## Thursday, December 26, 2013

### Measuring a black hole mass - you're doing it right

1.  The orbit of every planet is an ellipse with the Sun at one of the two foci.
2. A line joining a planet and the Sun sweeps out equal areas during equal intervals of time.
3. The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.
Kepler's laws are among the most fundamental laws of astronomy.
Basically, they describe the orbits of planets around the Sun (or any "small" object around a much more massive central object), under the assumption that the gravitational field can be considered Newtonian (even if historically quite the opposite happened, with Newton using Kepler's orbits to derive his laws of gravity).
The orbits of all planets in the Solar system are very well described, to first order, by these laws. Only after centuries of observations of Mercury, the closest to the Sun, it was possible to notice post-Keplerian deviations due to relativistic effects.
When Kepler's laws say "proportional", the proportionality factor involves the masses of the objects (this was found by Newton). For example, in this approximation the third law is actually
where a is the semi-major axis of the orbit (the radius if the orbit is circular), G (=6.67384 × 10-11 m3 kg-1 s-2) the gravitational constant, M the mass of the central object, and T the orbital period.
It is therefore possible to use the orbit of the small object to infer the mass of the big one, if we have an idea of the size of the orbit.

One nice example? The measurement of our Galaxy's central supermassive black hole.
Several groups have been able to measure accurately the mass of this black hole by tracking the movement of several stars around it.
In the animated GIF above, a nice illustration of the procedure. Every orbit is an ellipse having in one of its foci, marked by the red cross in the center of the picture, an "invisible" object. This object, in order to describe the orbits of all the tracked orbiting points, must have a mass of about 4 million solar masses.
Here is a quite complete description of the work done by several groups to obtain this result.
Enjoy!

## Friday, December 20, 2013

### Medium-sized black holes? Probably not.

Ultraluminous X-ray sources (ULXs) are accreting black holes, i.e. black holes that are "eating" matter from a companion star. They are called ultraluminous because their luminosity is too high to be explained by "normal" accretion on stellar-mass black holes, i.e. black holes formed by the collapse of a single big star (from 8 up to ~100 masses of the Sun).
A step behind. During accretion, matter falls towards a central object. This matter heats up in the process, and this heat is freed in form of radiation. This radiation in turn "pushes" on the matter that keeps falling in, and a point is reached when the luminosity produced is comparable to the push by the infalling matter and so no higher luminosity can be achieved. This is called the Eddington luminosity and is a well known quantity in accretion studies. This luminosity scales with the mass of the central object, so that supermassive black holes (billions of times the mass of the Sun) will be able to radiate at much larger luminosities than stellar-mass black holes (mass several times the Sun)
Well, ULXs radiate at much more than the Eddington luminosity for stellar-mass black holes, so the first things that comes to mind is that they are bigger than stellar-mass black holes, and so they are members of the evasive class of Intermediate-mass black holes. Right?
Not so fast, my friend. People like these japanese researchers have done a great deal of simulations to show that it is possible to overcome the Eddington limit some extent.
Only problem: it was impossible to tell which of the two hypotheses was more right until 2012, since the few X-ray satellites capable of observing ULXs were sensitive only up to 10 keV, where the models started to really give incompatible predictions.
In this old post we talked about the launch of the NuSTAR satellite. Well, that was the turning point.
NuSTAR observed several ULXs and was able to finally strongly point in one direction. See the animated GIF above: the blue points are NuSTAR data, and they clearly follow better two models (the ones cutting off above 10 keV) than the others, while data from the XMM satellite weren't able to make a difference. This cutoff is considered a signature of super-Eddington accretion and permitted to estimate the mass of these ULXs to be in the high-end of the stellar-mass range.

Here is a press release of these studies. Enjoy!

## Sunday, December 15, 2013

### Enrico Fermi on Einstein's theory of special relativity

Yesterday I came across some fantastic notes by a young Enrico Fermi on Einstein's special relativity, which were included in "Asimmetrie", an outreach magazine issued by the Italian Institute for Nuclear Physics (INFN). After some search I found an English translation (by Robert Jantzen, I think).

The reading is really mind-blowing (well, at least for me...) and even more so considering Fermi was 21 at the time...

Enjoy!

 Apparently, there are no pictures of Fermi and Einstein together, so I turned down to this one...

## Wednesday, December 11, 2013

### Recommended by us: "MicroBooNE, in 3-D"

 Tingjun Yang (left) and Wesley Ketchum lead the effort to develop new 3-D reconstruction  software for the MicroBooNE experiment. Here they stand inside the MicroBooNE  time projection chamber.Photo: Reidar Hahn
“
Imagine your job is to analyze the data coming from Fermilab's MicroBooNE experiment.

It wouldn't be an easy task. MicroBooNE has been designed specifically to follow up on the MiniBooNE experiment, which may have seen hints of a fourth type of neutrino, one that does not interact with matter in the same way as the three types we know about. The big clue to the possible existence of these particles is low-energy electrons.
But that experiment could not adequately separate the production of electrons from the production of photons, which would not indicate a new particle. MicroBooNE's detector, an 89-ton active volume liquid-argon time projection chamber, will be able to. To take advantage of this, every neutrino interaction in the chamber will have to be examined to determine if it created an electron or a photon.
And there will be a lot of interactions to study — the MicroBooNE collaboration expects to see activity in their detector once every 20 seconds, including nearly 150 neutrino interactions each day.
If all goes to plan, human operators won't have to worry about any of that. When MicroBooNE switches on next summer, it will sport one of the most sophisticated 3-D reconstruction software programs ever designed for a neutrino experiment.
According to Wesley Ketchum and Tingjun Yang, two postdocs leading the software development team at Fermilab, MicroBooNE's computers will be able to accurately reconstruct neutrino interactions and automatically filter the ones that create electrons. The key to accomplishing this lies in the design of the time projection chamber.

Continue to read on Fermilab Today

## Monday, December 9, 2013

### La sezione d'urto "plettro-bicchiere"

In questo post volevo parlarvi di un fatto curioso capitatomi questo fine settimana durante un concerto del gruppo scozzese dei Biffy Clyro al Live Music Club di Trezzo sull'Adda (MI).

Naturalmente il fatto accaduto ha un rilevanza, seppur marginale, con la fisica nel raccontarvelo c’è quindi l’intento di comunicare come, la quasi totalità dei fenomeni che ci accadono, possono essere analizzati con un approccio scientifico e razionale. Ma entriamo nel vivo del racconto: durante l’esibizione del “gruppo spalla” i Walking papers, io e il mio amico ci siamo recati al bancone del bar, situato su un lato del locale, per acquistare da bere. Appena ricevute le bevande, un bicchiere di birra da 0.40L (e un bicchiere di Montenegro), ci siamo apprestati a ritornare approssimativamente al centro del locale dove ci aspettavano gli altri nostri due amici. Contemporaneamente all’atto dell’acquisto delle bevande il gruppo spalla finiva la sua esibizione e procedeva ai classici saluti e all’usuale lancio dei plettri per la chitarra* quando ad un certo punto sentiamo un rumore nelle nostre vicinanze e riceviamo alcuni schizzi di birra o qualche altro liquido.  Un po’ confusi ci guardiamo e ci chiediamo che cosa mai fosse accaduto, personalmente non avevo compreso la situazione, avevo sentito un colpo nel mio bicchiere di plastica** (di Montenegro) e poi avevo ricevuto degli schizzi ed ho pensato subito che esso fosse attribuibile al quel “balzetto” indotto da un bicchiere deformato che  ritorna nella sua configurazione originale e produce uno schizzo a seguito della agitazione della superficie del liquido contenuto al suo interno. Ho comunicato tempestivamente la mia interpretazione del fenomeno al mio amico il quale tuttavia mi ha guardato e mi ha riferito: “no! ti dico che è entrato un plettro nel mio bicchiere”; io l’ho guardato stranito e un po’ incredulo perché avevo sentito una botta nel mio bicchiere ed ero convinto dipendesse quindi dal mio e non che gli schizzi provenissero dal suo bicchiere o da un altro, quando però egli ha recuperato con le sue stesse mani il plettro all’interno del suo bicchiere mi son dovuto “arrendere” all’evidenza. Ebbene si, un plettro lanciato dal palco da alcuni componenti del gruppo, aveva dapprima colpito il mio bicchiere per poi dirigersi all’interno del bicchiere di birra del mio amico producendo degli schizzi. Tutto questo ci ha lasciato abbastanza perplessi e abbiamo riso dell’accaduto, passando subito al vaglio i parametri coinvolti per valutare una prima stima della probabilità del fatto e classificandolo in maniere affrettata quantomeno come “poco probabile”, ma dal momento che la situazione non permetteva un approfondimento “serio”, mi son ripromesso di valutare meglio la questione in separata sede, ed eccomi qui a fare un po’ di stime :)

## Monday, November 25, 2013

### Highlights of Classical and Quantum Gravity

Good news today, the paper Tidal acceleration of black holes and superradiance by Vitor (Cardoso) and myself was selected by the Editorial Board of Classical and Quantum Gravity (CQG) to be one of the journal’s Highlights of 2012-2013!

Besides being now free to download, the Highlights will be promoted in a number of campaigns over the next year  as a representation of some of the most interesting and high-quality work in gravitational physics.

But what makes the paper really worth a reading is the first paragraph, where we managed to refer to both Italian novelist Italo Calvino and mighty rock band Pink Floyd... that's quite an impressive achievement for a scientific paper!

 If you wish to know what Pink Floyd's masterpiece "The Dark Side of the Moon" has to do with black holes, read the (not-very-technical) paper here.

## Saturday, November 23, 2013

### Visit to the Maryland Center for Fundamental Physics

 This week I was invited at the Center for Fundamental Physics in Maryland, where I gave a talk about black holes and fundamental light fields beyond the Standard Model. On the way back to the airport in Washington DC, I stopped by the Air & Space museum. Here is a picture of me before the Hubble Space Telescope. BTW, in The Mall in DC all museums belong to the Smithsonian Institute and they are free, amazing!)

## Tuesday, November 12, 2013

### [Recommended by us] Why Hot Water Freezes Faster Than Cold—Physicists Solve the Mpemba Effect

Aristotle first noticed that hot water freezes faster than cold, but chemists have always struggled to explain the paradox. Until now.

Water may be one of the most abundant compounds on Earth, but it is also one of more mysterious. For example, like most liquids it becomes denser as it cools. But unlike them, it reaches a state of maximum density at 4°C and then becomes less dense before it freezes.

In solid form, it is less dense still, which is why standard ice floats on water. That’s one reason why life on Earth has flourished— if ice were denser than water, lakes and oceans would freeze from the bottom up, almost certainly preventing the kind of chemistry that makes life possible.

Then there is the strange Mpemba effect, named after a Tanzanian student who discovered that a hot ice cream mix freezes faster than a cold mix in cookery classes in the early 1960s. (In fact, the effect has been noted by many scientists throughout history including Aristotle, Francis Bacon and René Descartes.)

The Mpemba effect is the observation that warm water freezes more quickly than cold water. The effect has been measured on many occasions with many explanations put forward. One idea is that warm containers make better thermal contact with a refrigerator and so conduct heat more efficiently. Hence the faster freezing. Another is that warm water evaporates rapidly and since this is an endothermic process, it cools the water making it freeze more quickly.

None of these explanations are entirely convincing, which is why the true explanation is still up for grabs.

Today Xi Zhang at the Nanyang Technological University in Singapore and a few pals provide one. These guys say that the Mpemba paradox is the result of the unique properties of the different bonds that hold water together.

What’s so odd about the bonds in water? Discover it HERE.

## Sunday, November 3, 2013

### La passione per lo studio delle stelle raccontata dall'astrofisica Marta Burgay

Ecco l'intervento nellla trasmissione di Rai Tre "Che tempo che fa" all'astrofisica Marta Burgay dell'osservatorio astronomico di Cagliari, dove si parla di radiotelescopi, pulsar, pulsar doppie, relatività generale e del lavoro e della passione dei ricercatori in generale :) Buona visione!!

## Festival della Scienza Bellezza

Genova, 23 ottobre_3 novembre 2013

Si intitola “Quello che non so” lo spettacolo conferenza dedicato ai grandi misteri della fisica contemporanea ideato dall’Infn per la serata inaugurale del Festival della Scienza di Genova, mercoledì 23 ottobre. Si tratta di un evento unico che propone un format sperimentale pensato per il grande pubblico in cui si alternano talk show scientifico e performance artistiche. Interverranno i protagonisti della scoperta del bosone di Higgs, valsa il Nobel per la Fisica 2013 a Peter Higgs e Francois Englert, Guido Tonelli (spokesperson emerito esperimento Cms) e Fabiola Gianotti – in collegamento dal Cern (spokesperson emerito esperimento Atlas). Accanto a loro Caterina Biscari (ricercatrice Infn e direttore del laboratorio Cells Alba di Barcellona) e Antonio Zoccoli (Giunta esecutiva Infn). Nello spettacolo "Quello che non so" la narrazione scientifica sarà accompagnata dalle suggestioni del mago delle bolle di sapone Marco Zoppi e dai quadri di sabbia animati dalla sand artist Gabriella Compagnone. A condurre la serata sarà Marco Castellazzi (Rai 3 Geoscienza). Lo spettacolo è una nuova versione, aggiornata nei contenuti e nell’impianto artistico, dell’evento "Lo Show dell’Universo" realizzato dall’Infn a Città della Scienza di Napoli nel settembre 2012.

## Monday, October 14, 2013

### Birth, death, resurgence (and death again) of an idea

One might think that only few great scientists are blessed with those “eureka” moments when, all in a sudden, a great discovery is standing just before their gleaming eyes, so clear and obvious that it cannot be wrong. In my experience, this expectation is very far from reality.

I think that many, if not all, people working on intellectual activities can experience the same feverish excitement that hit Archimedes in its tub. And they actually do so on a regular basis!

The thing is, the relevance of any scientific achievement is very personal and it is proportional to the effort one has put to reach it. No matter whether such achievement would be universally important or not, it will anyway be so for its discoverer. Only great scientists have the privilege to feel such excitement for great discoveries, but most scientists would anyway feel exactly the same emotion after solving much humbler problems, simply because they finally overcome some long-standing intellectual challenge.

There is another big difference between great discoveries and those made by the “scientist of the street”. The former can last forever whereas the latter hardly survive overnight. Furthermore, because Science is sadistic, the more relevant the discovery appeared at the beginning, the shorter the time it will survive. Therefore, although any scientist can feel the birth of her/his own ideas – whatever small its intrinsic impact might be – it is also true that most of us have also to face the frustration of seeing that idea dying as quickly as it was born. I like to believe the same happens to great scientists as well.

Sometimes this process repeats itself continuously, each new idea being accompanied by more mistrustful joy and its possible death being followed by less sorrow. I consider myself lucky in this respect, because I can easily get over-excited after having some new idea (if not in front of a computer, this usually happens on the way back walking from work, so my humble suggestion is to leave your car in the garage) but I don't feel particularly sad when such idea turns out to be completely wrong, as it happens most of the times.

Actually, I think this experience is common to the majority of my colleagues and it is truly fortunate that the excitement following some potential new idea largely overcomes the almost-unavoidable letdown for its failure. After all, I believe, such feeling is the real thrust of the scientific process, the reward any scientist is intimately working for.

---------
The one above is my own contribution to the outreach project "Birth of Ideas", created by Ana Sousa and Vitor Cardoso. If you have an interesting anecdote to tell, please read the instructions and submit your contribution!

## Saturday, October 12, 2013

### The 9 kinds of physics seminar

 The “Typical” starts innocently enough: there are a few slides introducing the topic, and the speaker will talk clearly and generally about a field of physics you’re not really familiar with.  Somewhere around the 15 minute mark, though, the wheels will come off the bus.  Without you realizing it, the speaker will have crossed an invisible threshold and you will lose the thread entirely.  Your understanding by the end of the talk will rarely ever recover past 10%.Read the rest on Many Worlds Theory

## Wednesday, October 2, 2013

### The Unbearable Baldness of Black Holes

One of the most awe-inspiring properties of black holes is their absolute simplicity, or as John Wheeler famously put it, "black holes have no hair". As their progenitor collapses, its memory is forever lost, and all that remains is a quiescient, bald black hole. In a new article in Physical Review Letters, a team of scientists (that only by chance includes me...) has shown that black holes can nevertheless "grow hair" in the presence of matter, connecting them to the rest of the host galaxy.

Black holes are almost xeroxed copies of one another, differing at most in mass and rotation. These objects are described by a solution discovered by Roy Kerr in 1963. Remarkably, Kerr black holes are ubiquitous in almost any other theory of gravity, to the extend that the "Kerr hypothesis" is the current paradigm in astrophysics. 

 First time I saw this picture was in one of Stephen Hawking's popular-science books, probably 'Brief History of Time'. It is supposed to describe the 'baldness' that this post refers too, am I the only one finding it a bit pathetic? :)
We have shown that in simple and attractive extensions of Einstein's theory (known as scalar-tensor gravity) black holes may not be described by the Kerr metric, as was previously thought. The crucial ingredient is the matter surrounding astrophysical black holes, typically in the form of accretion disks. The presence of matter triggers an instability that forces the bald Kerr black hole to develop a new charge -- a "scalar hair" -- connecting it to the matter around it and possibly to the entire galaxy.

This hair growth is accompanied by a peculiar emission of gravitational waves, potentially by upcoming laser interferometers, which may test the Kerr hypothesis and probe the very foundations of gravity.

Read what real outreach journalists wrote on this on:
NewScientist
Huffington Post
Portuguese newspaper Público

## Thursday, September 26, 2013

### Sardinia got ears!

Finally the Sardinia Radio Telescope (SRT) is ready to start its scientific mission, the inaugural ceremony will take place on September 30th (next Monday) in the presence of the Italian Minister of Education, University and Research, Prof. Carrozza.
 The Sardinian Radio Telescope based in San Basilio

SRT is located in Sardinia near San Basilio, a small village about 35km from Cagliari, my hometown. SRT is the largest radiotelescope in Italy (diameter: 64 meters) and one of the most advanced in the world.

SRT will join the first Very Large Baseline Interferometer (VLBI) network in Italy, meaning that these 3 facilities will operate as a huge interferometer whose effective dimension is comparable to the size of our country! This allows to reach angular resolutions which would be simply impossible with a single instrument. As one of the most advanced radiotelescopes worldwide, SRT will also contribute as a node of the European VLBI Network.

But so, what is a radiotelescope

## The 2013 Ig Nobel Prize CeremonyThursday, September 12, 12:00Sanders Theater, Harvard University(twitter: #IgNobel)

The 23nd First Annual Ig Nobel Prize Ceremony will introduce ten new Ig Nobel Prize winners. Each has done something that makes people laugh then think. The winners travel to the ceremony, at their own expense, from several continents. The Prizes are handed to them by a group of genuine, genuinely bemused Nobel Laureates, in Harvard's historic, largest theater filled with 1100 improbable persons, everything webcast live. The ceremony will include many other delights—see below. (For the latest Ig Nobel news, see the blog.)
Previews: New York TimesHuffington PostLowering the BarSRF

Webcast
The ceremony will as usual be webcast live. To watch, click below (or on other web sites!). Schedule:
• 11:35 pm (US eastern time) — The webcast begins.
• 11:40 pm —  Deborah Henson-Conant's pre-ceremony mini-concert.
• 12:00 pm — The ceremony begins.

The ceremony will be broadcast live via LiveStream. The webcast is available below. Enjoy!

## Wednesday, September 11, 2013

### Opinions of an Exile

What follows is the English translation (mostly done by Google Translator, so don't blame me too much) of this post written by an Italian researcher living in NYC. I found it quite apt to describe the feeling of various compatriots abroad when they look at our country.
------------------------------------------------------------

My name is Luca Cassetta, 32, from Milan , married, two cats, I am living in New York for almost three years and I am a scientific researcher.
Yes, I admit , I'm part of the brain drain!
I belong to that group of young (and not so young) people who have decided to leave Italy to seek their fortune abroad!

## Sunday, September 1, 2013

### Rubbia to be nominated "Senatore a vita" in the Italian Senate of the Republic.

Summer has gone and with it also my excuses to avoid writing. As a new (academic) year resolution, I commit myself to write more often and also to cover some specific research projects I'm recently involved in.

Anyway, I'm glad today to restart my writings with this news: yesterday Prof. Carlo Rubbia was created "Senatore a vita" (lifetime Senator) of the Italian Senate of the Republic. According to the Italian Constitution, the President of the Italian Republic can create up to 5 lifetime Senators among Italian citizens who have outstanding merits in science, arts, or social life.

 Nobel Laureate Prof. Carlo Rubbia

Carlo Rubbia will share honor and responsibility together with architect Renzo Piano, Prof. Elena Cattaneo, and conductor Claudio Abbado. As Napolitano himself put it, these nominees are an ideal 'passing the baton' after some historic lifetime senator has recently passed away (like Prof. Rita Levi Montalcini).

In Italy the news was followed by a flood of polemics: some advocated the fact that lifetime senators are yet another entry in taxpayers' bill, whereas the center-right-wing party [that is, Berlusconi's] pointed out that all new lifetime Senators were somehow center-left oriented and that this might be seen as a way to rearrange the equilibrium of the political forces within the Parliament.

## Monday, August 26, 2013

### Recommended by us: "The EMC effect still puzzles after 30 years"

Thirty years ago, high-energy muons at CERN revealed the first hints of an effect that puzzles experimentalists and theorists alike to this day.

Contrary to the stereotype, advances in science are not typically about shouting "Eureka!". Instead, they are about results that make a researcher say, "That’s strange". This is what happened 30 years ago when the European Muon collaboration (EMC) at CERN looked at the ratio of their data on per-nucleon deep-inelastic muon scattering off iron and compared it with that of the much smaller nucleus of deuterium.
The data were plotted as a function of Bjorken-x, which in deep-inelastic scattering is interpreted as the fraction of the nucleon’s momentum carried by the struck quark. The binding energies of nucleons in the nucleus are several orders of magnitude smaller than the momentum transfers of deep-inelastic scattering, so, naively, such a ratio should be unity except for small corrections for the Fermi motion of nucleons in the nucleus. What the EMC experiment discovered was an unexpected downwards slope to the ratio (figure 1) – as revealed in CERN Courier in November 1982 and then published in a refereed journal the following March (Aubertet al. 1983).

Continue to read on Cern Courier

## Tuesday, August 13, 2013

### Eventi: "L'isola di Einstein"

Vogliamo segnalarvi questo evento scientifico che vi farà trascorre due giornate estive nella natura, all'insegna dell'informazione e dell'intrattenimento scientifico.
Di che cosa si tratta?

L’ISOLA di EINSTEIN è la prima rassegna internazionale di spettacoli scientifici in italia.

E' un evento dedicato a scienza, tecnologia, natura e innovazione realizzato attraverso le tecniche più coinvolgenti della comunicazione scientifica e delle arti di strada. dimostrazioni e spettacoli scientifici presentati da esperti scienziati, comunicatori e artisti di strada, provenienti da diverse parti del mondo che si ritroveranno in Umbria, nel meraviglioso contesto dell’Isola Polvese del Lago Trasimeno, per un evento unico nel panorama nazionale e internazionale.

Scienziati e artisti utilizzeranno una moltitudine di linguaggi per parlare di scienza e innovazione coinvolgendo famiglie con bambini, studenti, pensionati e curiosi di tutte l'età.

Gli spettacoli si avvicenderanno in diverse zone dell’isola, sui battelli di collegamento tra l’isola e la terra ferma e sui moli di partenza e di approdo, dove il pubblico potrà assistere a mini dimostrazioni, pillole di scienza che suscitano attenzione, provocano divertimento e stimolano la curiosità del pubblico sui fenomeni naturali, le leggi scientifiche che li descrivono.

Il programma della giornata prevede una non stop di spettacoli scientifici, brevi dimostrazioni, curiosi esperimenti scientifici, storie e aneddoti sulla figura del grande scienziato che si alterneranno in varie zone dell'Isola dalle ore 15 del 7 settembre sino alle 19 del 8 settembre. Sarà inoltre allestita un'area con istallazioni interattive.

Per maggiori informazioni visita il sito web
Buona visita a tutti :)

## Wednesday, July 31, 2013

### Un UFO sorvola la Luna? L'indagine dell'internauta.

Cosa è questo oggetto non identificato (UFO) che appare sullo sfondo del nostro satellite?

Un'analisi a freddo porterebbe a pensare qualsiasi razionalista convinto che si tratti di un difetto fotografico o ancor peggio di un fotomontaggio bene ideato.
Un "invasato" di film di fantascienza ci vedrebbe sicuramente la storica navicella spaziale Enterprise dell'intramontabile serie televisiva Star Trek, per poi rendersi subito conto che l'ipotesi non può aver nessun fondamento e ripiegare in qualcosa di più verosimile...

## Monday, July 15, 2013

### Paper of the week: Quanto è stabile il fotone?

In questo articolo, pubblicato su Physical Review Letters, viene discussa la stabilità del fotone, testando la possibilità che esso possa decadere. Per fare ciò chiaramente dovrebbe possedere una seppur piccola massa, il chè non è a priori vietato da alcuna legge fisica (a parte qualche piccolo "dettaglio" sulla rinormalizzabilità della teoria, che però può essere risolto).

Ma facciamo un po’ di chiarezza: innanzitutto ciò che potrebbe suonare strano è il concetto di massa del fotone, infatti tutti o quasi tutti sappiamo che il fotone è una particella priva di massa, tuttavia asserzioni di questo tipo in fisica vanno corroborate da risultati sperimentali.
Esistono dei limiti sperimentali alla massa del fotone che possono essere determinati in svariati modi.
Un fotone con una massa non nulla avrebbe degli effetti osservabili, per esempio la legge di Coulomb ne verrebbe modificata e il campo elettromagnetico avrebbe un ulteriore grado di libertà. Se la legge di Coulomb non fosse esattamente valida, allora potrebbe causare la presenza di un campo elettrico all'interno di un conduttore cavo sottoposto ad un campo elettrico esterno. In questo modo è quindi possibile testare la legge di Coulomb con altissima precisione [2]. Un risultato nullo di tale esperimento ha fissato un limite di $$m \lesssim 10^{-14} eV$$ [3].

## Saturday, June 29, 2013

### Margherita Hack passed away

Aged 91, last night Prof. Margherita Hack has passed away. Hack has been the first woman to become the Director of an Astronomy Observatory in Italy. I am not sure how well-known she actually is outside Italian borders, but she was definitely one of the most influential scientists in the political and social scene in Italy.
 "Farewell Margherita! Go and teach angels that they do not exist"Astrophysicists, public-science communicator and politician, Margherita Hack has always been very active in pursuing and disseminating her alternative views on politics, independence of science, vegetarianism and atheism.

Margherita was a very appreciated popular-science writer, but probably she was known to the general audience mostly for her alternative and unconventional political views. The Italian cult blog "Spinoza.it" today commented: "Margherita Hack died. A Red Giant". Besides the catchword borrowed from astrophysics, the comment refers to Hack's strong left-wing political views. Over the years she was a candidate in regional and national elections with the Italian Communist Party (PCI) and with other movements, like "Democrazia Atea" (Atheist Democracy) that she co-founded in 2011.

Strong opposer of any pseudo-scientific belief and superstition, she joined CICAP, the Italian division of the "European Council of Skeptical Organizations" in 1989. Since 2002, she was Honorary President of the UAAR "Unione degli Atei e degli Agnostici Razionalisti" (Union of Rationalist Atheists and Agnostics). In 2005, she joined the Luca Coscioni Association for the freedom and independence of scientific research.

Ciao Margherita.

## Saturday, June 22, 2013

### Recommended by us: "Sterile-neutrino hunt gathers pace at Gran Sasso"

 The Borexino detector at Gran Sasso: the SOX experiment will soon be using it to look for sterile neutrinos. (Courtesy: Borexino collaboration)

Much-debated results suggesting the existence of a fourth kind of neutrino, described as sterile, are to be put to the test in a new experiment under Italy's Gran Sasso mountain. The physicists who have devised the experiment say that by using an existing solar-neutrino detector they can carry out an inexpensive yet thorough search for the hypothetical sterile neutrino.
Neutrinos are chargeless, almost massless subatomic particles that interact with ordinary matter only via the weak nuclear force. As a result they can pass through vast amounts of material undisturbed. To study them, physicists build huge detectors – the idea being that a large number of target nuclei will result in a few neutrino collisions that can be detected.
If they exist, then sterile neutrinos would be even more difficult to detect because they probably would not interact with ordinary matter at all – only with other neutrinos. They would do so via "oscillation", a well-established phenomenon in which ordinary neutrinos transform and re-transform continually from one of three flavours – electron, muon and tau – to another as they travel. Likewise, ordinary neutrinos would oscillate into sterile neutrinos and back again but probably over much shorter distances than those typical of normal neutrino oscillation.

## Wednesday, June 12, 2013

### MAKSIMOVIC. THE STORY OF BRUNO PONTECORVO: Support the project!!

Giuseppe Mussardo, professor of theoretical physics at  SISSA - Scuola Internazionale Superiore di Studi Avanzati - is making a documentary on the extraordinary story of the nuclear physicist Bruno Pontecorvo, with the help of Luisa Bonolis, who is an expert on the historical parts of Pontecorvo's life, and Diego Cenetiempo, the movie director.

The INFN (Italian Institute for Nuclear Physics), SISSA (International School for Advanced Studies) and ICTP (The Abdus Salam International Centre for Theoretical Physics) are the scientific Institutions that are providing the funds for the project. But you can also support it!!

"On September 1, 1950, at the dawn of the Cold War, the nuclear physicist Bruno Pontecorvo suddenly disappeared. His defection created a real political earthquake in Europe and in the USA: Pontecorvo was in fact a scientist known around the world for his expertise in the very delicate area of nuclear research. The story of his disappearance is one of the most fascinating mysteries of the cold war and the atomic era, with many questions still unanswered: if for someone he was a spy who revealed important atomic secrets to the Russians, for others he was a loyal socialist, who decided to join the USSR for the purpose of serving science with peaceful research on the secrets of Nature.
The movie aims to present the singular figure of this scientist, whose scientific adventure began with Enrico Fermi in Rome in the early 1930s and moved on making him one of the world experts of nuclear physics and a visionary scientist in the field of weak interactions and neutrino physics.
Born on 22nd of September 1913 in a Jewish family in Pisa, brother of the famous biologist Guido and the movie director Gillo, Bruno Pontecorvo’s life was strongly interlaced with 20th century history and the development of particle physics.
He fled fascist Italy to join in 1938 the group of Frédéric Joliot-Curie in Paris and, when the II World War broke in, he moved to the USA miraculously escaping on a bicycle from Paris occupied by the Nazis troops,. There, he got employed in oil companies in Oklahoma and, after the war, he firstly joined the nuclear program in Canada and later in England.
His defection to the URSS in 1950 was a turning point of his life. He worked until his death in Dubna, at the Joint Institute for Nuclear Research, focusing all his energies to the studies of high energy particles and, in particular, of the most elusive particle, the neutrino. In all his life, Pontecorvo was always at the frontiers of science, often being much ahead of his time for his scientific ideas, which were constantly related to fundamental phenomena. He had exceptional scientific intuitions, which went hand in hand with his brilliant qualities as an experimental physicist; his experiments and their design were always masterpieces. For these reasons Bruno Pontecorvo is an extraordinary ideal for present and future generations of physicists."

Follow the project on the website of the Pilgrim Film production, in the dedicated page: http://www.pilgrimfilm.it/pontecorvo.htm#/work
Visit also their  Vimeo channel: http://vimeo.com/user2638974/videos

## Tuesday, June 11, 2013

### Physics news: "Dall'Europa 3,5 mln per studiare neutrini sterili al Gran Sasso"

(AGI) - Roma, 11 giu. - Premiato dall'European Research Council con un finanziamento di 3,5 milioni di euro, e' partito da pochi giorni il progetto SOX (Short distance neutrino Oscillations with BoreXino). Il riconoscimento (ERC Advanced Grant) e' stato attribuito nell'ambito del VII programma quadro europeo a Marco Pallavicini, professore all'Universita' di Genova e ricercatore dell'Istituto Nazionale di Fisica Nucleare, Principal Investigator di SOX. Il progetto sara' sviluppato ai Laboratori Nazionali del Gran Sasso dell'INFN e avra' una durata di cinque anni.
L'obiettivo di SOX e' la rivelazione di neutrini particolari, detti "sterili", con il principale rivelatore di neutrini solari e geofisici oggi in funzione nel mondo, Borexino, sviluppato e messo in funzione ai Laboratori Nazionali del Gran Sasso dell'INFN da una collaborazione internazionale di circa 100 fisici provenienti da Italia, USA, Russia, Germania, Francia e Polonia. SOX studiera' un aspetto delle oscillazioni del neutrino, il fenomeno in base al quale i tre neutrini conosciuti (elettronico, muonico o tauonico) si trasformano l'uno nell'altro con variazioni periodiche durante la loro propagazione. In particolare, questo fenomeno, che e' stato osservato anche di recente dall'esperimento OPERA ai Laboratori INFN del Gran Sasso, presenta alcune anomalie e non spiega il numero di neutrini prodotti, inferiore a quanto previsto teoricamente. Una possibile spiegazione della "scomparsa" dei neutrini, suffragata anche da risultati recenti, prevede l'esistenza di altri tipi di neutrini, i neutrini sterili, che si mescolerebbero con i tre noti.
Non interagendo attraverso nessuna delle interazioni fondamentali previste dal Modello Standard (elettromagnetica, nucleare forte e debole), i nuovi neutrini sarebbero poi ancora piu' elusivi dei neutrini conosciuti. SOX, in particolare, studiera' nel dettaglio la scomparsa del neutrino elettronico a breve distanza dalla sorgente, gia' osservata da diversi esperimenti. L'esperimento sfruttera' un innovativo generatore artificiale di neutrini (o di antineutrini) posto vicino o all'interno del rivelatore Borexino presso i Laboratori Nazionali del Gran Sasso. Oltre allo sviluppo dell'innovativa tecnologia per produrre neutrini in grande quantita' a breve distanza dal rivelatore, saranno elementi chiave di questo esperimento l'elevatissima sensibilita' di Borexino, le sue grandi dimensioni, il livello estremamente basso di radioattivita' presente ai Laboratori del Gran Sasso. La sensibilita' attesa, in particolare, sara' sufficiente a garantire o una chiara scoperta o l'esclusione di neutrini sterili come spiegazione delle anomalie del neutrino. "In caso di successo, la dimostrazione dell'esistenza dei neutrini sterili significhera' l'apertura di una nuova era nella fisica fondamentale delle particelle e nella cosmologia", ha spiegato Marco Pallavicini, coordinatore del progetto. "Sarebbe il primo segnale inequivocabile dell'esistenza di particelle oltre il Modello Standard elettrodebole, con profonde implicazioni sulla nostra comprensione dell'Universo e nuovi indizi sulla natura della materia oscura. Nel caso di un risultato negativo - ha continuato - saremmo in grado di dare un sostanziale contributo al dibattito circa la realta' delle anomalie dei neutrini, avremmo esplorato l'esistenza di nuova fisica nelle interazioni di neutrini a bassa energia e saremo in grado di fornire misure di grande precisione, di grande utilita' per la rivelazione dei neutrini solari con Borexino". (AGI).

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## Wednesday, June 5, 2013

### Sabato a Cagliari: "I cacciatori del bosone di Higgs"

Sabato 8 giugno alle 18:00 presso il THotel in via dei Giudicati 66 a Cagliari, si terrà la conferenza "I cacciatori del bosone di Higgs"

Il 4 luglio 2012 rimarrà una data storica per la fisica: al CERN di Ginevra viene annunciata la prova sperimentale dell’esistenza del bosone di Higgs. Guido Tonelli ripercorre le tappe che hanno portato a questa straordinaria scoperta che ha coinvolto scienziati di tutto il mondo, tra cui i tantissimi italiani che lavorano al super acceleratore. Quali implicazioni avrà la scoperta sulla nostra attuale visione del mondo? Quali sfide deve oggi affrontare la fisica per comprendere meglio il nostro universo? Questi gli interrogativi cui si tenterà di dare risposta durante la conferenza moderata da Nicola Nosengo, giornalista freelance che collabora tra gli altri per Wired, Nature e The Economist.

La conferenza è il sesto appuntamento della rassegna "Dialoghi di scienza", organizzata da Sardegna Ricerche per raccontare le frontiere della ricerca in medicina, nei campi dell'energia e della fisica. Il ciclo di eventi comprende sette incontri tra conferenze e science café che si svolgono a Cagliari, presso il THotel e la Mediateca del Mediterraneo.

### Recommended by us: "Scientists: Do Outreach or Your Science Dies"

 “  Scientists, here’s the bottom line. If you don’t convince the public that your science matters, your funding will quickly vanish and so will your field. Put another way, the era of outreach being optional for scientists is now over. ( Continue to read on Scientific American)

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## Tuesday, May 28, 2013

### News: J-PARC leak signals poor sense of crisis

Staff lacked experience handling nuclear materials
 Ritual regret: Japan Atomic Energy Research Institute chief Satoru Kondo apologizes at a news conference Saturday in the village of Tokai, Ibaraki Prefecture. | KYODO
The release of radioactive material from a Japan Atomic Energy Agency facility in Tokai, Ibaraki Prefecture, last week suggests scientists still lack a sense of crisis and urgency about radiation dangers despite the 2011 Fukushima disaster.
At least 30 researchers at the Hadron Experimental Facility of the Japan Proton Accelerator Research Complex (J-PARC) sustained internal radiation exposure in Thursday’s accident.
An alarm went off at 11:55 a.m. Thursday in a radiation-controlled part of the Hadron facility when an experiment to generate elementary particles by aiming a proton beam at a target made of gold went haywire. After halting the experiment for the alarm, a researcher in charge decided there was no danger and restarted the equipment just 13 minutes later.
“The safety device went off correctly and there wasn’t a malfunction,” the senior researcher was quoted as saying later. Soon after, radiation readings in the facility spiked alarmingly to 4 microsieverts per hour — 10 times normal — and officials shut down the equipment. They then ventilated the facility and the internal readings dropped. But despite the fact that the fan had no radiation filters, it wasn’t until late Friday afternoon that they checked radiation levels outside the facility.“It was not an appropriate move,” a J-PARC official conceded.
The 1½ days it took the JAEA to report the accident to the Nuclear Regulation Authority, at 10:15 p.m. Friday night, angered both the prefectural and central governments.
“The prefecture is taking the incident seriously. People living nearby are feeling very anxious about the external radiation leak and the internal exposure (of the researchers),” said Shuichi Matsumoto, an official at Ibaraki’s nuclear safety steps division who helped search J-PARC Saturday to probe the incident.

 Ground zero: The facility from which unnamed radioactive substances leaked during a nuclear experiment in Tokai, Ibaraki Prefecture, is shown in this undated photo. | JAPAN ATOMIC ENERGY AGENCY/KYODO