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Frank and
Collider Physics
May 29, 2015
When Frank was a graduate student – 1971-77
May 29, 2015 J. Pilcher2
l A remarkable time for the Standard Modell The quark sector in 1971
l This still did amazing thingsn dozens of known states from threen mass rules relating known statesn predictions of new states ( )
J. Pilcher3
l Is that all there is? (Nov. 1974)
May 29, 2015
When Frank was a graduate student – 1971-77
PRL Dec. 2, 1974Mk I detector SLAC
Multihadrons
e+e-
µ+µ-
π+π-, K+K-
PRL Dec. 9, 1974
PRL Feb. 10, 1975 (Eichten, et al.)(earlier Applequist and Politzer)
c cbarexcitations
l And then there were four
J. Pilcher4
l What about the lepton sector?
l December 1975n Perl et al. report anomalous events from Mark I detector at the SPEAR e+e- collidern perhaps
May 29, 2015
When Frank was a graduate student – 1971-77
Prior to 1975
PRL 35, 1489 (1975)
. . .
J. Pilcher5
l Frank joins Stanford group as postdoc from 1977-79n working on the new DELCO experiment at SPEAR as well as E21 at Fermilabn author on definitive tau lepton measurements at SPEAR
May 29, 2015
When Frank was a graduate student – 1971-77
PRL July, ‘78
• Threshold below charmed particle production• Mass = 1782 +2
-7 MeV• Spin 1/2
PRL March, ‘79
• Electron energy spectrun => V-A decay• ρ = 0.72 ± 0.15 (0.75 for V-A)
• mν < 250 MeV• upper limit on lifetime• strongly suggestive of a new neutrino
J. Pilcher6
l Standard model of the late 70’s
l Remaining questionsn top quark?n additional generations?n mass generation of gauge bosons (Higgs mechanism => Higgs boson)n does it really all work at the 1% level?
May 29, 2015
When Frank was a graduate student – 1971-77
Quarks
Leptons
Gauge bosonsmediating interactions
7
l spectacular success of e+e- colliders prompts CERN to build LEP (Ecm = 200 GeV)n earlier e+e- machines SPEAR (7.4 GeV), DORIS (10 GeV), CESR (12 GeV), PEP (29 GeV),
PETRA (38 GeV)n Chicago joins OPAL experiment 1982
Frank, Mark, Kelby, men initial operation 1989n goals
search for further generations
measurement of number of neutrinos (from )
search for Higgs boson
test electroweak theory
May 29, 2015 J. Pilcher
Getting to what we know now (with Frank)
OPAL Presampler
PresamplerConstruction in
Accelerator Bldg
J. Pilcher8
l Frank convened the OPAL Heavy Lepton search groupn Wyatt and Frank on “sabatical” at CERN 1989-90
l Best current limit in PDG is GeVn surprisingly, no limits from the LHC [noted in the literature ]
tempora mutantur
May 29, 2015
Getting to what we know now (with Frank)
PRD 90, 013015 (2014)
John HobbsMike Redmond
19901996 1999
J. Pilcher9
l much OPAL work searching for the Higgs (with Mark and students)n first from ~ 5M Z decays via from ’89 – ’94
n from 728 pb-1 above the Z ’95 - ’00
n from all LEP experiments combined
May 29, 2015
Getting to what we know now (with Frank)
Low MassMH < 11.3 GeV
Medium Mass3 < MH < 25 GeV
High Mass24 < MH < 44 GeV
Hogan Nguyen
1992
J. Pilcher10
l Other Chicago students on OPAL
May 29, 2015
Getting to what we know now (with Frank)
High precision Z measurementsPhil Hart
W-boson mass measurementFrancesco Spano
e+e- → W+W-
J. Pilcher11
l ATLAS preparationsn 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 detectorn Frank’s led the Jet / Etmiss group
Assisted by Chicago postdoc Ambreesh Gupta
May 29, 2015
Getting to what we know now (with Frank)
Absolute scale uncertainty(accuracy of ruler)
Resolution(reading of ruler)
J. Pilcher12
l Collider experiments take a long timen costly, state-of-the-art hardware to build, many partners to agreen becoming more common features in other areas of science
l Collider experiments are remarkably powerful and incisiven LEP experiments (OPAL) from the 1990’sn LHC experiments (ATLAS) in the 2010’s
l ATLAS physicsn Higgs has finally been found (after ~40 years of searching)
May 29, 2015
What we know now
H → ZZ*→ℓ+ℓ-ℓ+ℓ- H → γγ H → WW*→ℓ+νℓ-ν H → τ+τ-
J. Pilcher13
l Higgs properties are being measuredn mass now known to 0.2%
important for many BSM predictionsn seen in many decay modes and
production mechanismsn LHC measurement program for Higgs
is just beginningany departures from SM are critical clues to BSM physics
May 29, 2015
What we know now
Combined mass results from ATLAS & CMS
Results for many decay modes and production channels
Coupling strengths to the Higgs
J. Pilcher14
l Standard Model is remarkably accuraten known from LEP and Tevatron
high precision tests of the electroweak theory involving dozens of observablesn reinforced by including measured Higgs mass in electroweak fitsn radiative corrections to the Higgs mass can become huge
some cut-off or cancellation is needed
n one answer is supersymmetrywe have been looking hard
May 29, 2015
What we know now
J. Pilcher15
l test
May 29, 2015
J. Pilcher16
l Test
May 29, 2015
J. Pilcher17
l ATLAS and CMS work welln likely to continue for the next 20 years
l The experiments are amazingly productive
May 29, 2015
What we know now
ATLAS: 421
CMS 407
Year
Number of publications
J. Pilcher18
l Currently open questionsn what limits the radiative corrections to the Higgs mass (naturalness problem)n the source of the fermion generations
“That’s just the way it is” has rarely been the answer in the past
n the nature of dark mattercan we produce it in the laboratory?
n the source of baryon-antibaryon asymmetry in the universe
May 29, 2015
What we will know when our students retire
Increasing mass
None of the above
J. Pilcher19
l Thanks to Frank for participating in this voyage of discovery over the past 40 yearsn He and I both look forward to seeing what at least the next 10 will bringn if not our students’ retirements
May 29, 2015
Conclusions
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