Neutrinos, with mass below 0.12 eV, are extremely difficult to observe directly. However, energy conservation in beta decay demanded such a particle. In beta decay a neutron transforms into a proton, emitting an electron and a neutrino. Neutrinos were observed conclusively through the inverse process, beta capture, in 1956. After a long wait, two of the discoverers received the 1995 Nobel Prize in Physics. In fact, an earlier Nobel Prize, in 1988, went to another group who had discovered the muon neutrino, a different particle from the original electron neutrino but in the same family. A third neutrino prize came in 2015 for evidence of neutrino oscillations, where electron neutrinos can change to muon neutrinos and vice versa. The oscillation was conclusive evidence that neutrinos have non-zero (although very small!) mass.
The earliest to be discovered among our particles, the positron, mass 0.51 MeV, is the antimatter partner of the electron. The electron and positron have the same mass, the same spin, and the same magnitude charge, although the positron charge is positive. When a positron and electron collide, both annihilate, creating photons that carry the energy of the positron and electron mass. In the late 1920's and early 1930's theorists found equations implying the existence of such a particle, and experimentalists unknowingly observed it. Carl Anderson first identified the positron in his data in 1932. Paul Dirac, who had theorized its existence, received the Nobel Prize in Physics in 1933, with a Nobel Prize for Anderson following in 1936. Among the scientists who had previously observed the positron without recognizing its significance were Irène Joliot-Curie and her husband Frédéric Joliot-Curie. (The Joliot-Curies were awarded the 1935 Nobel Prize in Chemistry, for finding a way to create new radioactive isotopes.)
The charm quark, mass 1.3 GeV, was first observed as part of charmonium, a charm and its antiparticle bound together. Two independent research groups, one at Brookhaven National Laboratory in New York and the other at the Stanford Linear Accelerator Center, made the discovery in 1974. The different capabilities of the two accelerators meant that it was easier for the Brookhaven group to find initial evidence for a new particle, but once the Stanford group tuned to the correct energy it was easier for them to make precision measurements of charmonium and its excited states. Because of the joint discovery, the ground state of charmonium retains the double name J/ψ, a combination of the letter names initially selected by the two separate groups. The 1976 Nobel Prize in Physics went to the leaders of the two experiments.
W and Z bosons, mass 80 and 91 GeV, transmit energy and momentum in weak interactions. Here "weak" is the name of a particular force relevant for subatomic particles, not an ordinary English adjective. The W and Z play the same role in the weak force that the photon does in electromagnetic interactions. They were first observed in 1983 by two collaborations working at CERN, the European center for high energy physics. In 1984 the Nobel Prize in Physics was shared between a leader of one of the collaborations and a physicist whose improvements to the particle accelerators themselves had made the measurement possible.
The discovery of the Higgs boson, mass 125 GeV, was announced on July 4, 2012. The measurements leading to the announcement happened over two years, with the long time scale needed to achieve the necessary level of statistical certainty. They were carried out independently by two separate international collaborations at CERN's Large Hadron Collider. (Our keynote speaker Fabiola Gianotti made one half of the announcement, as the spokesperson for one of the collaborations.) Even the two years of direct data acquisition was only a small part of the entire effort to find the Higgs. The possibility of such a particle was first theorized in 1964, although without any precise idea of its mass, and experimentalists had been carrying out serious searches for two decades. The Nobel Prize was quickly awarded, in 2013, to two of the surviving theorists who had posited the particle almost 50 years earlier. The experimental collaborations, with thousands of contributing scientists, are far more difficult to recognize under the Nobel Prize rule of having at most three recipients.