# Are there ever electrons in the outcome of proton-proton collisions?

I have explored a google-search for days but I could not find a list of stantard outcomes of p-p collisions: they just say there are tens up to hundreds particles.

Can you say (or give a link) what is the lowest number of particles and what they are? Does that occur at lower energies?

In particular , I'd like to know if there are negative charges (electrons, muons negative pions...) among the shattered particle and what is the greatest number of such charges that can be found after a collision.

• – mpv Sep 26 '16 at 7:32
• @mpv, thanks for the link, but that is of no great help,"...muons,...a couple of pions.." is generic, what is the charge of those pions? Is 'a couple' 2 or a few? The focus of my question is: what is the max number of negative charges that we (can) find among the debris of p-p collision? and that is independent of the probability. Since we start with 2 positive charges, if we find 2 negatives do/should we find 4 positives? – user104372 Sep 26 '16 at 7:39
• The number of products is not given. It is random. That is why Lubos is not stating any exact numbers. The only thing that must be obeyed are the conservation laws: the total energy and momentum must be conserved. Also the baryon number and lepton number. Anything else can be arbitrary. But in real experiments you will not see some insane results. Most probable results are with reasonably limited amount of products. – mpv Sep 26 '16 at 7:59
• @mpv, I am not asking for random data, I am asking what is actually recorded in experiments, have 6 or more negative charges (including eventual charges different from -1) have been observed, for example? – user104372 Sep 26 '16 at 10:09

The maximum number of negative charge among the products of proton-proton collision is limited only by the energy of the collision. The electrons will be created together with positrons, which cancels the charge. All the products together must have total charge 2, which means there can be 1,000 electrons + 1,000 positrons + some other 2 positively charged particles (to sum the total charge of all products to 2). All the products need to have their mass/energy and momentum equal to the energy and momentum of the incoming protons.

Electron + positron mass is 511 + 511 = 1.022 MeV. If your incoming protons had total energy something over 1.022 GeV, their collision can produce 1,000 electrons. If your protons have energy over 1.022 TeV, their collision can produce 1 million electrons. It is just extremely unlikely, but not forbidden.

In terms of actual measured data, most papers focused on multi lepton production deal with final states containing 2-4 leptons. For example in this paper you can see that in 20.3 inverse femtobarn of proton-proton collisions (ATLAS data) there were 85 events with 4 electrons, 156 events with 4 muons, etc (see Table 5). In general, multi lepton events are interesting, as they can help the search for new physics. See for example here or here.

• Thanks, but can you specify what exactly has actually been observed (and at what energies), against what is possible? – user104372 Sep 26 '16 at 7:59
• @user104372 - There are huge datasets at CERN (and other accelerators) - so big they are on the forefront of 'big data'. Become a particle physicist and trawl through it all... – Jon Custer Sep 26 '16 at 14:56
• @user104372 I updated the answer a little bit. But it is difficult to find data on more than 4 leptons in a single collision. – mpv Sep 26 '16 at 15:55
• @user104372 CMS made their (slightly processed) 2011 data set (and the tools to use it) openly available. If you've the time and patience you could run down these kinds of events for yourself. But no one builds an exact catalog because there are many thousands of final states available at high energies. – dmckee --- ex-moderator kitten Sep 26 '16 at 16:25
• Thanks mpv, "If your incoming protons had total energy something over 1.022 GeV, their collision can produce 1,000 electrons.." but that does not account for the energy lost in overcoming the huge repulsive electrostatic force, does it? – user104372 Sep 27 '16 at 5:04

I have explored a google-search for days but I could not find a list of stantard outcomes of p-p collisions: they just say there are tens up to hundreds particles.

The only "standard" outcome is that depending on the energy of the incoming protons, at leas two baryons ( neutrons or protons) will come out, and the total charge of all particles should be two. From then on one has to study multiplicity distributions for charged particles at each energy studied and there are a lot of publications. This article has a review for charged particle multiplicities:

This article summarizes and critically reviews measurements of charged-particle multiplicity distributions and pseudorapidity densities in p+p(pbar) collisions between sqrt(s) = 23.6 GeV and sqrt(s) = 1.8 TeV. Related theoretical concepts are briefly introduced. Moments of multiplicity distributions are presented as a function of sqrt(s). Feynman scaling, KNO scaling, as well as the description of multiplicity distributions with a single negative binomial distribution and with combinations of two or more negative binomial distributions are discussed.

It needs a lot of interest and background in analysing data to be understood.

Can you say (or give a link) what is the lowest number of particles and what they are? Does that occur at lower energies?

Always the minimum is two, for all energies, called elastic proton proton scattering.Example for high energy and low energy. From then on one has individual channels . The multiplicity distributions give the probability of generating a specific number of charged particles when a proton hits a proton at a specific energy.

In particular , I'd like to know if there are negative charges (electrons, muons negative pions...) among the shattered particle and what is the greatest number of such charges that can be found after a collision.

There are charged pions and (kaons which decay into pions) which will decay to muons ( mostly) and electrons and more exotic resonances which will also decay into muons and electrons. A great multiplicity of channels that has to be studied and modeled individually. Of course conservation of charge will be observed, the sum being +2.