Two-pion femtoscopic correlations in Be+Be collisions at $$\sqrt{s_{\text {NN}}} = 16.84$$ GeV measured by the NA61/SHINE at CERN
H. Adhikary, P. Adrich, K. K. Allison, N. Amin, Evgeny Andronov, T. Antičić, I. C. Arsene, M. Bajda, Y. Balkova, M. Baszczyk, D. Battaglia, A. Bazgir, S. Bhosale, M. Bielewicz, A. Blondel, M. Bogomilov, Y. Bondar, N. Bostan, A. V. Brandin, W. Bryliński, J. Brzychczyk, M. Buryakov, A. F. Camino, M. Ćirković, M. Csanád, J. Cybowska, T. Czopowicz, C. Dalmazzone, N. Davis, A. Dmitriev, P. von Doetinchem, W. Dominik, P. Dorosz, J. Dumarchez, R. Engel, Г. Феофилов, L. Fields, Z. Fodor, M. Friend, А. А. Гарибов, M. Gaździcki, O. Golosov, V.M. Golovatyuk, M. Golubeva, K. Grebieszkow, F. Guber, S. N. Igolkin, S. Ilieva, A. Ivashkin, A. Izvestnyy, K. Kadija, Н. И. Каргин, N. Karpushkin, E. Kashirin, M. M. Kielbowicz, V. A. Kireyeu, H. Kitagawa, R. Kolesnikov, D. Kolev, Y. Koshio, V. Kovalenko, S. Kowalski, B. Kozłowski, A. Krasnoperov, W. Kucewicz, M. Kuchowicz, M. Kuich, A. Kurepin, Á. László, M. P. Lewicki, G. I. Lykasov, V. Lyubushkin, M. Maćkowiak-Pawłowska, Z. Majka, A. Makhnev, B. Maksiak, A. Malakhov, A. Marcinek, A. D. Marino, K. Márton, Hermann-Josef Mathes, T. Matulewicz, V. Matveev, G. L. Melkumov, A. Merzlaya, Ł. Mik, A. Morawiec, S. Morozov, Y. Nagai, T. Nakadaira, M. Naskręt, S. Nishimori, V. Ozvenchuk, O. Panova, V. Paolone, O. Petukhov, I. Pidhurskyi, R. Płaneta, P. Podlaski, B. Popov
Abstract
Abstract This paper reports measurements of two-pion femtoscopic correlations in Be+Be collisions at a beam momentum of 150 $$A\,\hbox {GeV}\!/\!c$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>A</mml:mi><mml:mspace/><mml:mtext>GeV</mml:mtext><mml:mspace/><mml:mo>/</mml:mo><mml:mspace/><mml:mi>c</mml:mi></mml:mrow></mml:math> (energy available in the center-of-mass system for nucleon pair $$\sqrt{s_{\text {NN}}} = 16.84$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msqrt><mml:msub><mml:mi>s</mml:mi><mml:mtext>NN</mml:mtext></mml:msub></mml:msqrt><mml:mo>=</mml:mo><mml:mn>16.84</mml:mn></mml:mrow></mml:math> GeV) by the NA61/SHINE experiment at the CERN SPS accelerator. The obtained momentum space correlation functions can be well described by a Lévy distributed source model. The transverse mass dependence of the Lévy source parameters is presented, and their possible theoretical interpretations are discussed. The results show that the Lévy exponent $$\alpha $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>α</mml:mi></mml:math> is approximately constant as a function of $$m_{\text {T}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>m</mml:mi><mml:mtext>T</mml:mtext></mml:msub></mml:math> , and far from both the Gaussian case of $$\alpha = 2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>α</mml:mi><mml:mo>=</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:math> or the conjectured value at the critical endpoint, $$\alpha = 0.5$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>α</mml:mi><mml:mo>=</mml:mo><mml:mn>0.5</mml:mn></mml:mrow></mml:math> . The radius scale parameter R shows a slight decrease in $$m_{\text {T}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>m</mml:mi><mml:mtext>T</mml:mtext></mml:msub></mml:math> , which can be explained as a signature of transverse flow. Finally, an approximately constant trend of the intercept parameter $$\lambda $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>λ</mml:mi></mml:math> as a function of $$m_{\text {T}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>m</mml:mi><mml:mtext>T</mml:mtext></mml:msub></mml:math> was observed, similar to previous NA44 S + Pb results (obtained with a Gaussian approximation, but unlike RHIC results).