Observation of Enhanced Long-Range Elliptic Anisotropies Inside High-Multiplicity Jets in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>p</mml:mi><mml:mi>p</mml:mi></mml:math> Collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msqrt><mml:mrow><mml:mi>s</mml:mi></mml:mrow></mml:msqrt><mml:mo>=</mml:mo><mml:mn>13</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>TeV</mml:mi></mml:mrow></mml:math>
Aram Hayrapetyan, A. Tumasyan, W. Adam, J. W. Andrejkovic, T. Bergauer, S. Chatterjee, K. Damanakis, M. Dragicevic, Priya Sajid Hussain, M. Jeitler, Natascha Krammer, A. Li, D. Liko, I. Mikulec, J. Schieck, R. Schöfbeck, D. Schwarz, M. Sonawane, S. Templ, W. Waltenberger, C.-E. Wulz, M. R. Darwish, X. Janssen, P. Van Mechelen, E. S. Bols, J. D’Hondt, Soumya Dansana, A. De Moor, M. Delcourt, H. El Faham, S. Lowette, I. Makarenko, D. Müller, A. R. Sahasransu, S. Tavernier, M. Tytgat, G. P. Van Onsem, S. Van Putte, D. Vannerom, B. Clerbaux, A. Das, G. De Lentdecker, L. Favart, P. Gianneios, D. Hohov, J. Jaramillo, A. Khalilzadeh, K. Lee, M. Mahdavikhorrami, A. Malara, S. Paredes, L. Pétré, N. Postiau, Laurent Thomas, M. Vanden Bemden, C. Vander Velde, P. Vanlaer, M. De Coen, D. Dobur, Y. Hong, J. Knolle, Luka Lambrecht, G. Mestdach, K. Mota Amarilo, César Rendón, A. Samalan, K. Skovpen, N. Van Den Bossche, Jan van der Linden, Liam Wezenbeek, A. Benecke, A. Bethani, G. Bruno, C. Caputo, C. Delaere, I. S. Donertas, A. Giammanco, K. Jaffel, Sa. Jain, V. Lemaitre, J. Lidrych, Paola Mastrapasqua, K. Mondal, T. T. Tran, S. Wertz, G. A. Alves, E. Coelho, C. Hensel, T. Menezes De Oliveira, A. Moraes, P. Rebello Teles, M. Soeiro, W. L. Aldá Júnior, M. Alves Gallo Pereira, M. Barroso Ferreira Filho, H. Brandao Malbouisson, W. Carvalho, J. Chinellato, E. M. Da Costa, G. G. Da Silveira
Abstract
A search for collective effects inside jets produced in proton-proton collisions is performed via correlation measurements of charged particles using the CMS detector at the CERN LHC. The analysis uses data collected at a center-of-mass energy of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msqrt><a:mi>s</a:mi></a:msqrt><a:mo>=</a:mo><a:mn>13</a:mn><a:mtext> </a:mtext><a:mtext> </a:mtext><a:mrow><a:mi>TeV</a:mi></a:mrow></a:math>, corresponding to an integrated luminosity of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mn>138</c:mn><c:mtext> </c:mtext><c:mtext> </c:mtext><c:msup><c:mi>fb</c:mi><c:mrow><c:mo>−</c:mo><c:mn>1</c:mn></c:mrow></c:msup></c:math>. Jets are reconstructed with the anti-<e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:msub><e:mi>k</e:mi><e:mi mathvariant="normal">T</e:mi></e:msub></e:math> algorithm with a distance parameter of 0.8 and are required to have transverse momentum greater than 550 GeV and pseudorapidity <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:mrow><h:mrow><h:mo stretchy="false">|</h:mo><h:msup><h:mrow><h:mi>η</h:mi></h:mrow><h:mrow><h:mtext>jet</h:mtext></h:mrow></h:msup><h:mo stretchy="false">|</h:mo></h:mrow><h:mo><</h:mo><h:mn>1.6</h:mn></h:mrow></h:math>. Two-particle correlations among the charged particles within the jets are studied as functions of the particles’ azimuthal angle and pseudorapidity separations (<l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"><l:mi mathvariant="normal">Δ</l:mi><l:msup><l:mi>ϕ</l:mi><l:mo>*</l:mo></l:msup></l:math> and <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:mi mathvariant="normal">Δ</o:mi><o:msup><o:mi>η</o:mi><o:mo>*</o:mo></o:msup></o:math>) in a jet coordinate basis, where particles’ <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"><r:msup><r:mi>η</r:mi><r:mo>*</r:mo></r:msup></r:math>, <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline"><t:msup><t:mi>ϕ</t:mi><t:mo>*</t:mo></t:msup></t:math> are defined relative to the direction of the jet. The correlation functions are studied in classes of in-jet charged-particle multiplicity up to <v:math xmlns:v="http://www.w3.org/1998/Math/MathML" display="inline"><v:msubsup><v:mi>N</v:mi><v:mi>ch</v:mi><v:mi mathvariant="normal">j</v:mi></v:msubsup><v:mo>≈</v:mo><v:mn>100</v:mn></v:math>. Fourier harmonics are extracted from long-range azimuthal correlation functions to characterize azimuthal anisotropy for <y:math xmlns:y="http://www.w3.org/1998/Math/MathML" display="inline"><y:mrow><y:mo stretchy="false">|</y:mo><y:mrow><y:mi mathvariant="normal">Δ</y:mi><y:msup><y:mi>η</y:mi><y:mo>*</y:mo></y:msup></y:mrow><y:mo stretchy="false">|</y:mo></y:mrow><y:mo>></y:mo><y:mn>2</y:mn></y:math>. For low-<db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline"><db:msubsup><db:mi>N</db:mi><db:mi>ch</db:mi><db:mi mathvariant="normal">j</db:mi></db:msubsup></db:math> jets, the long-range elliptic anisotropic harmonic, <gb:math xmlns:gb="http://www.w3.org/1998/Math/MathML" display="inline"><gb:msubsup><gb:mi>v</gb:mi><gb:mn>2</gb:mn><gb:mo>*</gb:mo></gb:msubsup></gb:math>, is observed to decrease with <ib:math xmlns:ib="http://www.w3.org/1998/Math/MathML" display="inline"><ib:msubsup><ib:mi>N</ib:mi><ib:mi>ch</ib:mi><ib:mi mathvariant="normal">j</ib:mi></ib:msubsup></ib:math>. This trend is well described by Monte Carlo event generators. However, a rising trend for <lb:math xmlns:lb="http://www.w3.org/1998/Math/MathML" display="inline"><lb:msubsup><lb:mi>v</lb:mi><lb:mn>2</lb:mn><lb:mo>*</lb:mo></lb:msubsup></lb:math> emerges at <nb:math xmlns:nb="http://www.w3.org/1998/Math/MathML" display="inline"><nb:msubsup><nb:mi>N</nb:mi><nb:mi>ch</nb:mi><nb:mi mathvariant="normal">j</nb:mi></nb:msubsup><nb:mo>≳</nb:mo><nb:mn>80</nb:mn></nb:math>, hinting at a possible onset of collective behavior, which is not reproduced by the models tested. This observation yields new insights into the dynamics of jet evolution in the vacuum. © 2024 CERN, for the CMS Collaboration 2024 CERN