nick hadley dzero top iii (double secret probation) nick hadley the university of maryland october...

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