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Z+Jets Production at the Tevatron

Z+Jets Production at the Tevatron. Alon Attal IFAE - Barcelona 20/07/2007 EPS Conference, Manchester. Motivation. The Z + Jets channel is an important background for ZH and squark/gluino searches. Can be used to test pQCD at high Q 2. ZH  nn bb Search. squark/gluino MET + Jets Search.

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Z+Jets Production at the Tevatron

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  1. Z+Jets Production at the Tevatron Alon Attal IFAE - Barcelona 20/07/2007 EPS Conference, Manchester

  2. Motivation • The Z+ Jets channel is an important background for ZH and squark/gluino searches. • Can be used to test pQCD at high Q2. ZH  nnbb Search squark/gluino MET + Jets Search EPS Conference, 20/07/2007

  3. CDF Detector Calorimeter Drift Chamber Data & MC Samples • Use 1.7 fb-1 of data collected by the CDF detector. • Pythia Tune A MC for the unfolding, hadronization and underlying event effects. • Results compared with NLO predictions from MCFM • Up to 2 jets in the final state. • CTEQ 6.1M PDFs • The e+e- + jet final state only has ~10% background at CDF. • Select events with 66 < Mee < 116 GeV/c2 • MidPoint 0.7 jets • pT > 30 GeV • |yjet| < 2.1 jet EPS Conference, 20/07/2007

  4. Unfolding Detector resolution effects Acceptance / efficiency Method } Calorimeter towers Detector Level } Hadron Level • Non-pQCD Corrections • Hadronization • Underlying Event } Parton Level jet parton Beam remnants proton anti-proton Z Underlying Event (UE) e e EPS Conference, 20/07/2007

  5. Jet Shape • We test the accuracy of the hadronization process inside the MC by measuring the jet shape. • Jet shapes also sensitive to the underlying event. Energy dist. inside of jet extremely well modeled. EPS Conference, 20/07/2007

  6. Jet + UE Z0f=0 transverse plane calorimeter towers Dominated by the Underlying Event Energy Flow • We test the average UE energy is the same in data and MC. • Energy flow shows excellent agreement. • Systematic uncertainty derived from Tune A & DW variations. • Tune DW has less ISR and more mult. particle interactions EPS Conference, 20/07/2007

  7. Z + ≥ 1 Jet Systematic Uncertainties Z + ≥ 2 Jet • Systematics dominated by jet energy scale. • ~5% uncertainty from the electron ID eff. • Total uncertainty < 15% for all pT. • 6% luminosity uncertainty not shown. • Uncertainty on 2nd jet slightly larger than the 1st jet. • Uncertainties from NLO pQCD: • Renormalization / factorization scale (10-15%) • PDFs (2-10%) jet EPS Conference, 20/07/2007

  8. Differential Cross Section • Differential cross section measured for inclusive jet production. • Including at least 1 or 2 jets in the event. • Data well described by NLO pQCD prediction for all values of pT. jet EPS Conference, 20/07/2007

  9. Non-pQCD Corrections (CHAD) Larger corrections applied for subsequent jets EPS Conference, 20/07/2007

  10. Differential Cross Sec. in |yjet| • Also measure the incl. s as a function of |yjet|. • For |yjet| < 2.1. • Good agreement with MCFM prediction. EPS Conference, 20/07/2007

  11. Excellent agreement Integrated Cross Section Ratio of s(N)/s(N-1) ≈ as as(MZ) Constant NLO/LO ratio EPS Conference, 20/07/2007

  12. Z+4jets Events Only two Z + 4 jet events seen so far (first event displayed) Calorimeter Tower h/f View Detector Cross Section View EM Cal. Energy Hadronic Cal. Energy EPS Conference, 20/07/2007

  13. Summary • The Z+jets channel includes interesting physics and is an important background for several hadron collider searches. • We measured the Z+jets cross section. • With 1.7 fb-1 of CDF p-pbar data • Differential s for 1 and 2 jets • Differential as a function of pTand |yjet| • Integrated s for up to 3 jets • Good control of detector effects and understanding of non-pQCD corrections. • Overall, the data matches the SM prediction as described by NLO pQCD. • Looking forward to seeing more Z+4jet events with additional data. jet EPS Conference, 20/07/2007

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