Classification
Which is the lowest mass charged leptop?
Electron
Electron Mass-to-charge ratio ABC Preon Model Charmed baryons Atom
Electron-Classification Mass-to-charge_ratio-Origin ABC_Preon_Model-Deep_Inelastic_Collision_Results:_Determination_of_the_C_Preon_Mass Charmed_baryons-(2455)_history_and_mass Atom-Mass
In the Standard Model of particle physics, electrons belong to the group of subatomic particles called leptons, which are believed to be fundamental or elementary particles. Electrons have the lowest mass of any charged lepton (or electrically charged particle of any type) and belong to the first-generation of fundamental particles. The second and third generation contain charged leptons, the muon and the tau, which are identical to the electron in charge, spin and interactions, but are more massive. Leptons differ from the other basic constituent of matter, the quarks, by their lack of strong interaction. All members of the lepton group are fermions, because they all have half-odd integer spin; the electron has spin .
When charged particles move in electric and magnetic fields the following two laws apply:where F is the force applied to the ion, "m" is the mass of the particle, a is the acceleration, "Q" is the electric charge, E is the electric field, and v × B is the cross product of the ion's velocity and the magnetic flux density. This differential equation is the classic equation of motion for charged particles. Together with the particle's initial conditions, it completely determines the particle's motion in space and time in terms of "m"/"Q". Thus mass spectrometers could be thought of as "mass-to-charge spectrometers". When presenting data in a mass spectrum, it is common to use the dimensionless "m"/"z", which denotes the dimensionless quantity formed by dividing the mass number of the ion by its charge number. Combining the two previous equations yields:  formula_1. This differential equation is the classic equation of motion of a charged particle in vacuum. Together with the particle's initial conditions it determines the particle's motion in space and time. It immediately reveals that two particles with the same "m"/"Q" ratio behave in the same way. This is why the mass-to-charge ratio is an important physical quantity in those scientific fields where charged particles interact with magnetic or electric fields. 
The mass of the C preon can be determined by deep inelastic collision experiments, which are done by having a high energy electron beam collide with hadronic matter. For the case of the proton, these experiments observe that 35% of the proton momentum is contained by particles with positive charge, 17% by particles with negative charge, and 47% by particles of neutral charge. (Note that it is simple rounding error that leads the sum of these values to be 99%.) The parameters of the standard model were adjusted and various processes proposed so that the standard model agrees with these values by assigning 35% of the proton momentum to be carried by positively charged up quarks, 17% of the proton momentum to be carried by negatively charged down quarks, and the remaining 47% to be carried by charge neutral gluons. In the ABC model, it is readily observed that if the mass of the C particle is 68 GeV/c2, then 35% of the mass of the proton consists of the positively charged C particle, 18% by the mass of the negatively charged B particle, and 47% by the mass of the two uncharged A particles. Hence, by fitting a single parameter - the C mass - to the data, the ABC Preon Model fits all three data points. 
The lowest-mass was given the name "2455" by the Particle Data Group, using their convention that strongly decaying particles are known by a rough value of their mass. It was searched for since the early days of charmed baryon studies. Individual events in bubble chambers were several times touted by experiments as evidence of the particles, but it is unclear how one event of this sort can be used as evidence of a resonance. As early as 1979, there was reasonable evidence of the doubly charged state from the Columbia–Brookhaven collaboration. In 1987–89, a series of experiments (E-400 at Fermilab, ARGUS and CLEO) with much larger statistics, found clear evidence for both the doubly charged and neutral states (though the E-400 neutral state turned out to be a false signal). It became clear that the mass difference "m"() − "m"() is around . The singly-charged state was harder to detect, not because it is harder to produce, but simply because its decay via a neutral pion has more background and inferior resolution when detected by most particle detectors. It was not found (except for the report of a single event), until 1993 by CLEO. The intrinsic width of the is small by the standard of most strong decays, but has now been measured, at least for the neutral and doubly charged states, to be around by the CLEO and FOCUS detectors. The next state up in mass is the spin 3/2 state, usually known as the or the (2520). These are clearly going to be "wider" because of the extra phase space of their decay, which like the (2455) is to one pion plus a ground-state . Again, large statistics are necessary to claim a signal above the large number of - pairs that are produced. Again, the neutral and doubly charged states are experimentally easier to detect, and these were discovered in 1997 by the CLEO Collaboration. The singly charged state had to wait till 2001 by the time they had collected more data. 
The large majority of an atom's mass comes from the protons and neutrons that make it up. The total number of these particles (called "nucleons") in a given atom is called the mass number. The mass number is a simple whole number, and has units of "nucleons." An example of use of a mass number is "carbon-12," which has 12 nucleons (six protons and six neutrons). The actual mass of an atom at rest is often expressed using the unified atomic mass unit (u), which is also called a dalton (Da). This unit is defined as a twelfth of the mass of a free neutral atom of carbon-12, which is approximately . Hydrogen-1, the lightest isotope of hydrogen and the atom with the lowest mass, has an atomic weight of 1.007825 u. The value of this number is called the atomic mass. A given atom has an atomic mass approximately equal (within 1%) to its mass number times the mass of the atomic mass unit. However, this number will not be an exact whole number except in the case of carbon-12 (see below). The heaviest stable atom is lead-208, with a mass of . As even the most massive atoms are far too light to work with directly, chemists instead use the unit of moles. One mole of atoms of any element always has the same number of atoms (about Avogadro constant). This number was chosen so that if an element has an atomic mass of 1 u, a mole of atoms of that element has a mass close to one gram. Because of the definition of the unified atomic mass unit, each carbon-12 atom has an atomic mass of exactly 12 u, and so a mole of carbon-12 atoms weighs exactly 0.012 kg. 