First Measurement of A=4 Hypernuclei and Antihypernuclei at the LHC.

Journal: Physical Review Letters
Published:
Abstract

In this Letter, the first evidence of the _{Λ[over ¯]}^{4}He[over ¯] antihypernucleus is presented, along with the first measurement at the LHC of the production of (anti)hypernuclei with mass number A=4, specifically (anti)_{Λ}^{4}H and (anti)_{Λ}^{4}He. In addition, the antiparticle-to-particle ratios for both hypernuclei (_{Λ[over ¯]}^{4}H[over ¯]/_{Λ}^{4}H and _{Λ[over ¯]}^{4}He[over ¯]/_{Λ}^{4}He) are shown, which are sensitive to the baryochemical potential of the strongly interacting matter created in heavy-ion collisions. The results are obtained from a data sample of central Pb-Pb collisions, collected during the 2018 LHC data taking at a center-of-mass energy per nucleon pair of sqrt[s_{NN}]=5.02  TeV. The yields measured for the average of the charge-conjugated states are found to be [0.78±0.19(stat)±0.17(syst)]×10^{-6} for the (anti)_{Λ}^{4}H and [1.08±0.34(stat)±0.20(syst)]×10^{-6} for the (anti)_{Λ}^{4}He, and the measured antiparticle-to-particle ratios are in agreement with unity. The presence of (anti)_{Λ}^{4}H and (anti)_{Λ}^{4}He excited states is expected to strongly enhance the production yield of these hypernuclei. The yield values exhibit a combined deviation of 3.3σ from the theoretical ground-state-only expectation, while the inclusion of the excited states in the calculations leads to an agreement within 0.6σ with the present measurements. Additionally, the measured (anti)_{Λ}^{4}H and (anti)_{Λ}^{4}He masses are compatible with the world-average values within the uncertainties.

Authors
S Acharya, A Agarwal, G Aglieri Rinella, L Aglietta, M Agnello, N Agrawal, Z Ahammed, S Ahmad, S Ahn, I Ahuja, A Akindinov, V Akishina, M Al Turany, D Aleksandrov, B Alessandro, H Alfanda, R Alfaro Molina, B Ali, A Alici, N Alizadehvandchali, A Alkin, J Alme, G Alocco, T Alt, A Altamura, I Altsybeev, J Alvarado, C O Alvarez, M Anaam, C Andrei, N Andreou, A Andronic, E Andronov, V Anguelov, F Antinori, P Antonioli, N Apadula, L Aphecetche, H Appelshäuser, C Arata, S Arcelli, R Arnaldi, J G M C Arneiro, I Arsene, M Arslandok, A Augustinus, R Averbeck, D Averyanov, M Azmi, H Baba, A Badalà, J Bae, Y Baek, X Bai, R Bailhache, Y Bailung, R Bala, A Balbino, A Baldisseri, B Balis, Z Banoo, V Barbasova, F Barile, L Barioglio, M Barlou, B Barman, G Barnaföldi, L Barnby, E Barreau, V Barret, L Barreto, C Bartels, K Barth, E Bartsch, N Bastid, S Basu, G Batigne, D Battistini, B Batyunya, D Bauri, J Bazo Alba, I Bearden, C Beattie, P Becht, D Behera, I Belikov, A D Bell Hechavarria, F Bellini, R Bellwied, S Belokurova, L G Beltran, Y A Beltran, G Bencedi, A Bensaoula, S Beole, Y Berdnikov, A Berdnikova, L Bergmann, M Besoiu, L Betev, P Bhaduri, A Bhasin, B Bhattacharjee, L Bianchi, J Bielčík, J Bielčíková, A Bigot, A Bilandzic, G Biro, S Biswas, N Bize, J Blair, D Blau, M Blidaru, N Bluhme, C Blume, G Boca, F Bock, T Bodova, J Bok, L Boldizsár, M Bombara, P Bond, G Bonomi, H Borel, A Borissov, A Borquez Carcamo, E Botta, Y E Bouziani, L Bratrud, P Braun Munzinger, M Bregant, M Broz, G Bruno, V Buchakchiev, M Buckland, D Budnikov, H Buesching, S Bufalino, P Buhler, N Burmasov, Z Buthelezi, A Bylinkin, S Bysiak, J Cabanillas Noris, M F Cabrera, M Cai, H Caines, A Caliva, E Calvo Villar, J Camacho, P Camerini, F D Canedo, S Cantway, M Carabas, A Carballo, F Carnesecchi, R Caron, L A Carvalho, J Castillo Castellanos, M Castoldi, F Catalano, S Cattaruzzi, R Cerri, I Chakaberia, P Chakraborty, S Chandra, S Chapeland, M Chartier, S Chattopadhay, S Chattopadhyay, M Chen, T Cheng, C 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