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Diffractive results from DØ and prospects for Run II

Martijn Mulders

Fermilab

for the DØ collaboration

(with special thanks to C. Royon, M. Strang, A. Brandt,

J. Womersley and L.Coney for plots and useful discussions)

Xth Blois Workshop on Elastic and Diffractive Scattering, Helsinki , June 2003

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2Tevatron at Fermilab

p p

Run I ( 1992 - 1997 ) :

s =1.8 TeV

Run II ( 2001 - ? ) :

s =1.96 TeV

Batavia, Illinois

Main Injector & Recycler

Tevatron

Booster

p p

p source

Chicago

CDF

CDF

DØ

DØDØ

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3Examples of Soft Diffraction

• Modeled by Regge Theory

• Non-perturbative QCD

• No quantum number exchanged

– Synonymous with exchange of a Pomeron

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4Examples of Hard Diffraction

• Described by Different Models– DGLAP 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

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5Why study Diffractively Produced W?

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6Particle Kinematics

• The total center of mass energy is sqrt (s)

• The standard four-momentum transfer |t| is defined as

– |t| = (pf – pi)2

– |t| ~ (the scattering angle)

• The momentum fraction () taken by the Pomeron is defined as

– = 1 – xp = 1 – pf / pi

• Diffraction dominates for < 0.05

• Maximum diffractive mass (Mx) available is

– Mx = sqrt ( s)

pi pf

IP

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7Hard Diffraction

W boson has 80 times the mass of the proton !!

How can proton stay intact ??

100 times

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8Experimental Signature:

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9DØ Detector (Run I)

EM Calorimeter

L0 Detector

(nl0 = # tiles in L0 detector with signal 2.3 < || < 4.3)

End Calorimeter

Central Calorimeter

(ncal = # cal towers with energy above threshold)

Hadronic Calorimeter

Forward Gaps

EM Calorimeter

E > 150 MeV

2.0 < || < 4.1

Had. Calorimeter

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

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10

Z boson sample: Start with Run1b Z ee candidate sample

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

Data Samples

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11Multiplicity 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

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12W 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

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13Multiplicity in W Boson Events

DØ Preliminary

diffractive

Non-diffractive

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14Observation of Diffractive W/Z

• Observed clear Diffractively produced W and Z boson signals

fraction diffractive significance over Sample over All backgroundCentral 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

DØ Preliminary

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

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

where WD/W and ZD/Z are the measuredgap fractions from this measurement 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 gives

RD = 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 RatioW/Z Cross Section Ratio

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

Diffractive W Boson 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

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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)

This number is corrected for gap acceptance using MC giving 0.81 correction, so uncorrected value is (0.93 ± 0.44)% , consistent with our uncorrected data value:

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

Uncorrected measurements agree, but corrections derived from MC do not…

Our measured(*) gap acceptance is (21 ± 4)%, so our corrected value is 5.1% !(*) : derived from POMPYT Monte Carlo

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

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18

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 studied

with gaps only in Run I

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

DØ Run II Diffractive Topics

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19D0 Run II integrated luminosity

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D0 Run II data taking efficiency

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21Run I Run II: DØ Upgrade

All New Inner Tracker

New Muon Detectors & Shielding

Faster readout electronics

New Trigger, DAQ, and offline software

2 Tesla Solenoid Magnet

Silicon Vertex Detectors

Preshower

Detectors

Scint. Fiber Tracker

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22Rapidity Gap System Run II

• 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: 2.7 < < 4.4

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23Calorimeter Energy for Gap Triggers

DØ Preliminary

Gap+ JetTriggerNorth

Gap + JetTriggerSouth

EM energy North EM energy South

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24Leading Jet ET

Inclusive Jets North Gap Jets

South Gap Jets Double Gap Jets

ET (GeV) ET (GeV)

ET (GeV) ET (GeV)

DØ Preliminary

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25Forward Proton Detector Layout

• 9 momentum spectrometers composed 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

VetoQ4Q3

Q2

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26Quadrupole and Dipole acceptanceQuadrupole ( p or p ) :

Dipole ( p only) :_

_

) GeV ( 2t

) GeV ( 2t

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27FPD 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 channels, X planes have 16 channels

• Planes in a frame offset by ~2/3 fiber

• Each channel filled with four fibers

• 2 detectors in a spectrometer0.8 mm

3.2 mm

1 mm

17

.39 m

m

17.39 mm

UU’

XX’

VV’

Trigger

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28Segments to Hits

yx

10y

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

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29Tagged 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 raw elastic events

• About 1% (30 thousand) pass multiplicity cuts (used for ease of reconstruction and to try to handle high halo 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

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=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

DØ Preliminary

Initial Reconstruction

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31Spectrometer 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. P2D x (mm) P1D y vs. P2D y (mm)DØ Preliminary

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32Distributions after Alignment Correction

• After correction, now peaks at 0– 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 (would expect 0.6 GeV2 with clean beam). Shape is in agreement with expected angular acceptance from MC.

|t| (GeV2)-reco

DØ Preliminary

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TDC Timing from Trigger Tubes

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

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TDC Resolution

• Can see bunch structure of both proton and antiproton beam

• Can reject proton halo at dipoles using TDC timing

D1 TDC

D2

TD

C

pbar

p

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Conclusions

• First observation of diffractively produced Z bosons. Measurement of WD/W, ZD/Z and WD/ZD

• Early stand-alone analysis FPD (with 10 out of 18 Roman Pots) shows that detectors work

• FPD is now fully integrated in D0 readout

• Installation remaining pots later this year, and further commissioning FPD and trigger in progress

• Definition of rapidity gaps in Run II detector underway. Inclusion of FPD (anti-)proton tags expected soon

• Expect rich D0 diffractive physics program in Run II !!