Code 42
PDG Code 42 · Leptoquark
In the Particle Data Group's Monte Carlo particle numbering scheme, the shared ID list for particle-physics software, code 42 is the leptoquark (LQc), a hypothetical particle not yet observed.
Physicists' computer programs give every particle a number so they can talk to each other, and the Particle Data Group keeps the list. The photon is 22. The Higgs boson is 25. The graviton is 39. Number 42 is the leptoquark, a particle that would link the two families of matter, quarks and leptons. No one has ever found one. Its number is already waiting.
What it supports
An exact assigned code in the scheme the PDG calls the industry standard for event generators, detector simulators and analysis packages (introduced 1988, revised August 2025). One-of-a-kind exotic particles get codes 41 to 80, and the table lists R0 at 41 and LQc at 42. The Pythia 8 manual independently describes a scalar leptoquark "assigned PDG code 42".
What it does not
Not evidence that leptoquarks exist: the PDG review gives only search limits. Not a mass, charge or constant of nature. Codes are assigned in order, so 41 and 51 are taken too. Not IANA port 42 or any computing registry. Not Adams.
ExactnessExact
Form42
UnitPDG Monte Carlo particle ID
Strengthhard
When2025
Hung6 October 2026