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Measurement of exclusive pion pair production in proton–proton collisions at √s=7TeV with the ATLAS detector

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jats:titleAbstract</jats:title>jats:pThe exclusive production of pion pairs in the process jats:inline-formulajats:alternativesjats:tex-math$$pp\rightarrow pp\pi ^+\pi ^-$$</jats:tex-math><mml:math xmlns:mml=""> mml:mrow mml:mip</mml:mi> mml:mip</mml:mi> mml:mo→</mml:mo> mml:mip</mml:mi> mml:mip</mml:mi> mml:msup mml:miπ</mml:mi> mml:mo+</mml:mo> </mml:msup> mml:msup mml:miπ</mml:mi> mml:mo-</mml:mo> </mml:msup> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> has been measured at jats:inline-formulajats:alternativesjats:tex-math$$\sqrt{s}={7},\text {TeV}$$</jats:tex-math><mml:math xmlns:mml=""> mml:mrow mml:msqrt mml:mis</mml:mi> </mml:msqrt> mml:mo=</mml:mo> mml:mn7</mml:mn> <mml:mspace /> mml:mtextTeV</mml:mtext> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> with the ATLAS detector at the LHC, using jats:inline-formulajats:alternativesjats:tex-math$${80},{\upmu \textrm{b}}^{-1}$$</jats:tex-math><mml:math xmlns:mml=""> mml:mrow mml:mn80</mml:mn> <mml:mspace /> mml:msup mml:mrow mml:miμ</mml:mi> mml:mtextb</mml:mtext> </mml:mrow> mml:mrow mml:mo-</mml:mo> mml:mn1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> of low-luminosity data. The pion pairs were detected in the ATLAS central detector while outgoing protons were measured in the forward ATLAS ALFA detector system. This represents the first use of proton tagging to measure an exclusive hadronic final state at the LHC. A cross-section measurement is performed in two kinematic regions defined by the proton momenta, the pion rapidities and transverse momenta, and the pion–pion invariant mass. Cross-section values of jats:inline-formulajats:alternativesjats:tex-math$$4.8 \pm 1.0 \mathrm {\ (stat)} {~}^{+0.3}{-0.2} \mathrm {\ (syst)}\ {\upmu \textrm{b}}$$</jats:tex-math><mml:math xmlns:mml=""> mml:mrow mml:mn4.8</mml:mn> mml:mo±</mml:mo> mml:mn1.0</mml:mn> mml:mrow <mml:mspace /> mml:mo(</mml:mo> mml:mistat</mml:mi> mml:mo)</mml:mo> </mml:mrow> mml:msubsup mml:mrow <mml:mspace /> </mml:mrow> mml:mrow mml:mo-</mml:mo> mml:mn0.2</mml:mn> </mml:mrow> mml:mrow mml:mo+</mml:mo> mml:mn0.3</mml:mn> </mml:mrow> </mml:msubsup> mml:mrow <mml:mspace /> mml:mo(</mml:mo> mml:misyst</mml:mi> mml:mo)</mml:mo> </mml:mrow> <mml:mspace /> mml:mrow mml:miμ</mml:mi> mml:mtextb</mml:mtext> </mml:mrow> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> and jats:inline-formulajats:alternativesjats:tex-math$$9 \pm 6 \mathrm {\ (stat)} {~}^{+2}{-2} \mathrm {\ (syst)}\ {\upmu \textrm{b}} $$</jats:tex-math><mml:math xmlns:mml=""> mml:mrow mml:mn9</mml:mn> mml:mo±</mml:mo> mml:mn6</mml:mn> mml:mrow <mml:mspace /> mml:mo(</mml:mo> mml:mistat</mml:mi> mml:mo)</mml:mo> </mml:mrow> mml:msubsup mml:mrow <mml:mspace /> </mml:mrow> mml:mrow mml:mo-</mml:mo> mml:mn2</mml:mn> </mml:mrow> mml:mrow mml:mo+</mml:mo> mml:mn2</mml:mn> </mml:mrow> </mml:msubsup> mml:mrow <mml:mspace /> mml:mo(</mml:mo> mml:misyst</mml:mi> mml:mo)</mml:mo> </mml:mrow> <mml:mspace /> mml:mrow mml:miμ</mml:mi> mml:mtextb</mml:mtext> </mml:mrow> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> are obtained in the two regions; they are compared with theoretical models and provide a demonstration of the feasibility of measurements of this type.</jats:p>


Acknowledgements: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; ANID, Chile; CAS, MOST and NSFC, China; Minciencias, Colombia; MEYS CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS and CEA-DRF/IRFU, France; SRNSFG, Georgia; BMBF, HGF and MPG, Germany; GSRI, Greece; RGC and Hong Kong SAR, China; ISF and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MEiN, Poland; FCT, Portugal; MNE/IFA, Romania; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZŠ, Slovenia; DSI/NRF, South Africa; MICINN, Spain; SRC and Wallenberg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taiwan; TENMAK, Turkey; STFC, United Kingdom; DOE and NSF, USA. In addition, individual groups and members have received support from BCKDF, CANARIE, Compute Canada and CRC, Canada; PRIMUS 21/SCI/017 and UNCE SCI/013, Czech Republic; COST, ERC, ERDF, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union; Investissements d’Avenir Labex, Investissements d’Avenir Idex and ANR, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF, Greece; BSF-NSF and MINERVA, Israel; Norwegian Financial Mechanism 2014–2021, Norway; NCN and NAWA, Poland; La Caixa Banking Foundation, CERCA Programme Generalitat de Catalunya and PROMETEO and GenT Programmes Generalitat Valenciana, Spain; Göran Gustafssons Stiftelse, Sweden; The Royal Society and Leverhulme Trust, UK. The crucial computing support from all WLCG partners is acknowledged gratefully, in particular from CERN, the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (UK) and BNL (USA), the Tier-2 facilities worldwide and large non-WLCG resource providers. Major contributors of computing resources are listed in Ref. [43].


5106 Nuclear and Plasma Physics, 5107 Particle and High Energy Physics, 51 Physical Sciences

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European Physical Journal C

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