1 / 27

Hard Diffraction at DØ During Run I

Hard Diffraction at DØ During Run I. Michael Strang DØ Collaboration / Fermilab University of Texas, Arlington. Central Rapidity Gaps (Hard Color Singlet Exchange) Forward Rapidity Gaps (Hard Single Diffraction). DØ Detector. ( n l0 = # tiles in L0 detector with signal

eron
Télécharger la présentation

Hard Diffraction at DØ During Run I

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Hard Diffraction at DØ During Run I Michael Strang DØ Collaboration / Fermilab University of Texas, Arlington • Central Rapidity Gaps (Hard Color Singlet Exchange) • Forward Rapidity Gaps (Hard Single • Diffraction) Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  2. DØ Detector (nl0 = # tiles in L0 detector with signal 2.3 < |h| < 4.3) beam L0 Detector End Calorimeter Central Calorimeter EM Calorimeter Central Drift Chamber (ntrk = # charged tracks with |h| < 1.0) Hadronic Calorimeter (ncal = # cal towers with energy above threshold) Central Gaps EM Calorimeter ET > 200 MeV |h| < 1.0 Forward Gaps EM Calorimeter E > 150 MeV 2.0 < || < 4.1 Had. Calorimeter E > 500 MeV 3.2 < || < 5.2) Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  3. Particle Multiplicity Distributions Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  4. Measuring CSE Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  5. Hard Color Singlet Studies QCD color-singlet signal observed in ~ 1 % opposite-side events (p ) f Dh jet jet h Publications DØ: PRL 72, 2332(1994) CDF: PRL 74, 885 (1995) DØ: PRL 76, 734 (1996) Zeus: Phys Lett B369, 55 (1996) (7%) CDF: PRL 80, 1156 (1998) DØ: PLB 440, 189 (1998) CDF: PRL 81, 5278 (1998) • Newest Results • Color-Singlet fractions at • s = 630 & 1800 GeV • Color-Singlet Dependence on: • Dh, ET, s (parton-x) Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  6. Data Selection s = 1800 GeV high, medium, & low jet ET triggers s = 630 GeV low ET trigger Four data samples collected during 1994 - 1996: • Require centered event vertex • Cut events with spurious jets • Require single interaction • Leading jets with |h| > 1.9 • Dh > 4.0 (Opposite-side events) • ET cut: • ET > 12 GeV (low-ET 630, 7k events) • (low-ET 1800, 48k events) • ET > 25 GeV(med-ET 1800, 21k events) • ET > 30 GeV(high-ET 1800, 72k events) (Also same-side control samples at both CM energies using L0 trigger to suppress SD signal for background studies) Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  7. Measurement of fs Negative binomial fit to “QCD” multiplicity f Count tracks and EM Calorimeter Towers in |h| < 1.0 Dh jet jet h High-ET sample (ET > 30 GeV, s = 1800 GeV) fS = color-singlet fraction =(Ndata- Nfit)/Ntotal fS 1800 = 0.94  0.04stat 0.12sys % ET >30 GeV (Includes correction for multiple interaction contamination. Sys error dominated by background fitting.) Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  8. 630 vs. 1800 Multiplicities Jet ET > 12 GeV, Jet |h| > 1.9, Dh > 4.0 Opposite-Side Data Same-Side Data 1800 GeV: ncal ntrk ntrk ncal 630 Gev: ncal ncal ntrk ntrk fS 1800(ET =19.2 GeV) = 0.54  0.06stat 0.16sys % fS 630(ET = 16.4 GeV) = 1.85  0.09stat 0.37sys % 630 R1800 = 3.4  1.2 Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  9. Color Singlet Models If color-singlet couples preferentially to quarks or gluons, fraction depends on initial quark/gluon densities (parton x) larger x  more quarks Gluon preference: perturbative two-gluon models have 9/4 color factor for gluons • Naive Two-Gluon model (Bj) • BFKL model: LLA BFKL dynamics Predictions: fS (ET) falls, fS (Dh) falls (2 gluon) / rises (BFKL) Quark preference: • Soft Color model: non-perturbative “rearrangement” prefers quark initiated processes (easier to neutralize color) • Photon and U(1): couple only to quarks Predictions: fS (ET) & fS (Dh) rise Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  10. Model Fits to Data Using Herwig 5.9 s = 1800 GeV Soft Color model describes data Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  11. Fit Results Apply Bayesian fitting method, calculate likelihood relative to “free-factor model” (parametrization as weighted sums of relative fractions of quarks and gluons in pdf) Color factors for free-factor model: Cqq : Cqg : Cgg= 1.0 : 0.04 : 0 (coupling to quarks dominates) Data favor “free-factor” and “soft-color” models “single-gluon” not excluded, but all other models excluded (assuming S not dependent on ET and Dh) Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  12. Survival Probability • Assumed to be independent of parton x (ET , Dh) • Originally weak s dependence • Gotsman, Levin, Maor Phys. Lett B 309 (1993) • Subsequently recalculated • GLM hep-ph/9804404 • Using free-factor and soft-color model • (uncertainty from MC stats and model difference) • with Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  13. Hard Color Singlet Conclusions DØ has measured color-singlet fraction for: • 630 GeV and 1800 GeV same ET, h • as a function of ET and Dh at 1800 GeV fS shows rising trend with ET, h Measured fraction rises with initial quark content (Assuming the Survival Probability is constant with ET and Dh): • Consistent with a soft color rearrangement model preferring initial quark states Inconsistent with two-gluon, photon, or U(1) models  Cannot exclude single-gluon model Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  14. BFKL: Cox, Forshaw (manhep99-7) use a non-running as to flatten the falling ET prediction of BFKL (due to higher order corrections at non-zero t) Soft Color: Gregores subsequently performed a more careful counting of states that produce color singlets to improve prediction. Modifications to Theory Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  15. Hard Single Diffraction Studies Measure multiplicity here Measure min multiplicity here -4.0 -1.6 h 3.0 5.2 OR -5.2 -3.0 -1. h 1. 3.0 5.2 hep-ex/9912061, submitted to PLB • Gap fractions (central and forward) at s = 630 & 1800 GeV • Single diffractive x distribution Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  16. Data Selection • Require single interaction • Require central vertex • Gap Fraction : • (diffractive dijet events / all dijet events) • *Forward Jet Trigger • two 12GeV Jets |h|>1.6 • (@ 630, 28k events) • (@ 1800, 50k events) • * Central Jet Trigger • two 15(12) GeV Jets |h|<1.0 • (@ 630(12), 48k events) • (@ 1800(15), 16k events) • SD Event Characteristics: • *Single Veto Trigger • two 15(12) GeV Jets and no hits in L0 North of South array • (@ 630(12), 64k events) • (@ 1800(15), 170k events) Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  17. Event Characteristics 1800 Forward Jets Solid lines show show HSD candidate events Dashed lines show non-diffractive events • Less jets in diffractive events • Jets are narrower and more back-to-back • Diffractive events have less overall radiation • Gap fraction has little dependence on average jet ET Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  18. 630 vs. 1800 Multiplicities s = 1800 GeV: s = 630 GeV: Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  19. Fitting Method Example of fit for 1800 forward sample Signal is fit with a 2D falling exponential while background is fit with a 4 parameter polynomial surface Shapes are in agreement with Monte Carlo, the residual distributions are well behaved Distributions have c2/dof < 1.2 Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  20. Single Diffractive Results Measure Multiplicity here or -4.0 -1.6 -1.0 h 1.0 3.0 5.2 (Gap Fraction = # diffractive Dijet Events / # All Dijets) Data Sample Measured Gap Fraction 1800 Forward Jets 0.65% + 0.04% - 0.04% 1800 Central Jets 0.22% + 0.05% - 0.04% 630 Forward Jets 1.19% + 0.08% - 0.08% 630 Central Jets 0.90% + 0.06% - 0.06% Data Sample Ratio 630/1800 Forward Jets 1.8 + 0.2 - 0.2 630/1800 Central Jets 4.1 + 0.8 - 1.0 1800 Fwd/Cent Jets 3.0 + 0.7 - 0.7 630 Fwd/Cent Jets 1.3 + 0.1 - 0.1 * Forward Jets Gap Fraction > Central Jets Gap Fraction * 630 GeV Gap Fraction > 1800 GeV Gap Fraction Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  21. Comparison to MC fvisible = gap · fpredicted  gap *Add diffractive multiplicity from MC to background data distribution *Fit to find percent of signal events extracted  Find predicted rate POMPYT x 2 / PYTHIA *Apply same jet  cuts as data, jet ET>12GeV *Full detector simulation * Model pomeron exchange in POMPYT26 (Bruni & Ingelman) * based on PYTHIA * define pomeron as beam particle * Use different structure functions Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  22. Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  23. Pomeron Structure Fits • Demand data fractions composed of linear combination of hard and soft gluons, let overall  s normalization and fraction of hard and soft at each energy be free parameters • If we have a  s independent normalization then the data prefer : • 1800: hard gluon 0.18±0.05(stat)+0.04-0.03(syst) • 630: hard gluon 0.39±0.04(stat)+0.02-0.01(syst) • Normalization: 0.43±0.03(stat)+0.08-0.06(syst) with a confidence level of 56%. • If the hard to soft ratio is constrained the data prefer: • Hard gluon: 0.30±0.04(stat)+0.01-0.01(syst) • Norm. 1800: 0.38±0.03(stat)+0.03-0.02(syst) • Norm. 630: 0.50±0.04(stat)+0.02-0.02(syst) with a confidence level of 1.9%. • To significantly constrain quark fraction requires additional experimental measurements. • CDF determined 56% hard gluon, 44% quark but this does not describe our data without significant soft gluon or 100% quark at 630 Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  24. x Calculation Where  is the momentum fraction lost by the proton *Can use calorimeter only to measure *Weights particles in well-measured region *Can define for all events *Collins (hep-ph/9705393) true = calc · 2.2± 0.3 *  calculation works well * not dependent on structure function or center-of-mass energy Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  25. Single Diffractive x Distributions central s = 1800 GeV forward central s = 630 GeV forward  distribution for forward and central jets using (0,0) bin Dp p =   0.2 for s = 630 GeV Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  26. Summary • Measurements at both CM energies with same detector adds critical new information for examining pomeron puzzle • The higher rates at 630 were not widely predicted before the measurements • Pioneering work in Central Rapidity Gaps • Assuming x-independent survival probability, data support soft color rearrangement models (single gluon not excluded) • Modifications to theory based on data have occured • Forward gaps data • In a partonic pomeron framework require reduced flux factor combined with gluonic pomeron containing significant hard and soft components • Found larger fractional momentum lost by scattered proton than expected by traditional pomeron exchange • Results imply a non-pomeron based model should be considered. Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

  27. Gap Efficiencies  Efficiency tag events with gap =gap *Add diffractive multiplicity from MC to background data distribution *Fit to find percent of signal events extracted *Statistical error + MC energy scale error MC Sample 1800 FWD JET 1800 CENT JET Hard Gluon 74%  10% 34%  5% Flat Gluon 66%  9% 55%  7% Quark 61%  8% 18%  2% Soft Gluon 22%  3% 2.2%  0.8% MC Sample 630 FWD JET 630 CENT JET Hard Gluon 92%  16% 48%  6% Flat Gluon 71%  14% 60%  8% Quark 55%  11% 26%  3% Soft Gluon 23%  4% 6.0%  4.8% Lishep02, Feb 5, 2002, Rio de Janeiro, Brazil

More Related