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Posts Tagged ‘D0’

There has been a lot of press about the recent DØ result on the possible \(B_s \pi\) state. This was also covered on Ricky Nathvani’s blog. At Moriond QCD, Jeroen Van Tilburg showed a few plots from LHCb which showed no signal in the same mass regions as explored by D∅. Tomorrow, there will be a special LHC seminar on the LHCb search for purported tetraquark, where we will get the full story from LHCb. I will be live blogging the seminar here! It kicks off at 11:50 CET, so tune in to this post for live updates.

Mar 22, 2016 -12:23. Final answer. LHCb does not confirm the tetraquark. Waiting for CMS, ATLAS, CDF.

Mar 22, 2016 – 12:24. How did you get the result out so fast? A lot of work by the collaboration to get MC produced and to expedite the process.

Mar 22, 2016 – 12:21. Is the \(p_T\) cut on the pion too tight? The fact that you haven’t seen anything anywhere else gives you confidence that the cut is safe. Also, cut is not relative to \(B_s\).

Mar 22, 2016 – 12:18. Question: What are the fractions of multiple candidates which enter? Not larger than 1.2. If you go back to the cuts. What selection killed the combinatoric background the most? Requirement that the \(\pi\) comes from the PV, and the \(p_T\) cut on the pion kill the most. How strong the PV cut? \(\chi^2\) less than 3.5 for the pion at the PV, you force the \(B_s\) and the pion to come from the PV, and constrain the mass of \(B_s\) mass.

Mar 22, 2016 – 12:17: Can you go above the threshold? Yes.

Mar 22, 2016 – 12:16. Slide 9: Did you fit with a floating mass? Plan to do this for the paper.

Mar 22, 2016 – 12:15. Wouldn’t \(F_S\) be underestimated by 8%? Maybe maybe not.

Mar 22, 2016 – 12:13. Question: Will LHCb publish? Most likely yes, but a bit of politics. Shape of the background in the \(B_s\pi\) is different in LHCb and DØ. At some level, you expect a peak from the turn over. Also CMS is looking.

Mar 22, 2016 – 12:08-12:12. Question: did you try the cone cut to try to generate a peak? Answer: Afraid that the cut can give a biased estimate of the significance. From DØ seminar, seems like this is the case. For DØ to answer. Vincenzo Vagnoni says that DØ estimation of significance is incorrect. We also don’t know if there’s something that’s different between \(pp\) and \(p \bar{p}\).

Mar 22, 2016 – 12:08. No evidence of \(X(5568)\) state, set upper limit. “We look forward to hearing from ATLAS, CMS and CDF about \(X(5568)\)”

Mar 22, 2016 – 12:07. What if the production of the X was the same at LHCb? Should have seen a very large signal. Also, in many other spectroscopy plots, e.g. \(B*\), look at “wrong sign” plots for B and meson. All results LHCb already searched for would have been sensitive to such a state.

Mar 22, 2016 -12:04. Redo the analysis in bins of rapidity. No significant signal seen in any result. Do for all pt ranges of the Bs.

Mar 22, 2016 – 12:03. Look at \(B^0\pi^+\) as a sanity check. If X(5568) is similar to B**, then the we expect order 1000 events.

Mar 22, 2016 – 12:02.Upper limits on production given.

Mar 22, 2016 – 12:02. Check for systematics: changing mass and width of DØ range, and effect of efficiency dependence on signal shape are the dominant sources of systematics. All measurements dominated by statistics.

Mar 22, 2016 – 12:00. Result of the fits all consistent with zero. The relative production is also consistent with zero.

Mar 22, 2016 – 11:59. 2 fits with and without signal components, no difference in pulls. Do again with tighter cut on the transverse momentum of the \(B_s\). Same story, no significant signal seen.

Mar 22, 2016 – 11:58. Fit model: S-wave Breit-Wigner, mass and width fixed to DØ result. Backgrounds: 2 sources. True \(B_s^0\) with random track, and fake \(B_s\).

Mar 22, 2016 – 11:56.  No “cone cut” applied because it is highly correlated with reconstructed mass.

Mar 22, 2016 – 11:55. LHCb strategy: Perform 3 independent searches, confirm a qualitative approach, move forward with single approach with Run 1 dataset. Cut based selection to match D∅ strategy. Take home point. Statistics is 20x larger and much cleaner.

Mar 22, 2016 – 11:52. Review of DØ result. What could it be? Molecular model is disfavored. Diquark-Antidiquark models are popular. But could not fit into any model. Could also be feed down of  radiative decays. All predictions have large uncertainties

Mar 22, 2016 –  11:49. LHCb-CONF-2016-004 posted at cds.cern.ch/record/2140095/

Mar 22, 2016 – 11:47. The speaker is transitioning to Marco Pappagallo .

Mar 22, 2016 – 11:44. People have begun entering the auditorium for the talk, at the end of Basem Khanji’s seminar on \(\Delta m_d\)


It’s been a very exciting winter conference season here at DZero, one of the two huge experiments at the Fermilab Tevatron Collider.

The massive size of the DZero detector is evident in comparison to the size of the man standing near the top of the image. Credit: Fermilab

What’s the winter conference season? We pretty much take data all the time, and we analyze the data and produce dozens of results every year. These analyses are ongoing, but there are two big events in the year where experiments here and at the Large Hadron Collider at CERN aim to roll out new results. That’s the winter and summer conferences. It’s kind of like when the fashion designers send their latest creations down the runway, hoping to turn as many heads as possible. These conferences are where we introduce to the world our latest and greatest insights about the nature of the universe.

The biggest winter conference is “Rencontres de Moriond” held in the Italian Alps, and it just completed two weeks ago. The big summer conference changes from year to year, and last year it was the International Conference on High Energy Physics, or ICHEP, in Paris. I was fortunate to give a talk for DZero at that one (yes, a perk of being a physicist is that every now and then you get to go somewhere nice).

 A deluge of data:


As a scientist on DZero and head of the team that runs the data handling for many Fermilab experiments, things get busy in many ways when we gear up for the conference seasons. For example, physicists run computer programs to analyze the mountain of data that comes from the detector. The computers are always busy, but before the conferences they get super busy as people try to finish up their analyses. For those weeks we deliver around 200 terabytes of data per day! The amount of data in 200 terabytes is equivalent to watching a high-definition television station non-stop for 2 ½ years (that reminds me that my 5-year-old daughter needs to watch less TV)!! Our data-handling system is very robust and tends to run itself. But, this season the demand for data was so great that some future plans to make it more efficient had to get implemented very quickly. Fortunately, that all worked and now it’s ready for even greater demands that may be coming in the summer.

 The Results:


A smattering of results from DZero for the 2011 winter conferences. Click on image to make it larger. Credit: DZero

I’m also a “subgroup” convener, which means I organize a small group of analyses and the people doing them. Probably the most exciting result being presented this winter is the Tevatron mass exclusion for the Higgs boson, which was written about previously in Quantum Diaries. But there are lots of other new results as well, including two from my subgroup.

One result is an updated result, which means we’ve analyzed more data, from an analysis that looks for collisions that produce two Z bosons (ZZ). These events are very, very, very rare. In fact in the Standard Model, the theory that describes sub-atomic particles, the Higgs is the next rarer process. Showing that we can find ZZ proves that we really understand our detector and our data. And, in fact, the result shows that we find ZZ at the level the Standard Model predicts.

The other analysis looks for events that have a W boson and a photon (the latter is a particle of light). We now see a few hundred of these events and have a clear picture of the “radiation amplitude zero”, which is an interesting effect predicted by the Standard Model that says that the W and photon fly off in some directions more often than others.

I mentioned I was lucky enough to give a talk at last year’s big summer conference. It was exciting to be in Paris, which is my favorite foreign city and where I’m reminded how much of my high school French I’ve forgotten. But it was also exciting because that was the conference where the new LHC experiments showed their first results.

 This winter they had more results and joined us in comparing experiment with theory. While the LHC is just starting, as you may have heard, the Tevatron will wind down soon. But that doesn’t mean we’re done. We will have lots more data and lots more analyses, including possibly some new ones. The results from our final data set will be appearing at many summer and winter conferences to come!

— Adam Lyon