Measurement of photon production in the very forward direction in deep-inelastic scattering at HERA

F D Aaron,S Habib,S Levonian,G Buschhorn,J Cvach,M Jacquet,M Fleischer,E A De Wolf,E Gabathuler,P Van Mechelen,M Steder,A Rostovtsev,A Dubak,B Stella,J Feltesse,L Goerlich,I R Kenyon,C Kiesling,C Vallée,A Petrukhin,D Traynor,N Gogitidze,A Bunyatyan,D Haidt,B Delcourt,J Delvax,H Pirumov,S Ghazaryan,C Pascaud,F Sefkow,J Gayler,L N Shtarkov,A Baghdasaryan,V Lendermann,D Ozerov,D Wegener,S Egli,M Kapichine,V Lubimov,I Tsakov,B R Grell,H Zohrabyan,R C W Henderson,F Moreau,E Barrelet,A Makankine,K Begzsuren,S Baghdasaryan,T Ravdandorj,S Shushkevich,G Herrera,J Ferencei,A Valkárová,G Laštovička-Medin,A J Campbell,W Bartel,C Niebuhr,M Mudrinic,V Chekelian,P Truöl,A Glazov,U Straumann,J E Olsson,T Kluge,S Mikocki,E Malinovski,H Henschel,P D Thompson,P Pahl,Y Soloviev,A Dossanov,P Kostka,Y Vazdik,A Specka,T Greenshaw,V Brisson,V Spaskov,B Tseepeldorj,I Milcewicz-Mika,V Dodonov,D P C Sankey,K H Hiller,G Grindhammer,K Nowak,G D Patel,K Daum,Z Staykova,R Roosen,L Bystritskaya,M Kraemer,J Turnau,A Lebedev,L Lytkin,E Hennekemper,K Urban,J B Dainton,P Sopicki,R Felst,H U Martyn ,I Panagoulias,E Rizvi,S Schmitt,B List,J Meyer,C Helebrant,D Šálek,W Lange,J Kretzschmar,C Diaconu,Zhiqing Philippe Zhang ,M Hildebrandt,J Žáček,R Horisberger,A Morozov,A Fomenko,J Zálešâk ,J E Ruiz Tabasco ,J.c Bizot ,V Palichik,Th D Papadopoulou ,D Fischer ,K Černý ,V Andreev,J Braciník ,R Kogler,M Herbst,K B Cantun Avila ,X Janssen,G Brandt,Bogdan Povh ,D Bruncko,B Pokorny,A Eliseev,L Schoeffel,V Boudry,T H Tran,E Wuensch ,V Radescu,H.‐C Schultz‐Coulon ,C Kleinwort,K Lipka,J G Contreras,G Stoicea,D Pitzl,H Jung,J V Morris,J A Coughlan,S Backović ,V Černý ,P Marage,M Rotaru,R López-Fernández ,Florian Huber ,D South,A Mehta,I Smiljanić ,G Eckerlin,I Pićurić ,K Krueger ,I Božović-Jelisavc̆ić ,L Favart,P R Newman,T Naumann ,Jenny List ,P Reimer,D Hoffmann,S J Maxfield,S V Rusakov ,G Nowak,P Robmann,M Klein,A Schoening ,D Britzger,M Gouzevitch,A Belousov,Andreas Bernhard Meyer ,R Polifka,T Sloan,A Grebenyuk,R Plačakytė,S M Piec ,H Meyer,M Dobre,C Grab,M Sauter,M Pandurović ,E Pérez ,D Nikitin,A Fedotov,P Laycock,M P J Landon,E Elsen,K Mueller ,T Sýkora ,L Jönsson,A Zhokin,N Raičević ,F Zomer,Martin Brinkmann ,C Alexa,Federico Alberto Ceccopieri ,E Sauvan,Pavel A Belov ,T Hreus

doi:10.1140/epjc/s10052-011-1771-6

Abstract

The production of photons at very small angles with respect to the proton beam direction is studied in deep-inelastic positron–proton scattering at HERA. The data are taken with the H1 detector in the years 2006 and 2007 and correspond to an integrated luminosity of 126 pb−1. The analysis covers the range of negative four momentum transfer squared at the positron vertex 6<Q 2<100 GeV2 and inelasticity 0.05<y<0.6. Cross sections are measured for the most energetic photon with pseudorapidity η>7.9 as a function of its transverse momentum $p_{T}^{\mathrm{lead}}$ and longitudinal momentum fraction of the incoming proton $x_{L}^{\mathrm{lead}}$ . In addition, the cross sections are studied as a function of the sum of the longitudinal momentum fraction $x_{L}^{\mathrm{sum}}$ of all photons in the pseudorapidity range η>7.9. The cross sections are normalised to the inclusive deep-inelastic scattering cross section and compared to the predictions of models of deep-inelastic scattering and models of the hadronic interactions of high energy cosmic rays.

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