proton-proton physics with alice

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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 - PowerPoint PPT Presentation


ALICE Status Report

Proton-Proton Physicswith ALICELHC Days in SplitPalazzo Milesi Split, CroatiaOctober 5, 2010Jean-Pierre RevolCERNSun stone: Aztec calendar1

3/5 PHOS 7/18 TRD 18/18 TOF7/7 HMPID4/10 EMCAL01234567981112131415170123410162x2x2ITSTPCTRDTOFPHOSHMPIDL3 MagnetALICE detector completeExcept for: 4/10 EMCAL (approved 2009)7/18 TRD (approved 2002)3/5 PHOS (funding)


3/5 PHOS 10/18 TRD 18/18 TOF7/7 HMPID10/10 EMCAL01234567981112131415170123416102x2x2x2x2x3Tight installation scheduleimplying workingover Christmas!ALICE configurationin 2011

jpr/Split/Oct.2010Installation next Dec. 7-Feb 4 break 6 EMCAL supermodules (complete EMCAL) 3 TRD modules (10 out of 18) [factor 2 increase in J/ trigger acceptance] TRD completed in 2012 PHOS 4th module in 2012

ALICE goals for 2010Well within reach!4EnergyConditionsTriggersStatus 0.05Minimum Bias: 109760 M (11 nb1)7 TeV pp 0.05High Multiplicity: 5x10718.5 M (36 nb1)*L 6x1030 cm-2s-1Muon pairs: 100k-200k J/ 1000 55 M (55 nb1)**(1 to 3 pb-1) (~1 week requested) 0.05EmCal (commissioning)2.76 TeV pp 0.05Minimum Bias: 50 M (1 day) HI-2010 or 20112.76 TeV PbPbL 1025 cm-2s-1Minimum Bias$: fewx107* Overall goal at least a factor 10 over MB pp (150 nb-1)**Overall goal a few tens of thousand $ 50Hz and 106s = interactions/bunch crossingjpr/Split/Oct.2010Sigma = 8 barns [2micro.b-1 ~ 1.5x10**7 MB events]4First Physics ResultsALICE 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 particles900 GeV: EPJC: Vol. 65 (2010) 111900 GeV, 2.36 TeV: EPJC: Vol. 68 (2010) 897 TeV: EPJC: Vol. 68 (2010) 345 ratio (900 GeV & 7 TeV) PRL: Vol. 105 (2010) 072002 momentum distributions (900 GeV) PL B: Vol. 693 (2010) 53 Bose-Einstein correlations (900 GeV) PRD: Vol. 82 (2010) 052001Many more in preparation (7 TeV)


jpr/Split/Oct.2010First data, first surprise?Charged-particle multiplicity measurement in proton-proton collisions at s = 0.9 and 2.36 TeV (above Tevatron) with ALICE at LHCMeasurement at 0.9 TeV consistent with UA5dataAverage multiplicities at the new energy not described by modelsRelative multiplicity increase between 0.9 TeV & 7 TeV alsonot described by modelsNot a surprise after all!


jpr/Split/Oct.2010First data at 7 TeVCharged-particle multiplicity measurement in proton-proton collisions at s = 7 TeV with ALICE at LHCTrend seen between 0.9 TeV and 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)7

March 30th, First collisions at 7 TeV!jpr/Split/Oct.2010

NonSingleDiffractiveall InelasticInelastic Nch 1 in |h| 1) Delta = alpha.Pomeron -19Parton overlapAs 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)10

LHCWhat is new at LHC is that this overlap could occur for relatively high pT partons (Kharzeev Qs2 ~ 0.7 GeV2)Partons are prisoners of the proton whose transverse size only increases as lnsjpr/Split/Oct.2010Gives information about the partons at two different x valus10Proton Proton strategy for ALICEWhat 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 ALICEs programme as they are needed to provide a comparison with future HI collisionsComparison 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 information11Many reasons for ALICE to take pp collisions very seriouslyjpr/Split/Oct.2010Ir is looking for Indian that Colombus discovered America!!11Multiplicity measurementsCount pixel tracklets (vertex + 2 hits) in the two innermost layers of the ITSCorrect 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)12SPD1SPD2Fiducial window = = 25mdar80 mrad jpr/Split/Oct.2010

Multiplicity Distributions

no model describes correctly the data most of the stronger increase is in the tail of Nch Multiplicity Distribution 900 GeV Multiplicity Distribution 7 TeVPHOJETPYTHIA/ATLAS CSC tuneINEL>0 = at least one particle in || < 1) 13jpr/Split/Oct.2010

Comparison with other experimentsComparison 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 TeV for NSDHow to go from INEL >0 to INEL, NSD? normalize to an event class used by other experiments, butModel 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 ourselves14ALICECMSNSD eventsNSDINELSDDDSDDDjpr/Split/Oct.2010Systematics and results

15 Diffraction cross-sections somewhat known up to 1.8 TeV;Small extrapolation to 2.36 TeV justified.

Precision totally dominated by systematic errorsjpr/Split/Oct.2010pT Distributions at 900 GeV

Spectrum seems to get harder for more central rapidity MCs have hard time describing the full pT spectrumComparison with MCsComparison with other dataNSDINELjpr/Split/Oct.201016 versus Multiplicity

Change concentrated at pT > 1 GeV/c (pQCD) (surprisingly little change below 1 GeV/c ) MCs have hard time again! pT for different Multiplicities vs NchStudy pioneered by UA117jpr/Split/Oct.2010Mention UA1; models do not reproduce at all17

Material budgetHigh precision reached in central region(crucial at low pT ( , etc.)Expanding the charged particle multiplicity measurement to the forward region with the FMD18Not fully corrected

ITS material in simulation

MC and data agreewithin 5% in ||