Measurement of cross-counter leader fractions in an 18NM64: Detecting single and multiple atmospheric secondaries Alejandro Sáiz, 1 Warit Mitthumsiri, 1 David Ruffolo, 1 Paul Evenson, 2 and Tanin Nutaro 3 1 Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400, Thailand 2 Bartol Research Institute, University of Delaware, Newark, DE 19716, USA 3 Department of Physics, Faculty of Science, Ubon Ratchathani University, Ubon Ratchathani 34190, Thailand July 18, 2017 Alejandro Sáiz Cross-counter leader fractions ICRC2017, July 18, 2017 1 / 12
Outline Introduction Neutron Monitors The Princess Sirindhorn Neutron Monitor The Leader Fraction L Cross-counter Leader Fractions Absolute times and cross-counter distributions Cross-counter leader fraction and counter separation Discussion Summary and Conclusions Alejandro Sáiz Cross-counter leader fractions ICRC2017, July 18, 2017 2 / 12
Introduction Neutron Monitors Neutron Monitors ◮ Cosmic rays produce cascades of secondary particles on Earth’s atmosphere ◮ If energetic enough, secondary particles reach ground level ◮ Neutron monitors measure atmospheric neutrons from cosmic ray cascades Alejandro Sáiz Cross-counter leader fractions ICRC2017, July 18, 2017 3 / 12
Introduction The Princess Sirindhorn Neutron Monitor The Princess Sirindhorn Neutron Monitor (PSNM) ◮ PSNM operates since late 2007 ◮ Location: Doi Inthanon, Chiang Mai province, Thailand ◮ Altitude: 2560 m above sea level ◮ High vertical cutoff rigidity (16.8 GV) Alejandro Sáiz Cross-counter leader fractions ICRC2017, July 18, 2017 4 / 12
Introduction The Princess Sirindhorn Neutron Monitor PSNM is a standard 18-NM64: ◮ 18 proportional counter tubes ( 10 BF 3 gas) on a continuos row ◮ 30 tons of Pb as neutron producer ◮ Polyethylene neutron reflector and moderators One atmospheric neutron interacts with a Pb nucleus producing more neutrons, which are moderated by the polyethylene and finally detected in the proportional counters through: → 4 He + 7 Li * . n + 10 B − − Alejandro Sáiz Cross-counter leader fractions ICRC2017, July 18, 2017 5 / 12
Introduction The Leader Fraction L Neutron time delays 1000 (a) The neutron monitor data acquisition system 100 records time delays between successive neu- tron counts -1 ) n (s 10 ◮ Long time delays: counts from independent atmospheric neutrons 1 ◮ Short time delays: mostly from neutrons produced from the same Pb 0 20 40 60 80 100 120 140 nucleus = ⇒ information about cosmic t (ms) (b) 1000 ray energy 8 6 ◮ Cosmic rays with higher energy 5 4 3 produce higher energy atmospheric 2 neutrons -1 ) n (s 100 ◮ Neutrons with higher energy produce 8 dead time 6 larger numbers of neutrons in the Pb 5 4 ◮ Multiple neutrons produced together 3 2 in the Pb show short time delays 10 0.0 0.5 1.0 1.5 2.0 t (ms) Alejandro Sáiz Cross-counter leader fractions ICRC2017, July 18, 2017 6 / 12
Introduction The Leader Fraction L Leader fraction L Relevant parameter: the leader fraction L . ◮ Can be extracted from time delay histogram ◮ A “leader” is a count that did not follow a previous count ◮ L interpreted as the ratio between the number of atmospheric particles that produced at least one count, and the total number of counts ◮ Therefore L ≤ 1 ◮ L contains information about cosmic ray energy L normally defined as “same-counter” leader fraction ◮ It does not include correlations in nearby counters ◮ It may include some correlation of different atmospheric secondaries from the same CR primary ◮ In this work we study cross-counter time correlations (preliminary results) Long-term variations in L since late 2007 presented in the poster session Alejandro Sáiz Cross-counter leader fractions ICRC2017, July 18, 2017 7 / 12
Introduction The Leader Fraction L Figure: Leader fraction L and count rate C at PSNM since late 2007 (Banglieng et al, this conference). Alejandro Sáiz Cross-counter leader fractions ICRC2017, July 18, 2017 8 / 12
Cross-counter Leader Fractions Absolute times and cross-counter distributions ) -1 Cross-counter time delays N (ms =1 ∆ Long-time histogram =2 ∆ Short-time histogram ∆ =3 Long-time fit ∆ =10 =17 ◮ Definition of absolute times: Fit ∆ 9 10 individual oscillator sequence times to GPS time. Accuracy ∼ ± 3 µs ◮ Smaller dead-time effect 8 10 ◮ Distributions can be constructed for any ordered pair of counters ◮ For simplicity, we accumulate all counter combinations at the 7 same separation ∆ 10 0 2 4 6 8 10 ◮ Fit to the exponential “tail” t (ms) gives cross-counter leader Figure: Unnormalized distributions of fractions L ∆ cross-counter time delays t at counter separation ∆ of 1, 2, 3, 10, and 17. Each histogram represents ∼ 2600 h of data. Alejandro Sáiz Cross-counter leader fractions ICRC2017, July 18, 2017 9 / 12
Cross-counter Leader Fractions Cross-counter leader fraction and counter separation Cross-counter leader fraction L ∆ as a function of ∆ ∆ L 1 0.95 0.9 0.85 0.8 0 2 4 6 8 10 12 14 16 18 ∆ L ∆ increases with ∆ but never reaches L ∆ = 1 (no correlation). A value ∼ 0 . 997 seems independent of ∆ for counter separation > 5. Alejandro Sáiz Cross-counter leader fractions ICRC2017, July 18, 2017 10 / 12
Discussion Interpretation of a constant L ∆ � = 1 ◮ Time correlations in distant counters probably from correlated atmospheric secondaries produced by the same CR primary ⇒ “atmospheric leader fraction” in a counter pair ∼ 0 . 997 ◮ Total secondary leader fraction for the whole monitor: 0 . 997 18 ∼ 0 . 953 ◮ Monte Carlo simulations of independent atmospheric secondaries does not show significant cross-counter correlations (P.-S. Mangeard, private communication): Neutron, 10MeV, ZEN=0, AZI=0 Neutron, 10MeV, ZEN=0, AZI=0 Neutron, 100MeV, ZEN=0, AZI=0 Neutron, 100MeV, ZEN=0, AZI=0 Neutron, 1GeV, ZEN=0, AZI=0 Neutron, 1GeV, ZEN=0, AZI=0 Tube Tube Tube 18 18 18 10 4 16 16 16 3 10 3 10 14 14 14 3 10 12 12 12 2 10 10 10 10 2 10 2 10 8 8 8 6 6 6 10 10 10 4 4 4 2 2 2 0 1 0 1 0 1 0 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14 16 18 Tube Tube Tube ◮ Bare counters in PSNM station (no Pb, no reflector) show same-counter L between 0.996 and 0.998 ⇒ Bares measure atmospheric leader fraction? Alejandro Sáiz Cross-counter leader fractions ICRC2017, July 18, 2017 11 / 12
Summary and Conclusions Summary and Conclusions ◮ In previous work, we succeeded relating same-counter time delays with variations in CR spectrum ◮ Here we implement an absolute timing system for cross-counter time delay analysis ◮ Correlations between distant counters consistent with multiple atmospheric secondaries from the same CR primary ◮ We estimate the secondary leader fraction ∼ 0 . 953, which gives a secondary multiplicity of ∼ 1 . 049 ◮ Variations due to solar effects still under study Thank you for your attention Alejandro Sáiz Cross-counter leader fractions ICRC2017, July 18, 2017 12 / 12
Summary and Conclusions Chance coincidences R ( t ) is the probability of time delay ≥ t for a neutron count in one counter tube ◮ n ( t ) is the probability density function: n ( t ) ≡ − d R / d t ◮ α is the probability per unit time of having a new count If all the counts were independent: d R d R = e − α t d t = − α R , or d t ln R = − α , so and n = α e − α t = ⇒ a straight line in a log-linear plot of n ( t ) Alejandro Sáiz Cross-counter leader fractions ICRC2017, July 18, 2017 13 / 12
Summary and Conclusions Following counts Short time delays are dominated by counts of neutrons produced from the same Pb nucleus = ⇒ “following” counts ◮ Total distribution is not the sum of follower distribution and chance coincidences: distributions are not independent! ◮ Distribution of chance coincidences gets affected by followers, and vice versa The “conventional” way to estimate following counts: ◮ Number of counts during a short time window: multiplicity ◮ Contaminated by chance coincidences Alejandro Sáiz Cross-counter leader fractions ICRC2017, July 18, 2017 14 / 12
Summary and Conclusions Leader fraction If β ( t ) is the probability per unit time of a following count with delay t since the previous count from the same production event, then d R d � t 0 β ( t ′ ) d t ′ R = e − α t e − d t = − R ( α + β ( t )) , or d t ln R = − ( α + β ( t )) , so We define the nuclear part of R ( t ) as: � t 0 β ( t ′ ) d t ′ R n ( t ) ≡ e − Then n = α e − α t R n − e − α t d R n d t For long time delays, d R n / d t ≃ 0 and R n ≃ constant: R n ≃ R n ( ∞ ) ≡ L = ⇒ leader fraction, and n ≃ α L e − α t Alejandro Sáiz Cross-counter leader fractions ICRC2017, July 18, 2017 15 / 12
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