# Presentation: 803587

## 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**_

## FPD Installation

All of the castles  installed and tested, maintaining vacuum. 
All the tunnel electronics installed and cables laid.
The PU spectrometer is instrumented with full detectors and phototubes.
The other vertical pots and dipole spectrometer are instrumented with pseudodetectors (trigger scintillators only) to study halo. 
Cameras installed and safety review 
     complete 
63 MAPMTs have been ordered from Hamamatsu, expected delivery in late August

**All of the castles  installed and tested, maintaining vacuum. **
**All the tunnel electronics installed and cables laid**.
- The PU spectrometer is instrumented with full detectors and phototubes.
- The other vertical pots and dipole spectrometer are instrumented with pseudodetectors (trigger scintillators only) to study halo.
- Cameras installed and safety review
-      complete
**63 MAPMTs have been ordered from Hamamatsu, expected delivery in late August**

## 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**
-  Start with stand-alone DAQ 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 still a big**
**   ****concern**
-  Starting to think about physics a little!

## Tevatron Reconfiguration

- Run I

**Bypass**

- Run II

- S type
- spool

**Extended Bypass**

**Dipole**
**(C48-5)**

- Separator

- Castle

- Power Leads

- P type
- spool

**Q1**

**Dipole**
**(C48-5)**

**Low Beta**

**Low Beta**

_**Tevatron Reconfiguration**_

- (Same for D11 side)

- BEFORE:

- AFTER:

- DØ

- DØ

- Separator

- Modified girder

- Castle

**Girder modified**
**Bypass construction completed**
**Valves and other vacuum equipment purchased**

## (Arbitrary Scale)

- Dipole Region

- Quadrupole Region

## Slide 37