Arrondissement of Gex

Cessy (French pronunciation: [sesi]) is a commune in the Ain department in eastern France. The area was first inhabited by two farming families in the eleventh century, and as the town has grown its agricultural heritage has remained a significant feature, with the populated area surrounded by a vast expanse of fields and an annual agricultural festival.

The TOTEM experiment (TOTal Elastic and diffractive cross section Measurement) is one of the nine detector experiments at CERN's Large Hadron Collider. The other eight are: ATLAS, ALICE, CMS, LHCb, LHCf, MoEDAL, FASER and SND@LHC. It shares an interaction point with CMS. The detector aims at measurement of total cross section, elastic scattering, and diffraction processes. The primary instrument of the detector is referred to as a Roman pot. In December 2020, the D0 and TOTEM Collaborations made public the odderon discovery based on a purely data driven approach in a CERN and Fermilab approved preprint that was later published in Physical Review Letters. In this experimental observation, the TOTEM proton-proton data in the region of the diffractive minimum and maximum was extrapolated from 13, 8, 7 and 2.76 TeV to 1.96 TeV and compared this to D0 data at 1.96 TeV in the same t-range giving an odderon significance of 3.4 σ. When combined with TOTEM experimental data at 13 TeV at small scattering angles providing an odderon significance of 3.4 - 4.6 σ, the combination resulted in an odderon significance of at least 5.2 σ.

The Compact Muon Solenoid (CMS) experiment is one of two large general-purpose particle physics detectors built on the Large Hadron Collider (LHC) at CERN in Switzerland and France. The goal of the CMS experiment is to investigate a wide range of physics, including the search for the Higgs boson, extra dimensions, and particles that could make up dark matter. CMS is 21 metres long, 15 m in diameter, and weighs about 14,000 tonnes. Over 4,000 people, representing 206 scientific institutes and 47 countries, form the CMS collaboration who built and now operate the detector. It is located in a cavern at Cessy in France, just across the border from Geneva. In July 2012, along with ATLAS, CMS tentatively discovered the Higgs boson. By March 2013 its existence was confirmed.

Gex (French: [ʒɛks]; Arpitan: Gèx; Italian: Gesio) is a commune in the Ain department in eastern France and a subprefecture of the department. It lies 5 km (3.1 mi) from the Swiss border and 16 km (9.9 mi) from Geneva. It is a subprefecture of Ain.

The canton of Gex is an administrative division in eastern France. At the French canton reorganisation which came into effect in March 2015, the canton was reduced from 11 to 7 communes: Cessy Divonne-les-Bains Gex Grilly Sauverny Versonnex Vesancy

Ségny (French pronunciation: [seɲi]), also written Segny, is a commune in the Ain department in eastern France. Ségny is situated in the east of the department, in a district of the Lake Geneva / River Rhône basin known as the Pays de Gex. It lies on the important RN 5 trunk road from Paris to Geneva and is just five minutes by road from Geneva Cointrin International Airport. A local bus service connects Ségny to Geneva city centre, which is some 13 km (8.1 mi) away. Ségny became a member of the Pays de Gex Community of Communes on 1 January 1996. The commune is bordered by Cessy to the north, Versonnex to the east, Prévessin-Moëns and Ornex to the south, and Échenevex and Chevry to the west.

Communauté d'agglomération du Pays de Gex is the communauté d'agglomération, an intercommunal structure, centred on the town of Gex. It is located in the Ain department, in the Auvergne-Rhône-Alpes region, eastern France. Created in 1995, the administrative seat is located in its namesake commune of Gex. Its area is 404.9 km2. Its population was 98,257 in 2019, of which 13,121 lived in Gex proper.

Échenevex ([eʃnəvɛ]) is a commune in the Ain department in eastern France. As of 2020, it is the commune with the fifth highest median per capita income (€51,020 per year) in France.

Versonnex (French pronunciation: [vɛʁsɔnɛ]; Arpitan: Vèrzenèx) is a commune in the Ain department in eastern France.

Vesancy (French pronunciation: [vəzɑ̃si]) is a commune in the Ain department in eastern France. The commune has an average elevation of 650 m (2,130 ft) above sea level.

Chevry (French pronunciation: [ʃəvʁi]; Arpitan: Chevri) is a commune in the Ain department, in the region of Auvergne-Rhône-Alpes, eastern France. Chevry's inhabitants are called Chevrysiens. Chevry is located between Gex and Saint-Genis-Pouilly, on the departmental highway RD984, which is the primary access to the town. It is twenty minutes from the Swiss border near Geneva. The commune also includes the villages of Veraz (to the east) and Naz-Dessous (to the north). The town has several rivers: the Great Journans, Petit Journans, the Allondon and Janvoin.

Sauverny (French pronunciation: [sovɛʁni]; Arpitan: Sovèrnê) is a commune in the Ain department in eastern France. It is located between the Jura mountains in France and Lac Leman, bordering the Canton of Geneva, Switzerland.