dimanche 2 octobre 2016

Solar neutrinos: Oscillations or (almost) No-oscillations (?)

Neutrino oscillations disentangled from adiabatic flavor conversion : always mind your terminology!
Next Tuesday will be announced the Nobel prize in physics 2016. That makes two days left to think one more time about the interesting physics from the previous year, learning some lessons from the past:
The Nobel prize in physics 2015 has been awarded "... for the discovery of neutrino oscillations which show that neutrinos have mass". While SuperKamiokande (SK), indeed, has discovered oscillations, {the} Sudbury Neutrino Observatory (SNO) observed effect of the adiabatic (almost non-oscillatory) flavor conversion of neutrinos in the matter of the Sun. Oscillations are irrelevant for solar neutrinos apart from small electron neutrino regeneration inside the Earth. Both oscillations and adiabatic conversion do not imply masses uniquely and further studies were required to show that non-zero neutrino masses are behind the SNO results. Phenomena of oscillations (phase effect) and adiabatic conversion (the Mikheïev-Smirnov-Wolfenstein (MSW) effect driven by the change of mixing in matter) are described in pedagogical way.

In {the figure above} we show graphic representations of the neutrino oscillations and adiabatic conversion which are based on analogy with the electron spin precession in the magnetic field. Neutrino polarization vector in flavor space (“spin”) is moving in the flavor space around the “eigenstate axis” (magnetic field) whose direction is determined by the mixing angle 2θm. Oscillations are equivalent to the precession of the neutrino polarization vector around fixed axis, Fig. a. Oscillation probability is determined by projection of the neutrino vector on the axis z. The direction up of the neutrino vector corresponds to the νe, direction down – to νa. Adiabatic conversion is driven by rotation of the cone itself, i.e. change of direction of the magnetic field (cone axis) according to change of the mixing angle, Fig. b. Due to adiabaticity the cone opening angle does not change and therefore the neutrino vector follow rotation of axis.
Oscillations do not need the mass. Recall that it was the subject of the classical Wolfenstein’s paper [9] to show that oscillations can proceed for massless neutrinos. This requires, however, introduction of the non-standard interactions of neutrinos which lead to non-diagonal potentials in the flavor basis and therefore produce mixing. 
In oscillations we test the dispersion relations, that is, the relations between the energy and momentum, and not masses immediately. Oscillations are induced because of difference of dispersion of neutrino components that compose a mixed state... 
It is consistency of results of many experiments in wide energy ranges and different environments: vacuum, matter with different density profiles that makes explanation of data without mass almost impossible. In this connection one may wonder which type of experiment/measurement can uniquely identify the true mass? Let us mention three possibilities:
• Kinematical measurements: distortion of the beta decay spectrum near the end point. Notice that similar effect can be produced if a degenerate sea of neutrinos exists which blocks neutrino emission near the end point.
• Detection of neutrinoless double beta decay which is the test of the Majorana neutrino mass. Here complications are related to possible contributions to the decay from new L-violating interactions.
• Cosmology is sensitive to the sum of neutrino masses, and in future it will be sensitive to even individual masses. Here the problem is with degeneracy of neutrino mass and cosmological parameters.
In January 1986 at the Moriond workshop A. Messiah (he gave the talk [16]) asked me: “why do you call effect that happens in the Sun the resonance oscillations? It has nothing to do with oscillations, I will call it the MSW effect”. My reply was “yes, I agree, we simply did know how to call it. I will explain and correct this in my future talks and publications”. Messiah’s answer was surprising: “No way..., now this confusion will stay forever”. That time I could not believe him. I have published series of papers, delivered review talks, lectures in which I was trying to explain, fix terminology, etc.. All this has been described in details in the talk at Nobel symposium [17], and for recent review see [8]. 
Ideally terminology should reflect and follow our understanding of the subject. Deeper understanding may require a change or modification of terminology. At the same time changing terminology is very delicate thing and can be done with great care. 
In conclusion, the answer to the question in the title of the paper is 
“Solar neutrinos: Almost No-oscillations”.
The SNO experiment has discovered effect of the adiabatic flavor conversion (the MSW effect). Oscillations (effect of the phase) are irrelevant. Evolution of the solar neutrinos can be considered as independent (incoherent) propagation of the produced eigenstates in matter. Flavors of these eigenstates (described by mixing angle) change according to density change. At high energies (SNO) the adiabatic conversion is close to the non-oscillatory transition which corresponds to production of single eigenstate. Oscillations with small depth occur in the matter of the Earth.
A. Yu. Smirnov (Submitted on 8 Sep 2016)

lundi 29 août 2016

High (energy physics exploration) by East-west (collaboration on heavy ion collision experiments)

There is more than potential new elementary particles to understand fundamental interactions
This short note describes the long collaborative effort between Arizona and Krak´ow, showing some of the key strangeness signatures of quarkgluon plasma. It further presents an annotated catalog of foundational questions defining the research frontiers which I believe can be addressed in the foreseeable future in the context of relativistic heavy ion collision experiments. The list includes topics that are specific to the field, and ventures towards the known-to-be-unknown that may have a better chance with ions as compared to elementary interactions. 
Some 70 years ago the development of relativistic particle accelerators heralded a new era of laboratory-based systematic exploration and study of elementary particle interactions...  
The outcomes of this long quest are on one hand the standard model (SM) of particle physics, and on another, the discovery of the primordial deconfined quark-gluon plasma (QGP). These two foundational insights arose in the context of our understanding of the models of particle production and more specifically, the in-depth understanding of strong interaction processes. To this point we recall that in the context of SM discovery we track decay products of e.g. the Higgs particle in the dense cloud of newly formed strongly interacting particles. In the context of QGP we need to understand the gas cloud of hadrons into which QGP decays and hadronizes. Hadrons are always all we see at the end. They are the messengers and we must learn to decipher the message.
Jan Rafelski   (Submitted on 25 Aug 2016)

Exotic states of nuclear matter matter too
The year 1964/65 saw the rise of several new ideas which in the following 50 years shaped the discoveries in fundamental subatomic physics: 1. The Hagedorn temperature TH ; later recognized as the melting point of hadrons into 2. Quarks as building blocks of hadrons; and, 3. The Higgs particle and field escape from the Goldstone theorem, allowing the understanding of weak interactions, the source of inertial mass of the elementary particles. The topic in this paper is Hagedorn temperature 
 and the strong interaction phenomena near to TH . I present an overview of 50 years of effort with emphasis on: a) Hot nuclear and hadronic matter; b) Critical behavior near 
 ; c) Quark-gluon plasma (QGP); d) Relativistic heavy ion (RHI) collisions1 ; e) The hadronization process of QGP; f) Abundant production of strangeness flavor... 
A report on ‘Melting Hadrons, Boiling Quarks and TH’ relates strongly to quantum chromodynamics (QCD), the theory of quarks and gluons, the building blocks of hadrons, and its lattice numerical solutions; QCD is the quantum (Q) theory of color-charged (C) quark and gluon dynamics (D); for numerical study the space-time continuum is discretized on a ‘lattice’. Telling the story of how we learned that strong interactions are a gauge theory involving two types of particles, quarks and gluons, and the working of the lattice numerical method would entirely change the contents of this article, and be beyond the expertise of the author. I recommend instead the book by Weinberg [8], which also shows the historical path to QCD... 
Our conviction that we achieved in laboratory experiments the conditions required for melting (we can also say, dissolution) of hadrons into a soup of boiling quarks and gluons became firmer in the past 15-20 years. Now we can ask, what are the ‘applications’ of the quark-gluon plasma physics? Here is a short wish list:  
1) Nucleons dominate the mass of matter by a factor 1000. The mass of the three ‘elementary’ quarks found in nucleons is about 50 times smaller than the nucleon mass. Whatever compresses and keeps the quarks within the nucleon volume is thus the source of nearly all of mass of matter. This clarifies that the Higgs field provides the mass scale to all particles that we view today as elementary. Therefore only a small %-sized fraction of the mass of matter originates directly in the Higgs field; see Section 7.1 for further discussion. The question: What is mass? can be studied by melting hadrons into quarks in RHI collisions 
2) Quarks are kept inside hadrons by the ‘vacuum’ properties which abhor the color charge of quarks. This explanation of 1) means that there must be at least two different forms of the modern æther that we call ‘vacuum’: the world around us, and the holes in it that are called hadrons. The question: Can we form arbitrarily big holes filled with almost free quarks and gluons? was and remains the existential issue for laboratory study of hot matter made of quarks and gluons, the QGP. Aficionados of the lattice-QCD should take note that the presentation of two phases of matter in numerical simulations does not answer this question as the lattice method studies the entire Universe, showing hadron properties at low temperature, and QGP properties at high temperature 
3) We all agree that QGP was the primordial Big-Bang stuff that filled the Universe before ‘normal’ matter formed. Thus any laboratory exploration of the QGP properties solidifies our models of the Big Bang and allows us to ask these questions: What are the properties of the primordial matter content of the Universe? and How does ‘normal’ matter formation in early Universe work?  
4) What is flavor? In elementary particle collisions, we deal with a few, and in most cases only one, pair of newly created 2nd, or 3rd flavor family of particles at a time. A new situation arises in the QGP formed in relativistic heavy ion collisions. QGP includes a large number of particles from the second family: the strange quarks and also, the yet heavier charmed quarks; and from the third family at the LHC we expect an appreciable abundance of bottom quarks. The novel ability to study a large number of these 2nd and 3rd generation particles offers a new opportunity to approach in an experiment the riddle of flavor 
5) In relativistic heavy ion collisions the kinetic energy of ions feeds the growth of quark population. These quarks ultimately turn into final state material particles. This means that we study experimentally the mechanisms leading to the conversion of the colliding ion kinetic energy into mass of matter. One can wonder aloud if this sheds some light on the reverse process: Is it possible to convert matter into energy in the laboratory? The last two points show the potential of ‘applications’ of QGP physics to change both our understanding of, and our place in the world. For the present we keep these questions in mind. This review will address all the other challenges listed under points 1), 2), and 3) above; however, see also thoughts along comparable foundational lines presented in Subsections 7.3 and 7.4..
(Submitted on 13 Aug 2015 (v1), last revised 16 Sep 2015 (this version, v2))

 Snapshot of two colliding lead ions just after impact (simulation).

At a special seminar on 10 February 2000, spokespersons from the experiments on CERN's Heavy Ion programme presented compelling evidence for the existence of a new state of matter in which quarks, instead of being bound up into more complex particles such as protons and neutrons, are liberated to roam freely.
Theory predicts that this state must have existed at about 10 microseconds after the Big Bang, before the formation of matter, as we know it today, but until now it had not been confirmed experimentally. Our understanding of how the universe was created, which was previously unverified theory for any point in time before the formation of ordinary atomic nuclei, about three minutes after the Big Bang, has with these results now been experimentally tested back to a point only a few microseconds after the Big Bang. (CERN Bulletin 07/00; 14 February 2000)

jeudi 25 août 2016

The bumpy road to the discovery of quasars and massive black holes

Invitation to a Midsummer Night's Dream Reading

My intention in this talk is to share a story in which I was very fortunate to participate almost since the beginning, but which is often ignored by the young generation of astronomers. It is the story of the discovery of Massive Black Holes (MBHs). Since everybody in this assembly knows well the subject in its present stage of development, I thought indeed that it could be interesting to show how the ideas that people take for granted presently had such difficulties to emerge and to gain credence. I think that this subject allows, better than any others, to observe that research is not “a long quiet river”, and on the contrary evolves in a non-linear and erratic way, full of mistakes and of dead ends, and that it gives rise to passionate controversies. We will see that the story of MBHs is made of fruitless researches opening on unexpected discoveries, come-backs of visionary models which were first neglected, temporary very fashionable but wrong models, strong debates involving even new physical laws, misinterpretations responsible for decades of stagnation, thousands of papers and nights of the largest telescopes. But finally it opened on a coherent physical model and on a new vision of galaxy evolution. Since it is a long story, I have selected only a few fragments...
Suzy Collin (Submitted on 27 Apr 2006 (v1), last revised 1 Sep 2006 (this version, v3))

The article is not long in fact. I reproduce below its two figures as lobby cards to advertise its reading!

Figure 1. This radio map of NGC 6251, as published by Readhead, Cohen & Blandford in 1978, shows that a small jet 5 light-years long is aligned with a larger jet of 600 000 light-years, itself aligned with the direction of the radio lobes, separated by 9 millions light-years. The fact that the two jets at the small and intermediate scales are seen only on one side, while the lobes at large scale are almost symmetrical with respect to the galaxy, proves that the side of the jet directed towards us is relativistic boosted, and therefore that the bulk velocity of the jet is very close to the velocity of light. {It was a fundamental discovery to support the cosmological distance hypothesis of quasars}
Figure 2. Cartoon produced by McCray at the Cambridge summer school in 1977 and called “Response of astrophysicists to a fashionable new idea”. I extract a few lines from his paper: “Beyond the accretion radius, r, astrophysicists are sufficiently busy to not be influenced by the fashionable new idea. But others, within r, begin a headlong plunge towards it... In their rush to be the first, they almost invariably miss the central point, and fly off on some tangent... In the vicinity of the idea, communication must finally occur, but it does so in violent collisions... Some individuals may have crossed the rationality horizon rs beyond which the fashionable idea has become an article of faith. These unfortunate souls never escape. Examples of this latter phenomenon are also familiar to all of us.”
Pour le lecteur francophone je recommande chaudement la lecture d'un autre texte de Susy Collin-Zahn lui aussi extrêmement pédagogique et informatif sur les controverses autour des quasars et plus généralement autour du modèle cosmologique standard : La théorie du Big Bang rend bien compte des décalages observés publié sur le riche site Science... et pseudo-sciences.

mercredi 24 août 2016

The seven pillars of (heuristical) wisdom

... it helps to recall the definition of an expert as a man who knows all the mistakes possible in his field*. Our whole problem is to make the mistakes as fast as possible- my part- and recognize them** -your part! Can a unifying concept in one field be applied in another? Let me call on a septet of sibyls to say yes if they will.
Sayings of the seven sibyls
(1) The Unknown is Knowable
(2) Advance by Trial and Error 
(3) Measurement and Theory are Inseparable
(4) Analogy Gives Insight
(5) New Truth Connects with Old Truth
(6) Complementarity Guards against Contradiction
(7) Great Consequences Spring from Lowly Sources
 John Archibald Wheeler

* Approximate quote possibly attributable to Niels Bohr, the real one being "An expert is a person who has found out by his own painful experience all the mistakes that one can make in a very narrow field" according to Edward Teller.

Addendum on August 25, 2016:
Fluctuat [et,nec] mergitur
This post is dedicated to the whole community of physicists at LHC and is also a continuation of my comment on the blog Resonaance about the huge amount of research articles devoted to the now notorious excess of events at invariant mass around 750 GeV in pp → γγ collisions, first reported [1a, 1b] in the preliminary 2015 LHC data collected at 13 TeV and later fading away in the new 2016 LHC data [2a, 2b].

**For why it can be difficult to admit mistakes some psychologists have explained with the theory of cognitive dissonance.  

lundi 4 juillet 2016

Neutrino physics cold[ol] case{s}

The 20th century (story of the) neutrino
In the recent past, two Nobel Prizes were given to Neutrino Physics. In 2002 Ray Davis of USA and Matoshi Koshiba of Japan got the Nobel Prize for Physics while last year (2015) Arthur McDonald of Canada and Takaaki Kajita of Japan got the Nobel Prize. To understand the importance of neutrino research it is necessary to go through the story of the neutrino in some detail. 
Starting with Pauli and Fermi, the early history of the neutrino is described culminating in its experimental detection by Cowan and Reines. Because of its historical importance the genesis of the solar neutrino problem and its solution in terms of neutrino oscillation are described in greater detail. In particular, we trace the story of the 90-year-old thermonuclear hypothesis which states that the Sun and the stars are powered by thermonuclear fusion reactions and the attempts to prove this hypothesis experimentally. We go through Davis’s pioneering experiments to detect the neutrinos emitted from these reactions in the Sun and describe how the Sudbury Neutrino Observatory in Canada was finally able to give a direct experimental proof of this hypothesis in 2002 and how, in the process, a fundamental discovery i.e. the discovery of neutrino oscillation and neutrino mass was made. 
We next describe the parallel story of cosmic-ray-produced neutrinos and how their study by SuperKamioka experiment in Japan won the race by discovering neutrino oscillations in 1998. 
Many other important issues are briefly discussed at the end...
Milestones in the neutrino story

  • 1930 Birth of Neutrino: Pauli 
  • 1932 Theory of beta decay, ”Neutrino” named: Fermi
  • 1954 First detection of neutrino: Cowan and Reines 
  • 1964 Discovery of muneutrino: Lederman, Schwartz and Steinberger 
  • 1965 Detection of atmospheric neutrino: KGF 1970 Start of the solar neutrino experiment: Davis 
  • 1987 Detection of neutrinos from supernova: SuperKamioka 
  • 1998 Discovery of neutrino oscillation and mass: SuperKamioka
  • 2001 Discovery of tauneutrino: DONUT 
  • 2002 Solution of the solar neutrino puzzle: SNO 
  • 2005 Detection of geoneutrinos: KamLAND 
  • 2013 Detection of ultra high energy neutrinos from space: Ice Cube 

G Rajasekaran (Institute of Mathematical Sciences, Chennai & Chennai Mathematical Institute) (Submitted on 22 Jun 2016)

A potential 21st century counterpart...
What exactly is Dark Matter? New theories for what really constitutes Dark Matter appear to make the news headlines every week. At a slower pace, these theories are slowly being eliminated. We revisit this scientific thriller and make the case that condensed neutrino matter is a leading suspect. We provide a forensic discussion of some subtle evidence and show that independent experimental results due out in 2019 from the KATRIN experiment [1] will either be the definitive result or eliminate condensed neutrinos as a Dark Matter candidate... The ... experiment ... will have the sensitivity to determine the mass of the electron antineutrino down to 0.35 eV/c2 ... This mass range for the electron antineutrino is in direct contradiction to the upper bound claimed by the Planck satellite consortium. If KATRIN discovers a neutrino mass in this range, we contend that the cosmological blackbody radiation raw data analysis must be revisited and that it would be a major finding endorsing condensed neutrinos as the so-called Dark Matter, which everyone has been looking for.
(Submitted on 27 Jun 2016)
... and another speculative (rival?) one here

jeudi 16 juin 2016

Gravitational wave astronomy stays pitch-black (up to now)

No electromagnetic counterparts from optical wavelengths...
We present a search for an electromagnetic counterpart of the gravitational wave source GW151226. Using the Pan-STARRS1 telescope we mapped out 290 square degrees in the optical i_ps filter over a period starting 11.45hr after the LIGO information release (49.48hr after the GW trigger) and lasting for a further 28 days. We typically reached sensitivity limits of i_ps=20.3-20.8 and covered 26.5% of the LIGO probability skymap. We supplemented this with ATLAS survey data, reaching 31% of the probability region to shallower depths of m~19. We found 49 extragalactic transients (that are not obviously AGN), including a faint transient in a galaxy at 7Mpc (a luminous blue variable outburst) plus a rapidly decaying M-dwarf flare. Spectral classification of 20 other transient events showed them all to be supernovae. We found an unusual transient, PS15dpn, with an explosion date temporally coincident with GW151226 which evolved into a type Ibn supernova. The redshift of the transient is secure at z=0.1747 +/- 0.0001 and we find it unlikely to be linked, since the luminosity distance has a negligible probability of being consistent with that of GW151226. In the 290 square degrees surveyed we therefore do not find a likely counterpart. However we show that our survey strategy would be sensitive to Neutron Star-Nentron Star mergers producing kilonovae at D < 100 Mpc, which is promising for future LIGO/Virgo searches.
S. J. Smartt et al, (Submitted on 15 Jun 2016)

 ... to gamma ray ones
We present the Fermi Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) observations of the LIGO binary black hole merger event GW151226 and candi- date LVT151012. No candidate electromagnetic counterparts were detected by either the GBM or LAT. We present a detailed analysis of the GBM and LAT data over a range of timescales from seconds to years, using automated pipelines and new techniques for char- acterizing the upper limits across a large area of the sky. Due to the partial GBM and LAT coverage of the large LIGO localization regions at the trigger times for both events, differences in source distances and masses, as well as the uncertain degree to which emission from these sources could be beamed, these non-detections cannot be used to constrain the variety of theoretical models recently applied to explain the candidate GBM counterpart to GW150914.
J. L. Racusin et al, (Submitted on 15 Jun 2016)

mercredi 15 juin 2016

GW151226 : Second direct detection (first replication) of a gravitational wave detection !

Live : https://iframe.dacast.com/b/59062/c/268750 !

The first available animation !

The Paper !
We report the observation of a gravitational-wave signal produced by the coalescence of two stellar-mass black holes. The signal, GW151226, was observed by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) on December 26, 2015 at 03:38:53 UTC. The signal was initially identified within 70 s by an online matched-filter search targeting binary coalescences. Subsequent off-line analyses recovered GW151226 with a network signal-to-noise ratio of 13 and a significance greater than 5σ. The signal persisted in the LIGO frequency band for approximately 1 s, increasing in frequency and amplitude over about 55 cycles from 35 to 450 Hz, and reached a peak gravitational strain of 3.4±0.7±0.9×10-22. The inferred source-frame initial black hole masses are 14.2±8.3±3.7M and 7.5±2.3±2.3M, and the final black hole mass is 20.8±6.1±1.7M. We find that at least one of the component black holes has spin greater than 0.2. This source is located at a luminosity distance of 440±180±190 Mpc corresponding to a redshift of 0.09±0.03 ±0.04 . All uncertainties define a 90% credible interval. This second gravitational-wave observation provides improved constraints on stellar populations and on deviations from general relativity
GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence B. P. Abbott et al.* (LIGO Scientific Collaboration and Virgo Collaboration) (Received 31 May 2016; published 15 June 2016)