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  1. #41
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    Quote Originally Posted by Jimbo View Post
    You've already sent me a couple Gary, remember? I PMed you next month, and you shipped them off next year. They arrived yesterday.

    James.
    If they are anti-matter, does that mean that they don't matter?

  2. #42
    Junior Member NeitherMightier's Avatar
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    Default Real-Time Evaluation of LHC Hazards

    Has the Large Hadron Collider destroyed the world yet?

    I spent the summers of 2006 and 2007 in Geneva working on LHC electronics, and I'm about to start working here in California on detector prototypes for the planned Super-LHC upgrade. MODERATORS: please censor any anti-particle-physics sentiment, before it spreads and I'm out of a job.

    The most elegant argument for the safety of the LHC goes like this, but with more math:
    The LHC will open a new energy frontier for controlled, laboratory-reproducible collisions. Cosmologicaly speaking, however, they are not really exceptional. Stuff this energetic happens out in space often enough that if it were capable of producing results that we would consider catastrophic were they to occur in a laboratory, our universe would not be as it is.

    Alexander
    Last edited by NeitherMightier; 09-11-2008 at 01:28 AM. Reason: clarifying language

  3. #43
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    Nuclear fusion is safe in the reaches of outer space.

    Having it happen in Geneva may not be as acceptable....

  4. #44
    Know thyself holli4pirating's Avatar
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    Quote Originally Posted by Seraphim View Post
    So how do they create a detector to look for something that they do not know if it even exists?

    Photons-some sort of photonic detector

    Heat- thermal detector

    Higgs boson-????
    Various parts of the detectors work in different ways, and depending on the property to be measured, different aspects of the detector are utilized. For example, the ECAL, which detects and measures the energies of electrons, examines the curvature of the electrons as they move through magnetic fields, to determine their velocity. The direction they curve in tells you about the charge (positive or negative), and the radius of curvature gives information about the velocity. No electrons are able to escape the ECAL, so other layers of the detector (which lie further out) don't have to worry about picking up electrons or getting interference from them.

    In contrast, neutral particles are detected not by catching them, but by not catching them. By employing conservation laws, the total amount of energy and momentum that is produced by the collision, when looking in a given direction, should be zero. If the beam is thought to be traveling along a Z axis (imagine the beam coming right at you with the X axis going to the right and the y axis going up), then the projection of the energies onto the positive and negative sides of the X axis, for example, should be zero. If the result of measured energy or mementum is not zero, then you know there was at least one neutral particle that went through the detector without being picked up.

    This is often callet Met (with the e as a subscript), meaning missing energy transverse to the beam, and it can be used to find nutrinos.

    I don't know if the Higgs will be measured via Met, but that was just an example of how to measure something you don't know exists and can't even "detect."

    Quote Originally Posted by Bruno View Post
    There's a lot of equipment to finetune and calibrate etc. It will be some time before they will be up to the levels at which the higgs boson can possibly be detected.
    One huge part of this calibration is related to Met, as I described above. In any electronics that involve signal amplification (which all detectors do), there is an inherant amount of "noise" generated. This happens because sometimes a non-event will be amplified and, as a result, will look like an event. Another source of errors that is inherent in any detector is inteference or dead spots where cables, cooling elements, and gaps in the detector's layers are. All these elements are necessary in such large detectors. Furthermore, there can only be so many layers of detectors, and sometimes more might make the detectors more accurate but adding more would be impracticle.

    In addition, there are a number of phenomena that arise as a result of the rate of collisions. One, called "pile-up," is where not all the particles from the previous collision have left the detector, and some are read in the following event. There also might be "background;" one form of background occurs when two collisions occur in the same pass, but one is a hard collision (close to head on) and the other is a "scattering collision" (where the particles just come somewhat close). That will not yield a huge amount of particles, but there will be a nocitable result.

    This work was started before construction of the LHC was complete by analyzing simulation data. The simulations were updated to reflect the actual accelerator and detector as changes were made (or found), and the actual software that will be used to analyze real data was used (and it was also being upgraded constantly).

    Quote Originally Posted by Seraphim View Post
    Maybe black holes are the size of a marble?

    Ever measure one?
    The sizes of black holes cannot be measured directly, but they can be measured rather accurately. By examining gravitational lensing and the rate at which gasses are stripped off nearby stars, the sizes and masses of the black holes can be determined (to be more specific, I believe it is acutally the diamater of the event horizon that is detected).


    Quote Originally Posted by Seraphim View Post
    Nuclear fusion is safe in the reaches of outer space.

    Having it happen in Geneva may not be as acceptable....
    This is true, but I think that you might have misread the post. I believe the point of the post you are responding to was that the events that take place within the accelerator all take place safely in outer space and our atmosphere. That is not to say (and does not imply) that anything that happens in outerspace would be safe on earth. Nuclear fusion is a great example. A super nova is another.
    Last edited by holli4pirating; 09-11-2008 at 12:36 AM.

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  6. #45
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    Quote Originally Posted by Bruno View Post
    The interesting is apparently that 2 belgian scientists predicted the higgs boson before higgs. even higgs always admitted this. but his name was published first so it got his name.
    They didn't publish their results in Flemish, did they?

    j

  7. #46
    Junior Member NeitherMightier's Avatar
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    Quote Originally Posted by Seraphim View Post
    Nuclear fusion is safe in the reaches of outer space.

    Having it happen in Geneva may not be as acceptable....
    The outer-space argument applies to the results and events which we can't predict. Where we can predict results, as with proton-proton fusion reactions, we know that if they can happen, they won't happen often or fast enough to be a danger.

    Trust us . . . .

    Alexander

  8. #47
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    Quote Originally Posted by holli4pirating View Post
    Various parts of the detectors work in different ways, and depending on the property to be measured, different aspects of the detector are utilized. For example, the ECAL, which detects and measures the energies of electrons, examines the curvature of the electrons as they move through magnetic fields, to determine their velocity. The direction they curve in tells you about the charge (positive or negative), and the radius of curvature gives information about the velocity. No electrons are able to escape the ECAL, so other layers of the detector (which lie further out) don't have to worry about picking up electrons or getting interference from them.

    In contrast, neutral particles are detected not by catching them, but by not catching them. By employing conservation laws, the total amount of energy and momentum that is produced by the collision, when looking in a given direction, should be zero. If the beam is thought to be traveling along a Z axis (imagine the beam coming right at you with the X axis going to the right and the y axis going up), then the projection of the energies onto the positive and negative sides of the X axis, for example, should be zero. If the result of measured energy or mementum is not zero, then you know there was at least one neutral particle that went through the detector without being picked up.

    This is often callet Met (with the e as a subscript), meaning missing energy transverse to the beam, and it can be used to find nutrinos.

    I don't know if the Higgs will be measured via Met, but that was just an example of how to measure something you don't know exists and can't even "detect."



    One huge part of this calibration is related to Met, as I described above. In any electronics that involve signal amplification (which all detectors do), there is an inherant amount of "noise" generated. This happens because sometimes a non-event will be amplified and, as a result, will look like an event. Another source of errors that is inherent in any detector is inteference or dead spots where cables, cooling elements, and gaps in the detector's layers are. All these elements are necessary in such large detectors. Furthermore, there can only be so many layers of detectors, and sometimes more might make the detectors more accurate but adding more would be impracticle.

    In addition, there are a number of phenomena that arise as a result of the rate of collisions. One, called "pile-up," is where not all the particles from the previous collision have left the detector, and some are read in the following event. There also might be "background;" one form of background occurs when two collisions occur in the same pass, but one is a hard collision (close to head on) and the other is a "scattering collision" (where the particles just come somewhat close). That will not yield a huge amount of particles, but there will be a nocitable result.

    This work was started before construction of the LHC was complete by analyzing simulation data. The simulations were updated to reflect the actual accelerator and detector as changes were made (or found), and the actual software that will be used to analyze real data was used (and it was also being upgraded constantly).



    The sizes of black holes cannot be measured directly, but they can be measured rather accurately. By examining gravitational lensing and the rate at which gasses are stripped off nearby stars, the sizes and masses of the black holes can be determined (to be more specific, I believe it is acutally the diamater of the event horizon that is detected).




    This is true, but I think that you might have misread the post. I believe the point of the post you are responding to was that the events that take place within the accelerator all take place safely in outer space and our atmosphere. That is not to say (and does not imply) that anything that happens in outerspace would be safe on earth. Nuclear fusion is a great example. A super nova is another.
    Thanks Holli4.

    So, they don't detect the higgins thingys (this is the more appropriate terminology, BTW), they just look at what they can detect and back out the data from there.

  9. #48
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    Quote Originally Posted by NeitherMightier View Post
    The outer-space argument applies to the results and events which we can't predict. Where we can predict results, as with proton-proton fusion reactions, we know that if they can happen, they won't happen often or fast enough to be a danger.

    Trust us . . . .

    Alexander
    I was being a wise guy.

    I really don't think anything catastrophic will happen as a result of these experiments, but the scientists saying "well, it's safe enough in outer space...." seemed like a rather poor justification.

  10. #49
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    Another question:

    If you wrap a gerbil or mouse in tin foil, and put it in the LHC, can you accelerate it to near light speed?



    Try this little experiment at home: wrap a potatoe (my target audience spells it like that...) with tin foil, and put it in the microwave and see what happens. Don't worry, the bottom of the Apollo lunar lander sent to the moon was wrapped in foil, so it will probably be safe in your microwave too...

    On your way to Best Buy to get yourself a new microwave, you can ponder why it is that they need 60 jillion dollars for particle physics accelerators...this stuff isn't easy!

  11. #50
    Know thyself holli4pirating's Avatar
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    Quote Originally Posted by Seraphim View Post
    Thanks Holli4.

    So, they don't detect the higgins thingys (this is the more appropriate terminology, BTW), they just look at what they can detect and back out the data from there.
    That's pretty much the idea. Detect what you can through direct means, and figure out indirect ways to see everything else.

    Quote Originally Posted by Seraphim View Post
    Another question:

    If you wrap a gerbil or mouse in tin foil, and put it in the LHC, can you accelerate it to near light speed?
    In short, no. Accelerators use alternating magnetic fields to propel particles. Consider a single particle that is positively charged. If you were to put a negative magnet in front of it, it would move towards the magnet and start to move past it. Before the particle can be pulled back towards the magnet, switch the magnet's charge to positive. Now, instead of pulling the particle back, the magnet will push it further. By doing this repeatedly along a straight line or over and over around a circle, the particles reach high speeds.

    In older accelerators, there would be two D shaped magnets with a small gap in between. The particle, which was charged, would travel in a circular direction, and each time it got to the gap, the charge of the magnets (which was always opposite) would switch. So each time the particles jumped the gap, they would gain some energy, and the circle would widen. At some point, the particle will orbit with the same radius as the magnets, and if the particle is to go any faster, the magnetic field must me made stronger in order to contain the particle.

    In accelerators modern, lots of particles with the same charge travel in bunches. They will try to repel each other, as like charges do, and they must be "focused," or kept in a tight grouping. Other sets of magnets in various arrangements focus the beam as they move along the accelerator.

    You could probably make a table top accelerator that would accelerate macroscopic objects (things you could see), but the objects would have to be magnetic, and they would likely have to be physically in contact with the table.

    It is possible for students at a college level to build cyclotron accelerators that would accelerate ions or electrons, given that they have access to tools, perhaps a machine shop, and can get the parts for it.

    **Sorry for not using the normal quote feature
    Regarding "you can ponder why it is that they need 60 jillion dollars for particle physics accelerators...this stuff isn't easy!"


    Huge amounts of the cost are due to the high tech electronics, magnets, and materials for the detectors, many of which are purpose built and/or developed in order to make the accelerators. In addition, massive computing farms are necessary not only to process and analyze the data, but to select what events to record and actually record them at the rate they are produced. I don't remember the numbers, but even knowing how fast the particles travel, I was totally staggered when I heard the number of raw events (all the events) that occur per second, let alone the number that are filtered out before the meaningful ones are recorded.
    Last edited by holli4pirating; 09-11-2008 at 02:02 AM.

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