Entries - P

particle decay

The spontaneous process of one fundamental particle transforming into other fundamental particles. During this process, an fundamental particle becomes a different particle with less mass and an intermediate particle is created. For example, a W boson can decay into a tau and a neutrino. The intermediate particle then transforms into other particles. If the particles created are not stable - like the tau in this example - the decay process can continue.



Always spell out the name of the particle – do not use the mathematical symbol in text.

The mathematical symbols may only be used in diagrams when they are spelled out in full in the accompanying caption. See graphs and charts.

physics, style


Whenever you link to a PDF, make sure to put the link on the letters [PDF] inside square brackets. This is for people using the website on a mobile phone - PDFs can take a long time to load. 

Find out more about CERN in the general brochure [PDF]



Digit followed by % sign, no space:

Of the 5000 people who answered the survey, 10% were French.

58%, 90% etc

When calculating percentages, beware the "rose by/fell by X%" construction: an increase from 3% to 5% is a 2-percentage-point increase or a 2-point increase, not a 2% increase

Never use the "per thousand" symbol, ‰

0.001 not 1‰

For smaller decimals, house style decrees scientific notation:



Lower case. Not Petabyte, or worse, PetaByte

A unit of information equal to one thousand million million (1015) or, strictly, 250 bytes.

Almost overnight, companies are transitioning from storing gigabytes of data to managing terabytes, and even petabytes, of information.

computing, spelling, style


Capital P, lower case h, capital D. Note the lack of punctuaction. 

Jenny will defend her PhD thesis this year.


phone numbers

See telephone numbers



Plural: photons.

A particle representing a quantum of light or other electromagnetic radiation.


pie charts

Use only 2D pie charts, and label each slice with its corresponding percentage.

A rant about 3D pie charts

Never use 3D pie charts. They misrepresent data.

The important parameter of a pie chart is area. If the pie is represented in 3D, the foreshortening skews the area of each slice and the chart becomes misleading.

In the example below, the 1% slice is at the "back" of the chart – the perspective imposed makes that slice look smaller. Bringing this slice to the front would similarly skew the look of the chart, making the 1% slice look bigger.



Or PIN number (we realise PIN stands for personal identification number - but the tautology is in near universal use), not Pin or pin number



Not pi-meson.

place names

When quoting country, state or county names after the name of a town, set commas before and after:

New results were announced at the conference in Osaka, Japan, last week.


It is not necessary to say that London is in the UK. For all other UK cities, spell out explicitly that they are in the UK. 

A team of physicists from Manchester in the UK reported that…



An ionized gas consisting of positive ions and free electrons in proportions resulting in more or less no overall electric charge, typically at low pressures (as in the upper atmosphere and in fluorescent lamps) or at very high temperatures (as in stars and nuclear fusion reactors).

The current passed through a column of plasma.

See quark-gluon plasma


pm and am

See time


police officer

Not policeman.


A computer program; otherwise programme

A programme of activities. CERN's research programme.



A stable subatomic particle occurring in all atomic nuclei, with a positive electric charge equal in magnitude to that of an electron.

The mass of the proton is 1836 times greater than that of the electron. The atoms of each chemical element have a characteristic number of protons in the nucleus; this is known as the atomic number. The common isotope of hydrogen has a nucleus consisting of a single proton.


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