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Jet production in pp events at √s = 7 TeV with ATLAS

Jet production in pp events at √s = 7 TeV with ATLAS. Chiara Roda Universita` degli Studi and INFN di Pisa On behalf of the ATLAS Collaboration. Jets for which studies …. The huge jet production cross section will make jets ubiquitous at LHC …. 10 pb -1 @ 7 TeV few jets @ p T > 700 GeV

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Jet production in pp events at √s = 7 TeV with ATLAS

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  1. Jet production in pp events at √s = 7 TeV with ATLAS Chiara Roda Universita` degli Studi and INFN di Pisa On behalf of the ATLAS Collaboration C.Roda Universita`degli Studi & INFN Pisa, Italy

  2. Jets for which studies … The huge jet production cross section will make jets ubiquitous at LHC … 10 pb-1 @ 7 TeV few jets @ pT > 700 GeV D0 e CDF pTMax ~ 700 GeV • Background: jets will be one of the most important background to searches • PDF: sensitivity to high x pdf • Jets for discoveries: quark substructure, extra large dimension, resonant production 107 7 TeV C.Roda Universita`degli Studi & INFN Pisa, Italy

  3. Jets for which studies … The huge jet production cross section will make jets ubiquitous at LHC … 10 pb-1 @ 7 TeV few jets @ pT > 700 GeV D0 e CDF pTMax ~ 700 GeV • Background: jets will be one of the most important background to searches • PDF: sensitivity to high x pdf • Jets for discoveries: quark substructure, extra large dimension, resonant production 107 7 TeV • What I will show you: • What are the ingredient to build the jets • First results on characterisitcs and kinematics C.Roda Universita`degli Studi & INFN Pisa, Italy

  4. The ATLAS detector Length : ~ 46 m Radius : ~ 12 m Weight : ~ 7000 tons ~108 electronic channels 3000 km of cables See P.Iengo’s talk for more detailed description of general detector perfomance. C.Roda Universita`degli Studi & INFN Pisa, Italy

  5. ATLAS Calorimetry Different technologies in different ranges of pseudo-rapidities optimized to substain the radiation rate; High granularity and longitudinal segmentation ; Most difficult regions in section-junction zones. Wide calorimeter coverage to |η|<4.9 EM E-resolution: /E ~ 10%/E HAD E-resolution:/E ~ 50%/E  0.03 C.Roda Universita`degli Studi & INFN Pisa, Italy

  6. Yellow HAD CAL Green EM CAL C.Roda Universita`degli Studi & INFN Pisa, Italy

  7. Very inclusive trigger is provided by scintillators in a forward region (2.09 < |η| < 3.84) that require at least one hit on each hemisphere. No significant bias on the inclusive Jet Sample. Yellow HAD CAL Green EM CAL C.Roda Universita`degli Studi & INFN Pisa, Italy

  8. Data Sample and Event selection LHC Beam Stable +Data Quality Timing consistent with collision + Vertex from center of ATLAS -> background from beam related background negligible (<0.01%). + Jet Cleaning Total rec. luminosity @ √s=7 TeV 16 nb-1 Peak Luminosity = 2.1 1029cm-2s-1 The results I will show are using only a small part of whole data samples ( ). 8 colliding bunches ATLAS-CONF-2010-038 Beam Squeeze 3 colliding bunches Pile-up negligible (0.2%). C.Roda Universita`degli Studi & INFN Pisa, Italy

  9. What are the jets I will show you … JETS = CALORIMETER SIGNAL + JET ALGORITHM + CALIBRATION SCHEME C.Roda Universita`degli Studi & INFN Pisa, Italy

  10. What are the jets I will show you … JETS = CALORIMETER SIGNAL + JET ALGORITHM + CALIBRATION SCHEME Input calorimeter signal to jet reconstruction are topological clusters: HAD CALO SIGNAL ATLAS-CONF-2010-016 EM • collect the energy deposit from the hadronic shower in 3-dimensional space • built around a cell energy deposit with high signal-to-noise ratio • excellent noise suppression capability Understanding the calo signal characterics in our jets is a first step to understand jet structure Average agreement of Data and MC within few percent. Results confirmed on 7 TeV data C.Roda Universita`degli Studi & INFN Pisa, Italy

  11. The Jet algorithm JETS = CALORIMETER SIGNAL + JET ALGORITHM + CALIBRATION SCHEME • ATLAS has studied many jet algorithms and we aim at the possibility to have easily comparison with different jet algorithms. • The default algorithm chosen for first data is the recombination scheme algorithm AntiKT with R=0.4 or 0.6 (good experimental and theoretical characteristics): KT Jet transverse momentum p = -1 for AntiKT Full recombination scheme applied C.Roda Universita`degli Studi & INFN Pisa, Italy

  12. Jet calibration scheme JETS = CALORIMETER SIGNAL + JET ALGORITHM+ CALIBRATION SCHEME • Calibration is needed because (largest detector effects): • calorimeter response is different for hadrons and electrons (non-compensation) • need to correct for energy losses in inactive material • 4 schemes to correct for detector effects. • What we have now – the simplest: • EM+JES: EM jet + pT η dependent factor from MC  • only average pT value corrected; •  no attempt to improve resolution; • less affected by systematics. • More challenging – better resolution – require a more detailed understanding of Data. C.Roda Universita`degli Studi & INFN Pisa, Italy

  13. First check on calorimeter energy scale • Method: • select well isolated tracks • collect the calorimeter clusters around the track • measure Energy_Calorimeter/p_track • Main Problem: • Control of Background from overlapping Neutral particles C.Roda Universita`degli Studi & INFN Pisa, Italy

  14. First check on calorimeter energy scale • Method: • select well isolated tracks • collect the calorimeter clusters around the track • measure Energy_Calorimeter/p_track • Main Problem: • Control of Background from overlapping Neutral particles Data/MC agreement within ~ 5% for the whole rapidity range checked |η|<2.3. Calorimeter response at 7 TeV and 900 GeV completely consistent. 7 TeV extends up to 20 GeV. E/p + test beam + MC results have been used to give a first estimate of the JES which is 0(10%). JES is the largest systematics source in many Jet studies. ATLAS-CONF-2010-017 C.Roda Universita`degli Studi & INFN Pisa, Italy

  15. First jet observation in ATLAS • I will show Data/MC comparison: • phase space: |yjet|<2.8 & pTjet>30 GeV • Theoretical model: PYTHIA dijet events with MC09 tune (LO matrix element + Parton Shower) • Normalization is to unit area -> comparison are sensitive to shape differences • Comparison are shown at reconstructed level, detector unfolding is not done • Errors are statistical only … • Comparison Data/MC including luminosity, detector unfolding and systematic uncertainties will come soon… C.Roda Universita`degli Studi & INFN Pisa, Italy

  16. Jet Multiplicity ATLAS-CONF-2010-043 • Multiplicity with this small data sample already reaches 6 jets. • Very good description by the LO MC C.Roda Universita`degli Studi & INFN Pisa, Italy

  17. Uncalibrated energies Jet pT in the range 30-70 GeV C.Roda Universita`degli Studi & INFN Pisa, Italy

  18. Jet rapidity and pT spectra Very good agreement between data and MC. Small discrepancy observed @ y=-2.1 and y=0 under investigation. C.Roda Universita`degli Studi & INFN Pisa, Italy

  19. Jet-Jet Mass and Δϕ spectra in dijet events • 20% of selected events with at least 2 jets with pT>30 GeV & |y|<2.8. • Both distributions resonably described by the MC. ATLAS-CONF-2010-043 Fall due to the phase-space limit due to the pT and y cut MC slightly underestimate the Data for large Δϕ C.Roda Universita`degli Studi & INFN Pisa, Italy

  20. Jet shape… these are really collimated jets Average scalar sum fraction of jet pT momentum in annulus Demonstrate the collimated nature of jets Sensitive to UE and to fragmentation models Quite insensitive to the energy scale C.Roda Universita`degli Studi & INFN Pisa, Italy

  21. Jet shape… these are really collimated jets Average fraction of jet pT momentum in annulus Demonstrate the collimated nature of jets Sensitive to UE and to fragmentation models Quite insensitive to the energy scale Jets in data are broader than in MC, consistent with 900 GeV data ATLAS-CONF-2010-043 C.Roda Universita`degli Studi & INFN Pisa, Italy

  22. Charged particle flow around the jet Define the position of the second jet in the event Reference Jet Tracks pTtrack> 500 MeV & |ηtrack|<2.8 Average scalar sum of tracks pT vs φ-distance from jet axis in bins of jet-jet rapidity separation Δyjj C.Roda Universita`degli Studi & INFN Pisa, Italy

  23. ATLAS-CONF-2010-043 |Δyjj|<0.6 0.6<|Δyjj|<1.2 1.8<|Δyjj|<3.8 1.2<|Δyjj|<1.8 Good cross check of jet shapes with tracks Jets confirmed to be slightly broader in data Hadronic activity away from jets slightly underestimated from MC -> also confirmed by UE analysis (see J.Proudfoot’s Talk) C.Roda Universita`degli Studi & INFN Pisa, Italy

  24. Conclusions • Jets have been clearly observed in ATLAS with analysis of 1nb-1 data sample • The kinematical properties of the jets show the expected characteristics • The first checks on the jet energy scale point to a JES uncertainty of ~10% • Ready to start working on fancier calibration scheme to exploit our calorimeter performance at best • Many more interesting results, including jet cross sections studies are coming soon ! • Addictional information with all the ATLAS public results: • https://twiki.cern.ch/twiki/bin/view/Atlas/AtlasResults C.Roda Universita`degli Studi & INFN Pisa, Italy

  25. The event with highest pT jets EM Scale C.Roda Universita`degli Studi & INFN Pisa, Italy

  26. Back-up C.Roda Universita`degli Studi & INFN Pisa, Italy

  27. Pt and Eta @ EM scale C.Roda Universita`degli Studi & INFN Pisa, Italy

  28. Jet selection variables C.Roda Universita`degli Studi & INFN Pisa, Italy

  29. Selecting good jets for physics • Good jet selection: • No jets from noisy cells: • Sporadic burst of noise in Hadronic EndCap • Coherent noise in EM • No jets with large energy release not in coincidence with collision time (cosmic ray showers) ATLAS-CONF-2010-038 pT spectra of jets only requiring: Collisions + Data Quality shows a large tail … Fake jets arise from HW problems, LHC conditions or cosmic ray showers. About 0.01% of events rejected C.Roda Universita`degli Studi & INFN Pisa, Italy

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