5 ms·

I (with minimal physics background, I admit) would bet on systematic error. We're seeing one mass from one decay path, and a _very slightly different_ mass from

by gwillen 14y ago

I (with minimal physics background, I admit) would bet on systematic error. We're seeing one mass from one decay path, and a _very slightly different_ mass from a different decay path. The best explanation seems to _me_ to be that, for one or both of the decay paths, there's a problem in how we're computing the Higgs mass.

ars 14y ago
BTW 3GeV is not "very slightly different". It's the mass of 3 protons, which for subatomic particles is a lot.
stephengillie 14y ago
Wikipedia says this is possible with a more complex theory. Are we going with the simplest theory due to Occam's razor? The Minimal Standard Model as described above contains the simplest possible model for the Higgs mechanism with just one Higgs field. However, it also is possible to have an extended Higgs sector with additional doublets or triplets. The non-minimal Higgs sector favoured by theory are the two-Higgs-doublet models (2HDM), which predict the existence of a quintet of scalar particles: two CP-even neutral Higgs bosons h0 and H0, a CP-odd neutral Higgs boson A0, and two charged Higgs particles H±. https://en.wikipedia.org/wiki/Higgs_boson#Alternative_models https://en.wikipedia.org/wiki/Higgs_boson#Alternative_models
- ars 14y ago
  The W and Z bosons are basically the same, except one is charged and the other neutral. And due to that they have different masses. So it's certainly possible the same thing could be happening here.
  - gus_massa 14y ago
    The W and Z particles are a little more different. The W+- particles only interact with L-hilarity particles. The Z particle "prefers" the L particles, but also interacts with the R particles. It's more complicated. There is a W^0 particle that is the neutral equivalent of the W^+ and W^- particles, all of them have the same mass. There is another particle called A, that is like a photon with mass (but it "sees" the hypercharge of the particles, not the charge) Combining the W^0 and A particles, it's possible to get two new particles the Z^0 and the photon. In this combination the Z^0 has all the mass and the photon has no mass. It's more easy to understand some experiments using the Z^0 and the photon, so to make some explanations more clear it's better to use them instead of the W^0 and the A. IIRC, for low energy experiments it'd better to use Z^0 and photons, and for high energy experiments it's better to use W^0 and A.
    - deleted 14y ago
      [deleted]
    - ars 14y ago
      You are mixing conjectures from string theory and other theories with known physics. I can found no info on the W^0 or the A, R and L are a type of conjectured parity, not actual particles, and hypercharge is an obsolete concept. You should be more careful about where you learn physics, and very very careful to distinguish known physics, or theories with evidence from conjectures and ideas. Both are necessary - but don't mix them up.
      - gus_massa 14y ago
        What?! I'm taking only about particle physic (I don't know almost anything about string theory). The W^+,W^0 and W^- are a weak-isospin triplet of bosons that are the carriers of the "real" weak force, assuming that the SU(2)_L symmetry holds for the weak-isospin doublets (electron_L-neutrilo_L), ...,(up_quark_L, down'_quark_L),... (Sometimes the weak-isospin triplet is written as W_0,W_1 and W_2, using another base.) I rememberd incorrectly the name of of the particles "A". Sorry. The correct name is B^0. This is the of the field associated to the weak hypercharge with the U(1) symmetry. I know hat the old hypercharge is not more a very useful concept, but I was trying to simplify a little the notation and I dropped the weak part. All of this is the electroweak force theory (unification of the electromagnetic force and the weak force). http://en.wikipedia.org/wiki/Electroweak_interaction http://en.wikipedia.org/wiki/Electroweak_interaction In this theory each fermions can be classified as L or R chirality (it's a "property" of the particles, not an independent thing) (the mass of the particles makes this a little more complicated). The "real" weak" force only interacts with the L version of the particles. This has many experimental results, for example the ratio between the mass of the Z^0 and the W^+- particle is indirectly related to the ratio between the coupling of the Z^0 and the L and R electrons. All of this id proved beyond doubt, but it assumes that the particles doesn't have mass. They have an apparent mass created by the Higgs mechanisms (or something equivalent), so there must be Higgs bosons out there. So the only missing part is to prove the existence of the Higgs bosons, and it's almost done (5-sigmas next year?).
mileswu 14y ago
This is how I lean too. A few percent in a mass measurement is a pretty small systematic error and could easily come from something that has been overlooked or miscalibrated. There are a tens and hundreds of calibration and corrections that go into these detectors and analyses and it's all too easy to miss something. What really makes me convinced it is an experimental error is that CMS does not see the same mass discrepancy. If both independent experiments saw the same discrepancy then this would truly be really interesting new physics. Disclaimer: I am on ATLAS myself, though not associated with the Higgs groups. I can only comment on public results due to much information being confidential.

by gwillen 14y ago

ars 14y ago

BTW 3GeV is not "very slightly different". It's the mass of 3 protons, which for subatomic particles is a lot.

stephengillie 14y ago

Wikipedia says this is possible with a more complex theory. Are we going with the simplest theory due to Occam's razor? The Minimal Standard Model as described above contains the simplest possible model for the Higgs mechanism with just one Higgs field. However, it also is possible to have an extended Higgs sector with additional doublets or triplets. The non-minimal Higgs sector favoured by theory are the two-Higgs-doublet models (2HDM), which predict the existence of a quintet of scalar particles: two CP-even neutral Higgs bosons h0 and H0, a CP-odd neutral Higgs boson A0, and two charged Higgs particles H±. https://en.wikipedia.org/wiki/Higgs_boson#Alternative_models https://en.wikipedia.org/wiki/Higgs_boson#Alternative_models

ars 14y ago
The W and Z bosons are basically the same, except one is charged and the other neutral. And due to that they have different masses. So it's certainly possible the same thing could be happening here.
- gus_massa 14y ago
  The W and Z particles are a little more different. The W+- particles only interact with L-hilarity particles. The Z particle "prefers" the L particles, but also interacts with the R particles. It's more complicated. There is a W^0 particle that is the neutral equivalent of the W^+ and W^- particles, all of them have the same mass. There is another particle called A, that is like a photon with mass (but it "sees" the hypercharge of the particles, not the charge) Combining the W^0 and A particles, it's possible to get two new particles the Z^0 and the photon. In this combination the Z^0 has all the mass and the photon has no mass. It's more easy to understand some experiments using the Z^0 and the photon, so to make some explanations more clear it's better to use them instead of the W^0 and the A. IIRC, for low energy experiments it'd better to use Z^0 and photons, and for high energy experiments it's better to use W^0 and A.
  - deleted 14y ago
    [deleted]
  - ars 14y ago
    You are mixing conjectures from string theory and other theories with known physics. I can found no info on the W^0 or the A, R and L are a type of conjectured parity, not actual particles, and hypercharge is an obsolete concept. You should be more careful about where you learn physics, and very very careful to distinguish known physics, or theories with evidence from conjectures and ideas. Both are necessary - but don't mix them up.
    - gus_massa 14y ago
      What?! I'm taking only about particle physic (I don't know almost anything about string theory). The W^+,W^0 and W^- are a weak-isospin triplet of bosons that are the carriers of the "real" weak force, assuming that the SU(2)_L symmetry holds for the weak-isospin doublets (electron_L-neutrilo_L), ...,(up_quark_L, down'_quark_L),... (Sometimes the weak-isospin triplet is written as W_0,W_1 and W_2, using another base.) I rememberd incorrectly the name of of the particles "A". Sorry. The correct name is B^0. This is the of the field associated to the weak hypercharge with the U(1) symmetry. I know hat the old hypercharge is not more a very useful concept, but I was trying to simplify a little the notation and I dropped the weak part. All of this is the electroweak force theory (unification of the electromagnetic force and the weak force). http://en.wikipedia.org/wiki/Electroweak_interaction http://en.wikipedia.org/wiki/Electroweak_interaction In this theory each fermions can be classified as L or R chirality (it's a "property" of the particles, not an independent thing) (the mass of the particles makes this a little more complicated). The "real" weak" force only interacts with the L version of the particles. This has many experimental results, for example the ratio between the mass of the Z^0 and the W^+- particle is indirectly related to the ratio between the coupling of the Z^0 and the L and R electrons. All of this id proved beyond doubt, but it assumes that the particles doesn't have mass. They have an apparent mass created by the Higgs mechanisms (or something equivalent), so there must be Higgs bosons out there. So the only missing part is to prove the existence of the Higgs bosons, and it's almost done (5-sigmas next year?).

mileswu 14y ago

This is how I lean too. A few percent in a mass measurement is a pretty small systematic error and could easily come from something that has been overlooked or miscalibrated. There are a tens and hundreds of calibration and corrections that go into these detectors and analyses and it's all too easy to miss something. What really makes me convinced it is an experimental error is that CMS does not see the same mass discrepancy. If both independent experiments saw the same discrepancy then this would truly be really interesting new physics. Disclaimer: I am on ATLAS myself, though not associated with the Higgs groups. I can only comment on public results due to much information being confidential.