# Presentation: 527793

## Capacitive coupling measurements.

- G. Vidal-Sitjes, J. Burguet-Castells,
- J.J. Gomez-Cadenas, A.M. Tornero Lopez.

## Reminder of the model

## Example: bidirectional cross-talk

**TPC pads, probe, DAQ**

## Signal reconstruction: phase-lock technique

**One sector analyzed**
**645 alive channels (out of 662)**

## Observation

**Huge spread of channels electronic gain**
**2.5 daughter channels per channel**
**79% of parent charge appears in other pads**
**1237 cross-talk relations (all orders)**

## Order of the cross-talk signals.

**overall:**
**first order relations => 62% of cross-talk charge**
**                                       ****65% of the parent signal charge**

## First order relations

**Map of first order relations = map of couplings**

## Relations relative position 

**ROW**

**R PHI**

**Notes:**
Also very interesting for a MC evaluation of the effect is the difference in radius, as we see here in row number units,  and in rphi, as we see here in mm,  between the parent and daughter channels. We see that typically, the daughters are next to the parent in row and in rphi. This distribution here does not peak at zero because of the geometry of the pad plane, where very seldom there is a pad just above an other one, they are almost always shifted and the value of the shift depends on the radius.  

## Number and position of the parents

**~325 clean channels**

**position of clean channels**

**Notes:**
More interesting is the number of parents that a channel has, whose distribution is here. As we see here, about 325 pads are clean, no body talks to them, and thus, signals recorded in them are not influenced by cross-talk. Even more interesting is that, very fortunately, this pare are distributed like shown in this plot here, mainly in five rows and other shorter segments allowing to reconstruct “clean” clusters in this rows and segments.
Although clearly insufficient for good efficiency and performance the study of this clusters would allow the study of the detector performances in absence of cross-talk.

## Fitting the capacities & subtracting the XT signals

**Notes:**
Finally we fit the predicted signals to the observed ones in order to fit the capacities of the couplings, whose distribution we see here. This double structure here hints two possible types of couplings. In the fits, we do not only take into account the first order signals but we also consider all possible secondary signals superposed onto the first order one. If we subtract the predicted signals to the measured ones, overall, we remove 92% of the total observed first-order cross-talk charge. The distribution of the percentage of remaining cross-talk charge after the subtraction in an event per event basis is shown here. The distribution is fitted by a gaussian with a sigma of 4.5% which is quite good, and it has a mean value at around 7%. After eye-scanning the fits we understand this 7% bias and the tails of the distribution as the result of not taking into account in the subtraction second order signals superposed onto the first order ones, however they have been taken into account when fitting the capacity. 

## Assessment of the cross-talk effect on the TPC data with a fast MC simulation.

- G. Vidal-Sitjes, J.J. Gomez-Cadenas.
- With many thanks to Lara Scotchmer and Alexander Grossheim

## rΦ resolution. ANALOG signals.

**non equalized**

**cross-talk**

**both**

**σ=0.6 mm**

**σ=1.6 mm**

**σ=1.8 mm**

## rΦ resolution. DIGITIZED data (no threshold)

**non equalized**

**cross-talk**

**both**

**σ=0.6 mm**

**σ=1.5 mm**

**σ=1.8 mm**

## Energy resolution. Analog signals.

**σ=13%**

**σ=7%**

**σ=44%**

**non equalized**

**cross-talk**

**both**

## Energy resolution. Digitized data. (no threshold)

**non equalized**
**17%**

**cross-talk**
**14%**

**all: 40%**

**digitization**
**9%**

## Summary

|  | analog | digital |
| --- | --- | --- |
| non-eq. | 0.6 mm | 0.6 mm |
| x-talk | 1.6 mm | 1.5 mm |
| non-eq.+x-talk | 1.8 | 1.8 |

|  | analog | digital |
| --- | --- | --- |
| digitization |  | 9% |
|  non-eq. | 13% | 17% |
|  x-talk. | 7% | 14% |
| non-eq.+x-talk | 44% | 40% |

**Energy**

**r****Φ**

## Conclusions

- Capacitive model applied to a full sector.
- Model describes well all data, including bidirectional and all orders cross-talk.
- Model fully specified by transfer functions (MEASURED) and by capacitances (COMPUTED)
-  92% of cross-talk reduced on this data
- 1⁄2 of the channels are clear. Assessment of performances without cross-talk ongoing.
- MC result shows that the effect is 1.5 mm in resolution and 15% in energy resolution.

## Outlook	

- Apply correction algorithm on data and MC and compare residuals and energy resolution before and after correction.
- Prepare benchmark set of data to compare the performances of existing algorithms (resolution, minimum bias, speed...).
- Choose the best combination of algorithms (require/expect close cooperation among different groups)