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Information control from CERN January 27, 2009

Posted by dorigo in news, physics, science.
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A piece by Matthew Chalmers titled “CERN: the view from inside” has appeared yesterday on Physics World’s web site. It is an insightful interview to James Gillies, head of communications at CERN.

The interview focuses mostly on the media coverage of the LHC startup of last September 10th, and the steps that made it a global success, with an estimated exposure of one billion people. The point is made that now “LHC” can be used out of context without problems, but I hope the revenues to science are larger than that.

More interesting to us science bloggers is the description of how information on the September 19th incident was provided by CERN, and the measures that were put in place to prevent unwanted, uncontrolled news from leaking out in blogs and other unauthorized media. The LHC logbook was edited, pictures of the incident were password-protected. I do not think this is too worrysome: the management decided it was the best thing to do under the exceptional circumstances, and I do not blame them for being tight.

The piece ends up discussing the restrictive policy of the lab and its experiments to blogging. The point is made that unconfirmed rumors damage science, but the matter is not really discussed in detail in any way. People keep claiming that discussion of unconfirmed signals is nocuous to Science, but I continue to hear that it is nocuous to their interests. Do director generals want to be the ones releasing important lab information to protect us, or to protect their chair ? Do principal investigators insist that results are released only after a publication is sent to the journal to avoid waves of imprecise physics from being distributed to unarmed citizens, or to increase their exposure when they make an announcement ?

I insist on being naive on this matter. I think that scientific results on basic science do not belong to their discoverers, nor to the experimental collaboration: they, as much as the data they are based upon, belong to the people.

In the Physics World interview, Gillies claims that the lab will act to counter the public discussion of not-yet-confirmed three-sigma effects (the article  mentions this corresponds to a “less than 1% chance for a statistical fluke”, but I guess it was Matthew to get this inaccurate to simplify matters for his numerically-challenged audience -the probability  is actually 0.3%). Well, I think the laboratory will have to be very careful to get down to the level of bloggers: the CERN management seems to talk and think as if blogging was a controllable phenomenon, but believe me, it ain’t. Not until they close the whole internet thing down.

In May 2007 an anonymous comment left in my blog on a large signal of supersymmetric Higgs decays seen by the D0 collaboration in events with four b-quark jets started a runaway phenomenon which ended on the New York Times and on Slate, plus other media around the world. The D0 collaboration was not happy about it, but what could they do ? The answer is simple: nothing. I wonder whether the CERN experiments have aces up their sleeves instead…

Two or three resources for live video September 10, 2008

Posted by dorigo in news, physics, science.
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Thanks to readers of this blog, I can offer a few links to streaming video on LHC that appear to be working:

On a different note, the beam has made a full counter-clockwise turn about half an hour ago. In a while, there will be attempts at circulating in the opposite direction.

CERN under siege September 10, 2008

Posted by dorigo in news, physics, science.
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This morning CERN appears under siege. The management evidently wanted to arise as much interest as possible, and they got what they bargained for. To give you the flavor of the event, as seen from “behind the curtains”:

  • Coming to CERN took half an hour: long queues of cars at the entrances are caused by strict controls of passes by a tripled set of guards on duty. If you are not a user or a registered visitor, abandon the idea of sneaking in.
  • Visitor passes can be obtained at Building 33, which is the Visitors center, hosting also a nice exhibit with videos and other interactive displays. However, today there appears to be a queue and a host of reporters crowding the place. I would advise no attempt at getting a pass there either.
  • CERN made a honest effort to provide streaming video coverage of the event, but they got sucked in the black hole they organized with their own hands. Never underestimate the power of the web: the traffic is so high that there is little chance to see anything streaming but black photons out of the video frame. As for EVO, it does not even allow people to connect to the interface as of now. If you want to try your luck, however, be my guest.
  • The main Auditorium, where a presentation of the events unrolling today is being given, is also completely full, to the point that there are valets diverting the continuous stream of people trying to enter the large theatre to another building (Bldg 40, where the Atlas and CMS experiments have most of their offices), where nothing, however, appears to be going on.
  • The CMS control room is full of “experts”. I was originally scheduled to be on a day shift at the CMS tracker, but yesterday evening I was informed with the other shifters scheduled to attend the various parts of the detector that today’s shifts were taken over by the best crew we could put together. This is quite funny in the case of the CMS tracker, for a simple reason: it is going to be kept OFF today! So those experts will have their hands free to reach for glasses of wine and munchies provided as an exception to the rule. They will also be free to smile at the cameras pointed at them: the CMS control room will see a continuous stream of reporters in scheduled tours.

Maybe I need to explain, in this otherwise useless post, why the CMS tracker, which is the heart of the whole detector -it sits at the very core of the giant machine, and it is the first line of observation for the particles produced by the collisions, providing the most precise input on the trajectories of charged particles- why, I was saying, it will be kept OFF during this first historic day of proton running.

The CMS tracker (see picture on the right) is made of thin (300 microns thick) layers of silicon sensors, shaped in wafers with a side lined with narrow electrodes, spaced a few tens of microns from each other. When the silicon gets polarized by a few hundred volts of electric field, it acts as a solid-state ionization detector: the charged particles leave ions along their track, and the freed electrons drift in the electric field across the silicon to the thin strip-like electrodes, yielding a signal there. About 20,000 electrons are collected in two or three strips every time a particle crosses the 300 microns of silicon.

The scale of the tracker is impressive: there are a dozen layers of silicon sensors, for a total area of about a hundred square meters and several million electronic channels. Despite its huge scale (as far as these precision devices go), it is necessary to protect it from high radiation doses, because it deteriorates with time. Be sure to understand: this is a device that will sit for years at the core of CMS, where protons will hit protons forty million times a second, every time producing hundreds of particles flying in every direction. However, these are “normal” operations. Instead, today we will have protons circulating inside CMS for  the first time, and we cannot yet be sure that their orbit is fully under control. If the beam deviates even half an inch from its orbit in the 27 km ring, the  innermost silicon layers of CMS might be sprayed with a lot of unnecessary radation. This is relatively harmless when the detector is off, while it may damage the sensors if they are polarized with the normal electric field. Past experience (for instance, in CDF) has shown that until one gets a well-trained, stable beam, the silicon has to stay off. In CDF we burned a few sensors in a couple of beam incidents a few years ago, and the procedure to closely monitor the stability of the beam before turning on the silicon has become a standard.

So, the tracker will be OFF. A shifter at the tracker (there are two in each shift) usually sits in front of four screens running a graphical user interface which a child of five could easily operate. The shifter just needs to click a few buttons when they become red, and then click a icon showing a cartoon of Albert Einstein to solve most problems. If the problem persists, a phone call solves it. But today, the experts will be even less busy than that…

I will anyway drive to Point 5, where the CMS control room is, later today, to check how things are going and take a few pictures. But I expect no excitement other than that of observing the excitement of those who know less. A 450 GeV beam of protons will make a few turns around the ring: big deal, that is 6.7% of the design energy, and there will be only a few billions of them, which is orders of magnitude less than what LHC will manage next year. I will be more excited to see our detector light up when the first collisions will start. But for that, we will have to wait one full month.

On the supremacy of US over Europe in HEP July 20, 2008

Posted by dorigo in physics, politics, science.
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I just finished reading a very interesting piece by Donald Perkins (professor of Physics at Oxford University, and author of one of the most appreciated books on particle physics ever written) on he discovery of weak neutral currents. He discusses in detail the events that brought CERN to announce the discovery in 1973, and the ensuing debate following a negative result by the HPWF experiment, operating at Fermilab.

The history of the discovery is complex, so my quick and dirty summary below is going to leave much wanting. I do it anyways because I wish to introduce some considerations on the inferiority complex which plagued CERN in those years.

A paper by Weinberg and Salam in 1967 hypothesized a unification of weak and electromagnetic interaction by postulating the existence of both charged and neutral weak currents. The latter, however, had never been observed, while their effect was predicted to be comparable in size to that of charged currents. Because of that the paper by Weinberg and Salam was basically ignored for four years. In 1971, however, Gerald ‘t Hooft proved that the unified electroweak theory was renormalizable, and things started to change. Physicists started believing in the existence of neutral currents, and set out to actively seek them.

To search for neutral current interactions one could look for neutrino collisions with atomic nuclei. In a charged current interaction, the neutrino would change into a charged lepton -typically a muon, given the composition of neutrino beams saw the predominance of muon neutrinos. In a neutral current, instead, one would not observe any lepton downstream, but just the remnants of the nucleus and other light hadrons. These events were studied with the Gargamelle bubble chamber at CERN, which used a neutrino beam obtained from a 26-GeV proton beam. The typical signal, the appearance of a star of hadronic tracks, could be mocked by neutrons produced upstream, and the difficulty in calculating the rate of those events made the discovery of true neutral current events hard.

Another way one could observe neutral current interactions of neutrinos was through the collision of the neutrino with an electron: from the reaction \nu_\mu e \to \nu_\mu e one would only observe a energetic electron coming out of the blue, with a very small angle from the beam direction. Those events were however very rare, and in 1973 only three were found in more than a million pictures of the bubble chamber at CERN.

At the Bonn conference in August 1973 Gargamelle reported a ratio between neutral and charged current interactions from the neutrino and antineutrino beams of 0.21+-0.03 and 0.45+-0.09, respectively. The different behavior of antineutrinos was expected in the unified electroweak theory, but the results were initially greeted with skepticism, and for a while the CERN experimentalists were under a considerable amount of heat.

The reason was that the Fermilab experiment, which had initially reported (by Rubbia, at the same conference) a value of R=0.29+-0.09 for the mixed effect of neutrino and antineutrino interactions (which were not separable in the wide-band beam of Fermilab), had later claimed (although not published) a result consistent with zero contribution from neutral currents.

Let me now quote Perkins, because I find his account of the situation enlightening:

Today, CERN prides itself on being the world’s leading high-energy physics laboratory. Whether or not this is so, it is clear that 20 years ago [the article by Perkins was written in the nineties -TD], things were quite different […] CERN unfortunately did not have a similar reputation in its physics, and was still recovering from disasters […]. And during the 1960s it had been repeatedly beaten to the ground, for examples, over the discovery of the \Omega^- hyperon, the two types of neutrinos, and CP violation in K^0 decay. All these things could and should have been found first at CERN, with its far greater technical resources, but the Americans had vastly more experience and know-how. Even today, the scoreline in Nobel laureates in high-energy physics (counting from the end of WWII) tells the story: United States 26, Europe 6.

It is important to understand this legacy in inferiority in considering the attitudes at the time of people in CERN over the Gargamelle experiment. When the unpublished (but widely publicized) negative results from the HPWF experiment started to appear in late 1973, the Gargamelle group cane under intense pressure and criticism from the great majority of CERN physicists. […] many people believed that, once again, the American experiments must be right. One senior CERN physicist bet heavily against Gargamelle, staking (and eventually losing) most of the contents of his wine cellar! […] It is indeed a dramatic testimony to the rapidly changing fortunes in the world of high-energy physics that wat was undoubtedly the principal discovery during the first 25 years of the CERN laboratory was to be greeted initially with total disbelief by the vast majority of CERN physicists.

I wonder how the matter is perceived nowadays, fifteen years after the above words were written. In the meantime the top quark has been discovered, B_s mixing has been measured, new baryons have been found: all of that at Fermilab. By contrast, the LEP II experiments have basically been a fiasco, adding little to our knowledge of subnuclear physics except maybe a precise W mass measurement which is going to be surpassed by CDF alone very soon.