First measurement of D*+ vector meson spin alignment in Pb–Pb collisions at TeV

Acharya, S.; Agarwal, A.; Aglieri Rinella, G.; Aglietta, L.; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahmad, S.; Ahn, S. U.; Ahuja, I.; Akindinov, A.; Akishina, V.; Al-Turany, M.; Aleksandrov, D.; Alessandro, B.; Alfanda, H. M.; Alfaro Molina, R.; Ali, B.; Alici, A.; Alizadehvandchali, N.; Alkin, A.; Alme, J.; Alocco, G.; Alt, T.; Altamura, A. R.; Altsybeev, I.; Alvarado, J. R.; Anaam, M. N.; Andrei, C.; Andreou, N.; Andronic, A.; Andronov, E.; Anguelov, V.; Antinori, F.; Antonioli, P.; Apadula, N.; Appelshäuser, H.; Arata, C.; Arcelli, S.; Arnaldi, R.; Arneiro, J. G. M. C. A.; Arsene, I. C.; Arslandok, M.; Augustinus, A.; Averbeck, R.; Averyanov, D.; Azmi, M. D.; Baba, H.; Badalà, A.; Bae, J.; Bae, Y.; Baek, Y. W.; Bai, X.; Bailhache, R.; Bailung, Y.; Bala, R.; Baldisseri, A.; Balis, B.; Bangalia, S.; Banoo, Z.; Barbasova, V.; Barile, F.; Barioglio, L.; Barlou, M.; Barman, B.; Barnaföldi, G. G.; Barnby, L. S.; Barreau, E.; Barret, V.; Barreto, L.; Barth, K.; Bartsch, E.; Bastid, N.; Basu, S.; Batigne, G.; Battistini, D.; Batyunya, B.; Bauri, D.; Bazo Alba, J. L.; Bearden, I. G.; Becht, P.; Behera, D.; Belikov, I.; Bell Hechavarria, A. D. C.; Bellini, F.; Bellwied, R.; Belokurova, S.; Beltran, L. G. E.; Beltran, Y. A. V.; Bencedi, G.; Bensaoula, A.; Beole, S.; Berdnikov, Y.; Berdnikova, A.; Bergmann, L.; Bernardinis, L.; Betev, L.; Bhaduri, P. P.; Bhasin, A.; Bhattacharjee, B.; Lea, R.; Pagano, D.; Zurlo, N.; Bonomi, G.

doi:10.1007/JHEP10(2025)094

The first measurement of prompt D*+-meson spin alignment in ultrarelativistic heavy-ion collisions with respect to the direction orthogonal to the reaction plane is presented. The spin alignment is quantified by measuring the element rho(00) of the diagonal spin-density matrix for prompt D*+ mesons with 4 < p(T)< 30 GeV/c in two rapidity intervals, |y| < 0.3 and 0.3 < |y| < 0.8, in central (0-10%) and midcentral (30-50%) Pb-Pb collisions at TeV. Evidence of spin alignment rho(00)> 1/3 has been found for p(T)> 15 GeV/c and 0.3 < |y| < 0.8 with a significance of 3.1 sigma. The measured spin alignment of prompt D*+ mesons is compared with the one of inclusive J/psi mesons measured at forward rapidity (2.5 < y < 4).