Ferrara 2012

Second year report

1. Optimization of software trigger and χb studies in LHCb 2nd year report Alexander (Sasha) Mazurov Department of Physics University of Ferrara, Italy & LHCb experiment, CERN, Switzerland alexander.mazurov@cern.ch 30 November 2012 Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 1 / 20
2. Introduction About Me From Protvino, Russia. 1997-2002: Lomonosov’s Moscow State University, MS Calculate Mathematic and System programming. 2007-present: CERN, LHCb experiment. Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 2 / 20
3. Introduction LHCb experiment (1) One of the four largest experiments in Large Hadron Collider (LHC) 843 members, from 60 institutes in 16 Countries Forward spectrometer. Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 3 / 20
4. Introduction LHCb experiment (2) Core physics program is a searching for NEW physics with Charm and Beauty particles. Hot result (November 2012) First evidence for the B0 s → µ+µ− decay. Branching: 3.2+1.5 −1.2 × 10−9. Consistent with Standard Model Many experiments have been looking for this decay in the last 10 years. LHCb is the first to observe it! Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 4 / 20
5. Introduction My research 1 Trigger software profiling. DONE 2 Study of χb production. IN PROGRESS Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 5 / 20
6. Trigger software profiling Trigger software profiling Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 6 / 20
7. Trigger software profiling Trigger software profiling The trigger needs fast algorithms! Most experiments require a trigger in order to record interesting events at suitable rate. L0 Hardware Trigger 40MHz → 1MHz. Search for high pt, µ, e, γ, hadron candidates. High Level Software Trigger Farm HLT1: Add Impact parameter cuts HLT2: Global event reconstruction. 100 man/years work that has only 20-30 ms to process an average event. 29K CPUs or 1700 servers. 2 × 1015 bytes stored in 2012. Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 7 / 20
8. Trigger software profiling Profiler Auditor CPU Profiler Auditor CPU profiler tool is vital for trigger optimization. C++ library. Deployed into the core software framework in LHCb — Gaudi. Based on Intel R VTuneTMAmplifier XE User API Full and clear reports. Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 8 / 20
9. Trigger software profiling Profiler Auditor Example of trigger hotspot Hotspot was found. Allows to decrease CPU consumption by 5%. Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 9 / 20
10. Trigger software profiling Profiler Auditor CHEP2012: Talk and Paper This work was presented on ”Computing in High Energy and Nuclear Physics” conference. The largest of the conferenes in this area. The conference is held every 18 months. Paper ”Advanced Modular Software Performance Monitoring”, Journal of Physics: Conference Series. Was accepted for publishing. Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 10 / 20
11. Study of χb production Study of χb production Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 11 / 20
12. Study of χb production Optimizing the LHCb trigger is crucial in many measurement. In particular, decays with muons can be triggered on with unprecedented high efficiency (∼80%). The dimuon trigger: is not prescaled. is used in more than 50% of LHCb’s papers. Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 12 / 20
13. Study of χb production Motivation and Plan b¯ b system, which can be produced in different spin configurations, is ideal laboratory for QCD tests. It’s like a hydrogen atom in QCD. Measured mass Mass from theory States with parallel quark spins (S=1): S-wave Υ state. P-wave χb states, composed by 3 spin states χb(1,2,3) . Can be readily produced in the radiactive decays of Υ. χb(3P) state recently observed by ATLAS, D0 and LHCb. Study of χb production: 1 Measurement for Υ(NS) (N=1, 2, 3) cross sections in χb decays as a function of pT (NΥ) 2 Measurement of χb(0,1,2) (3P) mass. Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 13 / 20
14. Study of χb production Cross sections Cross sections formula In each pT (Υ) bin calculate: σ(χb→Υγ) σ(Υ) = Nχb→Υγ NΥ × Υ χb→Υγ = Nχb→Υγ NΥ × 1 reco γ Calculate for each Υ(nS), n = 1, 2, 3 and χb(mP), m = 1, 2, 3 Get N from fits: NΥ from m(µ+µ−) and Nχb→Υγ from [m(µ+µ−γ) − m(µ+µ−)] (for better resolution) Compute efficiency from Monte-Carlo simulation Luminosity = 1015 ± 35pb−1, data collected in year 2011. Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 14 / 20
15. Study of χb production Cross sections Reconstruction Models were built on top of RooFit toolkit and unbinned maximum likelihood fits were performed. For NΥ: invariant mass Signal: sum of 3 Crystal Ball functions Background: exponential function. For Nχb→Υ(1S)γ : mass difference Signal: 3 Gauss functions Background: √ x × e−τx × (c1 + a1x + a2x2) + e−τx × (c2 + a3x + a4x2) (not enough resolution to separate χb(0,1,2) ) Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 15 / 20
16. Study of χb production Cross sections Number of χb (NP) → Υ(1S) decays Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 16 / 20
17. Study of χb production Measurement of χb(3P) mass Measurement of χb (3P) mass Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 17 / 20
18. Study of χb production Measurement of χb(3P) mass Selection optimization Background subtraction We can reduce the background by tightening cut on pT (γ) Can make a precise measurement of mχb(3P) Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 18 / 20
19. Study of χb production Measurement of χb(3P) mass Very preliminary results Next steps: Determine systematic errors Photon energy calibration mχb(2P) [GeV /c2] mχb(3P) [GeV /c2] ATLAS 10.530 ± 0.0050 D0 10.551 ± 0.0140 LHCb (prev) 10.2660 ± 0.0060 10.535 ± 0.0100 This study 10.2709 ± 0.0035stat 10.515 ± 0.0074stat Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 19 / 20
20. Study of χb production Measurement of χb(3P) mass Summary 1 LHCb trigger allows to collect a huge sample of dimuon events. 2 Profiling High Level Trigger software at LHCb gives improvements in software performance and speed. 3 Started studying the production of χb particles in LHCb, through the reconstruction of χb → Υγ decays, with the Υ decaying to µ+µ−. 4 Determined χb → Υ(1S)γ yields as a function of pT (Υ(1S)). 5 Measured mass of the χb(3P) state, which has been recently observed at LHC and TeVatron. 6 Finalize analysis (efficiencies, other decays,...) in a few months timescale. Sasha Mazurov (University of Ferrara) Optimization and χb studies 30 November 2012 20 / 20