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CMS-PAS-BPH-16-002
Search for the X(5568) state in B0sπ± decays
Abstract: A search for resonance-like structures in the B0sπ± invariant mass spectrum is performed using an integrated luminosity of 19.7 fb1 of pp collisions at s= 8 TeV collected by the CMS experiment. The B0s candidates are reconstructed in the decay chain B0sJ/ψϕ, J/ψμ+μ, ϕK+K. With about 48,000 B0s-mesons reconstructed, the B0sπ± invariant mass distributions do not show any unexpected structures for different kinematic requirements imposed to the π±, B0s and B0sπ± candidates. An upper limit on the relative production of X(5568) and B0s multiplied by the branching fraction of the decay X(5568)B0sπ± is estimated to be 3.9% at 95% CL in the most conservative case.
Figures Summary References CMS Publications
Figures

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Figure 1:
Invariant mass distribution of the B0s candidates showing the data (black points with error bars), the total fit function (continuous thick red line), the signal functions (thin green curves), and the combinatorial background contribution (dashed blue line). The outermost vertical (blue) lines define the left and right B0s sidebands, while the innermost vertical (green) lines delimit the signal region.

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Figure 2:
MΔ(B0sπ±) distribution of events in the B0s signal (black points with error bars) and sidebands (continuous blue band) regions, where the second distribution is normalized to the first. The (red) vertical band indicates the region MX±ΓX around the mass of the claimed X(5568) state.

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Figure 3-a:
MΔ(B0sπ±) distribution of events in (a) the B0s signal region and (b) B0s sidebands with different ΔR (cone cut) requirements: no cut (black), ΔR< 0.4 (violet), ΔR< 0.3 (green), ΔR< 0.2 (blue) and ΔR< 0.1 (red). The uncertainties are not shown for the sake of clarity. The (red) vertical band indicates the region MX±ΓX around the mass of the claimed X(5568) state.

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Figure 3-b:
MΔ(B0sπ±) distribution of events in (a) the B0s signal region and (b) B0s sidebands with different ΔR (cone cut) requirements: no cut (black), ΔR< 0.4 (violet), ΔR< 0.3 (green), ΔR< 0.2 (blue) and ΔR< 0.1 (red). The uncertainties are not shown for the sake of clarity. The (red) vertical band indicates the region MX±ΓX around the mass of the claimed X(5568) state.

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Figure 4-a:
(a) J/ψK+K invariant mass distribution for events with the K+K invariant mass window removed and pT(B0s)> 25 GeV, pT(π±)> 1 GeV, pT(K±)> 1 GeV. The B0J/ψK+π decay contaminates the signal and the right sideband regions. (b) The corresponding MΔ(B0sπ±) distributions for the B0s signal (black points with error bars), B0s left sideband (red band, made of stars) and B0s right sideband (blue dotted band) regions. All distributions are equally normalized from the mass threshold up to 5.74 GeV. Contributions from B()1,2+B()0π+ decays (and charge-conjugates) are seen around MΔ(B0sπ±) 5.77 GeV and higher masses coming only from the B0s signal and right sideband regions.

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Figure 4-b:
(a) J/ψK+K invariant mass distribution for events with the K+K invariant mass window removed and pT(B0s)> 25 GeV, pT(π±)> 1 GeV, pT(K±)> 1 GeV. The B0J/ψK+π decay contaminates the signal and the right sideband regions. (b) The corresponding MΔ(B0sπ±) distributions for the B0s signal (black points with error bars), B0s left sideband (red band, made of stars) and B0s right sideband (blue dotted band) regions. All distributions are equally normalized from the mass threshold up to 5.74 GeV. Contributions from B()1,2+B()0π+ decays (and charge-conjugates) are seen around MΔ(B0sπ±) 5.77 GeV and higher masses coming only from the B0s signal and right sideband regions.

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Figure 5-a:
(a) MΔ(B0sπ±) distribution of events in the B0s 4 signal region (black points with error bars) with fit results superimposed (blue line). (b) The pull distribution for (a). The (red) vertical band indicates the region MX±ΓX around the mass of the claimed X(5568) state.

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Figure 5-b:
(a) MΔ(B0sπ±) distribution of events in the B0s 4 signal region (black points with error bars) with fit results superimposed (blue line). (b) The pull distribution for (a). The (red) vertical band indicates the region MX±ΓX around the mass of the claimed X(5568) state.
Summary
A search for the X(5568) state was performed by the CMS collaboration using 19.7 fb1 of pp collision data, collected at s= 8 TeV. Using a sample of about 48,000 B0s signal candidates, the B0sπ+ invariant mass spectrum is investigated. No significant structure is found around the mass claimed by the D0 Collaboration. The reconstruction procedure of the X(5568)B0sπ± candidates is verified using the decay channels B()+1,2B()0π+, which share a similar decay topology with X(5568)B0sπ± and are prominent in data. The absence of a peak is supported by the direct comparison with the events in the B0s sidebands, and by fits to the B0sπ+ invariant mass distribution with an X(5568) component included, using different kinematic selection requirements as well as variants of the background modeling, fit regions, and quality criteria. In every case the obtained yield of X(5568) is consistent with zero. An estimation of the upper limit on an X(5568) signal event yield was carried out, resulting in at most 198 at 95% CL.

The evaluation of an upper limit on ρX, which is the relative production rate of X(5568) with respect to B0s multiplied by the unknown branching fraction of the X(5568)±B0sπ± decay, is carried out using the formula

ρXσ(ppX(5568)+anything×B(X(5568)B0sπ±))σ(ppB0s+anything)=NX(5568)NB0sϵB0sϵX(5568)


where NB0s (NX(5568)) and ϵB0s (ϵX(5568)) are the yield and reconstruction efficiency of the decay B0sJ/ψϕ (X(5568)B0sπ±), respectively. The most conservative estimation of the efficiency ratio, determined from preliminary simulations, leads to an upper limit of ρX< 3.9% at 95% CL, which can be compared against the D0 measurement of (8.6 ± 1.9 ± 1.4)% [1].
References
1 D0 Collaboration Evidence for a B0sπ± state PRL (2016) , [PRLett.117,022003(2016)] 1602.07588
2 F.-K. Guo, U.-G. Meiβner, and B.-S. Zou How the X(5568) challenges our understanding of QCD Commun. Theor. Phys. 65 (2016), no. 5, 593--595 1603.06316
3 T. J. Burns and E. S. Swanson Interpreting the X(5568) 1603.04366
4 Karliner, Marek Doubly Heavy Tetraquarks and Baryons EPJ Web of Conferences 71 (2014) 00065
5 LHCb Collaboration Search for structure in the B0sπ± invariant mass spectrum LHCb-CONF-2016-004
6 CMS Collaboration Description and performance of track and primary-vertex reconstruction with the CMS tracker JINST 9 (2014) P10009 CMS-TRK-11-001
1405.6569
7 CMS Collaboration Performance of CMS muon reconstruction in pp collision events at s=7TeV JINST 7 (2012) P10002 CMS-MUO-10-004
1206.4071
8 CMS Collaboration The CMS experiment at the CERN LHC JINST 3 (2008) S08004 CMS-00-001
9 CMS Collaboration Measurement of the CP-violating weak phase ϕs and the decay width difference ΔΓs using the B0sJ/ψϕ(1020) decay channel in pp collisions at s= 8 TeV PLB757 (2016) 97--120 CMS-BPH-13-012
1507.07527
10 Particle Data Group Collaboration Review of Particle Physics CPC38 (2014) 090001
11 The ATLAS Collaboration, The CMS Collaboration, The LHC Higgs Combination Group Collaboration Procedure for the LHC Higgs boson search combination in Summer 2011 CMS-NOTE-2011-005
12 A. L. Read Presentation of search results: The CLS technique JPG28 (2002) 2693--2704, .[,11(2002)]
13 T. Junk Confidence level computation for combining searches with small statistics Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 434 (1999), no. 2, 435 -- 443
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