Central Exclusive Production at LHCb
Keywords:exclusive photoproduction, ultra-peripheral collisions, generalised parton distributions, parton distribution functions
The LHCb collaboration has measured central exclusive production of J/ф, ф(2S), and ϒ mesons as well as J/фJ/ф, J/фф(2S), ф(2S)ф(2S), and xcxc meson pairs in proton-proton collisions. The analyses of ϒ and charmonium pairs are performed at the centre-of-mass energies of 7 TeV and 8 TeV, and those of J/ф and ф(2S) are done at 7 TeV and 13 TeV. The analysis at 13 TeV involves the use of new shower counters. These allow a reduction in the background by vetoing events with activity in an extended region in rapidity. The measurements of central exclusive production at LHCb are sensitive to gluon distributions for Bjorken-x values down to 2×10−6 (at 13 TeV). An overview of the LHCb results is presented and compared to existing measurements of other experiments and theoretical calculations.
M. Burkardt. Impact parameter dependent parton distributions and off-forward parton distributions for C0. Phys. Rev. D 62, 071503 (2000). https://doi.org/10.1103/PhysRevD.62.071503
M. Burkardt. Impact parameter space interpretation for generalized parton distributions. Int. J. Mod. Phys. A 18, 173 (2003). https://doi.org/10.1142/S0217751X03012370
M. Diehl. Generalized parton distributions. Phys. Rept. 388, 41 (2003). https://doi.org/10.1016/j.physrep.2003.08.002
J.C. Collins, L. Frankfurt, M.S. Strikman. Factorization for hard exclusive electroproduction of mesons in QCD. Phys. Rev. D 56, 2982 (1997). https://doi.org/10.1103/PhysRevD.56.2982
A.V. Radyushkin. Nonforward parton distributions. Phys. Rev. D 56, 5524 (1997). https://doi.org/10.1103/PhysRevD.56.5524
I. Bedlinskiy et al., [CLAS]. Exclusive n electroproduction at W > 2 GeV with CLAS and transversity generalized parton distributions. Phys. Rev. C 95, 035202 (2017).
P.E. Bosted et al., [CLAS]. Target and beam-target spin asymmetries in exclusive pion electroproduction for Q2 > 1 GeV2. I ep > eп+n. Phys. Rev. C 95, 035207 (2017).
C. Adolph et al., [COMPASS]. Transverse target spin asymmetries in exclusive p0 muoproduction. Phys. Lett. B 731, 19 (2014).
C. Adolph et al., [COMPASS]. Exclusive w meson muo-production on transversely polarised protons Nucl. Phys. B 915, 454 (2017).
Fuchey et al., [Jefferson Lab Hall A]. Exclusive neutral pion electroproduction in the deeply virtual regime. Phys. Rev. C 83, 025201 (2011). https://doi.org/10.1142/9789814329569_0016
A. Airapetian et al., [HERMES]. Spin density matrix elements in exclusive w electroproduction on 1H and 2H targets at 27.5 GeV beam energy. Eur. Phys. J. C 74, 3110 (2014).
A. Airapetian et al., [HERMES]. Transverse-target-spin asymmetry in exclusive w-meson electroproduction. Eur. Phys. J. C 75, 600 (2015).
A. Airapetian et al., [HERMES]. Ratios of helicity amplitudes for exclusive p0 electroproduction on transversely polarized protons. Eur. Phys. J. C 77, 378 (2017).
F.D. Aaron et al., [H1]. Diffractive electroproduction of p and y mesons at HERA. JHEP 05, 032 (2010).
A. Aktas et al., [H1]. Measurement of F-2 (c (c) over-bar) and F-2 (b (b) over-bar) at high Q(2) using the H1 vertex detector at HERA. Eur. Phys. J. C 46, 585 (2006).
S. Chekanov et al., [ZEUS]. Exclusive electroproduction of J/ф mesons at HERA. Nucl. Phys. B 695, 3 (2004).
S. Chekanov et al., [ZEUS]. Exclusive p0 production in deep inelastic scattering at HERA. PMC Phys. A 1, 6 (2007). https://doi.org/10.1186/1754-0410-1-6
C. Adloff et al., [H1]. Diffractive photoproduction of ф(2S) mesons at HERA. Phys. Lett. B 541, 251 (2002).
A. Aktas et al., [H1]. Elastic J/ф production at HERA. Eur. Phys. J. C 46, 585 (2006). https://doi.org/10.1140/epjc/s2006-02519-5
C. Alexa et al., [H1]. Elastic and proton-dissociative photoproduction of J/ф mesons at HERA. Eur. Phys. J. C 73, 2466 (2013).
S. Chekanov et al., [ZEUS]. Exclusive photoproduction of y mesons at HERA. Phys. Lett. B 680, 4 (2009).
S. Afanasiev et al., [PHENIX]. Photoproduction of J/ф and of high mass e+e? in ultra-peripheral Au + Au collisions at vSNN = 200 GeV. Phys. Lett. B 679, 321 (2009).
T. Aaltonen et al., [CDF]. Observation of exclusive charmonium production and yy > м+м? in pp collisions at vs = 1.96 TeV. Phys. Rev. Lett. 102, 242001 (2009).
E. Abbas et al., [ALICE]. Charmonium and e+e? pair photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at vSNN = 2.76 TeV. Eur. Phys. J. C 73, 2617 (2013).
B. Abelev et al., [ALICE]. Coherent J/ф photoproduction in ultra-peripheral Pb-Pb collisions at vSNN = 2.76 TeV. Phys. Lett. B 718, 1273 (2013).
B. Abelev et al., [ALICE]. Exclusive J/ф photoproduction off protons in ultraperipheral p-Pb collisions at vSNN = 5.02 TeV. Phys. Rev. Lett. 113, 232504 (2014).
R. Aaij et al., [LHCb]. Exclusive J/ф and ф(2S) production in pp collisions at TeV. J. Phys. G: Nucl. Part. Phys. 40, 045001 (2013).
R. Aaij et al., [LHCb]. Updated measurements of exclusive J/ф and ф(2S) production cross-sections in pp collisions at TeV J. Phys. G: Nucl. Part. Phys. 41, 055002 (2014).
R. Aaij et al., [LHCb]. Measurement of the exclusive Y production cross-section in pp collisions at vs = 7 TeV and 8 TeV. JHEP 09, 084 (2015).
R. Aaij et al., [LHCb]. Central exclusive production of J/ф and ф(2S) mesons in pp collisions at vs = 13 TeV. JHEP 10, 167 (2018).
LHCb Collaboration. Study of coherent J/ф production in lead-lead collisions at vSNN = 5 TeV with the LHCb experiment. CERN-LHCb-CONF-2018-003.
N. Armesto et al. Exclusive vector meson production at high energies and gluon saturation. Phys. Rev. D 90, 054003 (2014). https://doi.org/10.1103/PhysRevD.90.054003
M.G. Ryskin. Diffractive J/ф electroproduction in LLA QCD. Z. Phys. C 57, 89 (1993). https://doi.org/10.1007/BF01555742
S.P. Jones et al. Probes of the small x gluon via exclusive J/ф and Y production at HERA and the LHC. JHEP 11, 085 (2013). https://doi.org/10.1007/JHEP11(2013)085
S.P. Jones et al. Exclusive J/ф process Tamed to probe the low-x gluon. arXiv:1609.09738.
C.A. Flett et al. Towards a determination of the low x gluon via exclusive J/ф production. arxiv:1907.06471.
K.C. Akiba et al. The HeRSCheL detector: High-rapidity shower counters for LHCb. JINST 13, P04017 (2018). https://doi.org/10.1088/1748-0221/13/04/P04017
M.E. Binkley et al, [E104]. J/ф photoproduction from 60 to 300 GeV/c. Phys. Rev. Lett. 48, 73 (1982). https://doi.org/10.1103/PhysRevLett.48.73
B.H. Denby et al., [E516]. Inelastic and Elastic Photoproduction of J/ф(3097). Phys. Rev. Lett. 52, 795 (1984). https://doi.org/10.2172/1433892
P.L. Frabetti et al., [E687]. A measurement of elastic J/ф photoproduction cross section at Fermilab E687. Phys. Lett. B 316, 197 (1993).
R. Aaij et al., [LHCb]. Observation of charmonium pairs produced exclusively in collisions. J. Phys. G: Nucl. Part. Phys. 41, 115002 (2014).
LHCb Collaboration. Central Exclusive Production at LHCb. CERN-LHCb-CONF-2011-022.
How to Cite
License to Publish the Paper
The corresponding author and the co-authors (hereon referred to as the Author(s)) of the paper being submitted to the Ukrainian Journal of Physics (hereon referred to as the Paper) from one side and the Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine, represented by its Director (hereon referred to as the Publisher) from the other side have come to the following Agreement:
1. Subject of the Agreement.
The Author(s) grant(s) the Publisher the free non-exclusive right to use the Paper (of scientific, technical, or any other content) according to the terms and conditions defined by this Agreement.
2. The ways of using the Paper.
2.1. The Author(s) grant(s) the Publisher the right to use the Paper as follows.
2.1.1. To publish the Paper in the Ukrainian Journal of Physics (hereon referred to as the Journal) in original language and translated into English (the copy of the Paper approved by the Author(s) and the Publisher and accepted for publication is a constitutive part of this License Agreement).
2.1.2. To edit, adapt, and correct the Paper by approval of the Author(s).
2.1.3. To translate the Paper in the case when the Paper is written in a language different from that adopted in the Journal.
2.2. If the Author(s) has(ve) an intent to use the Paper in any other way, e.g., to publish the translated version of the Paper (except for the case defined by Section 2.1.3 of this Agreement), to post the full Paper or any its part on the web, to publish the Paper in any other editions, to include the Paper or any its part in other collections, anthologies, encyclopaedias, etc., the Author(s) should get a written permission from the Publisher.
3. License territory.
The Author(s) grant(s) the Publisher the right to use the Paper as regulated by sections 2.1.1–2.1.3 of this Agreement on the territory of Ukraine and to distribute the Paper as indispensable part of the Journal on the territory of Ukraine and other countries by means of subscription, sales, and free transfer to a third party.
4.1. This Agreement is valid starting from the date of signature and acts for the entire period of the existence of the Journal.
5.1. The Author(s) warrant(s) the Publisher that:
– he/she is the true author (co-author) of the Paper;
– copyright on the Paper was not transferred to any other party;
– the Paper has never been published before and will not be published in any other media before it is published by the Publisher (see also section 2.2);
– the Author(s) do(es) not violate any intellectual property right of other parties. If the Paper includes some materials of other parties, except for citations whose length is regulated by the scientific, informational, or critical character of the Paper, the use of such materials is in compliance with the regulations of the international law and the law of Ukraine.
6. Requisites and signatures of the Parties.
Publisher: Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine.
Address: Ukraine, Kyiv, Metrolohichna Str. 14-b.
Author: Electronic signature on behalf and with endorsement of all co-authors.