Frank and Collider Physics May 29, 2015

When Frank was a graduate student – May 29, 2015J. Pilcher2 A remarkable time for the Standard Model The quark sector in 1971 This still did amazing things dozens of known states from three mass rules relating known states predictions of new states ( )

Is that all there is? (Nov. 1974) May 29, 2015J. Pilcher3 When Frank was a graduate student – PRL Dec. 2, 1974 Mk I detector SLAC PRL Dec. 2, 1974 Mk I detector SLAC Multihadrons e+e-e+e- e+e-e+e- µ + µ - π + π -, K + K - µ + µ - π + π -, K + K - PRL Dec. 9, 1974 PRL Feb. 10, 1975 (Eichten, et al.) (earlier Applequist and Politzer) PRL Feb. 10, 1975 (Eichten, et al.) (earlier Applequist and Politzer) c cbar excitations c cbar excitations And then there were four

What about the lepton sector? December 1975 Perl et al. report anomalous events from Mark I detector at the SPEAR e + e - collider perhaps May 29, 2015J. Pilcher4 When Frank was a graduate student – Prior to 1975 PRL 35, 1489 (1975)...

Frank joins Stanford group as postdoc from working on the new DELCO experiment at SPEAR as well as E21 at Fermilab author on definitive tau lepton measurements at SPEAR May 29, 2015J. Pilcher5 When Frank was a graduate student – PRL July, ‘78 Threshold below charmed particle production Mass = MeV Spin 1/2 Threshold below charmed particle production Mass = MeV Spin 1/2 PRL March, ‘79 Electron energy spectrun => V-A decay ρ = 0.72 ± 0.15 (0.75 for V-A) m ν < 250 MeV upper limit on lifetime strongly suggestive of a new neutrino Electron energy spectrun => V-A decay ρ = 0.72 ± 0.15 (0.75 for V-A) m ν < 250 MeV upper limit on lifetime strongly suggestive of a new neutrino

Standard model of the late 70’s Remaining questions top quark? additional generations? mass generation of gauge bosons (Higgs mechanism => Higgs boson) does it really all work at the 1% level? May 29, 2015J. Pilcher6 When Frank was a graduate student – Quarks Leptons Gauge bosons mediating interactions Gauge bosons mediating interactions

spectacular success of e + e - colliders prompts CERN to build LEP (E cm = 200 GeV) earlier e + e - machines SPEAR (7.4 GeV), DORIS (10 GeV), CESR (12 GeV), PEP (29 GeV), PETRA (38 GeV) Chicago joins OPAL experiment 1982 Frank, Mark, Kelby, me initial operation 1989 goals search for further generations measurement of number of neutrinos (from ) search for Higgs boson test electroweak theory May 29, 2015 J. Pilcher 7 Getting to what we know now (with Frank) OPAL Presampler Presampler Construction in Accelerator Bldg Presampler Construction in Accelerator Bldg

Frank convened the OPAL Heavy Lepton search group Wyatt and Frank on “sabatical” at CERN Best current limit in PDG is GeV surprisingly, no limits from the LHC [noted in the literature ] tempora mutantur May 29, 2015J. Pilcher8 Getting to what we know now (with Frank) PRD 90, (2014) John Hobbs Mike Redmond 1990 John Hobbs Mike Redmond

much OPAL work searching for the Higgs (with Mark and students) first from ~ 5M Z decays via from ’89 – ’94 from 728 pb -1 above the Z ’95 - ’00 from all LEP experiments combined May 29, 2015J. Pilcher9 Getting to what we know now (with Frank) Low Mass M H < 11.3 GeV Low Mass M H < 11.3 GeV Medium Mass 3 < M H < 25 GeV Medium Mass 3 < M H < 25 GeV High Mass 24 < M H < 44 GeV High Mass 24 < M H < 44 GeV Hogan Nguyen 1992 Hogan Nguyen 1992

Other Chicago students on OPAL May 29, 2015J. Pilcher10 Getting to what we know now (with Frank) High precision Z measurements Phil Hart High precision Z measurements Phil Hart W-boson mass measurement Francesco Spano W-boson mass measurement Francesco Spano e + e - → W + W -

ATLAS preparations Established “Combined performance” groups for calculation of physics objects from data electrons, muons, jets from quarks and gluons, photons involves combining data from many different parts of the detector Frank’s led the Jet / Etmiss group Assisted by Chicago postdoc Ambreesh Gupta May 29, 2015J. Pilcher11 Getting to what we know now (with Frank) Absolute scale uncertainty (accuracy of ruler) Absolute scale uncertainty (accuracy of ruler) Resolution (reading of ruler) Resolution (reading of ruler)

Collider experiments take a long time costly, state-of-the-art hardware to build, many partners to agree becoming more common features in other areas of science Collider experiments are remarkably powerful and incisive LEP experiments (OPAL) from the 1990’s LHC experiments (ATLAS) in the 2010’s ATLAS physics Higgs has finally been found (after ~40 years of searching) May 29, 2015J. Pilcher12 What we know now H → ZZ* → ℓ + ℓ - ℓ + ℓ - H → γγ H → WW* → ℓ + νℓ - ν H → τ + τ -

Higgs properties are being measured mass now known to 0.2% important for many BSM predictions seen in many decay modes and production mechanisms LHC measurement program for Higgs is just beginning any departures from SM are critical clues to BSM physics May 29, 2015J. Pilcher13 What we know now Combined mass results from ATLAS & CMS Results for many decay modes and production channels Results for many decay modes and production channels Coupling strengths to the Higgs

Standard Model is remarkably accurate known from LEP and Tevatron high precision tests of the electroweak theory involving dozens of observables reinforced by including measured Higgs mass in electroweak fits radiative corrections to the Higgs mass can become huge some cut-off or cancellation is needed one answer is supersymmetry we have been looking hard May 29, 2015J. Pilcher14 What we know now

test May 29, 2015J. Pilcher15

Test May 29, 2015J. Pilcher16

ATLAS and CMS work well likely to continue for the next 20 years The experiments are amazingly productive May 29, 2015J. Pilcher17 What we know now ATLAS: 421 CMS 407 Year Number of publications Number of publications

Currently open questions what limits the radiative corrections to the Higgs mass (naturalness problem) the source of the fermion generations “That’s just the way it is” has rarely been the answer in the past the nature of dark matter can we produce it in the laboratory? the source of baryon-antibaryon asymmetry in the universe May 29, 2015J. Pilcher18 What we will know when our students retire Increasing mass None of the above

Thanks to Frank for participating in this voyage of discovery over the past 40 years He and I both look forward to seeing what at least the next 10 will bring if not our students’ retirements May 29, 2015J. Pilcher19 Conclusions