1. Drell-Yan Spectrum and PDFs Dimitri Bourilkov University of Florida Di-lepton Meeting, LPC, FNAL, October 2, 2008

2. D.BourilkovDrell-Yan Spectrum and PDFs2 Introduction The “input” Drell-Yan spectrum contains information about: >Electroweak couplings >Parton Density Functions (PDFs) The “measured” DY spectrum adds the detector effects Concentrate on the “input” spectrum: the electroweak part is well known for masses not far from the Z peak, so we can say something about PDFs at LHC start-up Ad hoc fits vs more detailed descriptions >Ad hoc: parameters don’t carry much info >More detailed: say something about the underlying physics

3. D.BourilkovDrell-Yan Spectrum and PDFs3 Theory

4. D.BourilkovDrell-Yan Spectrum and PDFs4 PYTHIA Generation PYTHIA 6 and CTEQ61; di-electrons and di- muons Study generated spectrum 1 million events/channel generated in CMS acceptance region; keep events with both leptons in || < 2.4; In addition 250 K events with M > 120 GeV Can study different PDFs using LHAPDF In all plots the abscissa is mass in [GeV]

5. D.BourilkovDrell-Yan Spectrum and PDFs5 Incoming Partons Contributions from 5 flavors: need all PDFs! Up and down type quarks can be grouped together as their EW couplings are the same all uucd/u all ddsb

6. D.BourilkovDrell-Yan Spectrum and PDFs6 Incoming Partons above Z Contributions from 5 flavors: need all PDFs! Up and down type quarks can be grouped together as their EW couplings are the same all uucd/u all dds b

7. D.BourilkovDrell-Yan Spectrum and PDFs7 Fit PDF Weights Fit f q (x 1 )*f q (x 2 ) as a function of mass grouping up and down together Simple parameterization; needs refinement Area below 70 GeV exhibits much steeper slope (more sea quarks)

8. D.BourilkovDrell-Yan Spectrum and PDFs8 The DY Mass Spectrum I Fit the observed di-lepton mass 40-400 GeV (only 2 free parameters: normalization and Z mass; compute the electroweak part analytically in improved Born – may differ from PYTHIA!) Final state radiation reduces the observed mass, strong effect below the Z peak µ+µ- e+e-

9. D.BourilkovDrell-Yan Spectrum and PDFs9 Mass Corrections Correct the predicted spectrum with the ratio (observed/ propagator) mass known from the generator Large corrections for the Z “radiative escapes” e+e- µ+µ-

10. D.BourilkovDrell-Yan Spectrum and PDFs10 The DY Mass Spectrum II The correction works well around the Z peak, the  2 improves ~ 4.5 times ( but still high ) The high energy tail needs more work e+e- µ+µ-

11. D.BourilkovDrell-Yan Spectrum and PDFs11 On PDF Re-weighting I Re-weighting has been tested for total cross sections in Drell-Yan from the Z to high mass ( hep-ph/0605240 ), and works well What about differential distributions? Test the rapidity distribution of the Z: generate 41 samples of 100K events each with CTEQ6 (4.1 M in total) More tests needed

12. D.BourilkovDrell-Yan Spectrum and PDFs12 On PDF Re-weighting II

13. D.BourilkovDrell-Yan Spectrum and PDFs13 Outlook The DY spectrum contains PDF information in a wide kinematic range To improve the description a better representation of the PDFs is needed; some parameters may be left free and determined from the data Regions which can be studied right from the start: >Below 70 GeV: sea enhanced >50-90 GeV for the radiation effects >Above the Z ~< 200 GeV Detector effects to be included and their impact on the sensitivity estimated (di-electrons, di-muons) Confront with real data