1 / 38

Recent results from LHCb

Recent results from LHCb. Alessia Satta Roma Tor Vergata On behalf of LHCb Collaboration BORMIO 2011 XLIX International winter meeting on nuclear physics. Outlook. The LHCb experiment in a nutshell Detector and performance First results. The LHCb experiment at CERN. 730 authors

micheal
Télécharger la présentation

Recent results from LHCb

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. Recent results from LHCb Alessia Satta Roma Tor Vergata On behalf of LHCb Collaboration BORMIO 2011 XLIX International winter meeting on nuclear physics

  2. Outlook The LHCb experiment in a nutshell Detector and performance First results

  3. The LHCb experiment at CERN 730 authors 54 institutes 15 countries

  4. LHCb physic goals Main LHCb objective is the indirect search for New Physics performing precision measurements of CP violation and Rare decays in the b quark sector In indirect search NP enters through contributions from virtual heavy particles in loop-mediated processes modifying the SM prediction Higher scale can be accessed wrt direct search Mass scale, couplings and phase of NP can be accessed “Indirect discoveries” in the past suppression of FCNC → prediction of 2nd quark family CP violation → prediction of 3rd quark family

  5. CP violation measurements • CPV sensitive to NP phases • Within uncertainties, flavor changing data described by SM: Consistency is at 2  level. There are several 2…3  tensions • Improve measurements on CKM elements and challenge the Standard Model by overconstraining the unitarity triangle • Compare two measurements of the same quantity sensitive and not to the NP (tree vs loop) • γ: B(s) → D(s) K, B(s) →hh • Measure with high precision the Bs J/yfCPV phase which is predicted small on SM sensitive to NP contribution

  6. Rare decays • FCNC process, mediated by electroweak box and penguin diagrams in SM. • New Physics enters at same (i.e. loop) order and can give rise to comparably large deviations from SM predictions in: • Branching ratios. • Angular distributions. • CP asymmetries. • AFB BK*mm • BR Bsmm • CP of BK*g t s b W l+l- g,Z s b ? l+l-

  7. LHCb design overview LHCb Physics goal requires high statistics Exploit large bb production cross section at LHC @ √s=14 TeV 500-600b 80mb for bb or inelastic LHCb covers forward region: 1.9 < < 4.9 ● optimized for the strongly forward peaked heavy quark production at the LHC ● only ~4% of solid angle but keep ~40% of heavy-quark production cross section • LHCb designed to operate at an instantaneous luminosity of 2x1032cm-2s-1 factor 50 lower than LHC maximum to maximize single interaction per crossing. Disregard very busy events Unique h coverage

  8. LHCb detector Muon system RICH Detectors Vertex Locator Interaction point Tracking system Calorimeters

  9. Trigger • bb cross section is less than 1 % of the total inelastic cross section • interesting B decay channels have typical branching fractions of 10-5 • exploit generic B decay signature: decay products with large pT (“large” = few GeV) and high impact-parameter, well separated B decay vertex • L0 (Hardware) detect high PT lepton and hadron in muon and Calo • HLT Software uses all detector info

  10. Data taking • In 2009 LHC makes the pilot run. The first LHC collisions at √ s = 900GeV • On such data the velo was not closed • In 2010 LHC increases the energy reaching the √s = 7 TeV • Also a 0.31nb-1 at 900Gev • Impressive increases of the luminosity during the year • recorded 37.7 pb-1 at √s = 7 TeV • LHCb performs very well: data taking efficiency > 90% Last month

  11. 2010 running conditions and trigger • peak instantaneous luminosity almost 2 x 1032cm-2s-1 (LHCb design luminosity) but: with only 344 colliding bunches instead of 2622 at beginning of fill: up to more than 2.5 interactions per crossing on average significantly harsher conditions than design • multiple primary vertices • high occupancies, track multiplicities • detector & reconstruction cope better with these conditions than expected • main limitation found: HLT reconstruction time for very busy events • Despite that exploiting the trigger flexibility and adapt continuously to changing running condition high efficiency were reached. Design value

  12. Vertex and Impact parameter resolution Good primary vertex and Impact parameter resolution crucial for most of the analyses and trigger From data single hit resolution in Velo 4 m Good primary vertex resolution IP 15 mm for high Pt tracks For low Pt tracks worse than MC work on material description ongoing

  13. Tracking • Excellent momentum resolution crucial for good invariant mass and background reduction • High tracking efficiency crucial for multibody decays reconstruction • Tracking efficiency estimated with tag and probe: > 90% for tracks above few GeV TT OT Hit resolution agrees well with current simulation

  14. Tracking: excellent momentum resolution demonstrated

  15. RICH Particle identification • crucial for flavour tagging and for separation of B decays with identical topology, e.g.B0 → - ↔ B0 → K+-↔ Bs→ K+K- • efficiencies and mis-ID determined from data using tag-and-probe methods on → K+K-, Ks→ +-→ pp • performance found to be close to simulation over full momentum range

  16. Calorimeter PID • trigger on hadronic decay channels • reconstruction of final states with e,  D0.Kp0   Y(ns)ee c1,2J/  J/see

  17. Muon Identification • efficiency determined from data using tag-and-probe method on J/found to be > 90 % for p > 10 GeV • mis-ID probabilities K→, , p→ determined from data using tag-and-probe method on spall found to be < 2 % for p > 10 GeV • good agreement between data and simulation

  18. First LHCb results With the present integrated luminosity the LHCb physics core measurements not possible. Waiting for larger integrating luminosity several interesting analyses : Particle production Open Charm cross section Hidden charm cross section bb cross section Electroweak physics

  19. Ks production cross section • First measurement for LHCb with 2009 pilot run data √s =0.9TeV • Ks→π-π+ selection based on tracking and impact parameters • First test for detector calibration • New method to estimate luminosity using beam profiles estimated from vertices made by VELO tracks in beam-gas and beam-beam collisions Comparison with other experiment Comparison with PYTHIA Unique measurement at high rapidity and low Pt Good consistency with PYTHIA Expectation slightly harder PT Published Phys Lett B 693 (2010) 69-80

  20. Hadron production ratios Motivation:: Baryon number transport and Hadronisation MC tuning 2 analyses: V0 ratios (tracking &vertexing only) and p/p (+ RICH PID) Use minimum bias data No need to know absolute luminosity

  21. andKs ratios • Ksp-p+ and Lpp • Ks and Λ selection based on impact parameter of decay products and Ks and L wrt primary vertex • Systematics partially cancel • Data sample at 0.9TeV and 7TeV   Yields asymmetry clearly visible in raw mass plot

  22. Preliminary  and L/Ks L/L Baryon transport higher than predicted at √s 0.9 TeV L/Ks Baryon/Meson suppression lower than predicted

  23. Prompt p/p production ratio Pure samples of protons selected with RICH particle ID Calibration of efficiency and purity of RICH PID extracted from data Different interaction cross-sections in the material between p and p, particularly at low momentum Therefore limit analysis to tracks with P > 5 GeV

  24. Preliminary results √s =0.9TeV Baryon transport higher than predictions and consistent with Λ/Λ

  25. Prompt p/p production √s =7TeV Ratios become flatter as predicted by models Better agreement with MC

  26. Inclusive F production • Unique way to study strangeness production • Discrepancies from MC seen by all major LHC experiments • Test QCD fragmentation models in pp interactions in LHCb's kinematic region • Φ→K+K- candidates selection requires RICHPID information • Cross section measurement is performed in bins of PT and h Both tunings underestimate Φ production in the measured kinematic range

  27. Open Charm cross-section Same aspects of LHCb that makes us good for b -physics also aids charm physics Charm cross section ~20x larger than beauty First measurement at √s =7TeV Measurements down to very low Pt Current results: Cross section for D0,D+, D+*,Ds with 1.8nb-1 Measurement in 2D (Pt and h) Efficiency extracted both from data (PID) and from MC Removal of secondary charm ( from beauty decays) using IP Work in progress to add c and to increase data sample statistics

  28. D* , D0 cross section results σ(D*+;pT<8GeV/c,2<y<4.5)=676±137 μb PYTHIA prediction: σ(D*+;pT<8GeV,2<y<4.5)=653±1 μb σ(D0;pT<8GeV/c,2<y<4.5)=1488±182 μb PYTHIA prediction: σ(D0;pT<8GeV,2<y<4.5)=1402±2 μb

  29. D+, Ds cross section results σ(D+;pT<8GeV/c,2<y<4.5)=717±109μb PYTHIA prediction:509±1 μb σ(Ds+;pT<8GeV/c,2<y<4.5)=194±38μb PYTHIA prediction: 255±1 μb

  30. Open charm results Various cross-sections results are in agreement with MC predictions Using published fragmentation fractions σ(pp→HcX,2<y<4.5,pT<8GeV/c)=1.23±0.19mb Using PYTHIA to extrapolate to 4π, we obtain the following (preliminary) total open charm cross-section: σ(pp→cc)=6.10±0.93mb Result for total cross-section in 4π consistent with expectations ( σ(pp→cc) ≈ 20×σ(pp→bb) ) seen next for σ(pp→bb) Work ongoing to measure cross-sections with more data

  31. J/y production Very important measurement: J/ψ production mechanism not well understood, the color-octet model used to fit the CDF data doesn't describe the J/ψ polarization BJ/ψ X decays fundamental for the LHCb core physics program Large signal yield: Differential cross section d2σ/dptdy as a function of transverse momentum pT and rapidity y 14 bins in pt: 0 < pT < 14 GeV/c , X 5 bins in y: 2 < y < 4.5 Excellent mass resolution (~ 15 MeV/c2 depending on bin) 564603 +/- 924 5.2pb-1

  32. J/y production cross section Two measurements (pseudo proper time separation): prompt J/ψ: direct production in pp collisions or seed down from other charmonium states ( ψ(2S), χc ...) J/ψ from B decay Efficiencies are computed from Monte Carlo and are extensively checked on data with control samples Polarization affects a lot the detection efficiencies Quote results in three extreme cases for prompt production Polarization measure ongoing Luminosity 5.2 pb-1 From b Prompt Tails

  33. J/y cross section results Prompt J/y J/y from b Extrapolation to bb cross section in 4π via Pythia 6.4 with LEP branching ratio: Br(b→J/ψ+X) = (1.16±0.1)%

  34. J/y comparison with theory • A comparison with three different models is proposed. • LO and NLO NRQCD (Non Relativistic QCD summing color Singlet and color Octet) • NLO CEM (Color Evaporation Model) • The NLO NRQCD model seems to fit data reasonably well in the high Pt region, though the uncertainty is much large and there is a clear problem at low Pt.

  35. bb Cross Section: b → D0mnX reconstruct D0 in K- + decay mode reconstruct D0 - pairs from a common vertex select “D from B” by large impact parameter use wrong-sign D0  pairs to estimate backgrounds Signal L= 3pb-1 Prompt Fake Right sign Wrong sign

  36. bb cross section 2 samples: 3nb-1 data taken with open trigger and 11nb-1 with muon trigger : results in agreement b quark fragmentation fraction from LEP 17% systematic dominated by uncertainties in luminosity and Monte Carlo representation of the tracking efficiency Published Phys Lett B 694 (2010) 209 within LHCb acceptance ( 2 < η(Hb) < 6) σ (pp → HbX) = (75 ± 5.4 ± 13) μb using Pythia to extrapolate to full phase space σ (pp bbX) = (284 ± 20 ± 49) μb

  37. Electroweak physics • At LHCb unique possibility to measure Z, W in forward region • Such measurement probe PDF the low-x, high Q2 region inaccessible to other experiments • At the LHC unprecedented Q2 due to the higher beam energy • Reconstruction of Zmm and Wmn • PID tracking and trigger efficiency extracted from data • preliminary results from 16.5 pb-1 • All results in agreement with theory • Provide new constraint on proton PDF

  38. Conclusions • LHCb data taking started successfully • Very good detector performance despite of harder condition than design • Several analysis on going: • Particle production • Open and hidden charm • bb cross section • Electroweak • In 2011 expected luminosity ~1fb-1: core LHCb physics results expected • Eg. Bsmm (actually first result expected for winter conference) • Bs mixing CP • g from tree and loop • AFB BK*mm

More Related