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My work for HERA, LHC and ILC.

My work for HERA, LHC and ILC. Tuesday seminar November 27, 2007. Tomáš Laštovička. Introduction. I have joined LCFI group at Oxford in May 2007 PhD study: DESY – H1 Experiment where I finished my PhD – Humboldt University, Berlin Postdocs: DESY (2004)

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My work for HERA, LHC and ILC.

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  1. My work for HERA, LHC and ILC. Tuesday seminar November 27, 2007 Tomáš Laštovička

  2. Introduction • I have joined LCFI group at Oxford in May 2007 • PhD study: • DESY – H1 Experiment • where I finished my PhD – Humboldt University, Berlin • Postdocs: • DESY (2004) • CERN fellowship (2005-2007) – LHCb Experiment • 05/2007+ University of Oxford Keywords: silicon vertex detectors, QCD, structure functions, tracking, vertexing, programming, … Tomáš Laštovička

  3. DESY and the H1 Experiment ( ? – 2004 ) Tomáš Laštovička

  4. DESY – H1 Experiment • When deciding about master thesis topic at Charles University, Prague, I opted for DESY • This actually started my low Q2 (and low x) precision measurements period. • After finishing thesis I decided to continue the business and moved to DESY Zeuthen close to Berlin (still being student at Charles University, for some time). DESY Hamburg H1 Tomáš Laštovička

  5. Low Q2 inclusive cross sections • Member of ‘ELAN’ group – Inclusive Measurements and QCD fits • …which I had pleasure to convene in 2002-2005. • Focused on measurements of F2 and FL proton structure functions • Steep rise towards low Bjorken x is one of few HERA discoveries • F2 is not calculable from the first principles • Related to quark densities, in the leading order as Turn-over attributed to FL 1993 2000 Tomáš Laštovička

  6. Situation in 2002 (now even better coverage) low Q2 1999 dedicated run Low Q2 x-section and F2 determination at low x shifted vertex 2000 run Transition region between perturbative and non-perturbative kinematic range Tomáš Laštovička

  7. Spaghetti Calorimeter Shifted vertex Nominal vertex e+ p ~70cm Backward Silicon Tracker Key components I Tomáš Laštovička

  8. + e Key components II • SpaCal (Spaghetti Calorimeter) • 1192 square cells, lead-scintillating fibers • 0.2% calibr. precision at 27.6GeV • High efficiency L1 (LHCb’s L0) trigger (>99%) • x-y view: • Backward Silicon Tracker (BST) • scattered electron measurement • 95% track reconstruction efficiency • 20μm resolution • 8 planes, 16 segments each Tomáš Laštovička

  9. Analyses • >95% of analysis time was devoted to understanding and description of detector components • Detector calibration (SpaCal - electron, LAr - hadrons) • Alignment (BST, SpaCal, BDC) • Efficiency (BST) – quite a challenge • … • It was literally “pushing the limits” style of analysis • leading to some novel approaches, e.g. • F2 measurement from ISR events without measuring the scattered electron • FL determination at Q2 ~ 1GeV2 and below (next slide) - this region is too non-perturbative even for F2, not mentioning FL Tomáš Laštovička

  10. FL in the transition region • Status of 2003 preliminary analysis shown. • FL was actually never measured directly at HERA • low proton beam energy runs in 2007 (preliminary analysis in 2008?) Tomáš Laštovička

  11. Contribution to phenomenology and most enjoyful time I had in Physics so far… • Attempt to describe internal proton structure as a fractal: • …but much more colorful, of course! (QCD) • Use concept of fractal dimensions, estimate PDFs and fit F2. Tomáš Laštovička

  12. Contribution to phenomenology • This worked surprisingly well leading to lowest χ2 fit of F2 data • and it is going to be used in the forthcoming H1 publication as well. Tomáš Laštovička

  13. CERN and the LHCb Experiment ( 2005 – 2007 ) Tomáš Laštovička

  14. CERN fellowship • In 2004 I was awarded CERN research fellow position • and joined the LHCb Experiment in February 2005 • I started with • Metrology/Alignment of VELO (Vertex Locator) telescope • VELO-only fast simulations (rest of LHCb subdetectors not simulated) • Then I directed myself more into VELO-only reconstruction of generic tracks/vertices and its applications • Generic pattern recognition – PatVeloGeneric class • and Generic Vertex finding and reconstruction • Applications: • alignment issues, open velo, luminosity measurements, test-beam data, … Tomáš Laštovička

  15. Vertex Locator (VELO) • 21 tracking stations on two sides • 42 modules, 84 sensors • plus pile-up sensors • Optimised for • tracking of particles originating from beam-beam interactions • fast online 2D (R-z) tracking • fast offline 3D tracking in two steps (R-z then phi-z) • Velo halves are moved from the LHC beam by 30mm during the beam injection and tuning. R sensors φ sensors nominal vertex area pile-up veto sensors Tomáš Laštovička

  16. Open VELO tracking – aperture 30mm Ntr ≥ 4 Ntr ≥ 4 83 μm 108 μm Ntr ≥ 10 Ntr ≥10 54 μm 69 μm Designed beam-spot size: 70μm (100μm beam profiles) Tomáš Laštovička

  17. Ntr > 14 Luminosity measurements • Reconstruction of beam parameters from beam-gas interactions • in order to calculate beam overlap integral and thus luminosity. • It was my pleasure to lead luminosity measurements sub-group (a part of Production and decay models WG) Xenon simulation x y ~18μm VELO Designed beam-spot size: 70μm (100μm beam profiles) Tomáš Laštovička

  18. Z0→µ+µ- Possible application • Measure Z0→µ+µ- cross section as a function of rapidity (and scale, eventually). • Use the data in QCD fits to pin down proton PDFs at high scales but low x • Drell-Yan pair production is included in most of QCD fitters. • Compare with predictions without fitting the data… • Cross-check: it simply must agree (or there is a problem). • Presented at HERA-LHC workshop in 2006. Tomáš Laštovička

  19. VELO in test-beam I • Successful application of generic PR/vertexing algorithms on real VELO data (10 sensors mounted, 6 read out at once…) • allowed to see beam position from interactions in VELO tank, targets and in sensors themselves… • …which made minimum of 5 people happy and showing teeth: Tomáš Laštovička

  20. VELO in test-beam II • Panoramix display of typical VELO test-beam tracks with targets • vertices not shown but reconstructed. Tomáš Laštovička

  21. University of Oxford – LCFI group (ILC) ( May 2005 till now ) Tomáš Laštovička

  22. LCFI = Linear Collider Flavour Identification I am involved in: • Physics Higgs self-coupling: ZHH channel SUSY: sbottom Decay Analysis • Technical tasks Kalman Filter for Vertex Fitting Jet Tagging Algorithms (NNs, Boosted Decision Trees) Tomáš Laštovička

  23. Higgs Self-coupling? Higgs Potential • To experimentally determine the shape of the Higgs potential the self-coupling of the Higgs field must be measured • In Standard Model , independent measurement may reveal an extended nature of the Higgs sector: Higgs potential from MH as measured by λHHH some other completely fictional potential from an extended model Tomáš Laštovička

  24. Why ZHH channel? • Measurement of cross section gives a handle to measure the Higgs self-coupling constant. • Benchmark channel for ILC. • To evaluate various detector concepts. • Highly non-trivial to analyse. • Another option is WW fusion channel. • Small cross section (500GeV ILC). Tomáš Laštovička Roughly Δλ/λ ~ 1.75*Δσ/σ

  25. SUSY and Cosmology • There is 23% of Cold Dark Matter in Universe – as measurements tell us. • Neutralino is Dark Matter candidate. • During Universe expansion at some point supersymmetric particles are no longer produced but the existing ones may annihilate – the rate can be calculated. • In most of the SUSY parameter space there are still too many neutrinos left. • Cold Dark Matter favors some particular SUSY scenarios. For effective co-annihilation of particles the mass splitting should be small – leading to small energies of visible particles. Tomáš Laštovička

  26. sbottom and neutralino • If sbottom (stop) and neutralino have a small mass split they can account for co-annihilation in early Universe through this type of diagrams: • Sbottom can be produced at ILC, then it decays to b and neutralino: If the mass split is low (as suggested) this would lead to very soft b-jets and missing pT. Tomáš Laštovička

  27. ILC LEP and CDF/D0 Results • CDF/D0 – measurement at high masses but still relatively hard jets (due to triggers) which are not favored by the dark matter scenario. • LEP – able to measure in the region where the mass difference is only few GeV (?!) • ILC should not be much worse but at higher masses. • Small (meaning tiny) mass splitting is not accessible at ILC. Tomáš Laštovička

  28. Conclusions ? Tomáš Laštovička

  29. Thank you for attention… Tomáš Laštovička

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