Elastic Data Results

Jorge Molina

DATA ANALYZEDDATA ANALYZEDThe sample analysed consisted of 31 runs taken at:P1D = 17.05 mm (8.98 ) and P2D = 13.80 mm (8.70 )

In total were used 6 cuts requiring:

● Multiplicity 1: One or zero hits in each of 12 planes (6 x detector)

● Multiplicity 2: One segment per plane

● Segment cut: must exist 3 reconstructed segments per detector, ie: all 6 segments must be nonzero

● Fiducial cut: The distance yux-yuv between intersections of segments should not exceed in 2 of the gaussian distribution

● Background cuts: events too far from the MC simulations are not considered

● Acceptance cut: only the events that reaches the region allowed by simulation were considered

EFFICIENCY OF THE CUTSEFFICIENCY OF THE CUTS

The table shows the efficiency of each cut:

Note that most of the events registered were coming together at the same time, that were cleaned by the

multiplicity cuts.

Cut # of evts that survived the cuts

% of total

- 1308734 100

Multiplicity 1 78095 5.9

Multiplicity 2 29285 2.2

Segments 26428 2.0

Fiducial 21287 1.6

Noise 18569 1.4

Aceptance 17724 1.3

RESULTSRESULTSThe events that survived all the six cuts have the

distribution:

Events are peaked at zero as expected with a resolution of = 0.01868

EVENTS SURVIVEDEVENTS SURVIVED The correlation of the events that survived all cuts are:

The hitmaps in each detector are:

P1D P2D

SPATIAL RESOLUTIONSPATIAL RESOLUTION The spatial resolution in each detector comes from the

difference between the segments considered by the intersection of the uv segments minus intersection of ux

segments.

P1D = 136 m P2D = 155 m

dN/dt SPECTRA dN/dt SPECTRA The dN/dt distribution of all events reconstructed is:

The fit shows the bins that will be considered

At higher values than 1.3 GeV2 points looks doubtful

At lower values the uncertainty in the acceptance perturbs: we avoid that effect beginning at the fifth bin

Systematic errors due to the position of the Systematic errors due to the position of the detectorsdetectors

The error in the x position were assumed to be 10% of the 3 mm offset found in previous measurements. With the 0.3 mm relative variation of the pots, data were reconstructed, corrected by the unsmearing, and found that variation is negligible.

The error in the vertical position y were determined changing the position of the pots in 0.5 mm in the calculation of the acceptance. The dN/dt spectra measured then were divided by these two values of the acceptance obtaining the errors + and - respectively.

The average error was calculated by:

m = (+ + - )/2

Then this value was added in squared with the statistical error to obtain the systematic error in the vertical position:

y = (2est + 2

m )1/2

Note that the error bars in each bin of the dN/dt spectra are determined in this way

UNSMEARINGUNSMEARINGThe dN/dt spectra obtained with the events that survived all cuts must be corrected by the factor that takes into account the resolution of the detector: fres = f(t)ideal/f(t)measured

To obtain this factor a exponential function were used as ansatz, that was convolute with a linear function that describes the variation of the resolution in |t|

The error bands shows that at bigger values of |t|, the error in the reconstruction is bigger

UNSMEARINGUNSMEARING

After the correction by fres, the slope of the exponential function that fits the points went from 3.631 to 4.015 GeV-2.

The reconstruction program pushes the events to higher values of |t|

Systematic errors due to the unsmearing processSystematic errors due to the unsmearing process

Error in the smearing process comes from the determination of the parameters of the straight function t = m.t + n that describes the change in the resolution with |t|.

With the uncertainty m, the unsmearing process were repeated changing the parameter m by (m + m) to obtain the new value for the slope bm. The difference m = b – bm was considered the systematic error due to the parameter m.

The same procedure were repeated for the parameter n to obtain the error n = b – bn .

Contribution Contribution y to the error in the slopeto the error in the slope

The contribution of the uncertainty in the vertical position to the final error were calculated in the same way that the uncertainties m and n. The spectra dN/dt measured were divided by the acceptance changed in +0.5 mm, then unsmeared and obtained the new slope by, which difference with b gives the term y = by – b that will contribute to the final error.

The final error in the slope b is calculated through:

Final error in the slope bFinal error in the slope b

193.02222 ynmest

Where each term contributes to the final error in:

Uncertainty Contribution (%)

est 21.3

m 29.0

n 24.2

y 25.5

Finally the slope found is:

2193.0015.4 GeVb

COMPARISON WITH ANOTHER EXPERIMENTS COMPARISON WITH ANOTHER EXPERIMENTS The points corrected by the unsmearing procedure were

normalized by the points obtained by the E710 experiment (which agrees with CDF for dN/dt in the determination of

the slope b at low |t|).

The results are in excellent agreement with the model of M. Bloch showed in the figure

Warning: error bars needs thecontribution of the unsmearing errors In progress

BEAM STUDIES BY RAW EVENTS BEAM STUDIES BY RAW EVENTS

The x fibers (vertical ones) can be a tool to study the beam behaviour.

Looking at the distributions before and after multiplicity cuts reveals that in P1D are coming more particles at the left side (they must be rotated 180° for PD).

PARTICLES AT P2DPARTICLES AT P2DFor P2D the situation is more critical. The difference among the last fibers compared with the rest is much

bigger.

The multiplicity cuts cleaned up all the excess of events.

It means that the big majority of events recorded has two or more particles crossing the detector at the same time.

Measurements based in the timing revealed already that particles are being produced in the separator, may be due to beam-gas scattering or to the misalignment of the beam that are hitting somewhere in the middle between P1 and P2

Studying the hitmaps in both detectors in slices of |t| we have:

BEAM STUDIES BY RECONSTRUTED EVENTSBEAM STUDIES BY RECONSTRUTED EVENTS

We suspect since ~1.2

● Events in the | t | range

+ Total of events survived

Starting at |t|~1.2 GeV2 ellipses begins to look distorted. This is most evident in P2D, although we can

see in P1D the same effect, but more reduced.

+ Total of events survived

● Events in the | t | range

1) Proton antiproton elastic scattering was measured by the D0 Roman Pots.

2) Elastic data samples contain diffractive and halo backgrounds, most of which were removed by simple cuts.

3) The four momentum transfer range considered in the analysis were limited to the region

0.96 < |t| < 1.3 GeV2.

4) Data are well fitted by an exponential form, with the slope corrected by the unsmearing procedure which used a exponential as ansatz function.

5) The first measurement of the dN/dt slope in the region analysed, at c.m.s. energy of s = 1.96 TeV gave the result:

b = 4.015 0.193 GeV-2

CONCLUSIONSCONCLUSIONS

6) The error in the measurement are mostly dominated by the uncertainty in the determination of the resolution in the reconstruction of the trajectories.

7) The result of the slope found is in good agreement with the phenomenological model of M. Bloch based in measurements made by experiments E710 and CDF at

s = 1.8 TeV.

8) Was proposed a possible explanation for the behaviour of the beam, specially in the region

|t| > 1.3 GeV2.

9) Both detectors, P1D and P2D registered an excess of events in the outer part (relative to the centre of the Tevatron), most of which were cleaned by multiplicity cuts.