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Light jet energy scale determination with Top events

Light jet energy scale determination with Top events. E. Cogneras, D. Pallin , S. Binet. Purpose. The absolute energie scale will be know at the level of few percent at LHC start The calibration function varies with E and  => Get the light jet energy scale such that

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Light jet energy scale determination with Top events

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  1. Light jet energy scale determination with Top events E. Cogneras, D. Pallin, S. Binet

  2. Purpose • The absolute energie scale will be know at the level of few percent at LHC start • The calibration function varies with E and  • => Get the light jet energy scale such that E jet  E parton AOD Cone 04 Calibration function  (Ejet) = Eparton / Ejet EPart / E An example: Rome AOD  (Ejet) = 1. to 1.1 ‘cone 04’ E D. Pallin Rome workshop June 2005

  3. Purpose • Absolute jet scale essential for the Top mass measurement • A 1% miscalib induces a 0.9 GeV shift on the Top mass • => in-situ calibration for Top • calibration usable outside Top studies? M(jjb) M(lb) ATLFAST 1 year @ 1033 D. Pallin Rome workshop June 2005

  4. j1 n W1 W2 l(e,m) j2 t1 t2 b1 b2 How • Use the well defined W mass to rescale the jet energies from the W decay Wj1 j2 such that MW=MWPDG • Dont use any hypothesis for the calibration function • Dont rely on MC • difficulty : 2 jets with different energy, 1 # 2 • Select an enriched W sample from events D. Pallin Rome workshop June 2005

  5. Reconstructed W (cone 04) • AOD • ATLFAST • MW ~ 76 GeV ,  ~ 7 GeV • 40<E<500 GeV • AOD ~ ATLFAST except cosjj MW E Cosjj D. Pallin Rome workshop June 2005

  6. (1-costh) (1-cosjj) • AOD • ATLFAST Reconstructed W (cone 04) • AOD : <M jet>~ 10 GeV • ATLFAST: jets are massless • AOD and ATLFAST: jets are miscalibrated deviation for cosjj>0 Mj Cosjj Eth / E E D. Pallin Rome workshop June 2005

  7. (1-costh) (1-cosm) • AOD • ATLFAST Reconstructed W (cone 04) • AOD= Angle between the 2 jets recovered, shift only due to E miscalib. • ATLFAST: jets are massless, angle is not accurately defined => ~2 GeV shift on MW Cosm D. Pallin Rome workshop June 2005

  8. Method 1 to extract the E scale • compute R for k bins in E • apply kfactors on R and recompute R n times => R EPart / E AOD W Recons. No comb BKG E E D. Pallin Rome workshop June 2005

  9. Method1 Results after recalibration AOD 4000 W Recons. No comb BKG • Function found with any ‘a priori’ hypothesis before EPart / E Mw E after D. Pallin Rome workshop June 2005

  10. Method1 Results on Z+jets • Use the AOD Top sample to correct the jet energies of the AOD Z+jet sample • TOP 12000 jets, Z+jet 8000 jets • Apply same cuts on jets energies • => Top light jet scale works for all light jets Top Z+jets + EPart / E EPart / E + After calib ‘Top’ E E D. Pallin Rome workshop June 2005

  11. W selection • Selection for optimal mass measurement • Clean W sample with • 2 b tag • Cuts on Mt or Mt-Mw • Selection for commissioning • No b tag, cut on Mjlv ( see ivo van Vulpen talk) • Reduced b tag (with lower efficiency or 1btag only), cut on angles => W sample ~85% purity (see D Pallin talk Slovakia) • W sample ~85% purity (see D Pallin talk Slovakia) D. Pallin Rome workshop June 2005

  12. Comb. BKG W selection • Selection for optimal mass measurement AOD ATLFAST Mw 3 days at L=1033 D. Pallin Rome workshop June 2005

  13. Method1 with comb. BKG • Preliminary result with 1000 W +bkg evts • Calibration marginaly sensible to BKG (purity=85%) EPart / E AOD Very preliminary To reach the 1% precision on the E scale, 10000 W should be enough = 1month data taking 3 days at L=1033 E D. Pallin Rome workshop June 2005

  14. Method2 • If the angle between the 2 jets is not well determined (see ATLFAST example), Method 1 is not usable • Mw calibrated with Meth 1 not constant in function of cos ATLFAST Mwcorr/Mw cosjj D. Pallin Rome workshop June 2005

  15. Method2 • Need to • To disentangle the contributions from cosjj and E • To evaluate separately the correction E1 & E2 • perform a fit to constraint MW to MwPDG • evt by evt, compute 1E and 2E for the two jets and deduce E =f( E) • Allow E,  ,  to move within detector resolution D. Pallin Rome workshop June 2005

  16. Extract PEAK values for various energies FSR contrib =Ep/Ej  (E=Ei) Deduced function  = Eparton / Ejet=f(E) E (GeV) Method2 D. Pallin Rome workshop June 2005

  17. Method2 Results ATLFAST EPart / E E D. Pallin Rome workshop June 2005

  18. Method3 • Perform also a fit to constraint MW to MwPDG • Mix meth 1 and 2 • Constraints not given through the detector resolutions • define E corrections factor per bins in E • constraint cosjj =1 for cosjj =-1 • Mw corrected by E or cosjj in window [Mw : Mwpdg] D. Pallin Rome workshop June 2005

  19. Method3 Results • same results as Meth 2 • works on TOY MC • No cosjj correction found by the fit to AOD data EPart / E EPart / E After calib E E D. Pallin Rome workshop June 2005

  20. Conclusions • New methods investigated to get in-situ the light jet calibration for Top mass measurement • Preliminary results from AOD • AOD and ATLFAST comparable for top studies • 1% precision on the jet scale seems achievable in 1-2 month of data taking at 1033 • Top in-situ Light jet scale seems usable for all jet (if calibration done for jets with same selection) • Futur • Run all AOD files +physical BKG • Detailed look to jet algorithms D. Pallin Rome workshop June 2005

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