Neutrinos, Positrons, and Missed Encounters: The Scientific Interrelations of Majorana, Occhialini, and Schenberg

Abstract

This paper explores the intertwined scientific legacies of Ettore Majorana, Giuseppe Occhialini, and Mário Schenberg, three prominent physicists who made significant contributions to the fields of particle physics and astrophysics. By analyzing historical records, personal accounts, and scientific collaborations, the study highlights the roles these figures played in the discovery of the positron, the theoretical development of neutrinos, and the study of cosmic rays. Particular attention is given to the missed encounter between Schenberg and Majorana during Occhialini and Schenberg’s 1938 journey to Italy. The paper also examines the scientific connections among Majorana’s work on neutrinos, Occhialini’s experimental confirmation of Dirac’s predictions, and Schenberg’s contributions to stellar processes. This study aims to provide a detailed perspective on this moment in the history of science.

Keywords: Majorana disappearance 1938; Occhialini-Majorana encounter; Occhialini positron discovery; Majorana neutrino theory; URCA process

1. Introduction

The history of science is full of chance encounters and missed opportunities that often play relevant roles in the development of scientific discoveries and, at the same time, in personal tragedy. One such event occurred in the late 1930s when the scientific community received the shocking news of the sudden disappearance of Ettore Majorana, a brilliant and promising Italian theoretical physicist. Years later, in a recorded interview from 1990, the Italian experimental physicist Giuseppe Occhialini recounted a brief meeting he had with Ettore Majorana in January 1938, just two months before Majorana’s disappearance in March of that year. This brief encounter took place during Occhialini’s vacation trip to Italy in January 1938. As we shall see, the story associated with this trip is further enriched by the missed opportunity for one of the greatest Brazilian theoretical physicists, Mário Schenberg, also known as Mario Schönberg, to meet Majorana together with Occhialini during this journey. The main characters discussed in this paper are shown in Figure 1.

Figure 1
The main figures as they appeared in the late 1930s. Ettore Majorana (1906–1938(?)) is on the left, Giuseppe Occhialini (1907–1993) is in the center (his image is from the mid-1920s), and Mário Schenberg (1914–1990) is on the right.

In 1937, Occhialini arrived in Brazil to work as an assistant professor of physics at the University of São Paulo. In early January 1938, during a university vacation break, he returned to Italy. During this trip, Occhialini unexpectedly encountered Ettore Majorana while visiting Professor Carrelli at the Institute of Physics in Naples. Fifty years later, while recalling the elusive conversation he had with Majorana during this meeting, Occhialini mentioned that he had noted Majorana’s ambiguous remarks, which seemed to hint at his subsequent disappearance. However, while sympathetic to Majorana, he was unfortunately unable to grasp the depth of Majorana’s turmoil and thus, as we shall see, unable to offer any help.

On this trip from Brazil to Italy, Occhialini was travelling together with the promising theoretical physicist, Mário Schenberg. Interestingly, although Occhialini and Schenberg were traveling together, Schenberg did not accompany Occhialini on his visit to the Institute of Physics in Naples. Instead, Schenberg’s path diverged as he went to Rome to collaborate with Enrico Fermi, thereby missing the opportunity to meet Majorana.

In this paper, the absence of Schenberg from Naples is examined, along with a detailed exploration of the unique encounter between Majorana and Occhialini, and the missed opportunity for Schenberg to meet Majorana. By considering the connections between the scientific work of these three physicists, this paper aims to highlight their interconnected narratives, exploring how personal dramas and encounters reveal the complexities of the often-hidden human element behind the scientific activity.

The importance of the “missed encounter” between Schenberg and Majorana lies not only in the curiosity of an unrealized connection but also in the surrounding historical and scientific contexts. The documental evidences discussed in this text helps substantiate the historical plausibility of the encounter between Majorana and Occhialini. Although the information about this elusive meeting is primarily based on Occhialini’s oral testimony [¹], the additional sources discussed in this paper reinforce the possibility of this meeting, adding historically significant details to the period when Schenberg was in Rome, in particular Schenberg’s proximity to the historic encounter between Occhialini and Majorana. Though brief, this meeting acquired historical relevance due to the subsequent developments related to Majorana’s contributions to theoretical physics and his mysterious disappearance in March 1938.

In the next section, we describe the details of the meeting between Occhialini and Ettore Majorana, along with the verifiable historical records. Subsequently, in section ³, we discuss Schenberg’s absence and the missed opportunity to meet Majorana. In section ⁴, the paper explores the interrelationships between the works of these scientists. Finally, the paper’s conclusion is presented in section ⁵.

2. The Meeting between Occhialini and Majorana

Giuseppe Occhialini, often referred to as “Beppo”, arrived in Brazil on Thursday, August 12, 1937, to begin his work as an assistant to the Ukrainian-born Italian physicist Gleb Wataghin. Wataghin had emigrated from Italy to Brazil in 1934, dissatisfied with the Fascist government, and accepted an invitation to work at the University of São Paulo, where he focused on astrophysics and particle physics. As the head of the Physics Department at the University of São Paulo, Wataghin invited Occhialini to join him in São Paulo, and, likewise discontented with the Italian Fascist regime, accepted the invitation.

It is worth noting that in 1937 Gleb Wataghin participated in the application process for the chair of theoretical physics in Italy – the same process that would ultimately establish Ettore Majorana as a professor of theoretical physics at Naples. Despite his considerable talent and substantial scientific contributions, Wataghin, who was one of Majorana’s opponents for the chair, did not secure the position and remained in Brazil. However, while unsuccessful in his application, Wataghin was pivotal in the establishment of physics research and the creation of the Institute of Physics at the University of São Paulo. He played an important role in founding the Brazilian school of physics, which would later produce highly talented physicists such as Mário Schenberg, César Lattes, Marcello Damy, among others. Majorana, on the other hand, secured the position in a highly unusual manner bypassing the normal selection process largely due to the influence of Enrico Fermi. As a key member of the selection committee, Fermi, which would receive the Nobel Prize in Physics in 1938, strongly advocated for Majorana’s appointment based on his exceptional scientific reputation [¹].

Around that time, Occhialini had already collaborated with the experimental physicist Patrick Blackett at the Cavendish Laboratory at the University of Cambridge. This period was important for his career, as he made significant contributions to particle physics, particularly through his experimental work on cosmic rays, which played a key role in the experimental confirmation of the discovery of the positron – a topic that would also be relevant to Majorana’s own theoretical work.

In early January 1938, during the university break in Brazil, Occhialini returned to Italy for vacation, likely arriving there on Tuesday, January 18th, 1938 [¹]. The ship he traveled on was the ocean liner Oceania, which had Trieste as a final destination but made a half-day stop in Naples. Seizing the opportunity, Occhialini decided to visit Professor Carrelli, then director of the Institute of Physics at the University of Naples. During this visit, Occhialini had the now-famous chance encounter with Ettore Majorana. Years later in 1990, during a TV interview conducted three years before his death in December 1993, Occhialini gave a detailed account of this meeting to journalist Bruno Russo, who was filming a TV documentary about Ettore Majorana for the RAI 3 channel [²]. In this interview, Occhialini described the encounter as indelible and provided a vivid recollection of it:

“I met Majorana on my way back from Brazil to Italy, during the university break, in January 1938. The ship’s final landing was Trieste, but with a half-day stop in Naples, and so I had decided to go and meet Professor Carrelli at the Institute of Physics. As a matter of fact, as soon as I arrived in Naples, I rushed to meet him. When I arrived at the Institute it was almost one o’clock and I saw Professor Carrelli about to leave. We had quite a light conversation, and then there came a young man, dark eyes, dark hair, I thought he was a student. We introduced ourselves… it was Majorana.”

It is interesting to note that in an earlier interview to Charles Wiener in April 1971 [³], Occhialini mentions that his first and last meeting with Ettore Majorana took place in Naples in 1938. However, the full details of this encounter were not publicly disclosed until fifty years after it took place. In the 1990 interview, broadcast as part of the TV documentary mentioned, Occhialini shared additional details, recalling that during their brief conversation, Majorana subtly hinted at his imminent disappearance [²]:

“It’s strange”, I told him, “that having wanted to meet you for so long when living in Florence, this meeting has only been possible by going to Sao Paulo and back!”, Majorana reply was: “You have made it just in time, because if you had come a few weeks later, you wouldn’t have met me.”

Occhialini immediately understood the deeper meaning of Majorana’s final remark. In the 1990 television interview, Occhialini offers a personal and in-depth recounting of this moment [²]. As the interview progresses, he recalls his response to Majorana’s “odd” remark. At this point, Occhialini pauses for an extended, reflective silence, emphasizing the significance of this memory, while holding a cigarette in his right hand. “Beppo” then reveals his response to Majorana:

“This answer makes you even more interesting since I, back at the age of 18, found myself also repeating the same road$\mathrm{\dots }$ the same phrase.”

Here we make a short digression and mention that in this television interview, when concluding his recollection, the sentence ends with the words “same road”, however, in a very short time, “Beppo” corrects it to instead “same phrase” [²]. Here the word “road” is italicized because when it is mentioned during the interview, it seems like a repressed unconscious content, explained perhaps through the concept of “complex” as described by the psychologist Carl Jung. In more detail, the word “road” instead of the word “phrase” in this context might have unconsciously surfaced, bringing with it a set of related thoughts, feelings, and memories that subtly influenced Occhialini’s speech, much like how personal complexes can affect our behavior and expressions without us realizing it [⁴]. Obviously, the actual meaning of both sentences are the same, but the use of the word “road” has a more euphemistic context.

In any case, it is clear that Occhialini perceived a clue about Ettore’s possible fate. The enigmatic response of Majorana to Occhialini’s remark was:

“Dear Occhialini, there are people who talk about it, and people who do it. That’s why I repeat that if you had arrived a few weeks later, you wouldn’t have seen me.”

Clearly, this response suggests an impending decision from Majorana, implying that something significant is about to occur. From the perspective of the present, the phrase carries a hint of mystery and foreshadows Majorana’s eventual disappearance, making it both cryptic and prophetic. Looking in retrospect, these ambiguous remarks indeed can be viewed as a future indication of Majorana’s mysterious disappearance on March 26th, 1938.

Later, in the same 1990 interview, Occhialini recalls: “$\mathrm{\dots }$ it seemed absolutely impossible to me to report to anyone what had been said $\mathrm{\dots }$”. After this brief, occasional encounter, Occhialini reboarded the Oceania, continuing his journey to Trieste and arriving at his final destination on January 19th, 1938 [⁵].

Closely following [¹], one might conjecture, through the so-called emigration hypothesis, that the transatlantic ship Oceania could hold broader significance for the history of science, since it is possible that Majorana’s disappearance could be explained by suggesting that he used the same ship as a potential escape route to emigrate to Argentina. This theory was thoroughly explored by Erasmo Recami and Carlo Artemi, who provided a detailed hypothetical reconstruction [¹, ⁶].

The intriguing parallel, between the ship Oceania and Majorana, arises when considering that this ship, after another voyage to South America on February 4th from Trieste, set out again from Trieste to Buenos Aires on March 26th, which is the day of Majorana’s disappearance. The full account of this hypothesis, together with other points to consider, which will not be treated here, fuels speculation about Majorana’s possible escape to Argentina [¹].

It should be mentioned that the disappearance of Ettore Majorana has given rise to several hypotheses [⁷]. More recently, another hypothesis consider that Majorana emigrated to Venezuela, as proposed by the RAI 3 talk show “Chi l’ha Visto?”. This show published a statement that Majorana was alive between 1955 and 1959, living in Valencia, Venezuela, under the surname “Bini”. Following this fictitious or not “update”, it is a fact that in March 2011 the Rome Attorney’s Office reopened the case of Majorana’s disappearance based on a witness statement about meeting Majorana in Buenos Aires after World War II. Italian newspaper Corriere della Sera reported that a photograph taken in Argentina in 1955 had at least ten points of similarity with Majorana’s face [⁸]. Finally, in February 2015, the Rome Attorney’s Office declared that Majorana had been alive between 1955 and 1959, living in Valencia, Venezuela [⁹]. This led to the official closure of the case, concluding that his disappearance was likely a personal choice with no criminal evidence involved.

In his final known letter, which is the last telegram sent to Carrelli, Majorana writes:

“March 26, 1938

Dear Carrelli, I hope you got my telegram and my letter at the same time. The sea rejected me and I’ll be back tomorrow at the Hotel Bologna traveling perhaps with this letter. However, I have the intention of giving up teaching. Don’t think I’m like an Ibsen heroine, because the case is different. I’m at your disposal for further details.

E. Majorana”

It is very interesting that in his last known letter, Majorana references the female characters from the works of the Norwegian author Henrik Ibsen. In fact, a compelling parallel can be drawn between Majorana’s decision and the complex heroines depicted in Ibsen’s plays. These characters are profoundly shaped by the oppressive societal environments they inhabit, leading to critical life choices [¹⁰]. For instance, Nora in A Doll’s House and Hedda in Hedda Gabler confront societal expectations and personal dilemmas, often resulting in drastic emotional decisions. Nora chooses to leave her husband and children to pursue an independent life, while Hedda ultimately takes her own life [¹⁰].

Although Majorana does not explicitly mention any specific character type from Ibsen, his reference to not being an “Ibsen heroine” in his final letter suggests a self-awareness of the dramatic nature of his decision to withdraw from his academic career and possibly from life itself. However, he emphasizes that his situation is different from that of Ibsen’s characters, distancing himself from their emotional and impulsive tendencies, and implying that his decision is driven by rational decision rather than dramatic or emotional distress.

2.1. Can the meeting betweenOcchialini-Majorana be verifiedusing historical records?

In [¹], it is argued that the transatlantic vessel from which Occhialini disembarked in Naples, and which would continue to Trieste, was the previously mentioned ship Oceania. This ship, depicted in Figure 2, was owned by the Società di Navigazione Italia (Italia Line) based in Genoa [¹]. The regular service of Oceania route from Italy to South America and back included the Italian ports of Trieste and Naples, as well as the South American ports in the Brazilian cities of Pernambuco (Recife), Bahia, Rio de Janeiro, São Paulo (Santos), and also Montevideo in Uruguay, and Buenos Aires in Argentina [¹¹, ¹²].

Figure 2
MV Oceania in the 1930s.

Official records indicate that the ship Oceania, on its return to Italy from Argentina, docked in Brazil at the port of Santos, São Paulo, on January 4th, 1938, before making its first stop in Rio de Janeiro on January 5th, 1938 [¹²]. It then made another stop in Bahia, with its final stop in Brazil being in Recife on January 9th, 1938 [¹³]. Although no passenger list has been found, Occhialini’s report on the latitude effect for cosmic ray showers provides further details of this journey [⁵]. According to this paper, published in May 1938, experiments on cosmic ray showers were conducted aboard the Oceania during its January voyage from Bahia to Trieste, with cosmic ray intensities recorded at several geographic locations along the route. The data measurements were reported collected in Bahia and Recife, Brazil, and as the ship continued his journey, in Cabo Verde, then at the Canary Islands, Gibraltar, and Algiers, before reaching Italy, where stops included Naples, Ancona, and the final destination, Trieste [⁵].

Additional historical evidence supporting that the Oceania was indeed the vessel on which Occhialini and Schenberg departed from Brazil to Italy in early January 1938 can be found in records of their passage through Pernambuco (Recife) [¹⁴]. Figure 3, taken from the Brazilian newspaper O Diário de Pernambuco, displays a headline reporting the ship’s stop in Recife on January 9, 1938, noting that the Oceania was carrying 360 passengers en route to Trieste and Naples, including individuals identified as “Professor Giuseppe Occhialini” and “Mario Schenberg”.

Figure 3
Headline from Diário de Pernambuco on January 9, 1938, reporting the passage of the ship Oceania through Recife. The article highlights the presence of a “delegation”, namely Occhialini-Damy-Schenberg, from the University of São Paulo on board, traveling to Europe to study cosmic rays. Source: Diário de Pernambuco/Arquivo da Fundação Joaquim Nabuco, Recife (PE).

The article details the “scientific mission”, organized by Professor Gleb Wataghin, to conduct research on cosmic rays in Europe. The article even reports that Occhialini demonstrated the experimental equipment used for cosmic ray observations on board. It also mentions that Mario Schenberg, “$\mathrm{\dots }$ a distinguished former student of the Faculty of Engineering and Sciences of São Paulo, was accompanying him and traveling to Cambridge for further specialization$\mathrm{\dots }$”. Additionally, it is noted that during the ship’s stop in Recife, Occhialini and Schenberg, a native of the city, visited Boa Viagem Beach, one of its most famous attractions [¹⁴].

Notably, the report reveals that another person on this journey with Occhialini and Schenberg was the Brazilian experimental physicist Marcello Damy de Souza Santos, Occhialini’s assistant, who was responsible for constructing the experimental apparatus aboard the Oceania, intended for collecting data on cosmic rays in the equatorial zone during the ship’s passage from South America to Europe. Schenberg, who initially planned to go to Cambridge to work with Dirac, ultimately stayed in Italy, as we shall later see in detail, working with Fermi at the Institute of Physics on Via Panisperna in Rome for nearly the entire year of 1938.

Further evidence confirming Marcello Damy’s presence aboard the Oceania alongside Mario Schenberg and Giuseppe Occhialini during the January 1938 voyage from Brazil to Italy is supported by multiple independent sources. For instance, according to the Brazilian physicist José Leite Lopes [¹⁵], Damy traveled to Europe in the same period as Schenberg, with the ultimate destination of England to pursue doctoral studies at the University of Cambridge under a British Council scholarship. Although the scholarship was formally granted in June 1938, the text suggests that Damy was already in Europe as of January 1938, consistent with his initial journey aboard the Oceania.

Another source, such as [¹³], which highlights the life and impact of Brazilian engineer Luiz Freire, also provides further confirmation of Damy’s presence in the journey. Freire, particularly his role as a professor and mentor in Recife, where he lived and worked, was instrumental in guiding young talents, most notably physicists Mário Schenberg and José Leite Lopes, whose scientific potential he recognized and nurtured from an early age. In early January 1938, Luiz Freire met physicists Giuseppe Occhialini, Marcello Damy, and Mario Schenberg in Recife when the Oceania made a scheduled stop during its journey from Brazil to Italy. As noted in [¹³], in Freire’s 1938 article published in Diário de Pernambuco – likely the first in Brazilian media to mention cosmic ray research [¹³] – he explicitly refers to “the three young scientists – Italian Giuseppe Occhialini and Brazilians Mario Schenberg and Marcello Damy de Souza Santos” – and describes the latitude effect experiments on cosmic rays conducted with equipment installed by Occhialini and Damy [¹³].

While these sources confirm Damy’s presence aboard the Oceania [¹³, ¹⁵], it cannot be concluded with certainty that he accompanied Schenberg and Occhialini for the entirety of the voyage to the ship’s final destination. In fact, in a paper published later [⁵], Occhialini specifically acknowledges Damy’s contribution to data collection only during the Oceania’s route from Santos to Recife [⁵]. This detail implies that Damy may not have continued the entire trip to Europe, as Occhialini continued to report experimental data collected up to the ship’s arrival in Trieste. If Damy had remained on board, it is likely his collaboration would have extended to these later measurements as well. Due to these seemingly conflicting evidences, this paper assumes only the presence of Occhialini and Schenberg at the time of the ship’s arrival in Italy.

In any case, the sources clearly indicate that the ship’s journey to Italy indeed included a scheduled stop in Naples, further supporting the possibility of the unexpected meeting between Occhialini and Majorana. After departing from Recife, and including other stops, the ship docked in Naples on January 18, 1938. According to [¹], contemporary reports, such as those from the Neapolitan newspaper Il Mattino, confirm that the Oceania arrived in Naples on that date. If the ship docked at 7:00 a.m. and departed at 3:00 p.m., Occhialini’s account of visiting the Physics Institute and encountering Majorana during lunch appears at least plausible [¹].

It is highly likely that only Occhialini continued the journey to Trieste, though it is uncertain whether Schenberg departed for Rome from Naples or Trieste. Archival records suggest that Occhialini was in Manchester in March 1938 [¹⁶]. It seems almost certain that only Occhialini visited the Physics Institute in Naples, while Schenberg possibly remained on board the Oceania, given the limited time available, according to Occhialini’s statements about this brief visit, which eventually led to his meeting with Majorana.

In fact, despite both being on the same ship traveling to Italy, there are no historical records in which Schenberg mentioned Occhialini’s meeting with Majorana during this trip. This is particularly odd, given the later circumstances of Majorana’s famous disappearance and its lasting impact. One can only conclude that Occhialini never shared this encounter with either Schenberg or Damy. In his own recollections of the trip, Schenberg, while recalling the journey with Occhialini, never mentioned any stop in Naples, instead referring to his final destination as Rome [¹⁷, ¹⁸]. Schenberg returned to Brazil in April 1939 and continued working with Occhialini on many occasions. He passed away in 1990, likely never becoming aware of Occhialini’s meeting with Majorana, as he never mentioned anything of the sort.

3. The Lost Meeting Between Mário Schenberg and Ettore Majorana

Mário Schenberg is widely regarded as one of Brazil’s most significant theoretical physicist. As previously noted, he maintained a close personal and scientific relationship with Giuseppe Occhialini and Gleb Wataghin at the Institute of Physics at the University of São Paulo (IFUSP). In particular, Schenberg’s friendship with Occhialini spanned several decades, originating during the early days at IFUSP and continuing into their later years, as illustrated in Figure 4. This enduring relationship between Schenberg and Occhialini exemplifies not only their mutual respect but also their scientific collaborative spirit over the years [¹⁷, ¹⁸, ¹⁹].

Figure 4
(Left) Group photo from the late 1930s shows the staff of the Physics Department at USP. From left to right, the people in the photo are: Giuseppe Occhialini, Marcello Damy de Souza Santos, Yolande Monteux, Abrahão de Moraes, Mario Schenberg, Gleb Wataghin, and Francisco Bentivoglio Guidolin. Source: IFUSP Archives. (Right) Mario Schenberg (seated, left) and Giuseppe Occhialini (standing, right), both in their later years, engaged in a discussion, which highlights the collaboration between these two distinguished physicists [¹⁷, ¹⁹].

After Giuseppe Occhialini’s arrival in São Paulo in 1937, Schenberg was employed as an Assistant in Theoretical Physics, collaborating with Occhialini on cosmic ray research from 1937 onwards. During the travel journey from São Paulo to Naples/Trieste in January 1938, Occhialini and Schenberg performed a series of experimental measurements of cosmic ray showers [¹⁹]. As a productive result of this trip, Schenberg and Occhialini later published a joint paper detailing the variation in the intensity of cosmic ray showers with latitude and the presence of a soft component [²⁰].

Schenberg, upon arriving in Rome, as he explicitly states [¹⁹], visited the Institute of Physics at via Panisperna and met Prof. Gleb Wataghin, who was on vacation. Wataghin introduced him to Ugo Fano, an assistant to Enrico Fermi. Fano persuaded Schenberg to stay in Rome and work at Fermi’s institute. Schenberg agreed and ended up staying in Rome until October 1938. During his time there, from January-October 1938, Schenberg worked on the theoretical study of cosmic ray showers and the production of mesons. His numerical integration of the equations describing electron showers and his analysis of experimental data helped in understanding that cosmic rays were primarily composed of protons, not electrons, as was previously believed [¹⁹]. This work was significant in advancing the understanding of cosmic radiation and meson production, laying the foundation for further international collaborations in the field. For instance, the multiple and simultaneous production of mesons, was experimentally demonstrated later by Wataghin and Damy [²¹, ²²]. This collective experimental research later fostered an international cooperation between the University of São Paulo (USP) and the University of Chicago, which culminated in a 1941 expedition, led by American physicist Arthur Compton, to measure cosmic radiation in the interior of São Paulo using hydrogen balloons equipped with Geiger counters [²²].

Thus, while working with Fermi at the Physics Institute in Rome, Schenberg focused on the physics of cosmic rays, thereby continuing the research initiated during his voyage from Brazil with Occhialini. Later that year, his scientific journey took him to Zurich, where he worked with Wolfgang Pauli, and later in December 1938 to Paris, where he interacted with Joliot-Curie. Schenberg would returned to Brazil in April 1939 [¹⁹].

As far as we know, there are no historical records in which Mario Schenberg mentioned during his lifetime a direct personal encounter with Ettore Majorana as a result of his travel to Italy with Occhialini. In his interviews, see for instance [¹⁷, ¹⁸], Schenberg mentions the trip with Occhialini but only states that in the end he went to Rome. There was no mention whatsoever of Naples or Ettore Majorana, and despite being in Rome at the time of Majorana’s disappearance, one can conclude that he most likely never met Majorana. Similarly, “Beppo”, as already indicated, also never mentioned that someone was with him during his visit to the Institute of Physics in Naples on January 18th, 1938. Based on this, one concludes that Occhialini was alone at the time of his elusive meeting with Majorana in that early January afternoon.

Considering that the Oceania docked first in Naples before reaching Trieste, Schenberg probably went to Rome from Naples after passing through the required customs operations and, for whatever reason, was unable to join Occhialini’s visit to Carrelli’s institute. In his 1990 interview, Occhialini explicitly mentions that he had decided to stop in Naples, where the ship docked for half a day, to see Professor Carrelli at the Institute of Physics, but that he hurried and arrived late, around one o’clock in the afternoon, and found Carrelli just as he was about to leave. Thus, since both Schenberg and Occhialini arrived together in Naples on January 18, 1938, Schenberg, while likely staying on the ship due to perhaps an unspecified trivial matter, missed the opportunity to meet Majorana.

One cannot avoid mentioning that the recently late Prof. Erasmo Recami, a theoretical physicist and world-renowned biographer of Ettore Majorana, was a colleague of Mário Schenberg. In some archived letters exchanged with Mário Schenberg, there is no mention of Ettore Majorana in these letters¹. In Recami’s book The Majorana Case[⁶], for instance, there is no allusion of Schenberg in the section where Occhialini’s 1990 television testimony is briefly presented.

Another point interesting to mention is the first-hand testimony of Giuseppe Cocconi about the days following Majorana’s sudden disappearance in the Institute of Physics at Via Panisperna in Rome. In January 1938, after graduating, Giuseppe Cocconi was invited to join and work with Fermi at the Institute on the disintegration products of mesons produced by cosmic rays. While working with Fermi, Cocconi had, like Occhialini, also a brief encounter with Ettore Majorana. He mentions that after Majorana’s misterious disappearance, on March 26 1938, Fermi was greatly distressed as he searched for him [¹]. As we know, Majorana was never seen again. Fermi later emphasized, as Cocconi points out, Majorana’s unparalleled genius, comparing him to Galileo and Newton, and highlighting Majorana’s unmatched brilliance [¹], Fermi has been quoted as saying that: “Because you see, in the world there are various categories of scientists $\mathrm{\dots }$ But then there are the geniuses, like Galileo and Newton. Well, Ettore was one of these. Majorana had what no one else in the world had $\mathrm{\dots }$”.

Mário Schenberg, like Cocconi, was also working at the Institute of Physics in Rome at that time and was able to closely follow these events. Unfortunately, despite working there with Fermi between January and October 1938, there are no recorded accounts from Schenberg during his lifetime that mention Majorana or his mysterious disappearance.

4. The Interrelation between the Scientific Works of Majorana-Occhialini-Schenberg

4.1. Scientific interrelations and collaborative impacts

In his 1971 interview to Charles Weiner, Occhialini stated that, as a young physicist, he perceived Majorana as an immensely powerful professor of physics [³]. He admitted that he was unaware of the specifics of Majorana’s research, as he lacked the knowledge to fully grasp his work. While acknowledging his limited understanding of Majorana’s contributions to physics, Occhialini noted that he was more familiar with the work in spectroscopy conducted by Carrelli, due to his direct involvement and occasional meetings with him. Therefore, from this interview, one can infer that Occhialini’s primary interest when he landed in Naples in 1938 was to meet Carrelli, rather than Majorana.

It is important to note that by 1938, Majorana’s theoretical contributions to neutrino physics were already recognized as groundbreaking in the field of particle physics. In particular, Majorana proposed the innovative concept that neutrinos could be their own antiparticles – a theory that was ahead of its time and predated the experimental confirmation of neutrinos by about twenty years [²³]. Majorana’s theory on neutrinos provided a new perspective through which physicists could examine $\beta$-decay and the “ghost” nature of neutrinos. His work on infinite-component equations and the symmetrical theory of the electron and positron suggested that neutrinos, being electrically neutral, could exist as particles that do not distinguish between the forward and backward directions of time [⁷]. This concept, now known as Majorana neutrinos, challenged the prevailing Dirac theory, which necessitated a separate antiparticle for each particle.

4.2. Occhialini’s experimental workon cosmic rays

Giuseppe Occhialini’s experimental work play a significant role in the discovery of the positron, the antiparticle to the electron, and the study of cosmic rays. Working with Blackett in England, Occhialini developed techniques for photographing particle tracks, which led to the experimental verification of Dirac’s theoretical prediction of antimatter, parallel to work developed by Carl Anderson. His collaboration with Blackett on cloud chamber experiments revealed the presence of antimatter in cosmic ray interactions [²⁴].

Blackett once jokingly remarked that if Occhialini hadn’t taken a “long holiday”, they might have discovered the positron before Carl Anderson. Although Anderson was the first to publish photographic evidence of the positron and won the Nobel Prize in 1936, Blackett and Occhialini were the first to identify the connection between the positive electron they observed and the antimatter predicted by Dirac’s recent theory [²⁵].

Before the experimental confirmation of the positron, Ettore Majorana was highly skeptical of Dirac’s ideas. He viewed key concepts of Dirac’s theory, such as negative energies, as fundamentally incorrect. This skepticism eventually led him to publish in 1932 the paper “Relativistic Theory of Elementary Particles with Arbitrary Spin” [²⁶], which opposed Dirac’s theory. Majorana’s idea was that a particle could be identical to its own antiparticle was quite different from Dirac’s approach, i.e., particles and corresponding antiparticles as distinct entities. Dirac’s theory predicted the existence of the positron and this prediction was experimentally confirmed by Anderson-Occhialini-Blackett. As evidence for the positron began to accumulate, Dirac’s theory – and its concepts of the creation and annihilation of pairs of matter and antimatter particles – gained widespread acceptance.

It has been suggested, for instance in [⁷], that the confirmation of the positron and the subsequent validation of Dirac’s theory by Anderson in 1932, combined with family and personal issues – such as Majorana’s poor health – may have contributed to Ettore’s descent into depression, a period his biographers refer to as his “gloomy years” of isolation [¹]. This period is considered to have begun when he returned to Rome in the summer of 1933, following his time in Leipzig working with Heisenberg. Additionally, the death of his father, Fabio Majorana, in 1934 likely exacerbated his personal turmoil. This collection of events may have ultimately played a significant role in his decision to disappear.

In any case, it is likely that Ettore Majorana was perhaps more familiar with some of the results obtained by Occhialini than Occhialini was with Majorana’s theoretical work. Thus, despite the intrinsic connection between Occhialini and Majorana’s research neither of them touched on this topic during their brief conversation in January 1938.

In his 1990 interview, Occhialini suggested, based on his personal recollections and feelings after meeting with Ettore, that the suicide hypothesis was more convincing. This view closely aligns with that of Majorana’s former colleagues, such as Amaldi and Segrè [⁷], and by most of his relatives, with the exception of his mother [¹]. In fact, in a plea letter to the Italian Prime Minister Mussolini [¹, ⁶], following a letter of introduction by Enrico Fermi, Ettore’s mother, Dorina Corso Majorana, urges the authorities to intensify efforts to locate her son. When concluding the letter, she expressed her firm belief that Ettore, as a result of his intense dedication to his studies, was a “victim of science”. It is intriguing to consider that Ettore’s mother’s perspective may indirectly reflect the psychological impact that the experimental confirmation of the positron by Occhialini, and the subsequent validation of Dirac’s theory, had on Ettore’s personality. At that time, these experimental results overshadowed Majorana’s own theoretical efforts to understand the fundamentals of elementary particles.

Majorana’s strong reaction against Dirac’s theory eventually led him to propose in his 1937 paper “A symmetric theory of electrons and positrons” [²³] a symmetric formulation of the Dirac theory that elegantly removes the need for negative-energy states and introduces the possibility that neutrinos are their own antiparticles, what is now referred as the Majorana neutrino. Actually, the identity of neutrinos, whether they are of Dirac or Majorana type, remains an open question to this day, reflecting the lasting impact of their differing perspectives [²⁶]. If neutrinos are Majorana particles, they can cause a special type of decay called neutrinoless double beta decay ($0\nu \beta \beta$), where two electrons or positrons are emitted without accompanying neutrinos, violating the conservation of lepton number [²⁶]. This decay would be an important experimental signature, providing evidence for the Majorana nature of neutrinos. The energy released in such a decay would be concentrated in a specific energy line, making it distinct from the more common two-neutrino double beta decay ($2\nu \beta \beta$), where the energy is spread out [⁷, ²⁶].

The actual identity of neutrino’s nature has far-reaching implications, since if neutrinos are in fact Majorana particles, this would provide insights into why there is more matter than antimatter in the universe, potentially explaining one of the biggest mysteries in cosmology related to such asymmetry. Additionally, it would open up new possibilities for physics beyond the Standard Model, leading to potential breakthroughs in our understanding of fundamental forces and particles [²⁶].

4.3. Schenberg’s theoretical contributionson neutrinos

In fact, not only is Majorana’s scientific contribution often associated with the neutrino, but so too is that of Mário Schenberg. As Schenberg once mentioned, it was in 1934, during Fermi’s lectures in Brazil, that he first heard about the elusive particles proposed by Pauli, and later named “neutrinos” by Fermi and Amaldi. Later, working together with George Gamow, in Washington during the period 1940-41, Schenberg became deeply involved in the study of supernovae. Despite his initial lack of background in astrophysics, Schenberg made a significant observation by recognizing the role of neutrinos in the collapse processes of supernovae – a connection that had been largely overlooked [¹⁷]. Influenced by Fermi’s work on neutrinos, Schenberg pointed out to Gamow that previous studies had failed to account for neutrinos, leading to the formulation of the URCA process, a key mechanism determined by neutrinos in supernova phenomena and stellar dynamics [²⁷, ²⁸]. The URCA process, named after a casino in Rio de Janeiro which existed at that time, as recalled by Schenberg [¹⁹] due to the energy-money loss analogy, describes the rapid cooling of neutron stars through neutrino emission, a critical process for understanding supernova explosions.

In 1940, Gamow and Schenberg published a brief note [²⁷] explicitly discussing the role of neutrinos in stellar evolution. They pointed out that during normal thermonuclear reactions in stars, neutrinos carry away a small portion of energy, which, while not significant for the star’s equilibrium during its main sequence evolution, can become critical under certain conditions. As a star undergoes progressive contraction in its final evolutionary stages, neutrinos can rapidly carry away energy, thereby accelerating the star’s collapse. In their note, they proposed that this rapid collapse generates significant heat and increases thermal radiation, potentially serving as the primary mechanism behind observed supernova explosions. Subsequently, in 1941 a detailed model [²⁸], grounded in statistical physics, was developed to quantitatively determine the energy flux carried away by neutrino emission during the core collapse of a star. As given in equation (1), neutrino emission mechanism through the URCA process, as the authors propose, is governed by the following thermonuclear reactions [²⁸]:

(1) $$\{\begin{array}{c}{}_Z^{A}N+e^{-}\to {}_{Z-1}^{A}N+\text{antineutrino}\\ {}_{Z-1}^{A}N\to {}_Z^{A}N+e^{-}+\text{neutrino}\hfill \end{array}$$

In their 1941 paper, Gamow and Schenberg provide a detailed analysis linking neutrino emission to the dynamic stages of a star’s core collapse, a process governed by nuclear reactions involving various elements depending on the core’s state [²⁸]. The authors emphasize that neutrino emission serves as the primary cooling mechanism as the core contracts and evolves. In the start’s final stages, neutrino emission, particularly through the URCA process, involves the capture and emission of relativistic electrons.

The authors clarify that both neutrinos and antineutrinos are considered at each stage of the core’s collapse, as there is no discernible difference in their behavior during these reactions. Moreover, they note that the possibility of mutual annihilation of these particles within the stellar body can be neglected, as neutrinos escape the star with virtually no collisions [²⁸]. Interestingly, based on this observation, whether the neutrino is of Dirac or Majorana type would, in principle, make no difference in the URCA process and the subsequent cooling of the star.

In any case, the question of whether the identity of neutrinos can be determined through astrophysical fluxes remains open. Distinguishing between Dirac and Majorana neutrinos based solely on their behavior in weak interactions is extremely challenging due to the small mass of neutrinos and the chiral nature of weak interactions [²⁶]. Experiments aimed at determining the neutrino’s identity often focus on trying to observe the neutrinoless double-beta decay ($0\nu \beta \beta$) process.

Whether it is possible to distinguish between Dirac and Majorana neutrinos, generated in the URCA process, by studying their behavior under extreme conditions, such as the very high densities or strong magnetic fields found in stellar environments, remains uncertain. Studies suggest that even under such extreme conditions, the difference between Dirac and Majorana neutrinos remains elusive [²⁶], as the physical effects that might differentiate them are still too subtle to be easily observed. Supernovae, through the URCA process, could provide insight, as the intense magnetic fields might induce spin-flavor changes in neutrinos [²⁶]. For instance, a muon neutrino (ν_μ) might transform into an antimuon neutrino (${\overline{\nu }}_{\mu }$), and subsequently into an electron antineutrino (${\overline{\nu }}_e$), which could potentially be detected on Earth [²⁶]. If such processes are observed, they could offer important clues about whether neutrinos are Majorana or Dirac particles and their potential impact on supernova dynamics. However, detecting these effects is extremely challenging due to their subtlety and the difficulty in measurement.

5. Conclusions

The scientific legacies of Ettore Majorana, Giuseppe Occhialini, and Mário Schenberg are deeply intertwined through cosmic rays and neutrino’s research. Majorana’s pioneering theoretical work on neutrinos, Occhialini’s experimental confirmation of the positron, and Schenberg’s contributions to the understanding of cosmic rays and the neutrino’s role in stellar processes collectively advanced the frontiers of particle physics and astrophysics. Majorana’s insights into the nature of neutrinos, although initially met with skepticism, laid the groundwork for future explorations in particle physics. Occhialini’s work, particularly in the experimental domain, provided empirical validation for theoretical predictions, thereby solidifying the foundational principles of quantum mechanics and particle physics. Schenberg’s research further extended these developments into the realm of astrophysics, contributing to a deeper understanding of the processes governing stellar evolution and cosmic phenomena. Thus, each of these physicists, through their respective contributions, helped in shaping some of the main aspects of modern physics.

In conclusion, despite these significant contributions, the missed opportunity for Schenberg to meet Majorana during Occhialini’s visit to the Naples Institute of Physics in January 1938 remains an intriguing aspect of this historical narrative. The reasons for Schenberg’s absence remain speculative, and this missed opportunity further adds to the already enigmatic narrative surrounding Majorana’s life and mysterious disappearance. Whether Schenberg’s presence at this elusive meeting would have influenced Ettore’s personal trajectory remains uncertain, but it is unlikely to have altered the course of his history.

References

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• 1
  Some of these letters can be accessed in http://acervo.if.usp.br/

Publication Dates

• Publication in this collection
  13 Dec 2024
• Date of issue
  2025

History

• Received
  06 Sept 2024
• Reviewed
  07 Nov 2024
• Accepted
  17 Nov 2024