Self Quote Of The Week: Why You Can't Weigh Quarks Directly
    By Tommaso Dorigo | July 11th 2014 08:39 AM | 13 comments | Print | E-mail | Track Comments
    About Tommaso

    I am an experimental particle physicist working with the CMS experiment at CERN. In my spare time I play chess, abuse the piano, and aim my dobson...

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    In the process of revising a chapter of my book, I found a clip I would like to share here, as it contains an analogy I cooked up and which I find nice enough to be proud of. Well, two analogies, as you'll soon find out; here I am speaking of the cat weighing trouble at the end of the piece - the other is quite trivial.
    The topic is the widely different masses of fermions, the building blocks of our universe, and the trouble in making sense of it and of measuring precisely their values. Comments welcome!

    Mass is a mysterious intrinsic property of matter corpuscles. We are accustomed to confuse the mass of an object with its weight, since the two quantities are proportional to one another as long as we remain in the roughly constant gravitational field of Earth’s surface. But mass is not a force: rather, it is the attribute of a material body specifying how hard it is to change its status of motion. The larger the mass of an object, the stronger the pull one has to apply to set it in motion at a given speed, or to modify its trajectory.  It was the large mass of 2nd and 3rd generation fermions what prevented their discovery for the better part of the twentieth century; all that was known in the thirties were the proton, the neutron, the electron and its antiparticle, and the photon. In fact, mass can be created in particle reactions when the kinetic energy released in a collision is converted into new matter states, following the famous formula E=mc^2, where the squared speed of light in vacuum c^2 acts as a proportionality constant between energy E and mass m.

    To visualize just how different the masses of fermions are, and how mysterious it is that those incongruous entities all fit in the tidy scheme outlined above, try imagining that we were measuring fermion masses with a yardstick as if they were lengths in space, and we agreed that the length corresponding to the mass of the lightest charged fermion, the electron, fit in the first notch of our scale –say one inch. Under such circumstances, in order to measure distances corresponding to masses like that of the top quark, we would need a yardstick about a kilometer long! The whole point here is that the masses of elementary fermions constitute an unsolved enigma. We have learned how to measure them with good precision (except those of neutrinos, for which so far we only know that a proper yardstick should be able to discern lengths well below the nanometer), but the standard model gives neither any clue on the reason for the enormous range in results we find, nor for their observed pattern. In fact, fermion masses are free parameters of the model, which we are bound to infer only from the experimental measurement in order to complete the picture.

    It would be rather silly for us to stick to the dubious analogy of measuring masses with a yardstick. In the following chapters you will instead become familiar with a more standard treatment of mass and energy, two quantities which –with a convention simplifying matters a whole lot –can be sized up with the same units. All works in multiples of the electron-Volt, the energy that is imparted to a particle carrying the electric charge of one electron by moving it “upstream” through a potential difference of one Volt. The electron-Volt (usually written eV) is a quite small amount of energy: its order of magnitude is the energy of atomic transitions between nearby energy levels. It takes little more than a dozen eV to free the electron of a hydrogen atom from its electromagnetic bond with the nucleus, and less than one eV is enough to make the same electron jump from one atomic orbit to another. In this book we will often use a multiple of the eV called GeV, where the G stands for giga-, the ancient Greek prefix for a billion. A proton’s mass is close to a GeV, and so are the masses of many other composite bodies whose study has opened our way to the understanding of sub-nuclear physics.

    Now armed with a reasonable measurement unit, let us give a look at the mass hierarchy of the fundamental objects we have encountered so far. Neutrinos are the lightest elementary particles among fermions. They are much lighter than one eV! In fact they are so light that we have so far been unable to measure their mass. Next up is the electron, with a mass of 511 thousand eV –511 keV, where the prefix k signifies a thousand. The muon is still 200 times heavier, at 105 million electron-Volts: 105 MeV, where M stands for a million. The tauon, the heaviest lepton, is some further 17 times heavier at 1.77 GeV –where as noted above G stands for a billion. As for quarks, the lightest is the up quark, which weighs about 3 MeV, and the heaviest is the top quark, whose hefty mass totals 173 GeV. In-between lie the down quark (7 MeV), the strange quark (90 MeV), the charm quark (1.2 GeV), and the bottom quark (4.2 GeV).

    The numbers above let you appreciate the existence of an unsolved mystery. We in fact have no clue of the reason of that hierarchy of values, although the discovery of the Higgs boson has at least allowed us to cast the problem in different terms. You should also bear in mind that the ones I gave above are approximate numbers: the masses of all quarks except the top cannot be measured directly, as those particles can only be studied within hadrons, the bound states they form by combining in pairs or triplets. Like a cat that would not be convinced to stay still on a scale, quarks require us to use indirect methods to infer their mass. You can estimate your cat’s mass by subtraction, measuring yourself with and without the cat in your arms; similarly, you can size up quark masses by comparing the masses of hadrons that contain them or others.


    Dear Tommaso,
    It would take you one week at the most to thoroughly study/analyze The gem 5, 6, 7, 8, 9, and both the mass and inertia would not be the mystery for you any more.
    The first 4 texts are about how could had been derived that what we today call “relativity theory”, in the year 1900 already. You can skip that, and start from The gem (5).
    Please, do read The gem 5, 6, 7, 8, 9
    My intentions are good. I do not want to distract you. I just ask you to read something that I think might help you, might give you some new idea, might make your book better.
    Best wishes,

    Oddly enough, only today I came across this, while seeking to refresh my memory over photon wavelengths and electron volts:


    Frae Wikipedia

    In pheesics, the electron volt (seembol eV; an aa written electronvolt) is a unit o energy equal tae approximately 1.6×10−19 joule (seembol J). By defineetion, it is the amoont o energy gained (or lost) bi the charge o a single electron moved across an electric potential difference o ane volt. Thus it is 1 volt (1 joule per coulomb, 1 J/C) multiplied bi the elementary charge (e, or 1.602176565(35)×10−19 C). Tharefore, one* electron volt is equal tae 1.602176565(35)×10−19 J. Historically, the electron volt wis devised as a staundart unit o measur through its uisefuness in electrostatic pairticle accelerator sciences acause a pairticle wi charge q haes an energy E = qV efter passin through the potential V; if q is quotit in integer units o the elementary charge an the terminal bias in volts, ane gets an energy in eV.

    Yes, this is from SCOTS Wikipedia!

    * should be ‘ane’ — they missed this one in translation, methinks.

    Robert H. Olley / Quondam Physics Department / University of Reading / England
    Expect it is because you cannot weigh something that does not exist in any "real" way.

    Dear Tommaso,
    So far, the only one who really tried to help you about your question was Vera.
    Try to think for a moment about what is that – really, honestly – what prevents you to read what she proposed you?
    I am sure that you – like most people do, too – read, daily, many distracting things, unimportant things, and other whatnots. And you even enjoy in some of that. Some of that relaxes you, amuses you. Some of that makes you to regret because you wasted your time on reading that.
    That what Vera proposed you to read are the most important things, which have everything to do with your quest(s), and you refuse to see that. Ask yourself, honestly: Why is that so?

    We are prevented from reading what Vera proposes by the lack of a link or a reference...

    Dear Milica, or Vera, or whoever you are,

    I gave a look at the information and it looks not very different from a gazillion of other
    theory-of-everything-oh-so-simple-why-isnt-anybody-listening things that I have been
    exposed to in 10 years of serious blogging on experimental particle physics. I am sure
    many who are in a position similar to mine have similar experimences, too.

    I am not saying the stuff is not interesting, or that it is garbage, or that it is ridiculous. I
    honestly think that anybody who believes he or she is smarter than every theoretical
    physicist on the planet should spend the time to go through what exists, and to follow
    the usual channels to get their work considered. There are no shortcuts, unfortunately.
    I do sympathize with some non-academics who are indeed smart and have produced
    interesting studies. One of them is Carl Brannen: he was consistently prevented from
    posting preprints on the Cornell arxiv, but eventually he managed to get some stuff through,
    by "following the guidelines", let's say. He did produce some interesting stuff. It is not by
    chance that he is following the path to Academia now, although at a mature age.

    So, dear Tommaso,
    “you gave a look” , and you say “it looks not very different from a gazillion of other …”.
    Well, in Google (or in any other search-engine: Yahoo, Bing, Qwant, Blekko, Webcrawler, …), search for
    “two photons whirl”
    (with quotation marks)

    So, there are no other such things – only those written by Zoran.

    And, it is not just a scratch-idea, basic idea, initial idea of his, but thoroughly physically and mathematically explained and experimentally supported and sustained concept.
    (So sound and clear, that I – high-school pupil – understand it. In a way I understand i.e. Pythagoras’ theorem. This means, I do not need a second opinion, somebody else’s opinion, to assure me that Pythagoras’ theorem is true, and to know why it is true. I can derive it on my own, knowing exactly what and why am I doing while deriving and proving it.)
    And, Zoran then derives the Newton’s law of gravitation from that. Clearly, accurately, reasonably.

    Are there any other such theories, either “mainstream” or others? Well, no, there are not. That is what everybody is trying to achieve, but so far, nobody managed to do that.

    Or, please, provide me (us) a link to just one of “the gazillion not very different theories”, so that I, we, can see the similarities/differences, on our own, using the scientific method and Occam’s razor.

    It is not important Zoran, nor what he thinks, nor you and your opinion. The truth is that what is important, expressed through (with) words and equations, so that everybody, using his own sound reasoning can realize that it is the truth. I mean, the Newton’s laws are not accurate because Newton discovered them. They are not true because Newton discovered them. But it is very important that we know these laws. To learn them in the way to rediscover them on our own, using our own ability to think, with the teacher’s guidance, through experiments. That is the only way to really understand them.

    You are the researcher, and also the teacher. Please show me what is wrong in “The gem” texts. I do not see anything wrong there. And it is clear and simple, so it should not be the problem for you to pin-point the wrong (logically, mathematically, physically) things there. I know - you have more important things to do.

    You say “there are no shortcuts”. I know. Zoran showed us what he tried to do in the last 4 years. He used each regular way to acquaint the academic community with his work.
    And, I may say, somehow I feel the shame instead of those who reviewed his work. I can’t believe that they really wrote what they wrote. They either did not read it (or, like you, “gave a look”), dismissed it as soon they saw that it is not along the “mainstream” line, or they were so stunned, so shocked, that they simply did not want to give it a second, thorough thought. Because, if it is true, then what the hack did they do all their life …

    Me and my friend Vera (we became friends during Zoran’s 1-week-lectures) won’t distract you any more. You are writing a book.


    If you trap a massless photon in a mirror-box, you increase the mass of that system. Because photon momentum is a measure of resistance to change-in-motion for a wave moving on a linear open path, whilst mass is a measure of resistance to change-in-motion for a wave moving on a closed path. The wave nature of matter is not in doubt, and nor is [I]the mass of a body is a measure of its energy-content[/I]. Einstein even refers to the electron in his this. He reduces c to a dimensionless constant and gives expresssions such as √c/3π. I would not underestimate the difficulties faced by authors on this subject. Particularly since electron mass is nowadays described as a measure of its interaction with "the Higgs field", and not a measure of its energy-content.

    John Duffield
    Sorry, there's a mistake in the above and I can't fix it. Please disregard and I'll try again:

    If you trap a massless photon in a mirror-box, you increase the mass of that system. Because photon momentum is a measure of resistance to change-in-motion for a wave moving on a linear open path, whilst mass is a measure of resistance to change-in-motion for a wave moving on a closed path. The wave nature of matter is not in doubt, and nor is the mass of a body is a measure of its energy-content. Einstein even refers to the electron in his E=mc² paper. It's obvious that he thought of it as a body. We can diffract electrons, they have their magnetic moment and their spin, and in atomic orbitals "electrons exist as standing waves". So there's no mystery to mass. Think TQFT and see this, then think of the electron as a 511keV photon going round and round in a Dirac's belt "box" of its own making. As to why there's a mass hierarchy, a medical doctor called Andrew Worsley proposed a "quantum harmonics" solution wherein different massive particles have different topologies. See this. He reduces c to a dimensionless constant and gives expresssions such as √c/3π. I don't agree with everything he says, but I do think he's on to something.

    NB: I wouldn't underestimate the difficulties faced by authors on this subject. Particularly since electron mass is nowadays described as a measure of its interaction with "the Higgs field", and not a measure of its energy-content. The Higgs mechanism contradicts E=mc². The fix would be to say the Higgs field is the photon field. But then there's issues with the discovery of the Higgs boson.
    Sorry Milica, (and Tommaso, and others)
    Actually, there is no reason to appologize, I have to add this:
    Galileo expected the telescope to quickly make believers in the Copernican system out of all educated persons, but he was disappointed. He expressed his discouragement in a 1610 letter to Kepler:
    "My dear Kepler, what would you say of the learned here, who, replete with the pertinacity of the asp, have steadfastly refused to cast a glance through the telescope? What shall we make of this? Shall we laugh, or shall we cry?" It became clear that the Copernican theory had its enemies.
    Galileo's first instinct was turn to acquiring more knowledge for those few open minds he was able to reach--disciples such as monk Benedetto Castelli. Galileo wrote to Castelli: "In order to convince those obdurate men, who are out for the vain approval of the stupid vulgar, it would not me enough even if the stars came down on earth to bring witness about themselves. Let us be concerned only with gaining knowledge for ourselves, and let us find therein our consolation."
    Soon, however, Galileo decided that Copernicus was worth a fight. He decided to address his arguments to the enlightened public at large, rather than the hidebound academics. He saw more hope for gaining support among businessmen, gentlemen, princes, and Jesuit astronomers than among the vested apologists of universities. He seemed compelled to act as a consultant in natural philosophy to all who would listen. He wrote in tracts, pamphlets, letters, and dialogues--not in the turgid, polysyllabic manner of a university pedant, but simply and directly.

    The history repeats only because of the vanity. Let us act/behave more mature than our ancestors. Each and every bad behavior of people, each and every quarrel, is the result of vanity. Tame your vanity with your sapience, and read “The gem” text series. For the sake of all of us. That is what our children will learn about in primary school already, and in depth/details in secondary school already.
    “The gem” texts represent the one and only truly scientific, non abstract, reasonable, comprehensible fundamental physics which exists. Everything else on that subject, what was done in the last 100 years, is the pure mathematical mysticism. Modern sorcery. Vanity driven mind-illness. Let us be homo sapiens finally. We are capable for that.

    "In fact, mass can be created in particle reactions when the kinetic energy released in a collision is converted into new matter states,"

    Well, mass is the Minkowski length of the momentum four-vector. It doesn't change in a collision, right?

    Dear Anon,

    wrong. You have to consider two 4-vectors when you make a collision. Then energy
    and momentum conservation allow you to create new particle states with masses up
    to sqrt(s), where s is one of the three Mandelstam variables characterizing the collision.