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Preparation for measurement of strong coupling constant on CMS S.Shulga

Preparation for measurement of strong coupling constant on CMS S.Shulga. LPP, JINR (Dubna, Russia) Fr.Skarina Gomel State University, Belarus. International School-seminar “Actual problem of Microworld physics” Gomel, Belarus 23 July – 3 August, 2007. LPP JINR (Dubna, Russia)

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Preparation for measurement of strong coupling constant on CMS S.Shulga

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  1. Preparation for measurement of strong coupling constant on CMSS.Shulga LPP, JINR (Dubna, Russia) Fr.Skarina Gomel State University, Belarus International School-seminar “Actual problem of Microworld physics” Gomel, Belarus 23 July – 3 August, 2007

  2. LPP JINR (Dubna, Russia) Fr.Skarina Gomel State University (Belarus) P.Suhoi Gomel State Polytechnical University (Belarus) BLTP, JINR (Dubna, Russia) Participants: A.Zarubin – CMS HCAL coordinator, head of CMS group in JINR(Dubna) S.Shmatov – head of CMS physics group in JINR S.Shulga – responsible person for task “Alpha_s measurement at CMS” P.Moissenz – HCAL/JINR group leader V.Konoplyanikov – leader of Jet physics study in CMS/JINR M.Savina – theoretical group CMS/JINR O.Teryaev – theoretical group CMS/JINR K.Babich – responsible person for full simulation in Jet physics tasks in CMS/JINR physics group https://twiki.cern.ch/twiki/bin/view/CMS/MeasurementOfAlpha_s “Young scientists from Belarus and from Gomel region for work at CMS project are invited: Ph.D. positions in Laboratory of Particle Physics JINR” (S.Shmatov is contact person)

  3. Contents • Introduction: interplay QCD & experiment • Motivations of measurement • Methods of measurement for inclusive jet observables • Systematic uncertainties • MC tools • Conclusion & plans S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  4. Introduction: Jets & pQCD • The applicability of pQCD to an observable depends in general on two assumptions: • we must neglect hadronization effects; • the perturbative expansion has to be valid. • This usually means we should • examine scattering processes with large momentum transfer • use observables which are relatively insensitive to soft physics. • A Jet, by definition, is a cluster of individual hadrons • which are averaged out by the jet algorithm • to give a single object with a well defined direction. • The minimal jet transverse-energy cut ensures • that there is a substantial momentum transfer. • The averaging over individual hadrons ensures that jet distributions • are not sensitive to the behavior of soft QCD radiation. • In order to apply pQCD one can not ask question • about physics inside jet. W.T.Giele,E.W.N.Glover, D.Kosower, FERMILAB-CONF-94/350-T S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  5. Introduction: Jets & pQCD N.Glover, Challenges in pQCD Durham, Feb, 2002 S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  6. Introduction: Jets & pQCD So, pQCD ensures at conditions listed above : (renormalization) Davison E. Soper, CTEQ School, June 2007 S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  7. Introduction: Renormalization • For example, in Minimal Substraction • Renormalization scheme • is arbitrary in principle. • In practice is chosen • as a physics scale • Physics of scales less then inverse • is removed from the perturbative calculation. • Renormalization hides: • Ultra-violet divergences • and short-distance physics • (including new physics: • Quantum Gravitation, Grand Unification,…) • Effects of small time physics are absorbed • into the running coupling, • running masses, field operators,… S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  8. Introduction: Renormalization Davison E. Soper, CTEQ School, June 2007 S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  9. Introduction: Renormalization Scale dependence and independence • Why do we vary renormalization scale ? • The theoretical predictions used for • comparison with experiment should be • independent of • According to equation(2) • the change due to varying • the scale is formally higher order; • So, the uncertainty due to varying • the renormalization scale is way of guessing • the uncalculated higher order contributions (1) (2) Davison E. Soper, CTEQ School, June 2007 S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  10. p i X p j Introduction: Jet & Factorization Strategy is to factorize physical observable into a calculable Infra-Red Safe part and not calculable but universal part. Cross-section is convolution the long distance Parton Distribution Functions (PDF) and short distance hard scattering cross-section: • fi(x,F) are PDFs • x is parton momentum fraction • PDFs must be measured: can’t calculate • is partonic scattering cross section • Calculate as expansion in s(R) Calculate perturbatively Measure S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  11. Introduction: Factorization scale is factorization scale is boundary which separates long/short distance parts in cross-section. Davison E. Soper, CTEQ School, June 2007 S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  12. Introduction: Factorization scale dependence and independence In principle, can take any value: Cross-section should be independent of the choice. However, for and hard cross-section will contain large logarithms which will ruin the perturbative expansion. So, not to be much greater than Choice Since, is often taken as a measure of the magnitude of the uncalculated high order terms, choosing, say Davison E. Soper, CTEQ School, June 2007 S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  13. Introduction: Factorization Comparison of theory with experiments allows one to fit the parton distribution function at fixed scale Once PDFs are determined, they can be used to calculate the cross-section for other processes either to test the validity of QCD formalism or to predict the rate or characteristics of new processes for which the QCD processes are the background. Davison E. Soper, CTEQ School, June 2007 S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  14. Ultra-violet Renormalization hides/summarizes our ignorance of physics at huge scale in Infra-red/collinear Factorization hides/summarizes non-perturbative QCD physics at confinement scale in Introduction: Renormalization & Factorization The basic idea of factorization of collinear/soft (long-distance) physics is quite similar to those of renormalization of short distance (ultra-violet) divergences. analogy & correspondences “Renormalization” is factorization (of UV divirgences) “Factorization” is renormalization (of soft/colinear div.) Davison E. Soper, CTEQ School, June 2007 S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  15. Introduction: QCD & experiment Next steps to study interplay QCD & experiment are Technics of NLO calculation; Monte Carlo NLO generators at parton level including parton level jet finders; Full NLO Monte Carlo generators including parton shower, hadronization and particle level jet finders. These are the topics of separated lectures at modern specialized HEP schools… S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  16. Introduction: experimental determination of S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  17. Motivations Universality of the function provides the most powerful and decisive test of the validity of QCD S BethkeNucl.Phys.Proc.Suppl.121:74-81,2003 S at Q ~ 1 TeV is not measured W.-M. Yao et al., Journal of Physics G 33, 1 (2006) Review of Particle Physics S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  18. Motivations It is interesting to know S at Q ~ 1 TeV W.T.Giele, E.W.N.Glower, J.Wu, Determination of a_s at hadron colliders Phys.Rev.D, 1996 S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  19. S.Kluth,IHEP2006, Proceedings, March 31, 2007. Motivations Rel.err = 0.8% PDG, 2006: W.-M. Yao et al., Journal of Physics G 33, 1 (2006) Review of Particle Physics Rel.err = 5.7% stat. exp. theor. Rel.err = 4,4% S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  20. Measurements of PDF depend on and on the contrary. An extraction of using a given PDF set can therefore at best return input value used in fit of PDF. W.T.Giele,E.W.N.Glover, J.Yu, Determination of at hadron colliders. Phys.Rev. D 53. 1996. P.120 Method to measure which is independent of the input value of the PDF’s was pioneered in paper: Methods of measurement of strong coupling constant S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  21. Method of measurement (I) W.T.Giele,E.W.N.Glover, J.Yu, Determination of at hadron colliders. Phys.Rev. D 53. 1996. P.120 and are calculated in LO and NLO respectively with their theoretical uncertainties: - PDF uncertainties - and uncertainty due to scale dependence of finite order (NLO) of calculation. Parton level generator JETRAD used to calculate T^(0) and k_l. (1) (2) (2’) (3) S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  22. CDF W.T.Giele,E.W.N.Glover, J.Yu, Phys.Rev. D 53. 1996. P.120 Method of measurement (I) Rel.err = 6,7% Theor. scale: Rel.err = 4,2% stat. exp. theor. The error from using different PDF as input is approximately +/- 0,002 Theor. PDF: Rel.err = 1,7% S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  23. Similar method used in CDF for two jet cross section M. Okabe, Ph.D.Thesis, 1998 Measurements of strong coupling constant from 2 jet production cross section in 1.8 TeV proton-antiproton collisions CDF Method of measurement (II) (1) (1) S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  24. Method of measurement (II) CDF M.Okabe, Ph.D.Thesi, 1998 Rel.err = 7,7% S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  25. Method of measurement (III) H. Stenzel, Max-Planck-Institut fur Physik Determination of using jet cross section parameterizations at hadron colliders Similar method was studied by H.Stenzel for inclusive jets (ATLAS): 27/03/2001 S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  26. Method of measurement (III) H. Stenzel Normalization procedure: Jet Cross Section Parameterization Normalized differential cross section are parameterized with linear functions in 19 bins of ET. In each bin of ET, the cross section dependence on alpha_s calculated at NLO with package JETRAD for various sets of PDF’s, is fitted with linear functions (hypothesis) It is the same method as: W.Giele, E. Glower, hep-ph/9506441v1 July, 1995 S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  27. H. Stenzel Linear parameterization result of the normalized differential cross section in two bins of ET at LHC b~0,5E-2 b~1,65E-3 S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  28. Method of measurement (III) PDG, 2007: TEVATRON (rel.err.=0,1%) (rel.err.=6%) NLO scale uncertainty dominates the error on alpha_s. It means that one need NNLO to reduce theor. errors Syst. theoretical uncertainty only LHC Syst.exp. uncertainty for CDF: +/- 0.008 (rel.err. = 6,7%) (W.Giele,e.a. 1996) For CMS - ? H.Stenzel, ATL-PHYS-2001, 2001 (rel.err.=5%) S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  29. LHC S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  30. LHC S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  31. LHC S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  32. LHC CMS Physics TDR, V.II, 2006 20% S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  33. H. Stenzel For 30% X-sect. rel.error at 1 TeV:and Theor.error ~ 5% CDF&LHC experimental syst.error and are taken from CDF X-sect. 10% rel.err LHC X-sect. 10% rel.err Preliminary Preliminary LHC S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  34. CDF Why go beyond NLO ? LHC: NLO calculation of inclusive Jet cross-section will be enough. But, LHC experimental errors for other processes are often less than theoretical errors. S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  35. Tools: LHApdf-5.3.0 (release 28 June, 2007) The shaden green region shows the range of uncertainty due to source other then as calculated from eigenvector basis sets CTEQ6.1 (90% coinfidence range) Contains CTEQ6AB with 40 PDF sets alpha_s(M_Z) = 0.110 – 0.126. J.Pumplin e.a. Hep-ph/0512167v4, 2 Feb 2006 Uncertainties of inclusive jet Xsection Curves are for 0.110(short dash),…, 0.126(long dash). TEVATRON LHC 0,1 < y < 0,7 y < 1 S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  36. JETRAD(2002) installed , tested NLOjet++ installed, tested ? LHApdf-5.3.0 installed, tested fastNLO will be installed soon Packages Nearest plans Interfaces, analysis JETRAD/LHApdf-5.3.0/User ready NLOjet++/LHApdf-5.3.0/User ? Analysis scripts 30% Tasks: Following to references above : 30% ready Talks 28 August 2007 : LPP meeting We are going to have the studies of alfa_s measurement with new packages: JETRAD/LHApdf-5.3.0 (and NLOjet++/LHApdf-5.3.0) S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  37. GRACE ( j+X, 2j+X, … ) MC@NLO ( j+X, 2j+X will be included at the end 2007 ) Long-term plans NLO jets (partons + shower + hadronization) Packages S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

  38. At the LHC it will be possible to measure up to few TeV • by using inclusive jet events and it is a task of first runs; • Uncertainty on existing PDF could lead to 10% on the differential • cross section around transverse energy 1 TeV (CMS Physics TDR,2006); • Uncertainty due to dependence on the renormalization • and factorization scale is 5% (Stenzel, 2001); • A 3% error of the jet energy scale leads to 20% error • on the differential jet cross section at 1 TeV (CMS Physics TDR,2006); • A 30% error of the differential cross section leads • to 12% relative error on the strong coupling constant • (preliminary rough estimation); • For the first LHC runs it is not necessary to use NNLO calculation of • inclusive jet cross section because the theoretical error • are less then experimental one. Conclusion Any new ideas are welcome ! New participants in this business are welcome ! Many thanks for attention! S.Shulga, 24th July, Int.School-seminar, Gomel, 2007

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