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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What do we mean by fit of data in particle physics?
I am unable to clearly understand the meaning of fitting the data. Like in this paper of determination of mass and width of Z boson and number of neutrinos (from ALEPH detector)
Does it mean that ...
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Decay of Z boson
I have following queries regarding the decay width of Z boson.
In thisThomson's lectures, page 479, it says that decay of Z to hadrons have a large cross section because of factor 3 from colors. But, ...
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What is $\sigma_{i\eta i\eta}$?
In LHC experiments like, CMS there are variables like ieta which are used for designating the eta (pseudo rapidity) of each of the sub detector components.
There are several plots which I came ...
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Periodic multi-layer scattering of neutrons
I am trying to understand the reflectivity plot on slide 26 of Neutron optics,Soldner lecture.
1.Is the peak from $\theta$=0.0 to 0.4 due to total external reflection from the first upper surface?.
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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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Coherent scattering of neutrons
It is said that neutrons have small scattering angles in case of elastic coherent scattering. I am having some queries regarding the same.
Why do we call it coherent? I mean, we say that for coherent ...
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What is the difference between data-driven and semi-data-driven techniques?
I keep hearing the terms data-driven and semi-data-driven techniques(especially for background estimation) in many CERN analysis talks. I looked for their difference but didn't find any documentation ...
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How do we know that the 2012 LHC discovery is SM Higgs Boson and not a pseudo-dilaton?
To be more clear, are there any measurements or analysis done on the new particle to verify if it is SM Higgs boson and not a pseudo-dilaton.
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How do we know that we measure only the higgs and not 2 or more particles?
How do we know that we measure only the higgs boson and not also its superpartner, the width of the spike is quite wide (a few GeV).
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Why do we get preferential decay of particles in electron-muon scattering
I understood things mathematically but I am not able to convince myself intuitively. The query I am having is regarding the preferential decay of electron in electron-muon scattering.
$$\frac{d\sigma}{...
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Charged particles emiting radiation
I tried to find the reason by couldn't get the right answer. I wished to know that if both proton and electron have same acceleration, do they radiate same amount/amplitude of EM radiation. Also, ...
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Inelastic scattering problem [closed]
Regarding this example, I am unable to get the last step. The confusion I have is: I think that the threshold energy remains the same for both CM frame and lab frame(i.e $4m_p$). Hence, to get 4 ...
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Why can't the LHC detect heavy particles?
I am reading The Elegant Universe by Brian Greene.
In many places it's directly/indirectly mentioned that the LHC may not be able to detect (with the current technology) heavy particles to prove ...
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Parton distribution function interpretation
I wished to clarify the interpretation of parton density plot1.
Are the following interpretation correct?
First fix $Q^2$ for an experiment.
Then the area under each curve $\int_0^1 xf(x)dx$ ...
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What are the consequences of LHC results for supersymmetry? [duplicate]
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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Which process(interaction) is more probable?
I am bit confused with process " $q \bar{q}\rightarrow g$" and "$q \bar{q}\rightarrow Z^0$". I guess at high energies of LHC, weak interaction is more probable and hence "$q \bar{q}\rightarrow Z^0$" ...
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Why does both the electron and the antineutrino have spin only $+1/2$ in the Wu experiment?
In ${\rm Co}\rightarrow {\rm Ni}^* + e^- + \bar{\nu}_e$, the Wu experiment, it is said that $J_{co}$ = 5, $J_{Ni}$ = 4 and hence J of "$e^- + \bar{\nu}_e$" system is 1. If orbital angular momentum is ...
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What is a best fit branching fraction?
While describing the decay of Higgs to final states which are not allowed by standard model many papers report numbers like "The Branching fraction $B(H \rightarrow XY)<1\%$ at $95\%$ confidence ...
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Hard particles and soft particles
I am reading these names: hard particles and soft particles while reading literature related to jets but yet have not come across a formal definition classifying them. Does it mean that the particles ...
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How can you separate sub atomic particles and manipulate them? [duplicate]
Say, in Large Hadron Collider how can people separate a proton from an atom and then accelerate it and what is even more miraculous to collide it with another proton? It sound like impossible. ...
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Event selection cuts and cross section relation
I was working on experimental HEP project where I am bit confused. I generated 1000 MC events with say "x" cross section and without selection cuts. Now suppose I put some selection cuts while writing ...
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Information about the fundamental particles
Where can I get the most authentic information about the fundamental particles about all their properties(like charge, mass, spin, isospin, parity, hypercharge etc) which a particle physicist might be ...
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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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The Higgs boson
In a writeup about the Higgs Boson a comment was made that a particle discovered in the Cern collider looked like he elusive Higgs particle. When it is said that the particle (LOOKS) like the elusive ...
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Cut-flow in experimental particle physics (offline analysis)
In experimental particle physics, when analyzing data from some experiment we require a baseline event selection by applying "cuts" on kinematic variables such as the pseudorapidity $\eta$, transverse ...
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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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0-jet and 1-jet categories in experimental particle physics
In experimental particle physics at e.g. the LHC, the analysis of a certain process is often divided into categories described as "0-jet", "1-jet" and "2-jets", etc. Although it seems obvious, I want ...
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Why is Higgs particle detected much later than top quark when it's lighter? [duplicate]
The Higgs boson is lighter than the top quark. But the top quark was discovered in the mid-1990s where the Higgs boson escaped detection for two more decades. So if the energy has already been ...
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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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Gauge invariance of the standard model
It is known that the standard model is $SU(3)_c \times SU(2)_L \times U(1)_Y$ gauge invariant. But, my question is: This is possible, when we write the Lagrangian in terms of weak eigenstates or in ...
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What are isolated and non-isolated electrons/photons in trigger menus?
I am trying to understand the trigger menus of CMS(Compact Muon Solenoid). I understand the different selection cuts($E_T$ Threshold) that they use but they also keep mentioning about using isolated ...
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What is a $D^{0 \ast}$ meson?
What are the quark contents of $D^{0 \ast}$ meson?
How to distinguish between $D^{0 \ast}$ meson and $D^{0}$ meson as I guess both have same quark content.
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What is an LHC Fill?
According to the information I gathered from CERN wiki pages, an LHC fill is a collection of several good runs. Am I right? Also, is an LHC run defined as a discontinuous period of data collection ...
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What kind of data do simulation packages like PYTHIA or ISAJET programs produce?
I read in a CMS TDR (Compact Muon Solenoid Techincal Design Report) that "PYTHIA or ISAJET programs were run to produce minimum bias, QCD jet, top, Standard Model higgs, MSSM higgs or SUSY sparticle ...
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Higgs to 4 lepton decay width
I am bit confused with a statement I read. It talks about $H\to 4\ell$ decay width (higgs to 4 lepton). Now, higgs can decay through different modes. But, as far as I know it doesn't decay directly to ...
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Higgs to 4 lepton decay involving virtual photon
In Gluon gluon production of Higgs, is it possible for higgs to decay to following channels:
A pair of virtual photons which then decay to a pair of leptons each.
To an on shell Z boson and a virtual ...
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Could pp Collisions in the LHC produce Gravitons? [duplicate]
Could proton-proton Collisions in the LHC produce Gravitons?
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Number of flavors of quarks - a supersymmetry debate
My dad and I were debating over the number of flavors of quarks last night, and I'd kind of like to settle it.
I said there were six flavors of quarks - up, down, top, bottom, strange, and charm. He ...
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Cross-section for $t\bar{t}H$
I often see precision measurements of the $t\bar{t}H$ process at the (HL-)LHC justified by the statement that "it's the only cross-section that's directly proportional to the Higgs-top Yukawa coupling"...
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What is the maximal particle mass one can create via the LHC? Can we create dark-matter particles via the LHC?
Thanks to the LHC one can make particles collide and annihilate into other particles.
Therefore, currently, what is the mass of the most massive particle one could create theoretically given the ...
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What is Large about the LHC? [closed]
Does the Large in Large Hadron Collider describe the collider or the hadrons?
I looked into it a bit and am posting this to share my answer with the community. I'm also required to write so much in ...
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What are transverse momentum cuts for?
In experimental papers such as http://arxiv.org/abs/1603.02248 (page 5, section 3.2) there are requirements that the transverse momenta of certain particles are greater than a certain minimum amount ...
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Will the Large Hadron Collider "explode" if the power is turned up too high?
The Large Hadron Collider, at low power, accelerates particles such that much of the total energy provided goes towards increasing their kinetic energy and their masses increase to some extent as well,...
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How are anti quarks produced in $pp$ collision at LHC?
I remember reading that the background contains $q \bar{q}$ giving 4 leptons while studying the 4 lepton decay channel of Higgs boson. Since LHC is a $pp$ collider, I was wondering the source of anti-...
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What is the difference between Si pixel and Si strips used in CMS Inner tracker at CERN?
What is the difference between Si pixel and Si strips used in CMS at CERN? Both are used for tracking and as the CERN website mentions, they are also based on the same working principles. Or are they ...
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Why does LHC use a $pp$ collision and not $p\overline{p}$ collision?
Why does LHC use a $pp$ collision and not $p\overline{p}$ collision, when you actually only need one ring in $p\overline{p}$ as compared to two in $pp$.
Please answer in easy language (I am not much ...
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Highest man-made temperature: why only 470 MeV?
In 2012, the ALICE experiment at CERN achieved a temperature of 5.5 trillion kelvin (5.5 × 1012 K). This was regarded as the highest man-made temperature.
However, even this temperature seems ...
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Differences between reconstruction- and generation-level variables in HEP data
I am working on a CMS - related project where the ROOT trees contain both reconstruction-level and generation-level particle variables (like mass). However, I don't know the basic difference between ...
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LHC gamma radiation from proton-proton collisions
Online resources on radioactivity and gamma radiation at the LHC are primarily concerned with leaking protons, ones that escape the beam and hit various parts of the accelerator complex. Those protons ...
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B Quark physics at LHCb
In official LHCb papers, it is stated that the detector covers a pseudo-rapidity range of $2<\eta<5$, which translates to a range of angles wrt. the beamline of $\sim 1^\circ -15^\circ$ (which I ...
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