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Adam Davis | USLHC | USA

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Live Blogging of the LHCb Bs pi result

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 \(\Delta m_d\)

 

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  • George S. Williams

    “We also don’t know if there’s something that’s different between (pp) and (p bar{p}).”

    I brought this into the discussion in another forum and the idea was dismissed with reasoning that I didn’t think applied. Are there differences between (pp) and (p bar{p}) collisions (without having to invoke BSM) that could produce the discrepancy in the observations?

  • jesse

    You know what , Cern needs to be shut down right away .
    The research that is going on there ,, interdimentional,, in nature .
    You scientist have no right to indanger the human race and need to be stopped.
    Just saying. Your scientific research has always been and will keep being used for mass murder. All those killed are on your heads.