Observation of charmonium pairs produced exclusively in pp collisions

The paper is available here.


More detailed information: ANA note 2014-014


Abstract A search is performed for the central exclusive production of pairs of charmonia produced in proton-proton collisions. Using data corresponding to an integrated luminosity of 3 fb−1 collected at centre-of-mass energies of 7 and 8 TeV, J/ψJ/ψ and J/ψψ(2S) pairs are observed, which have been produced in the absence of any other activity inside the LHCb acceptance that is sensitive to charged particles in the pseudorapidity ranges (−3.5, −1.5) and (1.5, 5.0). Searches are also performed for pairs of P-wave charmonia and limits are set on their production. The cross-sections for these processes, where the dimeson system has a rapidity between 2.0 and 4.5, are measured to be

σ(J/ψ J/ψ) = 58 10(stat) 6(syst) pb,

σ(J/ψ ψ(2S) ) = 63+27−18(stat) 10(syst) pb,

σ(ψ(2S)ψ(2S)) < 237 pb,

σ(χc0χc0 ) < 69 nb,

σ(χc1χc1) < 45 pb,

σ(χc2χc2) < 141 pb,

where the upper limits are set at the 90% confidence level. The measured J/ψ J/ψ and J/ψ ψ(2S) cross-sections are consistent with theoretical expectations.


(pdf and eps versions are available under attachments).

Caption Figure
Figure 1: A representative Feynman diagram for pairs of charmonia produced through double pomeron exchange. Fig1.png
Figure 2: Left: Invariant masses of pairs of oppositely charged muons in events with exactly four tracks. Of the two possible ways of combining the muons per event, the one with the higher value for the lower-mass pair is plotted. Right: Invariant mass of the second pair of tracks where the first pair has a mass consistent with the J/ψ or ψ(2S) meson. When both masses are consistent with a charmonium, only the candidate with the higher mass is displayed. The curve shows an exponential fit in the region below 2500 MeV. Fig2a.png Fig2b.png
Figure 3: Invariant mass of the four-muon system in (left) J/ψ J/ψ and (right) J/ψ ψ(2S) events. Fig3a.png Fig3b.png
Figure 4: Number of tracks passing the J/ψ J/ψ exclusive selection after having removed the requirement that there be no additional charged tracks or photons. The shaded histogram is the expected feed-down from exclusive J/ψ ψ(2S) events. Fig4.png
Figure 5: Transverse momentum squared distribution of candidates for exclusively produced (left) J/ψ J/ψ and (right) dimuons whose invariant mass is between 6 and 9 GeV. The curves are fits to the data as described in the text. Fig5a.png Fig5b.png
Figure 6 (supplementary): Rapidity of J/ψ J/ψ candidates with p2T < 1 GeV2 compared to the acceptance-corrected rapidities for the Durham model. Fig6.png

-- KatharinaMueller - 29 Jul 2014

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PNGpng Fig1.png r1 manage 42.6 K 2014-07-29 - 12:27 KatharinaMueller  
Unknown file formateps Fig2a.eps r1 manage 9.4 K 2014-07-29 - 12:27 KatharinaMueller  
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PNGpng Fig2b.png r1 manage 9.9 K 2014-07-29 - 12:27 KatharinaMueller  
Unknown file formateps Fig3a.eps r1 manage 6.2 K 2014-07-29 - 12:27 KatharinaMueller  
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PNGpng Fig3a.png r1 manage 8.6 K 2014-07-29 - 12:27 KatharinaMueller  
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PNGpng Fig3b.png r1 manage 8.4 K 2014-07-29 - 12:27 KatharinaMueller  
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PDFpdf Fig4.pdf r1 manage 14.2 K 2014-07-29 - 12:27 KatharinaMueller  
PNGpng Fig4.png r1 manage 10.7 K 2014-07-29 - 12:27 KatharinaMueller  
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PDFpdf Fig5a.pdf r1 manage 15.0 K 2014-07-29 - 12:28 KatharinaMueller  
PNGpng Fig5a.png r1 manage 10.6 K 2014-07-29 - 12:28 KatharinaMueller  
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PNGpng Fig6.png r1 manage 12.2 K 2014-07-29 - 12:28 KatharinaMueller  
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