A lifetime of bribes March 31, 2009
Posted by dorigo in history, news, politics.Tags: berlusconi, bribes, chiesa, italian politics
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Do you remember Mario Chiesa ? Of course you don’t -seventeen years have passed since his arrest in flagrance of bribery, and, weren’t it for the explosive developments that ensued, his story would have only appeared as a one-column piece in local newspapers, and would have long been forgotten by now.
But Chiesa did make headlines for months in January 1992. The bribery system that was standing behind the curtains he took down as he spilt his guts bit by bit was one of gigantic proportions – italians were shown in a true coup de theatre how the current political system, led by Arnaldo Forlani’s Democrazia Cristiana and Bettino Craxi’s Partito Socialista, was one centered on systematic corruption. Politicians drew money from the business world in fixed percentages, and in exchange helped the businesses which paid those bribes; everybody thrived in this vortex of dirty funds. A few of the politicians got rich, but most of them contented themselves with their increased political means.The parties governing the country fed themselves to retain their power.
Of course, many had known about the whole thing for decades. The funny stories on Craxi and the Socialist Party were countless, and citizens who did not support the government with their votes felt a tad cleaner than those who did; all, however, stood in a sort of forbearance. But things changed overnight: Chiesa’s deposition constituted proof of the misdemeanor, and judges in Milano teamed in to expose the corruption with momentum.
Heads fell one after the other. Craxi fled to Hammamet, where he would spend the rest of his life in a gilded self-inflicted exile; others committed suicide; the toughest fought mightily in judicial courts, and some, as Mario Chiesa, did time. Those were the years of “Mani Pulite” (clean hands), which were saluted with relief by the largest part of the population.
Today, Chiesa is not the young, enterprising fellow he was back then. But he has apparently not lost his vice yet. He was arrested yesterday for charges of bribery, in a story of illicit drain of waste.
If I look back at these last 17 years, I cannot help smiling at the incredible turn-around which ensued. We once had a system whereby politicians received illegal funds to advantage businesses, and used those funds to retain their power. Now we have a system where the two subjects have become one and the same: this way, there is no more a passage of money: the politician and the businessman are the same person, which legislates in a perfect match of interests. He makes the laws that allow his businesses to thrive, and his businesses work to increase his political power. I do believe Berlusconi is serious when he says there is no conflict of interests in Italy: his is, in fact, quite the opposite: a matrimony.
The say of the week March 30, 2009
Posted by dorigo in games, humor.comments closed
“I read in the newspapers they are going to have 30 minutes of intellectual stuff on television every Monday from 7:30 to 8. to educate America. They couldn’t educate America if they started at 6:30.”
(G.Marx)
Latest global fits to SM observables: the situation in March 2009 March 25, 2009
Posted by dorigo in news, physics, science.Tags: CDF, DZERO, electroweak fits, Gfitter, Higgs boson, LEP, SLD, standard model, Tevatron, top quark, W boson
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A recent discussion in this blog between well-known theorists and phenomenologists, centered on the real meaning of the experimental measurements of top quark and W boson masses, Higgs boson cross-section limits, and other SM observables, convinces me that some clarification is needed.
The work has been done for us: there are groups that do exactly that, i.e. updating their global fits to express the internal consistency of all those measurements, and the implications for the search of the Higgs boson. So let me go through the most important graphs below, after mentioning that most of the material comes from the LEP electroweak working group web site.
First of all, what goes in the soup ? Many things, but most notably, the LEP I/SLD measurements at the Z pole, the top quark mass measurements by CDF and DZERO, and the W mass measurements by CDF, DZERO, and LEP II. Let us give a look at the mass measurements, which have recently been updated.
For the top mass, the situation is the one pictured in the graph shown below. As you can clearly see, the CDF and DZERO measurements have reached a combined precision of 0.75% on this quantity.
The world average is now at 
As far as global fits are concerned, there is one additional point to make for the top quark: knowing the top mass any better than this has become, by now, useless. You can see it by comparing the constraints on 
Then, let us look at the W mass determinations. Note, the graph below shows the situation BEFORE the latest DZERO result;, obtained with 1/fb of data, and which finds 
Here the situation is different: a better measurement would still increase the precision of our comparisons with indirect information from electroweak measurements at the Z. This is apparent by observing that the blue bars have width still smaller than the world average of direct measurements (again in green). Narrow the green band, and you can still collect interesting information on its consistency with the blue points.
Finally, let us look at the global fit: the electroweak working group at LEP displays in the by now famous “blue band plot”, shown below for March 2009 conferences. It shows the constraints on the Higgs boson mass coming from all experimental inputs combined, assuming that the Standard Model holds.
I will not discuss this graph in details, since I have done it repeatedly in the past. I will just mention that the yellow regions have been excluded by direct searches of the Higgs boson at LEP II (on the left, the wide yellow area) and the Tevatron ( the narrow strip on the right). From the plot you should just gather that a light Higgs mass is preferred (the central value being 90 GeV, with +36 and -27 GeV one-sigma error bars). Also, a 95% confidence-level exclusion of masses above 163 GeV is implied by the variation of the global fit 
I have started to be a bit bored by this plot, because it does not do the best job for me. For one thing, the LEP II limit and the Tevatron limit on the Higgs mass are treated as if they were equivalent in their strength, something which could not be possibly farther from the truth. The truth is, the LEP II limit is a very strong one -the probability that the Higgs has a mass below 112 GeV, say, is one in a billion or so-, while the limit obtained recently by the Tevatron is just an “indication”, because the excluded region (160 to 170 GeV) is not excluded strongly: there still is a one-in-twenty chance or so that the real Higgs boson mass indeed lies there.
Another thing I do not particularly like in the graph is that it attempts to pack too much information: variations of 
In this plot, the direct search results are introduced with their actual measured probability of exclusion as a function of Higgs mass, and not just in a digital manner, yes/no, as the yellow regions in the blue band plot. And in fact, you can see that the LEP II limit is a brick wall, while the Tevatron exclusion acts like a smooth increase in the global
From the black curve in the graph you can get a lot of information. For instance, the most likely values, those that globally have a 1-sigma probability of being one day proven correct, are masses contained in the interval 114-132 GeV. At two-sigma, the Higgs mass is instead within the interval 114-152 GeV, and at three sigma, it extends into the Tevatron-excluded band a little, 114-163 GeV, with a second region allowed between 181 and 224 GeV.
In conclusion, I would like you to take away the following few points:
- Future indirect constraints on the Higgs boson mass will only come from increased precision measurements of the W boson mass, while the top quark has exhausted its discrimination power;
- Global SM fits show an overall very good consistency: there does not seem to be much tension between fits and experimental constraints;
- The Higgs boson is most likely in the 114-132 GeV range (1-sigma bounds from global fits).
Zooming in on the Higgs March 24, 2009
Posted by dorigo in news, physics, science.Tags: CDF, DZERO, Higgs boson, LEP, MSSM, standard model, supersymmetry, Tevatron, top quark, W boson
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Yesterday Sven Heinemeyer kindly provided me with an updated version of a plot which best describes the experimental constraints on the Higgs boson mass, coming from electroweak observables measured at LEP and SLD, and from the most recent measurements of W boson and top quark masses. It is shown on the right (click to get the full-sized version).
The graph is a quite busy one, but I will try below to explain everything one bit at a time, hoping I keep things simple enough that a non-physicist can understand it.
The axes show suitable ranges of values of the top quark mass (varying on the horizontal axis) and of the W boson masses (on the vertical axis). The value of these quantities is functionally dependent (because of quantum effects connected to the propagation of the particles and their interaction with the Higgs field) on the Higgs boson mass.
The dependence, however, is really “soft”: if you were to double the Higgs mass by a factor of two from its true value, the effect on top and W masses would be only of the order of 1% or less. Because of that, only recently have the determinations of top quark and W boson masses started to provide meaningful inputs for a guess of the mass of the Higgs.
Top mass and W mass measurements are plotted in the graphs in the form of ellipses encompassing the most likely values: their size is such that the true masses should lie within their boundaries, 68% of the time. The red ellipse shows CDF results, and the blue one shows DZERO results.
There is a third measurement of the W mass shown in the plot: it is displayed as a horizontal band limited by two black lines, and it comes from the LEP II measurements. The band also encompasses the 68% most likely W masses, as ellipses do.
In addition to W and top masses, other experimental results constrain the mass of top, W, and Higgs boson. The most stringent of these results are those coming from the LEP experiment at CERN, from detailed analysis of electroweak interactions studied in the production of Z bosons. A wide band crossing the graph from left to right, with a small tilt, encompasses the most likely region for top and W masses.
So far we have described measurements. Then, there are two different physical models one should consider in order to link those measurements to the Higgs mass. The first one is the Standard Model: it dictates precisely the inter-dependence of all the parameters mentioned above. Because of the precise SM predictions, for any choice of the Higgs boson mass one can draw a curve in the top mass versus W mass plane. However, in the graph a full band is hatched instead. This correspond to allowing the Higgs boson mass to vary from a minimum of 114 GeV to 400 GeV. 114 GeV is the lower limit on the Higgs boson mass found by the LEP II experiments in their direct searches, using electron-positron collisions; while 400 GeV is just a reference value.
The boundaries of the red region show the functional dependence of Higgs mass on top and W masses: an increase of top mass, for fixed W mass, results in an increase of the Higgs mass, as is clear by starting from the 114 GeV upper boundary of the red region, since one then would move into the region, to higher Higgs masses. On the contrary, for a fixed top mass, an increase in W boson mass results in a decrease of the Higgs mass predicted by the Standard Model. Also note that the red region includes a narrow band which has been left white: it is the region corresponding to Higgs masses varying between 160 and 170 GeV, the masses that direct searches at the Tevatron have excluded at 95% confidence level.
The second area, hatched in green, is not showing a single model predictions, but rather a range of values allowed by varying arbitrarily many of the parameters describing the supersymmetric extension of the SM called “MSSM”, its “minimal” extension. Even in the minimal extension there are about a hundred additional parameters introduced in the theory, and the values of a few of those modify the interconnection between top mass and W mass in a way that makes direct functional dependencies in the graph impossible to draw. Still, the hatched green region shows a “possible range of values” of the top quark and W boson masses. The arrow pointing down only describes what is expected for W and top masses if the mass of supersymmetric particles is increased from values barely above present exclusion limits to very high values.
So, to summarize, what to get from the plot ? I think the graph describes many things in one single package, and it is not easy to get the right message from it alone. Here is a short commentary, in bits.
- All experimental results are consistent with each other (but here, I should add, a result from NuTeV which finds indirectly the W mass from the measured ratio of neutral current and charged current neutrino interactions is not shown);
- Results point to a small patch of the plane, consistent with a light Higgs boson if the Standard Model holds
- The lower part of the MSSM allowed region is favored, pointing to heavy supersymmetric particles if that theory holds
- Among experimental determinations, the most constraining are those of the top mass; but once the top mass is known to within a few GeV, it is the W mass the one which tells us more about the unknown mass of the Higgs boson
- One point to note when comparing measurements from LEP II and the Tevatron experiments: when one draws a 2-D ellipse of 68% contour, this compares unfavourably to a band, which encompasses the same probability in a 1-D distribution. This is clear if one compares the actual measurements: CDF
(with 200/pb of data), DZERO
(with five times more statistics), LEP II
(average of four experiments). The ellipses look like they are half as precise as the black band, while they are actually only 30-40% worse. If the above is obscure to you, a simple graphical explanation is provided here.
- When averaged, CDF and DZERO will actually beat the LEP II precision measurement -and they are sitting on 25 times more data (CDF) or 5 times more (DZERO).
Ten photons per hour March 23, 2009
Posted by dorigo in astronomy, games, mathematics, personal, physics, science.Tags: amateur astronomy, galaxies, NGC3690, physics problems
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Every working day I walk for about a mile to my physics department in Padova from the train station in the morning. I find it is a healthy habit, but I sometimes fear it also in some sense is a waste of time: if I catched a bus, I could be at work ten minutes earlier. I hate losing time, so I sometimes use the walking time to set physics problems to myself, trying to see whether I can solve them by heart. It is a way to exercise my mind while I exercise my body.
Today I was thinking at the night of stargazing I treated myself with last Saturday. I had gone to Casera Razzo, a secluded place in the Alps, and observed galaxies for four hours in a row with a 16″ dobsonian telescope, in the company of four friends (and three other dobs). One thing we had observed with amazement was a tiny speck of light coming from the halo of an interacting pair of galaxies in Ursa Major, the one pictured below.
The small speck of light shown in the upper left of the picture above, labeled as MGC 10-17-5, is actually a faint galaxy in the field of view of NGC3690. It has a visual magnitude of +15.7: this is a measure of its integrated luminosity as seen from the Earth. It is a really faint object, and barely at the limit of visibility with the instrument I had. The question I arrived at formulating to myself this morning was the following: how many photons did we get to see per second through the eyepiece, from that faint galaxy ?
This is a nice, simple question, but computing its answer by heart took me the best part of my walk. My problem was that I did not have a clue of the relationship between visual magnitude and photon fluxes. So I turned to things I did know.
Some background is needed to those of you who do not know how visual magnitudes are computed, so I will make a small digression here. The scale of visual magnitude is a semi-empirical one, which sets the brightest stars at magnitude zero or so, and defines a decrease of luminosity by a factor 100 per every five magnitudes difference. The faintest stars visible with the naked eye in a moonless night are of magnitude +6, and that means they are about 250 times fainter than the brightest ones. On the other hand, Venus shines at magnitude -4.5 at its brightest -almost 100 times as bright as the brightest stars-, and our Sun shines at a visual magnitude of about -27, more than a billion times brighter than Venus. The magnitude difference between two objects is in a relation with their relative brightness by a power law: 
Ok, so we know how bright is the Sun. Now, if I could get how many photons reach our eye from it every second, I would make some progress. I reasoned that I knew the value of the solar constant: that is the energy radiated by the Sun on an area of 1 square meter on the ground of the Earth. I remembered a value of about 1 kilowatt (it is actually 1.366 kW, as I found out later in wikipedia).
Now, how many photons of visible light arriving per second on that square meter of ground correspond to 1 kilowatt of power ? I reasoned that I did not remember the energy of a single visible photon -I remembered it was in the electron-Volt range but I was not really sure- so I had to compute it.
The energy of a quantum of light is given by the formula 
My brains were a bit strained by the simple calculation above, but I was relieved to get back an energy roughly equal to that I expected -in the eV range (one eV equals 
Now, if the Sun radiates 1 kW of power, which is a thousand Joules per second, how many visible photons do we get ? Here there is a subtlety I did not even bother considering in my walk to the physics department: only about half of the power from the Sun is in the form of visible light, so one should divide that power by two. But I was unhindered by this in my order-of-magnitude walk-estimate. Of course, 1 kW divided by 
Now, visual magnitude is expressed as the amount of light hitting the eye. A human eye has a surface of about 20 square millimeters, which is 20 millionths of a square meter: so the number of photons you get by looking straight at the sun (do not do it) is 
I was close to my goal now: the magnitude of the speck of galaxy I saw on Saturday is +15.7, the magnitude of the Sun is -27, so the difference is 43 magnitudes. This corresponds to 
Now, taking the number of photons reaching the eye from the Sun every second, and dividing by the ratio of apparent luminosities of the Sun and the galaxy, I could get 
Let me stress this: if you watch that patch of sky at night, the number of photons you get from that source alone is a few per hour! With my dobson telescope, which intensifies light by almost 10,000 times, I could get a rate of a few tens of photons per second, and the detail was indeed detectable!
If you are intested in the exact number, which I worked out after reaching my office and the tables of constants in the PDG booklet, I computed a rate of 
UPDATE: this post will remain as one clear example of how dangerous it is to compute by heart! Indeed, somewhere in my order-of-magnitude conversions above I dropped a factor 10^2 -which, mind you, is not horrible in numbers which have 20 digits or so; but when one wants to get back to reasonable estimates for reasonably small numbers, it does count a lot. So, after taking care of some other (more legitimate) approximations, if one computes things correctly, the number of photons from the galaxy seen with the unaided eye is more like two hundred per hour, and in the telescope it is of about 350 per second.
A seminar against the Tevatron! March 20, 2009
Posted by dorigo in news, physics, science.Tags: CDF, DZERO, Higgs boson, LHC, Tevatron
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I spent this week at CERN to attend the meetings of the CMS week – an event which takes place four times a year, when collaborators of the CMS experiment, coming from all parts of the world, get together at CERN to discuss detector commissioning, analysis plans, and recent results. It was a very busy and eventful week, and only now, sitting on a train that brings me back from Geneva to Venice, can I find the time to report with the due dedication on some things you might be interested to know about.
One thing to report on is certainly the seminar I eagerly attended on Thursday morning, by Michael Dittmar (ETH-Zurich). Dittmar is a CMS collaborator, and he talked at the CERN theory division on a tickling subject:”Why I never believed in the Tevatron Higgs sensitivity claims for Run 2ab”. The title did promise a controversial discussion, but I was really startled by its level, as much as by the defamation of which I felt personally to be a target. I will explain this below.
I have also to mention that by Thursday I had already attended to a reduced version of his talk, since he had given it on the previous day in another venue. Both I and John Conway had corrected him on a few plainly wrong statements back then, but I was puzzled to see he reiterated those false statements in the longer seminar! More on that below.
Dittmar’s obnoxious seminar
Dittmar started by saying he was infuriated by the recent BBC article where “a statement from the director of a famous laboratory” claimed that the Tevatron had 50% odds of finding a Higgs boson, in a certain mass range. This prompted him to prepare a seminar to express his scepticism. However, it turned out that his scepticism was not directed solely at the optimistic statement he had read, but at every single result on Higgs searches that CDF and DZERO had produced since Run I.
In order to discuss sensitivity and significances, the speaker made a un-illuminating digression on how counting experiments can or cannot obtain observation-level significances with their data depending on the level of background of their searches and the associated systematical uncertainties. His statements were very basic and totally uncontroversial on this issue, but he failed to focus on the fact that nowadays, nobody does counting experiments any more when searching for evidence of a specific model: our confidence in advanced analysis methods involving neural networks, shape analysis, and likelihood discriminants; the tuning of Monte Carlo simulations; and the accurate analytical calculations of high-order diagrams for Standard Model processes, have all grown tremendously with years of practice and studies, and these methods and tools overcome the problems of searches for small signals immersed in large backgrounds. One can be sceptical, but one cannot ignore the facts, as the speaker seemed inclined to.
Then Dittmar said that in order to judge the value of sensitivity claims for the future, one may turn to past studies and verify their agreement with the actual results. So he turned to the Tevatron Higgs Sensitivity studies of 2000 and 2003, two endeavours to which I had participated with enthusiasm.
He produced a plot showing the small signal of 
He commented that figure by saying half-mockingly that the data could have been used to exclude the standard model process of associated 
In fact, he went on to discuss the global expectation of the Tevatron on Higgs searches, a graph (see below) produced in 2000 after a big effort from several tens of people in CDF and DZERO.
He started by saying that the graph was confusing, and that it was not clear in the documentation how it had been produced, nor that it was the combination of CDF and DZERO sensitivity. This was very amusing, since sitting from the far back John Conway, a CDF colleague, shouted: “It says it in print on top of it: combined thresholds!”, then adding, with a pacate voice “…In case you’re wondering, I made that plot.” John had in fact been the leader of the Tevatron Higgs sensitivity study, not to mention the author of many of the most interesting searches for the higgs boson in CDF since then.
Dittmar continued his surreal talk with an overbid, by claiming that the plot had been produced “by assuming a 30% improvement in the mass resolution of pairs of b-jets, when nobody had not even the least idea on how such improvement could be achieved”.
I could not have put together a more personal, direct attack to years of my own work myself! It is no mystery that I worked on dijet resonances since 1992, but of course I am a rather unknown soldier in this big game; however, I felt the need to interrupt the speaker at this point -exactly as I had done at the shorter talk the day before.
I remarked that in 1998, one year before the Tevatron sensitivity study, I had produced a PhD thesis and public documents showing the observation of a signal of 
In the plots, you can see how the excess over background predictions moves to the right as more and more refined jet energy corrections are applied, starting from the result of generic jet energy corrections (top) to optimized corrections (bottom) until the signal becomes narrower and centered at the true value. The plots on the left show the data and the background prediction, those on the right show the difference, which is due to Z decays to b-quark jet pairs. Needless to say, the optimization is done on Monte Carlo Z events, and only then checked on the data.
So I said that Dittmar’s statement was utterly false: we had an idea of how to do it, we had proven we could do it, and besides, the plots showing what we had done had been indeed included in the Tevatron 2000 report. Had he overlooked them ?
Escalation!
Dittmar seemed unbothered by my remark, and he responded that that small signal had not been confirmed in Run II data. His statement constituted an even more direct attack to four more years of my research time, spent on that very topic. I kept my cool, because when your opponent offers you on a silver plate the chance to verbally sodomize him, you cannot be too angry with him.
I remarked that a signal had indeed been found in Run II, amounting to about 6000 events after all selection cuts; it confirmed the past results. Dittmar then said that “to the best of his knowledge” this had not been published, so it did not really count. I then explained it was a 2008 NIM publication, and would he please document himself before making such unsubstantiated allegations? He shrugged his shoulders, said he would look more carefully for the paper, and went back to his talk.
His points about the Tevatron sensitivity studies were laid down: for a low-mass Higgs boson, the signal is just too small and backgrounds are too large, and the sensitivity of real searches is below expectations by a large factor. To stress this point, he produced a slide containing a plot he had taken from this blog! The plot (see on the left), which is my own concoction and not Tevatron-approved material, shows the ratio between observed limit to Higgs production and the expectations of the 2000 study. He pointed at the two points for 100-140 GeV Higgs boson masses, trying to prove his claim: The Tevatron is now doing three times worse than expected. He even uttered “It is time to confess: the sensitivity study was wrong by a large factor!”.
I could not help interrupting again: I had to stress that the plot was not approved material and was just a private interpretation of Tevatron results, but I did not deny its contents. The plot was indeed showing that low-mass searches were below par, but it was also showing that high-mass ones were amazingly in agreement with expectations worked at 10 years before. Then John Conway explained the low-mass discrepancy for the benefit of the audience, as he had done one day before for no apparent benefit of the speaker.
Conway explained that the study had been done under the hypothesis that an upgrade of our silicon detector would be financed by the DoE: it was in fact meant to prove the usefulness of funding an upgrade. A larger acceptance of inner silicon tracking boosts the sensitivity to identify b-quark jets from Higgs decays by a large factor, because any acceptance increase gets squared when computing the over-efficiency. So Dittmar could not really blame the Tevatron experiments for predicting something that would not materialize in a corresponding result, given that the DoE had denied the funding to build the upgraded detector!
I then felt compelled to add that by using my plot Dittmar was proving the opposite thesis of what he wanted to demonstrate: low-mass Tevatron searches were shown to underperform because of funding issues, rather than because of a wrong estimate of sensitivity; and high-mass searches, almost unhindered by the lack of an upgraded silicon, were in excellent agreement with expectations!
The speaker said that no, the high-mass searches were not in agreement, because their results could not be believed, and moved on to discuss those by taking real-data results by the Tevatron.
He said that the 
“Possible at the Tevatron ? I believe that the WW continuum background is much larger at a ppbar collider than at a pp collider, so my personal conclusion is that if the Tevatron people want to waste their time on it, good luck to them.”
Now, come on. I cannot imagine how a respectable particle physicist could drive himself into making such statements in front of a distinguished audience (which, have I mentioned it, included several theorists of the highest caliber, including none less than Edward Witten). Waste their time ? I felt I was wasting my time listening to him, but my determination of reporting his talk here kept me anchored to my chair, taking notes.
So this second part of the talk was not less unpleasant than the first part: Dittmar criticized the Tevatron high-mass Higgs results in the most incorrect, and scientifically dishonest, way that I could think of. Here is just a summary:
- He picked up a distribution of one particular sub-channel from one experiment, noting that it seemed to have the most signal-rich region showing a deficit of events. He then showed the global CDF+DZERO limit, which did not show a departure between expected and observed limit on Higgs cross section, and concluded that there was something fishy in the way the limit had been evaluated. But the limit is extracted from literally several dozens of those distributions -something he failed to mention despite having been warned of that very issue in advance.
- He picked up two neural-network output distributions for a search of Higgs at 160 and 165 GeV, and declared they could not be correct since they were very different in shape! John, from the back, replied “You have never worked with neural networks, have you ?” No, he had not. Had he, he would probably have understood that different mass points, optimized differently, can provide very different NN outputs.
- He showed another Neural Network output based on 3/fb of data, which had a pair of data points lying one standard deviation above the background predictions, and the corresponding plot for a search performed with improved statistics, which had instead a underfluctuation. He said he was puzzled by the effect. Again, some intervention from the audience was necessary, explaining that the methods are constantly reoptimized, and there is no wonder that adding more data can result in a different outcome. This produced a discussion when somebody from the audience tried to speculate that searches were maybe performed by looking at the data before choosing which method to use for a limit extraction! On the contrary of course, all Tevatron searches of the Higgs are blind analyses, where the optimization is performed on expected limits, using control samples, and Monte Carlo, and the data is only looked at afterwards.
- He showed that the Tevatron 2000 report had estimated a maximum Signal/Noise ratio for the H–>WW search of 0.34, and he picked up one random plot from the many searches of that channel by CDF and DZERO, showing that the signal to noise there was never larger than 0.15 or so. Explaining to him that the S/N of searches based on neural networks and combined discriminants is not a fixed value, and that many improvements have occurred in data analysis techniques in 10 years was useless.
Dittmar concluded his talk by saying that:
“Optimistic expectations might help to get funding! This is true, but it is also true that this approach eventually destroys some remaining confidence in science of the public.”.
His last slide even contained the sentence he had previously brought himself to uttering:
“It is the time to confess and admit that the sensitivity predictions were wrong”.
Finally, he encouraged LHC experiments to looking for the Higgs where the Tevatron had excluded it -between 160 and 170 GeV- because Tevatron results cannot be believed. I was disgusted: he most definitely places a strong claim on the prize of the most obnoxious talk of the year. Unfortunately for all, it was just as much an incorrect, scientifically dishonest, and dilettantesque lamentation, plus a defamation of a community of 1300 respected physicists.
In the end, I am really wondering what really moved Dittmar to such a disastrous performance. I think I know the answer, at least in part: he has been an advocate of the
The say of the week March 19, 2009
Posted by dorigo in games, humor, internet, italian blogs, physics, science.Tags: humor, sentences
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“Questi c’hanno sistematici che fanno provincia“
[These fellas have got county-wide systematics]
(Xisy, from a comment in M.Dal Mastro’s blog)
Be flexible March 18, 2009
Posted by dorigo in personal, physics.Tags: gender correctness, sex, sexism
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I was quite surprised to see today a slide from an american CDF colleague, in a talk aimed at a general audience of physicists, containing the picture shown below.
Sure, the message is clear. Be flexible. And I would have nothing to object with regards to the means used to convey that message. However, I have learned the hard way that many -especially in the US- consider sexist things that I consider normal. Thus my surprise. The picture is nice and the girl is pretty, but there is something distinctly sexual in her posture -and please do not even try saying that it feels like that just to me “because I am a sex maniac”.
Streaming video for Y(4140) discovery March 17, 2009
Posted by dorigo in news, physics, science.Tags: B physics, CDF, discoveries, QCD, standard model, Tevatron
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The CDF collaboration will present at a public venue (Fermilab’s Wilson Hall) its discovery of the new Y(4140) hadron, a mysterious particle created in B meson decays, and observed to decay strongly into a 
From this site you can connect to streaming video (starting at 4.00PM CDT, or 9.00PM GMT – should last about 1.30 hours).
DZERO refutes CDF’s multimuon signal… Or does it ? March 17, 2009
Posted by dorigo in news, physics, science.Tags: anomalous muons, CDF, DZERO, new physics, standard model, Tevatron
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Hot off the press: Mark Williams, a DZERO member speaking at Moriond QCD 2009 -a yearly international conference in particle physics, where HEP experimentalists regularly present their hottest results- has shown today the preliminary results of their analysis of dimuon events, based on 900 inverse picobarns of proton-antiproton collision data. And the conclusion is…
DZERO searched for an excess of muons with large impact parameter by applying a data selection very similar, and when possible totally equivalent, to the one used by CDF in its recent study. Of course, the two detectors have entirely different hardware, software algorithms, and triggers, so there are certain limits to how closely one analysis can be replicated by the other experiment. However, the main machinery is quite similar: they count how many events have two muons produced within the first layer of silicon detector, and extrapolate to determine how many they expect to see which fail to yield a hit in that first layer, comparing to the actual number. They find no excess of large impact parameter muons.
Impact parameter, for those of you who have not followed this closely in the last few months, is the smallest distance between a track and the proton-antiproton collision vertex, in the plane transverse to the beam direction. A large impact parameter indicates that a particle has been produced in the decay of a parent body which was able to travel away from the interaction point before disintegrating. More information about the whole issue can be found in this series of posts, or by just clicking the “anomalous muons” tab in the column on the right of this text.
There are many things to say, but I will not say them all here now, because I am still digesting the presentation, the accompanying document produced by DZERO (not ready for public consumption yet), and the implications and subtleties involved. However, let me flash a few of the questions I am going to try and give an answer to with my readings:
- The paper does not address the most important question – what is DZERO’s track reconstruction efficiency as a function of track impact parameter ? They do discuss with some detail the complicated mixture of their data, which results from triggers which enforce that tracks have very small impact parameter -effectively cutting away all tracks with an impact parameter larger than 0.5cm- and a dedicated trigger which does not enforce an IP requirement; they also discuss their offline track reconstruction algorithms. But at a first sight it did not seem clear to me that they can actually reconstruct effectively tracks with impact parameters up to 2.5 cm as they claim. I would have inserted in the documents an efficiency graph for the reconstruction efficiency as a function of impact parameter, had I authored it.
- The paper shows a distribution of the decay radius of neutral K mesons, reconstructed from their decay into pair of charged pions. From the plot, the efficiency of reconstructing those pions is excessively small -some three times smaller than what it is in CMS, for instance. I need to read another paper by DZERO to figure out what drives their K-zero reconstruction efficiency to be so small, and whether this is in fact due to the decrease of effectiveness with track displacement.
- What really puzzles me, however, is the fact that they do not see *any* excess, while we know there must be in any case a significant one: decays in flight of charged kaons and pions. Why is it that CDF is riddled with those, while DZERO appears free of them ? To explain this point: charged kaons and pions yield muons, which get reconstructed as real muons with large impact parameter. If the decay occurs within the tracking volume, the track is partly reconstructed with the muon hits and partly with the kaon or pion hits. Now, while pions have a mass similar to that of muons, and thus the muon practically follows the pion trajectory faithfully, for kaons there must be a significant kink in the track trajectory. One expects that the track reconstruction algorithm will fail to associate inner hits to a good fraction of those tracks, and the resulting muons will belong to the “loose” category, without a correspondence in the “tight” muon category which has muons containing a silicon hit in the innermost layer of the silicon detector. This creates an excess of muons with large impact parameter. CDF does estimate that contribution, and it is quite large, of the order of tens of thousands of events in 743 inverse picobarns of data! Now where are those events in the DZERO dataset, then ?
Of course, you should not expect that my limited intellectual capabilities and my slow reading of a paper I have had in my hands for no longer than two hours can produce foulproof arguments. So the above is just a first pass, sort of a quick and dirty evaluation. I imagine I will be able to give an answer to those puzzles myself, at least in part, with a deeper look at the documentation. But, for the time being, this is what I have to say about the DZERO analysis.
Or rather, I should add something. By reading the above, you might get the impression that I am only criticizing DZERO out of bitterness for the failed discovery of the century by CDF… No, it is not the case: I have always thought, and I continue to think, that the multi-muon signal by CDF is some unaccounted-for background. And I do salute with relief and interest the new effort by DZERO on this issue. I actually thank them for providing their input on this mystery. However, I still retain some scepticism with respect to the findings of their study. I hope that scepticism can be wiped off by some input – maybe some reader belonging to DZERO wants to shed some light on the issues I mentioned above ? You are most welcome to do so!
UPDATE: Lubos pitches in, and guess what, he blames CDF… But Lubos the experimentalist is not better than Lubos the diplomat, if you know what I mean…
Other reactions will be collected below – if you have any to point to, please do so.
