Quarks, Hadrons and all that…

1. Quarks, Hadrons and all that… HW9 posted,due next Wed.See me aboutany exam “issues”by 4/16. Labs for next 2 weeks.Q&A Session…Bring questions ! See PHY106 Schedule link for web-based readings. Increasing mass Also, each quark has a corresponding antiquark.The antiquarks have opposite charge to the quarks

2. The 6 Quarks, when & where… Notice the units of mass !!! SLAC = Stanford Linear AcceleratorBNL = Brookhaven National Lab Proton mass = 0.938 [GeV/c2]

3. How do we know any of this? • Recall that high energy particlesprovide a way to probe, or“see” matter at the very smallestsizes. (Recall Electron microscope example). • Today, high energy accelerators produce energetic beams which allow us to probe matter at its most fundamental level. • As we go to higher energy particlecollisions: 1) Wavelength probe is smaller  see finer detail2) Can produce more massive objects, via E=mc2

4. Major High Energy Physics Labs(accelerators + detectors) Fermilab DESY SLAC KEK CERN CESR BNL

5. Tevatron 1.25 miles Main Injector Fermilab Accelerator (30 miles from Chicago) Experimental areas Top Quarkdiscovered here at FNALin 1995.

6. “Typical” Particle Detector ~ 6 ft

7. Typical physicist colleagues! Don’t ask me what they’re doing !

8. Back to matter & quarks…

9. Fundamental particles • We consider quarks to be fundamental, because so far we have been unable to “break them apart”. • As we increase the momentum of particles in our accelerators, we are able to resolve, or see, deeper into matter. • We are currently able to accelerate particles to energies of ~1 [TeV] = 1x1012 [eV]. • To what wavelength does this correspond? First convert [eV] to [J] !!!! l =hc/E = (6.6x10-34)(3x108) / 1.6x10-7 = 1.2x10-18[m] So, if quarks were bigger than this, we would be able to discern theirsubstructure. So far, they look to be smaller than this ! That is theyare at least 1000 times smaller than the proton ! Same is truefor electron  quarks (and electrons) are considered “fundamental”

10. Gold atom Silver atom Mass [GeV/c2] Proton Quark masses • 6 different kinds of quarks. • Matter is composed mainly of upquarks and down quarksbound in the nuclei of atoms. • The masses vary dramatically(from ~0.005 to 175 [GeV/c2]) • The heavier quarks are notstable, and decay to lighter quarksquite rapidly Example: t  b (~10-23 [s]) b  c (~10-12 [s]) c  s (~10-12 [s]) su (~10-7-10-10 [s]) More on quark decays later…

11. Q= +2/3 Particle Q= -1/3 Q= -2/3 Anti- Particle Q= +1/3 Anti-particles too ! • We also know that every particle has a corresponding antiparticle! • That is, there are also 6anti-quarks, they have opposite charge to the quarks. • So, the full slate of quarks are: Quarks Anti-Quarks

12. Hadron Jail q Proton Quark Confinement • Quarks are “confined” inside objects known as “hadrons”. We’ll learn more about hadrons in a bit… • This is a result of the “strong force” which we will discuss later…

13. Protons & Neutrons To make a proton:We bind 2up quarks of Q = +2/3and 1 down quark of Q = -1/3. The total charge is2/3 + 2/3 + (-1/3) = +1 !To make a neutron: We bind 2 down quarks of Q= -1/3with 1 up quark of Q = +2/3 to get: (-1/3) + (-1/3) + (2/3) = 0 ! So, it all works out ! But, yes, we have FRACTIONALLY CHARGED PARTICLES!

14. Why does the nucleus stay together ? So far, the only “fundamental” forces we know about are: (a) Gravity (b) EM force (Electricity + Magnetism) Which one of these is responsible for binding protons to protons and protons to neutrons ??? • Since like sign charges repel, it can’t be EM force? • Gravity is way, way, way too weak… Then what is it??? Strong Force This is the third fundamental force in nature and is by far thestrongest of the four forces. More on forces later…

15. HADRONS/BARYONS The forces which hold the protons and neutrons together in thenucleus are VERYstrong. They interact via the STRONG FORCE. Protons and neutrons are among a class of particles called “hadrons”(Greek for strong). Hadrons interact very strongly with other hadrons! Baryons are hadrons which contain 3 quarks (no anti-quarks).Anti-baryons are hadrons which contain 3 anti-quarks (no quarks). Wow, I’m somebody… I’m a Baryon! Me too, me too…

16. u s d u u u Are there baryons other than protons and neutrons? • Good question, my dear Watson… • The answer is a resounding YES ! • Other quarks can combine to form other baryons. For example: This combination is called a Lambda baryon, or L0 for shortWhat is the charge of this object?) This combination is called a Delta baryon, or D++ for shortWhat’s this one’s charge?

17. Proton Neutron Note: The neutron differs from a proton only by “d”  “u” quarkreplacement! Let’s make baryons! Quark up down strange Charge Q +2/3 -1/3 -1/3 Mass ~5 [MeV/c2] ~10 [MeV/c2] ~200 [MeV/c2] u u u d d d s s s u u d d u d Q = +1M=938 MeV/c2 Q = 0M=940 MeV/c2

18. Quark up down strange Charge, Q +2/3 -1/3 -1/3 Mass ~5 [MeV/c2] ~10 [MeV/c2] ~200 [MeV/c2] u u u d d d s s s Sigma (S+) Lambda (L) Sigma (S-) Let’s make some more baryons ! u u d d u s s d s Q = -1M=1197 MeV/c2Lifetime~1.5x10-10[s] Q = +1M=1189 MeV/c2Lifetime~0.8x10-10[s] Q = 0M=1116 MeV/c2Lifetime~2.6x10-10[s] These particles have been observed, they really exist, but decay fairlyrapidly. Is S- the antiparticle of S+ ??

19. d d c s d u Mesons • Mesons are also in the hadron family. • They are formed when a quark and an anti-quark “bind” together. (We’ll talk more later about what we mean by “bind”). What’s the charge of this particle? What’s the charge of this particle? What’s the charge of this particle? Q= 0, this strangemeson is called a K0 Q= -1, and this charmmeson is called a D- Q=+1, and it’s called a p+ M~500 [MeV/c2]Lifetime~0.8x10-10 [s] M~140 [MeV/c2]Lifetime~2.6x10-8 [s] M~1870 [MeV/c2]Lifetime~1x10-12 [s]