Alberto A. Colavita, INFN, TS Compass Upgrade proposal for the RICH1 electronics. A simple and rapidly executable way of partially getting rid of Halo events, using correlation functions, as if they were noise. Alberto A. Colavita, INFN, TS 11/30/2018 CSN1 - Lecce 23/09/2003

Showing the “noise” in the central region of the RICH1. 11/30/2018 CSN1 - Lecce 23/09/2003

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Schematic view of the classical architecture of the presently installed front-end 11/30/2018 CSN1 - Lecce 23/09/2003

The shape of a “normal” signal of an event. An artist’s rendition. 11/30/2018 CSN1 - Lecce 23/09/2003

Halo event, starting at t0 < 0 An artist’s rendition. 11/30/2018 CSN1 - Lecce 23/09/2003

Halo event starting at 1 ms > t0 >0 An artist’s rendition. 11/30/2018 CSN1 - Lecce 23/09/2003

What separates Halo events from good events ? The only discriminating parameter is the “time history” of the signal. We need to memorize the past, before the trigger, and part of the future after the trigger. 11/30/2018 CSN1 - Lecce 23/09/2003

What it takes to Upgrade the Four Half Chambers 60 BORAs comprising ~ 21000 pixels (chamber pads). To save the history of the signal we need to buffer at least ~ 1024 samples per signal/channel. If we samples every ~ 100 ns we preserve the last 102 ms of the signal. We need processing power in order to identify the Halo events from good events. 11/30/2018 CSN1 - Lecce 23/09/2003

To see the time history of the signal I need a new version of the Gassiplex front-end chip and of the general architecture !!!! Because we have little time to waste, we introduced simple modifications in order to meet IMEC’s September 15th prototyping run. 11/30/2018 CSN1 - Lecce 23/09/2003

New Version of Gassiplex (a) The new chip allows us to track simultaneously all 16 analog channels. The new Gassiplex can be described as a 16_IN – 16_OUT front-end chip. 11/30/2018 CSN1 - Lecce 23/09/2003

New Version of Gassiplex (b) The overall final gain is 5 times larger than in the present Gassiplex in order to allow a larger range of ADC division to be used. The peaking time was reduced to 500 ns in order to have the best possible S/N ratio and to increase the time resolution of the front-end. 11/30/2018 CSN1 - Lecce 23/09/2003

Why 8-bits are enough 11/30/2018 CSN1 - Lecce 23/09/2003

The new architecture 11/30/2018 CSN1 - Lecce 23/09/2003

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Strategy for local data treatment Sample every ~100 ns, place the two 8-bit results into a circular buffer of at least 1024 bytes/channel deep (storing ~100 ms of the signal). The BF531 DSP handles circular buffers using internal hardware. The DSP uses DMA to retrieve the samples from the ADCs, freeing core cycles. 11/30/2018 CSN1 - Lecce 23/09/2003

Algorithmic Procedure (a) When the trigger arrives, read the “write- pointer” of the circular buffer. Calculate the correlation of the experimental points with the 10-15 points describing the “pure” signal. The calculation starts from the oldest sample, in order to eventually wait for the future samples to arrive to the buffer. Find the peak of the correlations discriminating if it is large enough and in the right position in time. 11/30/2018 CSN1 - Lecce 23/09/2003

Algorithmic Procedure (b) If the peak is at the right (correct) place in time, fit the pure signal to the data points in order to find a better peak value than that furnished by the ADC. Then, write the event in an output buffer together with the channel ID. 11/30/2018 CSN1 - Lecce 23/09/2003

Showing the procedure 11/30/2018 CSN1 - Lecce 23/09/2003

The procedure behind the simulations We generate a Gaussian-noise background every time we need it. We have a “pure” signal described by a set of values {xi} of peak height = 1. In general the height is denoted by h. We calculate the correlation between the pure signal and the noise background. The sigma of the correlation is used to evaluate the visibility of a buried signal. We define S/N = h / snoise 11/30/2018 CSN1 - Lecce 23/09/2003

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Correlation of the “pure” signal with a signal buried in noise. The new detection method consist in comparing the peak of correlation between “pure” and buried signal with the sigma of the correlation between the “pure” signal and the random Gaussian-noise background. For example: is the peak larger than 2.5 or 3 * sigma (pure – Gaussian noise) ? 11/30/2018 CSN1 - Lecce 23/09/2003

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Simulations 11/30/2018 CSN1 - Lecce 23/09/2003

How do we detect a buried signal with the new correlation method ? We compute the correlation with a “pure” signal. We then locate the peak and ask is the peak is located in the 3 points centered around the proper peaking time. Then, we ask is the peak high enough? If YES to both questions we have a signal in time and contrast. 11/30/2018 CSN1 - Lecce 23/09/2003

How do we detect a buried signal with the classical correlation method ? I bury a “pure” signal in noise with a certain S/N ratio. We look at the value of the buried signal at the time it should peak. We ask if the value at peaking time is larger than, let’s say, 2.5 sigma-noise. If YES to the question we have a signal in “contrast”. 11/30/2018 CSN1 - Lecce 23/09/2003

Signal starts at t=0, then maximum is at the correct peaking time. correlation 0 % 0 % 0.6 % 0.6% Rich_now 11/30/2018 CSN1 - Lecce 23/09/2003

Sensitive of the correlation method with respect to Halo (off-time) signals. We add a “pure” signal, with a give S/N, to the Gaussian-noise starting at time t0 (- 3000 – 1000 ns). We ask if the peak of the correlation is at the right position and if the correlation is large enough. 11/30/2018 CSN1 - Lecce 23/09/2003

Sensitivity of the classical method with respect to Halo signals. We add a “pure” signal, with a give S/N, to the Gaussian-noise starting at time t0 (from -3000 to + 1000 ns). We analyze the sample at the “proper” peaking time of the buried signal. Decision is always the same, is the signal larger than 2.5 sigma-noise. 11/30/2018 CSN1 - Lecce 23/09/2003

0 % 0.6 % 11/30/2018 CSN1 - Lecce 23/09/2003

23 % 1.2% 2% ~ 100 ns 11/30/2018 CSN1 - Lecce 23/09/2003

Fitting the “pure” to the experimental values. 11/30/2018 CSN1 - Lecce 23/09/2003

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Precision Improvement obtained by fitting 38 % 13% Not enough statistics 11/30/2018 CSN1 - Lecce 23/09/2003

Counting Cycles of the DSPs 11/30/2018 CSN1 - Lecce 23/09/2003

Total cycle count: correlation and fitting. 2319 cycles, add 50% just in case for A safe total of 3500 cycles = 1.7 ns x 3500 = 5.95 ms ( 600 MHz, 25 U$ DSP) = 2.5 ns x 3500 = 8.75 ms (400 MHz, 8 U$ DSP) 11/30/2018 CSN1 - Lecce 23/09/2003

Status 11/30/2018 CSN1 - Lecce 23/09/2003

New Gassiplex to be delivered end of November, beginning of December. Algorithm almost finished. Front-tend control software, finished. Schematic 15 days to be finished. Layout finished 30%. 11/30/2018 CSN1 - Lecce 23/09/2003

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Schematic 11/30/2018 CSN1 - Lecce 23/09/2003

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