* A new LHC report sets new SUSY exclusions:
ATLAS Collaboration, "Search for supersymmetry in events with four or more leptons in sqrt{s}= 8 TeV pp collisions with the ATLAS detector" (2014)
Results from a search for supersymmetry in events with four or more leptons including electrons, muons and taus are presented. The analysis uses a data sample corresponding to 20.3 fb-1 of proton--proton collisions delivered by the Large Hadron Collider at sqrt{s} = 8 TeV and recorded by the ATLAS detector. . . . No significant deviations are observed in data from Standard Model predictions and results are used to set upper limits on the event yields from processes beyond the Standard Model. Exclusion limits at the 95% confidence level on the masses of relevant supersymmetric particles are obtained. In R-parity-violating simplified models with decays of the lightest supersymmetric particle to electrons and muons, limits of 1350 GeV and 750 GeV are placed on gluino and chargino masses, respectively. In R-parity-conserving simplified models with heavy neutralinos decaying to a massless lightest supersymmetric particle, heavy neutralino masses up to 620 GeV are excluded. Limits are also placed on other supersymmetric scenarios.
* The two LHC experiments, ATLAS and CMS, have presented a combined report on their single top quark production results (other than the critical top quark mass). Single top quark and top-antitop quark pair productions rates closely approximately the expected values.
Nine direct measurements of CKM matrix element Vtb are presented with a maximum precision of 4.1% and a minimum precision of 17%. The most precise measurement has a central value of 0.998 and the range of central values span from 0.97 to 1.13.
Since the number can't in principle ever exceed 1 (since the square of this value is defined to be the probability that a top quark will transform into a bottom quark rather than an strange quark or down quark when it decays by emitting a W boson), the six best fit results greater than 1 are consistent with a best fit to a 100% preference for the tb as opposed to the ts or td possibilities.
The reality is that estimates of Vtb inferred from direct measurements to Vts and Vtd are profoundly more precise than the direct measurements reported in this paper. Vts is 0.0404 to a precision of about 2.5%. Vtd is 0.00867 to a precision of about 3%. This implies that Vtb is 0.999146 to a precision of about 0.005% (about 1000 times as precise as the direct measurements of Vtb reported in this paper). (Note that all Vti values discussed above are actually the absolute value of those elements. The true value is a complex number that reflects the probability of CP violations in the Standard Model CKM matrix).
An ATLAS search ruled out flavor changing neutral current (FCNC) branching fractions in single top quark decays at rates in excess of about 3*10-5. CMS also didn't see FCNC's in single top quark decays, but ruled them out with far less precision.
Andrew: “In R-parity-violating simplified models with decays of the lightest supersymmetric particle to electrons and muons, limits of 1350 GeV and 750 GeV are placed on gluino and chargino masses, respectively. In R-parity-conserving simplified models with heavy neutralinos decaying to a massless lightest supersymmetric particle, heavy neutralino masses up to 620 GeV are excluded. Limits are also placed on other supersymmetric scenarios. …
ReplyDeleteIn addition to disfavoring WIMP dark matter, this collection of experimental data also disfavors SUSY models generally, because one of the core features of most popular SUSY models is that dark matter is explained as a stable lightest supersymmetric particle (LSP) that is a weakly interacting massive particle in the sub-TeV, super-GeV mass range. …
New experiments by the CMS experiment at the LHC rule out a heavy Higgs boson in most of the mass range from 200 GeV to 1 TeV. … These results force these extensions [SUSY Models] to assume that the extra Higgs boson is nearly degenerate in mass with the observed one, or is in excess of 1 TeV which rules out much of the "natural" parameter space of SUSY models. …”
Excellent reports.
Let us contemplate a salmon lake scenario. A salmon lake has zillions of shallow pot holes around it. Now, we are certain that the salmon is extinct in the lake. What is the chance to find some surviving salmons in those pot holes? Of course, for the SUSY devotees, they will still looking for salmons in the ‘cloud’ when we are all certain that no surviving salmon in any of the pot hole.
There is definitely a wiser way than invoking a religious parousia.
I don't think that the salmon lake scenario is a good analogy. There have been very well motivated theoretical reasons to search for new physics in the SUSY pond.
ReplyDeleteThe class of theories that are even capable of being consistent with existing evidence supporting the Standard Model is quite narrow.
SUSY is mathematically self-consistent at all energy scales. Until the Higgs boson was discovered at the mass it was discovered to have, it was entirely possible that the Standard Model equations would produce unphysical answers like probabilities greater than 100% or less than 100% of some kind of event happening in a process at high energies.
SUSY provides dark matter particle candidates in what amounts to an extension of the Standard Model that the Standard Model does not supply. And, it has really not begun to become apparent until the twenty teens that most or all SUSY WIMP dark matter candidates may be contradicted by observational evidence.
While a lack of evidence of SUSY at Tevatron wasn't encouraging, it hasn't been possible to really seriously directly search for SUSY over a very substantial part of the electroweak scale, where SUSY most naturally should e expected, until the LHC came on line, and searches that utilize the LHC had to be designed before that data was available.
Searching for new physics in the form of SUSY predicted phenomenology is very much an instance of looking in the deepest, richest part of the salmon lake, rather than one of looking in the shallow pot holes. Yes, there are holes in the search grid, but I think that most mainstream and big name SUSY theorists have, based on LHC results, are placing more home in high energy scale SUSY that is somewhat unnatural, than in "SUSY of the temporary LHC search gaps." They have turned their primary focus from the dead salmon lake to Lake Superior far upstream from the salmon lake.
Andrew: ‘Searching for new physics in the form of SUSY predicted phenomenology is very much an instance of looking in the deepest, richest part of the salmon lake, rather than one of looking in the shallow pot holes. Yes, there are holes in the search grid, but I think that most mainstream and big name SUSY theorists have, based on LHC results, are placing more home in high energy scale SUSY that is somewhat unnatural, than in "SUSY of the temporary LHC search gaps."’
ReplyDeleteThanks for the nice reply. You have misread my analogy, as I have declared that the salmon lake was done all searches in my analogy. Obviously, you would like to use a different metaphor (with many lakes). But, any way it was just a metaphor. The key issue is the ‘relevancy’.
SUSY can place its home way ‘above’ Planck scale (if it is possible), I will still declare that SUSY is dead if it has no ‘relevancy’ to this universe. ‘This’ universe is a system (closed or opened), that is, it has a gate. If the SUSY is inside the gate, it definitely is confined by the gate. If SUSY is outside of the gate, it can stay away from ‘this’ universe forever and thus has nothing to do with the gate of this universe. Then, where is the gate of this universe (this can be a debating point)? It can be described in two ways.
One, the gate locates at the weak-scale.
Two, see http://prebabel.blogspot.com/2013/11/why-does-dark-energy-make-universe.html
SUSY can place its home at wonder-wonder land, but it must send an ambassador to the vicinity of the ‘gate’ of this universe if it wants to have any relevancy to this universe. Thus, the only search is needed is its ambassador, not the whole clan. If no ambassador nears the gate, I will write it out right there.
andrew: “SUSY is mathematically self-consistent at all energy scales. Until the Higgs boson was discovered at the mass it was discovered to have, it was entirely possible that the Standard Model equations would produce unphysical answers … .”
ReplyDeleteEvery language (including the mathematics) has two personalities.
One, it is a large complex system and has internal structure, that is, it has laws and theorems for that structure. That structure could be isomorphic to other structures, such as a physics law could (perhaps, should) find a corresponding math theorem.
Two, it acts as a symbolic representation to describe a system of not itself, that is, its function being as a language. In this language capacity, it is ‘neutral’, not carrying any true/false value. Thus, we can describe a ‘fiction’ with a (any) language (including with mathematics), and there is a perfect self-consistent between the fiction and the language. So, every ‘ruled out’ physics theory was and will still be mathematically self-consistent. SUSY being mathematically self-consistent has no meaning of any kind to prove that it is not a fiction.
When Standard Model produces an unphysical answer, it is physics-inconsistent (something wrong about the physics, not about math), having nothing to do with any mathematical (only as a language) inconsistency.
A mathematically inconsistent theory is wrong. It may be wrong in ways that aren't terribly important at the moment, but it is wrong.
ReplyDeleteA mathematically consistent theory that can be fit with a proper choice of parameters to the empirical data, might be right.
Few models meet that latter test. All but one of those are wrong too, but they are a much more interesting place to look than the former.