ISMD 99 August 11,1999 Brown 1. Introduction 2. Single Diffractive 1800 & 630 GeV 3. Monte Carlo 4. Hard Double Pomeron Exchange 5. Central Gaps 6. Summary Rapidity Gaps at DØ Jorge Barreto DØ Collaboration / I. Fisica of UFRJ

Diffraction p p  p p p p  p (p) + X p p  p (p) + j j p p  p p + j j

DØ Detector (Forward Gaps) Energy Threshold  coverage EM Calorimeter150 MeV2.0<|  |<4.1 Had Calorimeter500 MeV3.2<|  |<5.2 Central Gaps: EM Calorimeter (200 MeV E T Threshold) Tracking (number of tracks)

..... L0 Detector beam

Event Displays

 or Measure Multiplicity here Measure Gap Fraction: *Forward Jet Trigger 2-12GeV Jets |  |>1.6 *46K 1800 *26K 630 * Inclusive Jet Trigger 2-15(12)GeV Jets |  |<1.0 *14K 1800 *27K 630 Study SD Characteristics: *Single Veto Trigger 2-15(12)GeV 1800 GeV 630 GeV (1K,24K) Hard Single Diffraction

1800GeV Multiplicities D0 Preliminary NL0 NCAL

630GeV Multiplicities D0 Preliminary NCAL NL0

2D Fitting Comments: A) Fit background where  2/dof stable. B) If unprobable  2/dof ( >1.0), then to be conservative scale errors by square root. (only needed when large statistics) C) Error statistical and from variation of fit parameters Signal and Background fit simultaneously

1800GeV Forward Jet Fit D0 Preliminary Measured gap fraction = 0.64%  0.05% (fit)

Systematics/cross-checks D0 Preliminary Data Cut 1800 Fwd Jet Fitted Gap Fraction Standard0.64% % % Jet Quality Cuts0.64% % % Vary Energy Scale +1  0.64% % % Vary Energy Scale -1  0.62% % % Luminosity<0.2E300.63% % % Luminosity>0.2E200.65% % % Threshold 10.68% % % (200MeV,600MeV,70MeV) Threshold 20.61% % % (300MeV,700MeV,100MeV) Vary Background fit0.64% % % 15GeV Jets0.62% % % Measured Fraction is Stable

Single Diffractive Results D0 Preliminary Data Sample Measured Gap Fraction 1800 Forward Jets0.64% % % 1800 Central Jets0.20% % % 630 Forward Jets1.23% % % 630 Central Jets0.91% % % * Forward Jets Gap Fraction > Central Jets Gap Fraction * 630GeV Gap Fraction > 1800GeV Gap Fraction Data Sample Ratio 630/1800 Forward Jets /1800 Central Jets Fwd/Cent Jets Fwd/Cent Jets  or Measure Multiplicity here

1800GeV Event Characteristics D0 Preliminary Diffractive Inclusive (solid); Non-Diffractive Inclusive (dashed) Diffractive Events Quieter Overall

POMPYT Monte Carlo p p  p (or p) + j j * Model pomeron exchange POMPYT26 (Bruni & Ingelman) * based on PYTHIA *define pomeron as beam particle P p * Structure Functions 1) Hard Gluon xG(x) ~ x(1-x) 2) Flat Gluon (flat in x) 3) Soft Gluon xG(x) ~x (1-x)^5 4) Quark xQ(x) ~ x(1-x) p p P  = 1 - x p (momentum loss of proton) Pomeron Exchanges dominate for  < 0.05

Monte Carlo Multiplicity D0 Preliminary POMPYT NL0 NCAL PYTHIA

POMPYT Hard Gluon Event Characteristics D0 Preliminary Hard Gluon 1800GeV (  0.1) Hard Gluon 630GeV (  0.2) POMPYT hard gluon events quieter and jets narrower than PYTHIA events POMPYT (0,0) inclusive  (solid); PYTHIA (dashed)

MC Rate Comparison D0 Preliminary Evt Sample Hard Gluon Quark 1800 FWD JET 2.1%  0.3%0.9%  0.1% 1800 CEN JET 2.8%  0.5% 0.5%  0.2% 630 FWD JET 4.6%  0.8% 2.2%  0.5% 630 CEN JET 5.1%  0.7% 1.4%  0.7% Evt Sample Soft Gluon DATA 1800 FWD JET 1.6%  0.3% 0.64%  0.05% 1800 CEN JET 0.1%  0.1% 0.20%  0.08% 630 FWD JET 0.9%  0.7% 1.23%  0.10% 630 CEN JET 0.1%  0.1% 0.91%  0.07% f visible =  gap · f predicted * Hard Gluon & Flat Gluon rates higher than observed in data *Quark and soft gluon rates are similar to observed (HG 1800fwd  gap~ 74%±11%, SG 1800fwd  gap ~23%±5%)   gap *Add multiplicity to background data distribution *Fit to find percent of signal events extracted  Find predicted rate POMPYT·2 / PYTHIA *Apply same jet  cuts as data, jet ET>12GeV *Full detector simulation

CDF Dijet Result 1800 GeV Forward Jets: Calorimeter twr: (1.8<|  |<3.5) PRL: (1997) Rjj = 0.75% ± 0.10% (corrected with Hard Gluon Gap Efficiency) DØ 1800 Forward Gap fraction (w/same correction) = 0.86% ± 0.07%

MC Combined Ratios D0 Preliminary Event Sample Hard GluQuark DATA 630/1800 FWD 2.2   /1800 CEN 1.8   FWD/CEN 0.8   FWD/CEN 0.9   * Hard Gluon & Flat Gluon higher central than forward jet rate --and higher than observed in data *Quark rates and ratios are similar to observed *Combination of Soft Gluon and harder gluon structure is also possible for pomeron structure

 Calculation D0 Preliminary Rates, Gap efficiency, Event characteristics all dependent on  probed. *Can use calorimeter only to measure *Weights particles in well-measured region *Can define for all events *  calculation works well *not dependent on structure function or center-of-mass energy *Collins (hep- ph/ )  true =  calc · 2.2± 0.3

Single Diffractive  Distribution, 1800GeV D0 Preliminary   0.1 at 1800GeV *  distribution for forward and central jets (0,0)bin: nominal (solid), high (dotted), and low (dashed)

Single Diffractive  Distribution, 630GeV D0 Preliminary   0.2 at 630GeV *  distribution for forward and central jets (0,0)bin: nominal (solid), high (dotted), and low (dashed)

 Distribution, 1800GeV D0 Preliminary * non-diffractive contribution extends tail *  distribution very different between diffractive and non-diffractive data *  distribution for forward and central jets single diffractive (0,0) bin nominal (solid) non-diffractive (calculate to  3.0) (dotted)

 Data/POMPYT D0 Preliminary similar  distributions *  distribution for 1800 GeV jets (0,0) bin nominal Diffractive data (solid); POMPYT Hard Gluon (dashed)

Double Gaps at 1800GeV |Jet  | 15 GeV Gap Region 2.5<|  |<5.2

DØ Preliminary Gap Region 2.5<|  |<5.2 Double Gaps at 630 GeV

(E T > 30 GeV,  s = 1800 GeV) Measured fraction (~1%) rises with initial quark content : Consistent with a soft color rearrangement model preferring initial quark states Inconsistent with two-gluon, photon, or U(1) models Measure fraction of events due to color-singlet exchange Phys. Lett. B (1998), hep-ex /  jet   Central Gaps Count tracks and EM Calorimeter Towers in |  |<1.0

Data favor “free-factor” and “soft-color” models “single-gluon” not excluded, but all other models excluded (assuming S not dependent on E T and  Apply Bayesian fitting method, calculate likelihood relative to “free-factor” model Fit Results Color factors for free-factor model: C qq : C qg : C gg = 1.0 : 0.04 : 0 (coupling to quarks dominates)

Jet E T > 12 GeV, Jet |  | > 1.9,  > 4.0 R 1800 = 3.4  1.2 Opposite-Side DataSame-Side Data 1800 GeV: 630 Gev: n cal n trk 630 vs 1800 f S 1800 (E T =19.2 GeV) = 0.54  0.06 stat  0.16 sys % f S 630 (E T = 16.4 GeV) = 1.85  0.09 stat  0.37 sys % 630

Summary I - SINGLE DIFFRACTIVE DATA: - Measure SD rapidity gap signal at both 1800 GeV and 630 GeV for forward and central jets - Diffractive events quieter and jets thinner than non- diffractive events - Diffractive jet E T distribution matches non-diffractive jet E T - -f(forward)>f(central); f(630GeV)>f(1800GeV) 1800 FWD JETS 0.64%  0.05% 1800 CENT JETS0.20%  0.08% 1800 FWD JETS 0.64%  0.05% 1800 CENT JETS 0.20%  0.08% 630 FWD JETS 1.23%  0.10% 630 CENT JETS 0.91%  0.07% - Measure SD - Measure SD  distribution (0,0): (higher than expected) -   1800GeV -   630GeV POMPYT OBSERVATIONS: - Event Characteristics consistent with harder structures - Rates and ratios prefer quark structure or combination hard/flat gluon with soft gluons II - DOUBLE GAP DATA: - Observe Double Gaps at both 1800 and 630 GeV III - CENTRAL GAPS Phys. Lett. B (1998)

630GeV Event Characteristics D0 Preliminary

MC Rates D0 Preliminary  Find predicted rate POMPYT·2 / PYTHIA *Apply same jet  cuts as data, jet ET>12GeV *Full detector simulation (error statistical) MC Sample1800 FWD JET1800 CENT JET Hard Gluon2.8%  0.1%7.1%  0.1% Flat Gluon3.6%  0.1%6.2%  0.1% Quark1.5%  0.1%2.6%  0.1% Soft Gluon6.8%  0.1%1.8%  0.1% MC Sample630 FWD JET630 CENT JET Hard Gluon5.4%  0.1%10.5%  0.1% Flat Gluon4.3%  0.1%10.1%  0.1% Quark4.2%  0.1% 5.7%  0.1% Soft Gluon8.6%  0.1% 1.8%  0.1% f visible = f predicted ·  gap

POMPYT Hard Gluon Jet ET D0 Preliminary Hard Gluon 630GeV POMPYT events need  0.1 at 1800GeV and  0.2 at 630GeV to match PYTHIA Jet ET distribution HG 630  0.1 (instead of 0.2) solid line PYTHIA dashed line

POMPYT Flat Gluon Event Characteristics D0 Preliminary Flat Gluon 1800GeV (  0.1) Flat Gluon 630GeV (  0.2) POMPYT Flat Gluon events quieter and jets thinner than PYTHIA events

POMPYT Quark Event Characteristics D0 Preliminary Quark 1800GeV (  0.1) Quark 630GeV (  0.2) POMPYT quark structrure events quieter and jets thinner than PYTHIA events

POMPYT Soft Gluon Event Characteristics D0 Preliminary Soft Gluon 1800GeV (  0.1) Soft Gluon 630GeV (  0.2) POMPYT soft gluon jet Et falls faster than PYTHIA

Assumed to be independent of parton x (E T  Originally weak  s dependence Gotsman, Levin, Maor Phys. Lett B 309 (1993) Recently recalculated GLM hep-ph/ Using free-factor and soft-color model (uncertainty from MC stats and model difference) with Survival Probability

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: f S (E T ) falls, f S (  ) falls/rises 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: f S (E T ) & f S (  ) rise

Monte Carlo Models FUse Herwig 5.9 to simulate color-singlet model ÕIncludes higher-order effects and DØ detector simulation ÕBFKL two-gluon exchange and t-channel photon exchange processes ÕDivide by QCD prediction to get f S (MC) FConstruct “coupling factor” models: color-singlet fraction is a function of pdf’s weighted by “coupling factors” f S depends on x (E T, ,  s) through pdf’s: f S = f norm {C qq q 1 q 2 + C qg q 1(2) g 2(1) + C gg g 1 g 2 } (C ij  coupling to initial state ij ) Two-gluon: C qq =1,C qg = 9/4,C gg =(9/4) 2 Soft color: C qq =1/9,C qg =1/24,C gg =1/64 Single-gluon: C qq = C qg = C gg = 1 Free-factor: color factors given by fit