Diffraction at DØ

Andrew BrandtUniversity of Texas at Arlington

E

Run I Run II Low-x Workshop June 6, 2003 Nafplion, Greece

Examples of Soft Diffraction

Modeled by Regge Theory Non-perturbative QCD No quantum number exchanged

– Synonymous with exchange of a Pomeron

Examples of Hard Diffraction

Described by Different Models– Ingelman-Schlein based (q/g partonic structure of Pomeron)– BFKL-based (gluon ladder structure of Pomeron)– Soft Color Interactions (non-perturbative effects of standard QCD)

Diffractively Produced Jets

Diffractively Produced W

Particle Multiplicity Distributions

DØ Detector (Run I)

EM Calorimeter

L0 Detector

beam

(nl0 = # tiles in L0 detector with signal2.3 < || < 4.3)

Central Drift Chamber

(ntrk = # charged tracks with || < 1.0)

End Calorimeter

Central Calorimeter

(ncal = # cal towers with energy above threshold)

Hadronic Calorimeter

Central Gaps

EM Calorimeter

ET > 200 MeV

|| < 1.0

Forward Gaps

EM Calorimeter

E > 150 MeV

2.0 < || < 4.1

Had. Calorimeter

E > 500 MeV3.2 < || < 5.2)

Why study Diffractive W Boson?

Data Samples

Z boson sample: Start with Run1b Z ee candidate sample

Central and forward electron W boson sample: Start with Run1b W e candidate sample

Multiplicity in W Boson Events

-2.5 -1.5 0 1.1 3.0 5.2

Minimum side

Peak at (0,0) indicates diffractive W boson signal (91 events)

DØ Preliminary

Plot multiplicity in 3<||<5.2

W Boson Event Characteristics

MT=70.4

ET=36.9

ET=35.2

Standard W Events Diffractive W Candidates

ET=35.1

ET=37.1

MT=72.5

DØ Preliminary

Observation of Diffractive W/Z

Observed clear Diffractively produced W and Z boson signals

Background from fake W/Z gives negligible change in gap fractions

Sample Diffractive Probability Background All Fluctuates to Data Central W (1.08 + 0.19 - 0.17)% 7.7Forward W (0.64 + 0.18 - 0.16)% 5.3All W (0.89 + 0.19 – 0.17)% 7.5All Z (1.44 + 0.61 - 0.52)% 4.4

ncalnL0

Diffractive W and Z Boson Signals

Central electron W Forward electron W

All Z

ncalnL0

ncal

nL0

DØ Preliminary

RD = (WD ) / ( ZD ) = R*(WD/W)/ (ZD/Z)

where WD/W and ZD/Z are the measuredgap fractions from this letter andR=(W)/ (Z) = 10.43 ±0.15 (stat) ±0.20 (sys)±0.10 (NLO)B. Abbott et al. (D0 Collaboration), Phys. Rev D 61, 072001 (2000).

Substituting in these values givesRD = 6.45 + 3.06 - 2.64

This value of RD is somewhat lower than, but consistent with, the non-diffractive ratio.

DØ Preliminary

W/Z Cross Section Ratio

Calculate = p/p for W boson events using calorimeter:

Diffractive W Boson

data

Etieyi/2E

•Sum over all particles in event: those with largest ET and closest to gap given highest weight in sum (particles lost down beam pipe at – do not contribute

•Use only events with rapidity gap {(0,0) bin} to minimize non-diffractive background

•Correction factor 1.5+-0.3 derived from MC used to calculated data

DØ Preliminary

CDF {PRL 78 2698 (1997)} measured RW = (1.15 ± 0.55)% for ||<1.1 where RW = Ratio of diffractive/non-diffractive W (a significance of 3.8)

We measured (1.08 +0.19 –0.17)% for ||<1.1

No problem right? Well…

CDF corrects data for gap acceptance using MC and get 0.81 correction, so get an uncorrected value (0.93 ± 0.44)% , which is still consistent with our uncorrected data value.

Our measured gap acceptance is (21 ± 4)%, so our corrected value is 5.1%!!

Comparison of other gap acceptances for central objects from CDF and DØ using 2-D method:DØ central jets 18% (q) 40%(g)CDF central B 22%(q) 37% overallCDF J/ 29%

It will be interesting to see Run II diffractive W boson results!

DØ/CDF Comparison

E

Soft Diffraction and Elastic Scattering: Inclusive Single Diffraction Elastic scattering (t dependence) Total Cross Section Centauro Search Inclusive double pomeron Search for glueballs/exotics

Hard Diffraction: Diffractive jet Diffractive b,c ,t , Higgs Diffractive W/Z Diffractive photon Other hard diffractive topics Double Pomeron + jets Other Hard Double Pomeron topics

Rapidity Gaps: Central gaps+jets Double pomeron with gaps Gap tags vs. proton tags

Topics in RED were studiedwith gaps only in Run I

<100 W boson events in Run I, >1000tagged events expected in Run II

DØ Run II Diffractive Topics

Run II Rapidity Gap System

Use signals from Luminosity Monitor (and later Veto Counters) to trigger on rapidity gaps with calorimeter towers for gap signal

Use calorimeter at Level 2 to further refine rapidity gaps

VC: 5.2 < < 5.9

LM: 2.5 < < 4.4

Calorimeter Energy for Gap Triggers

DØ Preliminary

E NorthLM Veto North

E SouthLM Veto North

E NorthLM Veto South

E SouthLM Veto South

Trigger on gap in Luminosity Monitor (LM) + two 25 Gev jets;

Sum EM energy

DØ Preliminary

Leading Jet ET

Inclusive Jets North Gap Jets

South Gap Jets Double Gap Jets

ET (GeV) ET (GeV)

ET (GeV) ET (GeV)DØ Preliminary

Forward Proton Detector Layout

9 momentum spectrometers comprised of 18 Roman Pots

Scintillating fiber detectors can be brought close (~6 mm) to the beam to track scattered protons and anti-protons

Reconstructed track is used to calculate momentum fraction and scattering angle– Much better resolution than available with gaps alone

Cover a t region (0 < t < 4.5 GeV2) never before explored at Tevatron energies

Allows combination of tracks with high-pT scattering in the central detector

D SQ2Q3Q4S A1A2

P1U

P2I

P2O

P1D

p p

Z(m)

D2 D1

233359 3323057

VetoQ4Q3Q2

FPD Detector Setup

6 planes per detector in 3 frames and a trigger scintillator

U and V at 45 degrees to X, 90 degrees to each other

U and V planes have 20 fibers, X planes have 16 fibers

Planes in a frame offset by ~2/3 fiber

Each channel filled with four fibers

2 detectors in a spectrometer

0.8 mm

3.2 mm

1 mm

17.39 mm

17.39 mm

UU’

XX’

VV’

Trigger

Tagged Elastic Trigger

NO HITS IN LMN OR LMS OR VCN OR VCS

NO EARLY HALO HITS IN A1U-A2U, P1D-P2D

IN TIME HITS IN A1U-A2U, P1D-P2D

A1U A2U

P2DP1D

P

Pbar Halo Early Hits

Approximately 3 million elastic events recorded About 1% (30,000) pass multiplicity cuts

– Multiplicity cuts used for ease of reconstruction and to remove halo spray background from Tevatron

• 1 or 0 hits in each of 12 planes of the PD spectrometer• Each frame of both PD detectors needs a valid segment (i.e. 6

segments total)• Segments turned into hits and then reconstructed into tracks

LMVC

Segments to Hits

yx

10

ux

v

Segments

(270 m)

Combination of fibers in a frame determine a segment

Need two out of three possible segments to get a hit– U/V, U/X, V/X

• Can reconstruct an x and y

Can also get an x directly from the x segment

Require a hit in both detectors of spectrometer

=p/p should peak at 0 for elastic

events!!Dead Fibers due to cables that have since been fixed

P1D

P2D

beam

Y

X

Y

Reconstructed

beam

Initial Reconstruction

DØ Preliminary

Spectrometer Alignment

Good correlation in hits between detectors of the same spectrometer but shifted from kinematic expectations– 3mm in x and 1 mm in y

P1D x vs. P1D x (mm) P1D y vs. P2D y (mm)

DØ Preliminary

t distribution

Before alignment

After alignment

Gaussian fit

After alignment correction, peaks at 0 (as expected for elastics); MC resolution is 0.013 (including z smearing and dead channels), data is 0.015, 1.15 times larger

The t distribution has a minimum of 0.8 GeV2; tmin is determined by how close the pots are from the beam, shape is in rough agreement with expected angular acceptance from MC.

Elastic Data Distributions

DØ Preliminary

TDC Timing from Trigger PMTs

From TDCs :

18ns = (396ns – L1/c) – L1/c

4ns = (396ns – L2/c) – L2/c

L1 = 56.7 m; L2 = 58.8 m

Tevatron Lattice:

L1 = 56.5m; L2 = 58.7m

TOF: 197ns 190ns

tp – tp = 18ns

tp – tp = 4ns

DØ Preliminary

TDC Resolution

Can see bunch structure of both proton and antiproton beam

Can reject proton halo at dipoles using TDC timing

D1 TDC

D2

TDC

pbar

p

DØ Preliminary

Summary and Future Plans Run II analysis still in early stages

Early FPD stand-alone analysis shows that detectors work

FPD is now integrated into DØ readout

Commissioning of FPD and trigger in progress

Definition of rapidity gaps in Run II detector underway

Tune in next year for first FPD physics results