Search for Long-Lived Neutral Particles Decaying to Quark-Antiquark Pairs in Proton-Proton Collisions at $\sqrt{s} =$ 8 TeV
<p>A search is performed for long-lived massive neutral particles decaying to quark-antiquark pairs. The experimental signature is a distinctive topology of a pair of jets, originating at a secondary vertex. Events were collected with the CMS detector at the CERN LHC in proton-proton collisions at a center-of-mass energy of 8 TeV. The data analyzed correspond to an integrated luminosity of <inline-formula><mml:math display="inline"><mml:mrow><mml:mn>18.5</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:msup><mml:mrow><mml:mi>fb</mml:mi></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math></inline-formula>. No significant excess is observed above standard model expectations. Upper limits at 95% confidence level are set on the production cross section of a heavy neutral scalar particle, <inline-formula><mml:math display="inline"><mml:mrow><mml:mi>H</mml:mi></mml:mrow></mml:math></inline-formula>, in the mass range of 200 to 1000 GeV, decaying promptly into a pair of long-lived neutral <inline-formula><mml:math display="inline"><mml:mrow><mml:mi>X</mml:mi></mml:mrow></mml:math></inline-formula> particles in the mass range of 50 to 350 GeV, each in turn decaying into a quark-antiquark pair. For <inline-formula><mml:math display="inline"><mml:mrow><mml:mi>X</mml:mi></mml:mrow></mml:math></inline-formula> with mean proper decay lengths of 0.4 to 200 cm, the upper limits are typically <inline-formula><mml:math display="inline"><mml:mrow><mml:mn>0.5</mml:mn><mml:mi>–</mml:mi><mml:mn>200</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>fb</mml:mi></mml:mrow></mml:math></inline-formula>. The results are also interpreted in the context of an R-parity-violating supersymmetric model with long-lived neutralinos decaying into a quark-antiquark pair and a muon. For pair production of squarks that promptly decay to neutralinos with mean proper decay lengths of <inline-formula><mml:math display="inline"><mml:mrow><mml:mn>2</mml:mn><mml:mi>–</mml:mi><mml:mn>40</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>cm</mml:mi></mml:mrow></mml:math></inline-formula>, the upper limits on the cross section are typically <inline-formula><mml:math display="inline"><mml:mrow><mml:mn>0.5</mml:mn><mml:mi>–</mml:mi><mml:mn>3</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>fb</mml:mi></mml:mrow></mml:math></inline-formula>. The above limits are the most stringent on these channels to date.</p>
arXiv_1411.6530.pdf
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openaccess_PhysRevD.91.012007.pdf
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