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DOE Review (Arlington TX, November 9, 2010)

Soft QCD/Minimum Bias Physics at ATLAS Edward Sarkisyan-Grinbaum. 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 ). Soft (low p T ) hadroproduction processes are not

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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 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 • modeling), 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 • (similar agreement at all beam energies) • 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 • Now have many new results with low-pT threshold • and higher energies

  12. Results on Mid-rapidity Densities ATLAS-CONF-2010-046 • Mid-rapidity density • (η≈0), pT>100 MeV: • at 900 GeV: • 3.486 ± 0.008(stat) ± 0.077(syst) at 7 TeV: 5.635 ± 0.002(stat) ± 0.049(syst) • 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 • In our with A.Sakharov model of constituent quarks+Landau’s • relativistic hydro the 2.36 data are reproduced and predictions • made for 7 TeV, agree with the data: arXiv:1004.4390 (in press)

  13. Further Studies • Single-particle distribution studieslimited to global characteristicsof • particle production, difficult to distinguish among models with different • different particle-production mechanisms • Next step needed: to study multi-particle distributions, correlations and • dynamicalfluctuations providing insight into soft multi-hadron dynamics • Rich field of investigation, applied in many earlier experiments, aided • in understanding and model development of underlying mechanisms • Requires more expertise, needs experienced people to be involved • as ATLAS is short of soft QCD experts compared to ALICE and CMS • E S-G proposed to organize a group with different but related analyses on • multi-particle distributions and correlations to concentrate on the subject • and to share techniques and methodology The Fluctuations and Correlations group established in March led by myself, with weekly meetings and a few analyses started. Now with many analyses ongoing, looking into readiness for publications next year 13

  14. 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 4-7 papers expected next year and many conference notes

  15. Forward-Backward Correlations • Study of forward-backward rapidity correlations or “b- • correlations” study, slope b shows the effect strength b-slope ATLAS VERY PRELIMINARY ‹nF›=a+b·nB • Rapidity range • dependence • and average • cluster energy • dependence – • test of models MC/data |η|-bin Analysis with Editorial Board

  16. Two-Particle Azimuthal Correlations • Two-particle η-Φ correlations: cluster structure 7 TeV ATLAS VERY PRELIMINARY • “Cluster” fit extracts size and range of cluster emission Analysis in progress, to be ready for winter confs.

  17. Multiplicity Spectra Scaling and Modeling • Multiplicity spectra fits and • KNO scaling: energy • independence of the • multiplicity spectrum and its • moments ATLAS VERY PRELIMINARY Negative Binomial (clan production model) fit to the multiplicity distribution in different rapidity intervals: ATLAS VERY PRELIMINARY • Reasonable agreement for ||<0.5 but • deviates for larger || (2 parameters: ‹n›, k) • Possible 2NBD fit: soft vs. semi-hard • component, 5 parameters Analysis with Editorial Board, for winter confs. • ALICE and CMS show KNO scaling and • NBD to hold for small central η intervals

  18. Two-particle Azimuthal Distributions • 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

  19. 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 ATLAS VERY PRELIMINARY • Main problems: reference sample of • non-correlated particle pairs, suitable fit • function (usually Gaussian) • Main interest: radius (R) & coherency • strength (λ) energy dependence, their • particle mass and multiplicity dependences • First results from ALICE, CMS available 7 TeV Work in progress, next year paper(s)

  20. “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 confs.

  21. 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) Fq ATLAS VERY PRELIMINARY data 7 TeV q=4 3 2 Non-statistical fluctuations rise NA22, πp 22GeV: low-pT effect UA1 ppbar 630 GeV • Studied in all types of collisions, different variables and dimensions Work in progress, next year paper(s)

  22. High-Multiplicity Thermalization • Study of very igh multplicity events to learn whether thermodynamic • equilibrium reached as theory predicts • Study of energy “correlators” with R3(n)=K32/3(n)/ |K2(n)| << 1, • higher-order correlators analyses as function of multiplicity n R3 ATLAS VERY PRELIMINARY • “thermalized” states • hard and • soft production Work in progress, next year paper

  23. Outlook and Plans • UTA has had a major role in minimum bias • trigger studies and validation of central detector • UTA has made essential contributions to • minimum bias paper publication • Under leadership of UTA a new group has been • formed and a rich program of analyses in • correlations and fluctuations has been set up • We have presented results at topical • workshops/conferences, and had convenorship • roles in these workshops/conferences • Many conference notes in pipeline for winter • 2010-2011 conferences, several papers • under preparation for publication in 2011

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