• John
  • Felde
  • University of Maryland
  • USA

Latest Posts

  • USLHC
  • USLHC
  • USA

  • James
  • Doherty
  • Open University
  • United Kingdom

Latest Posts

  • Andrea
  • Signori
  • Nikhef
  • Netherlands

Latest Posts

  • CERN
  • Geneva
  • Switzerland

Latest Posts

  • Aidan
  • Randle-Conde
  • Université Libre de Bruxelles
  • Belgium

Latest Posts

  • TRIUMF
  • Vancouver, BC
  • Canada

Latest Posts

  • Laura
  • Gladstone
  • MIT
  • USA

Latest Posts

  • Steven
  • Goldfarb
  • University of Michigan

Latest Posts

  • Fermilab
  • Batavia, IL
  • USA

Latest Posts

  • Seth
  • Zenz
  • Imperial College London
  • UK

Latest Posts

  • Nhan
  • Tran
  • Fermilab
  • USA

Latest Posts

  • Alex
  • Millar
  • University of Melbourne
  • Australia

Latest Posts

  • Ken
  • Bloom
  • USLHC
  • USA

Latest Posts


Warning: file_put_contents(/srv/bindings/215f6720ac674a2d94a96e55caf4a892/code/wp-content/uploads/cache.dat): failed to open stream: No such file or directory in /home/customer/www/quantumdiaries.org/releases/3/web/wp-content/plugins/quantum_diaries_user_pics_header/quantum_diaries_user_pics_header.php on line 170

Archive for May, 2009

Physics Last Month

Sunday, May 31st, 2009

Now that the school year is over, and I’m only working one job instead of two, I have just a little more time on my hands to catch up on things that I’m backlogged on.  One thing that I’m finally getting some traction on is my reading of Physics Today, the monthly magazine published by the American Institute of Physics that is a benefit of membership to any of AIP’s member societies (including the American Physical Society).  It really is a nice publication, and I wish I could keep up with it more, as there is often timely news in there that is less timely by the time I get to it.  (Don’t even get me started on American Scientist, the high-quality magazine of Sigma Xi, which I also really enjoy for its well-written articles on all scientific fields, which I think I’m now a year behind on.)

Anyhow, I have finally managed to finish Physics April (before the end of May, even!).  I’m glad I got to this particular edition, which was devoted to John Wheeler (1911-2008), a theoretician who spent many years on faculty at Princeton.  I had certainly heard of the guy, and definitely had it in the back of my head that he was Richard Feynman’s thesis adviser, and had co-written an important textbook on general relativity.

But the April articles taught me that he was so much more than that!  Wheeler started out in nuclear physics, where he worked with Niels Bohr to develop the liquid-drop model of nuclear physics, and helped develop the atomic and hydrogen bombs.  But in the 1950’s, he had the courage to completely change his field of research, and started working in general relativity.  I had no idea that at the time, GR was considered something of an intellectual backwater.  But he developed many interesting GR concepts, such as the black hole (he invented that famous name too) and the possibility of gravitational waves (which I’ve discussed here before).  And then, still later in life, he made another switch and started exploring issues of quantum measurement, which at the time was considered best left to philosophers.  That too he made into a scientifically rigorous pursuit.  (Philosophy is also rigorous, but not in the same way!)

But all the more amazing is that in the midst of all this, he mentored a very large number of students, many of whom became leaders of the field in their own right.  In forty years at Princeton, he supervised 43 PhD theses and another 43 senior undergraduate theses.  As a professor myself, that’s many more students than I could ever imagine working with, if nothing else because good mentoring can be so time-intensive (and I don’t even claim to be a good mentor, necessarily).  When I read about the likes of Wheeler, I sometimes wonder why I bother to come in to work each day.  But I suppose we all find our little ways to contribute.

Share

端午节纪念的科学家

Sunday, May 31st, 2009

5月28日是端午节,我在厦门出差,深夜才返回北京。

端午节是纪念屈原的节日,也捎带上伍子胥。我的家乡是屈子行吟之地,历来纪念风俗较浓。屈原以香草美人自喻,在《九歌,湘夫人》中有“沅有芷兮澧有兰,思公子兮未敢言”。因此澧水别名兰江,沅江别名芷江。我的家乡澧县很多场所以兰江为名,如兰江桥、兰江公园、兰江商场、兰江剧院等。芷江机场则是抗日战争时盟军远东的第二大军用机场。

端午节的风俗有赛龙舟、吃粽子、挂艾叶菖蒲、用艾蒿水洗澡、喝雄黄酒等。也许是条件限制,最出名的风俗赛龙舟我反而没见过。小时候喝过雄黄酒,用雄黄酒点眉心,后来知道雄黄是有毒的,就不喝了。艾蒿仿佛是包治百病的仙草,我母亲前不久还带来给我女儿泡水喝,治消化不良。

一个诗人,被整个民族几千年来隆重纪念,而且还扩展到了东亚、东南亚许多国家,实在是很了不起的。但是少为人知的是,屈原不仅是伟大的诗人、政治家,也是一名伟大的科学家,其思想深度不亚于比他大40岁的亚里士多德。当然,叫自然哲学家可能更合适一点,反正自然哲学也是物理的别名。他的《天问》前几句是:
曰遂古之初,谁传道之?(译文)请问远古开始之时,谁将此态流传导引?
上下未形,何由考之?    天地尚未成形之前,又从哪里得以产生?
冥昭瞢闇,谁能极之?   明暗不分浑沌一片,谁能探究根本原因?
冯翼惟像,何以识之?   迷迷蒙蒙这种现象,怎么识别将它认清?
明明闇闇,惟时何为?   白天光明夜晚黑暗,究竟它是为何而然?
阴阳三合,何本何化?   阴阳参合而生宇宙,哪是本体哪是演变?
圜则九重,孰营度之?   天的体制传为九重。有谁曾去环绕量度?
惟兹何功,孰初作之?   这是多么大的工程。是谁开始把它建筑?
斡维焉系,天极焉加?   天体轴绳系在哪里?天极不动设在哪里?
八柱何当,东南何亏?   八柱撑天对着何方?东南为何缺损不齐?
九天之际,安放安属?   平面上的九天边际,抵达何处联属何方?
隅隈多有,谁知其数?   边边相交隅角很多,又有谁能知其数量?

现代科学的特征包括实证、理性、同行评议等要素。屈原问“圜则九重,孰营度之?”这是典型的实证主义。“隅隈多有,谁知其数?”还有量化的想法。这与后来的“子曰”或“毛主席教导我们”式的证明就完全不同。由于古文的高度精炼,时间久远,对天问的理解也各不相同。李政道先生在《中国古代的物理与天文》里指出, “九天之际,安放安属?隅隈多有,谁知其数?”是指出了古人“天圆地方”理论的矛盾。如果天是圆的、地是平的,就会相交,成“九天之际”。这相交的边沿是“安放安属”,谁愿意在哪个交界的地方?“隅隈多有,谁知其数?”,边边角角太多,相交显然不合理。因此,天是圆的,地一定也是圆的。我觉得“上下未形,何由考之?”把考翻成产生不太合理,不如直接翻成考证。天地都还未成形,那时候的情形谁看见了,并把它“传道”下来?这是典型的理性思维。当然他不知道光速是有限的,观察离我们百亿光年远的星系,就可以了解百亿年前的宇宙,甚至逼近宇宙诞生之初。

作为伟大的诗人,2300年来同行评议自然汗牛充栋,毋须细说。另类的考证也不少。有人说他不是投泊罗江自杀的,是楚王派船追上他,包粽子扔到江里的。老百姓不敢说,只好用赛龙舟、包粽子等隐喻来揭示事件真相。孙次舟、朱自清、闻一多等人考证屈原是同性恋,是楚王的男宠。还有人考证屈原的家乡不是湖北秭归,是湖南汉寿。作为科学家,似乎没有太多同行来评议。李政道先生评了一回。衣阿华大学的杨炳麟教授在香山科学会议的报告上用“惟兹何功,孰初作之?”来勉励大亚湾实验。大概精研古代典籍的科学家太少了。

Share

Still busy

Friday, May 29th, 2009

Since the detectors were ready for proton collisions last year before the explosion in the LHC forced a long delay for repairs, you might think we have nothing to do but wait right now (for those of us not working on the repairs).  After all, we were ready last year, weren’t we?  Well, yes and no.  I, for one, am busier now than I have been in quite a while.
While we were definitely ready for data last year, we were only expecting to have a short data-taking period before the usual long winter shutdown of the LHC.  So we planned to use the small amount of data during the long shut down to calibrate our detector and prepare for a longer run where we could accumulate enough good data to produce our first results.
After the LHC incident, we instead ran our detector for several months with no beam, and accumulated data about millions and millions of muons traveling through our detector.  And in fact with these data we have been able to do much of the calibration work we had planned to do anyway with the collision data.  So we’ve still been able to do a lot of the calibration we planned to do, although we haven’t been able to do all we could have done with collision data.
We also always have some small parts of our detector which fail and need to be repaired or replaced.  And we also have found that a few things that need to be extremely reliable (such as parts to transmit our data from usually inaccesible places underground to the surface that we rarely have access to for repairs) that we installed last year just weren’t as reliable as they were supposed to be and already need to be replaced with redesigned parts.  So this part of our work also hasn’t changed much with the LHC delay.
Another thing we are working on right now is putting in place software to analyze the first data when we get it.  While we were ready to record data last year, we did not have done all the software tools to analyze it quickly.  If we have collisions this year, we plan to already have in place the tools to analyze that data and have first results ready in a few months.
Finally, we found out a few months ago that next year’s run of the LHC will be at a slightly lower energy than the final design calls for (10 TeV instead of 14 TeV).  This affects us a bit because our simulations were done with the 14TeV energy in mind, so re-doing these simulations at 10TeV is another thing people have been working on.
So we are quite busy, and not just waiting for the LHC folks to finish the repairs.  But whenever the repairs are done, we will be even more ready for the data than last year!

Share
Biometric scan for me!

Biometric scan for me!

Gordon's skillfully taken photo of the ALICE pit

Gordon's skillfully taken photo of the ALICE pit

alicetour6

Another cool photo. Here you can see the "muon arm" of the ALICE detector. Muons have their trajectories bent by one of the largest warm dipole magnets in the world, and they deposit tiny amounts of energy in the detectors

Wow. Look at that. Let's take a photo :-)

Wow. Look at that. Let's take a photo 🙂

Me in front of ALICE. I was asked to pose as cheesily as possible. I think I did well!

Me in front of ALICE. I was asked to pose as cheesily as possible. I think I did well!

My lovely boyfriend is coming to visit me for the weekend, so I won’t be blogging for the next couple of days. However, I thought I would just post a few photos before I go and get him from the airport. These were taken last week when I took a handful of PhD students plus one postdoc to explore the ALICE detector. Working on CERN experiments themselves, my friends out here are more familiar with this sort of thing than the usual “visitors”, so I was rather surprised to see how many of them wanted to see ALICE. I can only take 7 at a time on my own (no more will fit in the lift!) so I am hoping for space to take another group soon. For many UK-based students and postdocs, ALICE is the mysterious fourth element – they know it is there but have never seen it, because who would show it to them? Of course, I jumped at the opportunity to show off our great detector! It was rather a pain getting through the security doors and biometric scan, but all that effort was worth it. It struck me, once we reached the bottom 50 metres underground, that no matter who the audience, everyone reacts the same when they see detectors like this. My mind was cast back to all the various kinds of people I have given tours to, and to when I saw it for the first time myself. It doesn’t matter whether they know nothing about it, have seen it before, or know it rather close to inside out. Everyone, old and young, scientist or not, for it or against it, immediately feels the overwhelming awe of the acheivement reflected in it, and has the same knee-jerk reaction. They get out their camera. “I am not forgetting this!” Thanks to Gordon Ball and Sara Traynor for the photos. 🙂

Share

Visiting Nagoya university.

Thursday, May 28th, 2009

Last Tuesday, I have visited Nagoya university, to give a talk at GCOE colloquium. The talk was on cosmic superstrings, which I have been working on for more than 5 years. I hope I could deliver my feeling that in fact this fascinating possibility to find superstrings in the sky. The break-through work by Copeland, Myers and Polchinski revived the possibility from the 1985 Witten’s work — It would be wondeful if one can see the macroscopic gigantic superstring/D-brane in the sky! I am rather involved with purely theoretical aspects of this problem, the reconnection of colliding strings. The reconnection probability of the cosmic strings, whatever the identity of them is, is in fact relevant for any observation of them. Interestingly, this physics is related to tachyon condensation in Sen’s conjecture on D-brane annihilation.  Field theory strings appear not only in cosmology but also in condensed matter theory and even in low energy QCD and high density QCD : and they are all realized in a certain limit by a low energy limit of D-brane configurations, that is intriguing.

I wanted to ask a question to a collegue there, how GUTs and cosmic strings are seriously unified. In fact, there is an interesting paper which states that, under some assumptions, viable SUSY GUTs should support existence of cosmic strings. I liked to know how viable the assupmtions are. At the dinner after the talk, I could enjoy an opinion by the person who works on GUTs, and I am very satisfied. Well, long time ago, monopoles are one of the serious identifier of GUTs, and nowadays, after we have seen WMAP data coninciding with inflationary scenario of the universe,  I think we can say that cosmic strings are at the same stage, or rather to say, we need to add cosmic strings as serious ones for GUT study. I really hope that some gravitational wave bursts may be observed in the near future.

This morning, in a train to commute to my office, I found a tiny but new idea on my project. It was really a happy moment. I was about to miss my station to get off. Sometimes it is good to be confined in a crowded train, since you cannot read any paper, you cannot calculate on papers, you cannot do any other things, than just thinking. Every day I commute to my office by train for about one hour, and I feel that it is good for my physics. This morning was evidence for the statement —  or maybe just a justification for my statement which was made not to face my reality to spend two hours in trains everyday….

Share

Proton and electron

Thursday, May 28th, 2009

We still play with PDG site. Let’s see the property of proton. Please click “Baryon” after “Particle Listing” to enter the world of baryons, which are the family of three-quarks bound states. You will click “p” for proton from “N (Nucleon) baryons” to get a PDF file on proton.

Again, a lot of properties of proton are reported. Let’s focus on the value of the neutrality of matter;

(qp + qe )/ e < 1.0 x 10-21.

of which result was got from observation on neutrality of the sulfur hexafluoride, SF6 (Ref. Physical Review A (1973) 1224).

We can see the difference of absolute value of charges between proton and electron is less than 10-21! In other words, in such a precision, the absolute charges of proton and electron are identical. Of course, atoms should have neutrality, but interesting point is the size or level of neutrality.

Proton is constructed of 2 up-quarks and one down-quark .The standard theory assumes up-quark has +2/3 charge, down-quark has -1/3 charge in the unit of the absolute charge of electron. Of course electron is assumed to have -1 charge.

It is, however, just assumption,then ,as usual, experiments have been performed to check.

This assumption has no theoretical bases, the following becomes a question; why absolute values of electron and proton charges have the same value. This is one of reasons to go to the beyond the standard theory or the grand-unified theory (GUT), in which electron and quarks should have reason for their charge.

In addition, we have another necessity for the relation of -1, +2/3, -1/3 among electron, up-quark and down-quark. You may have heard about the word, ‘generation’. Usually it is explained that electron-neutrino, electron, up-quark and down-quark form the 1st generation, muon, muon-neutrino, muon, charm-quark and strange-quark do the 2nd one, and finally tau- neutrino, tau, top-quark and bottom-quark do the third one.

The predictable theory must have such a group. You can make summation of the total charge in each generation: electron-neutrino has 0, electron has -1, up-quark has +2/3, but there are three types up-quarks, red up-quark, green up-quark and blue up-quark, then the charge from up-quark in total is +2/3×3=+2. Also there are three types of down-quark, then -1/3×3=-1. As a result, the total charge of each generation is 0-1+2-1=0!!

I said “predictable theory”. If the sum of charge in each generation differs from 0, then that theory loses the predictability, i.e., it just gives us the infinite probability of the reaction, which has no meaning at all.

That’s why the result on the value of the neutrality of matter is important and this is unknow part of the structure of nature.

もう少しPDGで遊んでみます。今度は陽子について見てみましょう。”Particle Listing”から”Baryon”をクリックして3つのクォークからなるバリオン粒子の世界に入ってみます。で、”N (Nucleon) baryons”から陽子(proton)を意味する”p”をクリックすると、陽子に関する測定値が書いてあるPDFファイルが開きます。

ここでは、”the value of the neutrality of matter”(物質の電荷の中性さの度合い)に注目してみます。;

(qp + qe)/e < 1.0 x 10-21.

これは六フッ化硫黄ガスを使ってその中性度を測った実験からの結果です。(論文はPhysical Review A (1973) 1224です。)

電子と陽子の電荷の絶対値の差は10-21以下の違いという結果です。逆に言うと、電子と陽電子の電荷の絶対値はこの精度までまったく同じといってよいということです。御存知のように、陽子は素粒子ではなく、2つのアップクォークとひとつのダウンクォークからできています。標準理論では、アップクォークは電子の電荷量の絶対値を基準にして、+2/3の電荷を持っており、ダウンクォークは–1/3です。もちろん電子は–1.

しかし、これは理論的な仮定なので、例によって実験が行われてチェックされるというわけです。仮定と申しましたが、それは結局、明確な理由を想定していないことと同じです。クォークが組み合わさった陽子と電子がたまたま同じ電荷で、逆の符号を持っていて原子を構成して驚くべき精度で中性になっている。何故由来の違う電子とクォークでそんなことが起きているのか?これに答えたいとして考えられたのが、大統一理論(GUT)です。

もともと原子が中性なのだから、そういうものでしょう、とも言えるのですが、実はこの驚くべき一致が理論の根本を握っているという事実があります。問題を整理すると、何故、電子、アップクォーク、ダウンクォークの電荷が-1,+2/3,-1/3という関係にあるのか?

ということですが、実はこれが「世代」という考え方に関係があります。よく素粒子の説明で「世代」という言葉がでてきます。電子ニュートリノ、電子、アップクォーク、ダウンクォークで組を作っていて、それを「第1世代」と呼びます。地球上の物質はほとんど、この世代でできています。加速器などで、エネルギーをあげると、もっと重い素粒子が組みを作っていることがわかり、ミューオンニュートリノ、ミューオン、チャームクォーク、ストレンジクォークです。それが「第2世代」。もっとエネルギーをあげると見えてきたのが、「第3世代」で、タウニュートリノ、タウ、トップクォーク、ダウンクォークです。

「組をつくる」とはどういうことでしょう?それが、組毎の電荷の和と関係があります。たとえば、「第1世代」の電荷は、電子ニュートリノは0、電子は-1、アップクォークは+2/3、でも実はアップクォークは3つ存在して、赤アップクォーク、緑アップクォーク、青アップクォークなので、3倍になり、+2/3×3=2となります。同じようにダウンクォークも赤・緑・青の3種が存在するので、-1/3×3=-1です。それで第1世代の電荷を全て足すと、0-1+2-1=0、となり、0になります。

組になっている素粒子の電荷の和が厳密に0になっていないと、その理論で何か詳しい計算をしたとき、たとえば素粒子反応の確率を計算すると、答えは無限大ということになってしまうことがわかっています。これはつまりその理論では何も現象を説明することができないことを意味します。電子とクォークの電荷の関係がきっちりと合っていないと、理論が構成できない。

こういったわけで、原子の中性度というのは、理論を作るうえで大変重要な性質になっています。電子と陽子という全く異なる起源を持つ素粒子にそんな厳密な関係が要求されているということには何か意味があるのだろうと考え、それが大統一理論を作る大きな動機のひとつとなっています。

Share

The past couple of weeks have been busy as usual. Work is always busy, of course, but the weekends have been packed as well. Last weekend was the Memorial Day holiday so I took the train down to St. Louis to visit some family. Yep, that’s right, the train. Its no secret that the inter-city train system in the US pales in comparison to its European counterpart, but fortunately Amtrak is still around serving major cities.

St. Louis Arch from my train seat

St. Louis Arch from my train seat

Amtrak train car en route to St. Louis

Amtrak train car en route to St. Louis

The week before, my father didn’t tell me what it was about, but he let on that he was super excited to ask me about something when he saw me. So my last Quantum Diaries post I mentioned was inspired by a 6th grader. Well, I guess this one is inspired by a 60 year old, because the question my dad could not wait to ask me, that had him practically giddy with excitement, was, “What is antimatter?” Guess what. My parents saw Angels and Demons last week!

Fortunately, I was well prepared to answer my father’s question, as I had just attended Marcela Carena’s public lecture last Thursday at Fermilab (here’s the full video stream of the event). As others have mentioned in several places, public lectures were organized around the country to coincide with the release of the film in order to answer just this question being asked by my dad and others like him.

Ramsey Auditorium at Fermilab at the start of the Angels and Demons Antimatter lecture last Thursday

Ramsey Auditorium at Fermilab at the start of the Angels and Demons Antimatter lecture last Thursday

The event at Fermilab was a great success with a packed Ramsey Auditorium and a fun-filled and informative lecture from Marcela. She began by welcoming the audience to the biggest antimatter factory in the world, Fermilab! which pretty much answered the first question on many people’s minds, “Is antimatter even real?”

The term ‘antimatter’ refers to otherwise normal particles, but whose various quantum properties are all reversed from their normal matter counterparts.  The most obvious and most important of these is electric charge.  So an antielectron is just like the regular electron except it has positive charge (hence, we call it the positron).  An antiquark is just like a regular quark except its charge is opposite. And a regular ol’ proton is made of three quarks which add up to positive one charge (up+up+down = 2/3Q + 2/3Q – 1/3Q = +1Q) and an antiproton is made up of the three corresonding antiquarks (antiup+antiup+antidown = -2/3Q – 2/3Q + 1/3Q = -1Q).  Its sorta just that simple. In principle, you can take this logic further. Just like a proton and electron bound together makes hydrogen, an antiproton and positron bound would make antihydrogen. 6 antiprotons, 6 antineutrons, and 6 positrons would make anticarbon, and so on. I suppose enough antiwood and antiglue could be assembled into an antichair for an antiperson to sit on. (incidentally, antihydrogen is as far as we have gotten in the science laboratory and they managed to make just 9 antihydrogen atoms each lasting a fraction of a second).

What the book and movie exploit in the story is the rather thrilling fact that when a bit of matter meets its antimatter counterpart, !PUFF!, they annihilate into a tiny burst of energy.  Here at Fermilab we are constantly creating antiprotons to push into our particle accelerators and send on a collision course with a bunch of regular protons moving in the opposite direction. When they collide, !PUFF!, a tiny burst of energy (Okay, so you can add energy to the annihilation effect if the particles are moving when they collide. Most of the energy here is actually from the protons and antiprotons tremendous velocities, 99.9999 percent of the speed of light in a vacuum or about the speed of light – 700 mph, which is why we work so hard to get them going so fast).  Einstein’s famous equation tells us that this energy E can convert into mass since E = mc^2.  This mass is the particles we see and study in our detectors.

Marcela Carena welcoming the audience to the largest antimatter factory in the world!

Marcela Carena welcoming the audience to the largest antimatter factory in the world!

So what is the difference between these matter/antimatter collisions at Fermilab and the ones in the movie which are capable of releasing enough energy to destroy multiple square miles of buildings in Rome? Quantity. In the movie they use 1/4 of a gram of antimatter as a weapon. It turns out this modest enough sounding number is an incredible amount of antimatter! Perhaps the most fun fact in Marcela’s talk last week: in the entire history of Fermilab running the antiproton source for several decades, 24 hours a day, 7 days a week, we have produced only about 2 billionths of one gram of antiprotons! Instead of a huge explosion you might be able to power a light bulb for a few moments.

Another important difference between the movie and real life antimatter is containment and storage. Of the 2 billionths of a gram created over the decades at the Lab, none of it is still around. It all harmlessly collided with regular matter and !PUFF! is gone – most of it in the center of our particle detectors. But even when it didn’t, to an antiproton, the world just so happens to be made of a huge amount of very dangerous regular matter!

Which brings me to one of the really exciting open questions in particle physics research today. Where in the world did all the antimatter go? Physicists believe strongly that matter and antimatter would have been produced in symmetric, equal amounts in the earliest moments of the Universe. All of our theories and experimental results point to this conclusion. Yet here we are, safely living in a matter dominated Universe with no threat of being annihilated by stray antimatter. It could have been different. We could all be made of positively charged electrons circling around negatively charged protons. If it were that way we wouldn’t know the difference. It seems even more likely that all of the intense energy in the early moments after the Big Bang would have created matter and antimatter in equal numbers which immediately would have annihilated against itself back into intense energy – but then we wouldn’t be here today to blog about it, so we know that’s not how it went down.

Instead, something in the way the Universe works at the most basic level prefers negative electrons and positive protons (matter). Some asymmetry must exist between the opposing forms such that matter ultimately won out and was able to form the Universe we inhabit. Experiments have actually provided clues, but revealed nothing strong enough to have let matter win out totally as it seems to have done. But where is always the last place we look? Why, among the elusive neutrinos, of course.

It turns out this is the Holy Grail of modern neutrino physics research. It is possible that neutrinos violate the matter/antimatter symmetry in such a way as to explain the Universe that we live in. And the next generation of huge experiments which will send intense beams of neutrinos 100’s of miles through the Earth hope to take a peak at exactly this issue: can neutrinos explain why only one variety of matter has come to dominate our Universe and allowed us the opportunity to be here to ask the question in the first place?

Share

While having a snack before my early evening meeting a few weeks ago, I picked up a copy of the CERN Bulletin to read. One of the articles I read was a column by the CERN Director General called Living in the spotlight, in which he discusses the benefits, pitfalls, and responsibilities of communicating with the public and the media. It occurs to me that now, with the schedule confusions of last fall receding into the past and our new start date still months away, may be a great time to discuss some of these issues in principle, without the backdrop of current events. Director General Heuer writes:

Particle physics has always operated in a fully open and transparent way. It’s in our DNA to do so. Meetings are open to all comers, and it is important that we continue to foster such a culture of transparency. Nevertheless, we need to be aware that we are much more in the public spotlight than ever before.

We have to be aware that when we are speaking to colleagues in open meetings, giving stories to our home institutions’ internal publications, or writing messages to the CERN community in the Bulletin, the eyes of the world are on us. That doesn’t mean that we should be less candid than we’ve been in the past, but it does imply a greater degree of responsibility in the way we communicate. We must be sure that what we are saying avoids any kind of particle physics ‘shorthand’ that could be misinterpreted, and that results are not communicated until they have passed normal internal peer review procedures.

I agree completely with Dr. Heuer.  Our collective scientific effort benefits from communicating information openly, and particle physicists have long been pioneers in developing systems for quick global communication of our results.  But in a time of increased (and extremely welcome) public interest in our work, we should take some care in the way we express ourselves.  The question is not what we can talk about in public; we can talk about almost everything. Rather, the question is: what are the rare exceptions to that rule?

The policies of the ATLAS experiment, which I work on, specify two things that collaboration members can’t talk about in public fora.  First, we can’t reveal experimental results in progress.  The reason most often cited for this is that we want to be sure of our answers before we present them publicly, which is extremely important, but personally I think that there’s also an issue of giving credit where credit is due.  Internally, there are many people working on many things that will contribute to a final experimental measurement; there may be multiple parallel analyses that will later be merged, and there are many lower-level efforts that will contribute to any given analysis.  I think it’s important to acknowledge that no ATLAS result will ever be the work of a single person, and it’s important to present our collective discoveries in a way that’s acceptable to all the contributors.  In practice, this means a fairly long process for paper approval and an author list that runs to about ten pages, but that’s the best system we’ve got.

The other limitation in the ATLAS policy on public communication is that we can’t talk about other peoples’ private comments or remarks in internal meetings.  This is simply a matter of general courtesy; our work would be pretty unpleasant if anything we said or did might show up in a public forum.  So as great as it would be to make a blog entry out of an entertaining story about my advisor, I can’t.  In fact, I cannot publicly confirm or deny that there are any entertaining stories about my advisor at all.

Although I’m officially bound only by the rules of my experiment, I believe that there are broader reasons to be careful about public comments.  We want to give an accurate sense of what our work is like, and an accurate impression of our present understanding of how the universe works.  (For some audiences, that actually means emphasizing clarity over detailed accuracy, but that’s a question of tactics rather than strategy.)   We should also extend basic politeness to colleagues in a broader sense than simply our own experiments; people on other projects and at other labs deserve the same respect we give our coworkers.

I would even say it’s appropriate to take care to portray particle physics and its institutions in a positive light — but I need to be clear about the reasons for, and the limits of, that statement.  I try, in what I say publicly, to explain the importance that I see and the excitement that I feel about the work I’m a part of; in other words, I want to portray it in a positive light because I see it in a positive light.  But when mistakes are made or problems arise, the overriding public interest and the ultimate interest of the field is in an accurate portrayal of how things are going.  We should be willing to publicly discuss problems and give constructive criticism.  Such discussions help us improve, and only if we’re willing to have them do the ordinarily positive things we say become believable and useful to all of you out there.

Share

Thunder strikes

Tuesday, May 26th, 2009
A thunderstorm, seen from the relative safety of the subway stop in Garching.

A thunderstorm, seen from the relative safety of the subway stop in Garching.

Ok, it is really summer now. After some hot days, today southern Germany was hit by massive thunderstorms. Luckily I saw it coming, right after a colloquium talk at the MPI for Physics, so I made it in time to the subway. However, once I got home to Garching, things were really bad: Several inches of water on the streets, rain pouring down, lightning and thunder everywhere. So here I was, trapped in the subway station, waiting for things to get better. Well, at least I tried to take a picture with my mobile phone. Admittedly, it does not look quite as bad as it felt right then and there, but now, dry again, I’m really looking forward to summer.

Share

Just a nice little quote for now. On friday I met Prof. Johann Rafelski, theoretical physicist, Professor of Physics at the University of Arizona since 1987 and co-author of “Hadrons and Quark Gluon Plasma” with Jean Letessier, among many other things. He is an inspiring man, and I wanted to take the opportunity to catch him whilst he was at CERN for the day to discuss some of the physics ALICE hopes to do in the coming months. During our discussion, I asked some questions that I had shared with my supervisor regarding the book. My supervisor studied Physics and Philosophy and has an incredible ability to sort through abstract mathematics and pinpoint the meaning in a way which makes sense to me. Rafelski told me something over lunch in response to my questions that really made me smile.

“A philosopher knows how to think. A theorist knows how to manipulate the equations. An experimentalist knows what is possible.”

That is what I am. An experimentalist. To complete my PhD, I will need to find out what, of the many interesting theoretical possibilities regarding my measurement, may be detected in the constraints of our experiment, and to establish what any given possibility will look like. The great thing about collaborative work is that people come together to share in their skills, and as I have said before, it is crucial to the development of science. Those with the expertise to establish theories and try to assess their consequences will be looking to us, the experimentalists, working (for example at the LHC) to use what they can tell us to interpret what is really seen. It feels good to be a cog in the works. 🙂

Share