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Proton-Proton Physics with ALICE

Proton-Proton Physics with ALICE. LHC Days in Split Palazzo Milesi Split, Croatia October 5, 2010. Jean-Pierre Revol CERN. ALICE detector complete Except for: 4/10 EMCAL (approved 2009) 7/18 TRD (approved 2002) 3/5 PHOS (funding ). 3/5 PHOS 7/18 TRD 18/18 TOF 7/7 HMPID

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Proton-Proton Physics with ALICE

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  1. Proton-Proton Physics with ALICE LHC Days in Split Palazzo Milesi Split, Croatia October 5, 2010 Jean-Pierre Revol CERN

  2. ALICE detector complete Except for: 4/10 EMCAL(approved 2009) 7/18 TRD(approved 2002) 3/5 PHOS (funding) 3/5 PHOS 7/18 TRD 18/18 TOF 7/7 HMPID 4/10 EMCAL 2x EMCAL 2x TOF 4 5 3 6 2 HMPID TRD 7 TPC 1 8 0 ITS 9 17 10 16 15 11 14 12 13 L3 Magnet 4 0 3 1 PHOS 2 jpr/Split/Oct.2010

  3. Installation next Dec. 7-Feb 4 break • – 6 EMCAL supermodules(complete EMCAL) • – 3 TRD modules (10 out of 18) [factor 2 increase in J/ψ trigger acceptance] • – TRD completed in 2012 • – PHOS 4th module in 2012 3/5 PHOS 10/18 TRD 18/18 TOF 7/7 HMPID 10/10 EMCAL ALICE configuration in 2011 2x 2x 2x 4 5 3 2x 6 2 7 1 2x 8 0 9 17 10 16 15 11 14 12 13 4 0 Tight installation schedule implying workingover Christmas! 3 1 2 jpr/Split/Oct.2010

  4. ALICE’ goals for 2010 μ = interactions/bunch crossing • Well within reach! * Overall goal at least a factor 10 over MB pp (150 nb-1) **Overall goal a few tens of thousand ϒ $≈ 50Hz and 106s jpr/Split/Oct.2010

  5. First Physics Results jpr/Split/Oct.2010 • ALICE running well; a wealth of physics results already published, mostly on large cross-section phenomena! • ALICE published results (6 publications): • Multiplicity density and distributions of charged particles • 900 GeV: EPJC: Vol. 65 (2010) 111 • 900GeV, 2.36TeV: EPJC: Vol. 68 (2010) 89 • 7TeV: EPJC: Vol. 68 (2010) 345 • ratio (900GeV & 7TeV) PRL: Vol. 105 (2010) 072002 • momentumdistributions (900GeV) PL B: Vol. 693 (2010) 53 • Bose-Einstein correlations (900GeV) PRD: Vol. 82 (2010) 052001 • Many more in preparation (7 TeV)

  6. First data, first surprise? jpr/Split/Oct.2010 • Charged-particle multiplicity measurement in proton-proton collisions at √s = 0.9 and 2.36 TeV (above Tevatron) with ALICE at LHC • Measurement at 0.9 TeVconsistent with UA5data • Average multiplicities at the new energy not described by models • Relative multiplicity increase between 0.9 TeV & 7 TeV alsonot described by modelsNot a surprise after all!

  7. First data at 7 TeV March 30th, First collisions at 7 TeV! jpr/Split/Oct.2010 • Charged-particle multiplicity measurement in proton-proton collisions at √s = 7 TeV with ALICE at LHC • Trend seen between 0.9 TeVand 2.36 TeV for NSD and INEL confirmed by data at √s = 7 TeV;However, measurement forevent class INELN>0 only, as diffractive processes not yetknown at 7 TeV (see later)

  8. Inelastic Nch ≥ 1 in |h|<1 Relative increase in dNch/dh ALICE CMS NonSingleDiffractive all Inelastic fits ~ s0.1 Particle production vs √s dNch/dh versus√s jpr/Split/Oct.2010 Increase with energy significantly stronger in data than in MC’s ALICE & CMS agree to within 1 s (< 3%) [NSD at 2.36 TeV] dNch/dh increase with √s well described by a power law

  9. Particle production vs √s Martin Poghosyan Predicted correctly the CMS point at 7 TeV jpr/Split/Oct.2010 • At high energy, Mueller-Kancheli graph: From which we obtain D≡ (αP -1) = 0.2 (was 0.12 before). • We have entered the realm of non-perturbative QCD and of Pomerons, etc., important at LHC: • Particle production is dominated by soft mechanisms; • Global properties need proper account of non-perturbative processes (Diffractive processes, etc) (in many cases, main source of systematic uncertainties).

  10. LHC Parton overlap Partons are prisoners of the proton whose transverse size only increases as lns What is new at LHC is that this overlap could occur for relatively high pTpartons(Kharzeev Qs2 ~ 0.7 GeV2) jpr/Split/Oct.2010 As low x (~Q2/s) values are reached, both the parton density and the parton transverse sizes increase, there must be a scale (q2 < Qs2) where partons overlap. When this happens, the increase in the number partons would become limited by gluon fusion (ggg)

  11. Proton Proton strategy for ALICE Many reasons for ALICE to take pp collisions very seriously jpr/Split/Oct.2010 What we do not know precisely is how parton overlap will manifest itself in pp collisionsstudy ALL aspects of pp collisions in a systematic way, especially extreme properties pp collisions always part of ALICE’s programme as they are needed to provide a comparison with future HI collisions Comparison goes also the other way (from pp to HI): “is QGP produced in pp collisions?” Unique features of ALICE (Low pT and Particle ID capability) can provide unique information

  12. Multiplicity measurements Fiducial window = ΔθΔφ = 25mdar×80 mrad SPD2 SPD1 jpr/Split/Oct.2010 Count pixel tracklets (vertex + 2 hits) in the two innermost layers of the ITS Correct for detector effects (acceptance, efficiency), using a detector response matrix obtained from MC simulations.(deconvolution method to minimize dependence on model) Normalize result to specific event class (NSD, INEL or INELN>0)

  13. Multiplicity Distributions Multiplicity Distribution 7 TeV Multiplicity Distribution 900 GeV PHOJET PYTHIA/ATLAS CSC tune – no model describes correctly the data – most of the ‘stronger increase’ is in the tail of Nch INEL>0 = at least one particle in |η| < 1) jpr/Split/Oct.2010

  14. Comparison with other experiments NSD events ALICE CMS SD SD DD DD jpr/Split/Oct.2010 • Comparison with other experimentsrequires the same event class definition! • Excellent agreement with UA5 at 0.9 TeV,with CMS at both 0.9 and 2.36 TeVfor NSD • How to go from INEL >0 to INEL, NSD? normalize to an event class used by other experiments, but • Model dependent and largest source of systematic uncertainty  must be measured! (cross-section and kinematics) • At 0.9 TeV & 1.8 TeV data from UA5 & E710 and CDF (ALICE used measured values) • At 7 TeV no data yet! Wait for TOTEM measurement, or measure it ourselves NSD INEL

  15. Systematics and results – Diffraction cross-sections somewhat known up to 1.8 TeV; Small extrapolation to 2.36 TeV justified. – Precision totally dominated by systematic errors jpr/Split/Oct.2010

  16. pT Distributions at 900 GeV Comparison with other data Comparison with MC’s INEL NSD – Spectrum seems to get harder for more central rapidity– MC’shave hard time describing the fullpT spectrum jpr/Split/Oct.2010

  17. <pT> versus Multiplicity pT for different Multiplicities <pT> vsNch • – Change concentrated at pT> 1 GeV/c(pQCD) (surprisingly little change below 1 GeV/c) • – MC’shave hard time… again! jpr/Split/Oct.2010 Study pioneered by UA1

  18. Material budget • High precision reached in central region(crucial at low pT ( , etc.) • Expanding the charged particle multiplicity measurement to the forward region with the FMD MC and data agree within 5% in |η|<0.9 ITS material in simulation SSD Not fully corrected SDD SPD jpr/Split/Oct.2010

  19. Tracking improvements • ITS resolution well comparable to simulation and close to design value (CDF/running and STAR/future upgrade for comparison) • Improved tracking for multiplicity measurement (40% gain in resolution compared to Pixel tracklets): Important for best use of high statistics ALICE ITS CDF STAR Upgr. jpr/Split/Oct.2010

  20. TPC dE/dx s≈5-6% π K No vertex cut ! Cherenkov ring imaging HMPID P ALICE has excellent particle identification ALICE PID detectors Vertex detector pT(min)<100MeV TOF 150k channels! s ≈ 88 ps jpr/Split/Oct.2010 PLC 20J. Schukraft 20

  21. KaonpTdistributions Identified Particle pT pKp K → m n K0S → pp ITS dE/dx TPC dE/dx TOF Identified particles √s = 900 GeV jpr/Split/Oct.2010 Many cross-checks: for kaons (6 measurements)

  22. Charged π, K and p at √s = 900 GeV Spectrawithstatistical and systematicuncertainties Lévy functionfitsdescribe data well jpr/Split/Oct.2010

  23. Strange particles at √s = 900 GeV Very detailed study of identified particle production, useful for model tuning and for comparison with Heavy Ions jpr/Split/Oct.2010

  24. Particle ratios vspT ALICE Preliminary ALICE Preliminary Poor agreement with Monet Carlo, but good agreement with other experiments … jpr/Split/Oct.2010

  25. K/π ratio at √s = 900 GeV jpr/Split/Oct.2010 Confirming slow rise vs √s7 TeV data analysis in preparation

  26. Λ/2Ks0 ratio at √s = 900 GeV Note: STAR and ALICE data are Feed-down corrected (12-15% correction at ~ 2 GeV/c) |y| < 0.75 7 TeV data analysis (huge statistics) will tell us more jpr/Split/Oct.2010 ALICE pp at 900 GeV similar to STAR at 200 GeV But different from CDF (630GeV/1800GeV) and UA1 (630GeV) proton-antiproton data for pT > 1.5 GeV/cComparison under study: trigger, acceptance, feed-down corrections,

  27. K*→ K p X → L p W → L K Much more to come: strange particles S*→ L p We want high statistics studies (pT, multiplicity dependence, etc.) jpr/Split/Oct.2010

  28. Charmed particles D0→ K ppp D+→ K pp D*→ D0 p √s = 7 TeV:– new signals– more decay modes – pT distributions D0→ K–p+ Goal: total cross section statistics limited at low pT 109evts to measure below 1 GeV/c Ds+→ Φπ+→ K+K–p+ Lowest pT reach for ALICE

  29. J/y → m+m-, y = 2.5–4.1 J/ψ at √s = 7 TeV J/y → e+e- |y| < 1 – Hard to measure J/y with our current low luminosity (also 1st year Pb–Pb luminosity will be verylowpriority to MB in pp) – ‘proof of performance’ higher luminosity later this year (μμ) and next year Acceptance and efficiency corrected distributions Compared to MC generator (CDF parameterization) Two η ranges

  30. 900 GeV: |y|<0.5 7 TeV; |y|<0.5 0.9 TeV: p/p = 0.957±0.006(stat) ±0.014(syst) 7 TeV: p/p = 0.990±0.006(stat) ±0.014(syst) Proton-antiproton ratio Related to probability to transport baryon number from η= 8.9 to 0 Measurement suggested by B. Kopeliovich αSJ = 0.5, and αP = 1.2, C ~ 9 (Red curve) – Most precise ratio measurements so far – For the first time, compatible with no asymmetry, in central region 30

  31. Multiplicity dependence of pp properties Using L0 trigger from Pixels fast_OR is QCD describing all high multiplicity events? jpr/Split/Oct.2010 Dependence of <pT>, size of interaction region, topology, strangeness and charm contents, correlations, , etc. being studied. To be extended using high multiplicity triggers.

  32. Source Radius vs Multiplicity (Phojet) Bose Einstein Correlations Multiplicity overlap between pp and HI. Scaling with M similar to STAR but different from HI pp sizes smaller than HI at same multiplicities • Quantum Mechanical enhancement of identical Bosons at small momentum difference • enhancement of like-sign pions at low momentum differenceqinv=|p1-p2|, as function of multiplicity and pair momentumkT = |pT1+pT2|/2

  33. S┴ vs Multiplicity 900 GeV S┴ vs Multiplicity 7 TeV Event shape analysis small S┴: large S┴: Transversesphericity S┴,defined as a function of eigenvaluesof the momentum tensor Sxy ALICE performance Guy Paic & Antonio Ortiz HM events more spherical than models jpr/Split/Oct.2010

  34. Df (w.r.t. Leading Particle) Df (w.r.t. Leading Particle) Underlying Event Studies Uncorrected Data 7 TeV 900 GeV • Less back-to-back-ishthan MC • Is it related to the effect seen in shape analysis jpr/Split/Oct.2010

  35. Conclusion jpr/Split/Oct.2010 • Many signs that pp collisions are not yet well understood: • Global event properties (Multiplicity, pT spectra, etc.) • Identified particle production • √s dependence of multiplicity • Particle correlations, etc. • All current MC generators need tuning • We have already learned a lot with our first ~ 10 nb–1 • ALICE is now concentrating its effort on the preparation for first Heavy Ion collisions (on November 11?)

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