CDC 09 04 2008

125 MHz Clock test

A scope trace can say more than a 1000 words:

figure 1: Output of the 125 MHz clock.

Everything is set up to run with the external clock.

Change incident angle

Before we had the two scintillators positioned one above the other. In this way we selected cosmic rays with an incident angle of 90 degrees (compared to the straws). The upper scintillator is placed on the other end of the CDC: 2m away (in z) from the other scintillator. Before we had a rate of 0.65 Hz. I calculated the incident angle to be 17 degrees, which means that we expect a rate of 0.0556 Hz. We see a rate of 0.0767 Hz - that would mean a average incident angle of 20 degrees. I will take data till the new cable arrives (Wednesday) and then analyze the data and compare with previous situation.

FYI: we could tilt the chamber to any angle we want - we just have to be careful.

More analysis of cosmic data

The preAmp is not at Carnegie Mellon University - so I have some time to do some more analysis. I will always show two figures, on the left side is always with the cosmic rays at 90 degrees, the right side has the cosmic rays at 20 degrees (on average).

Let's start with the raw energy spectrum of straw 15

figure 1a: Raw energy spectrum of straw 15 (90 degree cosmic rays).

figure 1b: Raw energy spectrum of straw 15 (20 degree cosmic rays).

Everything below 1750 ADC channels is considered low energy noise and is therefore cut away. The resulting energy spectra are in figure 2a+b.

figure 2a: Energy spectrum of straw 15 (90 degree cosmic rays).

figure 2b: Energy spectrum of straw 15 (20 degree cosmic rays).

You see the funny structure in the end -> it does not changes with the incident angle of the cosmic rays => No physics in this thing.

Now what about the amplitude spectrum of ch 15, it is shown in figure 3 and 4 (without - with energy cut): The preAmp is not at Carnegie Mellon University - so I have some time to do some more analysis. I will always show two figures, on the left side is always with the cosmic rays at 90 degrees, the right side has the cosmic rays at 20 degrees (on average).

Let's start with the raw energy spectrum of straw 15

figure 3a: Raw amplitude spectrum of straw 15 (90 degree cosmic rays).

figure 3b: Raw amplitude spectrum of straw 15 (20 degree cosmic rays).

figure 3a: Amplitude spectrum of straw 15 (90 degree cosmic rays).

figure 3b: Amplitude spectrum of straw 15 (20 degree cosmic rays).

There are two thing important here:

• There is a funny peak again that does not change when the incident angle changes - this is a problem when calculation overflows/total events (later more)
• The amplitude spectrum disappears when going to 20 degrees incident angle

The ratio overflows (amplitude) / total number of events:

• 0.0357 for 90 degree cosmic rays
• 0.0153 for 20 degree cosmic rays

What about the Energy as a function of amplitude spectra => is this funny structure correlated? Those are shown in figure 4a-b:

figure 4a: Energy vs amplitude of straw 15 (90 degree cosmic rays).

figure 4b: Energy vs amplitude of straw 15 (20 degree cosmic rays).

This funny structure is correlated!!! --> Is this the preAmp that clips?

Let's go on - How do the drift time spectra look like? THey are shown in figure 5a-b

figure 5a: Drift time straw 15 (90 degree cosmic rays).

figure 5b: Drift time of straw 15 (20 degree cosmic rays).

Let's zoom in (figure 6a-b):

figure 6a: Close up of drift time straw 15 (90 degree cosmic rays).

figure 6b: Close up of drift time of straw 15 (20 degree cosmic rays).

One can see a peaked structure in the right side and the same structure on top of the time spectrum shown in the left side. I wonder if this again is correlated with the funny structure before.

As last figure I would like to show the drift time spectrum of the overflow events. They are shown in figure 7a-b:

figure 7a: Drift time of overflows of straw 15 (90 degree cosmic rays).

figure 7b: Drift time of overflows of straw 15 (20 degree cosmic rays).

These overflows contain real events!