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Yen-Jie Lee (MIT) For the CMS collaboration 3rd Heavy Ion Jet Workshop, Lisbon 09 July, 2014

Yen-Jie Lee (MIT) For the CMS collaboration 3rd Heavy Ion Jet Workshop, Lisbon 09 July, 2014. nPDF sensitive observables in CMS. Introduction. LHC energies allow measurements of photons, W , Z bosons and high p T jets in heavy ion collisions

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Yen-Jie Lee (MIT) For the CMS collaboration 3rd Heavy Ion Jet Workshop, Lisbon 09 July, 2014

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  1. Yen-Jie Lee (MIT) For the CMS collaboration 3rd Heavy Ion Jet Workshop, Lisbon 09 July, 2014 nPDF sensitive observables in CMS 3rd Heavy Ion Jet Workshop

  2. Introduction 3rd Heavy Ion Jet Workshop • LHC energies allow measurements of photons, W, Z bosons and high pT jets in heavy ion collisions • Jets and photons: sensitive to quark and gluon PDF • W and Z bosons: sensitive to (anti-)quark PDF J.Phys. G39 (2012) 015010 W/Z bosons

  3. 3rd Heavy Ion Jet Workshop Nuclear Parton Distribution Function p Pb Gluon nPDF/PDF comparison between EPS09, EKS98, nDS and FGS10 PDF nPDF François Arleo and Jean-Philippe Guillet http://lapth.cnrs.fr/npdfgenerator/

  4. Expected modification in PbPb collisions 3rd Heavy Ion Jet Workshop • Good theoretical control on high pT photons, Z and W bosons • Expected modification of high pT photon and Z production at the LHC energy due to nPDF: 0-20% level Z bosons ArXiv:1010.5392 Photons PbPb 5.5 TeV ArXiv:1103.1471

  5. W and Z boson production in PbPb 3rd Heavy Ion Jet Workshop CMS-PAS-HIN-13-004 PLB 715 (2012) 66 W ~10%precision Z Confirmed binary scaling in PbPb collisions

  6. Photon and Z boson RAA in PbPb 3rd Heavy Ion Jet Workshop Photon RAA PLB 710 (2012) 256 Z boson RAA vs. yZ CMS-PAS-HIN-13-004 Results are consistent with theoretical expectation Limited by statistical and systematical uncertainties

  7. Electroweak probes in pPb collisions 3rd Heavy Ion Jet Workshop • Asymmetric system: • Motivates measurements of forward-backward asymmetry and rapidity distributions J.Phys. G39 (2012) 015010

  8. Z bosons in pPb @ 5.02 TeV 3rd Heavy Ion Jet Workshop

  9. Z bosons in pPb @ 5.02 TeV • Dimuon invariant mass in [60, 120] GeV/c2 • Muon selection • pTμ > 20 GeV/c • |ημlab| < 2.4(muon detector coverage) • Asymmetric acceptance in rapidity in the center-of-mass frame due to the boost • 2183 Z candidates pPb→Z→μμ CMS-PAS-HIN-14-003 3rd Heavy Ion Jet Workshop

  10. Z bosons in pPb @ 5.02 TeV • dσ/dy shifted to center-of-mass frame • Uncertainties dominated by statistical uncertainties • Consistent with scaled pp predictions CMS-PAS-HIN-14-003 3rd Heavy Ion Jet Workshop

  11. Z bosons in pPb @ 5.02 TeV • Nuclear effects expected in the forward and backward regions CMS-PAS-HIN-14-003 3rd Heavy Ion Jet Workshop

  12. Z bosons in pPb @ 5.02 TeV 3rd Heavy Ion Jet Workshop • Forward-backward ratio expected to be more sensitive to nuclear effects • Without nuclear effects should be 1 • Hint of nuclear effects visible • Large uncertainties both on data and nuclear PDF central predictions CMS-PAS-HIN-14-003

  13. Z bosons in pPb @ 5.02 TeV 3rd Heavy Ion Jet Workshop • Compared to POWHEG+PYTHIA • Agreement seen in high pT High pT CMS-PAS-HIN-14-003

  14. Z bosons in pPb @ 5.02 TeV 3rd Heavy Ion Jet Workshop • Compared to POWHEG+PYTHIA • Agreement seen in high pT • Deviations seen at low pT, consistent with 7 & 8 TeV pp results Low pT pT=0 High pT CMS-PAS-HIN-14-003

  15. Z bosons in pPb @ 5.02 TeV 3rd Heavy Ion Jet Workshop • Compared to POWHEG+PYTHIA • Agreement seen in high pT • Deviations seen at low pT, consistent with 7 & 8 TeV pp results • Compared to PYTHIA6 Z2 • Better agreement at low pT(similar to 7 & 8 TeV pp results) pT=0 Low pT High pT CMS-PAS-HIN-14-003

  16. W bosons in pPb @ 5.02 TeV 3rd Heavy Ion Jet Workshop • More difficult to reconstruct but ten times more statistics than Z W → eν • ~20 000 candidatesin both electron and muon channels W → μν

  17. W bosons in pPb @ 5.02 TeV 3rd Heavy Ion Jet Workshop • Event selection • pTμ / e > 25 GeV/c • |η μ (e)lab| < 2.4 (2.5) • Quality and isolation requirements • Veto on dilepton events • Fitting the missing transverse energy for both charges and every η bin • Templates for QCD from data-based method and electroweak (Z→μμ / ee, W→τν) from simulation CMS-PAS-HIN-13-007

  18. W bosons in pPb @ 5.02 TeV • Combined cross section compared to NLO theory predictions with and without nuclear effects from EPS09 • New data to constrain the nPDFs Predictions from H. Paukkunen, C. A. Salgado, JHEP 1103 (2011) 071 CMS-PAS-HIN-13-007 3rd Heavy Ion Jet Workshop

  19. W bosons in pPb @ 5.02 TeV • Charge asymmetry • Sensitive probe of the up to down quark PDF ratio • Isospin symmetry (Ru = Rd) assumed in nPDF fits • Assuming Rd < Ru would decrease the charge asymmetry in negative η • Luminosity (experimental) and scale (theory) uncertain-ties cancel in asymmetries p fragmentation Pb fragmentation CMS-PAS-HIN-13-007 3rd Heavy Ion Jet Workshop

  20. W bosons in pPb @ 5.02 TeV • Forward-backward asymmetry • More sensitive to nuclear modifications • Different behavior of different charges→hint of Ru ≠ Rd ? CMS-PAS-HIN-13-007 3rd Heavy Ion Jet Workshop

  21. W bosons in pPb @ 5.02 TeV 3rd Heavy Ion Jet Workshop • Forward-backward asymmetry of the charge-summed W bosons • Good sensitivity for nuclear modification of parton distributions • Probes the shadowing over anti-shadowing and/or EMC effect • χ2 probabilities of 10% with CT10 and 27% with including EPS09 CMS-PAS-HIN-13-007

  22. Charged particles and jets in pPb collisions 3rd Heavy Ion Jet Workshop • Expected size of the effects ~ 0-20% JHEP 1310 (2013) 213 ~10% Int.J.Mod.Phys. E22 (2013) 1330007 ~20%

  23. 3rd Heavy Ion Jet Workshop Charged particle RpPbcompared to EPS09 Enhancement of high pT charged particles with respect to the interpolated pp reference can not be explained by nPDF CMS-PAS-HIN-12-017 • Measured RpPb for charged particles in |ηCM|<1 compared to y=0 EPS09 prediction for π0

  24. Charged particle Yasym in the CM frame in pPb 3rd Heavy Ion Jet Workshop Measurement without pp reference CMS-PAS-HIN-12-017 • Yield asymmetries in the CM frame: Pb-going/p-going side • Low-pT yields are significantly larger on the Pb-going side high-pT yields are similar (for DS events)

  25. Charged particle Yasym in the CM frame in pPb 3rd Heavy Ion Jet Workshop Int.J.Mod.Phys. E22 (2013) 1330007 CMS-PAS-HIN-12-017

  26. Charged particle Yasym in the CM frame in pPb 3rd Heavy Ion Jet Workshop

  27. 3rd Heavy Ion Jet Workshop Nuclear Modification Factor (Jets) CMS-PAS-HIN-14-001

  28. Jet RpPb and forward backward ratio 3rd Heavy Ion Jet Workshop CMS-PAS-HIN-14-001 • Sensitivity limited by systematical uncertainty • Consistent with no modification

  29. Dijet pseudorapidity distribution in pPb collisions 3rd Heavy Ion Jet Workshop ArXiv 1401.4433 Jet quenching from dijet analysis in pPb: dijet asymmetry <2% No significant jet quenching seen in γ-jet analysis in pPbNo sizable deviation from unity found in jet RpPb Jets for nPDF studies (pp PDF) EMC Anti-shadowing Anti-shadowing EMC Shadowing Boosted PYTHIA6 Z2 @ 5.02 TeV Shadowing = (η1+η2)/2

  30. Compare to CT10 and CT10+EPS09 3rd Heavy Ion Jet Workshop ArXiv 1401.4433 Hannu’s QM14 talk

  31. Dijet η vs. forward calorimeter energy in pPb 3rd Heavy Ion Jet Workshop ArXiv 1401.4433 …? p+π p+2π p = (η1+η2)/2 The large modification can not be explained by nPDF “Color fluctuation”?“Fluctuating proton size”? “Energy-momentum conservation”? (See Doga’s talk)

  32. Summary 3rd Heavy Ion Jet Workshop • Confirmed Binary scaling in pPb and PbPb collisions • Z and W production: modification of quark parton distribution function • Inclusive charged particle RpPb: • Enhancement at high pT to be understood • Inclusive jet measurement RpPb: • No indication of jet quenching • Consistent with no modification within large uncertainty • Dijet eta: consistent with EPS09, suggest gluon EMC effect

  33. 3rd Heavy Ion Jet Workshop • Backup slides

  34. Electroweak boson and dijet production in pPb collisions 3rd Heavy Ion Jet Workshop Forward/ Backward (in CM) Forward/ Backward (in lab) Dijet η Z boson W boson PDF (pp) nPDF(pPb) PDF (pp) nPDF (pPb) PDF (pp) nPDF (pPb) Measurement of W / Z / dijet rapidity distributions  sensitive to nPDF

  35. Electroweak boson and dijet production in pPb collisions 3rd Heavy Ion Jet Workshop Forward/ Backward (in CM) Forward/ Backward (in lab) Dijet η Z boson W boson ηdijet= (η1+η2)/2 PDF (pp) PDF (pp) nPDF(pPb) PDF (pp) nPDF (pPb) PDF (pp) nPDF (pPb) Measurement of W / Z / dijet rapidity distributions  sensitive to nPDF pPb data: consistent NLO with nPDF, inconsistent NLO with pp PDF

  36. Photon-jet: fraction of photons with a jet partner 3rd Heavy Ion Jet Workshop pPb PbPb 30-100% PbPb 0-30% Fraction ? Photon pT Photon pT Photon pT Jet pT>30 GeV Jet |η|<1.6 No significant modification in pPb collisions Isolated photons lost the away-side jet partner in central (head-on) PbPb collisions

  37. Z bosons in pPb @ 5.02 TeV 3rd Heavy Ion Jet Workshop • Inclusive Z production cross section in pPb collisions • Compared to NLO POWHEG calculation scaled by A=208 • Restricted rapidity range to reduce uncertainties on the acceptance correction • Results consistent with σpp × A

  38. W bosons in pPb @ 5.02 TeV • Cross section as a function of η in laboratory frame • Electron and muon results agree → combination is performed CMS-PAS-HIN-13-007 3rd Heavy Ion Jet Workshop

  39. 7TeV 3rd Heavy Ion Jet Workshop

  40. 3rd Heavy Ion Jet Workshop • pPb and PbPb collisions: • Electroweak probes: Isolated photons, W and Z bosons • pPb collisions: • Charged particle RpPb • Jet RpPb • Dijet

  41. Introduction 3rd Heavy Ion Jet Workshop • LHC energies allow first measurements of Z and W bosons in heavy ion collisions • Electroweak bosons are essentially not perturbed by the QCD medium → observed binary scaling in PbPb collisions • Constrain nuclear PDFs with pPb data • CMS-PAS-HIN-14-003→ Z in pPb 2013 • CMS-PAS-HIN-13-007→ W in pPb 2013 W CMS-PAS-HIN-13-004 PLB 715 (2012) 66 ~10%precision Z new

  42. Nuclear parton distribution functions (nPDFs) 3rd Heavy Ion Jet Workshop J.Phys. G39 (2012) 015010 • Nuclear PDF parametrizations • Z and W bosons aresensitive to (valence) quarkand (sea) antiquark contentof the nucleus • Dominant processes (LO)

  43. 3rd Heavy Ion Jet Workshop Isolated high pT photons • Solution: measurement of the isolated photons • Decay photons from hadrons in jets such as π0, η γ γ are largely suppressed • UE subtracted isolation variables are developed NLO LO γ γ Isolated γ Non-isolated same object to the detector Isolated Isolated Non-isolated

  44. 3rd Heavy Ion Jet Workshop

  45. 3rd Heavy Ion Jet Workshop

  46. 3rd Heavy Ion Jet Workshop

  47. 3rd Heavy Ion Jet Workshop

  48. 3rd Heavy Ion Jet Workshop

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