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    Guest Post: Giorgio Chiarelli, Tevatron's Silver Wedding
    By Tommaso Dorigo | November 5th 2010 06:58 AM | 31 comments | Print | E-mail | Track Comments
    About Tommaso

    I am an experimental particle physicist working with the CMS experiment at CERN. In my spare time I play chess, abuse the piano, and aim my dobson...

    View Tommaso's Profile
    Giorgio Chiarelli is a particle physicist. His research activity has been based largely at the Fermi laboratory near Chicago, US, at the CDF experiment. In 1994-96 he actively participated in the discovery of the top quark and in the first measurements of that particle's properties. Later, after directing the construction of a part of the new CDF detector, he moved its research interests toward the search for the Higgs boson. Currently he is a INFN research director in Pisa, where he leads the CDF-Pisa group. In the most recent years he dealt with problems connected with the communication of science. Giorgio gladly accepted an invitation from Peppe Liberti and myself to recount the story of the first Tevatron collisions, which happened exactly 25 years ago. You can find an Italian version of this guest post in Peppe's blog.

    Where were you on October 13, 1985?


    Possibly you were not even born! Likely, if nothing special happened to you, you do not remember... Some of you might only remember that the crisis between Italy and US, due to the hijacking of the "Achille Lauro" and the confrontation of the US Delta Force with Italian Carabinieri had just reached its climax.

    Not me. I do remember.


    I was in the CDF Control Room, and as a young physicist of the Collider Detector at Fermilab, that night I was anxiously watching the display of our detector hoping to see the first proton-antiproton collisions at the Tevatron Collider. We had spent the Summer bringing the detector (still incomplete, yet functional) to life and day after day, shift after shift (that is: 8 hours in the control room watching screens and checking numbers on displays that now looks like prehistoric!) waiting to see protons collide with antiprotons. CERN was ahead of us and the
     collider was operational, but their energy (630 GeV in the center of mass) was lower than ours (aming to 2 TeV for summer-fall 1985 we settled for 1.6).


    However hour after hour, shift after shift, day after day we had all being frustrated. Roy Schwitters (our leader) was unhappy, and so all of us down to the youngest like me. We were frustrated and yet we kept our faith and keep working.

    My last shift ended at midnight. I was supposed to go home...and then there were only a few hours of attempts left. By 8 AM the whole 1985 run was to come to an end. The machine had to be shutdown to start the improvements on magnets and of the whole system...I was tired, still something drag me on. One of my co-shifters was Sergio Bertolucci. Now you all know he is the CERN Research Director, he has always been inspirational. Sergio suggested me to stay...we all were going to sleep for good in a few hours anyway.

    I stayed.


    And then, we had our last chance. Last shot for collisions. There were no journalists, no NYT, no televisions, there was no media. But suddenly we saw the first events showing up in our displays! After weeks of beam-gas collisions (that is collisions of protons-more unlikely antiprotons- with residual gas in the otherwise empty beam pipe) it was clear that those splashes of particles were something else.


    The excitement was tremendous. Everybody was looking at screens and printing events. Bob Kephart was also trying to measure (let's say the number of tracks per unit rapidity -a measure of the angle with respect to the beamline) seen by the detector he built (the VTPC, Vertex Time Projection Chamber). The phone started to ring. Suddenly the whole tireness was gone. Everybody came by. Leo Lederman (back then Fermilab Director and not yet Nobel Laureate), Alvin Tollestrup (together with Roy our inspirational leader). Cathy Newman-Holmes came from home with her daughter (I think she was less than two years old) as well as many others who had been working hard for months and years and were willing to share the joy. When the beam (last shot!) was gone, the bubbling came in (it was not forbidden back then).



    Somebody took a shot of Channel 13 (in jargon: the channel where the beam situation was on display on standard TV set) using a Polaroid and pasted it on the CDF logbook (a REAL book, not yet e). Then we all signed that page. You can see it on the right.

    That night, with no google and no media, the Tevatron Collider Physics Programme started and a page in history of physics was written. It is still alive and well, after twentyfive years, and

    I still have several prints of the event display, and a picture of the CDF logbook hanging in my office.

    Comments

    Bonny Bonobo alias Brat
    Thanks Giorgio and Tommaso for this really interesting article. I wondered what you meant when you said
    When the beam (last shot!) was gone, the bubbling came in (it was not forbidden back then).
    Are you talking about bubble chambers or maybe bottles of champagne? After looking up bubble chambers at http://teachers.web.cern.ch/teachers/archiv/hst2000/teaching/resource/bubble/bubble.htm#The%20Bubble I wondered why this bubbling is now forbidden? The CERN teaching materials says that
    Although extinct, bubble chamber pictures are remembered fondly, like dinosaurs. Unlike dinosaurs they provide a direct way of seeing events that are real today.
    Doesn't that make them still a useful cross validation tool for the 3 level trigger computer system and detectors that have now replaced them?
    My article about researchers identifying a potential blue green algae cause & L-Serine treatment for Lou Gehrig's ALS, MND, Parkinsons & Alzheimers is at http://www.science20.com/forums/medicine
    I'm guessing that "bubbly" is what is meant, as in champagne, and that "forbidden" refers to a policy about alchohol in the control room.

    good guess, Tracy!

    Hi Helen,

    > Doesn't that make them still a useful cross validation tool for the 3 level trigger computer system and detectors that have now replaced them?

    For this kind of accelerators, they would be too slow.
    In the time needed to take a picture, several collisions would superimpose.

    Indeed, the last time they were used for a major discovery was in the 70's: the discovery of weak neutral currents by the Gargamelle experiment:
    http://en.wikipedia.org/wiki/Gargamelle
    And this was possible because the rate of events was very small, hence the speed of detector response was not a critical parameter.

    There are still many low-rate signals of interest for particle physics (e.g., whatever involves neutrinos), so you may wonder why bubble chambers are not very popular for that, nowadays.
    The reason is that a bubble chamber is complicated to operate, and the complication grows exponentially with size of the chamber. For example, the precision of momentum measurement demands the trajectory of the tracks not to be disturbed by convective motion in the liquid; just imagine how challenging is to keep a liquid almost perfectly still, everywhere in its volume, when this volume is comparable with a house.
    Gargamelle was already extremely challenging, because of its size.
    And its size was not very large by nowaday's standards: in order to get a chance to discover what still remains to be discovered, the active volumes must be much larger.
    So, in this kind of physics (like neutrino physics) totally tracking detectors are still used, conceptually analogous to bubble chambers, but not bubble chambers.
    But even these conceptually-analogous-to-bubble-chambers detectors are too slow for tracking collisions at a high-rate accelerator like Tevatron; even worse, LHC. In general, we have no way with the current technology to provide the same visual quality of a bubble chamber within a few tens of nanoseconds.

    > What sort of bubble trail would a Higgs Boson make in a bubble chamber I wonder?

    None, because it would decay within ~10^-24 s after its production, which is probably at least 21-22 orders of magnitude faster than the typical time of bubble formation.
    But you would see the trails of its daughters and nieces... That would be cool, indeed.

    dorigo
    Thanks Andrea for the thorough answer - it is so nice when you find your work done quickly and well before you have a chance to start it!
    Cheers,
    T.
    Bonny Bonobo alias Brat
    Thanks Andrea for such a detailed explanation of why these bubble chambers have become redundant and were only useful for detecting low-rate signals, like whatever involves neutrinos.
    Gargamelle was already extremely challenging, because of its size. And its size was not very large by nowaday's standards: in order to get a chance to discover what still remains to be discovered, the active volumes must be much larger. So, in this kind of physics (like neutrino physics) totally tracking detectors are still used, conceptually analogous to bubble chambers, but not bubble chambers.
    What are these totally tracking detectors that are still used today, made from? Presumably they are not the electromagnetic calorimetry detectors that  use the expensive lead tungstate that Tommaso mentions in his 'The First ZZ Event in CMS' article?
    What sort of bubble trail would a Higgs Boson make in a bubble chamber I wonder? None, because it would decay within ~10^-24 s after its production, which is probably at least 21-22 orders of magnitude faster than the typical time of bubble formation.

    But you would see the trails of its daughters and nieces... That would be cool, indeed.

    Could the trails of these daughters and nieces that you would see in the bubble chamber liquid resulting from the brief creation of the Higgs Boson particle be the same WW or ZZ pairs, two Z bosons, Z bosons, pairs of high-momentum muons and four energetic muons that Tommaso also talks about in his 'The First ZZ Event in CMS' article or would they be something else, more like grandaughters or great-nieces or even grandsons? Would a tiny new particle of matter or mass remain in the liquid in any form after being physically created by the so called 'God Particle'?
    So, CMS has seen the first ZZ event in the four-muon decay channel. It is a spectacular event, as you can clearly see with your own eyes: apart from the four muons very little extra particles are produced.
    Sorry if these are stupid questions which reflect my very limited understanding of this subject.

    My article about researchers identifying a potential blue green algae cause & L-Serine treatment for Lou Gehrig's ALS, MND, Parkinsons & Alzheimers is at http://www.science20.com/forums/medicine
    dorigo
    Hi Helen,

    nowadays we use silicon trackers, made of thin slices of silicon crystal, biased with an electric field. As charged tracks pass the 300 microns of silicon they leave behind about 20,000 electron-hole pairs (holes are atoms devoid of an electron). The electrons drift and are collected by narrow electrodes, made of metal implants that run along the silicon layer. CMS has a dozen such layers, so that tracks are reconstructed with very high accuracy.

    The Higgs, the W, the Z, the top quark... all heavy particles have fantastically short lifetimes. They decay where they are created, for even at the speed of light they fail to traverse an atom's width before disintegrating.

    Cheers,
    T.
    Bonny Bonobo alias Brat
    Thanks Tommaso for explaining this, silicon crystals have many amazing properties don't they? So if one did have a bubble chamber hypothetically big enough to physically and tangibly show the decaying daughters and nieces or grandaughters and grandnieces of a Higgs boson which itself has too brief a lifetime to even create a bubble, what would these be called and what would they look like? Does anyone even know?

    I found this photo of a bubble chamber high energy particle detection of a muon pi mu e decay at http://teachers.web.cern.ch/teachers/archiv/HST2005/bubble_chambers/BCwe...

    This picture was taken in the CERN 2m hydrogen bubble chamber. (We think the incoming beam consists of charged kaon  particles at 10 GeV/c.) The little curly electron near the collision point tells us that negative particles turn to the left.

    The track that starts going to the right before looping round is a charged pion. It stops and decays to a charged muon and a muon neutrino. The muon can only receive about 30 MeV/c in this decay and can only travel about 1 cm in hydrogen before it, itself, stops. It then decays into an anti-electron (positron) (which spirals characteristically), an electron neutrino and a muon-antineutrino .



    Somehow this seems a lot easier to understand to me than some of the electronic graphs that we normally see showing the particle collisions and decays.
    My article about researchers identifying a potential blue green algae cause & L-Serine treatment for Lou Gehrig's ALS, MND, Parkinsons & Alzheimers is at http://www.science20.com/forums/medicine
    dorigo
    Very nice picture Helen. Yes, these are easy - there is only one particle decaying into others. Particle physics has made a lot of advancements from these bubble chamber images, so it is not surprising that it is easier to understand those pictures before one can grasp the LHC collisions. In fact, I do show these pictures to my students...

    Cheers,
    T.
    Bonny Bonobo alias Brat
    So with the modern computers that you are now using, are you still able to track one particle decaying into others and then select something like 'bubble chamber photo format' and see a computerized simulation of this path?
    My article about researchers identifying a potential blue green algae cause & L-Serine treatment for Lou Gehrig's ALS, MND, Parkinsons & Alzheimers is at http://www.science20.com/forums/medicine
    dorigo
    Yes, we can do that... See the posts on the Omega b discovery:

    http://dorigo.wordpress.com/2008/09/19/omega-b-the-new-baryon-nailed-by-d0/

    http://www.science20.com/quantum_diaries_survivor/real_discovery_omega_b_released_cdf_today


    But typically we are only interested in the collective property of "hadron jets", streams of particles that betray the kinematics of quarks and gluons. Besides, of course, electrons, muons, photons, neutrinos... Particles that do not decay in the detector.

    Cheers,
    T.
    Bonny Bonobo alias Brat
    Thanks for these links Tommaso, they are really interesting. A couple of questions arose however when reading them. In 2008 you wrote

    Actually, for theorists the thing which is way the most important is the production rate: understanding the production mechanisms is tough. Our current understanding of the mechanisms whereby a energetic collision creates states like the Omega b is still rather sketchy. Quantum chromodynamics, the theory of strong interactions that bind colored quarks in colorless hadrons, can be used to calculate precisely the production rate of b and s quarks only in special cases; for others, some parametrizations are needed…All in all, it is possible to predict, with some degree of uncertainty, how frequently we may obtain those three quarks in the final state; but predicting the probability of their binding into a (bss) triplet requires to understand the action of lower-energy phenomena, and it currently still requires a good deal of black magic. Because of these difficulties, the number of Omega b events produced for a given amount of Tevatron proton-antiproton collisions is an intrinsically interesting quantity.

    Is this still the case?

    And in the other link you said

    If you ask me, the one above is among the sancta sanctorum of Physics Pictures - one of the most beautiful pictures Man has ever taken. A frame which contains strong, electromagnetic, and weak forces all summarized in a firework display of quantum mechanics at work. Simply delightful. What is more, from the curvature of all the tracks left in the bubble chamber, one can measure the mass of all the unstable bodies participating in the reaction! The mass in fact confirmed the hypothesis beautifully. In a future post I will challenge you to make the exercise of computing the Omega mass from the measured four-momenta of the tracks you see in the picture - it is material I discuss during my course of subnuclear physics.

    Did you write that future post, and if so do you have the link please?
    My article about researchers identifying a potential blue green algae cause & L-Serine treatment for Lou Gehrig's ALS, MND, Parkinsons & Alzheimers is at http://www.science20.com/forums/medicine
    Hi Helen,
    no, I did not write it. Sometimes I forget my own ideas...
    I will see what I can do, though.
    Cheers,
    T.

    vongehr
    "even at the speed of light they fail to traverse an atom's width before disintegrating"

    At the speed of light, time dilatation would make sure they survive. What you mean is that they are so heavy that they are too slow to be helped by that effect, and so they succumb to their small half-life time.
    Hi Sascha,
    well, I meant to convey the shortness of their life time with some semi-quantitative statement, but I did not want to bring in time dilation and beta-gamma factors...
    Cheers,
    T.

    Bonny Bonobo alias Brat
    Sorry to be so persistent Andrea, but do you have any idea of what the trails of the daughters and nieces of a Higgs Boson would look like in a bubble chamber? Apart from being very cool of course.


    My article about researchers identifying a potential blue green algae cause & L-Serine treatment for Lou Gehrig's ALS, MND, Parkinsons & Alzheimers is at http://www.science20.com/forums/medicine
    Hi Helen, no problem, I find it an interesting intellectual exercise actually :)
    The SM Higgs boson is neutral, therefore it would be invisible, but let's say that it decays into b and anti-b quarks (which is its expected dominant decay at relatively low mass). Those quarks would hadronize, so the observable particles would be hadrons. Among the possibilities, you could see B+ and B- hadrons, which being charged would leave a trail before decaying.
    Their lifetime is short, just 10^-12 s, but with an appropriate boost this would be dilated by a relativistic factor, making the trail long enough to be in principle visible. Then, being unstable, those hadrons would decay into a handful of other particles.
    So, in conclusion: two short (sub-millimeter) tracks followed by sprays of other particles.
    The two short tracks would be seen as originating from the same point; back to back or not, depending on the motion of the Higgs particle itself.
    Quite a remarkable signature!
    Unfortunately, one thing we know already about Higgs production is that, if it exists, it must be a very low-rate process, hence only very high-rate machines have any chance to observe it.

    Now that I think, there is a counter-example to what I said a couple of comments ago, which could make you happy: the MOEDAL experiment at LHC:
    http://web.me.com/jamespinfold/MoEDAL_site/Welcome.html
    It is a tracking device, although not a bubble chamber.
    It is designed such that highly ionizing particles (as some hypothetical new particles could be) would leave a permanent track in the detector. It would exploit the high rate of LHC (because also these new particles would be rare) and still record a visible track (to be optically analyzed) that can stand out of the huge background.
    The drawback is that this is a very specialized experiment, designed for essentially just one thing. Flexibility demands other kinds of devices (like... the other technologies employed by LHC experiments!)
    I guess that a crucial argument for its approval was its low cost, giving a high reward/risk ratio. This ratio is normally maximized by flexible multi-purpose detectors, although expensive...

    Bonny Bonobo alias Brat
    Thank you very much Andrea for doing this intellectual exercise in response to my question and for providing this link to the MOEDAL experiment and all of the educational literature and presentations there.
    Now that I think, there is a counter-example to what I said a couple of comments ago, which could make you happy: the MOEDAL experiment at LHC: http://web.me.com/jamespinfold/MoEDAL_site/Welcome.html It is a tracking device, although not a bubble chamber.
    You're right this does make me very happy to know that this experiment is being planned.
    The MoEDAL (Monopole and Exotics Detector at the LHC) project is such an experiment. The prime motivation of MoEDAL is to directly search for the Magnetic Monopole or Dyon and other highly ionizing Stable (or pseudo-stable) Massive Particles (SMPs) at the LHC.

    The most obvious possibility for an SMP is that one or more new states exist which carry a new conserved, or almost conserved, global quantum number.  For example, SUSY with R-parity, extra dimensions with KK-parity, and several other models fall into this category.

    The third class of SMP which could be accessed by MoEDAL  has multiple electric charge such as the black hole remnant, or long-lived doubly charged Higgs bosons. 
    My article about researchers identifying a potential blue green algae cause & L-Serine treatment for Lou Gehrig's ALS, MND, Parkinsons & Alzheimers is at http://www.science20.com/forums/medicine
    Hi Helen,
    bubbling from bottles of Champagne. I think that it is now (formally) forbidden to drink on DOE premises unless you have an appropriate authorization to do so..

    Hank
    And yet when you are on shift for an experiment they make you buy food for people?   Modern civilization has it all wrong.
    dorigo
    Good guess  Tracy :) I am sure that's precisely what Giorgio means.
    Cheers,
    T.
    So, it is mentioned that CERN was running its SppS at some 630 GeV and the Tevatron started at 1.6GeV. I am curious to know if there was any difference in the their results due to the increase in the c.m. E?
    Other than reaction cross section, which is affected by the c.m. E, what else can be affected? And what differences were there? I will try to apply the answers to the newly commissioned LHC.

    Hi,
    the difference in energy acts in two ways (at first order)
    1) you have more energy and therefore you can create heavier objects (E=mc**2)
    2) the cross section (i.e. the probability of a given process) to happen increases with available energy.

    dorigo
    Anon, the same processes are produced, but because of the higher energy, the rate of rare processes (those implying the creation of massive bodies) increases strongly, enabling more thorough studies.
    Only if new particles existed with masses unreachable at the lower energy, would one see a qualitative difference in the results, apart from the depth of the investigations.
    Cheers,
    T.
    Thanks Tommaso,

    Based on your answer, then our need for more and more powerful colliders will never end. If we add to this, that linear, lepton, colliders are needed to study "new" particles properties, if any, in their clean environment, then I think the field of particle physics needs huge amount of money. Unless we can find something really interesting, the future of the field of PP is uncertain!
    Am I right?

    dorigo
    There are reasons that make theorists believe the LHC may find new things. If the LHC does not, it will be very hard to believe a new accelerator, three or five times more powerful, can do anything meaningful.

    A linear collider is similarly useful only if the LHC finds new particles whose study is best done in electron-positron collisions.

    Best,
    T.
    Thanks Tommaso,
    That's encouraging indeed! Let's hope we will find some new physics either at the Tevatron or the LHC, otherwise finding a job as particle physicist will be harder than it is now!

    Best,

    You can drink champagne at Fermilab, it's just that you need have an officially approved bartender from food services to serve it. Which multiplies the cost by a LARGE factor...

    dorigo
    That's only if you drink cheap champagne, anon!
    T.
    Hey Giorgio! Thanks for telling that great old story. Our japanese friends also brought sake to the control room, which was delightful, and then we all went to Roy Schwitters house on site when the sun came up and made pancakes!

    David Smith (see my signature in the logbook!)

    Hey David! Thanks for showing up in this blog...You should have been with us last Friday...It was bittersweet (and followed by a lot of bubbling!).