First measurement of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi mathvariant="normal">Λ</mml:mi><mml:mrow><mml:mi>c</mml:mi></mml:mrow><mml:mo>+</mml:mo></mml:msubsup></mml:math> production down to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>p</mml:mi><mml:mi>T</mml:mi></mml:msub><mml:mo>=</mml:mo><mml:mn>0</mml:mn></mml:mrow></mml:math> in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>p</mml:mi><mml:mi>p</mml:mi></mml:mrow></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>p</mml:mi></mml:math>-Pb collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msqrt><mml:msub><mml:mi>s</mml:mi><mml:mrow><mml:mi>N</mml:mi><mml:mi>N</mml:mi></mml:mrow></mml:msub></mml:msqrt><mml:mo>=</mml:mo><mml:mn>5.02</mml:mn></mml:mrow></mml:math> TeV
S. Acharya, D. Adamová, A. Adler, G. Aglieri Rinella, M. Agnello, N. Agrawal, Z. Ahammed, S. Ahmad, S. U. Ahn, I. Ahuja, A. Akindinov, M. Al-Turany, D. Aleksandrov, B. Alessandro, H. M. Alfanda, R. Alfaro Molina, Bushra Ali, A. Alici, N. Alizadehvandchali, A. Alkin, J. Alme, G. Alocco, T. Alt, I. Altsybeev, M. N. Anaam, C. Andrei, A. Andronic, V. Anguelov, F. Antinori, P. Antonioli, N. Apadula, L. Aphecetche, H. Appelshäuser, C. Arata, S. Arcelli, M. Aresti, R. Arnaldi, Jhoao Gabriel Martins Campos Almeida Arneiro, I. C. Arsene, M. Arslandok, A. Augustinus, R. Averbeck, M. D. Azmi, A. Badalà, J. Bae, Y. W. Baek, X. Bai, R. Bailhache, Y. Bailung, A. Balbino, A. Baldisseri, Bartosz Baliś, D. Banerjee, Z. Banoo, R. Barbera, F. Barile, L. Barioglio, M. Barlou, G. G. Barnaföldi, L. S. Barnby, V. Barret, L. Barreto, C. Bartels, K. Barth, E. Bartsch, N. Bastid, S. Basu, G. Batigne, D. Battistini, B. Batyunya, D. Bauri, J. L. Bazo Alba, I. G. Bearden, C. Beattie, P. Becht, D. Behera, I. Belikov, A. D. C. Bell Hechavarria, F. Bellini, R. Bellwied, S. Belokurova, V. Belyaev, G. Bencédi, S. Beolè, A. Bercuci, Y. Berdnikov, A. Berdnikova, L. Bergmann, Mihaela Gabriela Besoiu, L. Betev, Partha Pratim Bhaduri, A. Bhasin, M. A. Bhat, B. Bhattacharjee, L. Bianchi, N. Bianchi, J. Bielčík, J. Bielčíková, J. Biernat, A. P. Bigot
Abstract
The production of prompt ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}$ baryons has been measured at midrapidity in the transverse momentum interval $0<{p}_{T}<1 \text{GeV}/c$ for the first time, in $pp$ and $p$--Pb collisions at a center-of-mass energy per nucleon-nucleon collision $\sqrt{{s}_{NN}}=5.02\phantom{\rule{0.16em}{0ex}}\text{TeV}$. The measurement was performed in the decay channel ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}p{K}_{S}^{0}$ by applying new decay reconstruction techniques using a Kalman-Filter vertexing algorithm and adopting a machine-learning approach for the candidate selection. The ${p}_{T}$-integrated ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}$ production cross sections in both collision systems were determined and used along with the measured yields in Pb--Pb collisions to compute the ${p}_{T}$-integrated nuclear modification factors ${R}_{p\mathrm{Pb}}$ and ${R}_{AA}$ of ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}$ baryons, which are compared to model calculations that consider nuclear modification of the parton distribution functions. The ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}/{D}^{0}$ baryon-to-meson yield ratio is reported for $pp$ and $p$--Pb collisions. Comparisons with models that include modified hadronization processes are presented, and the implications of the results on the understanding of charm hadronization in hadronic collisions are discussed. A significant ($3.7\ensuremath{\sigma}$) modification of the mean transverse momentum of ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}$ baryons is seen in $p$--Pb collisions with respect to $pp$ collisions, while the ${p}_{T}$-integrated ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}/{D}^{0}$ yield ratio was found to be consistent between the two collision systems within the uncertainties.