Questions tagged [large-hadron-collider]

World's largest particle accelerator built by the CERN (European Organization for Nuclear Research) near the Franco-Swiss frontier near Geneva, Switzerland. It is designed to collide beams of protons with a centre of mass energy of up to 14 TeV. It contains the important detectors ALICE, ATLAS, CMS and LHCb.

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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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What would be the impact of slighty higher mass for the $W$ boson? [closed]

With the recent announcement from CDF https://cerncourier.com/a/cdf-sets-w-mass-against-the-standard-model/ placing it at the mass at $$80,433.5 \pm 6.4\; \text{(stat)} \pm 6.9\; \text{(syst) MeV},$$ ...
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What does the inverse background efficiency represent?

I am reading a paper from the ATLAS experiment on the identification of tau jets from background jets and came across this figure: I am struggling to find what the formula is for the inverse ...
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What are "effective" operators and what is meant by effective operators "at the LHC"?

My research supervisor told me to read about this topic but is currently on leave for the next two weeks. I believe it is related to effective field theory but please could someone elaborate on what ...
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3 votes
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What are the Higgsless Theories that can explain the Higgs boson detection at the LHC?

As many know, in 2012 the Higgs Boson was "detected" at the LHC. I have read that the Higgs boson was not actually directly observed, but the existence of the Higgs boson in the standard ...
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Are the rest frames of particles in LHC detectors approximately inertial?

Years ago as an undergraduate, I studied new-physics contributions to the reaction $ cb \rightarrow tb $ in the case that the $t$ subsequently decays as $t\rightarrow be^+\nu_e$. I considered the ...
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How is the collison area cleaned between lead nuclei collisions at the LHC?

My question involves my lack of understanding present in my thought experiment, so I am looking for corrections in my language or mental model. At the Large Hadron Collider (LHC) collisions happen ...
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3 answers
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Why $R(D)$ is not measured in LHCb and only $R(D^*)$ is measured?

Measurement of $R(D)$ and $R(D^*)$ are important probe of lepton universality violation. They are defined as the ratios of branching fractions: $$R(D^{(*)}) = \frac{\mathcal{B}(B\rightarrow D^{(*)}\...
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What do objects mean in CERN's collision visualisation?

Trying to find a legend for some of the collision visualisations from CERN's CMS, ALICE or other experiments. The visualisation below is from the CMS Higgs Seminar (4 July 2012). What are the things ...
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Parton, detector and particle level at LHC [closed]

What is the difference between parton, detector and particle level in high energy physics? I found a similar question but I couldn't understand the explanation for detector and particle level given ...
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Median discovery/exclusion significance calculation

I was wondering, when using the Asimov approximations for the median discovery or exclusion significance $$Z_0 = \sqrt{2((s+b) \ln(1+ s/b)-s)}$$ are the expected number of signal s and background b ...
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6 votes
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How can a person be hit by a high-energy proton beam?

There is this somewhat famous story of a Russian particle physics Ph.D. student from the 70s, who stuck his head into a particle collider and got hit by a beam of high-energy protons. For more details ...
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How to calculate the direction of the missing transverse energy (MET)?

How exactly do you calculate the direction of the missing transverse energy? This paper (arXiv:1412.2641), for example, makes use of it to get some cuts. Adding to this, how can you correlate this to ...
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Why is magnetic field characterized in "Tesla" in case of a solenoid, but in terms of "magnetic field integral" (in $T \cdot m$) in case of a toroid?

Why is the magnetic field characterized in units of "Tesla" in the case of a solenoid, while it is typically characterized in terms of the "magnetic field integral" (so in $T\cdot ...
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1 answer
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How does collision of particles create more particles?

I mean, how do real particles get created in a collider like the LHC? Is it right that the LHC just gives energy to a pair of virtual particles that were generated by the quantum vacuum making them ...
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Did a particle really seem to go backwards in time during a collision experiment at LHC?

I distinctly remember the news of a weird particle which seems to have gone backwards in time .Probably a Higgs singlet It was probably a high energy collision between proton and proton . A particle ...
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2 votes
4 answers
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How long does the LHC take to accellerate a particle to its full speed? How long would a linear accellerator have to be to reach the same energies?

I'm wondering how long it takes the LHC to accelerate particles from rest to their top speed at 6.5 TeV. And related, how long a hypothetical linear accelerator would have to be to accelerate ...
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What if particle colliders cannot find anything beyond the standard model? [closed]

What if the LHC and further colliders can not find anything beyond the Standard Model? Nightmare scenario: LHC can not find anything beyond the SM-Higgs-like boson. VLHC, the linear collider or the ...
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Why can't I assume the quarks inside a hadron move together?

Looking at the following Feynman diagram: Using conservation of energy, we can see that in the rest frame of $D^0$, the energy of $K^-$ is higher than its rest energy. Meaning, it is in motion. I ...
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11 votes
3 answers
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How does a booster work in a particle accelerator like the LHC?

In the proton synchrotron booster (PS) booster at the LHC, protons are accelerated from $50 \, \text{MeV}$ to about $1.4 \,\text{ GeV}$. This takes about a second to accomplish. Since the radius of ...
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How can we detect particles that have no electric charge?

Particle accelerators look for electric changes, but what if particle has no effect on other particles or an electric charge, would we not detect it?
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Have we ruled out the Minimal Supersymmetric Standard Model (MSSM)?

This question is inspired by a Physics Stackexchange question posted 8 years ago (The future of supersymmetry). The question that I have is very similar to the question in the above link, except that ...
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5 votes
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Future Plans for Searches for Supersymmetry in the LHC

Due to the failure of the LHC to discover supersymmetry so far (July 2021), the simplest and the likeliest supersymmetric models (e.g. the MSSM) have been ruled out, and the confidence in ...
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Dalitz Plot Analysis and Kinematics

I have trouble understanding the fundamental properties of Dalitz plots. For example the Dalitz plotz for the J/Psi (which is treated as unknown) to 3pion decay: I.e. we now have the invariant masses $...
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Has the sign of the quartic SM Higgs coupling ever been measured?

I know that for the SM we assume that the quartic coupling of the Higgs $\lambda_H>0$ due to vacuum stability, but in principle for $\lambda_H<0$ vacuum stability could still be safe if we have ...
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How can we control the resolution in experiments (collider, accelerator, etc.)?

Consider for example we perform the electron-proton scattering experiment. If we accelerate the incident electron with a certain energy, then it means that we can control the center-of-mass energy of ...
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Why is the radius of the circular motion of electron half the radius of the inner part of the detector in Large Hardon Collider?

In a solution to IPhO 2018 question "Where is the neutrino?" part A2, it is written that "the radius of the circular motion is half the radius of the inner part of the detector". ...
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2 answers
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Are we looking at the CERN Supercollider's results the wrong way? [closed]

As some background, I really don't know all that much about physics except what I study in school. So, this question might make me sound like a noob, but I hope I can be beared with. Anyway, I watched ...
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Luminosity of beamdump experiments

There is formula for luminosity of fixed-target experiments: $$L = \Phi\rho l$$ $\Phi$ is the flux of incoming beam (particles per second), $\rho$ - density of target, $l$ - lenght of target. We can ...
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Why are jets misidentified as leptons?

I understand that jets come from the process of a proton-proton collision and the QCD confinement which create more quark-anti quark pair that emit this jets of particles. These jets of particles what ...
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Is there any relationship between the recent LHCb results on lepton universality violation and Bells Ineqalities? [closed]

Link to article re LHCb results As a layperson, my knowledge is limited to what i can understand from pop sci books. Having recently read about (although not quite understood!) Bells Theorem, it ...
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Muons and Electrons Rare Beauty decay

Concerning this recent news from CERN: CERN data on ‘beauty quarks’ behaviour may rewrite physics as we know it (TRT World, 24 March 2021) My son and I (now 13yo) have been doing home based weighing ...
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Higgs to gauge bosons branching ratios

Why does the Higgs to $WW$ branching ratio dominate the $ZZ$ branching ratio so much? Their couplings are quite similar, so what could explain the fact that, at high energies, there are many more $H^0 ...
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Does the LHC measure the mass of the Higgs or its decay products?

I'm sure this sounds like a daft question but I can't find anything all that helpful online to answer this, not even on the CMS website. Is the LHC measuring the actual mass of the Higgs boson or is ...
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Could the sun be used as a particle accelerator?

Large particle colliders require a lot of energy, and inputing more and more energy usually produce more and more interesting results. Assuming that the required collider, detectors, etc. can be ...
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1 vote
1 answer
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Can LHC experiments detect muons and antimuons equally?

Are the LHC experiments such as ATLAS or CMS equally effective at detecting antimuons as they are at detecting muons? Or is there an asymmetry? If you had 50 muons and 50 antimuons, would the numbers ...
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Integrated luminosity in a Monte Carlo Simulation

Suppose we have a Monte Carlo simulation comprising momenta values. How do we calculate the integrated luminosity? There is no time and all values are discrete so I don't understand how I should ...
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Sum of momenta of two protons in LHC

Sum of momenta of two protons in LHC moving in opposite directions is assumed to be zero but it can't be exactly zero so how close does it get to zero?
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2 votes
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What is granularity in particle physics?

What is granularity in particle physics? It is used throughout "The ATLAS Experiment at the CERN Large Hadron Collider" http://nordberg.web.cern.ch/PAPERS/JINST08.pdf without being defined ...
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What is natural width in particle physics?

What is the meaning of the term "natural width" in particle physics? From http://nordberg.web.cern.ch/PAPERS/JINST08.pdf, page 2: ... there is a range of production and decay mechanisms, ...
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Why the research of unstable collision particles not present in ordinary stable matter is important in high-energy physics?

What is the point and merits of researching artificial made collision product unstable non natural occurring and not present in ordinary stable matter particles? Like for example leptoquarks. ...
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Data rate of Atlas and CMS, LHC's detectors too slow?

There is a technical question I always curious about to ask a CERN expert? I have read, http://nordberg.web.cern.ch/PAPERS/JINST08.pdf, page 5, that the data sampling rate, number of stills taken from ...
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9 votes
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Does the recent "3-sigma" result at LHCb account for the number of different tests of beyond standard model physics that have been done?

Recently there has been quite a lot of media interest generated by a reported observation of beyond-standard-model physics at the LHC with a "three sigma" degree of statistical significance. ...
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Breakthrough at the Large Hadron Collider -Leptoquarks skepticism?

I have came across this recent development in the LHC: Breakthrough at the Large Hadron Collider: https://www.youtube.com/watch?v=qR6P0aRqYf8 Leptoquarks and leptons - quarks unification: https://en....
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Have they used the LHC to see if any subparticles fly off a particle before collision?

Have they used the LHC to see if a particle gives off any subparticles precollision?
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2 votes
1 answer
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Is there a way to determine the production method of a Higgs boson created via collisions in the LHC?

So I'm aware that there are several currently accepted production methods for Higgs boson, such as gluon fusion. When a Higgs boson is detected is it possible to determine the production method from ...
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Collinear factorisation in QCD: why can we multiply probabilities?

In the collinear factorisation equation for a QCD cross-section, schematically $$ \sigma_{AB\to X} = f^A_a \otimes \hat{\sigma}_{ab\to X} \otimes f^B_b , $$ we essentially convolute the probability ...
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3 votes
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What is diffractive dissociation in collisions?

Correct me if I am wrong: If we collide protons with protons then we can have elastic scattering, inelastic scattering (large momentum transfer between partons), and diffractive dissociation. I am ...
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2 votes
0 answers
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How do we know if quantum black holes were made in the LHC? [duplicate]

CERN claims that there's a possibility of formation of tiny 'quantum' black holes inside the LHC. So, if that ever happens (or have already happened), will the observers ever know about it? Can in any ...
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3 votes
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What properties of dark matter can we derive from each of the available methods for probing the physics of dark matter?

This is probably a long shot but it's worth trying. My question is the following: What properties of dark matter can we derive from each of the available methods for probing the physics of dark matter?...
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