## Grow Triops with your kids!April 13, 2009

Posted by dorigo in personal, science.
Tags: ,

Just a short, advertising post to mention a very entertaining “scientific toy” for children. Filippo was given a box for his birthday, “Triassic Triops”, a toy made in USA by Triops Inc., three weeks ago. The box rested untouched for a while, until Filippo asked me to try it. The figure on the cover shows a mean-looking crustacean, and it took me a while to decide to try and grow those creatures in our home.

The box contains a small plastic tank, an envelope with gravel and tiny wood bits to create a reasonable habitat in the tank, a tiny box containing about 20 eggs, a tape-on thermometer, and a parcel of food pellets, plus instructions and a plastic pipette. Instructions are quite precise and easy to follow, but the hard part is to find a place in your home where you can stabilize the temperature: these creatures will hatch and grow only if the temperature is in the 22-29°C range.

We followed instructions carefully by using bottled water and waiting until the temperature had stabilized, but once eggs had to be dropped in the tank I was rather amazed: the little box did not seem to contain anything! Only by looking very carefully could I spot tiny grains smaller than half a millimeter across.

Nothing happened for a couple of days, but then we started to see two or three teeny-tiny little beings swimming around. We started feeding them, and they grew quite fast. I have no idea why only few of the eggs hatched, but I am really not sure whether there were twenty originally in the box, nor whether I managed to drop all of them in the tank…

In ten days, two triops have grown to about two-thirds of an inch in length (see right), probably killing the third one in the process (its carcass is still floating around). They are happily swimming day and night, and they eat all the pellets I put in the tank in the matter of a couple of hours… According to instructions, the life cycle of these amazing creatures is of about one to three months. They should grow to about two inches length -roughly the size of a small shrimp. Then they will die, and -by totally drying the tank, and pouring warm water in again- it should be possible to revive their eggs, if they have produced any.

The interesting thing about these creatures is that they have remained biologically identical to the original beings that populated our earth in the Triassic age. Quoting from the leaflet:

“Millions of years before Tyrannosaurus Rex ruled the earth, Tripos Longicaudatus was evolving a method of reproduction that allowed the developing embryos (developing eggs) to survive the drying up of the temporary ponds. This amazing process is known as suspended animation, or diapause. Scientists have found that Triops eggs can remain dormant for more than 25 years. In other words, the little Tripos slept while the dinosaurs disappeared”.

Regardless of the accuracy of the above reconstruction, I think it is really amazing to drop dried eggs into water and see creatures growing up in it. Try it with your kids: fun is assured!

## Things I should have blogged on last weekApril 13, 2009

Posted by dorigo in cosmology, news, physics, science.
Tags: , , , , ,

It rarely happens that four days pass without a new post on this site, but it is never because of the lack of things to report on: the world of experimental particle physics is wonderfully active and always entertaining. Usually hiatuses are due to a bout of laziness on my part. In this case, I can blame Vodafone, the provider of the wireless internet service I use when I am on vacation. From Padola (the place in the eastern italian Alps where I spent the last few days) the service is horrible, and I sometimes lack the patience to find the moment of outburst when bytes flow freely.

Things I would have wanted to blog on during these days include:

• The document describing the DZERO search of a CDF-like anomalous muon signal is finally public, about two weeks after the talk which announced the results at Moriond. Having had in my hands a unauthorized draft, I have a chance of comparing the polished with the unpolished version… Should be fun, but unfortunately unbloggable, since I owe some respect to my colleagues in DZERO. Still, the many issues I raised after the Moriond seminar should be discussed in light of an official document.
• DZERO also produced a very interesting search for $t \bar t h$ production. This is the associated production of a Higgs boson and a pair of top quarks, a process whose rate is made significant by the large coupling of top quarks and Higgs bosons, by virtue of the large top quark mass. By searching for a top-antitop signature and the associated Higgs boson decay to a pair of b-quark jets, one can investigate the existence of Higgs bosons in the mass range where the $b \bar b$ decay is most frequent -i.e., the region where all indirect evidence puts it. However, tth production is invisible at the Tevatron, and very hard at the LHC, so the DZERO search is really just a check that there is nothing sticking out which we have missed by just forgetting to look there. In any case, the signature is extremely rich and interesting to study (I had a PhD doing this for CMS a couple of years ago), thus my interest.
• I am still sitting on my notes for Day 4 of the NEUTEL2009 conference in Venice, which included a few interesting talks on gravitational waves, CMB anisotropies, the PAMELA results, and a talk by Marco Cirelli on dark matter searches. With some effort, I should be able to organize these notes in a post in a few days.
• And new beautiful physics results are coming out of CDF. I cannot anticipate much, but I assure you there will be much to read about in the forthcoming weeks!

## Quake homeless “enjoy a weekend of camping”April 8, 2009

Posted by dorigo in news, politics.
Tags: ,

The quiz of the day: who uttered such a profanity today, during an interview to german television, referring to the victims of the destructive earthquake who destroyed part of central Italy two days ago ?

I will give you a few hints. It is the same person who just a few days ago embarassed Italy at the G20, the same person who a few years ago suggested in a verbal exchange at the european parliament that Schultz, a german socialist, would make a very good nazist kapo’.

Ok, if you haven’t figured it out already, check it out on the times online.

I am ashamed of the person Italians has elected as their representative, and I feel especially bad since now I cannot even tell myself that the US president is even worse anymore.

## Milind Diwan: recent MINOS resultsApril 8, 2009

Posted by dorigo in news, physics, science.
Tags: , , , ,

I offer below another piece of the notes I took at the NEUTEL09 conference in Venice last month. For the slides of the talk reported here, see the conference site.

Milind’s presentation concentrated on results of muon-neutrino to electron-neutrino conversions. Minos is a “Main-Injecor Neutrino Oscillation Search”. It is a long-baseline experiment: the beam from the Main injector, Fermilab’s high-intensity source of protons feeding the Tevatron accelerator, can be sent from Batavia (IL) 735km away to the Soudan mine in Minnesota. There are actually two detectors, a near and a far detector: this is the unique feature of MINOS. The spectra collected at the two sites are compared to measure muon neutrino disappearance and appearance. The near detector is 1km away from the target.

The beam is a horn-focused muon-neutrino one. Horns are parabolic-shaped magnets. 120 GeV protons originate pions, which are focused by these structures; negative ones are defocused, and the beam contains predominantly muon neutrinos from the decay of these pions. The accelerator provides 10-microsecond pulses every 2.2 seconds, with $3.3 \times 10^{13}$ protons per pulse. 95% of the resulting neutrino flux is $\nu_\mu$, 4% are $\bar \nu_\mu$.

Besides the presence of two detectors in line, another unique feature of the Fermilab beam is the possibility to move the target in and out, shifting the spectrum of neutrinos that come out, because the focal point of the horns changes. Two positions of the target are used, corresponding to two beam configurations. In the high-energy configuration one can get a beam centered at an energy of 8 GeV or so, while the low-energy configuration is centered at 3 GeV. Most of the time Minos runs with the 3 GeV beam.

Detectors are a kiloton-worth of steel and scintillator planes in the near detector, and 5.4-kT in the far detector. Scintillator strips are 1 cm thick, 4.1 cm wide, and their Moliere radius is of 3.7cm. A 1-GeV muon crosses 27 planes. The iron in the detectors is magnetized with a 1 Tesla magnetic field.

Minos event topologies include CC-like and NC-like events. A charged-current (CC) event gives a muon plus hadrons: a long charged track from the muon, which is easy to find. A neutral current (NC) event will make a splash and it is diffuse, since all one sees is the signal from the disgregation of the target nucleus; an electron CC event will leave a dense, short shower, with a typical electromagnetic shower profile. The three processes giving rise to the observed signatures are described by the Feynman diagrams below.

The analysis challenge is to put together a selection algorithm capable of rejecting backgrounds and select CC $\nu_e$ events. Fluxes are measured in the near detector, and they allow to predict what can be found in the far detector. This minimizes the dependence on MC, because there are too many factors that may cause fluctuations in the real data, and the simulation cannot possibly handle them all. So they carry out a blind analysis. They check background estimates with independent samples: this serves the purpose of avoiding to bias oneself with what one should observe. They generate many simulated samples not containing an oscillation signal, to check all analysis procedures.

Basic cuts are applied on their data sample to ensure data quality. Fiducial volume cuts provide rejection to cosmic ray backgrounds. Simple cuts lead to a S/N ratio of 1:12. By “signal” one means the appearance of electron neutrinos. $\nu_e$ events are selected with artificial Neural Networks, which use the properties of the shower, the lateral shower spread, etcetera. These can discriminate NC interactions from electron-neutrino-induced CC interactions. After the application of the algorithm, the S/N ratio is 1/4. At this stage, one important remaining source of background is due to muon-neutrino CC backgrounds which can be mistaken from electron-neutrino ones when the muon is not seen in the detector.

They can select $\nu_e$ events with a “library event matching” (LEM). This matches the data event with a shower library, reconstructing the fraction of the best 50 matches which are electron-neutrino events. This is more or less like an evolved “nearest-neighbor” algorithm. As a result, they get a better separation. However, according to the speaker this method is not ready yet, since they still need to understand its details better.

[As I was taking these notes, I observed that data and Monte Carlo simulation do not match well in the low-ANN output region. The speaker claims tha the fraction of events in the tail of the Monte Carlo distribution can be modeled only with some approximation, but that they do not need to model that region too well for their result. However, it looks as if the discrepancy between data and MC not well understood. Please refer to the graph shown below, which shows the NN output in data and simulation at a preselection level.]

Back to the presentation. To obtain a result, the calculation they performis simple: how many events are expected in the far detector ? The ratio of far to near flux is known, 1.3E-6. This includes all geometrical factors. For this analysis they have 3E20 protons on target. They expect 27 events for the ANN selection, and 22 for the LEM analysis.

They need to separate backgrounds in NC and CC, so they do a trick: they take data in two different beam configurations, then they look at the spectrum in the near detector, where they expect muon-type events to be rejected much more easily because they are more deflected. From this they can separate the two contributions.

Their final result for the predicted number of electron-induced CC events is 27+-5 (stat)+-2 (syst).

A second check on the background calculation consists in removing the muon in tagged CC events, and use these for two different calculations. One is an independent background calculation: they can add a simulated electron to the event raw data after removing the muon. This checks whether the signal is modeled correctly. From these studies they conclude that the signal is modeled well.

The results show that there is indeed a small signal: they observe 35 events, when they expect 27, in the high-NN output region, as shown in the figure above. For the other method, LEM, results are consistent. The energy spectrum of the selected events is shown in the graph below.

With the observation of this small excess (which is compatible with predictions), a confidence level is set in the plane of the two parameters $\sin^2 2 \theta_{13}$ versus $\delta_{cp}$, at 90%. It goes up to 0.35, with a small oscillation dependent on the value of $\delta$. You can see it in the figure on the right below.

The speaker claims that if the excess they are observing disappears with further accumulated data, they will be able to reach below the existing bound.

The other result of MINOS is a $\delta M^2$ result from disappearance studies. The signal amounts to several hundred events of deficit. They can put a limit on an empirical parameter which determines what fraction of the initial flux has gone into sterile neutrinos. They have 6.6E20 protons on target now taken. The fraction of sterile
neutrinos is less than 0.68 at 90%CL.

## What is the Y(4140)? The plot thickensApril 6, 2009

Posted by dorigo in news, physics, science.
Tags: , , ,

I read with interest -but it would probably be more honest to say I browsed, since I could understand less than 50%- a preprint released three days ago on “The hidden charm decay of Y(4140) by the rescattering mechanism“, by Xiang Liu, from Peking University (now at Coimbra, PT). The Y particle has been recently discovered by CDF.

The existence of the several new resonances of masses above 3 GeV recently unearthed by B factories and by the CDF experiment poses a challenge to our interpretation of these states as simple quark-antiquark bound states, because of their properties -in particular, their decay pattern and their natural widths.

Already with the first “exotic” meson discovered a few years ago (and recently measured with great precision by CDF), the X(3872), the puzzle was evident: at a mass almost coincident with twice the mass of conventional charmed mesons (states which are labeled “D”, which are composed of two quarks: a charm and a up or down quark, like $D^+ = c \bar d$ or $D^\circ = c \bar u$), the X was immediately suggested to be a molecular state of two D particles. I wrote an account of the studies of the nature of the X particle a few years ago if you are interested -but mind you, the advancements in this research field are quick, and I believe the material I wrote back then is a bit aged by now.

The paper by Liu tries to determine whether the interpretation of the Y particle as a pure second radial excitation of P-wave charmonium ($\chi_{cJ}''$, with $J=0,1$) holds water once the observed branching ratio of the Y into the final state seen by CDF ($Y \to J/\psi \phi$), and the measured decay width, are compared to a theoretical calculation.

The nice thing about the decay of the Y into the observed final state is that it occurs only through a so-called “rescattering” mechanism, by means of the diagrams shown in the graph below (the ones shown refer to the J=0 hypothesis of the $\chi_{cJ}''$, but similar diagrams are discussed for the J=1 state in the paper).

As you can see, the Y produces the two final state particles by means of a triangle loop of D mesons. These diagrams usually describe rare processes, and in fact Liu’s calculations end up finding a small branching fraction. I am unable to delve into the details of the computation, so I will just state the result: the typical values of the branching ratio $B(Y \to J/\psi \phi)$ depend on a parameter, $\alpha$ which, if taken in a “reasonable” range of values, provides estimates in the ballpark of a few $10^{-4}$. This appears inconsistent with the observation provided by the CDF experiment.

Clearly, work is in progress here, so I would abstain from concluding anything definite on the matter. So, for now, let us call this an indication that the simple interpretation of the Y as a excited charmonium state is problematic.

## 3 megatons strike in central ItalyApril 6, 2009

Posted by dorigo in news, science.
Tags:

A destructive earthquake has struck last night in central Italy, at 3.32AM in a mountainous region of the Appennini, close to the city of L’Aquila. The magnitude of the earthquake has been estimated at 6.3 on the Richter scale, for a release of energy equal to about 3 megatons of TNT (not 16 as I previously reported, which corresponds to 6.7 degrees in the Richter scale).

Many small towns close to the epicenter report more than half of the houses grounded. The biggest worries come from L’Aquila, which counts about 70,000 inhabitants; but many smaller towns scattered around in the mountainous region of the Abruzzi have certainly suffered major damage. There are reports of tens of dead bodies already extracted from the rubble. I will have updates here as soon as I gather more information.

UPDATE: while dead bodies continue to be drawn out from collapsed buildings, a disturbing detail emerges. It transpires that a researcher at the Gran Sasso national laboratories had predicted the event, and had warned that a disastrous seismic event would occur. Giampaolo Giuliani had recorded a large release of radon gas from the ground on March 29th, and had concluded that an earthquake would probably take place in the matter of hours. Giuliani had predicted the event would happen a week before it actually did, and on March 31st the head of civil protection Guido Bertolaso had bitterly criticized the prediction and “quegli imbecilli che si divertono a diffondere notizie false” (those imbeciles that enjoy diffusing false news). Giuliani is facing charges of causing a false alarm, but he was right after all.

UPDATE: here are a few excerpts from an interview given by Giampaolo Giuliani this morning:

“Se commento adesso c’e’ il rischio che a me domani mi mettono in galera. Allora, non e’ vero, e’ falso, che i terremoti non possono essere previsti. Sono quasi dieci anni che noi riusciamo a prevedere eventi nel raggio d’azione di 120-150 chilometri dai nostri rivelatori.”
“Sono tre giorni che vedevamo un forte incremento di Radon. I forti incrementi di Radon, al di fuori delle soglie di sicurezza, significano forti terremoti.”
“Anche la tecnologia classica avrebbe potuto prevederlo. Se qualcuno fosse stato a lavorare, ai posti dovuti, o se qualcuno si fosse preoccupato.”
“Questa notte anche la sala sismica si sarebbe potuto accorgere che sarebbe avvenuta una forte scossa. Il mio sismografo indicava una forte scossa di terremoto e ce l’avevamo online, tutti potevano osservarlo, e tanti lo hanno osservato e si sono resi conto che le scosse crescevano.”

(“If I comment now there is the risk that tomorrow I get imprisoned. Now: it is not true, it is false, that earthquakes cannot be predicted. We have been able to predict events for almost ten years in a range of 120-150 kilometers from our detectors.”

“In the last three days we saw a large increase of Radon. Large increases of Radon, above safety thresholds, mean strong earthquakes.”

“Even classic technology could have been used to predict it. If somebody had been working, at their place, or if somebody had gotten worried.”

“Tonight even the seismic room could have realized that a strong shake was going to happen. My seismograph indicated a strong earthquake and we had it online, everybody could watch it, and many did and realized that the tremors were increasing.”)

UPDATE: Michelangelo Ambrosio, a director of research of the INFN (national institute for nuclear physics) section in Napoli, thus defends the claims of Giuliani:

“trascurare con superficialita’ le applicazioni di nuove tecnologie solo perche’ proposte da ricercatori non appartenenti allo establishment preposto a tale funzione e’ una negligenza criminale di cui oggi paghiamo le conseguenze.”

(“Disregarding with superficiality the applications of new technologies only for the reason they are brought forward by researchers not belonging to the establishment addressing those functions is a criminal neglect of which today we all pay the consequences”.)

## Just a linkApril 5, 2009

Posted by dorigo in Blogroll, news, physics, science.
Tags: , ,

I read with amusement (and some effort) a spanish account by Francis (th)E mule of Michael Dittmar’s controversial seminar of last March 19th. I paste the link here for several reasons: since I believe it might be of interest to some of you, to have a place to store it, and because I am not insensitive to flattery:

“Entre el público se encontraba Tomasso Dorigo [...] (r)esponsable del mejor blog sobre física de partículas elementales del mundo”

Muchas gracias, Francis -but please note: my name spells with two m’s and one s!

## Religions against women, everywhereApril 4, 2009

Posted by dorigo in news, politics, religion.
Tags: , , ,

Maybe you might get the impression that I am discovering hot water with this post, and in that case I apologize. But I cannot help logging in this site that I insist in being constantly amazed at the virulence, the shamelessness, and the violence which religious activists use on a daily basis against women, everywhere on this poor planet.

We are all used to the ferocious laws against women in islamic countries, the beating to death of mothers and daughters for futile reasons, the lack of civil rights of women there. We all breathed a sigh of relief when the Talibans were eradicated from power in Afghanistan -only to wake up later and find out that nothing much has changed. In general, when we discuss the rights of women, the situation in arab countries is the obvious issue to deal with.

Things, however, are not qualitatively very different in more “civilized” countries. Take Italy as a very clear example. A western country, a democracy, a secular power which should be able to legislate free from religious ingerence. But it is not so: through lobbying, declarations of archbishops, preaches by Pope Ratzinger, and sermons in the churches, the Vatican managed to convince the italian government to pass a law that for all practical purposes prevents in vitro fertilization. Women who want to get pregnant with medical aid have to travel to Spain or Ukraine, if they can afford it. Worse still, the health of women who accept the italian rules on assisted procreation is put to risk by insane rules whose denominator is the belief that “the embryo is sacred and has to be defended” -even at the risk of the owner of the womb. Every sperm is sacred: one cannot help hearing the old song by Monty Python sung in the background every time Cardinal Bagnasco or one of his accolites is seen on national television.

There would be other things to discuss -Ratzinger’s fight against condoms in Africa, for instance, is directed first and foremost against women. Or the idiotic laws against stem cell research. But I want to mention something else here today.

What prompts me to write about religion and women today is the news about a picture of the new Israeli government of Benyamin Netanyahu, which contains -the horror, the horror- two women: Limor Livnat, minister of Culture and Sport, and Sofa Landver, minister of Immigration. These two women were amidst 28 men in a picture taken yesterday, and shown on most israeli newspapers. The devil is in the details: see the two versions, and decide for yourself which one is the original and which one appeared on ultra-orthodox newspapers, Sha’a Tovah and Yated Ne’eman.

No violence was moved, nobody was hurt. But to me, the photoshopped picture is if possible even more disturbing than an “ordinary” violent act against a woman. Because it comes from a supposedly respectable institution, in a “civilized” country.

If I were Netanyahu, I would force the newspapers editors to publish the original pictures and present their excuses to the ministers, to the people of Israel, and to us all. Otherwise, some of the reasons why we root for Israel against arab fundamentalists are lost, and Israel itself becomes weaker in its struggle for survival.

## Wealth, poverty, and progressive taxationApril 4, 2009

Posted by dorigo in news, politics.
Tags: , ,

A note left by a colleague in his facebook page:

I just can’t get these numbers out of my head: The 500 richest people on earth earn more than the bottom 416 million.

That’s 416 million – not 416 thousand, or 4.16 million, but 416,000,000 – much more than the entire population of the United States.

So if some ideologue decided to even out wealth distribution between these two extremes, each of those top 500 earners would see their net worth reduced by a factor of a million! They would lose 99.9999% of their wealth, while the bottom 416 million people would see their assets double.

I’m used to large and small numbers, from my work, but this amazes me. The numbers come from an opinion by Nicholas D. Kristof published in the International Hearald Tribune yesterday, 3-April-2009, and he cites the U.N.

And my reaction:

Hi M., that is indeed striking -and disgusting, in a way. I would not ask the 500 richest people to share all their wealth. If they just gave away half of what they have, 416 million people would still get a 50% increase of their means. That would be a little bit less ideologic and maybe only decent!
Probably the only way about this is not to intervene in a rotten situation, but change the rules. Progressive taxation is the way. The economic situation in the world lends itself to strong intervention, and I think what they G20 decided this week is a step in the right direction, but still a bit too shy.

## NeuTel 09: Oscar Blanch Bigas, update on Auger limits on the diffuse flux of neutrinosApril 3, 2009

Posted by dorigo in astronomy, cosmology, news, physics, science.
Tags: , , ,

With this post I continue the series of short reports on the talks I heard at the Neutrino Telescopes 2009 conference, held three weeks ago in Venice.

The Pierre Auger Observatory is a huge (3000 km^2) hybrid detector of ultra-energetic cosmic rays -that means ones having an energy above 10^18 eV. The detector is located in Malargue, Argentina, at 1400m above sea level.

There are four six-eyed fluorescent detectors: when the shower of particles created by a very energetic primary cosmic ray develops in the atmosphere, it excites nitrogen atoms which emit energy in fluorescent light, collected in telescope. It is a calorimetric measurement of the shower, since the number of particles in the shower gives a measurement of the energy of the incident primary particle.

The main problem of the fluorescent detection method is statistics: fluorescent detectors have a reduced duty cycle because they can only observe in moonless nights. That amounts to a 10% duty cycle. So these are complemented by a surface detector, which has a 100% duty cycle.

The surface detector is composed by water Cherenkov detectors on the ground, which can detect light with PMT tubes. The signal is sampled as a function of distance from the center of shower. The measurement depends on a Monte Carlo simulation, so there are some systematic uncertainties present in the method.

The assembly includes 1600 surface detectors (red points), surrounded by four fluorescence detectors (shown by green lines in the map above). These study the high-energy cosmics, their spectra, their arrival direction, and their composition. The detector has some sensitivity to unidentified ultra-high energy neutrinos. A standard cosmic ray interacts at the top of atmosphere, and yields an extensive air shower which has an electromagnetic component developing on the ground; but if the arrival direction of the primary is tilted with respect to the vertical, the e.m. component is absorbed when it arrives on the ground, so it contains only muons. For neutrinos, which can penetrate deep in the atmosphere before interacting, the shower will instead have a significant e.m. component regardless of the angle of incidence.

The “footprint” is the pattern of firing detectors on the ground. It encodes information on the angle of incidence. For tilted showers, the presence of an e.m. component is strong indication of neutrino shower. An elongated footprint and a wide time structure of signal is seen for tilted showers.

There is a second method to detect neutrinos. This is based on the so-called “skimming neutrinos“: the Earth-skimming mechanism occurs when neutrinos interact in the Earth, producing a charged lepton via charged current interaction. The lepton produces a shower that can be detected above the ground. This channel has better sensitivity than neutrinos interacting in the atmosphere. It can be used for tau neutrinos, due to early tau decay in the atmosphere. The distance of interaction for a muon neutrino is 500 km, for a tau neutrino is 50 km. for electrons it is 10 km. These figures apply to 1 EeV primaries. If you are unfamiliar with these ultra-high energies, 1 Eev = 1000 PeV = 1,000,000 TeV: this is roughly equivalent to the energy drawn in a second by a handful of LEDs.

Showers induced by emerging tau leptons start close to the detector, and are very inclined. So one asks for an elongated footprint, and a shower moving at the speed of light using the available timing information. The background to such a signature is of the order of one event every 10 years. The most important drawback of Earth-skimming neutrinos is the large systematic uncertainty associated with the measurement.

Ideally, one would like to produce a neutrino spectrum or an energy-dependent limit on the flux, but no energy reconstruction is available. Observed energy depends on the height at which the shower is developing, and since this is not known for penetrating particles as neutrinos, one can only give a flux limit for them. The limit is in the range of energy where GZK neutrinos should peak, but its value is an order of magnitude above the expected flux of GZK neutrinos. A differential limit in energy is much worse in reach.

The figure below shows the result for the integrated flux of neutrinos obtained by the Pierre Auger observatory in 2008 (red line), compared with other limits and with expectations for GKZ neutrinos.