Beam Neutrinos

http://www.hep.shef.ac.uk/cartwright/home/images/neutrino-spectrum.gif

The two plots are the on-axis spectrum and the 2 degree (I think) spectrum.

The energy spectra tells you everything about the angle. For a simple analogy, the neutrinos directly on the axial path of the beam have the highest energy, and the ones off axis have less and less energy. Imagine the beam is a group of cars on a large flat space, and they encounter some debris. The cars that completely miss the debris continue on in a straight line, although at a slightly slower speed because they were afraid to hit the debris. The cars that high the debris and turn a couple of degrees off their original path will slow be slowed a bit more than the cars that hit nothing. In a more extreme case the cars that hit major debris and deflect 90 degrees of path will be significantly slowed down. This is very similar to the way the neutrino beam behaves.

The beam is similar to the car example because the beam starts out as something other than neutrinos. The beam is then smashed into a big block of something (bowler will probably know), and some neutrinos come flying out the other end. The highest energy neutrinos will be right on axis with the original beam, and the energy decreases from there. This effect can be very carefully measured right after the source, and thus characterized.

Later, when the neutrinos are observed in the far detector, this energy level can be measured to confirm its original angle.

The energy spectra tells you everything about the angle. For a simple analogy, the neutrinos directly on the axial path of the beam have the highest energy, and the ones off axis have less and less energy. Imagine the beam is a group of cars on a large flat space, and they encounter some debris. The cars that completely miss the debris continue on in a straight line, although at a slightly slower speed because they were afraid to hit the debris. The cars that high the debris and turn a couple of degrees off their original path will slow be slowed a bit more than the cars that hit nothing. In a more extreme case the cars that hit major debris and deflect 90 degrees of path will be significantly slowed down. This is very similar to the way the neutrino beam behaves.

The beam is similar to the car example because the beam starts out as something other than neutrinos. The beam is then smashed into a big block of something (bowler will probably know), and some neutrinos come flying out the other end. The highest energy neutrinos will be right on axis with the original beam, and the energy decreases from there. This effect can be very carefully measured right after the source, and thus characterized.

Later, when the neutrinos are observed in the far detector, this energy level can be measured to confirm its original angle.

Told you it would be better than mine.

Imagine the beam is a group of cars on a large flat space, and they encounter some debris. The cars that completely miss the debris continue on in a straight line, although at a slightly slower speed because they were afraid to hit the debris. The cars that high the debris and turn a couple of degrees off their original path will slow be slowed a bit more than the cars that hit nothing. In a more extreme case the cars that hit major debris and deflect 90 degrees of path will be significantly slowed down. This is very similar to the way the neutrino beam behaves.

What makes you think that the beams are spreading out because they're running into anything? They would naturally spread out just as the beam from a laser pointer naturally spreads out.

Ergo, since the neutrinos aren't "hitting" anything to spread out one wouldn't expect the energy spectra to be any different.

I think you may have taken the metaphor a little directly. There is some similarity in the maths but the origin is different. The spectrum actually comes from the decay of charged particles used to generate the neutrinos, not from a scattering interaction. Obviously neutrino scattering is negligable,

Ya, that is my bad. Actually what happens is the cars go driving into the field, and the debris consist of rockets. When the cars hit a rocket, the rocket goes whizzing off in roughly the same direction as the car. If the car glaces off the rocket debris, the rocket is only partially activated, and so it goes whizzing off slower than the other rockets.

As for the laser pointer comparison, the neutrino beam is more like a laser, highly focused. If you point a real laser at the moon (in RET at least) you can detect it when it bounces back, and that is 384,403 km away.
Before impacting the target, the original beam is highly focused through a magnetic horn, which results in an extremely narrow beam of particles, which results in an extremely narrow beam of neutrinos:
http://en.wikipedia.org/wiki/Magnetic_horn

How do we know the horn works? Because it has been tested by many experiments:
http://en.wikipedia.org/wiki/List_of_neutrino_experiments

The energy spectra doesn't tell you anything about its angle. Please stop talking nonsense.

I can't believe Bishop has the balls to try and make out he knows more about neutrino experiments than these guys. 

I welcome his arguments. A lot of the underlying physics is analogous to other more common situations. It is all about understanding the geometry of things and how they interact.

ITT: Tom Bishop pwns 'Neutrino Physicists'.

I think you may have taken the metaphor a little directly. There is some similarity in the maths but the origin is different. The spectrum actually comes from the decay of charged particles used to generate the neutrinos, not from a scattering interaction. Obviously neutrino scattering is negligable,

I'm sorry, but how does the energy spectra of the neutrinos change if they're not hitting anything?

Ya, that is my bad. Actually what happens is the cars go driving into the field, and the debris consist of rockets. When the cars hit a rocket, the rocket goes whizzing off in roughly the same direction as the car. If the car glaces off the rocket debris, the rocket is only partially activated, and so it goes whizzing off slower than the other rockets.

I'm not sure what you're trying to say. So are they hitting something or aren't they?

If you're saying that the neutrinos which diverge from the angled path would hitting matter, opposed to the ones on the straight line path, why would that be? Is there not matter along the straight line path to hit?

If the neutrinos are going to be hitting matter any way it goes, straight or angled, how can the "energy spectra" tell us anything at all?

I'm afraid this "energy spectra" thing you made up is not very thought through.

My failure to explain a complex physics phenomenon to you whilst having no information about your physics background or previous experience does not indicate I am making things up. There are many papers on neutrinos experiments that I could point you to, but I imagine you expect me to flesh out the details in this forum regardless.

In the T2K neutrino source, a beam of protons is accelerated to an energy of 50GeV, and are directed to a target area. The protons strike the target and produce positive pions (an many other particles), which are a type of positively charged meson. After the decay target is a magnetic horn that focuses the pions into a very tight beam. In an average of 26ns a pion decays into a muon and a muon neutrino. After the magnetic horn the neutrino beam spreads out due to the different possible angles that the muon neutrino can be emitted as it decays from the pion. Each of these decay angles results in a certain energy spectrum due to the particle momentum and other factors. Page 3 of the following paper contains a graph of the neutrino energy spectra at angles of interest in T2K:
http://www.iop.org/EJ/article/1742-6596/110/8/082023/jpconf8_110_082023.pdf?request-id=229db4bf-e8dd-4ab7-9f0e-0ea620a78d6d

Because T2K is looking for evidence of neutrino oscillations, neutrinos at the 600MeV energy level are desirable, hence the experiment is conducted 2.5 degrees off axis. The energy of the neutrinos observed in the near and far detectors can be measured by the momentum of the particles produced in neutrino collisions.

ITT: Tom Bishop pwns 'Neutrino Physicists'.

I am just glad he finally came to chat. You gave up months ago and adolf einholm forgot where the General discussion boards were.

ITT: Tom Bishop pwns 'Neutrino Physicists'.

I agree that at least he is debating. Reminds of a song, 'You say it best when you say nothing at all'. The idea that the energy that a particle has depends on its angle is not so unusual. The physics of the situation we have here is that a paticle decays into amongst other things a muon neutrino. A particle going in the same direction as the decaying parent will have the most energy. Although this is a decay not a collision, from the perpective of momentum conservation its pretty much the same situation, one particle gives its momentum to another. Rather like if I stirke a snooker ball with a given force it will go fastest if I strike it such that it goes 'forward'. If I strike it so that it goes almost at 90 degrees then it will go significantly slower

ITT: Tom Bishop pwns 'Neutrino Physicists'.

Just to clarify I am not a physicist. I am a mechatronics (mechanical, electrical, computer) engineering student (for the next 3 months anyway). I worked in a high energy research facility for 8 months and had to understand how the project worked in order to help finish the data acquisition system. There are many aspects of neutrino physics that I cannot explain in full mathematical detail, hence I must resort to analogies.

Where is the evidence that the neutrinos being detected are the same as the ones being emitted?

Where is the evidence that the neutrinos being detected are the same as the ones being emitted?

Confidence is built due to the timing of the observations and the energy spectrum.
For timing in K2K identical atomic clocks were synchronized and driven to the two sites. T2K uses GPS timing as it is much cheaper than atomic clocks. The probability of a coincidence solar neutrino strike at both the near and far detectors drops as more neutrino events are observed.

The momentum and direction of the neutrino can be calculated from the interaction geometry. Commonly a muon neutrino will interact with a nucleus in a detector and cause the emission of a muon. This muon will have roughly the same direction as the neutrino and a predictable momentum. The detector is surrounded in a magnetic field, which causes the muon to deflect, and allows its momentum to be measured. There are several other techniques to measure the momentum but that is the basic one.

In T2K the primary axis of the beam is directed 2.5 degrees below the near detector. On axis, the mean neutrino energy is 2GeV, whereas the mean energy 2.5 degrees off axis is 0.6Gev. Most of the near detector is lined up at 2.5 degrees off axis, but the INGRID detector is in a plus shape centered directly on axis with the beam. The INGRID detector can be used to verify that the beam is pointing where it should be, and that the energy spectra is as expected.

The energy spectra is measured again in the far detector Super K. Here the Cherenkov radiation of the interacting neutrino produces a ring of light on the inside of the Super K chamber, which is lined with photomultiplier tubes. Due to the timing and shape of the ring the energy and flavor of the neutrino can be determined.

My failure to explain a complex physics phenomenon to you whilst having no information about your physics background or previous experience does not indicate I am making things up. There are many papers on neutrinos experiments that I could point you to, but I imagine you expect me to flesh out the details in this forum regardless.

You're not being entirely coherent with how this works.

The momentum and direction of the neutrino can be calculated from the interaction geometry. Commonly a muon neutrino will interact with a nucleus in a detector and cause the emission of a muon. This muon will have roughly the same direction as the neutrino and a predictable momentum.

Your explanation now seems to be that the neutrino will hit atoms in a detector like billiard balls and cause muons to be spit out in an opposite direction towards the detector. Igoring the assumption that the muons would be spit out in exactly opposite directions (whereas billiard balls would not), how does the detector distinguish from one muon coming in at one angle and another muon coming in at a similar angle 2 degrees away?

Where is the control? Is this control sensitive enough to distinguish between a couple of degrees?

Would the people involved in this experiment even consider the possibility that the earth is flat and that it's possible for a neutrino following horizontally along the surface of the earth to hit the detector? I doubt they did. And if they were not considering that possibility, I doubt that they would do much in the way of creating controls to rule out the possibility of a flat earth.

In T2K the primary axis of the beam is directed 2.5 degrees below the near detector. On axis, the mean neutrino energy is 2GeV, whereas the mean energy 2.5 degrees off axis is 0.6Gev. Most of the near detector is lined up at 2.5 degrees off axis, but the INGRID detector is in a plus shape centered directly on axis with the beam. The INGRID detector can be used to verify that the beam is pointing where it should be, and that the energy spectra is as expected.

This experiment is occurring extremely close to the earth's surface and it is not conclusive that the neutrinos are passing through the earth.

When shooting the neutrinos two degrees below the horizon line, there does not seem to be a control to rule out the possibility that the neutrinos may be spreading out, as the laser from a laser beam spreads out, and is following along the surface of the earth to the detector. The experimenters, believing to be on a RE two degrees below the horizon, would not even consider this possibility.

Quote from: ERTW on January 29, 2010, 11:26:30 PM

My failure to explain a complex physics phenomenon to you whilst having no information about your physics background or previous experience does not indicate I am making things up. There are many papers on neutrinos experiments that I could point you to, but I imagine you expect me to flesh out the details in this forum regardless.

You're not being entirely coherent with how this works.

Quote

The momentum and direction of the neutrino can be calculated from the interaction geometry. Commonly a muon neutrino will interact with a nucleus in a detector and cause the emission of a muon. This muon will have roughly the same direction as the neutrino and a predictable momentum.

Your explanation now seems to be that the neutrino will hit atoms in a detector like billiard balls and cause muons to be spit out in an opposite direction towards the detector. Igoring the assumption that the muons would be spit out in exactly opposite directions (whereas billiard balls would not), how does the detector distinguish from one muon coming in at one angle and another muon coming in at a similar angle 2 degrees away?

Where is the control? Is this control sensitive enough to distinguish between a couple of degrees?

Would the people involved in this experiment even consider the possibility that the earth is flat and that it's possible for a neutrino following horizontally along the surface of the earth to hit the detector? I doubt they did. And if they were not considering that possibility, I doubt that they would do much in the way of creating controls to rule out the possibility of a flat earth.

Quote

In T2K the primary axis of the beam is directed 2.5 degrees below the near detector. On axis, the mean neutrino energy is 2GeV, whereas the mean energy 2.5 degrees off axis is 0.6Gev. Most of the near detector is lined up at 2.5 degrees off axis, but the INGRID detector is in a plus shape centered directly on axis with the beam. The INGRID detector can be used to verify that the beam is pointing where it should be, and that the energy spectra is as expected.

This experiment is occurring extremely close to the earth's surface and it is not conclusive that the neutrinos are passing through the earth.

When shooting the neutrinos two degrees below the horizon line, there does not seem to be a control to rule out the possibility that the neutrinos may be spreading out, as the laser from a laser beam spreads out, and is following along the surface of the earth to the detector. The experimenters, believing to be on a RE two degrees below the horizon, would not even consider this possibility.

The experiment can easily tell the difference between a couple of degrees. The effects its trying to measure have a far more subtle effect than that. We use detectors very close to measure the energy spectra accurately. This can then be compared to the far detector allowing a confirmation of a number of physical phenomena, including but not limited to the angle of the far detector with respect to the beamline.

If the Earth was not round then these experiments would not work because the difference between the assumed geometry of the Earth and its true geometry would be a much larger effect than the aims of the experiment.

The experiment can easily tell the difference between a couple of degrees.

How?

Where is the control experiment which distinguishes neutrinos from 2 degrees and neutrinos from 0 degrees?

Quote

The experiment can easily tell the difference between a couple of degrees.

How?

Where is the control experiment which distinguishes neutrinos from 2 degrees and neutrinos from 0 degrees?

In T2K the primary axis of the beam is directed 2.5 degrees below the near detector. On axis, the mean neutrino energy is 2GeV, whereas the mean energy 2.5 degrees off axis is 0.6Gev.

Honestly Tom, I'm beginning to think that you are dense enough to absorb neutrinos. 

I don't see any control experiments for those assumptions. I just see figures and nothing to back it up.

How would a neutrino decrease or increase its energy coming in at a slightly different angle?  

Well the position of the detector fixes the angle. I mean the far detector weights 50kton and sits in a mine. It really doesn't move an appreciable amount, so whatever the angle maybe, its fixed. Can we agree on that? I posted a link earlier in this thread to the difference in energy spectrum between the neutrino beam on-axis and the neutrino beam at 2 degrees. So the question is, are we able to distinguish these spectra from each other. The answer is yes, easily. This data for T2K is not available yet because it hasn't been taken. Currently the neutrino beam is being commissioned so is only strong enough to see events a the near detector which ERTW has posted pictures of. However previous long baseline experiments K2K (couple of degrees into the Earth), KamLAND(variable degrees as it used nuclear reactors in different places), CNGS(more than K2K less than MINOS, 4ish) and MINOS(maybe more than 5degrees I think, I forgot its baseline) all have peer reviewed papers on the open acess pre-print server arXiv.

If theres enough demand I may make a version of my thesis theory section with no maths and pretty pictures that people can read if they so desire and I can find the will. That said there are excellent introductions already on arXiv that are better I could write. Theres a review called the non-physicists guide to neutrino oscillations or something that doesn't really require much understanding of tricky physics.

I don't see any control experiments for those assumptions. I just see figures and nothing to back it up.

How would a neutrino decrease or increase its energy coming in at a slightly different angle?  

Lets be honest, I could make the numbers up and I could probably get away with it, unless ERTW rumbles with me. If I don't make them up ill be accused of it anyway. So people can go onto arXiv and find out for themselves, that way someone else gets accused of making it up.

I don't see any control experiments for those assumptions. I just see figures and nothing to back it up.

How would a neutrino decrease or increase its energy coming in at a slightly different angle?  

The INGRID detector is directly on axis with the beam, and as expected it observes less events at angles further off axis. As for the figures graphing neutrino energy spectrum vs angle, they are produced from direct observation near the source. Each of the several dozen neutrino experiments listed earlier was and is interested in this energy spectrum, and hence the measurement has been verified many times. I found several papers relevant to the prediction and measurement of the neutrino energy spectrum, however I need some time to understand it better myself before I can explain it.

Contains a mathematical derivation of part of the energy spectra relationship:
http://www.springerlink.com/content/l07g4j084555m271/fulltext.pdf

Page 10 contains a measurement of the energy spectrum on axis vs 1 degree off axis.
http://nwg.phy.bnl.gov/~diwan/talks/others/chiaki-BNLUCLA05.pdf

Contains detailed results from the SciBar experiment, which makes a more accurate measurement of the neutrino energy spectrum:
http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=01589311

Contains a derivation and observations of neutrino energy spectra emitted from a reletivistic plasma:
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1983A%26A...125..121G&db_key=AST&page_ind=0&plate_select=NO&data_type=GIF&type=SCREEN_GIF&classic=YES

If you have too much time on your hands, here is a 268 page PHD thesis on solar neutrino flux measurements:
http://www.sno.phy.queensu.ca/sno/papers/OrebiGannThesis.pdf

This presentation explains how and why the magnetic horn is used to focus the neutrino beam. Page 27 specifically explains why we would want to measure the beam off axis:
http://www.google.ca/url?sa=t&source=web&ct=res&cd=31&ved=0CAcQFjAAOB4&url=http%3A%2F%2Fwww2.ph.ed.ac.uk%2Fsussp61%2Flectures%2F08_Harris_AcceleratorNeutrinoOscillationPhysics%2FHarris_lecture1.ppt&rct=j&q=neutrino+energy+spectrum+vs+angle&ei=GWhnS7rqPJSusgOI3ID0BA&usg=AFQjCNHrtunWfjRVL_f2wvYBqg8hP_TCzg&sig2=Q7DdIUW2HhTJS76WhrcNVw

Enjoy.

Quote from: Tom Bishop on February 01, 2010, 03:14:59 PM

I don't see any control experiments for those assumptions. I just see figures and nothing to back it up.

How would a neutrino decrease or increase its energy coming in at a slightly different angle?  

Lets be honest, I could make the numbers up and I could probably get away with it, unless ERTW rumbles with me. If I don't make them up ill be accused of it anyway. So people can go onto arXiv and find out for themselves, that way someone else gets accused of making it up.

Rumble Rumble Rumble. And yes, we could always just make up the numbers. That is why its so important that you all help Johannes build a neutrino experiment in his back yard.

The cats and dogs vs. snakes argument isn't valid, because dogs and cats and snakes became the way they are due to the exact same biological process of evolution.  Neutrinos do not necessarily have to behave like photons because they are governed by different processes.  The behavior of photons is governed by electromagnetism (in the standard model, photons are the electromagnetic force carriers), while the behavior of neutrinos is governed largely by the weak force.  However, there is some overlap between the two forces, which is why the unifying electro-weak theory of Glashow, Weinberg, and Salam is needed to derive the energy spectrum of the neutrinos, as the derivation that ERTW posted earlier shows.

This.
Also, this could be useful re-posted here.

I provided a lot of relevant material and explanations on neutrino energy spectrum, so if anyone has any objections other than "you made it up", go ahead.

You should be credited for bumping this thread and keeping it alive. I don't understand how FE'ers can maintain such contradictory realities at once. I can only assume that they believe you are part of the conspiracy or they just choose to ignore the contents of this thread. It is mind boggling.

The trouble is its the only thread on this forum where someone (actually two people) really understand whats going on.