Counting Quarks. University of Southampton. Our goal is to learn about the particles of nature using real data from accelerators We will not explore the theory too much just what you see…
University of Southampton
Our goal is to learn about the particles of nature using real data from accelerators
We will not explore the theory too much just what you see…
Nuclear matter (“hadrons”) is made of quarks – we are going to experimentally determine how many quarks there are…
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What did you drink with your breakfast this morning?
OPAL real data from accelerators
Some Simple Events real data from accelerators
Strong Nuclear Force real data from accelerators
The force between quarks grows with distance !!!!!
Energy builds up between them until many quarks are produced that arrange themselves into strong force neutral hadrons – we see jets…
Taus are heavier electrons again – 3500 times heavier… real data from accelerators
They decay to quarks and electrons/muons in the detector…. Yuk!
The Weak Nuclear Force (Beta Decay) real data from accelerators
Neutrinos only interact by the weak force – once produced we never see them again…
The likelihood that a W will decay to quarks or leptons is the same.. If we produce Ws and count the relative probabilities of outcomes we can count how many quarks there are…
WW Events at LEP real data from accelerators
The decays are so fast you’ll only see the final products in the detector…
Each W can decay to e, m, t plus a neutrino
Each W can decay to two quarks
Double hadronic decay
Double leptonic decay
Events 11-20 (30 sec) real data from accelerators
Events 21-30 (15 sec) real data from accelerators
Events 31-40 (15 sec) real data from accelerators
Events 41-50 (15 sec) real data from accelerators
8 real data from acceleratorsWhat sort of WW decay is this?
Events 51-60 (15 sec) real data from accelerators
Results real data from accelerators
We know there are three sorts of leptons (e,m,t) so there are 9 ways to get double leptonic events
DL = 9
If there are N quarks we expect N double hadronic events
DH = N
& mixed decays
M = 2 x 3 x N = 6 N
We saw ?
We saw ?
We saw ?
N=? N=? N=?
What should we have got? real data from accelerators
LEP has enough energy to make four quarks
BUT – there is an additional factor of three because each quark has three different sorts of charges associated with the strong force
N = 6