Thursday, July 21, 2011

Major Physics Conference In Progress

The Europhysics Conference in progress right now in France has dumped a vast number of experimental physics papers with the latest results from greatly expanded data sets at LHC and all of the other major experiments going on in the world onto the Internet. viXra log is live blogging some of the results.

Some highlights:

* Previous measured mass differences between top quarks and antitop quarks were probably experimental error. Current results are consistent with no mass difference, a result that is strongly preferred theoretically.

* Muon magnetic anomaly measures may also have been a result of poor theoretical estimates and experimental error, although this is a weaker finding as only one or two papers that weren't definitive addressed this point.

* There are hints of possible new particles at 327 GeV of mass or higher. But, the data is thin. The statistical significance is high, but we are talking about less than a dozen observations out of billions and we can't fit the data to a particular model. For example, the results don't seem to look like the decays of a next generation top quark. The results are also not clearly being replicated.

* The constraints on masses for SUSY particles is greatly increased to ca. 800 GeV or more. In SUSY, the heavier the lighest supersymmetric particle is, the lighter the Higgs boson must be, so the new results disfavor the entire SUSY enterprise if a Higgs boson is not discovered at the very low end of the mass range not yet excluded by experiment.

* Dozens of different studies have been conducted from every angle to find a Higgs boson and not have produced paydirt. While it isn't excluded either, there is not strengthening signal in the data as the data set gets larger and larger. The biggest bumps in the data suggesting a Higgs boson might exist at a particular mass are no bigger than they were when the data sets were much smaller than they are at this conference. The Standard Model may soon have to cope with a way to go Higgless, although this could still come out either way for another six months or so.

UPDATE: A press release and presentation timing and rumors suggest an announcement that the Higgs mass is most likely in the narrow range of 114 GeV to 137 GeV (and if that is the highlight of the conference, as it appears it will be, presumably not a confirmed siting of the elusive boson), based to a fair extent on precision indirect data on top quark mass and other precision electroweak measurements and apparently by excluding areas not previously ruled out rather than actually affirmatively seeing anything. In other words, it is either cornered or absent. The bottom of the range is unchanged (and that is where SUSY fans hope to find it, since the lower it is, the heavier and hence more elusive other SUSY particles can be and thus save the theory). The top of the range has been creeping down from 158 GeV with most effort since earlier this year already focused on the 140 GeV and under range. In other words, the announced rumor, if correct, is only a slight narrowing of the target range from other announcements in the last year and would not be a huge discovery.

* Exclusion ranges for a fourth generation quark have increased to above 400 GeV but fourth generation fermion models are looking increasingly attractive because B meson and other precision experiments are showing that the CKM matrix that governs the probability that quarks turn into other kinds of quarks in weak force interactions is overconstrained in a three generation standard model fermion scenario, and because the changes to the Standard Model involved in adding a fourth generation of fermions would not be radical and also seems to be favored by some neutrino studies.

The apparent impossibility of consisting fitting the experimental data to the CKM matrix is arguably the biggest beyond the Standard Model experimental conclusion of the Conference that is likely to endure for any length of time (also here, "We present updated results for the CKM matrix elements from a global fit to Flavour Physics data within the Standard Model theoretical context. We describe some current discrepancies, established or advocated, between the available observables. These discrepancies are further examined in the light of New Physics scenarii."). The abstract of one of these papers says, in part:

We present the summer 2011 update of the Unitarity Triangle (UT) analysis performed by the UTfit Collaboration within the Standard Model (SM) and beyond. Within the SM, combining the direct measurements on sides and angles, the UT is over-constrained allowing for the most accurate SM predictions and for investigation on the tensions due to the most recent updates from experiments and theory.

Some past findings that spurred beyond the Standard Model theory like top-antitop assymetry and g2muon, as well as numerous "bumps" that didn't pan out in single experiment runs that weren't replicated at below "discovery" level 4 or 5 sigma significance all seem to be going away and the new "bumps" at this conference have not convinced me that they have much staying power yet. But, the CKM matrix has been looking as if it is at risk of being overconstrained for some time and is a good place to look for hints of beyond the Standard Model behavior as a result of its basic structure which would be like a partial periodic table if it turns out that it is incomplete and omits some quark types. Moreover, if the CKM matrix is broken, the strong experimental constraints on the values in the matrix that can be determined with high accuracy provide considerable insight into what the missing values of an expanded CKM matrix must be, and hence which fermions may yet be out there to be discovered and what they might be like.

* There are only a handful of new cosmology and gravity papers, but they seem to support some major refinements to prevailing theories about large scale structure formation in the universe and other big picture issues.

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