CMS-PAS-HIN-18-011

CMS-PAS-HIN-18-011
Angular correlations in exclusive dijet photoproduction in ultra-peripheral PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV
CMS Collaboration
July 2020

Abstract: Exclusive dijet photoproduction has been measured in ultra-peripheral lead-lead (PbPb) collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV. The analysis is based on a data sample corresponding to an integrated luminosity of 0.38 nb $^{-1}$ collected by the CMS Collaboration. For each dijet, the transverse momentum vectors of the leading and subleading jets are measured and their vector sum and vector difference determined. The azimuthal angle between the vector sum and vector difference defines an angle $\phi$ . The distribution of $\phi$ and, in particular, the second Fourier harmonic ${<} \cos(2\phi) {>}$ is measured. The dependence of ${<} \cos(2\phi) {>}$ on the sum of the jet momentum vectors provides the first azimuthal anisotropy measurement related to exclusive dijet production.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to PRL.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Distributions of the maximum distance in pseudorapidity between the most backward jet and a track in an event (left) and the backward rapidity gap (right) shown for data and reconstructed RAPGAP MC (see text for details).
png pdf	Figure 1-a: Distribution of
png pdf	Figure 1-b: Distribution of the backward rapidity gap shown for data and reconstructed RAPGAP MC (see text for details).
png pdf	Figure 2: Magnitudes of the vector sum ( $Q_{\mathrm{T}}$ ) and vector difference ( $P_{\mathrm{T}}$ ) of the two jets (top left) and their correlation (top right) for the events that pass the selection criteria. The diagonal line illustrates the $P_{\mathrm{T}} > Q_{\mathrm{T}}$ requirement. Invariant mass (bottom left) and rapidity (bottom right) of the dijet candidates after further $Q_{\mathrm{T}}$ and $P_{\mathrm{T}}$ requirements. The lines show the prediction of the RAPGAP MC.
png pdf	Figure 2-a: Magnitudes of the vector sum ( $Q_{\mathrm{T}}$ ) and vector difference ( $P_{\mathrm{T}}$ ) of the two jets. The lines show the prediction of the RAPGAP MC.
png pdf	Figure 2-b: Correlation of the vector sum ( $Q_{\mathrm{T}}$ ) and vector difference ( $P_{\mathrm{T}}$ ) of the two jets for the events that pass the selection criteria. The diagonal line illustrates the $P_{\mathrm{T}} > Q_{\mathrm{T}}$ requirement.
png pdf	Figure 2-c: Invariant mass of the dijet candidates after further $Q_{\mathrm{T}}$ and $P_{\mathrm{T}}$ requirements. The lines show the prediction of the RAPGAP MC.
png pdf	Figure 2-d: Rapidity of the dijet candidates after further $Q_{\mathrm{T}}$ and $P_{\mathrm{T}}$ requirements. The lines show the prediction of the RAPGAP MC.
png pdf	Figure 3: The mixed event distributions obtained from data and compared to the RAPGAP prediction after full simulation and reconstruction (blue line). The left panel shows the $\phi$ distribution while the right panel shows the second harmonic of this distribution as a function of $Q_{\mathrm{T}}$ . Both the statistical (error bars) and systematic (magenta boxes) uncertainties are shown. Dashed histograms show the toy-MC distribution including the effect of detector smearing (see text for details).
png pdf	Figure 4: The left panel shows the $\phi$ distribution while the right panel shows the second harmonic of this distribution for the data, as a function of $Q_{\mathrm{T}}$ . The corresponding distributions from RAPGAP after full simulation and reconstruction are also shown (blue lines). Both the statistical (error bars) and systematic (green boxes) uncertainties are shown.

Tables
png pdf	Table 1: ${<} \cos(2\phi) {>}$ systematic uncertainties.

Summary

In summary, for the first time, angular correlations present in exclusive dijet photoproduction have been studied using ultra-peripheral lead-lead collisions at

${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV. The second moment of the angular distribution,

${<} \cos(2\phi) {>}$ , where

$\phi$ is the angle between the vector sum and vector difference of the leading and subleading jet transverse momenta, has been measured as a function of the momentum sum of the two jets. This analysis amounts to the first, yet essential, step towards the extraction of the Wigner or Husimi gluon distributions, which are believed to be the most fundamental gluon distributions. It also introduces new techniques for the analysis of jet angular correlations in exclusive dijet events at colliders.

References
1	A. J. Baltz et al.	The physics of ultraperipheral collisions at the LHC	PR 458 (2008) 1	0706.3356
2	J. G. Contreras and J. D. Tapia Takaki	Ultra-peripheral heavy-ion collisions at the LHC	Int. J. Mod. Phys. A 30 (2015) 1542012
3	CMS Collaboration	Coherent $J/\psi$ photoproduction in ultra-peripheral PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 2.76 TeV with the CMS experiment	PLB 772 (2017) 489	CMS-HIN-12-009 1605.06966
4	CMS Collaboration	Evidence for light-by-light scattering and searches for axion-like particles in ultraperipheral PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV	PLB 797 (2019) 134826	CMS-FSQ-16-012 1810.04602
5	CMS Collaboration	Measurement of exclusive $\rho(770)^0$ photoproduction in ultraperipheral pPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV	EPJC 79 (2019) 702	CMS-FSQ-16-007 1902.01339
6	CMS Collaboration	Measurement of exclusive $\Upsilon$ photoproduction from protons in pPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV	EPJC 79 (2019) 277	CMS-FSQ-13-009 1809.11080
7	ALICE Collaboration	Coherent $J/\psi$ photoproduction in ultra-peripheral Pb-Pb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 2.76 TeV	PLB 718 (2013) 1273	1209.3715
8	ALICE Collaboration	Charmonium and $e^+e^-$ pair photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 2.76 TeV	EPJC 73 (2013) 2617	1305.1467
9	ALICE Collaboration	Exclusive $\mathrm{J/}\psi$ photoproduction off protons in ultra-peripheral p-Pb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV	PRL 113 (2014) 232504	1406.7819
10	ALICE Collaboration	Coherent $\psi$ (2S) photo-production in ultra-peripheral Pb Pb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 2.76 TeV	PLB 751 (2015) 358	1508.05076
11	ALICE Collaboration	Coherent $\rho ^{0}$ photoproduction in ultra-peripheral Pb-Pb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 2.76 TeV	JHEP 09 (2015) 095	1503.09177
12	ALICE Collaboration	Coherent J/ $\psi$ photoproduction at forward rapidity in ultra-peripheral Pb-Pb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV	PLB 798 (2019) 134926	1904.06272
13	ALICE Collaboration	Energy dependence of exclusive $\mathrm {J}/\psi$ photoproduction off protons in ultra-peripheral p--Pb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV	EPJC 79 (2019) 402	1809.03235
14	ATLAS Collaboration	Evidence for light-by-light scattering in heavy-ion collisions with the ATLAS detector at the LHC	NP 13 (2017) 852	1702.01625
15	ATLAS Collaboration	Observation of light-by-light scattering in ultraperipheral Pb+Pb collisions with the ATLAS detector	PRL 123 (2019) 052001	1904.03536
16	M. Strikman, R. Vogt, and S. N. White	Probing small x parton densities in ultraperipheral AA and pA collisions at the LHC	PRL 96 (2006) 082001	hep-ph/0508296
17	V. Guzey and M. Klasen	Diffractive dijet photoproduction in ultraperipheral collisions at the LHC in next-to-leading order QCD	JHEP 04 (2016) 158	1603.06055
18	P. Kotko et al.	Estimating nonlinear effects in forward dijet production in ultra-peripheral heavy ion collisions at the LHC	EPJC 77 (2017) 353	1702.03063
19	T. Altinoluk, N. Armesto, G. Beuf, and A. H. Rezaeian	Diffractive dijet production in deep inelastic scattering and photon-hadron collisions in the color glass condensate	PLB 758 (2016) 373	1511.07452
20	Y. Hagiwara et al.	Accessing the gluon Wigner distribution in ultraperipheral $pA$ collisions	PRD 96 (2017) 034009	1706.01765
21	H. Mantysaari, N. Mueller, and B. Schenke	Diffractive dijet production and Wigner distributions from the color glass condensate	PRD 99 (2019) 074004	1902.05087
22	Y. Hatta, B.-W. Xiao, and F. Yuan	Probing the small- x gluon tomography in correlated hard diffractive dijet production in deep inelastic scattering	PRL 116 (2016) 202301	1601.01585
23	Y. Hatta, B.-W. Xiao, and F. Yuan	Gluon tomography from deeply virtual compton scattering at Small-x	PRD 95 (2017) 114026	1703.02085
24	A. Dumitru, V. Skokov, and T. Ullrich	Measuring the Weizsacker-Williams distribution of linearly polarized gluons at an electron-ion collider through dijet azimuthal asymmetries	PRC 99 (2019) 015204	1809.02615
25	Y. Hagiwara, Y. Hatta, and T. Ueda	Wigner, Husimi, and generalized transverse momentum dependent distributions in the color glass condensate	PRD 94 (2016) 094036	1609.05773
26	Y. Hagiwara, Y. Hatta, B.-W. Xiao, and F. Yuan	Elliptic flow in small systems due to elliptic gluon distributions?	PLB 771 (2017) 374	1701.04254
27	J. Zhou	Elliptic gluon generalized transverse-momentum-dependent distribution inside a large nucleus	PRD 94 (2016) 114017	1611.02397
28	CDF Collaboration	Observation of exclusive dijet production at the Fermilab Tevatron $p^- \bar{p}$ collider	PRD 77 (2008) 052004	0712.0604
29	ZEUS Collaboration	Production of exclusive dijets in diffractive deep inelastic scattering at HERA	EPJC 76 (2016) 16	1505.05783
30	S. R. Klein and H. Mantysaari	Imaging the nucleus with high-energy photons	Nature Rev. Phys. 1 (2019) 662	1910.10858
31	W. Busza, K. Rajagopal, and W. van der Schee	Heavy ion collisions: the big picture, and the big questions	Ann. Rev. Nucl. Part. Sci. 68 (2018) 339	1802.04801
32	U. Heinz and R. Snellings	Collective flow and viscosity in relativistic heavy-ion collisions	Ann. Rev. Nucl. Part. Sci. 63 (2013) 123	1301.2826
33	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
34	H. Jung	Hard diffractive scattering in high-energy e p collisions and the Monte Carlo generator RAPGAP	CPC 86 (1995) 147
35	F. D. Aaron et al.	Measurement of the cross section for diffractive deep-inelastic scattering with a leading proton at HERA	EPJC 71 (2011) 1578	1010.1476
36	H1 Collaboration	Diffractive dijet photoproduction in ep collisions at HERA	EPJC 70 (2010) 15	1006.0946
37	S. R. Klein et al.	STARlight: A Monte Carlo simulation program for ultra-peripheral collisions of relativistic ions	CPC 212 (2017) 258	1607.03838
38	GEANT4 Collaboration	GEANT4: A Simulation toolkit	NIMA 506 (2003) 250
39	CMS Collaboration	Particle-flow reconstruction and global event description with the CMS detector	JINST 12 (2017) P10003	CMS-PRF-14-001 1706.04965
40	M. Cacciari, G. P. Salam, and G. Soyez	The anti- $k_t$ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
41	M. Cacciari, G. P. Salam, and G. Soyez	FastJet User Manual	EPJC 72 (2012) 1896	1111.6097
42	CMS Collaboration	CMS tracking performance results from early LHC operation	EPJC 70 (2010) 1165	CMS-TRK-10-001 1007.1988
43	CMS Collaboration	Jet energy scale and resolution in the CMS experiment in pp collisions at 8 TeV	JINST 12 (2017) P02014	CMS-JME-13-004 1607.03663
44	CMS Collaboration	Constraining gluon distributions in nuclei using dijets in proton-proton and proton-lead collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV	PRL 121 (2018) 062002	CMS-HIN-16-003 1805.04736
45	CMS Collaboration	Observation of long-range near-side angular correlations in proton-proton collisions at the LHC	JHEP 09 (2010) 091	CMS-QCD-10-002 1009.4122