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DOE Review (Arlington TX, November 9, 2010)

Soft QCD/Minimum Bias Physics at ATLAS Edward Sarkisyan-Grinbaum (University of Texas, Arlington). DOE Review (Arlington TX, November 9, 2010). Minimum Bias Studies. PYTHIA 900 GeV/7TeV. /(~14mb). /(~9mb). /(~49mb). σ tot = σ el + (σ ND + σ SD +σ DD ).

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DOE Review (Arlington TX, November 9, 2010)

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  1. Soft QCD/Minimum Bias Physics at ATLAS Edward Sarkisyan-Grinbaum (University of Texas, Arlington) DOE Review (Arlington TX, November 9, 2010)

  2. Minimum Bias Studies PYTHIA 900 GeV/7TeV /(~14mb) /(~9mb) /(~49mb) σtot = σel + (σND + σSD +σDD) Soft (low pT) hadroproduction processes are not well predicted, Monte Carlo models need to be tuned to the data Use these data to better understand tracking, detector, simulation, and reconstruction

  3. Motivation • Multiplicity and kinematic variables are the first measured observables and provide fundamental information on the interaction dynamics • Improves our understanding of different QCD effects, • total cross section, jet production, mass reconstruction • Collision energy dependence is of great interest, • asymptotic regime of QCD partonic (quark-gluon) picture • Extremely important for tuning Monte Carlo models, for heavy-ion physics, high luminosity detector upgrades (many minimum bias events pile-up at high luminosity, so very sensitive to minimum bias modelling), new physics discoveries ●7 TeV?

  4. Minimum Bias Trigger Scintillator • 32 independent wedge-shaped plastic scintillators • (16 per side) read out by PMTs, 2.09<|η|<3.84* *Pseudorapidity is defined as η = -½ ln (tan (θ/2)), θ is the polar angle with respect to the beam • Designed for triggering on min bias events, >99% efficiency • MBTS timing used to veto halo and beam gas events • Also being used as gap trigger for various diffractive subjects UTA took a major role in min bias trigger validation and MBTS commissioning due to the importance of this detector for commissioning ATLAS central detector and to help publish early physics

  5. ATLAS Inner Detector • Includes different tracking subdetectors such as Pixel detectors, silicon SemiConducter Tracker (SCT) and Transition Radiation Tracker (TRT), |η|<2.5 • Main detector to measure charged tracks • Well modeled by Monte Carlo

  6. Stable beam collision events First ATLAS events in December 2009 used MBTS trigger √s= 900 GeV

  7. First ATLAS Results • First ATLAS 900 GeV paper published: • Physics Letters B 688 (2010) 21-42 • Big efforts, 40+ people, meetings all times of day+night, lots of supporting notes, provides a reference for all following analyses Followed by 7 TeV results (based on first 7 TeV collisions in March 2010): ATLAS-CONF-2010-024 (April 2010), ATLAS-CONF-2010-046 (July 2010); publication soon!

  8. Measurements for Minimum Bias Distributions of hadrons (primaries) within a phase-space accessible to the ATLAS Inner Detector Pseudorapidity η = -½ ln (tan (θ/2)) Data collected at 900 GeV, 2.36 TeV in December 2009, and at 7 TeV starting in March 2010

  9. ID Performance vs. MC: 900 GeV Phys. Lett. B 688 (2010) 21 Good agreement between data and MC observed Validated tracking algorithms and detector

  10. pT vs. Nch: 900 GeV vs. 7 TeV Phys. Lett. B 688 (2010) 21 ATLAS-CONF-2010-024 MC does not describe the physics too well, more deviation with energy increase, leads to new MC tunes Low nch is highly influenced by description of diffractive component

  11. Comparison of pT for different experiments: 900 GeV • First ATLAS publication: • Phys. Lett. B 688 (2010) 21 pT>500 MeV, nch≥1 • Good agreement for • the same selection • criteria • Today: many new results at low-pT threshold • and higher energies

  12. Results on mid-rapidity densities ATLAS-CONF-2010-046 • Mid-rapidity density (η≈0), pT>100 MeV: • 3.486 ± 0.008(stat) ± 0.077(syst) at 900 GeV, 5.635 ± 0.002(stat) ± 0.049(syst) at 7 TeV • Measurements 5-20% higher than Monte Carlo predictions • ATLAS AMBT1 and MC09(c) close to the pT>500 MeV data • No model describes the low-pT measurements: more tunes • needed

  13. Beyond Minimum Bias Analysis More detailed studies of multi-particle production (led by E S-G) Many analyses undergo under ATLAS soft QCD Multiparticle Correlations and Fluctuations subgroup umbrella

  14. “Correlations” Papers • Study of forward-backward rapidity correlations or “b- • correlations” study, slope b shows the effect strength • Rapidity range dependence • and average cluster energy • dependence – test of models Analysis with Editorial Board

  15. “Correlations” paper • Two-particle η-Φ correlations: cluster structure • “Cluster” fit extracts size and range of cluster emission Analysis in progress, to be ready for winter confs.

  16. “Correlations” paper - IV • Multiplicity spectra fits and • KNO scaling: energy • independence of the • multiplicity spectrum and its • moments Negative Binomial (clan production model) fit to the multiplicity distribution in different rapidity intervals (UA5 900 GeV): • fulfills in |y|<0.5 but deviates for larger • intervals (2 parameters: ‹n›, k) • possible 2NBD fit: soft vs. semi-hard • component, 5 parameters (back-up slides) Analysis with Editorial Board, for winter confs. • ALICE and CMS show KNO scaling and • NBD to hold for small central η intervals

  17. “Correlations” paper • Correlations of soft particles in ΔΦ around the leading jet • Allows accurate measurements of QCD (partonic) angular • correlations, sensitive to Monte Carlo ATLAS-2010-082 Further analysis on two-particle azimuthal correlations is ongoing

  18. Bose-Einstein Correlations • Bose-Einstein (two- & three-particle) correlations: enhancement • in identical particle (boson) correlation function at near momenta • Provides estimate on particle emission source size (radius), • coherency vs. chaoticity in the hadroproduction process • Main problems: reference sample of • non-correlated particle pairs, suitable fit • function (usually Gaussian) • Main interest: radius energy dependence, • its particle mass dependence, multiplicity • dependence • First results from ALICE, CMS available Work in progress, next year paper(s)

  19. “Ridge” effect • Long-range (|Δη|>2) near-side (ΔΦ=0) angular two-particle • correlations – unexpected in pp collisions, thought purely nuclear • matter effect • Observed by CMS using high-multiplicity events at 7 TeV • (09/2010) Work in progress, expected for winter/spring conferences

  20. Dynamical Multiparticle Correlations • Search for dynamical (non-Poissonian) fluctuations in small • phase space intervals (factorial multiplicity moments, • intermittency, QCD fractality/self-similarity, phase transition) • Study of genuine multi-particle correlations (factorial cumulant • moment method) q=4 3 2 Non-statistical fluctuations rise NA22, πp 22GeV: low-pT effect UA1 ppbar 630 GeV • Studied in all types of collisions Work in progress, next year paper(s)

  21. High-Multiplicity Thermalization • Study of very high multiplicity (VHM) events to learn whether • thermodynamic equilibrium is reached as predicted • Study of energy “correlators” with R3(n)=K32/3(n)/|K2(n)| << 1, • higher-order correlators analyses as function of multiplicity n q=4 3 2 Work in progress, next year paper(s) • “thermalized” states • hard and • soft production

  22. Outlook and Plans • Many ongoing interesting analyses • Many analyses expected to be ready for • winter 2010-2011, spring 2011 conferences • Next year many papers expected

  23. Back-up slides

  24. Efficiencies: 7 TeV ATLAS-CONF-2010-046 Tracking reconstruction efficiency Trigger efficiency Vertex reconstruction efficiency Detector and tracking well understood

  25. ‹pT› vs. nch: 900 GeV vs. 7 TeV ATLAS-CONF-2010-046 900 GeV 7 TeV New ATLAS tune better describes the data. More studies ongoing.

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