__________________________________C. Avila, small x workshop, Sep. 17 2003

ELASTIC SCATTERING IN D0 EXPERIMENT

Carlos AvilaUniversidad de Los Andes

Bogota, Colombia

__________________________________C. Avila, small x workshop, Sep. 17 2003

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.

__________________________________C. Avila, small x workshop, Sep. 17 2003

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

__________________________________C. Avila, small x workshop, Sep. 17 2003

DAQ USED FOR FPD COMMISIONING

Temporary DAQ used while FPD was integrating to D0 DAQ.

Capability for reading out one Spectrometer.

__________________________________C. Avila, small x workshop, Sep. 17 2003

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.

__________________________________C. Avila, small x workshop, Sep. 17 2003

1. Events were rejected if there was a fiber plane with multiple hits.

2. We required 3 reconstructed fiber segments per detector.

3. Required that reconstructed coordinates from UX and UV planes agreed within 2 standard deviations (Fiducial cut).

4. 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:

__________________________________C. Avila, small x workshop, Sep. 17 2003

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.

__________________________________C. Avila, small x workshop, Sep. 17 2003

EVENTS THAT SURVIVED ALL CUTS

D0 Preliminary D0 Preliminary

D0 Preliminary

__________________________________C. Avila, small x workshop, Sep. 17 2003

SPATIAL RESOLUTIONDetermined from the difference between coordinates obtained from UV segment and coordinates obtained from UX segment.

D0 Preliminary

__________________________________C. Avila, small x workshop, Sep. 17 2003

ACCEPTANCE CORRECTIONS

covered by the PD spectrometer.

We also determine the error in acceptance due to error in detector position.

D0 Preliminary

__________________________________C. Avila, small x workshop, Sep. 17 2003

t distribution (uncorrected)

D0 Preliminary

__________________________________C. Avila, small x workshop, Sep. 17 2003

|t| slices in each detector

P1D P1D P2DP2D

__________________________________C. Avila, small x workshop, Sep. 17 2003

|t| range covered with the data shown here

__________________________________C. Avila, small x workshop, Sep. 17 2003

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:

__________________________________C. Avila, small x workshop, Sep. 17 2003

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

In the forward region we simulate:

dtd

dtd

dtd

dtd ncnc

)exp(16

)1(

)2

exp()()(

)(4

22

2

2

42

tBdtd

tBt

tGtdtd

ttG

dtd

Tn

Tcn

c

Add Tevatron lattice and include beam emittance in the simulation.

__________________________________C. Avila, small x workshop, Sep. 17 2003

A possible measurement of the Total cross section?

inelelt

nT NNdt

dN

1116

02

With beam injection lattice:

__________________________________C. Avila, small x workshop, Sep. 17 2003

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

__________________________________C. Avila, small x workshop, Sep. 17 2003

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.