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Announcements

Announcements.

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Announcements

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  1. Announcements Based on a student’s input, I have now made the solutions to theHW available in the Physics Library. (Rm 208 Physics Building).They are on restricted reserve, which means you can check them out,but they must stay in the library.Solutions will be posted on the Monday after they are due.If you do not hand in the assignment by then, it cannot be counted…The first set of exercises from Lab1, and HW’s 1 & 2 are now available for you..

  2. Review from last time

  3. Gold atom Silver atom Mass [GeV/c2] Proton A bit more on quarks • 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]) • Why is matter made only ofup & down quarks ? • This will be answered later!

  4. Q= +2/3 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 6 anti-quarks, they have opposite charge to the quarks. • So, the full slate of quarks are: Quarks Particle

  5. Hadron Jail q Quark Confinement • Quarks are “confined” inside hadrons (baryons or mesons). We do not see them as “free” particles (likeelectrons, for example). • This is a result of the “strong force” which we will discuss later…

  6. 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!

  7. BARYONS The forces which hold the protons and neutrons together in thenucleus are VERYstrong. Protons and neutrons are among a class of particles called “hadrons”(Greek for strong). Hadrons interact very strongly! 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…

  8. This combination is called a Lambda baryon, or L0 for shortWhat is the charge of this object?) u s d This combination is called a Delta baryon, or D++ for shortWhat’s this one’s charge? 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:

  9. Proton Neutron Note: The neutron can be turned into a proton by simply replacing a“d” quark by a “u” quark! 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

  10. Quark up down strange 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-) Sigma (S+) Lambda (L) Sigma (S0) Let’s make some more baryons ! u u u d d u d d s s s s Q = 0M=1116 MeV/c2 Q = +1M=1189 MeV/c2 Q = 0M=1192 MeV/c2 Q = -1M=1197 MeV/c2

  11. Color • I have been showing quarks as being either RED,GREEN or BLUE. • It turns out that quarks have a property called “COLOR”. This property is as intrinsic to the quarks as “electric charge”. • This intrinsic property is not really a visible color, but it helps to visualize the property, which can have3 values. • We will discuss this in greater detail when we start talking about the strong force.

  12. Color (cont) • For now, assume that quarks come in 3 colors: • RED, GREEN, BLUE • Anti-quarks have “anti-color” • ANTIRED, ANTIGREEN, ANTIBLUE • Baryons always have 1 of each color. Antibaryons have one of each anti-color.

  13. Spin • There’s another intrinsic property which Quarks have known as “spin”. • For convenience, you can think of it as a spinning top, but this is just a conceptual aid… • Quarks have spin S = ½.

  14. “Spin up” SZ = +1/2 • “Spin down” SZ = - 1/2 Spin Up Spin Down Spin “Direction” • Think of S as indicating “how fast” the top is spinning (it’s the magnitude of the spin). • However, there may also be a direction. • Think of SZ as the indicator of the direction of the axis of rotation.

  15. Baryon Spin What is S and SZ of a baryon containing quarks q1, q2, and q3 ? q1 q2 q3 SZ Total Spin, S -3/2 3/2 -1/2 1/2 or 3/2 -1/2 1/2 or 3/2 -1/2 1/2 or 3/2 +1/2 1/2 or 3/2 +1/2 1/2 or 3/2 +1/2 1/2 or 3/2 +3/2 3/2

  16. ? Example Consider this Spin ½ baryon. What must be the color of the quark with the “?” inside?a) blue b) white c) colorless d) yellow What must be the value of SZ of the quark with the “?” inside?a) +1/2 b) –1 c) –1/2 d) 0 If the red quark had spin down, what would be the value of SZof the “?” quark? a) +1/2 b) –1 c) –1/2 d) +1/2 or –1/2

  17. Some of the Spin 1/2 Baryons with u,d,s quarks You should be able to read and extract information from a table like this

  18. A few Spin 3/2 Baryons Since baryons contain 3 quarks, their intrinsic spin (S) can only be: 1/2 or 3/2

  19. d d c s d u • 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”). • Because they are hadrons, they must be colorless. So, the quarkhas color, and the antiquark has “anticolor” Mesons What’s the charge of this particle? What’s the charge of this particle? What’s the charge of this particle? Q=+1, and it’s called a p+ Q= -1, and this charmmeson is called a D- Q= 0, this strangemeson is called a K0

  20. Like baryons, mesons also have spin, because the quarks of whichthey are made have spin. • Consider a meson composed of quarks q1 and q2. q2 Meson Spin q1 SZ Total Spin, S -1 1 0 0 or 1 0 0 or 1 +1 1

  21. Some Spin 0 Mesons with u,d,s quarks

  22. Some Spin 0 Mesons with u, d, c, b quarks

  23. Up & down quarks make up protons & neutrons • Quarks have an intrinsic property known as color, of whichthere are 3 varieties: red, green or blue. • Quarks also have a property known as Spin, and have Spin = 1/2. • Hadrons refer to strongly interacting particles: Baryons & Mesons • Baryons contain 3 quarks: 1 red + 1 green + 1 blue colorlessThey may have spin 1/2 or spin 3/2. • Mesons contain 1 quark & 1 antiquark: rr, gg, or bb  colorlessThey may be spin 0, or spin 1 Summary

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