# Presentation: 547054

## Top Turns Ten Symposium

- The DØ Graduate Student Perspective

- Jim Cochran
- Iowa State University
- (formerly SUNY Stony Brook & UC Riverside)

## Who am I representing ?

- Ian Adam, Paul Bloom, Dylan Casey, Geary Eppley, Tom Fahland, Eric Flattum, Patrick Gartung, Cecilia Gerber, Steven Glenn, Azriel Goldschmidt, Gervasio Gomez, Jose Luis Gonzalez-Solis, Peter Grudberg, A. Raul Hernandez-Montoya, Ting Hu, John Jiang, Hossain Johari, Michael Kelly, Gregory Landsberg, Hailin Li, Leonel Magana-Mendoza, Manuel Martin, James McKinley, Ajay Narayanan, Alberto Sanchez-Hernandex, Georg Steinbruek, Jamal Tarazi, Jie Yang, John Yetter, Jaehoon Yu, Qiang Zhu

- WZ physics (W/Z PT, e/ id, Z() fitting, similar analyses (WW))

- my fellow 133 students of the last millennium!

- Erfan Amidi, V. Balamurali, Alexander Belyaev, Vipin Bhatnager, Dhiman Chakraborty, Su-Min Chang, Suyong Choi, Sailesh Chopra, Cathy Crestinger, Ray Hall,Frank Hseih, Robert Kehoe, Jean Francois Lebrat, Martin Mason, Jeff McDonald, Myungyun Pang, Harpreet Singh, Eric Smith, Scott Snyder, Peter Tamburello, Joey Thompson, Erich Varnes, Eunil Won, Haowei Xu, Cary Yoshikawa

- top

- Braden K. Abbott, Levan Babukhadia, John Balderston, Mrinmoy Bhattacharjee, Wei Chen, David Cullen-Vidal, Daniel Elvira, Sal Fahey, Kathy Fatyga, Ki Suk Hahn, James Jaques, Steve Jerger, Tacy Joffe-Minor, Soon Yung Jun, Chang Lyong Kim, John Krane, Yi Cheng Liu, Gian Di Loreto, Robert Madden, Kristal Mauritz, Brent May, Andrew Milder, Freedy Nang, Jill Perkins, Paul Rubinov, Christopher Shaffer, Robert Snihur, Tracy Taylor Thomas, Yeonsik Yu

- QCD (jet id, jet energy scale, QCD backgrounds)

- Rich Genik, Mark Goforth, Ambreesh Gupta, Dan Karmgard, Bryan Lauer, Adam Lyon, Doug Norman, Nirmalya Parua, Marc Paterno, H. C. Shankar, Prajakta Singh, Mark Sosebee, Guoliang Wang, Djoko Wirjawan

- New Phenomenon (similar analyses)

- Gene Alvarez, Wagner Carvalho, Kevin Davis, Regina Demina, David Fein, Tong Hu, Thorsten Huehn, Eric James, Guilherme Lima, Thomas McKibben, Christopher Murphy, Vitor Oquri, Alex Smith, Andre Snajder, David Vititoe

- Bottom physics ( id, b-tagging)

- Richard Astur ,Jeffrey Bantley, Ties Behnke, John Borders, Sarah Durston, Fabrice Feinstein, Terry Geld, Terry Heuring, Robert Hirosky, Jonathan Kotcher, Bo Pi, Domenic Pizzuto, Alain Pluguet, Srini Rajagopalan

- Detector, Testbeam, Instrumentation

## How did DØ Organize Itself ?

- _Physics Groups_
- bottom
- New Phenomenon
- QCD
**Top**
- WZ

- _Detector Groups_
- Vertex
- Transition-Radiation
- Drift Chamber (**Central** & Forward)
- Calorimeter (EM & Hadronic, **Central** & Forward)
- Muons (Central, Forward, & SAMUS)
- Trigger

- Groups, subgroups, subsubgroups, ...  (like all HEP experiments)

- _Service Groups_
- General Computing
- Calibration & Alignment
- Production (data & **MC**)
- Simulation
- Resource Management

- _Particle id_
- electrons
- muons
- jets
- ETmiss

## So many topics and so many stories ... it was a very fun time

- Guided by my old logbooks – old email is much more elusive!

- A few dominant themes:
-  worries!
-  trying to do the right thing
-  the saga of event 417
-  victory over the forces of darkness

- I worked on the e analysis so will give the perspective from this channel

- (despite the large sleep deficit)

## The Big Worry ...

-  ... that we would screw up !

- Neutron lifetime

- Historical evolution of _published_ measurements from the PDG

- Ks lifetime

- B+ lifetime

- gV/gA

-  width

- m(B0)

## What screw-ups did we worry about most ?

-  overlooking something (lack of thoroughness)
-  unintentional bias !

- Strangely comforting – and bias was something we can work to avoid

## We had thought we would be greeted as liberators ...

- We seemed to be thwarted at every turn

- It was as if our beloved quark were being held hostage ...

- ... and the ransom ?
- our blood, sweat, frustration, and sanity seemed not to be enough!

## Do the right thing(s)

- Some comfort can be gained from backing off on the cuts and comparing background estimate with data ...

## And after we had finalized our selection, we did just this

- But they didn’t agree!

## What had we missed ?

- And since our cut on ETmiss(total) was low (10 GeV), many passed our selection

- and has little effect on tte

- So, we changed our selection and added a cut on ETmiss(calorimeter)

## The e Visits

- As Run 1a progressed, I was occasionally visited by senior members of the collaboration (often with minions in tow) who had “discovered” tt  *e* events which I had apparently missed

- Each time we dutifully staged the event(s) and looked it over with great care ...

- The “muon” was not obvious junk!
- (although it did have some problems – reco gave pT ~ 8 GeV/*c* & no CD track !)
- And the other aspects of the event were truly spectacular!

##  seems to have actually gone through a crack in the A layer

- ET(electron) = 98.8  1.6 GeV
- ET(jet 1) = 24.9  4.3 GeV
- ET(jet 2) = 22.3  5.6 GeV
- ET(jet 3) = 6.7  3.6 GeV
- ETmiss(total) = 100.7 GeV
- ETmiss(cal) = 120.0 GeV

-  seems to have actually gone through a crack in the A layer
- Reco used some nearby spurious A-layer hits  pT ~ 8 GeV/*c*

- magnet iron

## Call in the experts

- To clarify our understanding of the muon, it was necessary to

- Vertex track & TRD info also confirmed

## Side view of Event 417

## Lego view of Event 417

## The fallout from the various 417 studies led to permanent improvements in the reconstruction (but no change in our analysis)

- There was much effort to determine the likelihood that 417 is top *vs* background – was the birth of DØ’s multivariate methods effort

- And as you’ll hear from Meena, many wanted to claim discovery on this one event

## Once the excitement on event 417 eventually died down

- it took months!

- We focused on collecting and studying more events

- And I discovered the “power of top”

- “We” decided how to allocate DØ’s limited offline computing resources

- but it was easy for me: I needed only to say
- “well, that may affect the top results for conference X”
- to get my way

## And on the rare occaisions when that didn’t work ...

- I was forced to use the power of the “cc”

- Instead I would cc certain “sometimes volatile” members of the top group

- The recipients of such emails were typically in my office within 5 minutes!

- This is not to say the top group had free reign over the DØ’s computing resources

## Resource contentions aside, 

-            the “post-417” years saw a reoptimization for high-mass top

- These new cuts took us on into the discovery period, and beyond

- (was somewhat anti-climactic)

- And at LHC, many regard top as a calibration or background - sniff

## Showing that we could indeed overcome our demons

- Event 417 was only the first of many top quarks to be liberated ...

## ... but the story is never really over

- And time has allayed our worries to some degree ...