are not so many pictures of such a peculiar mass of flesh and blood. The same thing is clear if one notices “bed” and “azores”, which both are due to my posting pictures of those things in the past.

Other miscellaneous hints:

• I am not the only one in the world who misspells Stephen Hawking’s first name.
• Same goes with tracheostomy
• And tragically, the number of people who misspell my own first name are about 3% of the total. Not a negligible signal.

Overall, it is a bit depressing to see the naked truth that many of your visitors came by by accident, and will never show up again -if not for another accident. But this is the internet. A community where people do what they like, and sometimes -rarely, but it does happen- try to learn something.

During the last ten years I have graduated 11 undergraduate students in Physics, plus tutored four PhD students through to their title. Despite this variety of personalities that have crossed my path in forming their credentials as physicists, there is one single example of “my student” which stands above all, for continuity and results, and that example is Giorgio Cortiana.

Giorgio joined our group in 2000 as a summer student at Fermilab, and he worked during the months of August and September with me at the design of a trigger we were putting together to collect Higgs bosons in the forthcoming Run II. Following the positive experience, he asked our group for a thesis in CDF, and worked with me at the same topic, a multijet trigger for Higgs events.

He graduated with the highest score, and entered Padova’s PhD program at the end of 2002. CDF data was just starting to pour in in reasonable amounts, and Giorgio’s PhD time span was well-placed to allow us to invent something new. We started working at a search for top pair decays including tau leptons and jets, a channel nobody had ever considered due to its apparent trouble -a huge background from QCD events. We, however, were soon convinced our search could yield a pleasant surprise.

And indeed we struck gold when, in early 2004, we found out that by extending the search to an inclusive signature of missing transverse energy and jets -which allowed to include events where one of the top quarks decayed to an electron or a muon which failed the tight lepton identification criteria- we soon obtained a large signal of events that other searches had totally ignored.

With the data we had selected, Giorgio and I obtained CDF’s third-best measurement of the top pair production cross-section, and we soon published a paper on Physics Review Letters. In the meantime, Giorgio also obtained his PhD, which was soon followed by a research grant to continue working with our group in Padova. The plan of the grant was to measure the top quark mass with the decays he had collected in the inclusive missing Et plus jets search: he did it very effectively, and he published another nice paper in record time. While he was doing that, he also had his hands full in a new re-design of the CDF calorimeter trigger, again focused on a more efficient collection of Higgs events. He took an important role in the project as responsible for the monitoring of the trigger, and his group completed the task in due time: CDF now has a much more effective identification of jets at trigger level 2, and this means a sizable increase in Higgs sensitivity.

Despite these successes, we had to witness once again how Italy is not generous with young researchers. Bright, young and able, with the highest academic title in his pocket Giorgio -as hundreds like him- is deprived of job security, and has to accept a salary which in other countries would be refused by a graduate student. So he recently started looking for a better position outside Italy, and he of course found one very soon. He gave a farewell seminar in Padova last week (if I have a chance I will describe his interesting talk here), and he is now off to Munich, where he is joining the ATLAS group. ALAS, I would say, since I at least hoped he would end up in a CMS group instead: that would have allowed me to continue collaborating with him…

The best of luck to Giorgio then. I am sure he will be appreciated in his new group. In the meantime, I have to reckon with a thinning group of collaborators: Julien left three months ago… To ATLAS too!

Jeff is a physics professor at the University of Cassino, and a long-time colleague and friend of mine. He worked in the SLD and CDF collaborations as a particle physicist, but later moved on to study radiation damage on silicon detectors for particle and astroparticle applications.

Besides admiring him for his wicked sense of humor, which he uses to make the workplace around him always a pleasant place, I have the highest esteem of Jeff as a professor, because he is quite skilled in explaining physics concepts in simple terms. He always looks for the most intuitive way to understand things, as you might appreciate in the contribution he offers below.

The following describes a very elegant and simple derivation of the relativistic formula for the addition of velocities, .

It is due to David Mermin. I fell in love with it and have been telling it for the past four years now to the students of my general physics course. The students are first year telecommunications and electrical engineering students. Before sitting in on my course all of them have heard about Einstein and most of them heard the expression “the velocity of light is constant”. I do not have the time to discuss special relativity in detail. My course is quite traditional. I discuss reference frames, inertial frames, Galilean transformations and covariance of Newton’s laws. I then point out that when describing mechanical waves the frame that is stationary respect to the medium is a special reference! In particular the wave motion can be made to disappear by moving respect to the medium with a velocity equal to that of the wave. It is clear at this point that the constancy of the velocity of light cannot be understood by assuming Newton’s laws and then modeling light as a mechanical wave in a medium (the ether). I then restate the constancy of the velocity of light and begin Mermin’s derivation.

The derivation uses:

• only one reference frame (no use of Lorentz transformations),
• simple kinematics (always good to brush up on),
• the constancy of the velocity of light (something that every telecommunications and electrical engineering student should know),
• the idea that some things are invariant; i.e. while many quantities are relative, observers will agree on some absolutes.

Consider a train of length L moving along the x-axis at a constant velocity v respect to an inertial frame of reference (the observer watching the events unfold). At the trailing end of the train a loaded gun is aimed in the forward direction and fired at time : the bullet and flash of light emerge and travel in the forward direction with different speeds: w the velocity of the bullet, c the velocity of light. A mirror at the front end of the train reflects the light back towards the advancing bullet. Let f be the fraction of the length of train that the reflected light travels before meeting up with the bullet. The constancy of light (Einstein’s dictum) tells us that the velocity of light in the forward direction is equal to the velocity of light in the backward direction; i.e. .

The space-time plot looks like this:

Let be the time for the light flash to reach the forward-going mirror and be the time the reflected light needs to return from the mirror and meet up with the forward-moving bullet. Simple kinematics allows us to label the space-time plot:

Simple algebra:

It is important to note that the expression for f we just obtained is valid if the velocity of light in the forward and backward direction are equal. Note:

• A classical pre-Einstein physicist would say this expression is valid only if the observer is stationary respect to the ether frame.
• On the other hand Einstein says that any inertial observer would use the same velocity of light; i.e. Einstein tells us that this expression is valid for any observer (generic inertial frame).

Following Einstein we consider a particular observer (frame), one that is moving along with the train. For this observer the velocity of the train is . For clarity let us use the symbol u to indicate the velocity of the bullet with respect to this observer; i.e. with respect to the train.

Suppose the train has 10 windows and the reflected light and the bullet meet up at the third window from the front (). It is important to realize that all observers will agree on the value of f. The fraction f is an invariant!

The constancy of the velocity of light allows us to impose the invariance of f the following way:

Q.E.D. !

I have wanted to write some version of the present post for a while, and so it is a relief to publish it at last. In fact, it is rather strange to have completely avoided discussing in my blog the problem I have invested the best part of my research time in the last three months -plus a fair share of last year’s thinking-, and it was due time that I filled that void somehow.

Unfortunately, strange as it may seem, there are topics in my research activities that are hard to explain in simple terms. The problem I have been working on is not difficult to state, nor too difficult to solve, but it is extremely complicated and varied, so that a comprehensive description is challenging. However, I want to make an attempt…

The problem I have been dealing with, together with a small and focused group of bright colleagues (Sara Bolognesi, Marco De Mattia, and Chiara Mariotti: lads from Padova and ladies from Torino University) is the one of calibrating the momentum of charged tracks detected by the CMS experiment at CERN.

After being produced in a proton-proton collision in the core of CMS, charged particles have their position measured in a dozen layers of silicon detector before they hit the calorimeter system; the few penetrating ones surviving the encounter with trillions of heavy nuclei are also detected by the large set of muon chambers situated outside them. With the information provided by the silicon detectors -and, for muon candidates, by the muon system- a very performant and refined software algorithm reconstructs and fits the trajectory of the track, providing a measurement of the five parameters describing the helical trajectory; most notably, the curvature inside the solenoid, which yields a precise determination of transverse momentum through the formula (where B is the magnetic field intensity -about 4 Tesla- and is transverse momentum).

There are a number of reasons why a precise determination of the momentum of charged tracks is crucial. Let me just flash a few:

1. Charged particles are measured with a better precision than neutral ones, and a careful determination of their momentum allows to calibrate in turn other parts of the detector.
2. Some physics measurements such as the mass of the W boson rely heavily on track momentum.
3. The identification of a high-mass resonance -say a new Z’ boson- may require the reconstruction of its decay, and a scale error on the momentum of those high-energy tracks translates in a worse resolution in the Z’ mass, and a diminished discovery reach.
4. B-physics crucially needs charged tracks to be precisely reconstructed in order for exclusive B decays to be extracted from backgrounds.

So how do we do it ?

We use resonances. A few neutral particles -vector mesons and the Z boson- decay to pairs of muons, and they can thus be extracted with small backgrounds from the data (events with two muons are easy to collect with CMS, and muons have the benefit that they are “perfect” tracks in several ways). We know the mass of these particles with great accuracy, thanks to previous experiments:

• The Z boson mass is known to be , a 0.023% precision.
• The Y(1S), the ground state of the vector meson family, has its mass known as , a 0.0028% measurement.
• The Y(2S) mass is , a 0.0031% measurement.
• The Y(3S) mass is , a 0.005% measurement.
• The J/Psi, the ground state of the vector meson family, has its mass known as , a 0.0004% measurement.
• The Psi(2S) has mass , a 0.001% measurement.

All the above particles are easy to trigger on, collect, reconstruct, and measure. With CMS we expect to collect thousands of these decays every day of running. Their mass can be measured on a event-by-event basis by reconstructing the momentum of the two muons they decayed into, using the relativistic equation

where M is the resonance mass, E is the muon energy, and P is the muon momentum vector.

By comparing the average mass of each reconstructed resonance to the reference values above, we get to know the scale of our momentum measurement, ; every time we measure a momentum we then do , forget P, use P’, and we are done. Easy enough, wouldnt’ you agree ?

Sure. Easy enough. But actually kind of lame. With the millions of dimuon resonances we collect, can’t we do something better ? Our detector is, in fact, a quite complicated set of devices. The momentum scale -or, to be precise, the bias on the momentum measurement- depends on very subtle effects, such as tiny distorsions in the magnetic field generated by the 4-Tesla solenoid, occasional mis-alignment (by a few microns, that is) of one of the thousands silicon sensors, erratic behavior of the reconstruction algorithm in very particular regions of the detector. We can, and we must, check the bias on our measured momentum more closely, because it in turn gives us a chance to verify the B field map, check the alignments, validate the reconstruction code.

In the simplified formulas described above to determine a corrected momentum P’, you might have noticed that we used the invariant mass of the two muons making the resonance, rather than each muon separately. Indeed, the decayed particle is not produced at rest in the laboratory frame of reference, so we cannot expect that the two muons share evenly their parent’s energy, M/2 each. Only by combining their momenta can we get a number to compare to the reference value. Or is there a smarter way ?

There is a smarter way. Strangely enough, to my knowledge it has not been used in the past for this application. Let me explain in short what it is. I will try to make this as simple as possible, but not simpler - in Einstein’s style.

In the formula for the relativistic mass above enters the energy and momentum -or better, if you allow a slip into special relativity jargon, quadrimomentum. We can, in purely symbolic terms, write:

where we have made explicit the fact that the computed invariant mass is a function f of the quadrimomenta of the two muons, and that each of the two quadrimomenta is in turn a function of many (i, in the formula) other variables, collected in two i-dimensional vectors x . These variables are the measured characteristics of the track: its angles, the region of the detector it crosses, its electric charge, you name them.

Still here ? Ok. The next step is to realize that what we really would love to have is a measurement of the momentum as a function of the particular characteristics x of the track, and not just , which only depends on the curvature . Through a knowledge of we could get sensitive to the effects mentioned above -B field distorsions, alignment errors, reconstruction biases.

There is a simple way: we can compute the probability that we observe a mass M, if the reference value is , as a function of the measured quantities of each muon, by assuming a functional form for the way the momentum P depends on the parameters. So let us write:

where the new function g( ) describes how the momenta vary with the vector of measured track parameters , and is a vector of unknown variables describing the function g( ).

(To let you understand what the heck I am talking about, assume that your detector measures a track momentum with a bias depending on momentum itself:

,

with , and , . This function describes momenta which are underestimated by 0.2% for small P, correctly estimated for P=10 GeV, and overestimated by 1% for every additional increase of P by 50 GeV. )

Using the parametrization, we compute for each event the measured mass as a function of the variables . WIth these numbers we finally form a likelihood function:

which of course implicitly depends on the functional form we have chosen for g. By maximizing L as a function of the parameters, we obtain their most likely values, and we are done: we get to know how our track momentum depends on its characteristics .

In the discussioon above I have not given much emphasis on the fact that the true form of the “bias function” g( ) is not known. One can in fact test different hypotheses with the data, and the value of the likelihood will be a measure of how well they describe the experimental situation. There’s more: the likelihood can be studied as a function of each of the components of the vector x, allowing to spot biases which require a more subtle parametrization.

The above discussion is a simplified view of the problem: In reality, things are much more complicated. Here is a short list of details I hid under the carpet above:

• We model the probability to observe a given mass in the likelihood function by convoluting a Lorentzian function (the Breit-Wigner, which is the true form of the mass distribution of the resonance) with a gaussian resolution function; the gaussian has parameters which also get fit simultaneously with the bias parameters . The figure below shows the probability distribution function of a measurement of mass M and resolution for a Z boson: for each point in the plane, defined by the two values , the probability is the height of the surface. Notice how the probability grows as the resolution increases, for values of mass very far from the true resonance mass (for instance, for a mass of 71 GeV-the left boundary of the surface), while the opposite happens for values of mass close to it.

• the fitter also assumes a functional form for the background (which is unavoidably included in the dataset containing the resonances), and fits it together with the bias and resolution parameters;
• Each of the six considered resonances can be fit individually, or all together. The window around the peaks defining events used or not used in the computation requires an optimization;
• The fitter iterates several times the whole procedure: after bias parameters are extracted, momenta get corrected, and a new parameter extraction must return values which are compatible with no bias.
• And so on…

The algorithm is indeed quite complicated. I spent the last three months implementing the fitting of resolution and background, and the algorithm is not yet complete but it now works well. It is particularly satisfactory to be able to launch the program on a set of resonances, and extract all at once not just the parameters that allow momenta to be corrected, but also a precise estimate of momentum resolution as a function of track kinematics - something that would once require detailed studies with simulations. All is now squeezed out of the data!

The work is far from over. With the help of my colleagues, we will test the code on a very large sample of simulated events in the next few months, to be ready for the data which will hopefully start pouring in this fall… But the work will only be started then: we plan to fit chunks of data on a monthly basis, checking the stability of the detector and the track reconstruction, and producing a correction function to be used by all analyses in need of a precise momentum measurement… It really is a long-term plan!

“The secret to creativity is knowing how to hide your sources.“

(Undisclosed source)

Update: Ok, if you happen to not know the author of the above, a hint: he also said…

“If we knew what we were doing, it would not be called research, would it ?“

(courtesy Jeff)