Particle Physics
Physics 313a
Fall 2000

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General course information
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Homework and exam solutions (PDF) on TriReserve

General course information:

Steve Wasserbaech
Office: Stokes 115 (telephone 896-4972)

Contacting me.
Please feel free to drop in at my office any time, or make an appointment if you prefer.  I will also be happy to reply to your e-mails.  It's OK to call me at home (658-9719) occasionally (before 10pm, please).

Course description and objectives.
This is a course on the fundamental particles and their interactions.  We will discuss the details of the so-called Standard Model, which is consistent with (almost) all existing experimental observations.  Students will become familiar with the Standard Model, experimental techniques of particle physics, and some of the current issues and experiments.

Text and sources.
The required text is Introduction to Elementary Particles by David Griffiths.  You are also required to obtain a copy of the Review of Particle Physics (2000), as explained in the first homework assignment.

Some related titles:

Regular attendance: You are expected to attend all classes.  More than two absences for reasons other than illness will be considered excessive.  If you are ill or expect to miss class due to special circumstances, an e-mail message to that effect will be appreciated.

Preparation:  You should come to class prepared.  You will be expected to read the assigned material fairly carefully before class so you can participate in the discussion.  As evidence of this preparation, each student is expected to bring at least one question, in writing, to be discussed in class and handed in.

Homework:  There will be regular homework assignments.  You are expected to complete the homework on time, giving clear and coherent solutions to the problems.  Late assignments are accepted up to one week past the due date but receive only 2/3 credit.  Exception: when you are in a bind, I will grant a one-week extension with no loss of credit.  Hand in or e-mail your extension requests on the regular assignment due date.  Limit: two extensions per student during the semester, to be used on two different assignments.

Exams: There will be two take-home exams: a midterm and a final.  Each will be two hours in duration, and will be closed book except for a page of notes.

The grade for the course will be based on the following weighting:
Homework assignments:
Midterm exam:
Final exam:
Questions for discussion:

Excessive absences would also be considered in the final evaluation.

Honor Code.
You should work alone on the take-home exams and refer only to your page of notes.

Certain homework problems will be designated "individual" problems for which no consultation with classmates is permitted, but any other sources may be used.  You are allowed and encouraged to discuss any other homework problem with the other students, but only after attempting the problem yourself for at least 30 minutes.  You must write up your solutions yourself.

Reading assignments.
The following reading assignments are to be completed before class on the dates given.  All readings are from Griffiths unless otherwise noted.  Each student is expected to bring to class and hand in (at least) one question related to the reading assignment for the day.
Date Assignment
Thu 7 Sep 2000 Introduction and Sections 1.1-1.5
Tue 12 Sep 2000 Sections 1.6-1.11 and all of Chapter 2
Thu 14 Sep 2000 Chapter 3
Tue 19 Sep 2000 Sections 4.1-4.3
Thu 21 Sep 2000 [None]
Tue 26 Sep 2000 Sections 4.4-4.5
Thu 28 Sep 2000 Sections 4.6-4.9
Tue 3 Oct 2000 Skim Sections 5.1-5.6; read Sections 5.7-5.8
Thu 5 Oct 2000 Sections 5.9-5.10
Tue 10 Oct 2000 [None]
Thu 12 Oct 2000 Section 6.1
Tue 24 Oct 2000 Sections 6.2-6.5
Thu 26 Oct 2000 Sections 6.6 and 7.1
Tue 31 Oct 2000 Sections 7.2-7.4
Thu 2 Nov 2000 Sections 7.5-7.6
Tue 7 Nov 2000 Sections 7.7-7.8
Thu 9 Nov 2000 Sections 7.9 and 8.1-8.2
Tue 14 Nov 2000 [None]
Thu 16 Nov 2000 Sections 8.3-8.4
Tue 21 Nov 2000 Sections 8.5-8.6 and 10.1
Thu 23 Nov 2000 [Thanksgiving]
Tue 28 Nov 2000 Sections 10.2-10.3
Thu 30 Nov 2000 Sections 10.4-10.5
Tue 5 Dec 2000 Section 10.6
Thu 7 Dec 2000 Sections 10.7 and 11.1-11.2
Tue 12 Dec 2000 Sections 11.3-11.6
Thu 14 Dec 2000 Sections 11.7-11.9

Homework assignments.
Assignments are due in class on the dates given below.  (But you can hand them in up to 5 pm on the due date with no penalty.  To find out about longer extensions, please see the general course information.)
HW # Due date Assignment
1 Tuesday 
12 Sep 2000
A. Order a copy of the "Review of Particle Physics" from the Particle Data Group, .  (You are welcome to order other items as well, and it's all free.)
B. Griffiths, Problems 1.1 and 1.3.
2 Tuesday
19 Sep 2000
Griffiths, Problems 1.7, 1.8(a), 2.3, 2.5, 2.6, 2.7.
3 Tuesday
26 Sep 2000
A. Griffiths, Problems 3.4, 3.12, 3.16, 3.17(a,d), 3.19, 3.22, 3.23.
B. Individual problem (do not collaborate with your classmates): p0 mesons of energy E = 500 MeV (in the laboratory frame) are produced in a certain experiment.  What is the energy distribution (in the lab) of photons produced in the decay p0-> gg ?  The mesons decay with an isotropic angular distribution.
4 Tuesday
3 Oct 2000
Griffiths, Problems 4.2, 4.3, 4.11, 4.32, 4.37.
10 Oct 2000
5 Tuesday
24 Oct 2000
A. Griffiths, Problem 6.1.
B. A lepton l decays to mnn with a branching fraction of 17.4%.  The decay rate for l -> mnn is 5.99 × 1011 s-1.  What is the mean lifetime of l ?
C. Refer to the Review of Particle Physics for data.
   a) Calculate the total decay rate G for the K0short.
   b) Calculate the partial decay rate G(K0short -> pen).
   c) Repeat a) and b) for the K0long.
6 Tuesday
31 Oct 2000
A. Griffiths, Problem 6.15, parts a and b only.
B. The PEP-II electron-positron collider achieves a luminosity of 1033 cm-2 s-1 at a center of mass energy of 10.6 GeV.  (a) How long does it take to obtain an integrated luminosity of 1 pb-1?  (b) About how long would it take to produce one hundred e+e--> t+t- interactions, if the cross section for this process is 0.77 nb at 10.6 GeV? 
C. Individual problem: A positron of energy 27.5 GeV collides head on with a proton of energy 820 GeV in the HERA collider at the DESY lab in Hamburg, Germany.  What is the center of mass energy?
D. Individual problem: A proton of energy E collides with a proton at rest in the lab.  What value of E corresponds to the kinematic threshold for p p -> p p p pbar?
7 Nov 2000
7 Tuesday
14 Nov 2000
Griffiths, Problems 7.2, 7.15, 7.25, 7.26.  [For Problem 7.2 you may use the anticommutator relation {si, sj } = 2di j , which is derived in Problems 4.19 and 4.20.]
8 Tuesday
21 Nov 2000
Griffiths, Problems 7.30(a), 7.31, 7.34, 7.36.  [You need not compare the answers to Problems 7.35 and 7.36.]
9 Tuesday
28 Nov 2000
A. In class we analyzed the reaction e+e-->m+m-and found ds/dW = [(hbar2a2)/(4c2s)] (1 + cos2q).
   (a) Calculate the total cross section in pb for e+e-->m+m-at Ecm = 29 GeV (the energy at which the original PEP collider was operated in the early 1980's).
   (b) If my muon detectors cover only the angular range q = 20° to 160° (in the CM frame), what effective total cross section would I see at Ecm = 29 GeV?
B. (Optional) Read the new Higgs paper by ALEPH and bring at least one question to class.  Go here to download it.  [By the way, the L3 Collaboration has a new Higgs paper too.  Click here.]
10 Tuesday
5 Dec 2000
A. Problem 10.17.  Besides GF and qw, one other input is needed: a = 1/137.
B. Problem 10.20.  Take into account that the top quark mass is now known to be around 173 GeV/c2.  (Do not assume 2mt < MZ.)  In (a), use the polarization vector em = (0, 0, 0, 1) for the incoming Z boson.  (Yes, it is component 3 that is nonzero.)  In (c), assume that the fourth generation consists of a light neutrino plus a heavy charged lepton and two heavy quarks, so that only the neutrino can be produced in Z decays.
11 Thursday
14 Dec 2000
1. The total cross section for nm-nucleon scattering is about s = 0.6E × 10-38 cm2 for neutrinos of energy E (in GeV) incident on stationary nucleons.  How far must a beam of 100 GeV muon neutrinos travel in iron for the neutrino flux to be reduced by a factor of 2?
2. (a) Estimate the mean ionization energy loss for a proton with p = 2.4 GeV/c when it passes (at normal incidence) through a silicon wafer 300 mm thick.
   (b) Estimate the rms Coulomb scattering angle q0 for the situation in (a).
   (c) Estimate the average bremsstrahlung energy loss for 10 GeV electrons passing through the same wafer.
3. Consider a simple charge particle tracking system consisting of three planes of drift chambers at x = 0, D, and 2D, immersed in a uniform magnetic field B in the +z direction.  The system is used to measure the momenta of charged pions that are moving in the +x direction when they cross the first detector plane.  The y coordinate of each pion's trajectory is measured with an uncertainty s in each of the three planes.
   (a) What is the radius of curvature, R, of the trajectory for a pion of momentum p?
   (b) What is the sagitta s of the arc of the trajectory between x = 0 and 2D for a pion of momentum p?  Assume D/R << 1, so that small angle approximations may be used, and keep only the leading dependence on D/R.
   (c) What is the measured sagitta in terms of the three measurements y0, yD, and y2D?
   (d) What is the uncertainty on the measured momentum if D = 1 meter, B = 1 Tesla, s = 150 mm, and p = 20 GeV/c?  What is the uncertainty if p = 100 GeV/c?  Neglect all sources of uncertainty except that in the y coordinate measurements.  Is our assumption that D/R << 1 valid in these cases?

Jump to:
General course information
Reading assignments
Homework assignments
Homework solutions (PDF) on TriReserve

Steve Wasserbaech,