Questions tagged [particle-physics]

Particle physics is the study of the fundamental forces of nature as they are embodied in the interactions of elementary and composite particles at high energies and short time and distance scales.

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How does a spring's maximum compression ratio change with decreasing it's free length for a coiled helical spring(compression)?

I'm just looking for a simple expression formula for how maximum spring compression changes with free length of a coiled helical spring, say a Compression spring. A way of understanding what I mean by ...
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Did I understand RG correctly?

I am currently self-studying Renormalization Group (RG) in Condensed matter physics (in preparation for graduate school while I'm in Alternative Military Service). While I'm writing bunch of ...
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Energy and Momentum conservation in Bhabha scattering

I came across this question here which was asking my exact initial question (I even came from Griffiths problem 2.4 too!). But the given answer gave me a lot more questions which I think constitute ...
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How was Potassium used to estimate the effect of backgrounds in the Homestake experiment?

I'm trying to understand some of the details of the Homestake experiment, which attempted to measure the rate of neutrino production by the sun. In particular, I'm interested in how Davis et. al. ...
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If Mass Defect for a Stable nuclei is positive, why is its packing fraction negative?

Mass Defect = Mass (Initial : Mp + Mn) - Mass(Final : Observed) So if Mass Defect is positive, it means the nucleus is stable. But it is known ...
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Parity and intrinsic parity definitions

The action of parity operator on wavefunctions is defined as a reflection in the origin $$\hat{P}\Psi(\boldsymbol{r},t)=\Psi(\boldsymbol{-r},t)$$ In particle physics, though some books define its ...
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Which neutral atom-based quantum sensor is hardest to build/operate?

I am currently going through the presentation, "Sensing with neutral atoms", by Grant Biedermann. I understand that, according to the talk, there are a large number of different sensing ...
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What is the role of Hermitian Hamiltonians in relativistic QFT?

In single-particle quantum mechanics, the probability of finding the particle in all space is conserved due to the hermiticity of the Hamiltonians (and remains equal to unity for all times, if ...
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How to test for possible negative mass of dark matter?

What is the phenomenology of how to test if dark matter has possibly a negative mass (WP negative mass) in particle physics experiments, cosmology or astrophysics? I lately came across this ...
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Why were sparks created in Rutherford's alpha particle scattering experiment?

So I just read that when alpha particle hit the gold foil sparks were created. And these flashes were used to determine the angle of scattering. So were the sparks created because the alpha particles (...
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Do microwaves make polar molecules spin or vibrate? [duplicate]

I’ve been reading about how microwave ovens heat up your food and I keep finding conflicting answers (some say it vibrates, others say it spins). On the one hand, I’ve also read that heat is the ...
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Vacuum Transitions and Lorentz Symmetry Breaking

There are many "bumblebee" models 1, 2 where Lorentz invariance is violated usually resulting from a local vector or tensor field acquiring a nonzero vacuum expectation value We do not know ...
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Why does production of electron come with either electron neutrino or positron?

I read that when an electron is produced, it always comes either with an electron neutrino or with a positron. Why is that so? Why doesn't an electron come instead with say a muon neutrino or antimuon?...
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Fusion energy origin

In fusion , I have understood so far that two light nuclei fuse to form a heavy nucleus. The nucleons in the light nuclei experience lesser binding energy as compared to the nucleons in heavy nucleus ...
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Experiments check out theories but who or what checks out the experiments? [closed]

There is a classic saying which goes more or less like this: If your theory is not verified by the experiment then it is wrong! Specifically for the field of particle physics, lately experiments ...
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How many massless particles are there in closed bosonic string theory?

How many massless particles are there for closed strings in bosonic string theory? Page 53 of String Theory and $M$-Theory by Becker and Schwarz states that there are 576 massless states for the $N = ...
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Finding $\Sigma$ wavefunctions from proton wavefunction. Any operator which can achieve this?

Knowing the isospin part of the wavefunction of the proton, it is possible to find that of the neutron by applying the isospin lowering operator $I_-$ which sits horizontally to the left of the proton ...
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Product of Lorentz invariant factors may be Lorentz non-invariant

I'm evaluating an integral and I have three cases to consider. The result of that integral must be Lorentz invariant and independent of center-of-mass momentum. One of the cases I'm certain is in fact ...
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$\rho$ and $\omega$ mesons decays

As far as I understand, typical decay for $\omega$ meson is into $3\pi$, while for $\rho^0$ is into $2\pi$. In fact they are quite similar particles (same spin, parity, similar masses). Why this ...
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Why there is maximum $n$ ($n_{Debye}$) for mode counting in phonon?

Hi! I'm curious about the description in my textbook of maximum $n \rm (n_{debye})$ in mode counting for phonon. I can realize the $n$ has maximum, because $\lambda_n(min) = 2a(\rm{lattice-constant})$....
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Why does the Strange Quark have Strangeness -1?

I have been trying to find an explanation for the strange quarks negative strangeness value, I understand the term strangeness predates the quark model, but I'm unsure if terminology carry over is the ...
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What is the mathematical expression for the Higgs boson coupling constant?

I have been searching around and cannot get an expression for the Higg's coupling constant. By 'coupling constant', I mean for the strong force $$\alpha_S=\frac{{g_S}^2}{4 \pi \hbar c}\approx 0.1\tag{...
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Can free electrons pass through the holes?

In crystalline silicon, when we say that free electrons can move until they fall into a hole, is it possible for that free electron to pass through the hole and continue to move?
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Is Lepton Flavour Universality an accidental symmetry of the Standatd Model?

Is Lepton Flavour Universality an accidental symmetry of the Standatd Model? If it is, why? How does it emerge from the Standard Model?
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Where does the Energy for $W$ and $Z$ Boson Emission come from?

I understand that the Weak interaction is mediated by the $W$ and $Z$ bosons, and that their huge masses are the reason for the Weak interaction's short range. However, I cannot find an explanation ...
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Deriving isospin factors in phenomenological pion nucleon nucleon interactions

Preface One commonly finds this interaction Lagrangian in phenomenology (ignoring constants): $$\mathscr{L} \propto \bar\psi \gamma^5\gamma^\mu \vec\tau\psi \cdot \partial_\mu \vec\pi \tag{1}$$ ...
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Pile-up events in collider experiments and the average number of interactions

Is the average number of interactions a measure of the amount of pile-up events (pollution background events to hard-scatter events)? if not, why is always presented as an indication and how accurate ...
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Can Energy and Momentum Conservation prevent Particle Interactions?

I understand that Quantum Numbers must be preserved during particle interactions, which prevents certain interactions from occurring. However, as Energy and Momentum must also be conserved, are there ...
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In Particle Physics what does the Rest Mass notation: 95$^{+9}_{−3}$ MeV/c$^2$ mean?

On the Wikipedia page for the Strange Quark, I came across the following notation for defining its mass: 95$^{+9}_{−3}$ MeV/c$^2$ Following the reference link brings me to this page, which shows a ...
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Why is the decay channel $H \to \gamma\gamma$ direct evidence that the spin of the Higgs must be different from one?

The title says it all really, I searched this website and came across a post with a question titled Why is the Higgs boson spin 0?. But it doesn't really answer my question in the title. But this next ...
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The mathematics of different particle rotations

So, in general (if I understand this correctly): Force particles behave differently than matter particles under rotation The matter particles need a 720° rotation to put them back into their initial ...
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How To Interpret Cross-Section vs. WIMP Mass Graph?

I'm a bit confused about how to interpret experimental data when it comes to dark matter. For example, in this figure from the XENON1T experiment, is it correct in saying that the upper bound for the ...
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Higgs field has no charged component, how do we justify this?

I've recently learnt about EW symmetry breaking. For the weak isospin doublet higgs field, $$\phi=(\phi^{+}, \phi^{0})$$ We have a vacuum state where $|\phi|=v/\sqrt{2}$, for the vacuum expectation ...
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Does the Higgs field have an energy?

I have many questions about the notion of space. I learned that at the quantum level, energy became quantized and that the infinite sum of energy states can no longer be substitued by integrals (...
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How are we sure that the measured proton spin puzzle will be also observed similarly in the neutron thus a neutron spin puzzle?

The EMC experiment in 1988 using muons' deep inelastic scattering, has reported that the contribution of the valence quarks triplet (i.e. up-up-down) in the proton was measured to contribute as little ...
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Choosing a renormalization point where the amplitude is not defined?

This lecture note goes through the renormalization of the s-channel one-loop correction to the four-point function $\Gamma(s,t,u)$ in $\lambda \phi^4$-theory. It uses Pauli-Villars regularization, ...
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Is the free spectrum of a theory, way above the symmetry breaking scale, massless?

I have asked a similar unanswered question, focused on different aspects, here. My intuition regarding statements frequently made about this issue is that, if a theory contains a breaking pattern $G \...
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Final state radiation and Bremsstrahlung [closed]

Is the final state radiation, whereby a photon is emitted, of a particle caused by Bremsstrahlung, or are the two different effects?
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If particles are also waves cant we invert them by making it reflect off a fixed boundary?

When a pulse on a rope gets reflected off a fixed boundary, it phase shifts 180° and inverts itselfs. If particles are also waves, will doing an equivalent thing create antiparticles? Is it possible ...
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How to study particle physics? [closed]

I finished my first year of PhD in physics this year (consisted of coursework on general physics). We have to work on a research starting by next year. I want to study particle physics but there are ...
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Tadpole VEV from a fermion loop?

We have one extra complex scalar $\Phi$ beyond the Standard Model (BSM) protected by an $U(1)$ global symmetry, which is broken by an Yukawa coupling $ y_\Phi \Phi \overline{\chi} \chi$, where $\chi$ ...
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How can a flavour changing neutral current be drawn for the higgs decay to two down-type quarks?

I am trying to draw a Feynman diagram for the decay $ h \rightarrow d+\bar{s} $, but I'm struggling to create one which makes sense. So far I have this diagram: . Please could someone explain what is ...
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Addition of four-momenta in scattering amplitude of nucleon-anti-nucleon pair in scalar Yakuwa theory

Intro I'm studying QFT using David Tong's lecture notes. In section 3.5 on examples of scattering amplitudes in scalar Yukawa theory, the scattering amplitude $A$ of a nucleon-anti-nucleon scattering ...
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Two questions about the Higgs decay mode graph

I have two questions reading this graph which shows the Higgs decay mode: I know the mass of Higgs bosons is measured to be around 125 GeV, which is the solid line on the graph, so I wonder why could ...
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Even if the Standard Model was found to be complete and in a stable vacuum, could a transition into a false vacua and then decaying change it?

In theory (please correct me if I am wrong in any point), if our vacuum were metastable (i.e. in a "false vacuum" state), it could go through a phase transition into a stable state (a "...
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Is the mass of Higgs bosons measured only through the decay into photons?

I'm reading an essay discussing the measurement of Higgs boson mass: https://cms.cern/news/cms-precisely-measures-mass-higgs-boson, which says that the latest and more accurate measurement results ...
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How to simplify three body decay phase space in terms of invariant mass $q^2$?

We know three body phase space is written as: $$\mathrm d\pi^3 = \frac1{2M_1}\frac{1}{(2\pi)^5}\int\frac{d^3 p_2}{2E_2} \int\frac{d^3 p_3}{2E_3} \int \frac{d^3 p_4}{2E_4} \delta^4(p_1-p_2-p_3-p_4)$$ ...
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How can I interpret this result of Higgs boson decay?

I'm reading this webpage which introduces the idea of measuring the mass of Higgs bosons with high precision: https://cms.cern/news/cms-precisely-measures-mass-higgs-boson . They presented this ...
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Latest experimental evidence for properties of the Higgs boson

I'm trying to find out the most up to date properties for the Higgs boson (like its mass, charge, spin-parity). For now, just focussing on the mass of the Higgs boson, the most up-to-date information ...
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Suppose a massless particle is moving at the speed of light does that mean that the massless particle now gains mass? Not talking about photons here

I have a massless particle moving at the speed of light (the particle is not a photon). Will the particle gain mass according to the equation $E = mc^2$? How or why not?
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