Dzero Top III (Double Secret Probation) Nick Hadley The 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 – – Nick Hadley “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
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 Nick Hadley Science Vol 289, Issue 5488, 2260 -2262 , 29 September 2000
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 1000 s of events, chose to plot l+-l mass data up to 3 Ge. V, ignoring ten events in overflow bin. After J/ψ discovery, overflow events all at 3. 1 Ge. V. – Similar story for cosmic ray muon data, (now undergrad exp!) showing parity violation, key plot not studied until after discovery by someone else. 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 Ge. V – Good news! PEP and PETRA would discover top, see toponium, Nick Hadley
Top History • Bad news: PEP, PETRA, Tristan, Spp. S, SLC, LEP all looked – Top wasn’t found. Only limits. • Theoretical Top mass kept pace. Top was always a few Ge. V 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 Ge. V (natural units ħ=c =1, 750 ml = 24 oz = 24 Ge. V) Summon postdoc to do the addition 4. Publish • Nick Hadley Call experimental colleague and tell him to “keep working hard” as top is “just around the corner”.
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, m 2 j vs m 3 j – 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. Nick Hadley Dzero Top Discovery PRL 1135 citations
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 Abachi to Zylberstejn Thanks to all Nick Hadley
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