Today’s plan Reminder: Final Exam (Friday May 5, time 13:30-15:30). More Chapter 9 material Reminder: Final Exam (Friday May 5, time 13:30-15:30). Schedule for presentations: Friday April 28 Anirvan (LHCb pentaquark); Tommy (CPV in the B system); Makana (discovery of the Higgs) Monday May 1 Tyler (discovery of the top quark), James (new detector technology) 1984 Nobel Prize to Carlo Rubbia and Simon van der Meer for the discovery of the W, Z bosons. Francois Englert and Peter Higgs, 2013 Nobel Prize Practice Final now posted

Question: How is this different from the other ratio of neutrino cross-sections that we have studied ?

CHARM2 experiment at CERN

Neutrino electron scattering kinematics Conserve zero components of the 4 vectors and balance transverse and longitudinal components of the momenta. Add and subtract neutrino energy and electron energy

Neutrino electron scattering kinematics (cont’d) Insert the first eqn. Ei’s cancel Inequality since the neutrino is not detected.

Data from CHARM2 at CERN Geiregat, D. et al. (1991); Phys. Lett. B259 499

Question: How do we make neutrino or anti-neutrino beams ? Use negative pions for anti-neutrino beams and positive pions for neutrino beams

Adapted from Yao. W. –M. et al. (2006); J. Phys. G. 33 1 Notice semi-log scale and the small errors at the Z0 from LEP data

High Energy Physics History: finding NP in AFB (using interference) Gargamelle discovered weak neutral currents in 1973; SLAC found parity violation in e N scattering in 1978. This set the stage for the discovery of the Z0 boson by UA1 and UA2. Measure the forward-backward asymmetry in di-muon production There is a significant deviation from the symmetric cos2 θ expectation of QED.

High Energy Physics History: finding NP in AFB (using interference) The effect was seen at experiments at DESY in Germany and at SLAC Gargamelle discovered weak neutral currents in 1973; SLAC found parity violation in e N scattering in 1978. This set the stage for the discovery of the Z0 boson by UA1 and UA2. Conclusion: There is a Z boson at higher energy even though colliders of the time did not have enough to produce it

Gargamelle (CERN Bubble chamber experiment) discovered weak neutral currents in 1973; SLAC found parity violation in e N scattering in 1978. DESY then found forward-backwards asymmetry in lepton scattering. This set the stage for the discovery of the W and Z bosons in direct production at UA1.

Direct Production of the W and the Z0 at the SPS in proton-anti-proton collisions Hint: Question: What are the Feynman diagrams for W- and Z0 production for sqrt(s)=540 GeV in proton-anti-proton collisions ? Question: Why do the colors of the two quarks have to be opposite ? The production is dominated by valence quarks at UA1, UA2. Typical production cross-sections are 530 pb for We nu and 35 pb for Zee

Albajar, C. et al. (1987); Z. Phys. C 36 33 Glashow, who won the Nobel in 1979, was quoted in Time as saying, "The book is a fair picture.” The quotation followed a statement from Taubes that Rubbia "has a history of distorting and exaggerating his experimental results.” Time published a letter last week from Glashow that calls the book "sensationalized" and says Rubbia "is a physicist in the tradition of Galileo and Fermi, with only a wee bit of Machiavelli thrown in.”

Need a fairly hermetic detector. Question: What does that mean ? Need a fairly hermetic detector. Rubbia, C. (1985); Rev. Mod. Phys. 57 699 © Nobel Foundation Missing momentum vector is shown here.

A new way of displaying the data in the calorimeter A new way of displaying the data in the calorimeter. Lego plots introduced at UA1. Adapted from Rubbia, C. (1985); Rev. Mod. Phys. 57 699 Introduce two new analysis variables: pseudo-rapidity and ΔR. These variables are still used at the LHC. Question: What is the spike ?

Look at the transverse momentum (with respect to the beamline) and also use ETmiss Question: Why ? The region near the beamline is not well-instrumented and particles can go down the beampipe.

Adapted from Albajar, C. et al. (1989); Z. Phys. C 44 15 Angular distribution of the electron from the W boson decay. Adapted from Albajar, C. et al. (1989); Z. Phys. C 44 15 Note that this argument assumes the W is a weakly decaying particle.

Recent very precise measurement of the W mass from the D0 experiment at Fermilab. Abazov, V. M. et al. (2012); Phys. Rev. Lett. 108 151804 What is this Ans: Fit residual divided by uncertainty.

Rubbia, C. (1985); Rev. Mod. Phys. 57 699 © Nobel Foundation Question: What should we plot for the Z0 boson ?

Adapted from Albajar, C. et al. (1987); Z. Phys. C 36 33

Question: Does the Z boson decay into equal pseudoscalar mesons Question: Does the Z boson decay into equal pseudoscalar mesons ? How about into two scalar mesons ?

Once the Z0 was discovered in p-anti p collisions, build a “Z0 factory” using e+e- collisions. Build a 27km circumference tunnel for LEP = “Large Electron Positron” Collider. N.B. The LEP tunnel was re-used for the LHC.

The width of the Z0 in hadrons (determined by scanning in e+e- center of mass energy) Adapted from LEP&SLD (2006); Phys. Rep. 427 257 Question: How can one determine the total width of the Z0 ?

by Permission of Particle Data Group and the Institute of Physics The invisible width of the Z0 boson is determined by the number of light neutrino species W. –M. et al. (2006); J. Phys. G. 33 1 by Permission of Particle Data Group and the Institute of Physics Very important measurement made by the four experiments at LEP: ALEPH, DELPHI, OPAL and LC Question: How do we determine the invisible width of the Z0 ?