Diffraction at D

1
Diffraction at DØ

• Andrew Brandt
• University of Texas at Arlington

Run I
Run II
Manchesster Workshop December, 2003
Manchester, UK
2
DØ Run I Gaps

• Pioneered central gaps between jets
  Color-Singlet fractions at ?s 630 1800 GeV
  Color-Singlet Dependence on Dh, ET, ?s
  (parton-x). PRL 72, 2332(1994) PRL 76, 734
  (1996)
• PLB 440, 189 (1998)
• Observed forward gaps in jet events at ?s 630
  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.
• PLB 531, 52 (2002)
• Observed W and Z boson events with gaps measured
  fractions, properties first observation of
  diffractive Z.
• PLB 574, 169 (2003)
• Observed jet events with forward/backward gaps
  at ?s 630 and 1800 GeV

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 lt h lt 5.9
LM 2.5 lt h lt 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.
• Luis Mendoza, Los Andes Columbia)

5
Forward Proton Detector
p
P1U
P2O
Q4
D
Q2
Q3
S
Q2
S
Q4
Q3
A1
A2
D2
D1
P1D
P2I
Veto
59
57
23
33
33
23
0
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 -gt Much better
  resolution than available with gaps alone
• Cover a t region (0 lt t lt 3.0 GeV2) never before
  explored at Tevatron energies
• Allows combination of tracks with high-pT
  scattering in the central detector

6
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 gapsjets Double
pomeron with gaps Gap tags vs. proton tags
Topics in RED were studied with gaps only in Run
I
lt100 W boson events in Run I, gt1000 tagged events
expected in Run II
7
Tevatron Modifications
Bypass
BEFORE
Sep
Sep
Sep
p
Sep Girder
Tunnel Floor
Pit Floor
Run I Girder Configuration
Modifying accelerator takes time and money in
this case 2 years and 300k
8
Castle Design
Worm gear assembly
50 l/s ion pump
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
9
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.
10
Acceptance
Dipole acceptance better at low t, large
x Cross section dominated by low t
Combination of QD gives double tagged events,
elastics, better alignment, complementary
acceptance
11
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
12
Detector Construction
At the University of Texas, Arlington (UTA),
scintillating and optical fibers were spliced and
inserted into the detector frames.
DONT SPLICE
The cartridge bottom containing the detector is
installed in the Roman pot and then the cartridge
top with PMTs is attached.
13
Detector Status

• 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 (mostly for MAPMTs).
• During the shutdown
• (Sep-Nov. 2003), the final eight
• detectors and associated readout
• electronics were installed.

A2 Quadrupole castle with all four detectors
installed
14
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
15
Operations

• Currently FPD expert shifters inserting pots and
  Captains remove pots and set 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)

Commissioning phase long and personnel intensive
16
Elastic Trigger
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

17
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

18
Elastic Data Distributions
After alignment and multiplicity cuts (to remove
background from halo spray)
??p/p
dN/dt
Acceptance loss
Residual halo contamination
?
The fit shows the bins that will be considered
for corrected dN/dt
Events are peaked at zero, as expected, with a
resolution of ?? 0.019
19
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!)
20
Dipole TDC Resolution
p
D2 TDC
p halo from previous bunch

• Can see bunch structure of both proton and
  antiproton beam
• Can reject proton halo at dipoles using TDC
  timing

D1 TDC
Timing is important
21
Fall Shutdown Work
Primary GoalsInstallation of final 8 detectors
and full readout system (new TPP and AFE
boards)Tunnel1) Installation and testing
of final 8 detectors2) Pot motion tests 3)
New 12V LVPS installation 4) Amp/shaper
testsrepairs for new detectors5) LVDT tests6)
Radiaton shielding Cameralight work 8)
Extension cord work for ORC9) TLDs
installedCollision Hall1) Installation and
testing of new TPP boards and AFE's2) Cable
repairs 3) HV for final detectors4) DFE
installationControl Room/Fixed Counting
house1) Automatic pot insertion tests2)
Uncabling small control room 3) FPD_LM
commissioning in progress4) ACnetrate watcher
mods5) Pots in/out dispaly switch 6) TM
commissioning XLab 31) Detector assembly
Always a lot of work to do in tunnel access
and reliable robust detector, electronics and pot
motion system essential
22
FPD Trigger and Readout
23
FPD Readout
Front View of PW08 (11/10/03)
24
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.

25
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/N7

4.0
New board- 1 cable attached
26
New TPP/AFE Pedestals
27
Standalone 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

28
Dipole Diffraction Results
Geometrical Acceptance 14s (Monte Carlo)
Data
?
Flat-t distribution
?
0.08
0.06
0.04
0.02
0.
t (GeV2 )
t (GeV2 )
29
Run II Diffractive Z ? µµ
Event Display
MZ all
gap
MZ gap
muons
Tagged Z event in FPD
30
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 ready to take data after
  shutdown (12/03)
• Tune in next year for first integrated FPD
  physics results

31
Lessons Learned

• Bigger project than you (I) might think more
  manpower, time, cost, CABLES
• Using other peoples electronics is risky
• Need a budget and some level of priority (Beyond
  the Baseline Syndrome)
• Early integration is essential
• Good contacts in the Accelerator Division are
  crucial
• Halo not well-understood
• Grounding issues
• Elastics for alignment, redundancy needed
• Splicing fibers is painful
• Need more access than you might think

Not to mention software effort track
reconstruction, Monte Carlo alignment, database,
online, etc.