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Quarknet Syracuse Summer Institute Strong Forces, finale

Quarknet Syracuse Summer Institute Strong Forces, finale. Last time – Key points. Feynman diagrams: pictorial representation of interaction between fundamental particles and force carriers. Both “scattering” and decays Energy and momentum conservation applies at each “vertex”

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Quarknet Syracuse Summer Institute Strong Forces, finale

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  1. QuarknetSyracuse Summer InstituteStrong Forces, finale

  2. Last time – Key points • Feynman diagrams: pictorial representation of interaction between fundamental particles and force carriers. • Both “scattering” and decays • Energy and momentum conservation applies at each “vertex” • The mass of an object is a measure of it’s “self-energy”. • Strong & EM force can only add or remove qq pairs,they CANNOT change the quark not the lepton type.

  3. Example of strong decay s s u d • Strong decay. • Note the gluonproduces a qqpair. • The original quarksare still there! • Could also get gdd, which would still yieldp+p0. r+ s u K- p0 g g u u K+ p+ Another example • Could also get gdd, whichwould then yieldK0 and K0. f0 The r+ meson is an excite state of a (ud). How does it decay?

  4. Another strong decay b b b B0 g d B0 The Y(4S) has been the “work-horse” for studying B meson decays over the last 20 years! What if the guu ? Y(4S) • The Y(4S) is the bound state of a ( b b) • The “4S” is the same spectroscopic notation as in “4s” in H-atom! • That is, principal quantum number n = 4 & l = 0 for the bb system

  5. The bb atoms! To get these data, CLEO collided e- and e+, varying the beam energy from 4.725 GeV to 5.81 GeV. Simply count the #events that produce hadrons. CLEO Collaboration 9460 MeV 10023 MeV 10355 MeV 10580 MeV • The peaks correspond to the production of bb resonances. • Only the Y(4S) has mass > 2xMB , allowing it to decay into BB[MB= 5279 MeV] • The Y(1S) – Y(3S) cannot decay to BB; they decay in other ways to hadrons, or even leptons. • How do the splitting here compare to the H-atom? Why? • Any idea what’s the “stuff” under the peaks?

  6. Electromagnetic decay c c e+ J/y e- This is an example of an electromagnetic decay. The original c c quarks have annihilated into pure energy (a photon), which then transformed back into mass (pair of leptons). This J/y decay occurs about 6% of the time. The J/y meson is a ( c c )

  7. Back to the “simple” proton p • For a high school student, knowing it’s made of 3 quarks (uud) is probably sufficient. • But, so you’re aware … it’s much more complicated! • The quarks are continually interacting by exchanging gluons. • The gluons can split into quark-antiquark pairs. • These qq pairs are “virtual”… they pop in & out of existence.

  8. So, at the Large Hadron Colliderwe’re doing this v ~ c v ~ c In the collisions, we are not looking at a whole proton scattering off another whole proton. Rather we are really looking at quarks and gluons interacting with each other.

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