Particle identification plays a crucial role in the study of isospin dynamics, and several identification techniques have been developed in the last decades. Amongst them, the pulse shape analysis methods allow to identify those

fragments that are fully stopped in a single detector layer by studying the shape of the signal induced by the impinging fragment. The correlation of the maximum of

the induced current signal with the energy of the fragment is known to give a good isotopic identification, but requires to acquire the current signal. However, when

the current signal isn’t available, it can be reconstructed from the digitized charge signal. The algorithms used for the reconstruction are presented briefly along with the first results obtained during the DIGIGARF experiment at LNL

Barlini, S.

Bini, M.

Bruno, M.

Ottanelli, P.

Pasquali, G.

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2019-19065-2Colloquia: EuNPC 2018IL NUOVO CIMENTO 42 C (2019) 65Particle identification using current maximum obtainedfrom chargeFirst results of the DIGIGARF experimentP. Ottanelli(1)(2), G. Pasquali(1)(2), M. Bini(1)(2), S. Barlini(1)(2),M. Bruno(3)(4), A. Buccola(1)(2), A. Camaiani(1)(2), G. Casini(1),C. Ciampi(1)(2), M. Cicerchia(5)(6), M. Cinausero(5), D. Dell’Aquila(7),D. Fabris(8), L. Francalanza(9)(10) C. Frosin(1)(2), F. Gramegna(5),I. Lombardo(11), G. Mantovani(5)(6), T. Marchi(5), S. Meneghini(3),L. Morelli(3)(4)(∗), A. Olmi(1)(2), G. Pastore(1)(2), G. Poggi(1)(2),A. A. Stefanini(1)(2), S. Valdré(1)(2), G. Verde(11) and M. Vigilante(9)(10)(1) INFN, Sezione di Firenze - Firenze, Italy(2) Dipartimento di Fisica, Università di Firenze - Firenze, Italy(3) INFN, Sezione di Bologna - Bologna, Italy(4) Dipartimento di Fisica, Università di Bologna - Bologna, Italy(5) INFN, Laboratori Nazionali di Legnaro - Padova, Italy(6) Dipartimento di Fisica, Università di Padova - Padova, Italy(7) NSCL, MSU - East Lansing, MI 48824, USA(8) INFN, Sezione di Padova - Padova, Italy(9) Dipartimento di Fisica, Università di Napoli “Federico II” - Napoli, Italy(10) INFN, Sezione di Napoli - Napoli, Italy(11) INFN, Sezione di Catania - Catania, Italyreceived 5 February 2019Summary. — Particle identification plays a crucial role in the study of isospindynamics, and several identification techniques have been developed in the lastdecades. Amongst them, the pulse shape analysis methods allow to identify thosefragments that are fully stopped in a single detector layer by studying the shape ofthe signal induced by the impinging fragment. The correlation of the maximum ofthe induced current signal with the energy of the fragment is known to give a goodisotopic identification, but requires to acquire the current signal. However, whenthe current signal isn’t available, it can be reconstructed from the digitized chargesignal. The algorithms used for the reconstruction are presented briefly along withthe first results obtained during the DIGIGARF experiment at LNL.(∗) Present address: GANIL, CEA/DRFCNRS/IN2P3, 14076 Caen, FranceCreative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 P. OTTANELLI et al.1. – The Garfield+RCo apparatusThe GARFIELD+RCo apparatus ( [1] and references therein) is a 4π apparatus forcharged particle detection and identification hosted in the third experimental hall atLegnaro National Laboratories of INFN. The apparatus is managed by the NUCL EXcollaboration, which is also involved in the FAZIA project ( [2] and references therein).The RingCounter (RCo from now on) is a three stage telescope placed at forward angles(5◦ < θ < 17◦). The first stage is a Ionization Chamber (IC), it is followed by a layerof 300μm silicon (Si) strip detectors and by CsI(Tl) scintillators (45mm thick). Thesilicon layer is made up of 8 pie-shaped Si pads (sectors), each divided in 8 annularstrips. Fragments that are stopped inside the Si layer can be identified in charge usingthe standard ΔE−E technique applied to the IC and the Si layerBruno. To achieve massidentification, the pulse shape analysis methods (PSA from now on) are used. Duringthe R&D phase, the FAZIA collaboration has tested two PSA methods, based on the twocorrelations “Energy vs Charge rise time” (Qrise from now on) and “Energy vs Currentmaximum” (Imax), showing that the latter has better performances in terms of isotopicidentification [3]. However, up to now the RCo apparatus was capable of exploiting onlythe Qrise method, since the Imax requires to acquire the current signal which is notdirectly measured by the apparatus.The readout electronic of RCo is fully digital, and each detector is read by a dedicatedfront-end channel. The front-end electronics is currently being upgraded, and the oldchannels, which have a 12-bit ADC and a DSP for signal processing [4], will be replaced.The new front-end channels have a 14-bit ADC (hence a higher precision of the digitalelectronics) and are equipped with a FPGA [5] for advanced signal processing.2. – Current maximum extractionWe have developed an algorithm for the extraction of the current maximum from thecharge signal. The first step of the extraction algorithm is the interpolation of the chargesignal using the “Smoothing Spline” method [6-9](1) to obtain an interpolated (continu-ous) charge signal. The second step is the differentiation and sampling of the interpolatedcharge signal that produces a sampled reconstruction of the current signal, from whichthe maximum is extracted. Both steps can be implemented with good approximationin terms of finite impulse response linear filters. They have been implemented on theFPGA of the new RCo digitizers, so that only the Imax value is transmitted to the ac-quisition system and not the full digitized signal, thus greatly reducing the needed datathroughput.3. – First Results of the DIGIGARF experimentTo test the new electronic board and the algorithms for the extraction of the currentmaximum we studied the reaction 16O + 12,13C at 107 MeV/nucleon with the RCodetector at LNL (DIGIGARF experiment - april/may 2018). The signals coming from thesilicon layer of RCo have been acquired with both the old and new front-end electronics(1) Smoothing spline interpolation is similar to cubic spline interpolation. The only differenceis the introduction of a smoothing effect that reduces interpolation artefacts and filters out highfrequencies. At variance with proper interpolation, the resulting signal is not constrained topass through the original samples.PARTICLE IDENTIFICATION USING CURRENT MAXIMUM OBTAINED FROM CHARGE 30 20 40 60 80 100 120Rise TIme [ns]020406080100120Si Energy [A.U.]0100200300400500600700a) Rise Time PSA (old board, 12-bits)0 20 40 60 80 100 120Rise Time [ns]020406080100120Si Energy [A.U.]0100200300400500600b) Rise Time PSA (new board, 14-bits)0 50000000Imax [A.U.]020406080100120Si Energy [A.U.]0100200300400500c) Imax PSA (new board, 14-bits)Fig. 1. – The three PSA plots used for the comparison. In (a) the rise-time vs energy correlationobtained with the old FEE board, in (b) the same correlation with the data from the new FEEand in (c) the new Imax-Energy correlation. In all the plots the16O elastic scattering is evidentand the regions associated with Z = 5, 6, 7 can be easily identified.50 55 60 65 70PI0100200300400500countsa) Rise Time PSA (12-bit old board)50 55 60 65 70PI0100200300400500600countsb) Rise Time PSA (14-bit new board)50 55 60 65 70PI0100200300400500600countsc) Maximum current PSA (14-bit new board)Fig. 2. – PI distributions obtained by linearization of the three plots in fig. 1. The isotopes ofBoron (leftmost peaks in each plot), Carbon (middle peaks) and Nitrogen (rightmost peaks) areseparated in all the three plots. Since there is no qualitative difference between them a morequantitative approach is needed to compare the performances of the three methods.5 5.5 6 6.5 7Z0.70.80.911.11.2FoM Rise Time (old)Rise Time (new)Imax (new)FoM of two main peaksFig. 3. – FoM values obtained from the PI distributions in fig. 2. For each element the twomost populated isotopes are considered. The FoM values are presented in table I. The pointsare shifted along the x-axis to make error bars more readable.4 P. OTTANELLI et al.Table I. – The FoM values for the two most intense isotopic peaks of Boron, Carbon andNitrogen, obtained by fitting the PI distributions in fig. 2 with a bi-gaussian fit. The errors onthe fit parameters are assumed to be independent and are propagated to the FoM.Rise Time PSA (old) Rise Time PSA (new) Imax PSA (new)10,11B 0.97 ± 0.09 1.11 ± 0.12 1.12 ± 0.1112,13C 0.84 ± 0.04 0.97 ± 0.04 0.97 ± 0.0413,14N 0.73 ± 0.05 0.74 ± 0.04 0.82 ± 0.05in order to allow a full comparison of the different identification methods. To take intoaccount also the effect of the increased digital precision, the Qrise PSA plot obtainedwith the old electronic board is taken as a reference. For the comparison of the threePSA methods the data coming from the best performing Si detector (Strip 4, sector 1)are used in order to reduce the contribution of the detector to the isotopic resolution,and the three plots of fig. 1 are obtained.The linearization procedure described in [10] is used to assign to each detected frag-ment a Particle Identification (PI) number, so that all the fragments that are placed nearthe same ridge of the plot are assigned similar PI values. The outcome of the linearizationof the three plots of fig. 1 is presented in fig. 2, where the peaks corresponding to theisotopes of B, C, and N are evident. The separation between adjacent peaks is estimatedusing the FoM parameter [11], which for two gaussian peaks is defined as:FoM =|C1 − C2|2.35(σ1 − σ2)(1)where C1 and C2 represent the centroids and σ1 and σ2 the standard deviations of the twopeaks. The higher the FoM, the better is the peak separation The FoM values obtainedfor the two most intense peak for B, C, N are presented in table I and fig.3. ConsideringBoron and Carbon isotopes, the FoM increases when using data collected with the newelectronic board, suggesting that this increment is due to the higher precision of theADC. On the other hand, for Nitrogen the FoM increases when using the Imax method,in agreement with published results [3]. The obtained results are very preliminary, andfurther measurements exploiting better performing silicon detectors (such as the FAZIAones) will be a stricter test of the performances of our algorithm for current maximumextraction.REFERENCES[1] Bruno M. et al., Eur. Phys. J. A, 49 (2013) 128;[2] Bougault R. et al., Eur. Phys. J. A, 50 (2014) 1;[3] Pasquali G. et al., Eur. Phys. J. A, 50 (2014) 86;[4] Pasquali G. et al., Nucl. Instr. Meth. A, 570 (2007) 126;[5] Altera, Cyclone III manual https://www.altera.com/products/fpga/cyclone-series/cyclone-iii/support.html[6] Unser M. et al., IEEE TSP, 41 (1993) 821;[7] Unser M. et al., IEEE TSP, 41 (1993) 834;[8] Pastore G. et al., Nucl. Instr. Meth. A, 860 (2017) 42;[9] Reinsch C. H., Numerische Mathematik, 10 (1967) 177;[10] Bardelli L. et al., Nucl. Instr. Meth. A, 654 (2011) 272;[11] Winyard R.A. et al., Nucl. Instr. and Meth., 95 (1971) 141;

Particle identification using current maximum obtained

from charge

http://eprints.bice.rm.cnr.it/20447/1/ncc11805%20%281%29.pdf

Particle identification using current maximum obtained from charge

Abstract

Similar works

Full text

Available Versions

Scientific Open-access Literature Archive and Repository