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EPJC65:111 (2010). First ALICE Results from Proton-Proton Collisions. Jan Fiete Grosse-Oetringhaus, CERN/PH for the ALICE collaboration Rencontres de Moriond 14. 19. March 2010, La Thuile, Italy. full. full. EMCAL , 0 , jets. L3 Magnet. T0/V0 Trigger. ACORDE Cosmic trigger. - PowerPoint PPT Presentation

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  • First ALICE Results from Proton-Proton CollisionsJan Fiete Grosse-Oetringhaus, CERN/PHfor the ALICE collaboration

    Rencontres de Moriond14. 19. March 2010, La Thuile, ItalyEPJC65:111 (2010)

    First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

  • A Large Ion Collider ExperimentNot shown: ZDC (at 116m)Dipole

    First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

  • DetectorsV0 scintillator arrayTrigger2.8 < h < 5.1 and -1.7 < h < -3.7Silicon Pixel Detector (SPD)Two innermost layers of the Inner Tracking System (ITS)Radii of 3.9/7.6 cm (|h| < 2.0/1.4) Trigger & Tracking|h| < 1.4; pT > 50 MeV/c9.8 M channelsTracklet: 2 points + vertexDuring 2009 data-taking 80% activeDetector AcceptanceSPD physics efficiency for primaries(2009 configuration80% active)pT (GeV/c)EfficiencyALICE Performancework in progressh

    First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

  • Trigger for MB PhysicsALICE measures MB properties for all inelastic (INEL) and non single-diffractive (NSD) events Inclusive trigger ("MB1") for INEL: central pixel hit (SPD) or forward scintillator (V0)One particle in 8 h units(Trigger-)sensitive to 95-97% of the inelastic x-sectionTwo-arm trigger ("V0AND") for NSDBoth forward scintillatorsOne particle in 2.8 < h < 5.1 and one in -1.7 < h < -3.7Pythia0.9 TeVGenerated multiplicity in |h| < 1Trigger efficiencyALICE Performancework in progress

    0.9 TeV (in %)NDSDDDPythiaMB11007792V0AND982949PhojetMB11008698V0AND983466

    First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

  • Data SampleAnalysis based on900 GeV: 186k collision events out of 430k total2.36 TeV: 41k collision eventsMC adapted to mean vertex position and spreadSPD moduleCluster yieldDataMCALICE Performancework in progressALICE Performancework in progressEventsRatio Data / MCfirst layersecond layeryield in first and second layer compatible within 0.5%inefficient sector no significant effect on resultALICE Performancework in progressz vertex distribution (cm)

    First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

  • dNch/dh MeasurementBasically if the detector was perfect

    But there is Detector acceptance, tracking efficiencyDecay, conversions, stopping, etc.Vertex reconstruction efficiency/bias, trigger efficiency/biasLow momentum cut-offThree corrections neededTrack-to-particle correctionVertex reconstruction correctionTrigger bias correctionPrimary particles = charged particles produced in the collision and their decay products excluding weak decays from strange particles

    First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

  • dNch/dh Measurement (2)Use the number of triggered events without reconstructed vertex to constrain the "0 bin"Assess background from control triggers (single bunch passing, no bunch passing)Background with activity < 0.02%At 2.36 TeV no control triggersUse 0 bin from MC larger syst. errorAverage correction factorsTracking: 1.53Events (INEL): 1.05Events (NSD): 1.02 [+8.3% (NSD) 6.8% (SD)]Subtraction of SD tracks for NSD: 3%hdNch/dhALICE Performancework in progressBeam-inducedbackground

    Main systematic uncertainties (%)at 900 GeVINELNSDFractions SD/DD/ND0.62.8MC dependence2.01.0Detector efficiency1.5

    First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

  • dNch/dhNB: CMS data points do not include charged leptons ~1.5 % differenceALICE, CMS: stat. and syst. uncertainty added quadraticallyALICE, CMS: stat. and syst. uncertainty added quadraticallyhdNch/dhhdNch/dh* only stat. error

    dNch/dh in |h| < 0.5ALICE, CMS: stat. and syst.uncertainty added quadratically0.9 TeV2.36 TeVINELNSDINELNSDALICE preliminary3.02 0.073.58 0.113.77 0.234.44 0.16ALICE EPJC65:111 (2010)3.10 0.263.51 0.29CMS JHEP 02 (2010) 0413.48 0.134.47 0.16UA5 Z. Phys. C33 1 (1986)3.09 0.05*3.43 0.05*

    First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

  • dNch/dh (2)Larger increase from 0.9 to 2.36 TeV at mid-rapidity as in MC generators

    ALICE, CMS: stat. and syst. uncertainty added quadraticallypoints at the same energy slightly shifted

    in %INELNSDALICE prel.24.8 +6.1-3.024.0 +3.9-1.3CMS28.4 3.0Pythi aD6T19.718.7ATLAS CSC19.218.3Perugia-019.618.5Phojet17.514.5

    First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

  • Multiplicity DistributionsEfficiency, acceptance Resolution vs. bin size bin flowCorrection by unfoldingDetector responseProbability that a collision with the true multiplicity t is measured as an event with the multiplicity mVertex reconstruction, trigger bias correctionLike for dNch/dh, but in unfolded variables (true multiplicity) because it is applied after unfoldingtrue multiplicitymeasured multiplicity|h| < 1ALICE Performancework in progress

    First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

  • Unfolding using c2-MinimizationOne free parameters per bin for unfolded spectrum Ut RegularizationPrefer constant locallyPrefer linear function locallyUse number of triggered events without vertex to estimate vertex efficiency in 0 bin from dataSystematic uncertainties evaluated by using modified response matricesIterative Bayesian unfolding as cross-checkRegularizations

    Blobel, CERN Comp.School 1984:0088Nucl.Instrum.Meth.A362:487-498,1995

    First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

  • Multiplicity DistributionsDistributions in limited h-regionsVertex range reduced a region in which every event has full h-acceptanceConsistent with UA5 results for NSD at 0.9 TeVUA5: ZP C43,357

    First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

  • Multiplicity DistributionsPhojet provides a good description at 900 GeV, but fails at 2.36 TeVDistribution at 2.36 TeV closer to Pythia with Atlas CSC tuneQualitatively same conclusions for NSDMC generators do not describe the energy dependence of the tail of the distribution correctly

    First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

  • SummaryThe pseudorapidity density and multiplicity distributions at 0.9 and 2.36 TeV have been presentedConsistent with UA5 and CMSMC generators do not describe the energy-dependence of the average multiplicity as well as the tail of the distributions correctlyMany other analyses on the way, including Charged particle pT, identified particles pT (, K, p), strangeness production (K0, , , ), baryon-antibaryon asymmetry, Bose-Einstein correlations, 0 spectra, event structure, azimuthal correlations, - correlationsSee talks by Jacek Otwinowski, Francesco NoferiniNational Geographic News (4th Dec) .a machine called ALICE....found that aproton-proton collision recorded on November 23rd created the precise ratio of matter and antimatter particles predicted from theory..Other opinions on MB physics:

    First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

    900 GeV: LHC10a8, LHC10a12 (104867-92)900 GeV: 92k in run 104824-52 (accepted MB1); 94k in run 104867,90,92run 104967,90,92Stat. uncertainty on MC values < 0.1%D6T/Atlas: Pythia 6.4.14 - Perugia-0: Pythia 6.4.21 - Phojet 1.12 with Pythia 6.2.14LHC10a8_run104867_8

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