Central Exclusive Production at LHCb

  • C. Van Hulse University College Dublin
Keywords: exclusive photoproduction, ultra-peripheral collisions, generalised parton distributions, parton distribution functions

Abstract

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.

References

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.

Published
2019-09-17
How to Cite
Van Hulse, C. (2019). Central Exclusive Production at LHCb. Ukrainian Journal of Physics, 64(7), 595. https://doi.org/10.15407/ujpe64.7.595
Section
New Trends in High-Energy Physics (Conference materials)