Why study Diffractive W Boson?Why study Diffractive W Boson?

Data SamplesData 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

hep-ex/0308032;Accepted by Phys. Lett B

Multiplicity in W Boson EventsMultiplicity 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)

Plot multiplicity in 3<||<5.2

W Boson Event CharacteristicsW 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

Observation of Diffractive W/ZObservation 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

DØ/CDF ComparisonDØ/CDF Comparison

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 methods adopted by both collaborations: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!

Run I Gaps Run I Gaps

• 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

Run II Improvements Run II Improvements

•Larger luminosity allows search for rare processes

•Integrated FPD allows accumulation of large hard diffractive data samples

•Measure , t over large kinematic range

•Higher ET jets allow smaller systematic errors

•Comparing measurements of HSD with track tag vs. gap tag yields new insight into process

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 TopicsDØ Run II Diffractive Topics

Run II Rapidity Gap SystemRun II Rapidity Gap System

Use signals from Luminosity Monitor and Veto Counters (designed at UTA)

to trigger on rapidity gaps with calorimeter towers for gap signal Work in progress (Mike Strang UTA, Tamsin Edwards U. Manchester);

no time to present in this talk

VC: 5.2 < < 5.9

LM: 2.5 < < 4.4

Forward Proton Detector LayoutForward 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 < 3.0 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

Castle DesignCastle Design

50 l/s ion pump

Beam

Worm gear assembly

Step motor

Detector

• Constructed from 316L Stainless Steel• Parts are degreased and vacuum degassed• Vacuum bettter than 10-10 Torr• 150 micron vacuum window• Bakeout castle, THEN insert fiber detectors

Thin vaccum window

All 6 castles with 18 Roman pots comprising the FPD were constructed in Brazil, installed in the Tevatron in fall of 2000, and have been functioning as designed.

A2 Quadrupole castle installed in the beam line.

Castle StatusCastle Status

AcceptanceAcceptance

Quadrupole ( p or )p

Dipole ( only)p

MX (G

eV)

450

400

350

280

200

GeV2

GeV2

450

400

350

20

200

MX (G

eV)

Geo

met

ric

A

ccep

tan

ce Dipole acceptance better at low |t|, large Cross section dominated by low |t| Combination of Q+D gives doubletagged events, elastics, better alignment, complementary acceptance

FPD Detector DesignFPD Detector Design

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 m

m

17.39 mm

UU’

XX’

VV’

Trigger

Detector ConstructionDetector ConstructionAt the University of Texas, Arlington (UTA), scintillating and optical fibers were spliced and inserted into the detector frames.

The cartridge bottom containing the detector is installed in the Roman pot and then the cartridge top with PMT’s is attached.

• 20 detectors built over a 2+ year period at UTA.

• In 2001-2002, 10 of the 18 Roman pots were instrumented with detectors.

• Funds to add detectors to the remainder of the pots have recently been obtained from NSF (should acknowledge funding from UTA REP, Texas ARP, DOE, and Fermilab as well).

• During the shutdown (Sep-Nov. 2003), the final eight detectors and associated readout electronics have been installed.

P2 Quadrupole castle withup and down detectors installed

Detector StatusDetector Status

M.Strang

Pot motion is controlled by an FPD shifter in the DØ Control Room via a Python program that uses the DØ online system to send commands to the step motors in the tunnel.

The software is reliable and has been tested extensively. It has many safeguards to protect against accidental insertion of the pots into the beam.

Pot Motion SoftwarePot Motion Software

FPD Trigger and ReadoutFPD Trigger and Readout

Stand-alone DAQStand-alone DAQ

•Due to delays in DØ trigger electronics, we have maintained our stand-alone DAQ first used in the fall 2000 engineering run.

•We build the trigger with NIM logic using signals given by our trigger PMT’s, veto counters, DØ clock, and the luminosity monitor.

•If the event satisfies the trigger requirements, the CAMAC module will process the signal given by the MAPMT’s.

•With this configuration we can read the fiber information of only two detectors, although all the trigger scintillators are available for triggering.

In-time hits in AU-PD detectors, no early time hits, or LM or veto counter hits

A1U A2U

P2DP1D

P

Pbar Halo Early Hits

LMVC

bp

bfpxp

bpp

Approximately 3 million elastic triggers taken with stand-alone DAQ

About 1% (30,000) pass multiplicity cuts

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

Elastic TriggerElastic Trigger

Segments to HitsSegments 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 ReconstructionInitial Reconstruction

DØ Preliminary

Spectrometer AlignmentSpectrometer 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

After alignment and multiplicity cuts (to remove background from halo spray):

Events are peaked at zero, as expected, with a resolution of = 0.019

Elastic Data DistributionsElastic Data Distributions

dN/dtdN/dt=p/p

Acceptanceloss Residual halo

contamination

The fit shows the bins that will be considered for corrected dN/dt

After unsmearing and acceptance corrections,the data points were normalized to the points obtained by the E710 experiment

The results are in excellent agreement with the model of M. Bloch showed in the figure

Warning: error bars need thecontribution of the unsmearing errors in progress

219.002.4 GeVb

“Final” dN/dt Results“Final” dN/dt Results

Dr. Jorge Molina, (LAFEX, Brazil)defended his thesis on these results 10/31/03 (first FPD thesis!)

Dipole TDC ResolutionDipole TDC Resolution

Can see bunch structure of both proton and antiproton beam

Can reject proton halo at dipoles using TDC timing

CDF does not have this capabilityD1 TDC

D2

TD

C

p

p halo frompreviousbunch

Standalone Readout vs. AFE ReadoutStandalone Readout vs. AFE Readout

Standalone Readout Uses a trigger based on

particles passing through trigger scintillators at detector locations

No TDC cut– this cut removes lower

correlation (halo) in y plot

Diffracted pbars fall in upper correlation of y plot

AFE readout Similar correlations Uses trigger:

– one jet with 25GeV and North luminosity counters not firing

This trigger suppresses the halo band

Dipole Diffraction ResultsDipole Diffraction Results

Geometrical Acceptance 14σ (Monte Carlo) Data

|t| (GeV2 )

Flat-t distribution

0.

0.02

0.06

0.04

0.08

|t| (GeV2 )

MZ all

MZ gap

Tagged Z event in FPD

Event Display

gapmuons

Run II Diffractive Z → µµRun II Diffractive Z → µµ

Summary and Future PlansSummary and Future Plans

Early FPD stand-alone analysis shows that detectors work,

will result in elastic dN/dt publication (already 1 Ph.D.)

FPD now integrated into DØ readout (detectors still work)

Commissioning of FPD and trigger in progress

Full 18 pot FPD will start taking data after shutdown (12/03)

Tune in next year for first integrated FPD physics results