Jets and QCD in D 0 Experiment Physics

Jets and QCD in D 0 Experiment Physics at Extreme Energies Hanoi, Vietnam July 23, 2000 V. Šimák Institute of Physics ASCR, Prague for the DÆ Collaborations Hanoi, July 23, 2000 V. Šimák

Outline • Inclusive Jet Cross Section : – at 1800 Ge. V – at 630 Ge. V – Ratio of Inclusive Jet Cross Sections • Dijet Triple Differential Cross Section • Dijet Mass Spectrum All theoretical comparisons done with JETRAD Hanoi, July 23, 2000 V. Šimák 2

y _ p p x z h = - ln [ tan (q / 2) ] |h| < 4. 2 l int> 7. 2 (total) Transverse segmentation Dh x D = 0. 1 x 0. 1 Electrons: s. E / E = 15% /ÖE + 0. 3% Pions: s. E / E = 45% /ÖE + 4% Hanoi, July 23, 2000 V. Šimák

Inclusive Jet Cross Section at Ös = 1800 Ge. V ½h½<0. 5 ± 8% Hanoi, July 23, 2000 +12% -10% V. Šimák +24% -20% 4

Inclusive Jet Cross Section at Ös = 1800 Ge. V (DÆ) ½h½<0. 5 • JETRAD m. F= m. R= ETMax /2 , Rsep=1. 3, for |h|< 0. 5 For all PDF’s probabilities between 47 -90% Hanoi, July 23, 2000 V. Šimák 5

Inclusive Jet Cross Section at Ös = 630 Ge. V = 536 nb-1 ½h½<0. 5 Hanoi, July 23, 2000 V. Šimák 6

Inclusive Jet Cross Section at Ös = 630 Ge. V • Some discrepancy at low ET, errors are large , but there is overall agreement. Hanoi, July 23, 2000 V. Šimák 7

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. Hanoi, July 23, 2000 V. Šimák 8

Dijet Triple Differential Cross Section 1994 -1995 Collider run (run 1 b): =92 ± 6 pb-1 preliminary results Require at least two reconstructed jets Trigger Jet: ET > 60 Ge. V Probe Jet : ET > 30 Ge. V 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. Hanoi, July 23, 2000 V. Šimák 9

Dijet Triple Differential Cross Section (DÆ) OS 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 ) Hanoi, July 23, 2000 V. Šimák 10

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 Hanoi, July 23, 2000 V. Šimák 11

Dijet Triple Differential Cross Section (DÆ) m = ET/2 0. 0<|h|<0. 5<|h|<1. 0<|h|<1. 5<|h|<2. 0 Hanoi, July 23, 2000 V. Šimák 12

Dijet Triple Differential Cross Section (DÆ) m = E/2 0. 0<|h|<0. 5<|h|<1. 0<|h|<1. 5<|h|<2. 0 Hanoi, July 23, 2000 V. Šimák 13

Dijet Triple Differential Cross Section (DÆ) m = E/2 0. 0<|h|<0. 5<|h|<1. 0<|h|<1. 5<|h|<2. 0 Hanoi, July 23, 2000 V. Šimák 14

Dijet Mass Distribution Smeared Cross Section Unsmeared 200 -220 Ge. V: 8% Error 800 -1400 Ge. V: 30% Error Hanoi, July 23, 2000 V. Šimák 15

“Typical DØ Dijet Event” MJJ = 1. 18 Te. V Q 2 = ET, 1×ET, 2= 2. 2 x 105 Ge. V 2 ET, 1 = 475 Ge. V, h 1 = -0. 69, x 1=0. 66 ET, 2 = 472 Ge. V, h 2 = 0. 69, x 2=0. 66 Hanoi, July 23, 2000 V. Šimák 16

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Compositeness Contact Predictions QCD + M Hanoi, July 23, 2000 V. Šimák cos 19

Compositeness Calculations Eichten 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 Te. V (LL) PRL 77, 438(1996) Hanoi, July 23, 2000 V. Šimák 20

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 (CTEQ 3 M, CTEQ 4 HJ, MRST, …) with agreement with D 0 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 Te. V no new physics so far Hanoi, July 23, 2000 V. Šimák