1 / 18

Forward-Backward Charge Asymmetry in Z production at the LHC

Forward-Backward Charge Asymmetry in Z production at the LHC. Introduction ATLAS & CMS Detectors FB asymmetry measurement study Conclusions. Mohamed Aharrouche (LAPP-Annecy ) (for the ATLAS and CMS Collaborations). Motivation. Forward-Backward asymmetry

dasha
Download Presentation

Forward-Backward Charge Asymmetry in Z production at the LHC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Forward-Backward Charge Asymmetry in Z production at the LHC • Introduction • ATLAS & CMS Detectors • FB asymmetry measurement study • Conclusions Mohamed Aharrouche(LAPP-Annecy ) (for the ATLAS and CMS Collaborations) IVIIthRencontres de Moriond-QCD

  2. Motivation • Forward-Backward asymmetry • Provides a test of the Standard Model (i.e. universality) • At Z-pole • Determination of the Weinberg effective angle and the precision on this value AFB = b(a – sin²(eff)) • At high mass • Sensitive to many scenarios of physics beyond the Standard Model J. L. Rosner, Phys. Rev. D 35 (1987) U. Baur et al. Phys.Rev. D57 (1998) K. Sliwa et al.ATL-PHYS-2000-018 IVIIthRencontres de Moriond-QCD

  3. LHC Proton-Proton collisions at ECM = 14 TeV ATLAS and CMS: general purpose detectors Z factory Production ~1.5x107 events/year at low luminosity (1033cm-2s-1) From qq annihilation xqxqbar ~ 4x10-5 Longitudinal momentum PL = 0.5*√s*(xq -xqbar) Decay To two energetic fermions with opposite charge 70% to quarks pair: dominated by the background leptonic decay channels: cleaner Z Properties at LHC IVIIthRencontres de Moriond-QCD

  4. e-  q q e+ Charge Asymmetry • Parity violation in the neutral current • Consequence: Asymmetry in the angular distribution of leptons from Z decay • Theprobabilities to produce a lepton with a polar angle  and with π- are different • Theta dependence of the cross section IVIIthRencontres de Moriond-QCD

  5. Detectors ATLAS CMS ●4T Solenoid (for muons & inner tracker) ● Pure silicon tracker (pixel + strips) (||<2.6) ● Homogeneous EM calorimeter + hadronic sampling Calo. ( ||<4.9) ●2T Solenoid for inner tracker ● Tracker: silicon (pixel + strips) and TRT (||<2.5) ● Sampling calorimetry (||<4.9) ● Toroid system for muons IVIIthRencontres de Moriond-QCD

  6. Detector requirements • Z→μ+μ- • Muons detection limited • Acceptance (|| < 2.7) • Z→e+e- • electrons can be detected in very forward regions (||<4.9) • No tracker in ||>2.5 • At least one electron should be in the central region • Opposite charge assigned to the forward electron =2.5 • All events • |e1|<2.5 |e2|<4.9 • |e1| & |e2| < 2.5 IVIIthRencontres de Moriond-QCD

  7. e- * p p cos(*) • Defined in the Collins-Soper frame to take into account the non zero transverse momentum of the in incoming quark • In pp collisions we suppose that the quark direction is the same as the Z boost Dielectron around the Z mass (Mz±6 GeV) IVIIthRencontres de Moriond-QCD

  8. Quark direction all events Events with quark direction correctly estimated Less than 60% of events with correct quark direction at |Y| < 1 IVIIthRencontres de Moriond-QCD

  9. Counting method AFB= (F-B)/(F+B) F= number of events with cos*>0B= number of events with cos*<0 ee invariant mass(GeV) Calculating AFB Forward events Backward events IVIIthRencontres de Moriond-QCD

  10. GeV Case 1 Case 2 38% Analysis method - Z→e+e- • Distinguish the detector regions: • Case-1 • electrons in central region: (||<2.5) • Case-2 • One fiducial electron (||<2.5) andother electron (||<4.9) • Selection: • Two high PT electrons (PT > 20 GeV) • Mass window MZ±6 GeV • Missing Et cut < 20 GeV • Fast simulation • Signal • Drell-Yan events Ze+e- • Background • QCD dijets (dominant) • ttbar • 1 year at high luminosity (100 /fb) • All events • Case 1 • Case 1 & |y(Z)|>1 • All events • Case 2 • Case 2 & |y(Z)|>1 IVIIthRencontres de Moriond-QCD

  11. Case 2 Case 1 Z→e+e- results • AFB vs YZ rapidity • sensitivity increases with forward electrons • (statistical) δAFB vs forward electron/jet rejection • Forward electron efficiency fixed at 50% IVIIthRencontres de Moriond-QCD

  12. Z→e+e- results cont. LEP: δsin2efflep = 1.6x10-4 (stat and syst) IVIIthRencontres de Moriond-QCD

  13. Can we measure electrons with such requirements in the forward region? IVIIthRencontres de Moriond-QCD

  14. 1- BkgEff Forward electrons • Full simulation • electrons from Ze+e- • QCD jets • Discriminant analysis • Multivariate • 5 selected input variables • Energy fraction of the most energetic cell • Longitudinal moment • ... 2.5<||<3.2 3.2<||<4.9 signal backg Neural network output IVIIthRencontres de Moriond-QCD

  15. Systematics! • Ongoing study to answer to: • Can we control the systematics? • Can we use AFB to constrain PDFs at LHC? preliminary IVIIthRencontres de Moriond-QCD

  16. Conclusions • Very large statistics expected in Z production at LHC • The determination of the weak mixing angle with a high statistical precision (10-4) seems reachable • Requirements: • At least one electron in the central region • Electron efficiency more than 50% in the forward region • e/jet rejection > 100 in the forward region IVIIthRencontres de Moriond-QCD

  17. Extra Slides IVIIthRencontres de Moriond-QCD

  18. AFB – Z’→μ+μ - CMS IVIIthRencontres de Moriond-QCD

More Related