# Presentation: 803589

## DØ Hard Diffraction in Run I and Prospects for Run II

- Andrew Brandt
- DØ / University of  Texas, Arlington

-   Intro and  Run I Hard Diffraction Results
**  ****Forward Proton Detector**

- Low-x Physics 2001
- June 28, 2001
- Krakow, Poland

## Event Topologies

-  p p  p p

-  p p  p (p) + X

-  p p  p (p) + j j

-  p p  p  p + j j

_**Event Topologies**_

**Notes:**
Some example of diffractive processes 
responsible for 40 % of the total p-pbar cross section

Elastic
Single diffraction
Double diffraction

Soft: Rapidity Gaps
Hard: Jet structure

## Event Characteristics

## Hard Color-Singlet Exchange

_**Hard Color-Singlet Exchange**_

- Count tracks and EM  Calorimeter Towers in || < 1.0

- jet

- jet

- 

- 

- 

-  (ET > 30 GeV, s = 1800 GeV)

**Measured fraction (~1%) rises with initial quark content **:
***Consistent ***with a soft color rearrangement model preferring initial quark states
***Inconsistent*** with two-gluon, photon, or U(1) models

- Measure fraction of  events
- due to color-singlet exchange

** ****Phys. Lett. B 440 189 (1998)**

## 1800 and 630 GeV Multiplicities

- s = 1800 GeV

- s = 630 GeV

## SD Event Characteristics

_**SD Event Characteristics**_

** **

_**POMPYT Monte Carlo**_

-   p p   p (or p) + j j

- * Model pomeron exchange POMPYT26 		          (Bruni & Ingelman)
-  	* based on PYTHIA 				*define pomeron as beam particle

- P

-  p

-           * Structure Functions
- 	1) Hard Gluon xG(x) ~ x(1-x)
- 	2) Flat Gluon  (flat in x)
- 	3) Quark   xG(x) ~ x(1-x)
- 	4) Soft Gluon xG(x) ~ (1-x)5

-  p

-  p

- P

-  = 1 - xp	 (momentum loss of proton)

## hep-ex/9912061

## Single Diffractive  Distributions

-  distribution for forward and central jets using (0,0) bin

- p
-   p

- =

-   0.2 for s = 630 GeV

- s = 1800 GeV
- forward

- central

- s = 630 GeV
- forward

- central

## Double Gaps at 1800 GeV|Jet | < 1.0, ET>15 GeV

- Demand gap on one side,  measure multiplicity on opposite side

**Gap Region 2.5<|********|<5.2**

_**Double Gaps at 1800 GeV**_**|Jet ********| < 1.0, E****T****>15 GeV**

- DØ Preliminary

## Double Gaps at 630 GeV|Jet | < 1.0, ET>12 GeV

- Demand gap on one side,  measure multiplicity on opposite side

**Gap Region 2.5<|********|<5.2**

_**Double Gaps at 630 GeV**_**|Jet ********| < 1.0, E****T****>12 GeV**

- DØ Preliminary

## Diffractive W

**n****cal**

**Peak at (0,0) indicates diffractive W**
**with a signal on the 1% level**

_**Diffractive W**_

******s =1800 GeV**

**n****cal**

**n****L0**

**n****L0**

## Gap Summary

-   **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**
-    Finalizing papers and attempting to combine results

## A Few New Interesting Things

-  Gap fractions at 630 are higher than
-   1800 for Central Gaps and Hard SD,
-   but comparable for Double Gaps
-  Double gap events with 15 GeV jets
-   are about as rare as top events
-  Diffractive W’s and Z’s have similar
-    gap fractions

## FPD Layout

**Series of 18 Roman Pots forms 9 independent**
**momentum spectrometers allowing measurement**
**of proton momentum and angle.  **
** ****1 Dipole Spectrometer ( ****p**** ) ********min**
** ****8 Quadrupole Spectrometers  ****(****p****  or **** p****,  up or down,**
** ****left or right)**** t > t****min**

**Q4**

**D**

** ****S**

**Q3**

**S**

**A1**

**A2**

**P****1****UP**

**p**

**  ****Z(m)**

**D1**

**  ****Detector**

**  ****Bellows**

** ****Roman**
**    ****Pot**

_**FPD Layout**_

**23**

**33**

**59**

**33**

**23**

**0**

**57**

**P****2****OUT**

**Q2**

**P****1****DN**

**    ****P****2****IN**

**D2**

**Q4**

**Q3**

**Q2**

## Physics Topics with the FPD

- 1)  Diffractive jet production
- 2)  Hard double pomeron exchange
- 3)  Diffractive heavy flavor production
- 4)  Diffractive W/Z boson production
- 5)  New physics
- 6)  Inclusive double pomeron
- 7)  High-|t| elastic scattering
- 8)  Total cross section
- 9)  Inclusive single diffraction
- FPD allows DØ  to maximize Run II physics

## Data Taking

-  No special conditions required
-  Read out Roman Pot detectors for all events
-    (can’t miss                       )
-  A few dedicated global triggers for diffractive
-   jets, double pomeron, and elastic events
-  Use fiber tracker trigger board -- select
-    , |t| ranges at L1, **readout DØ standard**
-   Reject fakes from multiple interactions
-     (Ex. SD + dijet) using L0 timing, silicon
-     tracker, longitudinal momentum conservation,
-     and scintillation timing
-   Obtain large samples (for 1 fb-1):
-  **~ 1K     diffractive W bosons**
** ****~ 3K     hard double pomeron**
** ****~500K  diffractive dijets**

-    with minimal impact on standard DØ
-     physics program

## Run II Event Displays

_**Run II Event Displays**_

- Hard Diffractive Candidate

- Hard Double Pomeron Candidate

## Diffractive Variables

_**Diffractive Variables**_

- pBeam

- pF

- P

- For                TeV

- Pomeron Exchange

- Non-diffractive

- For

-    (**Note**:                                          )

- GeV

- GeV

- GeV

## Acceptance

_**Acceptance**_

- Quadrupole ( *p* or     )

- Dipole (      only)

- Dipole acceptance better at low |t|, large 
- Cross section dominated by low |t|

- 0    0.02   0.04
-     1.4   1.4     1.3
-      2      35     95

- MX(GeV)

- 450
- 400
- 350
- 280
- 200

- GeV2

- GeV2

- 450
- 400
- 350
- 280
- 200

- MX(GeV)

- 

- 

**Geometric ******** Acceptance**

## Quadrupole + Dipole Spectrometers 

_**Quadrupole + Dipole Spectrometers**_** **

-  The combination of quadrupole and
-  dipole spectrometers gives:
-    1) Detection of protons and anti-protons
-         a) tagged double pomeron events
-         b) elastics for alignment, calibration,
-             luminosity monitoring
-         c) halo rejection from early time hits
-    2) Acceptance for low and high |t|
-    3) Over-constrained tracks for
-         understanding detectors and
-         backgrounds

## FPD Commissioning

_**FPD Commissioning**_

**Notes:**
Dipole castles installed at the Tevatron tunnel

Electronic crate with:
Motor drivers
Amplifier boards
Interface boards
Rack monitor
 Smoke detector

## Roman Pot Castle Design

-  Parts are degreased and vacuum degassed
-  Plan to achieve 10-11 Torr
-  Will use Fermilab style controls
-  Bakeout castle, then insert fiber detectors

_**Roman Pot Castle Design**_

- Detector

- 50 l/s ion pump

- Beam

- Worm gear assembly

- Step motor

## Roman Pot

**Roman Pot**

**Notes:**
Responsible for taken the Pot close to the beam

Roman Pot constructed at NIKHEF a Netherlands

Very thin and resistant window : 
not interfere with the scattered particle
Resist to the high vacuum  

## The Detector

- 4 Fiber bundle
- fits well the
- pixel size of
- H6568 16 Ch.
- MAPMT
- 7 PMT’s/detector
- (most of the cost)

_**The Detector**_

**U**

**U’**

## Detector Construction

-  Four fibers are aligned together in the frame to     	make a channel
-  X frame also includes trigger scintillating rod
- Bicron optical epoxy is used to secure the fibers 	into the frame once completely assembled
-  After curing, channels are mapped to appropriate 	location in cookie, PMT calibration fibers 	are included, lengths are measured and 	final gluing with optical epoxy is done

_**Detector Construction**_

## Beyond the Engineering Run:
FPD Installation and Commissioning

All of the castles should be installed and tested by March 1st, 2001. 
All the tunnel electronics will be installed and cables will all be laid. 
The dipole spectrometer will be instrumented with full detectors and phototubes. 
The vertical spectrometers and one horizontal  spectrometer will be instrumented with pseudodetectors (trigger scintillators only) to study halo.  
Still looking for funds to purchased the phototubes for the other castles. 
We hope to be ready to take data with a Phase I (10 pot) FPD in late summer. 

- FPD Installation and Commissioning
- All of the castles should be installed and tested by March 1st, 2001. 
- All the tunnel electronics will be installed and cables will all be laid. 
- The dipole spectrometer will be instrumented with full detectors and phototubes. 
- The vertical spectrometers and one horizontal  spectrometer will be instrumented with pseudodetectors (trigger scintillators only) to study halo.  
- Still looking for funds to purchased the phototubes for the other castles. 
- We hope to be ready to take data with a Phase I (10 pot) FPD in late summer. 

**Jan. 12, 2001 Commissioning meeting:**

## Castles Installed

_**Castles Installed**_

**Notes:**
A1 and A2 castles close to the separator

## Pot Motion: LVDT vs. Encoder

_**Pot Motion: LVDT vs. Encoder**_

## Hit Reconstruction

-  This event (from Engineering Run data)
- represents a hit in our detector at the location:
- 	xd = 5.6 mm
- 	yd = 3.8 mm

## Run II HSD Improvements

-  Measure , t over large kinematic range
- Integrated FPD trigger allows large data samples
- Higher ET  jets allow smaller systematic errors
- Comparing measurements of HSD with track tag vs. gap
-   tag yields new insight into process
-  Can calibrate calorimeter  measurement without MC

## June-August Run Plan

-  Dedicated FPD shifts with pots inserted
-    close to beam (2 full detectors, 8 with
-    only trigger scintillators)
-  Start with stand-alone DAQ/trigger in
-   small control room then integrate into
-   DØ
-  Full system tests
-  Debugging, data-taking, algorithm
-   development, pot insertion procedure,
-   documentation, etc.

## Long Range Plan

-  Install 8 more detectors (total of 10) during
-    September shutdown
-  Begin data taking with full DØ detector
-    and trigger list in October
-  Demonstrate working system, usefulness
-   of horizontal plane, and secure funding
-   for remaining MAPMT in 2002
-  Early papers:
-    NIM
-    Elastic t-distribution
-    Single diffraction distributions
-    Diffractive jet production
-    Double tagged double pomeron exchange

## Conclusion

** ****Tremendous progress in installation and**
**   ****commissioning**
** **Entering a new phase of  FPD:
-   1) Installation almost complete
-   2) **We have funding!**
-  Emphasis shifts to software and operations
-  **Trigger hardware and firmware a MAJOR  **
**   ****concern**
-  Starting to think about physics a little!