Jets and QCD in D0 Experiment

Jets and QCD inD0 Experiment Physics at Extreme Energies Hanoi, Vietnam July 23, 2000 V. Šimák Institute of Physics ASCR, Prague for the DÆ Collaborations

Outline • Inclusive Jet Cross Section : • at 1800 GeV • at630 GeV • Ratio of Inclusive Jet Cross Sections • Dijet Triple Differential Cross Section • Dijet Mass Spectrum All theoretical comparisons done with JETRAD V. Šimák

y _ p p x z Transverse segmentation Dh x D  = 0.1 x 0.1 h = - ln [ tan (q / 2) ] |h|< 4.2 l int> 7.2 (total) Electrons: sE / E = 15% /ÖE + 0.3% Pions: sE / E = 45% /ÖE + 4%

Inclusive Jet Cross Section at Ös = 1800 GeV ½h½<0.5 ±8% +12% +24% -10% -20% V. Šimák

Inclusive Jet Cross Section at Ös = 1800 GeV (DÆ)½h½<0.5 • JETRAD mF= mR= ETMax /2 , Rsep=1.3, for |h|< 0.5 For all PDF’s probabilities between 47-90% V. Šimák

Inclusive Jet Cross Section at Ös = 630 GeV ½h½<0.5 = 536 nb-1 V. Šimák

Inclusive Jet Cross Section at Ös = 630 GeV • Some discrepancy at low ET, errors are large , but there is overall agreement. V. Šimák

Ratio of Inclusive Jet Cross Sections Same discrepancy exists in ratio of the scaled cross sections. QCD predictions seem to be 20% higher than expected. V. Šimák

Dijet Triple Differential Cross Section 1994-1995 Collider run (run 1b): =92 ± 6 pb-1 preliminary results Require at least two reconstructed jets Trigger Jet: ET > 60 GeV Probe Jet : ET > 30 GeV No restriction on additional jets. Measurement as input to PDF’s: gluon distribution is most interesting. Both experiments use JETRAD for theoretical comparisons with different PDF’s. V. Šimák

OS Dijet Triple Differential Cross Section (DÆ) SS Beam line • Divide data sample into four eta bins: -- 0.0<|h|<0.5, 0.5<|h|<1.0, 1.0<|h|<1.5, 1.5<|h|<2.0 • Divide each eta bin into two subsamples: -- events with 2 jets on the Opposite Side (OS) -- events with 2 jets on the Same Side (SS). • ET of both jets are measured so there are two entries per event into each of the eight the cross sections. • JETRAD using m = E/2 Note that the renormalization and factorization scale are chosen to be: -- mf = mr = E/2 ( max jet ) V. Šimák

Dijet Triple Differential Cross Section (DÆ) 0.0<|h|<0.5 1.0<|h|<1.5 0.5<|h|<1.0 1.5<|h|<2.0 V. Šimák

m= ET/2 Dijet Triple Differential Cross Section (DÆ) 0.0<|h|<0.5 0.5<|h|<1.0 1.0<|h|<1.5 1.5<|h|<2.0 V. Šimák

m= E/2 Dijet Triple Differential Cross Section (DÆ) 0.0<|h|<0.5 0.5<|h|<1.0 1.0<|h|<1.5 1.5<|h|<2.0 V. Šimák

Smeared Cross Section Unsmeared Dijet Mass Distribution 200-220 GeV: 8% Error 800-1400 GeV: 30% Error V. Šimák

“Typical DØ Dijet Event” MJJ = 1.18 TeV Q2 = ET,1×ET,2= 2.2x105 GeV2 ET,1 = 475 GeV, h1 = -0.69, x1=0.66 ET,2 = 472 GeV, h2 = 0.69, x2=0.66 V. Šimák

V. Šimák

cos M Compositeness Contact Predictions QCD + V. Šimák

Compositeness CalculationsEichten et al., Rev. Mod. Phys. 56, 579 (84) Eichten et al., Phys. Rev. Lett 50, 811 (83)Chivukula et al., Phys. Lett. B 380, 92 (96)Lee, Phys. Rev. D 55, 2591 (97)Lane, hep-ph/9605257 (96)Suggested Scale: 1.6 TeV (LL)PRL 77, 438(1996)  V. Šimák

Conclusions • 1800 Inclusive Cross Sec. • No significant excess • Excellent agreement with theory • 630 Inclusive Cross Sec. • NLO predictions ~20% high • Experimental measurements consistent • Ratios 630/1800 • NLO predictions ~20% high. • Experimental measurements consistent • Triple Differential Cross Section: • NLO QCD with recent PDF’s (CTEQ3M, CTEQ4M, CTEQ4HJ, MRST,…) with agreement with D0 within the systematic uncertainties • Cross sections for possible inputs to PDF’s • 1800 Dijet Mass • NLO QCD in agreement with the data • Compositeness Scale > 2.4 TeV • no new physics so far

Jets and QCD in D0 Experiment