TY - JOUR

T1 - Constraints on the χc1 versus χc2 Polarizations in Proton-Proton Collisions at √s=8 TeV

AU - The CMS collaboration

AU - Sirunyan, A. M.

AU - Tumasyan, A.

AU - Adam, W.

AU - Ambrogi, F.

AU - Bergauer, T.

AU - Dragicevic, M.

AU - Erö, J.

AU - Escalante Del Valle, A.

AU - Flechl, M.

AU - Frühwirth, R.

AU - Jeitler, M.

AU - Krammer, N.

AU - Krätschmer, I.

AU - Liko, D.

AU - Madlener, T.

AU - Mikulec, I.

AU - Rad, N.

AU - Schieck, J.

AU - Schöfbeck, R.

AU - Spanring, M.

AU - Waltenberger, W.

AU - Wulz, C. E.

AU - Zarucki, M.

AU - Drugakov, V.

AU - Mossolov, V.

AU - Suarez Gonzalez, J.

AU - Darwish, M. R.

AU - De Wolf, E. A.

AU - Di Croce, D.

AU - Janssen, X.

AU - Kello, T.

AU - Lelek, A.

AU - Pieters, M.

AU - Rejeb Sfar, H.

AU - Van Haevermaet, H.

AU - Van Mechelen, P.

AU - Van Putte, S.

AU - Van Remortel, N.

AU - Blekman, F.

AU - Bols, E. S.

AU - Chhibra, S. S.

AU - D'Hondt, J.

AU - De Clercq, J.

AU - Lontkovskyi, D.

AU - Lowette, S.

AU - Barnyakov, A.

AU - Blinov, V.

AU - Dimova, T.

AU - Kardapoltsev, L.

AU - Skovpen, Y.

N1 - Publisher Copyright: © 2020 CERN. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/4/24

Y1 - 2020/4/24

N2 - The polarizations of promptly produced χc1 and χc2 mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at s=8 TeV. The χc states are reconstructed via their radiative decays χc→J/ψγ, with the photons being measured through conversions to e+e-, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χc2 to χc1 yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ→μ+μ- decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum.

AB - The polarizations of promptly produced χc1 and χc2 mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at s=8 TeV. The χc states are reconstructed via their radiative decays χc→J/ψγ, with the photons being measured through conversions to e+e-, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χc2 to χc1 yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ→μ+μ- decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum.

KW - W-TRANSVERSE-MOMENTUM

KW - P(P)OVER-BAR COLLISIONS

KW - PP COLLISIONS

KW - QUARKONIUM PRODUCTION

KW - ANGULAR-DISTRIBUTION

KW - ANGLE DISTRIBUTION

KW - CROSS-SECTIONS

KW - DECAYS

KW - LEPTONS

KW - PIONS

UR - http://www.scopus.com/inward/record.url?scp=85084721870&partnerID=8YFLogxK

U2 - 10.1103/PhysRevLett.124.162002

DO - 10.1103/PhysRevLett.124.162002

M3 - Article

C2 - 32383915

AN - SCOPUS:85084721870

VL - 124

JO - Physical Review Letters

JF - Physical Review Letters

SN - 0031-9007

IS - 16

M1 - 162002

ER -