# Can you help with particle physics?

• m_ridsdale
In summary, the conversation discusses the use of lepton universality and lepton-quark symmetry to estimate branching ratios for certain reactions. The first question (a) is deemed not possible without quark mixing, as quarks can only change flavor within their own generation. The second question (b) looks at the ratio of masses between the particles involved. The conversation then delves into the observation of certain processes as evidence for weak neutral currents, with the conclusion that the observation of antielectronneutrino + e- -> antielectronneutrino + e- is not considered unambiguous evidence due to the possibility of the reaction occurring with a W boson.
m_ridsdale
I'd really appreciate any help you can give me with the following questions:

Use lepton universality and lepton-quark symmetry (ignore quark mixing) to estimate the branching ratios for:

a) b -> c + e- + anti-electronneutrino
b) tau -> e- + anti-electronneutrino + tauneutrino

Surely (a) is not possible without quark mixing? Isn't it true that without quark mixing, quarks can change flavour but only within their generation, e.g. can have u -> d but not u -> s?

b) I think for this question I just need to look at the ratio of the masses of the mu and the e-, since all differences in their interactions are due to their difference in mass, is this correct? So the answer I would give would be mass(e-)/mass(mu).

Why does observation of the process
antimuneutrino + e- -> antimuneutrino + e-
constitute unambiguous evidence for weak neutral currents, whereas the observation of
antielectronneutrino + e- -> antielectronneutrino + e-
does not?

I've no idea about this, I'd have thought either scattering process could be an electromagnetic interaction; doesn't any interaction involving the Z have an equivalent involving photons?

This one's a little advanced for Homework Help. We typically get inclined planes and calculus problems. It will be more likely to get noticed here, in Theoretical Physics.

I'll take a stab at it later.

Originally posted by m_ridsdale
I'd really appreciate any help you can give me with the following questions:

Use lepton universality and lepton-quark symmetry (ignore quark mixing) to estimate the branching ratios for:

a) b -> c + e- + anti-electronneutrino
b) tau -> e- + anti-electronneutrino + tauneutrino

Surely (a) is not possible without quark mixing? Isn't it true that without quark mixing, quarks can change flavour but only within their generation, e.g. can have u -> d but not u -> s?
agreed.

b) I think for this question I just need to look at the ratio of the masses of the mu and the e-, since all differences in their interactions are due to their difference in mass, is this correct? So the answer I would give would be mass(e-)/mass(mu).
shouldn t it be the ratio of the tau to the electron for this reaction?

Why does observation of the process
antimuneutrino + e- -> antimuneutrino + e-
constitute unambiguous evidence for weak neutral currents, whereas the observation of
antielectronneutrino + e- -> antielectronneutrino + e-
does not?

I've no idea about this, I'd have thought either scattering process could be an electromagnetic interaction; doesn't any interaction involving the Z have an equivalent involving photons?

photons cannot couple to neutral particles. so photons cannot interact with neutrinos.

but i d say the nu_e reaction is not unambiguous evidence for weak neutral currents, because it this reaction could procede with a W boson. not so in the nu_mu case.

## 1. What is particle physics?

Particle physics is the branch of physics that studies the fundamental particles and their interactions. It aims to understand the nature of matter and the forces that govern the universe at the smallest scales.

## 2. How is particle physics relevant to everyday life?

Particle physics may seem abstract, but it has many practical applications that impact our daily lives. For example, particle accelerators are used in medical imaging and cancer therapy, while the development of new materials and technologies often relies on our understanding of subatomic particles.

## 3. What is the Large Hadron Collider (LHC)?

The Large Hadron Collider (LHC) is the world's largest and most powerful particle accelerator, located at the European Organization for Nuclear Research (CERN) in Switzerland. It allows scientists to study the smallest particles and recreate conditions similar to those in the early universe.

## 4. What are some current questions in particle physics?

Some current questions in particle physics include the nature of dark matter and dark energy, the existence of extra dimensions, and the unification of the fundamental forces. Scientists are also searching for new particles and studying the properties of known ones.

## 5. How can I get involved in particle physics research?

There are many ways to get involved in particle physics research, including pursuing a degree in physics or a related field, participating in internships or summer programs at research institutions, and joining scientific collaborations. It's also important to stay updated on current research and advancements in the field.

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