Observation of a pseudoscalar excess at the top quark pair production threshold
Hayrapetyan, Aram, Makarenko, Vladimir, Tumasyan, Armen, Adam, Wolfgang, Andrejkovic, Janik Walter, Benato, Lisa, Bergauer, Thomas, Damanakis, Konstantinos, Dragicevic, Marko, Giordano, Cristina, Hussain, Priya Sajid, Jeitler, Manfred, Krammer, Natascha, Li, Ang, Liko, Dietrich, Mikulec, Ivan, Schieck, Jochen, Schöfbeck, Robert, Schwarz, Dennis, Shooshtari, Maryam, Sonawane, Mangesh, Waltenberger, Wolfgang, Wulz, Claudia-Elisabeth, Janssen, Tahys, Kwon, Hyejin, Ocampo Henao, Daniel, Van Laer, Thomas, Van Mechelen, Pierre, Bierkens, Jas, Breugelmans, Nordin, D'Hondt, Jorgen, Dansana, Soumya, De Moor, Alexandre, Delcourt, Martin, Heyen, Felix, Hong, Yanwen, Kashko, Pavlo, Lowette, Steven, Makarenko, Inna, Müller, Denise, Song, Juhee, Tavernier, Stefaan, Tytgat, Michael, Van Onsem, Gerrit Patrick, Van Putte, Senne, Vannerom, David, Bilin, Bugra, Clerbaux, Barbara, Das, Aloke Kumar, De Bruyn, Isabelle, De Lentdecker, Gilles, Evard, Hugues, Favart, Laurent, Gianneios, Paraskevas, Khalilzadeh, Ali, Khan, Fakhri Alam, Malara, Andrea, Shahzad, Muhammad Aamir, Thomas, Laurent, Vanden Bemden, Max, Vander Velde, Catherine, Vanlaer, Pascal, Zhang, Fengwangdong, De Coen, Maarten, Dobur, Didar, Gokbulut, Gul, Knolle, Joscha, Lambrecht, Luka, Marckx, David, Skovpen, Kirill, Van Den Bossche, Niels, van der Linden, Jan, Vandenbroeck, Jules, Wezenbeek, Liam, Bein, Samuel, Benecke, Anna, Bethani, Agni, Bruno, Giacomo, Cappati, Alessandra, De Favereau De Jeneret, Jerome, Delaere, Christophe, Giammanco, Andrea, Guzel, Ahmet Oguz, Lemaitre, Vincent, Lidrych, Jindrich, Malek, Paul, Mastrapasqua, Paola, Turkcapar, Semra, Alves, Gilvan, Barroso Ferreira Filho, Mapse, Coelho, Eduardo, Hensel, Carsten, Menezes De Oliveira, Thales, Mora Herrera, Clemencia, Rebello Teles, Patricia, Soeiro, Mariana, Tonelli Manganote, Edmilson José, Vilela Pereira, Antonio, Aldá Júnior, Walter Luiz, Brandao Malbouisson, Helena
Abstract
Abstract A search for resonances in top quark pair ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">t</mml:mi> </mml:mrow> <mml:mover> <mml:mrow> <mml:mi mathvariant="normal">t</mml:mi> </mml:mrow> <mml:mo accent="true">―</mml:mo> </mml:mover> </mml:mrow> </mml:math> ) production in final states with two charged leptons and multiple jets is presented, based on proton–proton collision data collected by the CMS experiment at the CERN LHC at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> <mml:mo>=</mml:mo> <mml:mn>13</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mtext>TeV</mml:mtext> </mml:mrow> </mml:math> , corresponding to 138 fb −1 . The analysis explores the invariant mass of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">t</mml:mi> </mml:mrow> <mml:mover> <mml:mrow> <mml:mi mathvariant="normal">t</mml:mi> </mml:mrow> <mml:mo accent="true">―</mml:mo> </mml:mover> </mml:mrow> </mml:math> system and two angular observables that provide direct access to the correlation of top quark and antiquark spins. A significant excess of events is observed near the kinematic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">t</mml:mi> </mml:mrow> <mml:mover> <mml:mrow> <mml:mi mathvariant="normal">t</mml:mi> </mml:mrow> <mml:mo accent="true">―</mml:mo> </mml:mover> </mml:mrow> </mml:math> threshold compared to the non-resonant production predicted by fixed-order perturbative quantum chromodynamics (pQCD). The observed enhancement is consistent with the production of a color-singlet pseudoscalar ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mn>1</mml:mn> </mml:msup> <mml:msubsup> <mml:mtext>S</mml:mtext> <mml:mn>0</mml:mn> <mml:mrow> <mml:mo stretchy="false">[</mml:mo> <mml:mn>1</mml:mn> <mml:mo stretchy="false">]</mml:mo> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> ) quasi-bound toponium state, as predicted by non-relativistic quantum chromodynamics. Using a simplified model for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mn>1</mml:mn> </mml:msup> <mml:msubsup> <mml:mtext>S</mml:mtext> <mml:mn>0</mml:mn> <mml:mrow> <mml:mo stretchy="false">[</mml:mo> <mml:mn>1</mml:mn> <mml:mo stretchy="false">]</mml:mo> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> toponium, the cross section of the excess above the pQCD prediction is measured to be <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>8.8</mml:mn> <mml:msubsup> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.2</mml:mn> </mml:mrow> </mml:msubsup> <mml:mstyle scriptlevel="0"/> <mml:mtext>pb</mml:mtext> </mml:mrow> </mml:math> .