## Greek BlogNovember 1, 2010

Posted by dorigo in Blogroll, internet, language, news, personal, physics, science.

I had forgotten to link it from here, but the internet always provides a chance for redemption. So here I go. A couple of months ago I have opened another wordpress blog, where I write on particle physics – in Greek. This is a rather extravagant choice, and I think I need to spend a few words explaining it.

First of all, there is my love of the language, which I have been studying for two years. It is a difficult language to master, due to the interplay of several factors: the different alphabet, the enormous wealth of words, and the rather quick evolution of rules and uses. Maybe because of these challenges, I have found it quite entertaining to get on top of it.

The second reason for writing in Greek is, in fact, that I have yet a lot to learn, and I think that writing about science is a very good exercise, allowing me to find a solution to the translation problems I may encounter if I discuss about my job – physics – in that language.

The third reason is that I think there is no offer whatsoever in the web for a blog about particle physics in Greek (if you know any, let me know). So I might just try to fill that hole myself.

In short, the new blog is an experiment. I do not know, nor can predict, how long it will last; for now, if you know modern Greek please stop by. Below is a list of my recent efforts:

## ICHEP blogJuly 12, 2010

Posted by dorigo in astronomy, Blogroll, cosmology, internet, news, physics, science.

Just one line here to mention that since May there is a new blog out there – a temporary blog that will cover the end of July event in Paris – the International Conference on High Energy Physics -, how we get there, and the aftermath. The effort includes several well-known bloggers in high-energy physics, and is definitely worth following.

You can visit it here.

## Some recent posts you might want to readMarch 6, 2010

Posted by dorigo in Blogroll, internet, news, physics, science.
Tags: , , , , , , , ,

As the less distracted among you know, I have moved my blogging activities to scientific blogging last April. I wish to report here a list of interesting posts I have produced there in the course of the last few months (precisely, since the start of 2010). They are given in reverse chronological order and with zero commentary – come see if you are curious.

## One million hitsJune 29, 2009

Posted by dorigo in Blogroll, internet, news, personal, physics.

While this site has been basically inactive for over two months, it still draws some residual traffic due to google searches and links; so the hit counter has continued to click after April 15th, although at a rate of roughly a third of what it did before.

Today’s news is that we got past the millionth click. Thanks to everybody for your interest in particle physics and in my reports. Please visit www.scientificblogging.com/quantum_diaries_survivor to keep up-to-date with particle physics!

## Physics Highlights – May 2009June 2, 2009

Posted by dorigo in news, physics, science.
Tags: , , , , , , ,

Here is a list of noteworthy pieces I published on my new blog site in May. Those of you who have not yet updated their links to point there might benefit from it…

Four things about four generations -the three families of fermions in the Standard Model could be complemented by a fourth: a recent preprint discusses the possibility.

Fermi and Hess do not confirm a dark matter signal: a discussion of recent measurements of the electron and positron cosmic ray fluxes.

Nit-picking on the Omega_b Discovery: A discussion of the significance of the signal found by DZERO, attributed to a Omega_b particle.

Nit-picking on the Omega_b Baryon -part II: A pseudoexperiments approach to the assessment of the significance of the signal found by DZERO.

The real discovery of the Omega_b released by CDF today: Announcing the observation of the Omega_b by CDF.

CDF versus DZERO: and the winner is…: A comparison of the two “discoveries” of the Omega_b particle.

The Tevatron Higgs limits strenghtened by a new theoretical study: a discussion of a new calculation of Higgs cross sections, showing an increase in the predictions with respect to numbers used by Tevatron experiments.

Citizen Randall: a report of the giving of honorary citizenship in Padova to Lisa Randall.

Hadronic Dibosons seen -next stop: the Higgs: A report of the new observation of WW/WZ/ZZ decays where one of the bosons decays to jet pairs.

## Post summary – April 2009May 1, 2009

Posted by dorigo in astronomy, Blogroll, cosmology, internet, news, personal, physics, science, social life.
Tags: , , , , , , , , , , , ,

As the less distracted among you have already figured out, I have permanently moved my blogging activities to www.scientificblogging.com. The reasons for the move are explained here.

Since I know that this site continues to be visited -because the 1450 posts it contains draw traffic regardless of the inactivity- I am providing here monthly updates of the pieces I write in my new blog here. Below is a list of posts published last month at the new site.

The Large Hadron Collider is Back Together – announcing the replacement of the last LHC magnets

Hera’s Intriguing Top Candidates – a discussion of a recent search for FCNC single top production in ep collisions

Source Code for the Greedy Bump Bias – a do-it-yourself guide to study the bias of bump fitting

Bump Hunting II: the Greedy Bump Bias – the second part of the post about bump hunting, and a discussion of a nagging bias in bump fitting

Rita Levi Montalcini: 100 Years and Still Going Strong – a tribute to Rita Levi Montalcini, Nobel prize for medicine

The Subtle Art of Bump Hunting – Part I – a discussion of some subtleties in the search for new particle signals

Save Children Burnt by Caustic Soda! – an invitation to donate to Emergency!

Gates Foundation to Chat with Bloggers About World Malaria Day – announcing a teleconference with bloggers

Dark Matter: a Critical Assessment of Recent Cosmic Ray Signals – a summary of Marco Cirelli’s illuminating talk at NeuTel 2009

A Fascinating New Higgs Boson Search by the DZERO Experiment – a discussion on a search for tth events recently published by the Tevatron experiment

A Banner Worth a Thousand Words - a comment on my new banner

Confirmed for WCSJ 2009 – my first post on the new site

## !! Moving !!April 15, 2009

Posted by dorigo in news, personal, travel.

Effective today: after forty months of service on wordpress, my blogging activity is moving to scientific blogging, an excellent site which collects many top-notch science writers. As soon as I manage to work it out, I will provide here a widget with links to my posts on that site, and possibly I will keep this site from being reported as mature by making a monthly entry with a link to the most interesting read in the new site. Other necessary adjustments are also in order, fixing some external links etcetera. But really, if you love me, please follow me there now.

I know, I can almost hear some of you complaining about this uncalled-for, unanticipated decision: this has indeed been a quick resolution, and quite un-characteristically the idea has not been submitted in advance here, to make a dry run and hear your opinions on the plan before it became a fact.

So, why am I doing it ? There are several answers to this question, and you may pick the one you like the most.

1) Blogging for me is about reaching as large an audience as possible, because I do conceive it as an educational mission. I have repeatedly explained here that I do not feel guilty for the time I invest on blogging, because my research position does not require me to teach, and I am glad to distribute through the internet some of the knowledge I have had the chance to accumulate through my studies and my job. Now, the target site of this move will increase my reach of potential readers, especially ones that might be interested in particle physics but have so far not realized it is not beyond their understanding capabilities. This by itself is a valuable asset.

2) While this blog has served my large ego extremely well, providing me with surprising opportunities and gratifications over the course of these forty months, I have realized that in its present form its further growth is problematic. Moving to scientificblogging.com will supply fresh air, new ideas, and a possibility to interact more closely with a stimulating crew of writers.

3) The real question is, why not ? I am not losing paternity or rights on my writings, the interface and functionalities at the new site are no worse, the freedom to write what I like is assured to stay unchanged. There are paid ads there, that is true; however, I have decided to trust the owner of the site that it will remain as non-invasive and reasonable as it looks now. As for the slight loss of control that the move entails, there are a couple of things to say also against wordpress itself, for instance the obligatory, auto-generated “possibly related” links that are supplied to every post, or the arbitrary taking down of this site I have experienced due to my failure to delete spam comments.

4) As for money, that is really not the reason. No, really. I will indeed get paid in the new site, but the sum I will earn is not going to change appreciably the depth of my pockets. Rather, I see the higher visibility I am expecting there as a reward, which will possibly help any future endeavour I might be entertaining myself with fantasizing about. Like writing a book.

So, it is your turn now to speak up and tell me what you think of this. I know, nobody likes change. But change is a fundamental ingredient of life, and specifically, one associated with growth.

## Testing the Bell inequality with Lambda hyperonsApril 14, 2009

Posted by dorigo in news, physics, science.
Tags: , , ,

This morning I came back from Easter vacations to my office and was suddenly assaulted by a pile of errands crying to be evaded, but I prevailed, and I still found some time to get fascinated by browsing through a preprint appeared a week ago on the Arxiv, 0904.1000. The paper, by Xi-Qing Hao, Hong-Wei Ke, Yi-Bing Ding, Peng-Nian Shen, and Xue-Qian Li [wow, I'm past the hard part of this post], is titled “Testing the Bell Inequality at Experiments of High Energy Physics“. Here is the abstract:

Besides using the laser beam, it is very tempting to directly testify the Bell inequality at high energy experiments where the spin correlation is exactly what the original Bell inequality investigates. In this work, we follow the proposal raised in literature and use the successive decays $J/\psi \to \gamma \eta_c \to \Lambda \bar \Lambda \to p \pi^- \bar p \pi^+$ to testify the Bell inequality. [...] (We) make a Monte-Carlo simulation of the processes based on the quantum field theory (QFT). Since the underlying theory is QFT, it implies that we pre-admit the validity of quantum picture. Even though the QFT is true, we need to find how big the database should be, so that we can clearly show deviations of the correlation from the Bell inequality determined by the local hidden variable theory. [...]

Testing the Bell inequality with the decay of short-lived subatomic particles sounds really cool, doesn’t it ? Or does it ? Unfortunately, my quantum mechanics is too rusty to allow me to get past a careful post which explains things tidily, in the short time left between now and a well-deserved sleep. You can read elsewhere about the Bell inequality, and how it tests whether pure quantum mechanics rules -destroying correlations between quantum systems separated by a space-like interval- or whether a local hidden variable theory holds instead: and besides, almost anybody can write a better account of that than me, so if you feel you can help, you are invited to guest-blog about it here.

Besides embarassing myself, I still wanted to mention the paper today, because the authors make a honest attempt at proposing an experiment which might actually work, and which could avoid some drawbacks of all experimental tests so far attempted, which belong to the realm of quantum optics. In their own words,

Over a half century, many experiments have been carried out [...] among them, the polarization entanglement experiments of two-photons and multi-photons attract the widest attention of the physics society. All photon experimental data indicate that the Bell inequality and its extension forms are violated, and the results are fully consistent with the prediction of QM. The consistency can reach as high as 30 standard deviations. [...] when analyzing the data, one needs to introduce additional assumptions, so that the requirement of LHVT cannot be completely satisfied. That is why as generally considered, so far, the Bell inequality has not undergone serious test yet.

Being totally ignorant of quantum optics I am willing to buy the above as true, although, being a sceptical son of a bitch, the statement makes me slightly dubious. Anyway, let me get to the point of this post.

Any respectable quantum mechanic could convince you that in order to check the Bell inequality with the decay chain mentioned above, it all boils down to measuring the correlation between the pions emitted in the decay of the Lambda particles, i.e., the polarization of the Lambda baryons: in the end, one just measures one single, clean angle $\theta$ between the observed final state pions. The authors show that this would require about one billion decays of the $J/\psi$ mesons produced by an electron-positron collider running at 3.09 GeV center-of-mass energy (the mass of the J/psi resonance): this is because the decay chain involving the clean $\Lambda \bar \Lambda$ final state is rare: the branching fraction of $J/\psi \to \eta_c \gamma$ is 0.013, the decay $\eta_c \to \Lambda \bar \Lambda$ occurs once in a thousand cases, and finally, each Lambda hyperon has a 64% chance to yield a proton-pion final state. So, 0.013 times 0.001 times 0.64 squared makes a chance about as frequent as a Pope appointment. However, if we had such a sample, here is what we would get:

The plot shows the measured angle between the two charged pions one would obtain from 3382 pion pairs (resulting from a billion $J/\psi \to \eta_c \gamma$ decays through double hyperon decay) compared with pure quantum mechanics predictions (the blue line) and by the Bell inequality (the area within the green lines). The simulated events are taken to follow the QM predictions, and such statistics would indeed refute the Bell inequality -although not by a huge statistical margin.

So, the one above is an interesting distribution, but if the paper was all about showing they can compute branching fractions and run a toy Monte Carlo simulation (which even I could do in the time it takes to write a lousy post), it would not be worth much. Instead, they have an improved idea, which  is to apply a suitable magnetic field and exploit the anomalous magnetic moment of the Lambda baryons to measure simultaneously their polarization along three independent axes, turning a passive measurement -one involving a check of the decay kinematics of the Lambda particles- into an active one -directly figuring out the polarization. This is a sort of double Stern-Gerlach experiment. Here I would really love to explain what a Stern-Gerlach experiment is, and even more to make sense of the above gibberish, but for today I feel really drained out, and I will just quote the authors again:

One can install two Stern-Gerlach apparatuses at two sides with flexible angles with respect to according to the electron-positron beams. The apparatus provides a non-uniform magnetic field which may decline trajectory of the neutral $\Lambda$ ($\bar \Lambda$) due to its non-zero anomalous magnetic moment i.e. the force is proportional to $d/n (- \mu B)$ where $\mu$ is the anomalous magnetic moment of $\Lambda$, B is a non-uniform external magnetic field and d/n is a directional derivative. Because $\Lambda$ is neutral, the Lorentz force does not apply, therefore one may expect to use the apparatus to directly measure the polarization [...]. But one must first identify the particle flying into the Stern-Gerlach apparatus [...]. It can be determined by its decay product [...]. Here one only needs the decay product to tag the decaying particle, but does not use it to do kinematic measurements.

I think this idea is brilliant and it might actually be turned into a technical proposal. However, the experimental problems connected to setting up such an apparatus, detecting the golden decays in a huge background of impure quantum states, and capturing Lambdas inside inhomogeneous magnetic fields, are mindboggling: no wonder the authors do not have a Monte Carlo for that. Also, it remains to be seen whether such pains are really called for. If you ask me, quantum mechanics is right, period: why bother ?

## Things I should have blogged on last weekApril 13, 2009

Posted by dorigo in cosmology, news, physics, science.
Tags: , , , , ,

It rarely happens that four days pass without a new post on this site, but it is never because of the lack of things to report on: the world of experimental particle physics is wonderfully active and always entertaining. Usually hiatuses are due to a bout of laziness on my part. In this case, I can blame Vodafone, the provider of the wireless internet service I use when I am on vacation. From Padola (the place in the eastern italian Alps where I spent the last few days) the service is horrible, and I sometimes lack the patience to find the moment of outburst when bytes flow freely.

Things I would have wanted to blog on during these days include:

• The document describing the DZERO search of a CDF-like anomalous muon signal is finally public, about two weeks after the talk which announced the results at Moriond. Having had in my hands a unauthorized draft, I have a chance of comparing the polished with the unpolished version… Should be fun, but unfortunately unbloggable, since I owe some respect to my colleagues in DZERO. Still, the many issues I raised after the Moriond seminar should be discussed in light of an official document.
• DZERO also produced a very interesting search for $t \bar t h$ production. This is the associated production of a Higgs boson and a pair of top quarks, a process whose rate is made significant by the large coupling of top quarks and Higgs bosons, by virtue of the large top quark mass. By searching for a top-antitop signature and the associated Higgs boson decay to a pair of b-quark jets, one can investigate the existence of Higgs bosons in the mass range where the $b \bar b$ decay is most frequent -i.e., the region where all indirect evidence puts it. However, tth production is invisible at the Tevatron, and very hard at the LHC, so the DZERO search is really just a check that there is nothing sticking out which we have missed by just forgetting to look there. In any case, the signature is extremely rich and interesting to study (I had a PhD doing this for CMS a couple of years ago), thus my interest.
• I am still sitting on my notes for Day 4 of the NEUTEL2009 conference in Venice, which included a few interesting talks on gravitational waves, CMB anisotropies, the PAMELA results, and a talk by Marco Cirelli on dark matter searches. With some effort, I should be able to organize these notes in a post in a few days.
• And new beautiful physics results are coming out of CDF. I cannot anticipate much, but I assure you there will be much to read about in the forthcoming weeks!

## Quake homeless “enjoy a weekend of camping”April 8, 2009

Posted by dorigo in news, politics.
Tags: ,