CDS (I) 2024 General Knowledge · Question 13 of 120

Correct — C, 100 GeV. The Higgs boson's measured rest mass is about 125 GeV — the Particle Data Group's 2024 summary table gives 125.20 ± 0.11 GeV — so among the four figures offered, 100 GeV is the only one anywhere near it. The stem asks for the value the mass is 'close to', and 100 GeV sits within about a fifth of the true figure, while every other option is out by a factor of hundreds or thousands. That also places the Higgs above the two other heavy bosons in the same PDG table, the W at 80.37 GeV and the Z at 91.19 GeV.

• (a)0.5 MeV — That is essentially the rest mass of the electron, 0.511 MeV. The Higgs is roughly a quarter of a million times heavier, so this is out by five orders of magnitude.
• (b)900 MeV — This is the scale of the proton (938 MeV) and the neutron (940 MeV). The Higgs is about 133 times heavier than a proton, so a nucleon-scale figure cannot be right.
• (d)1000 GeV — 1000 GeV is 1 TeV, roughly eight times the measured Higgs mass. No Standard Model Higgs boson sits at that energy; the LHC searched that region and found the particle far lower down.

The Higgs boson is the quantum of the Higgs field, the field that the Brout-Englert-Higgs mechanism holds responsible for giving mass to the elementary particles — the W and Z bosons above all, and the quarks and charged leptons through their coupling to it. It was the last particle of the Standard Model to be found. Its own mass is not predicted by the theory; it had to be measured, and the measurement is what the LHC experiments delivered.

This is an order-of-magnitude item, not an exact-value item, and it is fair to say the key's answer is the nearest of four rather than the true figure — 125 GeV is not 100 GeV. Two of the wrong options are recognisable decoys built out of masses a student should already know: 0.5 MeV is the electron and 900 MeV is the proton, so if those two ring a bell they can be struck out on sight. That leaves a choice between 100 GeV and 1000 GeV, and the useful anchor is that the Higgs is heavier than the W and the Z but of the same general scale, which puts it in the low hundreds of GeV rather than in the TeV range.

• The Particle Data Group's 2024 gauge-and-Higgs summary table lists the Higgs mass as 125.20 ± 0.11 GeV.
• The discovery of a Higgs-like particle was announced by the ATLAS and CMS collaborations at CERN on 4 July 2012.
• In the same PDG table the W boson mass is 80.3692 GeV and the Z boson mass is 91.1880 GeV — both lighter than the Higgs.
• François Englert and Peter Higgs shared the 2013 Nobel Prize in Physics for the theoretical mechanism confirmed by that discovery.

• Reading 'close to' as 'exactly' and rejecting 100 GeV because the true value is 125 GeV — the item wants the nearest order of magnitude.
• Mixing up the MeV and GeV rungs; 900 MeV is not close to 100 GeV but is a hundred times smaller.
• Believing the Higgs gives mass to everything, including the proton — most of a proton's mass comes from the binding energy of its quarks and gluons, not from the Higgs field.

Asked as a straight numerical-scale item; UPSC has also asked the Higgs from the conceptual side, on what its discovery would establish.

• practice — not a real PYQ

  The Higgs boson was announced as discovered in 2012 at which facility?

  • (a)Fermilab, USA
  • (b)The Large Hadron Collider at CERN
  • (c)KEK, Japan
  • (d)The Institute for Plasma Research, India

  Answer(b) The Large Hadron Collider at CERN — the ATLAS and CMS collaborations announced the discovery on 4 July 2012.

• practice — not a real PYQ

  Which of the following particles is the heaviest?

  • (a)Electron
  • (b)Proton
  • (c)W boson
  • (d)Higgs boson

  Answer(d) Higgs boson — at about 125 GeV it is heavier than the W boson (about 80 GeV), the proton (about 0.94 GeV) and the electron (about 0.0005 GeV).