ISMD 99 August 11,1999

Brown

1. Introduction

2. Single Diffractive Data @ 1800 & 630 GeV

3. Monte Carlo

4. Hard Double Pomeron Exchange

5. Central Gaps

6. Summary

Rapidity Gaps at DØJorge 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 Calorimeter 150 MeV 2.0<||<4.1 Had Calorimeter 500 MeV 3.2<||<5.2

Central Gaps: EM Calorimeter (200 MeV ET Threshold)

Tracking (number of tracks)

.

....

L0 Detector

beam

Event Displays

-4.0 -1.6 -1.0 1.0 3.0 5.2

orMeasure Multiplicity here

Measure Gap Fraction: *Forward Jet Trigger

2-12GeV Jets ||>1.6 *46K events @ 1800 *26K events @ 630

* Inclusive Jet Trigger 2-15(12)GeV Jets ||<1.0

*14K events @ 1800 *27K events @ 630

Study SD Characteristics: *Single Veto Trigger 2-15(12)GeV Jets

@ 1800 GeV (22K,38K) @ 630 GeV (1K,24K)

Hard Single Diffraction

1800GeV Multiplicities

D0 PreliminaryD0 Preliminary

NL0 NL0

NL0NL0

NCAL NCAL

NCAL NCAL

630GeV Multiplicities

D0 PreliminaryD0 Preliminary

NCAL NCAL

NCAL NCAL

NL0

NL0

NL0

NL0

2D Fitting

Comments:Comments:

A) Fit background where A) Fit background where 2/dof stable.2/dof stable. B) If unprobable B) If unprobable 2/dof ( >1.0), then to be conservative 2/dof ( >1.0), then to be conservative

scale errors by square root. (only needed when scale errors by square root. (only needed when large statistics) large statistics)

C) Error statistical and from variation of fit parametersC) Error statistical and from variation of fit parameters

Signal and Background fit simultaneouslySignal and Background fit simultaneously

32 //

32

1 sysx eess

sS

xybybxbbB 3210

1800GeV Forward Jet Fit

D0 PreliminaryD0 Preliminary

Measured gap fraction = 0.64% 0.05% (fit)

Systematics/cross-checks

D0 PreliminaryD0 Preliminary

Data Cut 1800 Fwd Jet Fitted Gap Fraction Standard 0.64% + 0.05% - 0.05%

Jet Quality Cuts 0.64% + 0.05% - 0.05%

Vary Energy Scale +1 0.64% + 0.04% - 0.06%

Vary Energy Scale -1 0.62% + 0.04% - 0.05%

Luminosity<0.2E30 0.63% + 0.06% - 0.06%

Luminosity>0.2E20 0.65% + 0.07% - 0.07%

Threshold 1 0.68% + 0.04% - 0.06%(200MeV,600MeV,70MeV)Threshold 2 0.61% + 0.05% - 0.05%(300MeV,700MeV,100MeV)Vary Background fit 0.64% + 0.05% - 0.05%

15GeV Jets 0.62% + 0.05% - 0.04%

Measured Fraction is Stable

Single Diffractive Results

D0 PreliminaryD0 Preliminary

Data Sample Measured Gap Fraction 1800 Forward Jets 0.64% + 0.05% - 0.05%1800 Central Jets 0.20% + 0.08% - 0.05%630 Forward Jets 1.23% + 0.10% - 0.09%630 Central Jets 0.91% + 0.07% - 0.05%

* Forward Jets Gap Fraction > Central Jets Gap Fraction

* 630GeV Gap Fraction > 1800GeV Gap Fraction

Data Sample Ratio 630/1800 Forward Jets 1.9 + 0.2 - 0.2630/1800 Central Jets 4.6 + 1.2 - 1.81800 Fwd/Cent Jets 3.2 + 0.8 - 0.5630 Fwd/Cent Jets 1.4 + 0.1 - 0.1

-4.0 -1.6 -1.0 1.0 3.0 5.2

orMeasure Multiplicity here

1800GeV Event Characteristics

D0 PreliminaryD0 PreliminaryTitle:(char1800.ps)Creator:(ImageMagick)Preview:This EPS picture was not savedwith a preview included in it.Comment:This EPS picture will print to aPostScript printer, but not toother types of printers.

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 - xp (momentum loss of proton)

Pomeron Exchanges dominate for < 0.05

Monte Carlo Multiplicity D0 PreliminaryD0 Preliminary

POMPYT

NL0

NL0

NCAL

NCAL

PYTHIA

POMPYT Hard Gluon Event Characteristics

D0 PreliminaryD0 PreliminaryTitle:(evtchar_hg.ps)Creator:(ImageMagick)Preview:This EPS picture was not savedwith a preview included in it.Comment:This EPS picture will print to aPostScript printer, but not toother types of printers.

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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 PreliminaryD0 PreliminaryEvt 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: 2.4<| |<4.2 BBC: 3.2<| |<5.9 opposite jets 2 jets ET>20 (1.8<||<3.5) PRL:179 2636 (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 RatiosD0 PreliminaryD0 Preliminary

Event Sample Hard Glu Quark DATA 630/1800 FWD 2.2 0.5 2.4 0.6 1.9 + 0.2 - 0.2630/1800 CEN 1.8 0.4 2.8 1.4 4.6 + 1.2 - 1.81800 FWD/CEN 0.8 0.2 1.8 0.7 3.2 + 0.8 - 0.5630 FWD/CEN 0.9 0.2 1.6 0.9 1.4 + 0.1 - 0.1

* 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 PreliminaryD0 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

i

yT

s

eE i

i

* calculation works well

*not dependent on structure function or center-of-mass energy

*Collins (hep-ph/9705393)

true = calc · 2.2± 0.3

Single Diffractive Distribution, 1800GeV

D0 PreliminaryD0 Preliminary

0.1 at 1800GeV

* distribution for forward and central jets (0,0)bin: nominal (solid), high (dotted), and

low (dashed)

i

yT

s

eE i

i

Single Diffractive Distribution, 630GeV

D0 PreliminaryD0 Preliminary

0.2 at 630GeV

* distribution for forward and central jets (0,0)bin: nominal (solid), high (dotted), and low (dashed)

Distribution, 1800GeV

D0 PreliminaryD0 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 PreliminaryD0 Preliminary

similar distributions

* distribution for 1800 GeV jets (0,0) bin nominal

Diffractive data (solid); POMPYT Hard Gluon (dashed)

Double Gaps at 1800GeV

|Jet | < 1.0, ET>15 GeV

Gap Region 2.5<||<5.2

DØ Preliminary

Gap Region 2.5<||<5.2

Double Gaps at 630 GeV

(ET > 30 GeV, s = 1800 GeV)

Measured fraction (~1%) rises with initial quark content :Consistent with a soft color rearrangement model preferring initial quark statesInconsistent with two-gluon, photon, or U(1) models

Measure fraction of events due to color-singlet exchange

Phys. Lett. B 440 189 (1998), hep-ex / 9809016

jet

jet

Central GapsCount tracks and EM Calorimeter Towers in ||<1.0

Data favor “free-factor” and “soft-color” models“single-gluon” not excluded, but all other modelsexcluded (assuming S not dependent on ET and

Data favor “free-factor” and “soft-color” models“single-gluon” not excluded, but all other modelsexcluded (assuming S not dependent on ET and

Apply Bayesian fitting method, calculate likelihoodrelative to “free-factor” model

Fit Results

Color factors for free-factor model: Cqq : Cqg : Cgg= 1.0 : 0.04 : 0 (coupling to quarks dominates)

Jet ET > 12 GeV, Jet || > 1.9, > 4.0

R1800 = 3.4 1.2

Opposite-Side Data Same-Side Data

1800 GeV:

630 Gev:

ncal ncal

ncalncal

ntrk

ntrk

ntrk

ntrk

630 vs 1800

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

SummaryI - 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 ET distribution matches non-diffractive jet ET

--f(forward)>f(central); f(630GeV)>f(1800GeV)1800 FWD JETS 0.64% 1800 FWD JETS 0.64% 0.05% 0.05%1800 CENT JETS1800 CENT JETS 0.20% 0.20% 0.08% 0.08%630 FWD JETS 1.23% 630 FWD JETS 1.23% 0.10% 0.10% 630 CENT JETS 0.91% 630 CENT JETS 0.91% 0.07% 0.07%

- - Measure SD Measure SD distribution (0,0): (higher than expected) - 0.1 @ 1800GeV

- 0.2 @ 630GeVPOMPYT 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. B440 189(1998)

630GeV Event Characteristics

D0 PreliminaryD0 Preliminary

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MC RatesD0 PreliminaryD0 Preliminary

Find predicted rate POMPYT·2 / PYTHIA

*Apply same jet cuts as data, jet ET>12GeV *Full detector simulation (error statistical)

MC Sample 1800 FWD JET 1800 CENT JET Hard Gluon 2.8% 0.1% 7.1% 0.1%Flat Gluon 3.6% 0.1% 6.2% 0.1%Quark 1.5% 0.1% 2.6% 0.1%Soft Gluon 6.8% 0.1% 1.8% 0.1%

MC Sample 630 FWD JET 630 CENT JET Hard Gluon 5.4% 0.1% 10.5% 0.1%Flat Gluon 4.3% 0.1% 10.1% 0.1%Quark 4.2% 0.1% 5.7% 0.1%Soft Gluon 8.6% 0.1% 1.8% 0.1%

f visible = f predicted ·gap

POMPYT Hard Gluon Jet ET

D0 PreliminaryD0 Preliminary

Hard Gluon 630GeV

POMPYT events need 0.1 at 1800GeV and 0.2 at 630GeV to match PYTHIA Jet ET distribution

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HG 630 0.1 (instead of 0.2) solid line

PYTHIA dashed line

POMPYT Flat Gluon Event Characteristics

D0 PreliminaryD0 Preliminary

Flat Gluon 1800GeV (0.1)

Flat Gluon 630GeV (0.2)

POMPYT Flat Gluon events quieter and jets thinner than PYTHIA events

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POMPYT Quark Event Characteristics

D0 PreliminaryD0 Preliminary

Quark 1800GeV (0.1)

Quark 630GeV (0.2)

POMPYT quark structrure events quieter and jets thinner than PYTHIA events

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POMPYT Soft Gluon Event Characteristics

D0 PreliminaryD0 Preliminary

Soft Gluon 1800GeV (0.1)

Soft Gluon 630GeV (0.2)

POMPYT soft gluon jet Et falls faster than PYTHIA

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• Assumed to be independent of parton x (ET

• Originally weak s dependence Gotsman, Levin, Maor Phys. Lett B 309 (1993)

• Recently recalculated GLM hep-ph/9804404

•Using free-factor and soft-color model (uncertainty from MC stats and model difference)

•

with

2.02.2)1800(

)630(

S

S

1.05.16301800 R

)1800(

)630()Model()Data( 630

18006301800 S

SRR

2.14.3)Data(6301800 R

8.02.2)1800(

)630(

S

S

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:

fS (ET) falls, fS () 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:

fS (ET) & fS () rise

R1800630 08 . (LO)

(LO)5.21 630

1800 R

Monte Carlo Models Use Herwig 5.9 to simulate color-singlet model

Includes higher-order effects and DØ detector simulation

BFKL two-gluon exchange and t-channel photon exchange processes

Divide by QCD prediction to get fS (MC) Construct “coupling factor” models: color-singlet

fraction is a function of pdf’s weighted by “coupling factors”

fS depends on x (ET, ,s) through pdf’s:

fS= fnorm{Cqqq1q2 + Cqgq1(2)g2(1) + Cgg g1g2}

(Cij coupling to initial state ij )

• Two-gluon: Cqq=1,Cqg = 9/4,Cgg=(9/4)2

• Soft color: Cqq=1/9,Cqg=1/24,Cgg=1/64• Single-gluon: Cqq= Cqg = Cgg = 1• Free-factor: color factors given by fit