# Presentation: 764773

##         ELASTIC SCATTERING IN D0 EXPERIMENT

- Carlos Avila
- Universidad de Los Andes
- Bogota, Colombia

## FPD has opened the opportunity to study        elastic scattering in the D0 experiment.  

**We show in this talk:****  **
-  The analysis of elastic triggers taken during FPD commissioning.
-  Prospects for increasing the t range that can be covered by FPD.

##     ELASTIC TRIGGER:  

- 31 runs taken with detectors located at 9    from beam. (    = beam width): P1D=17.05mm, P2D=13.80mm A1U=12.57mm, A2U=9.11mm
- Total of 1.3 million triggered events
- DAQ used for FPD commissioning: Nim logic and camac readout.

- LM COUNTERS  2.5<  <4.4
- VC COUNTERS  5.2<  <5.9

## DAQ USED FOR FPD COMMISIONING

- Temporary DAQ used while FPD was integrating to D0 DAQ.
- Capability for reading out one Spectrometer.

## HIT COORDINATE RECONSTRUCTION:

- We can reconstruct coordinates using the UV, UX, VX intersections  of fiber segments.
- Comparison of coordinates obtained by different intersections is useful to determine the spatial resolution of the detector.

## SELECTION OF ELASTIC EVENT CANDIDATES:

-  We required 3 reconstructed fiber segments per detector.
- Required  that reconstructed coordinates from UX and UV planes agreed within 2 standard deviations (Fiducial cut).
- Rejected events that were out of our MC expected elastic acceptance region (Acceptance cut).

| CUT | # EVENTS AFTER CUT |
| --- | --- |
|  No cut | 1,308,734 |
| Fiber multip. cut | 29,285 |
| Segments cut | 26,428 |
| Fiducial cut | 21,287 |
| Acceptance cut | 17,724 |

**SELECTION OF ELASTIC EVENT CANDIDATES:**

## FIBER MULTIPLICITY CUTS

- Majority of events recorded have multiple hits in our detectors.
- Particle showers seem to be produced in the separators located between P1 and P2.

## EVENTS  THAT SURVIVED ALL CUTS

-          D0 Preliminary

- D0 Preliminary

- D0 Preliminary

## SPATIAL RESOLUTION

**SPATIAL RESOLUTION**

- Determined from the difference between coordinates obtained from UV segment and coordinates obtained from UX segment.

- D0 Preliminary

##  ACCEPTANCE CORRECTIONS

-  covered by the PD spectrometer.
- We also determine the error in acceptance due to error in detector position.

- D0 Preliminary

##  t distribution (uncorrected)

-          D0 Preliminary

## |t| slices in each detector

- P1D

- P1D

- P2D

- P2D

## |t| range covered with the data shown here

## Can the FPD do studies of elastic events in the forward region?

- FPD could give some light about the  discrepancy between E710/E811 and CDF measurements of  total cross section:

## MC for elastic events can tell the FPD running conditions to reach lower |t| values: 

- In the forward region we simulate:

- Add Tevatron lattice and include beam emittance in the simulation.

## A possible measurement of the Total cross section?

- With beam injection lattice:

## Uncertainty on the measurement of  _TOT due to extrapolation to t=0 (50000 elastic events):  

| Position | |t|_range | Slope | _T(mb) |
| --- | --- | --- | --- |
| 8 | 0.05<|t|<0.5 | 16.91±0.08 | 0.67 |
| 9 | 0.12<|t|<0.5 | 16.74±0.12 | 1.42 |
| 10 | 0.16<|t|<0.5 | 16.98±0.17 | 2.29 |
| 11 | 0.20<|t|<0.5 | 17.10±0.17 | 2.46 |

| This error is only due to error in extrapolation. Still need to include error in the measurement of  N inelastic |
| --- |

## CONCLUSIONS

-  Proton Antiproton elastic events have been very useful to test the performance of FPD detector.
-  Analysis of elastic events recorded with the FPD in the range 0.9<|t|<1.7, during commissioning, is in a mature stage. It has proven difficult because we have fiber information from only one spectrometer.
-   After Dec. 2003 elastic triggers will have fiber information from full FPD system. FPD will be able to reach up to a |t| value of 4.5.
-  FPD detector rates have a large contribution from particle showers most likely produced in the electrostatic separators. Working with beam divisions on this issue.
-  FPD has a chance to make a new measurement of the Total cross section but requires special low luminosity store running with beam injection lattice. Only need a few hours of running to collect enough statistics.