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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1answer
180 views

How does the “Look Else Where Effect” affect the chances of detecting a false diphoton excess at the LHC?

Back in December 2015, there was found a 750 GeV diphoton excess in both CMS and ATLAS at the same location with a significance well above $3\sigma$; a 0.13% chance of being false. However, there ...
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164 views

Large Hadron Collider 2015 upgrade, what may we discover?

I realise that the initial answer to my question that may come to mind is, "we don't know yet, obviously" But my question is hopefully not opinion based. For example, does this upgrade have a ...
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204 views

Baryonic density in collision experiments

Does anyone know any way of estimating the net baryon density in collision experiments, e.g. in LHC, RHIC, or the upcoming ones at GSI-FAIR? I have comes across many hand-waving arguments, sample - ...
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527 views

How to integrate over rapidity for Parton Luminosities in LHC?

I want to make a comparison of parton luminosities between Tevatron and LHC. According to Factorization theorem the cross section in hadron colliders, as long as the partonic cross section has $\hat \...
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1answer
83 views

Current experimental evidence of lepton flavour violation other than neutrino oscillation

Is Lepton Flavour Violation (LFV) experimentally established in processes other than neutrino oscillation? This answer by Luboš Motl points out that Interestingly, CMS has detected a 2.5 sigma ...
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Where can we find LHC results talks online?

I'm looking to educate myself on some searches at the LHC, but I find it easier to understand what's going on if I watch a LHC results talk (e.g. by ATLAS, CMS, or an overall summary by a theorist) ...
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Why are the elastic and total cross-section of $pp$ collisions increasing as the C.O.M. energy grows?

Well, that's about it. I don't find any reasonable explanation for this fact. Are they transversally expanding as the energy increases? Please, remember that strong interactions are short ranged and ...
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53 views

How correlated are the statistical significances of the same signal/non-signal for CMS and ATLAS?

Consider a diphoton excess for both ATLAS and CMS at the same energy for two cases: false signal: I'd expect the two statistical significances to be uncorrelated true signal: I'd expect the two ...
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150 views

Branching ratio for a bound state

Consider the meson $\Upsilon(10860)$. It decays into $B\bar{B}$, $B\bar{B}^*+cc$ and $B^*\bar{B}^*$. The mass of $B$ is $5.28 ~\textrm{ GeV}$ and mass of $B^*$ is $5.33~\textrm{ GeV}$. The branching ...
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63 views

How much damage do high energy experiments impose on the LHC detection equipment?

I do appreciate that I am second guessing lots of experts who have already considered this aspect of high energy experimentation, but I have not seen a similar question, my apologies if I missed a ...
2
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1answer
102 views

Why in particle physics the background of resonance is a decaying exponential?

When in particle physics they plot the mass histogram we see a resonance on top of a decaying exponential background? Why is the background modeled to be that way? what is the physical explanation? ...
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1answer
77 views

How many different experimental configurations does the Large Hadron Collider have?

I understand that the LHC can collide protons with protons, heavy ions with heavy ions, or protons with heavy ions, giving three main configurations. But, I'm wondering: is that the only property that ...
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79 views

Nature of particle spectra at ALICE

I have a question regarding the nature of the particle spectrum at ALICE as a function of momentum. The spectra in question can be seen here. My question is, why is it that the particle spectrum in ...
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1answer
195 views

How do they draw collision pictures in Atlas?

Is the picture below a simulation? How to they draw these pictures? The picture is from here.
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53 views

Limits on stable charged particles

Are there generic model-independent limits on massive stable charged particles (say 10-500GeV)? I mean SU(2)/color singlets with just a hypercharge. For example the LEP search (CERN-EP/99-075) was ...
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30 views

Is it possible to replicate condition at planck time after big bang by smashing 2 protons really hard?

Because we need to achieve really really high temperature to mimick the condition just planck time after big bang, so suppose we can accelerate 2 protons at extremely close to speed of light and let ...
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51 views

How can a single particle hit many pixels in Large Hadron Collider?

In the Large Hadron Collider, the way particles are detected (specifically in ATLAS) is analogous to detecting photons using a photodiode(analogous is an exaggeration, but will suffice for the ...
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1answer
99 views

Can a rebranded super-symmetry be consistent with the null results at the LHC

To explain the null results on SUSY at the LHC, it continues to be assumed that the achievement of the energy threshold for the creation of the SUSY partners is beyond the capability of the ...
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37 views

high $p_T$ and low $p_T$ b-jet energy correction factor

For b-jets, to get the true transverse momentum using the reconstructed $p_T$, we use a correction factor $p_{T}^{gen}/p_{T}^{reco}$ obtained using MC. Now suppose I make a plot of $p_{T}^{gen}/p_{T}^{...
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Does the vertex efficiency include track reconstruction efficiency?

Consider a document of ATLAS collaboration on displaced vertex level efficiency. On the first two pages there is a description of cut-offs required to background free displaced vertex reconstruction. ...
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1answer
75 views

Particle detection at LHC - leptons and jets

Invariably, the events that are triggered on have large transverse momentum, so it seems plausible that a jet and a lepton are often detected in nearly the same point of the detector. In this ...
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35 views

Event rate for nuclear collisions covariant form

The event rate on a target of atomic mass $A$, with cross section per nucleus $\sigma$ is given by: $$dR=\dfrac{N_{A}}{A}\sigma\,mv\,dn$$ where $N_{A}$ is the Avogadro number, $m$ and $v$ are the mass ...
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73 views

Feynman type write up for particle physics observables?

In gist: Struggling particle physicist (on the verge of giving up) needs qualitative writeup/article of the various aspects of heavy-ion physics: Kinematics,transformation (Lab <-> Center of Mass)...
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638 views

Pile-up in LHC collisions and number of signal events

When counting the number of accepted events in a collider experiment, what is the effect of not considering the pile-up effect in e.g. proton-proton collisions at the LHC?
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106 views

Problem About Calculation of double Higgs production Cross Section (for gluon fusion) with FeynArts+FormCalc

I want to mention about my problem about FeynArts/FormCalc.I have tried to calculate LHC cross section for "gluon gluon -> H H" process at Standard Model. However, my result XS is quite different from ...
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66 views

Is there an upper-limit for sparticle masses?

I realize there are many flavors to supersymmetry theory but can the LHC reach the energy and luminosity levels past which if sparticles are not detected then supersymmetry can definitively be ruled ...
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1answer
63 views

High $p_T$ and high $Q^2$ in deep inelastic hadronic collisions

When reading about high energy collisions (for example proton-proton collisions at LHC), I always find the relation $Q\sim p_T$, which, for me, is hard to demonstrate. Moreover, I found statements ...
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74 views

Does this phrase in “Knocking On Heaven's Door”, refer to gravitons?

This is an extract from Knocking On Heaven's Door, by Randall (2011) The suprising fact is that if you have a stable particle whose mass corresponds to the weak energy scale that the LHC will ...
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63 views

Can TOTEM's T2 detector measure differential cross sections?

My current research involves making a prediction for data collected by the TOTEM experiment at the LHC. The experiment is primarily designed to measure the total inelastic and elastic scattering cross ...
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2k views

What is the relationship between Luminosity, Intensity, and Flux?

I am always confused by the terminology: In high energy particle scattering, and in particular, in the context of collider physics, what is the relationship between luminosity, intensity and flux? ...
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38 views

Why there is accelerator chain at LHC?

Why can the LHC not accelerate protons to several TeV in one go? What is the limitation? My Answer: First reason is to minimize the cost of LHC accelerator construction by utilizing the previous ...
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26 views

Total cross section in hadron colliders with optical theorem?

In hadron colliders (like LHC) the total cross-section is calculated using the optical theorem. The origin of this is the scattering of two particles which is solved with the Schrödinger equation ...
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18 views

Hadronization in a collider

Say, in a collision, do the quarks need to first hadronize to pions? Or is there a probability that they can hadronize directly to heavier particles like the charm quarks.(quark-anti-quark pair) The ...
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23 views

Effect of Lepton Flavor Universality (LFU) on Lepton Flavor Violation (LFV)

Does the search for Lepton Flavor Violation (LFV) get affected in any possible way when Lepton Flavor Universality (LFU) is used for background estimation? More specifically, because tau's show some ...
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16 views

Drell-Yan Process notes

As the title suggests, I am looking for notes on the Drell-Yan procedure. Specifically, I want to understand how the convolutions with the parton distribution functions appear and the general ...
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2answers
65 views

Collider Luminosity basics

In a collider experiment, the Luminosity is defined as the proportionality factor between the interaction rate and the interaction cross section $dN/dt = L\times\sigma$, with units of $cm^{-2}s^{-1}$. ...
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30 views

Invisible energy in a particle collision

I read a lot about the so-called "missing" energy in hadronic collisions. I always thought that it was mainly due to neutrinos and also nuclear deformations, but today I read that "on average, 30% of ...
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1answer
138 views

Proton Proton Collisions Cross Section Plot by Stirling

I am struggling to understand some details of the cross section plot by Stirling that is very often shown when talking about LHC physics. See e.g. here: http://www.hep.ph.ic.ac.uk/~wstirlin/plots/...
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113 views

Difference between optical potential and nuclear potential (used in neutron optics)

I am discussing a question related to elastic coherent scattering of neutron from a nucleus. I am referring to the terms (optical and nuclear potential) which are used on page 272 of the review ...
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175 views

What are the consequences of LHC results for supersymmetry?

Forgive me my ignorance, I'm just an undergrad. That said, I have listened a couple of talks and lectures in the last years - given by experts in the field - about the future of fundamental ...
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760 views

Polarization of W boson or Z boson

It is known that the massive gauge bosons W and Z have 3 states of polarization-one longitudinal and two transverse. So is it possible that by any means we can decrease it longitudinal polarization ...
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1answer
41 views

how to make a collider high luminosity?

Exactly what procedures are followed to increase the luminosity of a particle collider? Say when LHC increases its luminosity, does it increase the number of protons per bunch? If yes, then how?
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79 views

Estimated total number of Higgs events

How many Higgs events have been observed at the LHC? I understand that this is not terribly well defined question; I'm just after an order of magnitude estimate for the excess events in, let's say, ...
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50 views

Why do Higgs decays depend on the production method?

I'm reading about Higgs phenomenology and I have come across the following table. I don't see why gluon fusion to $b \bar{b}$ is considered to be "impossible" in this table. As far as I can tell, ...
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158 views

CMS magnetic field outside

The magnetic field at CMS is often given as 4 T. According to this picture the field outside the solenoid is just 2 T. Is this just because the field of a solenoid is not constant and decreases with ...
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59 views

References on the LHC experiments

I'm looking for a references / short book which discusses what is going on LHC collider - specific experiments, collision processes, analysis of data, how exactly the facility is operating (not ...
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2answers
123 views

question about other dimensions

The Big Bounce theory says that before the Big Bang there were other Big Bangs over and over. For example, the universe would have a Big Bang within it and then this new mini-universe would expand, ...