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Measurement of the Inclusive Z+jet(s) Production Cross Section at CDF

Measurement of the Inclusive Z+jet(s) Production Cross Section at CDF. Oriol Salt ó IFAE – Barcelona (for the CDF Collaboration) Pheno 2007 Madison, WI. Motivation. MET + 3 jets. Boson+jets is one of the major backgrounds for MET+jets final states: t-tbar production Higgs SUSY

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Measurement of the Inclusive Z+jet(s) Production Cross Section at CDF

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  1. Measurement of the Inclusive Z+jet(s) Production Cross Section at CDF Oriol Saltó IFAE – Barcelona (for the CDF Collaboration) Pheno 2007 Madison, WI

  2. Motivation MET + 3 jets • Boson+jets is one of the major backgrounds for MET+jets final states: • t-tbar production • Higgs • SUSY • Could be used in searches for compositeness, heavy objects decays, etc. • Test of pQCDat high momentum transfers and NLO predictions are available in some cases • It is also sensitive to Underlying Event and Hadronization modeling Z jet Pheno 2007 Madison, WI

  3. Z + jets • Z→ee + jets is a very clean signal • no missing ET • almost background free. • Z→ee + jets constitutes no background to MET+jets (SUSY signal) but allows to validate MC predictions for the rest of Z+jets and W+jets final states • Cross section is ~10 times lower than W+jets • with more than 1 fb-1 of data differential jet measurements are possible e e Z jet Pheno 2007 Madison, WI

  4. Z→ee + jets Cross Section • The measurements are performed in a well defined kinematic region • Z→ee • 66 < Mee < 116 GeV/c2 • ETe > 25 GeV • |h1e| < 1.0 |h2e| < 1.0 || 1.2 < |h2e| < 2.8 • Jets reconstructed with MidPoint algorithm with cone size R = 0.7 • pTjet > 30 GeV/c |yjet| < 2.1 DR(e,jet) > 0.7 • NLO pQCD prediction by MCFM • PDF set: CTEQ6.1M • Dynamic renormalization and factorization scale: • m2 = M2(Z) + pT2(Z) • Up to 2 jets in the final state • Rsep = 1.3 • Corrected for non-perturbative contributions Pheno 2007 Madison, WI

  5. Z + jets in hadronic collisions Calorimeter towers Unfold detector effects (detector simulation) Particles Correct for non-perturbative contributions: • Hadronization of the partons • Underlying Event (MonteCarlo simulation) Partons jet parton remnants proton anti-proton Z Underlying Event (UE) e e Pheno 2007 Madison, WI

  6. Jet Shape • The observable is sensitive to the hadronization and the Underlying Event • Very well described by the MonteCarlo simulation Pheno 2007 Madison, WI

  7. Energy flow Jet + UE • As already seen, the jet is described accurately • Also very good agreement in the part dominated by the Underlying Event Z0f=0 transverse plane calorimeter towers Dominated by the Underlying Event Pheno 2007 Madison, WI

  8. Cross Section Uncertainties CDF Run II Preliminary • The total systematic uncertainty is about 10% at low pTjet up to 15% • It is dominated by the a 3% to 14% uncertainty on the absolute jet energy scale, followed by a 5% uncertainty on the efficiency on indenifying the electrons. • Uncertainties at low pTjet are comparable to the uncertainties in the theory Pheno 2007 Madison, WI

  9. Cross Section vs. pTjet • Cross Section corrected to the hadron level • Good agreement of the NLO pQCD prediction corrected for UE and Hadronization effects. • Non-perturbative contributions up to 25% at low pTjet • Uncertainties at low pTjet are comparable to the uncertainties in the theory (10%) Pheno 2007 Madison, WI

  10. Cross Section vs. |yjet| • The cross section is also measured as a function of the jet rapidity • Good agreement with the NLO prediction • Non-perturbative contributions of ~15% Pheno 2007 Madison, WI

  11. Cross Section vs. jet multiplicity • Cross Section with respect to the inclusive number of jets • NLO predictions up to two jets in the final state • LO predictions up to 3 jets in the final state • Data supports a constant NLO/LO k-factor as a function of Njets • Non-perturbative contributions account for 15% of the cross section Pheno 2007 Madison, WI

  12. Summary • We measured the Z+jets production cross section as a function of pTjet, |yjet| and jet multiplicity • Very good agreement was found with the NLO predictions • We showed the size and importance of the non-perturbative contributions • The results will be an input for a Higgs search in the ZH(→nnbb) channel Tevatron Pheno 2007 Madison, WI

  13. Pheno 2007 Madison, WI

  14. Pheno 2007 Madison, WI

  15. Z→e+e- selection • Loose Central Electron • |h| < 1.0 • |z0| < 60 cm • pT > 10 GeV/c • ET > 25 GeV • Track quality cuts • > 3 Stereo SL w/ hits ≥ 5 • > 2 Axial SL w/ hits ≥ 5 • Iso4 – Leak < 0.1·ET • HadEm < 0.055 + 0.00045·ET • Fiduciality == 1 • Tight Central Electron • |h| < 1.0 • |z0| < 60 cm • pT > 10 GeV/c • ET > 25 GeV • Track quality cuts • > 3 Stereo SL w/ hits ≥ 5 • > 2 Axial SL w/ hits ≥ 5 • Iso4 – Leak < 0.1·ET • HadEm < 0.055 + 0.00045·ET • E/p < 2.0 OR pT < 50 GeV/c • Lshr < 0.2 • c2CES < 10.0 • -3.0 cm < Q·Dx < 1.5 cm • |Dz| < 3.0 cm • Fiduciality == 1 • Plug Electron • 1.2 < |h| < 2.8 • ET > 25 GeV • Iso4 < 4 • HadEm < 0.05 • c2PEM <= 10.0 Pheno 2007 Madison, WI

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