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

2. Tomáš Laštovička2 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, …

3. Tomáš Laštovička3 DESY and the H1 Experiment ( ? – 2004 )

4. Tomáš Laštovička4 DESY – H1 Experiment When deciding about master thesis topic at Charles University, Prague, I opted for DESY  This actually started my low Q 2 (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). H1 DESY Hamburg

5. Tomáš Laštovička5 Low Q 2 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 F 2 and F L proton structure functions  Steep rise towards low Bjorken x is one of few HERA discoveries  F 2 is not calculable from the first principles Related to quark densities, in the leading order as 1993 2000 Turn-over attributed to F L

6. Tomáš Laštovička6 low Q 2 1999 dedicated run Transition region between perturbative and non-perturbative kinematic range shifted vertex 2000 run Low Q 2 x-section and F 2 determination at low x Situation in 2002 (now even better coverage)

7. Tomáš Laštovička7 Key components I Backward Silicon Tracker Shifted vertex Spaghetti Calorimeter e+e+ p Nominal vertex ~70cm

8. Tomáš Laštovička8 Key components II Backward Silicon Tracker (BST)  scattered electron measurement  95% track reconstruction efficiency  20μm resolution  8 planes, 16 segments each e + 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:

9. Tomáš Laštovička9 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. F 2 measurement from ISR events without measuring the scattered electron F L determination at Q 2 ~ 1GeV 2 and below (next slide) - this region is too non- perturbative even for F 2, not mentioning F L

10. Tomáš Laštovička10 F L in the transition region Status of 2003 preliminary analysis shown. F L was actually never measured directly at HERA  low proton beam energy runs in 2007 (preliminary analysis in 2008?)

11. Tomáš Laštovička11 Contribution to phenomenology 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 F 2. and most enjoyful time I had in Physics so far…

12. Tomáš Laštovička12 Contribution to phenomenology This worked surprisingly well leading to lowest χ 2 fit of F 2 data  and it is going to be used in the forthcoming H1 publication as well.

13. Tomáš Laštovička13 CERN and the LHCb Experiment ( 2005 – 2007 )

14. Tomáš Laštovička14 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, …

15. Tomáš Laštovička15 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. nominal vertex area pile-up veto sensors R sensors φ sensors

16. Tomáš Laštovička16 Open VELO tracking – aperture 30mm 54 μm 69 μm N tr ≥ 10 N tr ≥ 4 83 μm 108 μm Designed beam-spot size: 70μm (100μm beam profiles)

17. Tomáš Laštovička17 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) N tr > 14 Xenon simulation ~18μm x y Designed beam-spot size: 70μm (100μm beam profiles) VELO

18. Tomáš Laštovička18 Possible application Measure Z 0 →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. Z 0 →µ + µ -

19. Tomáš Laštovička19 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:

20. Tomáš Laštovička20 VELO in test-beam II Panoramix display of typical VELO test-beam tracks with targets  vertices not shown but reconstructed.

21. Tomáš Laštovička21 University of Oxford – LCFI group (ILC) ( May 2005 till now )

22. Tomáš Laštovička22 LCFI = L inear C ollider F lavour I dentification 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)

23. Tomáš Laštovička23 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: as measured by λ HHH Higgs potential from M H some other completely fictional potential from an extended model

24. Tomáš Laštovička24 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). Roughly Δλ/λ ~ 1.75*Δσ/σ

25. Tomáš Laštovička25 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.

26. Tomáš Laštovička26 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 p T.

27. Tomáš Laštovička27 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. ILC

28. Tomáš Laštovička28 Conclusions ?

29. Tomáš Laštovička29 Thank you for attention…