Pete,
Here's a question that I often think about. There's no doubt that CERN will
reveal a host of interesting findings. Almost certainly a host of new
questions will then emerge. For this, if the past is any guide, a new and
much more powerful accelerator will be necessary. The present one has only
been possible as a joint effort by several countries. The next one might
require funding by the whole world. Even if this were possible, yet another
even more expensive might be necessary. What do CERN scientists think about
this? They must surely be asking this question between themselves.
Keith
At 19:54 20/11/2010 -0800, PeteVincent wrote:
On Sat, 20 Nov 2010, D and N wrote:
> Wow, Pete, way to go! You're in the history books now. Really cool! You
> and your family, no doubt, are very proud.
Well, I must admit I forwarded Makoto's email to my brother and my son.
My contribution to the work was quite small, as I was (as is often
the case) brought in at the last minute to provide extra assistance,
but I was able to solve few little problems which allowed some
detectors to be completed in time to have their experiment run
begin in time (or at all) a few years ago. Those detectors have
been replaced by high resolution silicon strip detectors (same
technology as IC chips) in the latest version of the apparatus.
>
> I thought you were in Japan when the breakthrough occurred--sending
> neutrinos site to site, was it? Lost the email, and a whole slate of
> others when we did a virus scan after installing high speed internet.
I was in Japan in September, but the Japan project - the T2K neutrino
experiment - is what I was working on over the last couple of years,
and thus not available to do more work with ALPHA, though they certainly
would have liked to have me aboard. Unfortunately, despite its high
public profile, ALPHA has had a very small funding base compared to
other accelerator physics projects. In fact the work I did for ALPHA
was sort of done in my spare time, in the sense that I was able to
do it only because there was a lull in the activity in the T2K
project.
Now that T2K is underway, I expect I'll only be required to go to
Japan for a couple of weeks per year of systems maintenance, like the
september trip. Meanwhile, I am currently assisting the accelerator
division in developing a new electron beam line, as my group (the
detector facility) is between big projects, while the lab is undertaking
this new development project during a period of fiscal restraint, and
haven't been able to bring in new people. It is an interesting change;
I'm learning all about electron guns and x-ray shielding, and meeting
people I've seen around the site for 20 years, but never worked with
before.
> Thanks for the step by step account of the process. I will reread it, of
> course, but it is clear as I go along. Once I get to the end, the most
> crystalline thing is that the work is mind-bogglingly microscopic.
I think the big thing to take away from the process as a whole is how
the advance of this kind of physical science involves a lot of careful
thinking about what each new step entails, what the experimental data
imply, and how the careful analysis and crosschecking then leads to
interpretations which show the way to the next modification of the
apparatus. The hardware becomes very complex, but each layer is the
result of this development process, and the thread of logic running
through it all enables us to be convinced that we are understanding
the events at these very tiny scales. It is a high refinement of
the process of evolution of technology, the sort of thing that James
Burke's Connections series was about.
Oh, in regards to my puzzlement about the means of shedding energy of
formation, I did some digging in the available online materials and I am
able to infer some hint of what happens. A few things: first, there is
definitely a thermal distribution effect going on - a large number of
Pbars are introduced into the e+ cloud in each cycle, a number of Hbar
atoms are produced, and almost all are immediately lost due to their
energy being too high. Then, some of the Hbar atoms can be formed at
highly excited states; in this case the released energy of formation is
relatively small, as much of it still being held in the bond. A lot of
these high energy states have what we would normally consider to be a
very short half life, in the order of milliseconds, but for this
experiment, that's a long time, so it can be that the creation, storage
and anihilation of the Hbar occurs before this stored energy has time to
be released. Another factor is the large cloud of cold positrons
surrounding the Hbar. In order for the Hbar to form, a three body event
is required wherein a second positron takes energy from the first
positron which is interacting with the Pbar, allowing it to slow enough
to be captured. And finally, once the Hbar has formed, the "surface"
of it presents as a positive charge, and so can interact thermally
with the e+ cloud, which can pull energy from it. Now because of the
mass difference, cold positrons don't cool Hbar atoms much, but it
contributes a bit.
> We'd heard about the Ministry putting the muzzle on scientists round the
> climate change issue. I guess that isn't their only area of concern?
If you are referring to my comment about the news embargo, no that's
just a part of the culture, nothing diabolical. During the SNO
experiment, for example, everyone was keen to hear the results, what
they were discovering about the rates of neutrino detection, over the
years the experiment was running. Several of the team members worked
here, and were around every day, but steadfastly refused to answer any
questions on the data, until the paper was published, whereupon they
held a seminar simultaneous with the publication. Some experiment groups
don't mind releasing preliminary results, depending on the situation,
but in most cases the group wants to poke at and beat on their data
until they're confident that they've understood it, particularly the
possible sources of error, and accounted for everything, before they
release their results to the community, so that there is no ambiguity,
no misunderstandings, and no misinterpretation. Part of this is that
experimentalists seem to feel very uncomfortable when theorists latch
onto preliminary data and use it as inspiration to conjure up new models
which turn out to be futile when later results refute the earlier.
-Pete
>
> Congrats again!
> Natalia
>
> On 11/19/2010 8:50 PM, pete wrote:
>> On Thu, 18 Nov 2010, D and N wrote:
>>
>>> Most of you have probably heard the news out of CERN that hydrogen
>>> anti-matter has finally been /captured /in a container for about a
second.
>>>
>>> The reports have varied, but the mention of the Canadian team, including
>>> physicists from Triumf, rang a bell. Congratulations to your colleagues,
>>> Pete!
>>>
>>> If you could, enlighten us on the real story.
>>>
>>> Natalia
>>
>> Sure. I've been out of the loop with this experiment for a while, and as
>> is common with big impact papers these days, there was a tight embargo
>> on the news until the public announcement. People on authors list gave
>> no hint how well things were progressing. Art Olin managed to sneak a
>> mini-seminar into a regular science division meeting yesterday,
>> simultaneous to the announcement; his talk was scheduled but there was
>> no indication he had anything new to reveal. I would have gone to see
>> what he had to say, anyway, except that it was at 10am. Just as I missed
>> the ALPHA Canada group picture a couple of years ago, which was taken at
>> about 10:15. Oh, well, Makoto emailed me my copy of the paper this
>> morning, and there's my name in the acknowledgements.
>>
>> I haven't seen any of the group around since then, as I have a few
>> questions myself on the details. Basically, as I described last time,
>> the trick to this process is convincing the antihydrogen (Hbar, in
>> physics jargon) to have quite low energy after being formed (equivalent
>> to heat for large numbers of atoms, or simply velocity for numbers down
>> in the double digits or less), so it can be held by the very weak force
>> generated by a strong magnetic field acting on the magnetic dipole of
>> the atom. The paper points out the problems which the initial group had
>> a decade ago (I can't tell if the paper is publically accessible, as we
>> have a blanket site-licence subscription to such websites here) as they
>> were feeding antiprotons (Pbars) into the reaction vessel at a few eV,
>> which was still too energetic to capture.
>>
>> The paper then goes on to describe a trick whereby the Pbars, which are
>> initially collected in a standard charged particle trap, after some
>> clever tricks to remove much of their energy, are gently nudged into
>> oscillating over through a low potential barrier into the region where
>> the antielectrons aka positrons (e+) are held, in a similar trap.
>> Counterintuitively, a "chirping" (frequency dropping) oscillation
>> applied to the field strength in the Pbar trap, across the frequency
>> range corresponding to the oscillation time of the Pbars as they bounce
>> back and forth within the confines of the trap, induces the antiprotons
>> to match the dropping frequency by travelling a little farther in each
>> oscillation, gaining a small amount of energy as they do so. Eventually,
>> in a couple of hundred microseconds, they've acquired sufficient energy
>> to just slip out of the trap, and across into the neighbouring space
>> where the e+ are held.
>>
>> The positrons, of which there are generally more (in this case two
>> million per cycle vs 30,000 Pbars), as they are easier to
>> generate and collect, coming in this case from a radioactive decay
>> source, are much colder than the Pbars, having been cooled by repeatedly
>> allowing the fastest ones to escape their trap in brief intervals,
>> separated by intervals where the remaining particles "rethermalize", ie
>> reforming the upper tail of the statistic distribution of their
>> energies. (It is planned in future to collect more Pbars per instance,
>> so that this trick can be applied to them as well, thus increasing
>> overall production efficiency. This is possible because the collection
>> time can be extended somewhat. The duration for the trapped Hbars can
>> also be extended far beyond the milliseconds of the current specimens,
>> as well, by the way. The short capture time was simply a feature of
>> the proof-of-principle nature of this particular trial.)
>>
>> The trick at this point is for the Pbars and e+ to combine into neutral
>> atoms without zinging off out of the trap (which has now shifted into
>> neutral particle magnetic trap mode). I'm not sure exactly how this
>> part works, as the deionization is highly exothermic. I rather suspect
>> that the reason they can do it is that they are only catching one Hbar
>> for every ten cycles, so there is only one Hbar there at a time. The
>> exothermic nature may only be a problem when there are a large number
>> of atoms each giving off the energy of formation as radiation, which
>> then gets scattered and degraded off the neighbouring atoms, being
>> absorbed as kinetic energy. With only a small number of candidate
>> atoms, the radiation may simply escape to deposit its heat in the
>> containment vessel instead. The other possibility is that there is
>> a considerable amount of Hbar being formed in each cycle, with all
>> the atoms initially acquiring sufficient energy to escape, but that
>> they then thermalize, off each other, before escaping, so that one in
>> ten times one of them is knocked just the right way to leave it with
>> a low velocity relative to the lab frame, and thus it gets snagged by
>> the trap.
>>
>> I will get this cleared up the next time I see one of the authors
>> wandering about, maybe next week.
>>
>> -Pete
>>
At 19:54 20/11/2010 -0800, you wrote:
On Sat, 20 Nov 2010, D and N wrote:
> Wow, Pete, way to go! You're in the history books now. Really cool! You
> and your family, no doubt, are very proud.
Well, I must admit I forwarded Makoto's email to my brother and my son.
My contribution to the work was quite small, as I was (as is often
the case) brought in at the last minute to provide extra assistance,
but I was able to solve few little problems which allowed some
detectors to be completed in time to have their experiment run
begin in time (or at all) a few years ago. Those detectors have
been replaced by high resolution silicon strip detectors (same
technology as IC chips) in the latest version of the apparatus.
>
> I thought you were in Japan when the breakthrough occurred--sending
> neutrinos site to site, was it? Lost the email, and a whole slate of
> others when we did a virus scan after installing high speed internet.
I was in Japan in September, but the Japan project - the T2K neutrino
experiment - is what I was working on over the last couple of years,
and thus not available to do more work with ALPHA, though they certainly
would have liked to have me aboard. Unfortunately, despite its high
public profile, ALPHA has had a very small funding base compared to
other accelerator physics projects. In fact the work I did for ALPHA
was sort of done in my spare time, in the sense that I was able to
do it only because there was a lull in the activity in the T2K
project.
Now that T2K is underway, I expect I'll only be required to go to
Japan for a couple of weeks per year of systems maintenance, like the
september trip. Meanwhile, I am currently assisting the accelerator
division in developing a new electron beam line, as my group (the
detector facility) is between big projects, while the lab is undertaking
this new development project during a period of fiscal restraint, and
haven't been able to bring in new people. It is an interesting change;
I'm learning all about electron guns and x-ray shielding, and meeting
people I've seen around the site for 20 years, but never worked with
before.
> Thanks for the step by step account of the process. I will reread it, of
> course, but it is clear as I go along. Once I get to the end, the most
> crystalline thing is that the work is mind-bogglingly microscopic.
I think the big thing to take away from the process as a whole is how
the advance of this kind of physical science involves a lot of careful
thinking about what each new step entails, what the experimental data
imply, and how the careful analysis and crosschecking then leads to
interpretations which show the way to the next modification of the
apparatus. The hardware becomes very complex, but each layer is the
result of this development process, and the thread of logic running
through it all enables us to be convinced that we are understanding
the events at these very tiny scales. It is a high refinement of
the process of evolution of technology, the sort of thing that James
Burke's Connections series was about.
Oh, in regards to my puzzlement about the means of shedding energy of
formation, I did some digging in the available online materials and I am
able to infer some hint of what happens. A few things: first, there is
definitely a thermal distribution effect going on - a large number of
Pbars are introduced into the e+ cloud in each cycle, a number of Hbar
atoms are produced, and almost all are immediately lost due to their
energy being too high. Then, some of the Hbar atoms can be formed at
highly excited states; in this case the released energy of formation is
relatively small, as much of it still being held in the bond. A lot of
these high energy states have what we would normally consider to be a
very short half life, in the order of milliseconds, but for this
experiment, that's a long time, so it can be that the creation, storage
and anihilation of the Hbar occurs before this stored energy has time to
be released. Another factor is the large cloud of cold positrons
surrounding the Hbar. In order for the Hbar to form, a three body event
is required wherein a second positron takes energy from the first
positron which is interacting with the Pbar, allowing it to slow enough
to be captured. And finally, once the Hbar has formed, the "surface"
of it presents as a positive charge, and so can interact thermally
with the e+ cloud, which can pull energy from it. Now because of the
mass difference, cold positrons don't cool Hbar atoms much, but it
contributes a bit.
> We'd heard about the Ministry putting the muzzle on scientists round the
> climate change issue. I guess that isn't their only area of concern?
If you are referring to my comment about the news embargo, no that's
just a part of the culture, nothing diabolical. During the SNO
experiment, for example, everyone was keen to hear the results, what
they were discovering about the rates of neutrino detection, over the
years the experiment was running. Several of the team members worked
here, and were around every day, but steadfastly refused to answer any
questions on the data, until the paper was published, whereupon they
held a seminar simultaneous with the publication. Some experiment groups
don't mind releasing preliminary results, depending on the situation,
but in most cases the group wants to poke at and beat on their data
until they're confident that they've understood it, particularly the
possible sources of error, and accounted for everything, before they
release their results to the community, so that there is no ambiguity,
no misunderstandings, and no misinterpretation. Part of this is that
experimentalists seem to feel very uncomfortable when theorists latch
onto preliminary data and use it as inspiration to conjure up new models
which turn out to be futile when later results refute the earlier.
-Pete
>
> Congrats again!
> Natalia
>
> On 11/19/2010 8:50 PM, pete wrote:
>> On Thu, 18 Nov 2010, D and N wrote:
>>
>>> Most of you have probably heard the news out of CERN that hydrogen
>>> anti-matter has finally been /captured /in a container for about a
second.
>>>
>>> The reports have varied, but the mention of the Canadian team, including
>>> physicists from Triumf, rang a bell. Congratulations to your colleagues,
>>> Pete!
>>>
>>> If you could, enlighten us on the real story.
>>>
>>> Natalia
>>
>> Sure. I've been out of the loop with this experiment for a while, and as
>> is common with big impact papers these days, there was a tight embargo
>> on the news until the public announcement. People on authors list gave
>> no hint how well things were progressing. Art Olin managed to sneak a
>> mini-seminar into a regular science division meeting yesterday,
>> simultaneous to the announcement; his talk was scheduled but there was
>> no indication he had anything new to reveal. I would have gone to see
>> what he had to say, anyway, except that it was at 10am. Just as I missed
>> the ALPHA Canada group picture a couple of years ago, which was taken at
>> about 10:15. Oh, well, Makoto emailed me my copy of the paper this
>> morning, and there's my name in the acknowledgements.
>>
>> I haven't seen any of the group around since then, as I have a few
>> questions myself on the details. Basically, as I described last time,
>> the trick to this process is convincing the antihydrogen (Hbar, in
>> physics jargon) to have quite low energy after being formed (equivalent
>> to heat for large numbers of atoms, or simply velocity for numbers down
>> in the double digits or less), so it can be held by the very weak force
>> generated by a strong magnetic field acting on the magnetic dipole of
>> the atom. The paper points out the problems which the initial group had
>> a decade ago (I can't tell if the paper is publically accessible, as we
>> have a blanket site-licence subscription to such websites here) as they
>> were feeding antiprotons (Pbars) into the reaction vessel at a few eV,
>> which was still too energetic to capture.
>>
>> The paper then goes on to describe a trick whereby the Pbars, which are
>> initially collected in a standard charged particle trap, after some
>> clever tricks to remove much of their energy, are gently nudged into
>> oscillating over through a low potential barrier into the region where
>> the antielectrons aka positrons (e+) are held, in a similar trap.
>> Counterintuitively, a "chirping" (frequency dropping) oscillation
>> applied to the field strength in the Pbar trap, across the frequency
>> range corresponding to the oscillation time of the Pbars as they bounce
>> back and forth within the confines of the trap, induces the antiprotons
>> to match the dropping frequency by travelling a little farther in each
>> oscillation, gaining a small amount of energy as they do so. Eventually,
>> in a couple of hundred microseconds, they've acquired sufficient energy
>> to just slip out of the trap, and across into the neighbouring space
>> where the e+ are held.
>>
>> The positrons, of which there are generally more (in this case two
>> million per cycle vs 30,000 Pbars), as they are easier to
>> generate and collect, coming in this case from a radioactive decay
>> source, are much colder than the Pbars, having been cooled by repeatedly
>> allowing the fastest ones to escape their trap in brief intervals,
>> separated by intervals where the remaining particles "rethermalize", ie
>> reforming the upper tail of the statistic distribution of their
>> energies. (It is planned in future to collect more Pbars per instance,
>> so that this trick can be applied to them as well, thus increasing
>> overall production efficiency. This is possible because the collection
>> time can be extended somewhat. The duration for the trapped Hbars can
>> also be extended far beyond the milliseconds of the current specimens,
>> as well, by the way. The short capture time was simply a feature of
>> the proof-of-principle nature of this particular trial.)
>>
>> The trick at this point is for the Pbars and e+ to combine into neutral
>> atoms without zinging off out of the trap (which has now shifted into
>> neutral particle magnetic trap mode). I'm not sure exactly how this
>> part works, as the deionization is highly exothermic. I rather suspect
>> that the reason they can do it is that they are only catching one Hbar
>> for every ten cycles, so there is only one Hbar there at a time. The
>> exothermic nature may only be a problem when there are a large number
>> of atoms each giving off the energy of formation as radiation, which
>> then gets scattered and degraded off the neighbouring atoms, being
>> absorbed as kinetic energy. With only a small number of candidate
>> atoms, the radiation may simply escape to deposit its heat in the
>> containment vessel instead. The other possibility is that there is
>> a considerable amount of Hbar being formed in each cycle, with all
>> the atoms initially acquiring sufficient energy to escape, but that
>> they then thermalize, off each other, before escaping, so that one in
>> ten times one of them is knocked just the right way to leave it with
>> a low velocity relative to the lab frame, and thus it gets snagged by
>> the trap.
>>
>> I will get this cleared up the next time I see one of the authors
>> wandering about, maybe next week.
>>
>> -Pete
>>
>>
>> _______________________________________________
>> Futurework mailing list
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>> https://lists.uwaterloo.ca/mailman/listinfo/futurework
>>
> _______________________________________________
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> https://lists.uwaterloo.ca/mailman/listinfo/futurework
>
>
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Keith Hudson, Saltford, England
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