CMS-FSQ-13-009

CMS-FSQ-13-009 ; CERN-EP-2018-225
Measurement of exclusive $\Upsilon$ photoproduction from protons in pPb collisions at $\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}} =$ 5.02 TeV
CMS Collaboration
28 September 2018
Eur. Phys. J. C 79 (2019) 277 [Erratum]
Abstract: The exclusive photoproduction of ${\Upsilon\mathrm{(nS)}}$ meson states from protons, ${\gamma{\mathrm{p}}} \to {\Upsilon\mathrm{(nS)}} \,{\mathrm{p}}$ (with $\mathrm{n}=$ 1, 2, 3), is studied in ultraperipheral pPb collisions at a centre-of-mass energy per nucleon pair of $\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}} =$ 5.02 TeV. The measurement is performed using the ${\Upsilon\mathrm{(nS)}} \to \mu^+\mu^-$ decay mode, with data collected by the CMS experiment corresponding to an integrated luminosity of 32.6 nb $^{-1}$ . Differential cross sections as functions of the ${\Upsilon\mathrm{(nS)}}$ transverse momentum squared ${p_{\mathrm{T}}}^2$ , and rapidity $y$ , are presented. The $\Upsilon\text{(1S)}$ photoproduction cross section is extracted in the rapidity range $\|y\| <$ 2.2, which corresponds to photon-proton centre-of-mass energies in the range 91 $< {W_{\gamma{\mathrm{p}}}} <$ 826 GeV. The data are compared to theoretical predictions based on perturbative quantum chromodynamics and to previous measurements.
Links: e-print arXiv:1809.11080 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Diagrams representing (a) exclusive ${\Upsilon}$ photoproduction, (b) proton dissociative, or "semiexclusive'', ${\Upsilon}$ photoproduction, and (c) exclusive dimuon QED continuum production in pPb collisions.
png pdf	Figure 1-a: Diagram representing exclusive ${\Upsilon}$ photoproduction.
png pdf	Figure 1-b: Diagram representing proton dissociative, or "semiexclusive'', ${\Upsilon}$ photoproduction.
png pdf	Figure 1-c: Diagram representing exclusive dimuon QED continuum production in pPb collisions.
png pdf	Figure 2: Invariant mass distribution of the exclusive muon pair candidates in the range 8 $< m_{\mu ^{+}\mu ^{-}} <$ 12 GeV that pass all the selection criteria, fitted to a linear function for the two-photon QED continuum (blue dashed line) plus three Gaussian distributions corresponding to the ${\Upsilon \mathrm {(1S)}}$ , ${\Upsilon \mathrm {(2S)}}$ , and ${\Upsilon \mathrm {(3S)}}$ mesons (dashed-dotted-red curves).
png pdf	Figure 3: Distributions of the (a) transverse momentum squared ${p_{\mathrm {T}}} ^2$ , and (b) rapidity $y$ of exclusive muon pairs with invariant mass 9.1 $< m_{\mu ^{+}\mu ^{-}} <$ 10.6 GeV after all selection criteria have been applied. Both distributions are compared to the expectations of signal and background contributions discussed in the text.
png pdf	Figure 3-a: Distribution of the transverse momentum squared ${p_{\mathrm {T}}} ^2$ of exclusive muon pairs with invariant mass 9.1 $< m_{\mu ^{+}\mu ^{-}} <$ 10.6 GeV after all selection criteria have been applied. The distribution is compared to the expectation of signal and background contributions discussed in the text.
png pdf	Figure 3-b: Distribution of the rapidity $y$ of exclusive muon pairs with invariant mass 9.1 $< m_{\mu ^{+}\mu ^{-}} <$ 10.6 GeV after all selection criteria have been applied. The distribution is compared to the expectation of signal and background contributions discussed in the text.
png pdf	Figure 4: Differential ${{\Upsilon}\mathrm {(nS)}} \to \mu ^+\mu ^-$ photoproduction cross section as a function of (a) ${p_{\mathrm {T}}} ^2$ and (b) rapidity $y$ , measured in pPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV. In the left plot, the data points are placed along the abscissa following the prescription of [57], and the solid line is an exponential fit of the form $e^{-b {p_{\mathrm {T}}} ^2}$ . In the right plot, the horizontal bars are shown to indicate the width of each $y$ bin. In both plots, the vertical bars represent the statistical uncertainties and the boxes represent the systematic uncertainties.
png pdf	Figure 4-a: Differential ${{\Upsilon}\mathrm {(nS)}} \to \mu ^+\mu ^-$ photoproduction cross section as a function of ${p_{\mathrm {T}}} ^2$ , measured in pPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV. The data points are placed along the abscissa following the prescription of [57], and the solid line is an exponential fit of the form $e^{-b {p_{\mathrm {T}}} ^2}$ . The vertical bars represent the statistical uncertainties and the boxes represent the systematic uncertainties.
png pdf	Figure 4-b: Differential ${{\Upsilon}\mathrm {(nS)}} \to \mu ^+\mu ^-$ photoproduction cross section as a function of rapidity $y$ , measured in pPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV. The horizontal bars are shown to indicate the width of each $y$ bin. The vertical bars represent the statistical uncertainties and the boxes represent the systematic uncertainties.
png pdf	Figure 5: Differential ${\Upsilon \mathrm {(1S)}}$ photoproduction cross section as a function of rapidity measured in pPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV in the dimuon rapidity region $\|y\| <$ 2.2, compared to various theoretical predictions [9,16,17,14,15,18]. The horizontal bars are plotted to indicate the width of each $y$ bin. The vertical bars represent the statistical uncertainties and the boxes represent the systematic uncertainties.
png pdf	Figure 6: Cross section for exclusive ${\Upsilon \mathrm {(1S)}}$ photoproduction, ${{\gamma} {\mathrm {p}}} \to {\Upsilon \mathrm {(1S)}} {\mathrm {p}}$ , as a function of photon-proton centre-of-mass energy, ${W_{{\gamma} {\mathrm {p}}}}$ , compared to previous HERA [19,21,20] and LHCb [30] data as well as to various theoretical predictions [9,16,17,14,15,18]. The vertical bars represent the statistical uncertainties and the boxes represent the systematic uncertainties.

Tables
png pdf	Table 1: Relative systematic uncertainties in percent in the measurements of $\mathcal {B}_{{{\Upsilon}\mathrm {(nS)}} \to \mu ^+\mu ^-} {\mathrm {d}}\sigma / {\mathrm {d}} {p_{\mathrm {T}}} ^2$ , the exponential $b$ slope of the ${p_{\mathrm {T}}} ^2$ spectrum, $\mathcal {B}_{{{\Upsilon}\mathrm {(nS)}} \to \mu ^+\mu ^-} {\mathrm {d}}\sigma /{{\mathrm {d}}}y$ , ${\mathrm {d}}\sigma _{{\Upsilon \mathrm {(1S)}}}/{{\mathrm {d}}}y$ , and $\sigma _{{{\gamma} {\mathrm {p}}} \to {\Upsilon \mathrm {(1S)}} {\mathrm {p}}}$ . Individual contributions, as well as total systematic uncertainties added in quadrature are presented. For the ${p_{\mathrm {T}}} ^2$ - and $y$ -differential cross sections, the values averaged over all bins are shown.
png pdf	Table 2: Differential exclusive ${{\Upsilon}\mathrm {(nS)}} \to \mu ^+\mu ^-$ photoproduction cross sections in four ${p_{\mathrm {T}}} ^2$ and $y$ bins. The first and second uncertainties correspond to statistical and systematic components, respectively.
png pdf	Table 3: Values of the ${\Upsilon \mathrm {(1S)}}$ photoproduction cross section in four rapidity $y$ bins, corresponding to four photon-proton ${W_{{\gamma} {\mathrm {p}}}}$ centre-of-mass energy ranges (with central $W_{0}$ value obtained following the procedure outlined in Ref. [57]), in pPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV. The symbols $N_{{{\Upsilon}\mathrm {(nS)}}}^{\text {back-sub}}$ , $N_{{{\Upsilon}\mathrm {(nS)}}}^{\text {unfol}}$ , and $N_{{{\Upsilon}\mathrm {(nS)}}}^{\text {corr}}$ represent the numbers of ${{\Upsilon}\mathrm {(nS)}}$ candidates after background subtraction, unfolding, and extrapolation with the $A^{\text {corr}}$ factor, respectively; $N_{{\Upsilon \mathrm {(1S)}}}$ is the extracted number of ${\Upsilon \mathrm {(1S)}}$ mesons, and $\mathrm{h}i$ is the theoretical effective photon flux (see text). The first (second, if given) uncertainty quoted corresponds to the statistical (systematic) component.

Summary

The first study of the exclusive photoproduction of

$\Upsilon \mathrm{(1S,2S,3S)}$ mesons, in the

$\mu^{+}\mu^{-}$ decay mode, from protons in ultraperipheral pPb collisions at

$\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}} =$ 5.02 TeV, has been reported using data collected with the CMS detector corresponding to an integrated luminosity of 32.6 nb

$^{-1}$ . The differential cross section

${\mathrm{d}}\sigma/{\mathrm{d}}{p_{\mathrm{T}}}^2$ and associated exponential slope

$b$ have been measured in the squared transverse momentum range

${p_{\mathrm{T}}}^2 < 1.0 GeV^2$ . The extracted value of

$b=$ 6.0

$\pm$ 2.1 (stat)

$\pm$ 0.3 (syst) GeV

$^{-2}$ is consistent with the slope measurement at other centre-of-mass energies. The exclusive

$\Upsilon\text{1S}$ photoproduction cross sections, differential in rapidity

$y$ and as a function of the photon-proton centre-of-mass energy

${W_{\gamma{\mathrm{p}}}}$ , have been measured in the range 91

$< {W_{\gamma{\mathrm{p}}}} <$ 826 GeV. Such measurements probe the region of parton fractional momenta

$x\approx 10^{-4}$ -

$10^{-2}$ in the proton, bridging a previously unexplored region between the HERA and LHCb measurements. The dependence of

$\sigma_{{\gamma{\mathrm{p}}} \to\Upsilon\text{1S}{\mathrm{p}}}$ on

${W_{\gamma{\mathrm{p}}}}$ is well described by a power law with an exponent smaller than that predicted by leading order perturbative quantum chromodynamics (pQCD) approaches. The exponent is, however, consistent with that extracted from a fit to the HERA and LHCb data, and with that predicted by next-to-leading-order pQCD calculations. The data, within their currently large statistical uncertainties, are consistent with various pQCD approaches that model in different ways the behaviour of the low-

$x$ gluon density.

References
1	A. J. Baltz et al.	The physics of ultraperipheral collisions at the LHC	Phys. Rep. 458 (2008) 1	0706.3356
2	S. Klein and J. Nystrand	Exclusive vector meson production in relativistic heavy ion collisions	PRC 60 (1999) 014903	hep-ph/9902259
3	D. d'Enterria	Quarkonia photoproduction at nucleus colliders	NPB Proc. Suppl. 184 (2008) 158	0711.1123
4	V. Budnev, I. F. Ginzburg, G. V. Meledin, and V. G. Serbo	The two photon particle production mechanism. Physical problems, applications, equivalent photon approximation	Phys. Rep. 15 (1975) 181
5	J. P. Lansberg et al.	Perspectives on heavy-quarkonium production at the LHC	AIP Conf. Proc. 1038 (2008) 15	0807.3666
6	L. L. Frankfurt, A. Freund, and M. Strikman	Diffractive exclusive photoproduction in DIS at HERA	PRD 58 (1998) 114001	hep-ph/9710356
7	L. Frankfurt, M. McDermott, and M. Strikman	A fresh look at diffractive $\mathrm{J}/\psi$ photoproduction at HERA, with predictions for THERA	JHEP 03 (2001) 045	hep-ph/0009086
8	A. D. Martin, C. Nockles, M. G. Ryskin, and T. Teubner	Small $x$ gluon from exclusive $\mathrm{J}/\psi$ production	PLB 662 (2008) 252	0709.4406
9	P. Jones, D. Martin, M. G. Ryskin, and T. Teubner	Probes of the small $x$ gluon via exclusive $\mathrm{J}/\psi$ and $\Upsilon$ production at HERA and LHC	JHEP 11 (2013) 085	1307.7099
10	A. Adeluyi, C. A. Bertulani, and M. J. Murray	Nuclear effects in photoproduction of heavy quarks and vector mesons in ultraperipheral PbPb and pPb collisions at the LHC	PRC 86 (2012) 047901	1208.6258
11	A. Adeluyi and T. Nguyen	Coherent photoproduction of $\psi$ and $\Upsilon$ mesons in ultraperipheral pPb and PbPb collsions at the CERN LHC	PRC 87 (2013) 027901	1302.4288
12	V. Guzey and M. Zhalov	Exclusive $\mathrm{J}/\psi$ production in ultraperipheral collisions at the LHC: constraints on the gluon distributions in the proton and nuclei	JHEP 10 (2013) 207	1307.4526
13	V. Guzey, E. Kryshen, M. Strikman, and M. Zhalov	Evidence for nuclear gluon shadowing from the ALICE measurements of PbPb ultraperipheral exclusive $\mathrm{J}/\psi$ production	PLB 726 (2013) 290	1305.1724
14	G. Sampaio dos Santos and M. V. T. Machado	Exclusive photoproduction of quarkonium in proton-nucleus collisions at the CERN Large Hadron Collider	PRC 89 (2014) 025201	1312.0770
15	G. Sampaio dos Santos and M. V. T. Machado	On theoretical uncertainty of color dipole phenomenology in the $\mathrm{J}/\psi$ and $\Upsilon$ photoproduction in pA and AA collisions at the CERN Large Hadron Collider	JPG 42 (2015) 105001	1411.7918
16	T. Lappi and H. Mantysaari	Incoherent diffractive $\mathrm{J}/\psi$ production in high energy nuclear DIS	PRC 83 (2011) 065202	1011.1988
17	T. Lappi and H. Mantysaari	$\mathrm{J}/\psi$ production in ultraperipheral Pb+Pb and p+Pb collisions at energies available at the CERN Large Hadron Collider	PRC 87 (2013) 032201	1301.4095
18	V. P. Goncalves, B. D. Moreira, and F. S. Navarra	Exclusive heavy vector meson photoproduction in hadronic collisions at LHC: Predictions of the Color Glass Condensate model for Run 2 energies	PRD 95 (2017) 054011	1612.06254
19	H1 Collaboration	Elastic photoproduction of $\mathrm{J}/\psi$ and $\Upsilon$ mesons at HERA	PLB 483 (2000) 23	hep-ex/0003020
20	ZEUS Collaboration	Exclusive photoproduction of $\Upsilon$ mesons at HERA	PLB 680 (2009) 4	0903.4205
21	ZEUS Collaboration	Measurement of elastic $\Upsilon$ photoproduction at HERA	PLB 437 (1998) 432	hep-ex/9807020
22	H1 Collaboration	Elastic and proton-dissociative photoproduction of $\mathrm{J}/\psi$ mesons at HERA	EPJC 73 (2013) 2466	1304.5162
23	ZEUS Collaboration	Measurement of the $t$ dependence in exclusive photoproduction of $\Upsilon\text{(1S)}}$ mesons at HERA	PLB 708 (2012) 14	1111.2133
24	S. J. Brodsky et al.	The QCD pomeron with optimal renormalization	JETP 70 (1999) 155	hep-ph/9901229
25	LHCb Collaboration	Exclusive $\mathrm{J}/\psi$ and $\psi$ (2S) production in pp collisions at $\sqrt {s}=$ 7 TeV	JPG 40 (2013) 045001	1301.7084
26	CMS Collaboration	Coherent $\mathrm{J}/\psi$ photoproduction in ultra-peripheral PbPb collisions $\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}} =$ 2.76 TeV with the CMS experiment	PLB 772 (2017) 489	CMS-HIN-12-009 1605.06966
27	ALICE Collaboration	Coherent $\mathrm{J}/\psi$ photoproduction in ultra-peripheral PbPb collisions at $\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}} =$ 2.76 TeV	PLB 718 (2013) 1273	1209.3715
28	ALICE Collaboration	Charmonium and $e^+e^-$ pair photoproduction at mid-rapidity in ultra-peripheral PbPb collisions at $\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}} =$ 2.76 TeV	EPJC 73 (2013) 2617	1305.1467
29	ALICE Collaboration	Exclusive $\mathrm{J}/\psi$ photoproduction off protons in ultra-peripheral pPb collisions at $\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}} =$ 5.02 TeV	PRL 113 (2014) 232504	1406.7819
30	LHCb Collaboration	Measurement of the exclusive $\Upsilon$ production cross section in pp collisions at $\sqrt{s}=$ 7 TeV and 8 TeV	JHEP 09 (2015) 084	1505.08139
31	L. V. Gribov, E. M. Levin, and M. G. Ryskin	Semihard processes in QCD	PR 100 (1983) 1
32	A. H. Mueller and J.-W. Qiu	Gluon recombination and shadowing at small values of $x$	NPB 268 (1986) 427
33	L. D. McLerran and R. Venugopalan	Gluon distribution functions for very large nuclei at small transverse momentum	PRD 49 (1994) 3352	hep-ph/9311205
34	CMS Collaboration	Description and performance of track and primary-vertex reconstruction with the CMS tracker	JINST 9 (2014) P10009	CMS-TRK-11-001 1405.6569
35	CMS Collaboration	Performance of CMS muon reconstruction in pp collision events at $\sqrt{s}=$ 7 TeV	JINST 7 (2012) P10002	CMS-MUO-10-004 1206.4071
36	CMS Collaboration	Status of zero degree calorimeter for CMS experiment	AIP Conf. Proc. 867 (2006) 258	nucl-ex/0608052
37	CMS Collaboration	The CMS trigger system	JINST 12 (2017) P01020	CMS-TRG-12-001 1609.02366
38	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
39	S. R. Klein and J. Nystrand	Photoproduction of quarkonium in proton-proton and nucleus-nucleus collisions	PRL 92 (2004) 142003	hep-ex/0311164
40	J. Nystrand	Photons and exclusive processes at hadron colliders	Proceedings of PHOTON2009, Hamburg, Germany, (2009) 286	1001.4746
41	C. F. v. Weizsacker	Radiation emitted in collisions of very fast electrons	Z. Phys. 88 (1934) 612
42	E. J. Williams	Nature of the high-energy particles of penetrating radiation and status of ionization and radiation formulae	PR45 (1934) 729
43	GEANT4 Collaboration	GEANT4--a simulation toolkit	NIMA 506 (2003) 250
44	J. Allison et al.	GEANT4 developments and applications	IEEE Trans. Nucl. Sci. 53 (2006) 270
45	J. Allison et al.	Recent developments in GEANT4	NIMA 835 (2016) 186
46	CMS Collaboration	Event activity dependence of $\Upsilon\text{(nS)}$ production in $\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}} =$ 5.02 TeV pPb and $\sqrt{s}=$ 2.76 TeV pp collisions	JHEP 04 (2014) 103	CMS-HIN-13-003 1312.6300
47	W. Verkerke and D. P. Kirkby	The RooFit toolkit for data modeling	in 13th International Conference for Computing in High-Energy and Nuclear Physics (CHEP 2003), p. MOLT007 SLAC, La Jolla, CA, US, March, 2003 eConf:C0303241/MOLT007	physics/0306116
48	Particle Data Group	Review of particle physics	CPC 40 (2016) 100001
49	G. D'Agostini	A multidimensional unfolding method based on Bayes' theorem	NIMA 362 (1995) 487
50	T. Adye	Unfolding algorithms and tests using RooUnfold	in PHYSTAT 2011 Workshop on Statistical Issues Related to Discovery Claims in Search Experiments and Unfolding, H. Prosper and L. Lyons, eds., p. 313 Geneva, Switzerland	1105.1160
51	CDF Collaboration	$\Upsilon$ production and polarization in ${{\mathrm{p}}}\bar{{\mathrm{p}}}$ collisions at $\sqrt{s}=$ 1.8 TeV	PRL 88 (2002) 161802
52	T. Sjostrand, S. Mrenna, and P. Skands	PYTHIA 6.4 physics and manual	JHEP 05 (2006) 026	hep-ph/0603175
53	A. J. Schramm and D. H. Reeves	Production of $\eta$ mesons in double pomeron exchange	PRD 55 (1997) 7312	hep-ph/9611330
54	L. A. Harland-Lang, V. A. Khoze, M. G. Ryskin, and W. J. Stirling	Standard candle central exclusive processes at the Tevatron and LHC	EPJC 69 (2010) 179	1005.0695
55	C. Loizides, J. Kamin, and D. d'Enterria	Improved Monte Carlo Glauber predictions at present and future nuclear colliders	PRC 97 (2018) 054910	1710.07098
56	CMS Collaboration	Luminosity calibration for the 2013 proton-lead and proton-proton data taking	CMS-PAS-LUM-13-002	CMS-PAS-LUM-13-002
57	G. D. Lafferty and T. R. Wyatt	Where to stick your data points: The treatment of measurements within wide bins	NIMA 355 (1995) 541
58	E. Iancu, K. Itakura, and S. Munier	Saturation and BFKL dynamics in the HERA data at small x	PLB 590 (2004) 199	hep-ph/0310338
59	V. P. Goncalves et al.	Color dipole predictions for the exclusive vector meson photoproduction in pp/pPb/PbPb collisions at Run 2 LHC energies	PRD 96 (2017) 094027	1710.10070
60	L. Favart, M. Guidal, T. Horn, and P. Kroll	Deeply virtual meson production on the nucleon	EPJA 52 (2016) 158	1511.04535
61	S. Dulat et al.	New parton distribution functions from a global analysis of quantum chromodynamics	PRD 93 (2016) 033006	1506.07443
62	NNPDF Collaboration	Parton distributions for the LHC Run II	JHEP 04 (2015) 040	1410.8849
63	L. A. Harland-Lang, A. D. Martin, P. Motylinski, and R. S. Thorne	Parton distributions in the LHC era: MMHT 2014 PDFs	EPJC 75 (2015) 204	1412.3989