1. The D0 Forward Proton Detector (FPD) Status
Jorge Barreto
UFRJ/CBPF - Brazil
pbar
D2 TDC p
D1 TDC

2. Forward Proton Detector Layout
P1U
P2O D S A1 Q2 Q4 Q3 Q2 D2 D1 A2 Q3 Q4 S
P1D
P2I
Veto 59 57 33 23 23 33
Z(m)
9 momentum spectrometers comprised of 18 Roman Pots
Scintillating fiber detectors can be brought close (~10 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) where the high t range was never before explored at Tevatron energies
Allows combination of tracks with high-pT scattering in the central detector

3. installed in the beam line.
Castle Status
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.
A1 Quadrupole castle
installed in the beam line.

4. 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
17.39 mm V’ V
Trigger X’ X U’ U
17.39 mm
1 mm
0.8 mm
3.2 mm

5. Detector Construction
At 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.

6. Segments to Hits
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 y x
10 u v

7. Detector Status
10 of the 18 Roman pots have been fully instrumented with detectors
Funds to add detectors to the remainder of the pots have recently been obtained
from NSF.
During the shutdown
(Sep-Nov. 2003), the final eight
detectors and associated readout
electronics are being installed.
P2 Quadrupole castle with
up and down detectors installed

8. Pot Motion Software
Pot motion is controlled 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.

9. Operations Currently FPD pots are inserted in every store
Commissioning integrated FPD
Have some dedicated FPD triggers, more when TM operational
Working towards automated pot insertion

10. Stand-alone DAQ – Phase 1
In phase I we used a stand-alone DAQ (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.

11. Quadrupole Elastic Data
A1U
A2U
P2D
P1D P
Pbar
Halo Early Hits LM VC
In-time hits in AU-PD detectors, no early time hits, or LM or veto counter hits
Over 1 million elastic trigger events taken with stand-alone DAQ
About 1% pass multiplicity cuts
Multiplicity cuts used for ease of reconstruction and to remove halo spray background

12. Initial Reconstruction
Reconstructed  Y
(mm)
beam
P1D
X (mm)
DØ Preliminary Y
(mm)
P2D
beam
=p/p should peak at 0 for elastic events!!
Dead Fibers due to cables that have since been fixed
X (mm)

13. Spectrometer Alignment
P1D x vs. P2D x (mm)
P1D y vs. P2D y (mm)
DØ Preliminary
Good correlation in hits between detectors of the same spectrometer but shifted from kinematic expectations
3mm in x and 1 mm in y

14. Elastic Data Distributions
Before
alignment
After
alignment
After alignment correction,
x peaks at 0 (as expected
for elastics)
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.
FPD is also a tool helping BD
Gaussian
fit
t distribution
DØ Preliminary

15. TDC Timing from Trigger PMTs
tp – tp = 18ns
TOF: 197ns ns
From TDCs :
18ns = (396ns – L1/c) – L1/c
4ns = (396ns – L2/c) – L2/c
 L1 = 56.7 m; L2 = 58.8 m
DØ Preliminary
tp – tp = 4ns
Tevatron Lattice:
L1 = 56.5m; L2 = 58.7m

16. TDC Resolution DØ Preliminary
Can reject proton halo at dipoles using TDC timing
Can see bunch structure of both proton and antiproton beam
1ns ~ 4 TDC channels
pbar
D2 TDC p
DØ Preliminary
D1 TDC

17. FPD Trigger and Readout – Phase 2

18. Standalone Readout vs. AFE Readout
No TDC cut
such cut removes lower correlation in y plot
Diffracted pbars fall in upper correlation of y plot
Uses a trigger based on particles passing through trigger scintillators at detector locations x1 y1
D0 Preliminary x2 y2
AFE readout
Uses trigger:
one jet with 25GeV and North luminosity counters not firing
This trigger suppresses the halo band
Similar correlations x1 y1
D0 Preliminary x2 y2

19. Dipole Diffraction Results - Alignment
All units in mm Y1 Y2
Raw data sample has 4640 events
Reconstruction of ~50% of events
Hit patterns: Misalignment?
Hit correlations: pbar halo?
Poor  and t distributions X1
Beam X2 X1 Y1
D0 Preliminary Y2 X2 
t (GeV2)

20. Dipole Diffraction Results - II
All units in mm
Shifts ΔY1= ΔY2=+2mm
Cut the pbar blob (X2 > -14mm)
Fair agreement between MC and Data
More realistic  and t distributions
Allow to study  vs t correlation MC
Data X1 X2 Y1 Y2 
t (GeV2)
D0 Preliminary

21. Dipole Diffraction Results - III
Geometrical Acceptance 14σ
Data 
Flat-t distribution 
0.08
D0 Preliminary
0.06
D0 Preliminary
0.04
0.02 0.
|t| (GeV2 )
|t| (GeV2 )

22. Run II Diffractive Z → µµ candidate

23. DØ Run II Diffractive Topics
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   E
<100 W boson events in Run I, >1000
tagged events expected in Run II

24. Summary and Future Plans
Run II analysis still in early stages
Early FPD stand-alone analysis shows that detectors work
FPD now integrated into DØ readout
Commissioning of FPD and trigger in progress
Gap results in Run II not yet approved
Full 18 pot FPD will start taking data after shutdown (12/03)
Tune in next year for first FPD physics results
Elastic cross section is used in measurement of luminosity (discrepancy between D0 and CDF)