Thank you very much. Today I will have to be describing you something different.
Something which I think is getting progressively more important which is the nature
and the presence of neutrinos as a particle, astro particle physics.
Now, let me say the discovery of the Higgs boson at CERN LHC, as said by Professor Veltman a minute ago,
will crown the successful standard model.
And will call for verifications of the Higgs boson couplings to the gauge bosons and to the fermions.
The neutrino masses and oscillations represent today a main experimental evidence and a possibility, a real possibility,
for physics beyond what he has so carefully described to you to be the standard model.
The only elementary fermions whose basic properties are still largely unknown, neutrinos,
must naturally be the one of the main priorities to complete our knowledge of the standard model.
Still unknown precisely the incredible smallness of the neutrino masses, compared to those of the other elementary fermions,
point out to some specific scenario which is all to be elucidated.
The astrophysical importance of neutrinos of course is immense. So is their cosmic evolution.
The beginning of experimental neutrino physics starts 1956 with the first observation of antineutrinos in a reactor,
the Savannah River Reactor by Cowan and Fred Reines. And it took them about 40 years precisely in order to get the Nobel Prize.
Fred Reines got the prize in 1995. The basic idea is a source, is a reactor.
Neutrino electron from Beta-decays and rich of fission products.
And there are essentially uranium isotopes which are the main responsibles.
And plutonium isotopes are mainl responsibles for the producing of these Beta-decays.
200 MeV for each event is the fission product.
There are 6 neutrino electrons produced for each fission which gives you an enormous amount of neutrinos.
There are 2*10^20 neutrino electrons per GeV thermal, each and every second.
And we are talking about a very large amount of power. Reactors are very large.
Therefore the number of neutrinos is absolutely astronomical.
The detection is relatively simple. It is based on a scintillator. It's based on inverse Beta-decay.
The neutrino electron plus the proton becomes a positron plus a neutron.
And then what you see is the rate and you observe then the spectrum and the only possible disappearance experiment.
In this graph here you see how the experiment occurs. The neutrino comes in. It hits the nucleus and produces an electron.
Which is a positron which is detected and the neutron and the neutron is wandering around for a few microseconds.
And then it's captured producing gamma ray captures.
So the signal between the gamma ray capture and the neutron and the signal for the positron are used
to detect the events in question.
In these experiments you don't see any other neutrinos, as you know, because the other neutrinos are much more...
are different than this.
Now many years have passed by, today we have much larger... huge experiments working on neutrino. Let me mention a few of them.
One is Daya Bay Experiment which is a set of 6 commercial reactor cores which uses something like 14.4 GeV of total particles.
And there are antineutrino detectors indicated to have a total mass of as much as 120 tones.
And the experiments are shown in this graph here.
Here is the reactor and these are the places where the experiments are located.
They are located underground in an axis of the order of several hundred metres of water equivalent
in order to remove the cosmic ray background. This experiment is a main experiment going on in China.
Another experiment worth mentioning is the RENO experiment.
Similar situation, you can see there 6 huge reactors producing neutrinos.
Those neutrinos are detected by a near detector at 250 metres, by a far detector under the mountain at 1.3 kilometres.
And you can see here how the thing is located physically. And this whole thing is now presently operating and it is in Korea.
Another important thing I like to mention at this point is the fact that developing countries
like Korea and China are becoming very strong and very successful in producing most important results
in this field of neutrino physics.
And finally the other important thing is the combination between accelerators and neutrino detectors.
Here you can see a picture of the CERN to Gran Sasso neutrino beam.
A beam from CERN which you see here, a well-known lake already described by Martinus Veltman a minute ago,
is emitting neutrinos which are traversing the Alps and they're coming under ground at up to 20 kilometres under the Po Valley.
And then because of the rotation of the earth they come up again and they emerge in a laboratory, very large laboratory,
which is located in Gran Sasso. Where you can see here the many various areas. And this is a place where the neutrinos arrive.
So the neutrinos travel for something like 730 kilometres between the introduction point and the arrival point
and during this distance many, many new, as you will see many, many new phenomena have occurred.
Oscillation phenomena like this. Now briefly speaking, how many neutrino species there are in nature?
This is the question that has already again Martinus mentioned about the fact 3 quarks in 3 families.
Neutrino oscillation established a picture consistent also with the mixing of 3 physical neutrinos.
Neutrino electron, neutrino muon and neutrino tau with the help of 3 mass eigenstates, v1, v2, v3 in a matrix operation.
The actual masses of neutrinos are, believe it or not, so far unknown.
All we know now is the difference in masses: the different mass between neutrino electron and neutrino muon or neutrino muon
and neutrino tau. But we do not have the actual masses. Although we know they are very small.
The sum of the strength of the couplings of all possible neutrino invisible states is observed by taking the zero particle.
Take the zero particle, let it decay, in the decay process some events are not visible because neutrino is not detectable.
Counting then also events which are invisible states, you can determine how many new types of neutrinos that are available.
All types of neutrinos should be connected to the zero. And you find their number is actually 3. It's not 35, it's only 3.
However, the question that we conclude, that the result in number of neutrinos which is 3 is only possible
if the neutrino in similarity with leptons have unitary strength.
You can have also some other additional elements which spread the number 3 out to a much larger number of objects.
At present experimentally measure 3 weak coupling strengths are rather poorly known leaving lots of room
for more exotic alternatives.
And there may be, ok, some evidence for the presence of a number of anomalies, what we called anomalies,
related to neutrinos which of course are highly speculative at the present moment.
They are quite interesting, they are quite exciting but very speculative.
And next years will be needed to confirm either yes or no experimentally.
And the story which we are going to mention which is the title more or less of my talk is the question of sterile neutrinos.
What are sterile neutrinos?
Sterile neutrinos are a hypothetical type of neutrinos that do not interact via any of the fundamental interaction,
the standard model except gravity.
Since per say they will not interact electromagnetically weakly or strongly, they are extremely difficult to detect.
If they are heavy enough they may also contribute to cold or dark matter and warm dark matter in the universe.
Sterile neutrinos may mix with ordinary neutrinos via a mass term. Evidence may be building after several experiments.
There are 2 fundamental experimental anomalies which appear to be present in this experimental data.
One is a light with a mass of the order of 1 eV^2, sterile neutrino from neutrino electron observation
starting from an initial neutrino mu accelerator experiment. And a second effect is neutrino disappearance.
When you count the number of neutrinos coming from a nuclear reactor you find that actually
you detect less neutrinos than should have been there starting from the production process.
And therefore there is room for some neutrino to have disappeared. To be there and not to be directly detectable.
And the same situation is also indicated with very intense megacurie electron conversion neutrino sources.
Which also are objects in which you take neutrino emissions from a source and that neutrino emission from the source...
You know how many there are coming from the source. You know how many you detect experimentally and you find the deficit.
So those deficits are at the present moment one of the main reasons of interest
and concern about the possibility of sterile neutrinos. How many are the sterile neutrinos.
Again nobody knows. The argument here is an example, you see in this drawing. You have one single sterile neutrino here.
You have the 3 neutrinos: neutrino tau, neutrino mu, neutrino E, in this order.
Maybe there are also turn around in different order but anyway they are there.
And then there is an additional sterile neutrino forth up there. This is a 3 for 1 models.
Now, neutrino mu to neutrino E interaction, a very tiny level, are expected from this process because neutrino mu
and sterile may interact with each other.
And neutrino E and sterile also may interact with each other. And the fact is that these 2 processes are possible.
And therefore you can have a situation which you see in apparent neutrino E production present in abundant, dominant neutrino mu.
Because of the intermediary passing through a single neutrino scalar, sterile neutrino event, neutrino S.
Now current measurements seem to indicate that perhaps not only 1 neutrino is available, there could be 2 sterile neutrinos.
This is in some theoretical model.
You can see here 2 sterile neutrinos getting together, together with standard 3 normal neutrinos.
And they are more complicated, more difficult and nobody really knows whether nature has decided to be otherwise.
Let me also point out to you that if you need to have in your hands neutrino parity violation,
the presence of at least 2 neutrinos, the sterile neutrino one is preferable. Now, all that is theory. Now, what about experiment.
The experimental story about neutrinos, sterile neutrinos started from a so called LSND anomaly.
Which is an experiment which was preformed something 20 years ago in which a very high intensity proton beam
coming from a proton accelerator at LAMPF has been put on target. And in this way you produce...
The pions produce muons, which are then decaying into electrons.
And electrons are then associated with antineutrino E and neutrino mu oscillations in this form.
And your signal which you detect in here is the presence of an anomaly of neutrino electrons in a familiar situation
which started from pions and muons. You should also have neutrino, antineutrino mu.
So antineutrino electrons instead of antineutrino mu. This is a very striking fact.
You can see plotted here the ratio of the length of the path, divided by the energy in MeV of the neutrinos.
And you can see this is metres per MeV, about 1 or 2 metres MeV. So it's a relatively short object, a few metres.
And you can see here a very substantial peak, this is the signal. And all the other backgrounds are very much smaller.
So you get a very strong excess of event or antineutrino electrons of unknown source. Which has 87 plus or minus 22 etc, etc.
Which has a probability of occurring relatively small but not that small, 0.2%.
And this gives you a 3.8 evidence for the oscillation. Such a result was there for a number of years, still unchallenged.
A new experiment was developed at Fermi Lab. It's called MiniBooNE. In this experiment it's more conventional.
You take a standard booster accelerator, you're producing targets for protons, protons becomes pions, pions become muons,
muons go through dirt and are caught by the detector.
And this experiment has also shown the presence of LSND anomaly. Both in neutrino and antineutrino.
You can see that from this graph. Here is the L over E, the length divided by the energy.
And you can see the neutrino, antineutrino both indicating a clear signal.
The result is compelling with respect to ordinary 2 neutrino fit indicating anomalous excess.
And the excess occurs about at the L over E, about 1 MeV per metre.
Now this reported effect is essentially within the experimental error compatible with LSND experiments
which well know was originally dominant in the antineutrino channel.
You can see here both the LSND old results and the new MiniBooNE results,
you see within the very large statistics and errors, maybe something is there.
This is certainly a big question mark which we have to understand better. Now back to the reactor experiments.
Reactor experiments are the ones which were studied initially by Cowan and Reines. You can see a general plot.
All we know about, in our present day nuclear reactors, you can see here the distance, reactor distance from the reactor itself.
This is 10 metres, this is 1 kilometres, this is 100 kilometres.
And you can see here essentially the rate of observed over predicted neutrinos.
I mean if nothing would happen, no oscillation would occur, neutrino will be a stable object. The ratio will be 1.
You make so many neutrinos and you collect the same number.
But indeed this is not so and this represents a very large amount of pieces of information which should becoming available.
You can see for this graph for instance that there is a solar neutrino anomaly which is well known, well measured,
which occurs at a mass difference which is quite small, 10^-5 eV^2.
In which essentially the neutrino electrons and neutrino mus are in fact oscillating with each other.
And the phenomenon of this oscillation is producing a drop in the rate of neutrino electrons
which are the only ones seen by the reactor. The reactor doesn't see neutrino mu.
The reactor doesn't see neutrino tau because they are not part of the... because the tau is too heavy and the mu is too heavy.
But still the neutrino E is present there.
So you see a cancellation, a very huge cancellation in the number of neutrinos produced by the solar neutrino anomaly.
Another anomaly was discovered in the period from '86 to '98 and this is a so called atmospheric neutrino anomaly
which relates essentially the neutrino mu with the neutrino tau.
And you can see here a second peak right there in the experimental data and the results are in agreement.
And then you have the reason for the argument today.
There is a certain part which is essentially terra incognita in which you find lots of experimental results. You see them here.
Which all happen to be for many, many different groups, which all happen to be some percent below the value
that should be the one predicted.
You can see that all these results are compatible with the event rate R, which is not 1 but is 0.93.
And this is essentially an anomaly which is somehow...
we have to explain: Why do we have less neutrinos out of any and every reactor that you expect to have?
The reason for that must be explained and so far is unknown.
A third point of information is coming from the so called gallium anomaly.
The gallium anomaly is an experiment which was used to study solar neutrinos.
Neutrinos from the sun were detected in experiment for instance in Gran Sasso laboratory.
And in this experiment you have done some measurements with a radioactive source.
A radioactive source is a neutrino source, a source in which a neutrino is emitted with a megacurie intensity.
And also a similar thing was done in Russia.
And the calibration signal produced by intense artificial capture processing in chromium and argon.
And you can see there is the way which the detector has been detecting, relatively simple detector.
And there again you find that alternate source. There are less neutrinos than you would like to have.
That you can see that the ratio between the neutrinos you actually detect in the experiment and the number of neutrinos
which you have produced by your source, that you have "bought", you calibrated, you generated, and this is less than 1.
And this best fitted value may favour the existence of undetected sterile neutrino with certain evidence
with a few standard deviations. And a broad range again.
Roughly the same values which correspond to the LSND experiment and to the MiniBooNE experiment.
So the mass difference squared the other one eV which is much greater than what the oscillation indicated in the curve.
So the question which comes about is: Is there a unified approach here? You can see here the 2 kinds of experiments.
These are the LSND anomalies indicated there which expect an antineutrino from accelerator driven.
And this is a possibility which is a whole spectrum now, not well identified between the angle of sine Theta and Delta M^2.
So all this area is allowed by the results coming from the LSND and MiniBooNE experiments.
And then you find the gallium reactors, the gallium and the reactor sources which are producing something there.
The most remarkable thing is that all these 2 elements are within this very huge area compatible
with a new situation which occurs of the order of about 1 eV^2.
1 eV^2 is really the mass range in which, for instance, dark mass will have some contributions.
And therefore the question is: Are they all true or some of them is true or nothing is true? Are they induced by common origin?
If they are common origin it's perfectly normal to expect that because the total phenomenon of disappearance
it has to be much greater because of disappearance to any possible final state.
Well, here we have a specific channel in which in fact the neutrino, the mu initially produced,
is transformed through neutrino sterile into neutrino electron and the probability for that has to be smaller.
So the question is, is there a unified approach of that. Now, the evidence for all this as I said is mounting.
Let me very briefly show to you, summarising what I said. LSND, old experiment, gave 3 point standard deviation.
MiniBooNE was performed both on neutrino and antineutrino. The combination of these events is 3.8 standard deviation.
The gallium absorption experiment has given us 2.7 Sigma. Reactor experiments as I've shown before...
The beta-fission, beta-decay they give about 3 standard deviations.
And there are some indications which are not real proof but some sort of indication from cosmology,
which say that perhaps some sterile neutrinos, if it's not incompatible with cosmology.
Maybe in some circumstances that could maybe even be connected to some cosmological arguments.
And the combined evidence of all these things is that we find it possible overall anomaly of about 1 eV^2.
And let me tell you the number for this is remarkable, its 3.8 + 3.8 + 2.7 + 3 + 2.
This is something which is worth looking at and very understood.
Will any of course these observations survive to a more complete analysis?
The study of questions? And for that we need some detection, detector development.
There is a major new detector development which is occurring now today which is a new powerful detector
which is called liquid argon bubble chamber.
Those people which remember the old days, old neutrino physicists,
can remember that about 30 years ago an experiment was performed by a bubble chamber called Gargamelle.
And that was the first real evidence that exists a neutral current.
It's because the Gargamelle that we saw with some neutrino electron observed
which were not supposed to be there that indeed the zero particle was a reality.
And this started the whole program and this experimentally was the argument
which was used in order to explain essentially a standard model as a result of it,
as beautifully explained a few minutes ago by Martinus Veltman.
Now, the Gargamelle bubble chamber is a very complicated.
Now we have a new development which is coming out which is called electronic chamber
which has very similar property of density, radiation length and collision length, in fact,
it has very similar events except it's done electronically. And it uses very large amount of target.
Many kilotons of detectors instead of a few tonnes. 3 tonnes was the mass of Gargamelle.
And it is essentially very similar from the point of view of the dimension.
Very quickly I will tell you what the basic idea of this is. Maybe I should skip all this because of time.
And show you more clearly how the thing works.
In this chamber you have a sort of a detector in which you measure essentially the time of a family of drift wires.
And these are the number of drift wire indicated there.
There's the time of the drift of the electrons, free electron in the liquid that's indicated there.
And whenever there is a pulse coming after a certain delay you have a signal which you record.
Those signals are all collected up by the electronic system and they become a way of reconstructing a track of an event.
Let me show you. There is very large ICARUS type detectors, liquid argon detector now operating under ground in Hall B of LNGS.
And it is quite a substantial hardware equipment as you can see.
Very large in terms of equipment, materials and everything else.
And essentially the basic element in here is essentially the fact that to make such an experiment work
you need to have incredible purification of the liquid argon.
Liquid argon which comes initially as part of air is containing a lot of oxygen.
The oxygen is of course an electro negative gas.
In order to be able to run this experiment you have to have in this site liquid argon,
a few part per trillion of the mass of the system.
And this is of course quite a small number. Events are reconstructed with this system.
These events are perfectly identical to the events you can see in the Gargamelle bubble chamber.
You can see here on top an event with a shower, on the bottom an event without a shower itself.
I mean events are contained for instance in this volume here. And when you expand it you can find each and every track.
So it's really a true visual detector which provides you to see everything which happens.
And it will be the basic tool which will be used in order to reach this kind of explanation
for these phenomena to virtual neutrinos.
Now let me also point out to you the key element in this is the fact that in a liquid argon bubble chamber
you can separate extremely nicely the single ionising events. Which is electron events.
From a pi zero event which proves it's 2 Gammas.
And you can see them separated in here. And the separation is absolutely superb.
And anyway these experiments are in fact the only in this way. There is one more point which is important.
We need at least 2 detectors in order to be able to detect this situation and essentially
as I said the length of energy has to be the same, as observed by the pervious anomalies.
You need the image detectors. There are magnetic spectrometers in there. You have to detect both neutrino and antineutrinos.
And you have to collect a very huge number of events.
We are talking about millions of events to study and answer these questions and identify very clearly both the neutrino mu
and neutrino E phenomena. The neutrino facility at CERN is described... is under discussion now, it's described here.
There are 2 detectors available.
One in the near position and one in the far position and they are all liquid argon detectors.
Fermi Lab is also advancing with a similar program. Here you can see 2 liquid argon detectors.
One at very close, 200 metres from the accelerator, the other one at about 700 metres, 800 metres from the accelerator
which is also doing similar program. Now, the important thing of this fact is that these accelerator experiments are not...
are looking at 2 identical detector at different distances. And there is all Monte Carlo calculations are cancelling out.
The neutrino spectra in the near and the far position are closely identical as you can see from this graph
and therefore any deviation from the perfect proportionality.
If you find the perfect proportionality between the 2 positions then the absence of neutrino oscillations
in the neutrino is actually eliminated.
Now the experiments are in fact going to look both at the LSND MiniBooNE of neutrinos, antineutrinos.
They are going to look at the Gellex-Reactor, plus reactor oscillatory disappearance.
An oscillatory disappearance may also be present in neutrino mu signals.
And we have to compare neutrino and antineutrino to see whether there is something associated with CP violation
which is behaving different from neutrino, antineutrinos.
As I said at the beginning in the absence of these anomalies the signal for the detectors
should be a precise copy to each other for all the experimental signatures and without the need of any calculation.
If you see a difference that it is. Now these events are in fact quite remarkably different.
You can see in this graph here the line of the LSND prediction window.
You can see there are various places there, 1, 2, 3, 4 which are possible places in which the event may occur.
And you see from the graph to the left that indeed the various values 1, 2, 3 and 4
correspond to vastly different distributions in the angle distribution observed by the liquid argon TPC.
And by the way also the intrinsic neutrino E background is shown
and you can see from that clearly that in fact the 2, 3 systems are quite remarkable.
This really would be a real definitive experiment of this. There are lots of curves showing that things is quite correct.
I will skip those. And essentially disappearances or anomalies also indicated there.
So the whole system is now coming to a situation which this kind of new experiments will give us all possible solutions.
Now this idea in a few more minutes will allow us to... There is a real revolution in the sterile neutrino searches.
And there are several other experiments besides the one I have described which are being developed from this.
There are radioactive sources by very large number of different experimental proposals throughout the world.
The reactors which are repeating the measurement again, they are stopped by zero beams
which are also being provided by the people.
And there are decaying flight beams like the one we are doing now in CERN or Fermi Lab and others.
All this enormous amount of effort is coming together.
We have here seen now today that there are 114 institutions which are working on this subject.
This is something of the magnitude of an LHC type experiment in terms of a total community of people.
Clearly the population now is working extremely hard in order to find out whether the phenomena are true or not.
Let me briefly use the 2 more minutes I have left to show you some of the other examples.
Here for instance is the example of a reactor which is called Lucifer.
Which is a characteristic of studying the neutrino oscillations. Very close to the target. This is done in France, in CEA.
And it certainly is a device which will improve quite a bit on the measurement of this terra incognita.
The other example here is the Daya Bay in China which I mentioned initially
where they want to produce a very large megacurie type of radioactive source which will produce neutrinos.
Those neutrinos will be produced inside this block
and here there will be detectors around to collect the information in multiple source location to probe sterile oscillations.
And you can see here very large magnitude detector, this is a very large swimming pool with a tremendous amount of equipment
and money and effort involved in this kind of project.
In fact, you can see that the fact that you can observe with a method,
it's a tiny little difference between what it should be with the oscillation and without the oscillation.
So the experiments are not simple. They are difficult and complicated. But the technology is really quite well advanced.
You can see here the graph showing where the sterile neutrino, its appearance should be.
And this is the line which theoretically you predict from the experiment, you can see maybe, maybe not, you will get an answer.
Putting together all these people working on sterile neutrinos you have a complete list of them in this list shows
that in fact there is a very large, rich scientific community which is now working on this subject.
The idea is that sterile neutrino area is this one.
And each and every one of these experiments is introducing some kind of additional information
which in fact will be of great value in order to understand whether this is just something fake
or whether there is a real window opportunity beyond the standard model.
In fact you can see here the various alternatives which are the various types of experimental programs, the vast neutrino program.
I think I will stop here, thank you very, very much for my presentation.