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