First ALICE Results from Proton-Proton Collisions 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

A Large Ion Collider Experiment T0/V0 Trigger full ACORDE Cosmic trigger full EMCAL γ, π0, jets 36% L3 Magnet TRD Electron ID (TR) 39% HMPID PID (RICH) @ high pT full TOF PID full PMD γ multiplicity full FMD Charged multiplicity full ITS Low pT tracking PID + Vertexing full Dipole TPC Tracking, PID (dE/dx) full MUON μ-pairs full PHOS γ, π0, jets 60% Not shown: ZDC (at ±116m) First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

Detectors V0 scintillator array Silicon Pixel Detector (SPD) Trigger Detector Acceptance Detectors V0 scintillator array Trigger 2.8 < h < 5.1 and -1.7 < h < -3.7 Silicon 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/c 9.8 M channels Tracklet: 2 points + vertex During 2009 data-taking 80% active h x y SPD Layer 1 SPD Layer 2 ALICE Performance work in progress Efficiency SPD physics efficiency for primaries (2009 configuration 80% active) pT (GeV/c) First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

Trigger for MB Physics ALICE 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-section Two-arm trigger ("V0AND") for NSD Both forward scintillators One particle in 2.8 < h < 5.1 and one in -1.7 < h < -3.7 Trigger efficiency ALICE Performance work in progress Pythia 0.9 TeV Generated multiplicity in |h| < 1 900 GeV: LHC10a8, LHC10a12 (104867-92) 0.9 TeV (in %) ND SD DD Pythia MB1 100 77 92 V0AND 98 29 49 Phojet 86 34 66 First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

Data Sample Analysis based on Events Analysis based on 900 GeV: 186k collision events out of 430k total 2.36 TeV: 41k collision events MC adapted to mean vertex position and spread ALICE Performance work in progress z vertex distribution (cm) inefficient sector  no significant effect on result ALICE Performance work in progress Data MC MC Data Tracklet Df Entries ALICE Performance work in progress Ratio Data / MC 900 GeV: 92k in run 104824-52 (accepted MB1); 94k in run 104867,90,92 Cluster yield second layer yield in first and second layer compatible within 0.5% ALICE Performance work in progress first layer SPD module First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

dNch/dh Measurement all events all events all events Basically if the detector was perfect But… there is Detector acceptance, tracking efficiency Decay, conversions, stopping, etc. Vertex reconstruction efficiency/bias, trigger efficiency/bias Low momentum cut-off Three corrections needed Track-to-particle correction Vertex reconstruction correction Trigger bias correction Primary particles = charged particles produced in the collision and their decay products excluding weak decays from strange particles all events no vertex trigger all events no vertex trigger all events no vertex trigger First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

dNch/dh Measurement (2) Beam-induced background 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 triggers Use 0 bin from MC  larger syst. error Average correction factors Tracking: 1.53 Events (INEL): 1.05 Events (NSD): 1.02 [+8.3% (NSD) – 6.8% (SD)] Subtraction of SD tracks for NSD: 3% ALICE Performance work in progress dNch/dh h Main systematic uncertainties (%) at 900 GeV INEL NSD Fractions SD/DD/ND 0.6 2.8 MC dependence 2.0 1.0 Detector efficiency 1.5 run 104967,90,92 First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

dNch/dh NB: CMS data points do not include charged leptons  ~1.5 % difference dNch/dh ALICE, CMS: stat. and syst. uncertainty added quadratically dNch/dh ALICE, CMS: stat. and syst. uncertainty added quadratically h h dNch/dh in |h| < 0.5 ALICE, CMS: stat. and syst. uncertainty added quadratically 0.9 TeV 2.36 TeV INEL NSD ALICE preliminary 3.02 ± 0.07 3.58 ± 0.11 3.77 ± 0.23 4.44 ± 0.16 ALICE EPJC65:111 (2010) 3.10 ± 0.26 3.51 ± 0.29 CMS JHEP 02 (2010) 041 3.48 ± 0.13 4.47 ± 0.16 UA5 Z. Phys. C33 1 (1986) 3.09 ± 0.05* 3.43 ± 0.05* * only stat. error 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 in % INEL NSD ALICE prel. 24.8 +6.1-3.0 24.0 +3.9-1.3 CMS 28.4 ± 3.0 Pythi a D6T 19.7 18.7 ATLAS CSC 19.2 18.3 Perugia-0 19.6 18.5 Phojet 17.5 14.5 points at the same energy slightly shifted Stat. uncertainty on MC values < 0.1% D6T/Atlas: Pythia 6.4.14 - Perugia-0: Pythia 6.4.21 - Phojet 1.12 with Pythia 6.2.14 ALICE, CMS: stat. and syst. uncertainty added quadratically First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

Multiplicity Distributions Efficiency, acceptance Resolution vs. bin size  bin flow Correction by unfolding Detector response Probability that a collision with the true multiplicity t is measured as an event with the multiplicity m Vertex reconstruction, trigger bias correction Like for dNch/dh, but in unfolded variables (true multiplicity) because it is applied after unfolding |h| < 1 ALICE Performance work in progress measured multiplicity LHC10a8_run104867_8 true multiplicity First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

Unfolding using c2-Minimization Regularizations One free parameters per bin for unfolded spectrum Ut Regularization Prefer constant locally Prefer linear function locally Use number of triggered events without vertex to estimate vertex efficiency in “0 bin” from data Systematic uncertainties evaluated by using modified response matrices Iterative Bayesian unfolding as cross-check Blobel, CERN Comp.School 1984:0088 Nucl.Instrum.Meth.A362:487-498,1995 First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

Multiplicity Distributions Distributions in limited h-regions Vertex range reduced a region in which every event has full h-acceptance Consistent with UA5 results for NSD at 0.9 TeV UA5: ZP C43,357 First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus

Multiplicity Distributions Phojet provides a good description at 900 GeV, but fails at 2.36 TeV Distribution at 2.36 TeV closer to Pythia with Atlas CSC tune Qualitatively same conclusions for NSD MC 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

Summary The pseudorapidity density and multiplicity distributions at 0.9 and 2.36 TeV have been presented Consistent with UA5 and CMS MC generators do not describe the energy-dependence of the average multiplicity as well as the tail of the distributions correctly Many other analyses on the way, including Charged particle pT, identified particles pT (π, K, p), strangeness production (K0, Λ, Ξ, Φ), baryon-antibaryon asymmetry, Bose-Einstein correlations, π0 spectra, event structure, azimuthal correlations, -φ correlations Other opinions on MB physics: National Geographic News (4th Dec) ‘….a machine called ALICE.... found that a proton-proton collision recorded on November 23rd created the precise ratio of matter and antimatter particles predicted from theory..’ See talks by Jacek Otwinowski, Francesco Noferini First ALICE Results from Proton-Proton Collisions - Jan Fiete Grosse-Oetringhaus