4 ms·

LHCb experiment discovers a new pentaquark

95 points by ljdk 8y ago

drilldrive 8y ago
So, what is a pentaquark exactly? The article doesn't say.
- kowdermeister 8y ago
  https://en.wikipedia.org/wiki/Pentaquark https://en.wikipedia.org/wiki/Pentaquark
- TheAdamist 8y ago
  if you click through on the 'read more' to: http://lhcb-public.web.cern.ch/lhcb-public/Welcome.html#Pentaq http://lhcb-public.web.cern.ch/lhcb-public/Welcome.html#Pent... including the detail that the quark state content is: "duucc: four quarks and one antiquark. " Theres a further 'read more' link to a powerpoint, http://moriond.in2p3.fr/QCD/2019/TuesdayMorning/Skwarnicki.pptx http://moriond.in2p3.fr/QCD/2019/TuesdayMorning/Skwarnicki.p... which is way out of my understanding
- Hattes 8y ago
  Penta = five. There's a picture of a ball with five balls in it. It decays to a proton (which as mentioned has three quarks) and another pair of a quark and an anti-quark. I'd say it's there.
- andrepd 8y ago
  Usually quarks are confined in composite particles of two (mesons) or three (baryons) quarks. However they can also in certain conditions form particles of 5 quarks (the pentaquarks).
  - drilldrive 8y ago
    Oh, so quarks can only be composites of two, three, and five? Any reason that could be stated in layman's terms?
    - dragonwriter 8y ago
      > Oh, so quarks can only be composites of two, three, and five? They can also be in fours. Possibly other configurations; the four and five quark configurations were theorized in 1964 but only confirmed in 2014 & 2015. > Any reason that could be stated in layman's terms? None at all, in fact, the source article does so: “In the conventional quark model, composite particles can be either mesons formed of quark–antiquark pairs or baryons formed of three quarks. Particles not classified within this scheme are known as exotic hadrons. When Murray Gell-Mann proposed the quark model in his fundamental 1964 paper, he mentioned the possibility of exotic hadrons such as pentaquarks, but it took 50 years to demonstrate their existence experimentally.” (There is slightly more detail on the read more link, too.)
      - JadeNB 8y ago
        > > Any reason that could be stated in layman's terms? > None at all, in fact, the source article does so …. Did you really mean "None at all"? The rest of your post seems to say the opposite.
    - andrepd 8y ago
      Quantum chromodynamics (the theory which describes the strong interaction) has a feature called colour confinement, which says that quarks will favour being in colourless configuration (where colourless = zero colour charge). The two easiest ways for this to happen are in mesons (two quarks: one quark and one antiquark of the same colour, like red + antired = colourless), or in baryons (three quarks: 1 red + 1 green + 1 blue = colourless) like the familiar proton and neutron. However other configurations are possible, these are just the simplest ones. In certain incredibly difficult to attain conditions, we can avoid producing either a two- or three-quark composite particle but produce instead a five-quark particle (e.g. 1 red + 1 green + 1 blue + 1 red + 1 antired = colourless). This "colour" means colour charge, it doesn't have any relation to the regular meaning of "colour of light".
      - deleted 8y ago
        [deleted]
afraca 8y ago
This is both entertainment and information, so to justify it I'll ask a question about this: https://www.youtube.com/watch?v=j50ZssEojtM https://www.youtube.com/watch?v=j50ZssEojtM (Large Hadron Rap) Are these goals still accurate or has new knowledge and engineering changed the goals of the detectors?
- sanxiyn 8y ago
  The rap is pretty bad. It lists four questions: dark matter, matter-antimatter asymmetry (aka baryogenesis, related to CP violation), Higgs boson, and hierarchy problem (why gravity is so weak; rap alludes extra dimension). We found Higgs boson, which is great. We are no closer to answer other three questions, and frankly, there was no reason to expect LHC to help there, it was all wishful thinking. Sure, it was possible, LHC would do what has never been done, but not very probable.
  - sand500 8y ago
    As I see it, we are basically putting more and more energy into these particle collisions and hoping something unexpected happens.

95 points by ljdk 8y ago

drilldrive 8y ago

So, what is a pentaquark exactly? The article doesn't say.

kowdermeister 8y ago
https://en.wikipedia.org/wiki/Pentaquark https://en.wikipedia.org/wiki/Pentaquark
TheAdamist 8y ago
if you click through on the 'read more' to: http://lhcb-public.web.cern.ch/lhcb-public/Welcome.html#Pentaq http://lhcb-public.web.cern.ch/lhcb-public/Welcome.html#Pent... including the detail that the quark state content is: "duucc: four quarks and one antiquark. " Theres a further 'read more' link to a powerpoint, http://moriond.in2p3.fr/QCD/2019/TuesdayMorning/Skwarnicki.pptx http://moriond.in2p3.fr/QCD/2019/TuesdayMorning/Skwarnicki.p... which is way out of my understanding
Hattes 8y ago
Penta = five. There's a picture of a ball with five balls in it. It decays to a proton (which as mentioned has three quarks) and another pair of a quark and an anti-quark. I'd say it's there.
andrepd 8y ago
Usually quarks are confined in composite particles of two (mesons) or three (baryons) quarks. However they can also in certain conditions form particles of 5 quarks (the pentaquarks).
- drilldrive 8y ago
  Oh, so quarks can only be composites of two, three, and five? Any reason that could be stated in layman's terms?
  - dragonwriter 8y ago
    > Oh, so quarks can only be composites of two, three, and five? They can also be in fours. Possibly other configurations; the four and five quark configurations were theorized in 1964 but only confirmed in 2014 & 2015. > Any reason that could be stated in layman's terms? None at all, in fact, the source article does so: “In the conventional quark model, composite particles can be either mesons formed of quark–antiquark pairs or baryons formed of three quarks. Particles not classified within this scheme are known as exotic hadrons. When Murray Gell-Mann proposed the quark model in his fundamental 1964 paper, he mentioned the possibility of exotic hadrons such as pentaquarks, but it took 50 years to demonstrate their existence experimentally.” (There is slightly more detail on the read more link, too.)
    - JadeNB 8y ago
      > > Any reason that could be stated in layman's terms? > None at all, in fact, the source article does so …. Did you really mean "None at all"? The rest of your post seems to say the opposite.
  - andrepd 8y ago
    Quantum chromodynamics (the theory which describes the strong interaction) has a feature called colour confinement, which says that quarks will favour being in colourless configuration (where colourless = zero colour charge). The two easiest ways for this to happen are in mesons (two quarks: one quark and one antiquark of the same colour, like red + antired = colourless), or in baryons (three quarks: 1 red + 1 green + 1 blue = colourless) like the familiar proton and neutron. However other configurations are possible, these are just the simplest ones. In certain incredibly difficult to attain conditions, we can avoid producing either a two- or three-quark composite particle but produce instead a five-quark particle (e.g. 1 red + 1 green + 1 blue + 1 red + 1 antired = colourless). This "colour" means colour charge, it doesn't have any relation to the regular meaning of "colour of light".
    - deleted 8y ago
      [deleted]

afraca 8y ago

This is both entertainment and information, so to justify it I'll ask a question about this: https://www.youtube.com/watch?v=j50ZssEojtM https://www.youtube.com/watch?v=j50ZssEojtM (Large Hadron Rap) Are these goals still accurate or has new knowledge and engineering changed the goals of the detectors?

sanxiyn 8y ago
The rap is pretty bad. It lists four questions: dark matter, matter-antimatter asymmetry (aka baryogenesis, related to CP violation), Higgs boson, and hierarchy problem (why gravity is so weak; rap alludes extra dimension). We found Higgs boson, which is great. We are no closer to answer other three questions, and frankly, there was no reason to expect LHC to help there, it was all wishful thinking. Sure, it was possible, LHC would do what has never been done, but not very probable.
- sand500 8y ago
  As I see it, we are basically putting more and more energy into these particle collisions and hoping something unexpected happens.