Friday wrap-up: LHC restart, dark photon, a drama in five acts...

Wherein I list some (mostly) recent happenings, ramble a bit, and provide links, in an order roughly determined by importance and relevance to particle physics. Views are my own. Content very definitely skewed by my own leanings and by papers getting coverage, and it may not even be correct. It is a blog after all...

• On the LHC restart, the short circuit was fixed on Monday by melting the offending metal fragment with an injection of 400 amps of current for a few milliseconds. Now the news is that "first beams could be circulating in the machine sometime between Saturday and Monday... Particle collisions at an energy of 13 TeV could start as early as June." 

• The NA48/2 Collaboration has submitted their search for the dark photon in $\pi^0\to \gamma A'$ decays, ruling out the remaining parameter space for the dark photon as an explanation for the muon $(g-2)$ anomaly.
  
  
  
  
  

• On the 'Evidence for dark matter in the inner Milky Way' front, we now have a 'Reply to Comment on "Evidence for dark matter in the inner Milky Way."' Will we see a 'Comment on "Reply to Comment on "Evidence for dark matter in the inner Milky Way"'? Stay tuned... 

• In a blog post from Tim Head, it turns out that machine learning can do pretty well at telling the difference between interesting and uninteresting papers on the arXiv, using only the title and abstract as input.

• Arkani-Hamed and Maldacena had a preprint out on Monday: "Cosmological Collider Physics." The paper is about how we might recognise the presence of new particles with inflaton interactions by their impact on primordial cosmological fluctuations. It is quite long (49+12 pages) and far outside my area, so I will leave it at that... I wonder if Tim Head's algorithm would classify the paper as interesting?

• NPR ran a story on the CRAYFIS project aimed at detecting high-energy cosmic rays with a network of smartphones, bringing >7000 people to the service.

• An arXiv preprint from Melbourne CoEPP and collaborators has pointed out that ATLAS and CMS have been led by theorists to perform searches for an unphysical dark matter EFT. To quote from the paper:
  
  As an example of a problem encountered with an $SU(2)_L$ violating EFT, consider the following operator:$$\frac{1}{\Lambda^2}(\overline{\chi}\gamma^\mu \chi)(\overline{u}\gamma_\mu u+\xi\overline{d}\gamma_\mu d)$$This Lagrangian violates $SU(2)_L$, unless $\xi=1$. The case of unequal $u$ and $d$ couplings was considered in Ref. [13], where a very strong constructive(destructive) “interference effect” was found for $\xi=-1(+1)$, the degree of which depends on the energy scale. The analysis of Ref. [13] was subsequently repeated by the LHC experimental collaborations ATLAS [14, 15] and CMS [16, 17]. We shall demonstrate that the large cross section enhancement for $\xi=+1$ is in fact due the production of longitudinally polarized W’s as a result of breaking gauge invariance.

• APS has spotlighted some lattice QCD results from investigators including CoEPP Adelaide node members which indicate that the Λ(1405) resonance has a molecular quark pair+triplet structure (arXiv version).

• Scientific American has a story on dark matter and the dinosaurs, inspired by the Rampino paper from February. They are refreshingly skeptical, and they mention the work of Randall-Reece and Abbas-Abbas, which was my main problem with prior articles -- overall a nice piece of science journalism!

• In video/audio media
• Watch a live event display from the NOvA neutrino experiment, and for some context here is a story.
• Jon Butterworth gave a public lecture at the Perimeter Instutute about the anticipation leading up to the discovery of the Higgs boson in 2012, "The Most Wanted Particle." [1 hour]
• A timelapse of the pixel tracker being installed inside CMS. [5 minutes]
• Conversations with an Astrophysicist on weak gravitational lensing. [36 minutes]
• Some more on card shuffles at Numberphile: a magic trick with a binary surprise. [9 minutes]

• There's an article and interview at Quanta with Yitang Zhang of bounded prime gaps fame. Also shown is the opening scene from the documentary on his life and work.

• I have only seen one April Fools' arXiv article making the rounds this week: A Farewell to Falsifiability. From the abstract, "... some far-thinking physicists have proposed instead that we should give up on the notion of Falsifiability itself. We endorse this suggestion but think it does not go nearly far enough. We believe that we should also dispense with other outdated ideas, such as Fidelity, Frugality, Factuality and other "F" words. And we quote a lot of famous people to support this view." There is some discussion on Peter Woit's blog as to whether this article from Ashoke Sen (Milner Prize winner) is also to be taken as an April Fools' submission, or just some pop-sci...

• In other April Fools' news, CERN (CMS by the looks of it) has discovered The Force, as well as dark energy. Last year Scientific American had a story on their history of April Fools'; this year they turned their backs on "false and misleading content".

• There is a total lunar eclipse tomorrow night (or the next morning, depending where you are). For those in Melbourne, totality will be between 10:58 pm and 11:02 pm!

• This week I became aware of a 1979 document on the CERN server from Ellis et al. called "Can one tell QCD from a hole in the ground? : a drama in five acts." It is indeed a drama in five acts, about QCD, with illustrations and figures!
  
  
  
  
  

• Lastly, some loosely science-related images from the week...
  
  Here is a photo from César Cantú of lightning in the ash cloud of Mexico's Colima volcano (hat-tip Bad Astronomy).
  
  
  
  
  Typhoon Maysak from Samantha Cristoforetti on the International Space Station.
  
  
  

Friday wrap-up: leptogenesis, displaced vertices, mass extinctions, data scraping...

Wherein I list some (mostly) recent happenings, ramble a bit, and provide links, in an order roughly determined by importance and relevance to particle physics.

• Doing the rounds lately has been a new mechanism for leptogenesis: (post-inflationary) Higgs relaxation leptogenesis. APS has a synopsis and Scientific American has a story (never let difficult physics stop a title containing both "Higgs" and "antimatter"). Kusenko, Pearce and Yang achieve the observed matter-antimatter asymmetry using this mechanism in only the minimal Type I see-saw model. The Type I see-saw is a very nice model for neutrino masses, and it can explain leptogenesis via the Fukugita-Yanagida mechanism (1986), but it is not possible to do both without ceding naturalness. For me, this provokes an interesting question: is there any way of doing natural leptogenesis in the Type I see-saw without adding new particles? The only ways I am aware of are resonant leptogenesis and neutrino oscillations. This could be another (and would be a nice selling point for the mechanism) if it can work with $M_N\lesssim 10^7$ GeV... but this requires further thought and investigation; in the examples they give (Figure 2) the right-handed neutrinos are much heavier than this requirement.

• Citizen scientists are looking for displaced vertices by eye in ATLAS event data. Find out more or try identifying some yourself at the official site.

• Tom Kibble's recollections on the history of electroweak symmetry breaking are online. I don't think there is anything in there that is particularly new, but it is a nice short document written at an accessible level. Here is an excerpt on the three-year gap between the Higgs mechanism and the electroweak theory:
  
  The 1964 papers [on avoiding the Goldstone theorem] from the three groups attracted very little attention at the time. Talks on the subject were often greeted with scepticism. By the end of that year, the mechanism was known, and Glashow’s (and Salam and Ward’s) SU(2)×U(1) model was known. But, surprisingly perhaps, it still took three more years for anyone to put the two together. This may have been in part at least because many of us were still thinking primarily of a gauge theory of strong interactions, not weak... A unified gauge theory of weak and electromagnetic interactions of leptons was first proposed by Weinberg later that year. Essentially the same model was presented independently by Salam in lectures he gave at Imperial College in the autumn of 1967 — he called it the electroweak theory... Weinberg and Salam both speculated that their theory was renormalizable, but they could not prove it... Renormalizability was finally proved by a young student, Gerard ’t Hooft, in 1971, a real tour de force using methods developed by his supervisor, Martinus Veltman.

• I'm seeing a bunch of articles linking mass extinctions to disk dark matter again this week. The origin appears to be a press release from NYU on a paper by a Professor of Biology who appears to be an expert in extinction events. You can read it in full for free here. The paper, which is in a monthly notices journal, seems to me to be largely a review, perhaps with the new suggestion of linking the work of Abbas-Abbas on clumpy dark matter capture causing large-scale volcanism with the Randall-Reece disk dark matter scenario to explain the ~35 Myr period in mass-extinction events. For that reason it is disappointing to not see any reference to those authors in the press release or the related articles circling around. Maybe as a consolation, given the buzz around those articles, it is clear that Randall's new book should sell by title alone!

• On the LHC restart, as of 16 Feb ATLAS and ALICE both have their magnets on, and there will be a press briefing about the restart on 12 March.
  

  @ALICEexperiment not alone anymore :) @ATLASexperiment pic.twitter.com/Pq4SqDk2nD
  — federico | ronchetti (@f_ronchetti) February 16, 2015

  nice cosmic ray track into the @ALICEexperiment #CERN #RUN2 pic.twitter.com/vVJ5WAiQdt
  — federico | ronchetti (@f_ronchetti) February 25, 2015

• You can vote here for the Large Hadron Collider to become an official Lego set! See it being made here.

• A new arXiv preprint shows that in elliptical galaxies, the central stellar velocity dispersion (a surrogate for the central black hole mass) is more tightly correlated to the total gravitating mass of the galaxy rather than the stellar mass, connecting central black holes of elliptical galaxies with their dark matter halo.

• A separate preprint has observed nearly-spherical streams of ionized gas winds coming from an active central black hole. Bad Astronomy has a nice article about it. The winds transfer energy into the galaxy well beyond the gravitational influence of the black hole, affecting the galaxy's evolution.

• I learned this week that it is actually fairly easy to extract data from a vector plot. This is a common task for the phenomenologist so I will explain two examples below for reference, since I haven't seen it written anywhere in detail; skip this point if you're not interested.
  
  Usually, if I need to scrape a plot (often exclusion curves) I just use WebPlotDigitizer, however there are some plots with many points or indiscernible lines which are not amenable to that method. For example, the BaBar limit on dark photons is a nightmare:
  
  
  
  
  
  But it is a vector plot, so in principle it should be possible to extract the information on how to draw the curve. Here is one way...
  
  First save the page of the .pdf as an .svg file (I used inkscape). When you open the .svg file in a text editor you will find some intuitive syntax describing how to draw the plot. We want to pick out the BaBar line, so I looked for an occurrence of stroke:#000000 (a black line) associated with a list of numbers. If you do this yourself you will find those numbers in the following context inside a "path" element:
  
  d="m 146.558,372.935 0.639,-122.326 1.668,4.96 1.625,1.169 ...
  
  According to the syntax, in general a path element contains a d="(path data)" attribute, where the ‘d’ attribute contains the moveto, line, curve (both cubic and quadratic Béziers), arc and closepath instructions. In the above case we have a lower case m which indicates relative moveto's which will draw the line of interest. To get the points then we just have to transcribe the list into our favourite format and write a for-do loop (or similar) to obtain absolute positions.
  
  In Mathematica, this can be done by replacing spaces with "},{" and adding opening and closing brackets to obtain the list:
  
  pts={{146.558, 372.935},{0.639, -122.326},{1.668, 4.96},{1.625, 1.169},...
  
  Then the for-do loop is just
  
  Lpts=Length[pts];
  relpts=pts;
  Do[
    relpts[[i]]=relpts[[i-1]]+relpts[[i]]
  ,{i,2,Lpts}]
  
  Which upon plotting looks like the following:
  
  
  
  
  
  Now all you have to do is rescale your axes!
  
  Another example is Fig. 3 of the recent BaBar long-lived particle search:
  
  
  
  
  After saving as a .svg, you will see that the plots are made up of many (many) points. Say you wanted all the cyan points. Each point appears as its own path object in the file like so:
  
  ...
           style="fill:#00ffff;fill-opacity:1;fill-rule:evenodd;stroke:none" /><path
           d="m 1087.05,7047.46 c 0,1.66 -1.35,3 -3.01,3 -1.65,0 -3,-1.34 -3,-3 0,-1.66 1.35,-3 3,-3 1.66,0 3.01,1.34 3.01,3"
           id="path16732"
           style="fill:#00ffff;fill-opacity:1;fill-rule:evenodd;stroke:none" /><path
           d="m 1085.84,7048.66 c 0,1.66 -1.34,3 -3,3 -1.65,0 -3,-1.34 -3,-3 0,-1.65 1.35,-3 3,-3 1.66,0 3,1.35 3,3"
  ...
  
  All the points you want are the coordinates after the m. So you just need to get them somehow. There are no doubt multiple approaches to this. In bash you could grep or awk or sed your way there. For this example I used the command
  
  $ sed -n '/fill:#00ffff/{n;p;}' BaBar1502.svg > cyanpts.dat
  
  to print to file all the lines after a line with a match for fill:#00ffff. If you paste that document into a spreadsheet program you can then pick off the numbers of interest into columns.

• In video media:
• A promo video from CERN with some nice shots of the LHC experiment: The LHC is preparing to start. [2 minutes]
• Here is a drone flying over the ALICE detector. [3 minutes]
• I missed this talk by Dan Hooper from a few weeks ago. Some talk on the central excess is at 28-46 mins. There is also a fun anecdote about astrophysicist Troy Porter. [1 hour]
• Katie Mack talking about Mars plumes, the star that passed through the Oort Cloud 70,000 years ago, the Europa Clipper mission, and Ceres on breakfast radio. Begins at 2:13. [9 minutes]
• SmarterEveryday is starting a space series with a personal touch. In the first video astronaut Don Pettit shows how he turns off the streetlight at the end of his driveway with a laser so that he can better view the night sky. [4 minutes]
• Mary Somerville, Alan Turing, and Stephen Hawking autographs in The Royal Society Charter Book at Objectivity. [5 minutes]

• Interstellar's rapidly spinning black hole was slowed down for aesthetic reasons during rendering, to reduce the resulting brightness asymmetry and blueshift.
  
  
  

• As we know, the arXiv surpassed $10^6$ papers last month and increased its article identifier sequence number to 5-digits to cope with the fact that they are nearing $10^4$ monthly submissions. Hot on arXiv's tail, now viXra has surpassed $10^4$ submissions! The real winner though is the snarxiv, with well over $\infty$ submissions...

• The bright spot on Ceres is actually two bright spots! (Ceres is opening its other eye...)
  
  
  

• This week we won't end on space images. Instead I reproduce a poem by Thomas Otto called "LHC" (I enjoyed the final stanza):
  
  I - LHC
  
  Cold
  Ice cold
  Arctic cold
  Nitrogen cold
  Argon cold
  Helium cold
  Colder than the cosmos:
  Superfluid Helium cold
  
  In the cold,
  Powerful currents
  Engender magnetic forces
  Ushering protons left and right.
  
  Protons travelling on the crests of ethereal waves
  Close to light speed
  100 billion at a time, a galaxy of protons.
  
  Wave after wave emerging from the cold
  Spilling galaxies into the void
  Galaxies of protons collide
  To re-create the origins.
  
  II - CMS
  
  A cylinder from glass and steel,
  A mythical animal hunched deep in its cave,
  Swallowing bunches of protons,
  Like a frog catching flies.
  
  Protons colliding, the debris on paths bent by magnetic forces
  Electrical signals through a network of cables
  The animal’s thoughts light up,
  A memory of the origins
  
  III - CERN
  
  Bright minds
  Tackling tough problems:
  Accuracy of the data,
  Beauty of the theory,
  And origins of the visible universe.
  
  Seasoned researchers,
  At ease with latest physical science:
  Handling strings and triggers,
  Seeing light in crystals,
  And integrating over 26 hidden dimensions.
  
  At lunchtime,
  A challenge like no other:
  Looking for a parking space,
  Queuing for a menu,
  And searching a place to put their meal tray.