Dihadron Transverse-Spin Asymmetries in Muon-Deuteron Deep-Inelastic Scattering
G. D. Alexeev, M. G. Alexeev, C. Alice, A. Amoroso, V. Andrieux, V. Anosov, S. Asatryan, K. Augsten, W. Augustyniak, C. D. R. Azevedo, B. Badelek, R. Beck, J. Beckers, Y. Bedfer, V. Benesova, J. Bernhard, F. Bradamante, A. Bressan, W. -C . Chang, C. Chatterjee, M. Chiosso, S. -U. Chung, A. Cicuttin, M. L. Crespo, D. D'Ago, S. Dalla Torre, S. S. Dasgupta, S. Dasgupta, M. Dehpour, F. Delcarro, I. Denisenko, O. Yu. Denisov, S. V. Donskov, N. Doshita, Ch. Dreisbach, W. Dün nweber, R. R. Dusaev, D. Ecker, P. Faccioli, M. Faessler, M. Finger, M. Finger, H. Fischer, K. J. Flöthner, W. Florian, J. M. Friedrich, V. Frolov, L. G. Garcia Ordòñez, O. P. Gavrichtchouk, S. Gerassimov, J. Giarra, D. Giordan o, A. Grasso, A. Gridin, M. Grosse Perdekamp, B. Grube, M. Grüner, A. Guskov, P. Haas, D. von Harrach, M. Hoffmann, A. Hoghmrtsyan, N. d'Hose, C. -Y. Hsieh, S. Ishimoto, A. Ivanov, T. Iwata, V. Jary, E. Jelinkova, R. Joosten, E. Kabuß, F. Kaspar, A. Kerbizi, B. Ketzer, G. V. Khaustov, T. Klasek, J. H. Koivuniemi, V. N. Kolosov, K. Kondo Horikawa, I. Konorov, A. Yu. Korzenev, A. M. Kotzinian, O. M. Kouznetsov, A. Koval, F. Kunne, K. Kurek, R. P. Kurjata, A. Kveton, K. Lavickova, S. Levorato, Y. -S. Lian, J. Lichtenstadt, P. -J. Lin, R. Longo, V. E. Lyubovitskij, A. Maggiora, N. Makke, G. K. Mallot, A. Maltsev, A. Martin, H. Marukyan, J. Marzec, J. Matoušek, T. Matsuda, C. Menezes Pires, F. Metzge r, W. Meyer, M. Mikhasenko, E. Mitrofanov, D. Miura, Y. Miyachi, R. Molina, A. Movsisian, A. Moretti, A. Nagaytsev, D. Neyret, M. Niemiec, J. Nový, W. -D. Nowak, G. Nukazuka, A. G. Olshevsky, M. Ostrick, D. Panzieri, B. Parsamyan, S. P aul, H. Pekeler, J. -C. Peng, M. Pešek, D. V. Peshekhonov, M. Pešková, S. Platchkov, J. Pochodzalla, V. A. Polyakov, P. Pucci, C. Quintans, G. Reicherz, C. Riedl, D. I. Ryabchikov, A. Rychter, A. Rymbekova, V. D. Samoylenko, A. S andacz, S. Sarkar, I. A. Savin, G. Sbrizzai, H. Schmieden, A. Selyunin, S. Seriubin, L. Sinha, D. Spülbeck, A. Srnka, M. Stolarski, M. Sulc, H. Suzuki, S. Tessaro, F. Tessarotto, A. Thiel, F. Tosello, A. Townsend, V. Tskhay, B. Valino ti, B. M. Veit, J. F. C. A. Veloso, A. Vijayakumar, M. Virius, M. Wagner, S. Wallner, K. Zaremba, M. Zavertyaev, M. Zemko, E. Zemlyanichkina, M. Ziembicki
TL;DR
The paper presents new COMPASS measurements of dihadron transverse-spin asymmetries in muon–deuteron DIS, extracting $A_{UT}^{\sin\phi_{RS}}$ via an unbinned likelihood fit and connecting it to the transversity PDFs $h_1^q(x)$ through the dihadron fragmentation function $H_{1,q}^{\sphericalangle}$. The formalism uses a leading-twist, collinear framework with structure functions $F_{UU}$ and $F_{UT}^{\sin\phi_{RS}}$, enabling a direct, model-light access to flavor-separated transversities and a point-by-point extraction of $h_1^{u_v}(x)$ and $h_1^{d_v}(x)$. The results show predominantly small asymmetries with a hint at large $x$, and, crucially, yield improved determinations of $h_1^{u_v}(x)$ and $h_1^{d_v}(x)$ that agree with Collins-based extractions and global fits (JAM/MAP), underscoring the consistency of collinear dihadron and TMD approaches. Overall, the measurements advance the flavour mapping of nucleon transverse spin and demonstrate the deuteron data’s pivotal role in constraining the $d$-quark transversity tensor charge.
Abstract
In 2022, the COMPASS collaboration performed semi-inclusive measurements of deep-inelastic muon-scattering on a transversely polarised deuteron (6LiD) target. From these data, transverse-spin-dependent dihadron asymmetries are extracted using pairs of oppositely charged hadrons. These asymmetries are directly sensitive to the quark transversity distributions and provide an independent handle on these fundamental quantities with respect to the Collins asymmetries measured in single-hadron production. The present results significantly improve upon the previous COMPASS deuteron measurements, which were the only available deuteron data worldwide, and reach a statistical precision comparable to that of the existing proton results from COMPASS. A small but nonzero asymmetry is observed at large Bjorken-x, consistent with theoretical expectations. A point-by-point extraction of the valence-quark transversity distributions yields, in particular, a substantially improved determination of the d-quark transversity. These measurements represent a major step towards a complete flavour mapping of the transverse-spin structure of the nucleon.