1. Andrew Brandt University of Texas at Arlington
Diffraction at DØ
Andrew Brandt
University of Texas at Arlington E h f
Run I
Run II
Low-x Workshop June 6, 2003
Nafplion, Greece

2. 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

3. 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

4. Run II Rapidity Gap System
VC:
5.2 < h < 5.9
LM:
2.5 < h < 4.4
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

5. Summary and Future Plans
Full 18 pot FPD will start taking data after shutdown (12/03)
Still work to do on detector and trigger commissioning
Manpower at Fermilab is the key issue
Detectors work as designed
Elastic Data analysis is moving towards publication
Integrated data is moving towards physics results
Full 18 pot FPD system now installed. After commissioning, data analysis with full system will be forthcoming
Elastic cross section is used in measurement of luminosity (discrepancy between D0 and CDF)

6. Forward Proton Detector
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 (~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

7. 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

8. Tevatron Modifications
Bypass
BEFORE:
Sep
Sep
Sep p
Sep Girder
Tunnel
Floor
Pit Floor
Run I Girder Configuration
Bypass
Sep
Pot
Sep Girder
Pit Floor
Hole in
Floor
Run II Girder Configuration
AFTER: p
Modifying accelerator takes time and money
in this case:
2 years and $300k
Elastic cross section is used in measurement of luminosity (discrepancy between D0 and CDF)

9. Castle Design Worm gear assembly 50 l/s ion pump Detector Beam
Thin vaccum
window
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
Detector
Beam
Step motor

10. 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.
A2 Quadrupole castle
installed in the beam line.

11. Acceptance x Quadrupole ( p or ) Dipole ( only)
MX(GeV)
450
400
350
280
200
GeV2 20 x
Geometric (f) Acceptance
Dipole acceptance
better at low |t|,
large x
Cross section
dominated by
low |t|
Combination of Q+D gives double
tagged events, elastics, better alignment, complementary acceptance

12. FPD 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
17.39 mm V’ V
Trigger X’ X U’ U
17.39 mm
1 mm
0.8 mm
3.2 mm

13. Detector Construction
At the University of Texas, Arlington (UTA), scintillating and optical fibers were spliced and inserted into the detector frames.
DON’T
SPLICE
The cartridge bottom containing the detector is installed in the Roman pot and then the cartridge top with PMT’s is attached.

14. Detector Status 20 detectors built over a 2+ year period at UTA.
In , 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 (mostly for MAPMT’s).
During the shutdown
(Sep-Nov. 2003), the final eight
detectors and associated readout
electronics were installed.
A2 Quadrupole castle with all
four detectors installed

15. This slide was made before Dec. 4 CDF accident
Pot Motion Software
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.
This slide was made before Dec. 4 CDF accident

16. Operations
Currently FPD expert shifters inserting pots and Captains removing pots and setting system to standby
Pots inserted every store
Commissioning integrated FPD
Have some dedicated diffractive triggers, more when Trigger Manager operational
Combine shifts with CFT, since similar readout system
Working towards automated pot insertion (CAP)

17. FPD Trigger and Readout

18. FPD Readout
Front View of PW08 (11/10/03)

19. TPP (Transition Patch Panel)
Interface to connect flat ribbon cables to AFE flex cables.
Decouples tunnel and platform grounds.
Discards extra charge to work within dynamic range of AFE.
Mimics shape of VLPC signals.

20. Resolution of Noise problem
Old board- 1 cable attached
10.0
Large rms pedestsal values with TPP/AFE setup (not seen in test stand)
Traced to a capacitive coupling between grounds
Isolating one of the grounding planes fixes the problem
Required redesign, very tight
schedule; new board also has optimized dynamic range S/N=7
4.0
New board- 1 cable attached

21. New TPP/AFE Pedestals

22. Fall Shutdown Work Always a lot of work to do in tunnel: access and
Primary Goals: Installation of final 8 detectors and full readout system (new TPP and AFE boards) Tunnel: 1) ***Installation and testing of final 8 detectors 2) ***Pot motion tests 3) New 12V LVPS installation 4) Amp/shaper tests+repairs for new detectors 5) LVDT tests 6) Radiaton shielding ; Camera+light work 8) Extension cord work for ORC 9) TLDs installed Collision Hall: 1) ***Installation and testing of new TPP boards and AFE's 2) Cable repairs 3) HV for final detectors 4) DFE installation Control Room/Fixed Counting house: 1) Automatic pot insertion tests 2) Uncabling small control room 3) FPD_LM commissioning in progress 4) ACnet+rate watcher mods 5) Pots in/out dispaly switch 6) TM commissioning X Lab 3 1) ***Detector assembly
Always a lot of work to
do in tunnel: access and
reliable robust detector,
electronics and pot motion
system essential

23. Elastic Trigger
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
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

24. Elastic Data Distributions
After alignment and multiplicity cuts (to remove background from halo spray):
=p/p
dN/dt
Acceptance
loss
Residual halo
contamination 
Events are peaked at zero, as expected, with a resolution of
 = 0.019
The fit shows the bins that will be considered for corrected dN/dt

25. FPD Integration Status
Full 18 detector system in readout.
Software in place and tested, FPD included in all DØ events.
FPD_LM TDC boards installed, being commissioned by Manchester; Vertex board for triggering still a few months away.
DFE boards complete, firmware has been implemented and is being tested. Thresholds to be tuned with new AFE/TPP setup.
Trigger manager commissioning in progress, first triggers using DFE within a couple months.
NIM/CAMAC trigger still in place for special runs.

26. Spectrometer Alignment
P1D x vs. P1D 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

27. Elastic Data Distributions
After alignment and multiplicity cuts (to remove background from halo spray):
=p/p
dN/dt
Acceptance
loss
Residual halo
contamination 
Events are peaked at zero, as expected, with a resolution of
 = 0.019
The fit shows the bins that will be considered for corrected dN/dt

28. “Final” dN/dt Results
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 the
contribution of the unsmearing errors  in progress
Dr. Jorge Molina, (LAFEX, Brazil)
defended his thesis on these results 10/31/03
(first FPD thesis!)

29. Dipole TDC Resolution p
D2 TDC
Can see bunch structure of both proton and antiproton beam
Can reject proton halo at dipoles using TDC timing
CDF does not have this capability
p halo from
previous
bunch
D1 TDC

30. Standalone Readout vs. AFE 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

31. Dipole Diffraction Results
Geometrical Acceptance 14σ (Monte Carlo)
Data 
Flat-t distribution 
0.08
0.06
0.04
0.02 0.
|t| (GeV2 )
|t| (GeV2 )

32. Run II Diffractive Z → µµ
Event Display
MZ all
gap
MZ gap
muons
Tagged Z event in FPD

33. Summary 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
Elastic cross section is used in measurement of luminosity (discrepancy between D0 and CDF)