1 / 35

DELPHI: the start of a journey in physics

Explore the impact of DELPHI on the careers of undergraduate and graduate students in physics, with a focus on personal experiences and the resulting opportunities for future employment.

janeyp
Download Presentation

DELPHI: the start of a journey in physics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. DELPHI: the start of a journey in physics Martijn Mulders Delphi “closing” Meeting May 29, 2008

  2. The last DELPHI meeting…? • Today we talk about “the closing” of DELPHI • But: DELPHI was also a learning school for many undergraduate and graduate students – often the first experience with High Energy Physics • For many students DELPHI was the *start* of a career in physics ...!

  3. Outline • Some statistics • My journey in physics • How did my experiences in DELPHI help me later during my career in physics ?? • “Closing” remarks

  4. DELPHI as a springboard • 252 theses on DELPHI thesis page • http://delphiwww.cern.ch/delsec/theses2.html • A detailed study by Tiziano • 1982-1999: obtained data on 671 students who obtained a degree with studies performed in the DELPHI experiment … ! • 748 theses of which 339 PhD • Eur.J.Phys. 22(2001) 139-148 • http://campore.web.cern.ch/campore/student_survey_slides.htm

  5. First job after DELPHI degree • More than 50% continue in science… • Not a single student without a job (as of 2000) % of total

  6. After the first job • More difficult to keep track… • Most continue with a second post-doc • A small but steady flow to the private sector (out of 158 tracked)

  7. My journey in Physics • DELPHI : 1996 – 2001 PhD, NIKHEF • first job : 2001 – 2005 Fermilab (RA)  Dzero • 2nd job : 2005 – now CERN (LD)  CMS

  8. DELPHI: the starting point • I was promised (or so I thought)… • In SUSY the Higgs mass has to be lower than mZ  if you join us you will find the Higgs or prove that SUSY is wrong! • My first working day at NIKHEF (march 1996) • We have a new post-doc, Niels Kjaer. You will work with him on the measurement of the W mass… • Niels turned out to be an excellent supervisor • Started to work on PUFIT • Implemented EnergyFlow display • In time for first WW event at LEP, DELPHI 9th of July 1996 … (Run 67777 event 16923)

  9. The first year at NIKHEF • How to include jet-broadness in the fit… • Small improvement • And Initial State Radiation • No improvement • Running at 172 GeV • first attempt at direct W mass measurement (qqqq channel) • What about 5-jet events? Consider all 10 combinations? • Niels: we have tried that before… but feel free

  10. Inner Detector shifts • Took on-call shifts for the Inner Detector • resident at CERN 1997-1998 • Run meetings… • Shifts… • Very exciting !! • Note: never had any serious issues • Detector, software, everything in good shape in 1996 • “ntuples” were ready and waiting for analysis…

  11. 5-jet hadronic WW event • What about 5-jets  10 possible pairings !!

  12. Sometimes more than 5 jets…

  13. ‘Complex’ analysis methods‏ • To make a long story short... • 1997 • Sprime(+), using constrained fit to estimate effective center-of-mass energy • “Ideogram” analysis: describing full ambiguity of the events – for direct measurement mW • 1998-1999 • Ideograms used in Higgs search (Ivo van Vulpen) • Ideograms with 60-fold ambiguity to measure mW

  14. Ideogram method • Take into account all ambiguities in event reconstruction to optimize statistical uncertainty • Eventually up to 60-fold event hypothesis: • 10 jet pairings for a 5-jet event • 3 clustering algorithms • with/without ISR mw likelihood m2 m2 dm1dm2 mw (GeV) m1 m1

  15. Use the fact that • Events at LEP are clean • Zpeak: Center-of-mass energy is known Mixed Lorentz Boosted Z0’s Full analysis`measure mZ’ Z0 “WW” Z0 • Data-based method to study jet systematics in MC and data

  16. MLBZ vs. Angle (1997 Z0 data) W mass bias  jet ‘quality’  sensitive to holes in detector... = Z0 data = Z0 MC HPC TPC EMF FCA ID

  17. MLBZ vs. Time (1998 data) • Difference data-MC • Stability versus time: • The average counts !! data - MC

  18. What I learned in DELPHI • Data analysis techniques • Challenging but fun! • To do a precision measurement is a lot of work • Systematics… • Deadlines • Meetings • Many people • Fortran, PAW

  19. 5th of September 2001 During the defense: Niels, in a suit In Holland, a thesis defense is a very serious matter…

  20. During the defense: After: Niels, in a suit Niels, still in a suit

  21. The next step • Thesis defense • The plan: • Go to Tevatron • Apply the Ideogram technique to measure the Top quark mass

  22. First year at the Tevatron • Reality: • At the start of Run II Dzero was not in a ‘running’ state !! • DAQ, Trigger, Reconstruction algorithms …. NOT ready • All C++ !! No Fortran  • L3Muon • Tried (and ~failed) to deliver working L3 muon filters  • L3DAQ • Helped with installation/commissioning completely new ethernet-based L3-DAQ system for DZero  • Muon algorithms & ID convenor • Reconstruction Algorithm development and maintenance • Managing a group 

  23. Understanding the data… Charged pt fraction = 0.19 muon + 2 hard scatter nd 5%

  24. mW @ LEP  mTop @ TeV • Use invariant mass of decay products to measure mass • Decay channel determined by W's • BR~10% di-lepton: small background 2 ν 's: under-constrained • BR~45% lepton+jets: . . . 1 ν: over-constrained • BR~45% all jets: largest backgrounds (clean events !) (trigger, underlying event, JES) 5 typical constraints: Σ px=0 Σ px=0 Σ py=0 Σ py=0 Σ pz=0 mW=80.4 Σ E =√s mW'=80.4 mW=mW' mt = mt' b W W W W b W W W W t t ? ? LEP Tevatron

  25. Potential gain demonstrated : D0 Run 1 Measurement: Mt= 180.13.63.9 GeV Nature Vol 429, Page 640 • LEP: a lot of work for 10-15% gain in precision • Dzero Run I Matrix Element method (l+jets channel) includes all jet combinations  improving statistical uncertainty by factor 2 ! (22 tt events)‏

  26. D0 Run II: Ideogram method Summer 2004 30% improvement ~ factor 2 in statistics!

  27. Ideogram result • But in the meantime: • Nick van Remortel: Ideograms for all-hadronic channel CDF PRL 98, 142001 • Matrix Element method, 2.1 fb-1 D0 Run II: 172.1 ± 1.1 ± 1.6 GeV (preliminary)

  28. The next stop on the journey... W mass, DELPHI Higgs? CMS !! CERN Top mass, Dzero

  29. Dzero  CMS • Came back to CERN in October 2005 • Joined CMS • Many familiar faces !! (Delphi, LEP, DZero, FNAL) • Combine the experiences • Learned in DELPHI: • Work in a large collaboration • Precision measurement, statistical techniques, systematics • Eye for detail: every little detail must make sense… • Not learned in DELPHI (but in Dzero): • Triggers! • The challenge of data analysis if not every detail is known • C++, Root, analysis with larger data volumes

  30. CMS: new challenges Magnet Test and Cosmic Challenge (2006) magnetic field map … with NIKHEF Hall probes and DELPHI colleagues: Teddy Todorov, Nicola Amapane, Dietrich Liko, Tiziano Camporesi… Muon Physics Object Group muon trigger, tracking and ID

  31. DELPHI in CMS

  32. Commissioning the detector • More Magnetic Field business • T

  33. “Closing” words • Today: “closing” meeting of DELPHI • Soon: “closing” of the LHC detectors … • This will mark the start of a new era of great experiments at CERN • The journey continues...!

  34. “Closing” the LHC Experiments

  35. What will we find…?

More Related