# Presentation: 336651

## Elastic Data Results

**Jorge Molina**

## The sample analysed consisted of 31 runs taken at:

**The 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**

## The table shows the efficiency of each cut: 

**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 |

## The events that survived all the six cuts have the   distribution:

**The events that survived all the six cuts have the ********  distribution****:**

- 

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

## The correlation of the events that survived all cuts are:

**The correlation of the events that survived all cuts are:**

**The hitmaps in each detector are:**

- P1D

- P2D

## P1D = 136 m

**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**

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

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

**The fit shows the bins that will be considered **
**At higher values than 1.3 GeV****2**** points looks doubtful**
**At lower values the uncertainty in the acceptance perturbs: we avoid that effect beginning at the fifth bin**

## 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 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 + 2m )1/2

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

## The 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 

**The 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: f****res ****= 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**

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

**After the correction by f****res****, 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|**

## 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 .

- 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:

- 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:

## 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 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 the
- contribution of the unsmearing errors  In progress

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

**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).**

## For P2D the situation is more critical. The difference among the last fibers compared with the rest is much bigger.  

**For 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**

## We suspect since ~1.2

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

- We suspect since ~1.2

-  Events in the | t | range

- + Total of events survived

## + Total of events survived

**Starting at |t|~1.2 GeV****2**** 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 GeV****2****. **
**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**

## 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 GeV****2****. **
**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.**