Nick Hadley Dzero Top III (Double Secret Probation) Nick Hadley The University of Maryland October...
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Nick Hadley
Dzero Top III(Double Secret Probation)
Nick HadleyThe University of Maryland
October 21, 2005
Nick Hadley
Overview
• Thanks to organizers for opportunity to speak on behalf of Dzero collaboration– some ambivalence about role as “old person”
• Tremendous effort from all on the experiment
• Appropriate (?) theme from literature– “We few, we happy few, we band of brothers…”– Maybe not…more like college dorm…– DØ Top Discovery Party in Barn -> Animal House– DØ -> Delta House
Nick Hadley
DØ
Nick Hadley
Dean Wormer
Nick Hadley
The Two Pitfalls of Searches
1. Finding something that isn’t there– Happens a lot, many things don’t exist
A FEW "SURE THINGS" THAT WEREN'T
Split A2 Berkeley and elsewhere, mid-1960s
5 sigma
A2 meson looked like two particles, until twin energy peaks fused
Zeta
DESY (Hamburg), Stanford University, and elsewhere, early 1980s
5 sigma
Apparent particle, thought to be the Higgs boson, died amid controversy in mid-1990s
"Axion" GSI (Darmstadt) and elsewhere, mid-1980s
6 sigma New heavy neutral particle vanished on closer inspection
PSR1829- 10's planet
Jodrell Bank Observatory, Manchester, U.K., 1991-92
"Hundreds of sigmas"
Signs of body circling a pulsar turned out to be due to Earth's orbit
Science Vol 289, Issue 5488, 2260-2262 , 29 September 2000
Nick Hadley
Two Pitfalls of Searches (cont)
2. Not finding something that is there– Might be worse, error of omission not commission–
– J/ψ could have been seen by other accelerators, not just BNL, SLAC.
– (Apocryphal) story of early Drell Yan experiment with 1000s of events, chose to plot l+-l mass data up to 3 GeV, ignoring ten events in overflow bin. After J/ψ discovery, overflow events all at 3.1 GeV.
– Similar story for cosmic ray muon data, (now undergrad exp!) showing parity violation, key plot not studied until after discovery by someone else.
0LK
Nick Hadley
Top Search
• Cautionary note:– Previously mentioned experiments done by
experienced scientists, many very distinguished, no obvious flaws in method or experiment
• Many wrong possibilities, only one right possibility.
Nick Hadley
Theoretical Guidance
• Top was charge +2/3 partner of b quark• Decay modes, properties “precisely”
specified by theory– Sort of…
• Some history– My first top talk was as a grad student on the
PEP TPC collaboration on “ Theoretical Predictions of Top Quark mass” in 1979 at a TPC group meeting.
– Theoretical consensus then: Top mass 13.5 GeV– Good news! PEP and PETRA would discover top,
see toponium,
Nick Hadley
Top History
• Bad news: PEP, PETRA, Tristan, SppS, SLC, LEP all looked– Top wasn’t found. Only limits.
• Theoretical Top mass kept pace. Top was always a few GeV away, just above the current experimental bound.
• Details of theory calculation– very, very complex. A detailed “how to”
follows
Nick Hadley
Top Mass Calculation (before discovery)
1. Difficult Choice: Aspen or Santa Barbara?
Nick Hadley
Top Mass Calculation (before discovery)
2. Call experimental colleague, get latest experimental limit on top mass
3. The calculation• M(theory) = M(experimental limit) + 24 GeV
(natural units ħ=c =1, 750 ml = 24 oz = 24GeV)
• Summon postdoc to do the addition
4. Publish• Call experimental colleague and tell him to
“keep working hard” as top is “just around the corner”.
Nick Hadley
Discovery Comments
• January 1995 began a very intense period From my notebook, note
irony, this was a “let’s go discover top” talk
Nick Hadley
Discovery Comments (cont)
• Of course, an enormous amount of effort was expended before January 1995. (“standing on the shoulders of giants”).
• Recently re-read hundreds of emails from the top discovery period.
– Interesting reading. Actually a pleasure, focus on the science and on discovery.
– Minds were open: (from a 1/14/95 email, “one matter that … looks interesting from a NP point of view was light stop”)
– A large number of people contributed.– More than 200 comments on PRL draft!
Nick Hadley
Discovery Comments (cont)
• Open Process– Top group meetings were open to all Dzero
collaborators– People were encouraged to speak (and they
did)
• Multiple analyses– 7 different channels– Tight cuts, loose cuts, mass, m2j vs m3j– Each played a role in convincing us top was
there
Nick Hadley
Acknowledgments
– The top discovery came from the efforts of a large number of people from all over the world.
Dzero Top Discovery PRL1135 citations
Nick Hadley
Acknowledgments
• Funding Agencies– Department of Energy (US)– National Science Foundation (US)– Commissariat a L’Energie Atomic (France)– Ministry for Atomic Energy, Ministry for Science and
Technology Policy (Russia)– CNPq (Brazil)– Departments of Atomic Energy and Science and Education
(India)– Colciencias (Colombia)– CONA-Cyt (Mexico)– Ministry of Education, Research Foundation & KOSEF (Korea)– A.P. Sloan Foundation
• Vision to do speculative, curiosity based research
Nick Hadley
Acknowledgments
• Fermilab Accelerator, Computing and Research Divisions– Luminosity was a key to the discovery– Timely analysis of data– Detector construction and operation
• Theorists– Top decay modes– Monte Carlos, ISAJET, HERWIG, PYTHIA,
VECBOS, studies of backgrounds and fragmentation
• CDF– Two experiments led to better science.
Nick Hadley
Acknowledgments
• Top Discovery required every part of the Dzero detector and all of the collaboration
– Vertex, CDC, FDC, TRD, Calorimeters, ICD, Luminosity, Muon System (WAMUS, FAMUS, SAMUS)
– Trigger, DAQ– Operations, calibration, software
Nick Hadley
List of Institutions on Dzero at time of discovery
Nick Hadley
Dzero Author List
Thanks to all
Abachi to Zylberstejn