Of Particular Significance

The Spin of the Higgs-Like Particle

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 03/12/2013

A quick note: I’ve had a number of questions from commenters about whether the new Higgs-like particle really has spin 0 (as it must if it is truly a Higgs particle) or whether it might have spin 2.  Well, spin 2 (with positive parity) is now strongly disfavored, as a result of new results from the ATLAS and CMS experiments at the Large Hadron Collider.  CMS has disfavored it at the 98.5-99.9% confidence level (the number depending on assumptions about whether the particle is produced in collisions of gluons or in collisions of a quark and anti-quark) using their data from the particle’s decays to two lepton/anti-lepton pairs.  ATLAS has disfavored it at the 95%-99% confidence level (similarly depending on assumptions) using their data from  decays of the new particle to a lepton, anti-lepton, neutrino and anti-neutrino.  Meanwhile, there is no reason for a spin-2 particle (especially with negative parity) to have the relative decay probabilities that are observed in the data, so the fact that all these probabilities are similar to those of a simple Higgs particle disfavors spin 2 and favors spin 0.  And there’s simply no theory of a spin-2 particle (with either parity) that doesn’t have other observable particles rather nearby in mass.    No one of these arguments is definitive, but in combination they are pretty convincing.

Meanwhile all the data is consistent with a spin 0 particle with decay probabilities roughly similar to that of a Standard Model Higgs (the simplest type of Higgs particle.)

So let’s stop spending much bandwidth on spin 2: it is disfavored by both ATLAS and CMS — directly by measurement of the particle’s spin, and indirectly via its relative probabilities to decay to various types of particles — and it is disfavored theoretically. The more important measurement is to check whether this apparently spin-0 particle really has positive parity, or whether it has a mix of positive and negative parity.

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9 Responses

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  3. Hi Matt

    Possibly a dumb question, but I thought parity described whether the particle was left-handed or right-handed, i.e. which way it spins relative to its motion. If it has no spin , how does it have a handedness?

  4. Two atoms were walking across a road when one of them said, “I think I lost an electron!” “Really!” the other replied, “Are you sure?” “Yes, I ‘m absolutely positive.”

  5. The uncertainty principle has broad physical and philosophical implications that were largely explored and articulated by Niels Bohr after Heisenberg’s statement of the principle. The Uncertainty principle establishes its importance in the everyday world in two ways, it rejects the idea held by classical physics that physical phenomena are uniquely tied to actions by deterministic causal laws, and that observables are independent of the observer. Until the statement of the uncertainty principle, Modern Physics held to that idea of a classical determinism, and the rejection of such determinism became a cause for descent between Einstein (as a believer in a classical determinism) and Bohr and the other supporters of the quantum revolution.
    The Heisenberg Uncertainty Principle (HUP) is not just a side result of quantum mechanics. In fact, it is arguably the most important fundamental concept behind all of quantum mechanics.
    General relativity is used to describe the mechanics of motion of very massive objects and makes very special use of the relative velocity of different objects through space. Quantum mechanics is used to describe the behavior of objects at very small distances from each other. Some of the most interesting aspects of cosmology are in the study of black holes and the conditions at the beginning of the universe; both of these things involve very massive objects occupying extremely tiny spaces(rupturing 3D spacetime?), and thus both of these situations suggest the use of both general relativity and quantum mechanics. However, because of the HUP, the restriction of the component particles to extremely small regions of space means that the velocities of the ensemble of particles must necessarily take on a wide range of very different velocities. Due to the dependence of velocity in relativity, this makes it impossible to combine the two cleanly.
    This uncertainty arises because the act of measuring affects the object being measured. The only way to measure the position of something is using light, but, on the sub-atomic scale, the interaction of the light with the object inevitably changes the object’s position and its direction of travel.

    Higgs particles’s(ripple) position and momentum in positive and and negative pressure is simultanious within 3D spacetime?

  6. The time between back-and-forth vibrations of a particle at rest is h / m c2 , where m is the mass of the particle, c is the speed of light, and h is Planck’s constant. There are various theoretical reasons to expect lightweight elementary particles to have spin no greater than 2, and for the only particle of spin 2 to be the graviton.

    Within 3D spacetime metric, the protrude in spacetime matrix, is allowed to have spin “0” for transcendental field. But in context with spinor, a 360 degree rotation transforms the numeric coordinates of a spinor into their negatives, and so it takes a rotation of 720 degrees to re-obtain the original values- may be not allowed in 3D spacetime metric? – but in higher energies , it is allowed in extra dimensions?
    But we have experimental limit of human consciousness, creating stroboscopic flips?
    The non zero equlibrium only depends on external force not intrinsic = Amplitude? – means, when transcendental field react with zero equlibrium of known particles, there is weakness in energy level of transcendental field- allowing negative pressure, to restore its physicalproperty(amplitude), it pull back to positive pressure?

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