DDDØ Hard Diffraction in DØ Hard Diffraction in Run I and IIRun I and II

DIS2000April 26, 2000Liverpool, UK

Andrew Brandt (DØ/UTA)

E

DDLearning about the Pomeron Learning about the Pomeron

• QCD is theory of strong interactions, but 40% of total cross section is attributable to Pomeron exchange -- not calculable and poorly understood

• Does it have partonic structure? Soft? Hard? Super-hard? Quark? Gluon? Is it universal -- same in ep and ? Is it the same with and without jet production?

• Answer questions in HEP tradition -- collide it with something that you understand to learn its structure

• Note: variables of diffraction are t and ~ M2

with FPD measure

without FPD just measure

dtd

d 2

pp

DDEVENT TOPOLOGIES

DD

Central Calorimeter

End Calorimeter

Central Drift Chamber (Tracking)

ntrk = # charged tracks

with || < 1.0

Hadronic Calorimeter

EM Calorimeter

ncal = # EM towers with ET > 200 MeV

and || < 1.0

(use E for || > 2.0)

DØ Calorimeter and Tracking

DDGap Definition

Detector coverage for gap definition

Thresholds:EM: 125 MeVHAD: 500 MeVHAD-END: 50 MeV

Gap definitions:1) Ncal=0 in (2.0,4.1)2) Ncal=0 in (2.0,5.2)3) Ncal=0 in (2.5,5.2)

Calorimeter Coverage EM HAD

Level 0 scintillator

1 2 4.1 5.2 1 2 4.1 5.2

DD

.

....

beam

DD

Measure Gap Fraction :(diffractive dijet events/all dijet events)

@1800 and 630 GeV *Forward Jet Trigger

two 12GeV Jets ||>1.6 * Inclusive Jet Trigger

two 15(12)GeV Jets ||<1.0 Study SD Characteristics: *Single Veto Trigger @1800 and 630 GeV two 15(12)GeV Jets

Hard Single Diffraction

-4.0 -1.6 3.0 5.2

Measure Mult here

-5.2 -3.0 -1. 3.0 5.2

Measure Mult here

OR

DD1800 and 630 GeV Multiplicities

D0 PreliminaryD0 Preliminary

s = 1800 GeV

s = 630 GeV

DD1800 GeV Forward Jet Fit

D0 PreliminaryD0 Preliminary

Measured gap fraction = 0.65% 0.04% (fit)

DDEvent Characteristics

D0 PreliminaryD0 Preliminary

DDSingle Diffractive Distributions

D0 PreliminaryD0 Preliminary

distribution for forward and central jets using (0,0) bin

i

yT

s

eE i

i p p=

0.2 for s = 630 GeV

s = 1800 GeV

forward

central

s = 630 GeV

forward

central

DDSingle Diffractive Results

D0 PreliminaryD0 Preliminary

Data Sample Measured Gap Fraction (#Diffractive Dijet Events/#All Dijets)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%

* Forward Jets Gap Fraction > Central Jets Gap Fraction

* 630GeV Gap Fraction > 1800GeV Gap Fraction

Data Sample Ratio 630/1800 Forward Jets 1.8 + 0.2 - 0.2630/1800 Central Jets 4.1 + 0.8 - 1.01800 Fwd/Cent Jets 3.0 + 0.7 - 0.7630 Fwd/Cent Jets 1.3 + 0.1 - 0.1

-4.0 -1.6 -1.0 1.0 3.0 5.2

orMeasure Multiplicity here

DDMC Rate Comparison

D0 PreliminaryD0 PreliminaryEvt Sample Hard Gluon Flat Gluon Quark 1800 FWD JET (2.2 0.3)% (2.2 0.3)% (0.8 0.1)%1800 CEN JET (2.5 0.4)% (3.5 0.5)% (0.5 0.1)%630 FWD JET (3.9 0.9)% (3.1 0.9)% (2.2 0.5)% 630 CEN JET (5.2 0.7)% (6.3 0.9)% (1.6 0.2)%

Evt Sample Soft Gluon DATA 1800 FWD JET (1.4 0.2)% (0.65 0.04)% 1800 CEN JET (0.05 0.01)% (0.22 0.05)%630 FWD JET (1.9 0.4)% (1.19 0.08)%630 CEN JET (0.14 0.04)% (0.90 0.06)%

f visible = gap · f predicted

* Hard Gluon & Flat Gluon rates higher than observed in data

(HG 1800fwd gap~74%±10%, SG 1800fwd gap~22%±3%)

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

DD630 and 1800 GeV Ratios

D0 PreliminaryD0 Preliminary

Event Sample Soft Glu DATA 630/1800 FWD 1.4 0.3 1.8 0.2630/1800 CEN 3.1 1.1 4.1 0.91800 FWD/CEN 30. 8. 3.0 0.7 630 FWD/CEN 13. 4. 1.3 0.1

* Hard Gluon & Flat Gluon forward jet rate is lower than central jet rate -- and lower 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

Event Sample Hard Glu Flat Glu Quark 630/1800 FWD 1.7 0.4 1.4 0.3 2.7 0.6630/1800 CEN 2.1 0.4 1.8 0.3 3.2 0.5 1800 FWD/CEN 0.9 0.2 0.6 0.1 1.6 0.3 630 FWD/CEN 0.8 0.2 0.5 0.1 1.4 0.3

DD

ncal

Peak at (0,0) indicates diffractive Wwith a signal on the 1% level

nL0

1.1 3 5. 21.1 3 5. 2

e MeasureMult.Here

MeasureMult.Here

Diffractive W

s =1800 GeVncal

nL0

DD

DØ Preliminary

Demand gap on one side, measure multiplicity on opposite sideDemand gap on one side, measure multiplicity on opposite side

Gap Region 2.5<||<5.2

Double Gaps at 630 GeV|Jet | < 1.0, ET>12 GeV

DDGap Summary

• Pioneered central gaps between jets, 3 papers, 3 Ph. D’s

• Observed and measured forward gaps in jet events at s = 630 and 1800 GeV. Rates much smaller than expected from naïve Ingelman-Schlein model. Require a different normalization and significant soft component to describe data. Large fraction of proton momentum frequently involved in collision.

• Observed jet events with forward/backward gaps at s = 630 and 1800 GeV

• Observed W and Z boson events with gaps

• Finalizing papers and attempting to combine results

DD

Series of 18 Roman Pots forms 9 independentmomentum spectrometers allowing measurementof proton momentum and angle.

1 Dipole Spectrometer ( p ) min

8 Quadrupole Spectrometers (p or p, up or down,

left or right) t > tmin

Q4D SQ2Q2Q3 Q3Q4S

A1QA1S

A2QA2S

P1Q

P2S

P1S

P2Q

p p

Z(m)

AD2 AD1

Detector B

ello

ws

Roman Pot

Forward Proton Detector Layout

233359 3323057

pBeam pF

P

2)( FBeam PPt P

Pxp

1

DDPhysics Topics with the FPD

1) Diffractive jet production

2) Hard double pomeron exchange

3) Diffractive heavy flavor production

4) Diffractive W/Z boson production

5) New physics

6) Inclusive double pomeron

7) High-|t| elastic scattering

8) Total cross section

9) Inclusive single diffraction

FPD allows DØ to maximize Run II physics

DDRun II Event Displays

Hard Diffractive Candidtate

Hard Double Pomeron Candidate

DDAcceptanceQuadrupole ( p or )p

Dipole ( only)p

Dipole acceptance better at low |t|, large Cross section dominated by low |t| ||6/ tedtd

0 0.02 0.04 1.4 1.4 1.3 2 35 95

(%)AQuadrupole Dipole

MX (G

eV)

450

400

350

280

200

GeV2

GeV2

450

400

350

280

200

MX (G

eV)

Geo

met

ric

A

ccep

tan

ce

DDQuadrupole + Dipole Spectrometers

The combination of quadrupole and dipole spectrometers gives:

1) Detection of protons and anti-protons a) tagged double pomeron events b) elastics for alignment, calibration, luminosity monitoring c) halo rejection from early time hits

2) Acceptance for low and high |t|

3) Over-constrained tracks for understanding detectors and backgrounds

DD

• Constructed from 316L Stainless Steel• Parts are degreased and vacuum degassed• Plan to achieve 10-11 Torr• Will use Fermilab style controls• Bakeout castle, then insert fiber detectors

Roman Pot Castle Design

Detector

50 l/s ion pump

Beam

Worm gear assembly

Step motor

DD

Thin windowand flangeassembly

Bellows

Detector is inserted into cylinder until it reaches thin window

Motor

Flangeconnectingto vacuum vessel

ThreadedCylinder

Roman Pot Arm Assembly

DD•Used finite element analysis to model different window options

•Built three types of pots and studied deflection with pressurized helium.

•150 micron foil with elliptical cutout gives excellent results

NIKHEF Window

DD

Six planes(u,u’,v,v’,x,x’)of 800 scintillatorfibers (’) planesoffset by 2/3fiber

The Detector

20 channels/plane(U,V)’16 channels/plane(X,X’)112 channels/detector2016 total channels80 theoretical resolution

DD

4 Fiber bundlefits well thepixel size ofH6568 16 Ch.MAPMT

7 PMT’s/detector(most of the cost)

The Detector

UU’

DDData Taking

• No special conditions required • Read out Roman Pot detectors for all events (can’t miss ) • A few dedicated global triggers for diffractive jets, double pomeron, and elastic events• Use fiber tracker trigger board -- select , |t| ranges at L1, readout DØ standard• Reject fakes from multiple interactions (Ex. SD + dijet) using L0 timing, silicon tracker, longitudinal momentum conservation, and scintillation timing• Obtain large samples (for 1 fb-1):

~ 1K diffractive W bosons ~ 3K hard double pomeron ~500K diffractive dijets

ttppp

with minimal impact on standard DØ physics program

DDOverall Conclusions

DØ has made significant progressin hard diffraction in Run I

A lot more to do in Run II

••••