First measurement of the underlying event activity at the LHC with $\sqrt{s} = 0.9$ TeV

V Khachatryan,L Gutay,W De Boer,I Kravchenko,M Wayne,F Drouhin,U Dosselli,G M Dallavalle,M Pimiä,S Semenov,Y J Lu,A Vilela Pereira ,K Lassila-Perini,R D’Alessandro,Y S Chung,M Kaya,A Ferrando,T Bergauer,S Y Jun,A P R Gay,Ch Thiebaux ,E Marinova,S Sharma,L Kreczko,K Mishra,M I Josa,A Whitbeck,M B Tonjes,W Białas ,Y Yang,D Treille,C Autermann,V Patras,E A Wenger,R Breedon,P Gupta,D Pagano,V Gavrilov,M Pieri,C Fernandez Bedoya,D Sprenger,S Maruyama,B Mangano,M Squires,M Marionneau,S M Silva Do Amaral ,L Felď ,L Levchuk,D Strom,H Teng,S Bilmiş ,L Wendland,M Chamizo Llatas,R K Choudhury,C K Lae,I A Cali,I Ahmed,D Bisello,J Zennamo,D Menasce,D Winn,A C Mignerey,D Reeder,Y Ma,P Raics,M Grünewald ,T Kress,L Kramer,G Martı́nez ,M Karim,J Tucker,E Calvo,P Capiluppi,D J Summers ,G Debreczeni,F Santanastasio,J Ellison,L Perera,N Cripps,L A T Bauerdick,Н Голубев ,D Bortoletto,M S Witherell ,O Prokofyev,A Gribushin,S Piperov,H S Chen,S B Beri,S Tkaczyk,A Kalogeropoulos,S Simon,D Piparo,P Nef,M U Mozer,G Masetti,N Chanon,S Greder,K Maeshima,A Satpathy,J Fay,J Schwandt,T R Fernandez Perez Tomei ,T Punz,E Casimiro Linares,V Valuev,L Fields ,S Vanini,S Goy Lopez,L Fanò,I Lazzizzera,S Won,T Frueboes,Min Yang ,L Benussi,R Schöfbeck,J Milošević ,J Speck,B Gomez Moreno ,C Charlot,Y Gershtein,M Feindt,M Vergili,P Bunin,C Jarvis,A Dominguez,J Ballin,B Wittmer,A Khukhunaishvili,R Pordes,T Signal,M Meschini,J Gilmore,K Kaschube,C Viviani,D Puigh,H Van Haevermaet,J Königsberg ,S Perriès ,S Sekmen,J Maes,Р Тенчини ,Y Chào ,A Oulianov,A Mohapatra,L Millischer,D M Newbold,J De Favereau De Jeneret,S Ganjour,V Genchev,Jiahui Wei ,A Hinzmann,M Müntel,D Liang,M Swartz,D Denegri,L Caminada,T Rovelli,F Ligabue,B Cox,S Gowdy,D Barge,M Murray,C Veelken,A Smoron,G Kaußen ,L Mirabito,E Mccliment,L Antonelli,S Hänsel,H Stadie,P Janot,D Lomidze,L Boldizsár ,M Bergholz,J Descamps,S Kwan,J Muelmenstaedt,D Colling,E B Ziebarth,J Duarte Campderros,S Ward,D Leslie,M Cuffiani,R Gomez-Reino Garrido,P Allfrey,P Papacz,S Linn,N Neumeister,P Harris,G H Hammad,L S Durkin,I Iashvili,J Warchol,H Pi,S I Cooper,V Miccio,P Tan,E Focardi,A Deisher,J P Cumalat,A Pozdnyakov,N Hörmann,L Sala,M Maggi,K Kaadze,В Жуков ,R López-Fernández ,K Goulianos,J Chen,W Adam,V Pavlunin,G Bolla,D Kotliński ,A Sakharov,B Gobbo,G Gómez ,N V Tran,F Rebassoo,E Yildirim,Andreas Bernhard Meyer ,B Clerbaux,D H Miller,A Saha,K Sumorok,R T D’agnolo ,J Rander,M Szleper,D Dutta,S Ragazzi,I Fisk,R Trentadue,G Merino,M Dubinin,S Schael,C Schwick,L Litov,P Kyberd,L Teodorescu,T Camporesi,A Beretvas,A Kyriakis,J Eugster,R.-S Lu,B Fabbro,A Belyaev,D Abbaneo,R Mankel,L Foà,C Lazaridis,D Orbaker,D Blöch ,J Incandela,R Rahmat,J Hauser,G Sultanov,J Bernardini,A Drozdetskiy,G Boudoul,V Monaco,J A Coarasa Perez,J Yelton,L Fiore,B Mura,D Baumgartel,S Elgammal,Y Kuessel,A Tricomi,M Weinberger,J Strauss,M Dragicevic,P Lobelle Pardo,A J Bell,E Kuznetsova,T Miceli,A Givernaud,M Velasco,W Hintz,P Eerola,N Darmenov,L Sulak,S Lee,L K Gibbons,H Park,M Johnson,B Stieger,M Aldaya Martin ,S Frosali,T Aziz,E Sexton-Kennedy,M Hohlmann,M Titov,D Uzun,A Rizzi,M E Pol,P Busson,D R Claes,E Appelt,Y H Chang,B Marangelli,J Temple,P Petkov,D Martschei,T Sabonis,R Y Zhu,D Lanske,R Hirosky,A Sznajder,A Kharchilava,L Barbone,A Campbell,O Gutsche,P Miné,M Ćwiok ,M C Fouz,B C Shen,R P Smith,N Colino,N Marinelli,Y Gao,H Brun,X Shi,E Laird,C Ferro,E Tuovinen,P Cole,K Kotov,R Godang,E Berry,H Enderle,M Kaur,S Stoykova,D Krofcheck,H F Heath,D Lelas,A Thea,S Oliveros,P Kalavase,S D Worm,J D’Hondt,T Adams,C Schäfer,G Abbiendi,G M Chen,A Romero,A T Laasanen,G I Veres,R A Ofierzynski,D Pellett,C Farrell,Y Yilmaz,G Karapostoli,T Kelly,W J Spalding,A Savin,K Öcalan ,A Holzner,R Remington,W Sun,Á László ,P Van Hove,J Lee,H Weber,E Shabalina,C Broutin,S C Tonwar,A Chatterjee,G Mitselmakher,V Kozhuharov,C Willmott,D Eckstein,H Pieta,D Stuart,O Koybasi,D Marlow,W D Zeuner,James Lamb ,O Atramentov,A Ghezzi,M Ruspa,R D Field,U Akgun,Z C Yang,M Ignatenko,T Mccauley,M Chan,A Gresele,P Lecomte,M Rodenburg,M Demarteau,G Dirkes,N Valls,T Geralis,J C Sanabria,L Wehrli,S Buontempo,L Orsini,K Mazumdar,C Bernet,R Lipton,N Amapane,V M Ghete,F A Triantis,I J Cabrillo,C Sander,K Gill,S C Kao,J Härkönen,E Yazgan,C Diez Pardos,G Bencze,F Pandolfi,A Montanari,G Daskalakis,M Stein,A Tropiano,E Twedt,G Mäggi ,R R Betts,S Mersi,A Nardulli,M Mazzucato,T Khurshid,S Vavilov,W Ko,A Vinogradov,D Daeuwel,M Valdata,M Kirsanov,P Zalewski,A Knutsson,S Argirò ,G Bruno,D Stickland,D Renker,N K Mondal,T Rodrigo,F Nowak,J Velkovska,P Gras,G Petrucciani,T Ma,M Bedjidian,V Grishin,W Clarida,R Jussen,Y F Liu,D C Son,S Belforte,P Paolucci,Michael Henry Schmitt ,H Liu,F Romano,J St John ,S Bhattacharya,C Hartl,T Maes,T Lampén,T Lomtadze,C N Nguyen,M Diemoz,P Limon,S Hagopian,C Jeong,A Linn,P E Marage,T Chwalek,J Mans,D Futyan,S Honc,S Padhi,R Schmidt,J G Smith,M I Asghar,S Park,C Milstène,E Eşkut ,G Anagnostou,K Kousouris,M Zanetti,N Pastrone,E Gülmez,Alberto Sánchez Hernández ,Q Ingram,D Silvers,K V Tsang,A T Meneguzzo,L Uvarov,W Lange,R Chierici,P Jindal,P Sonnek,M Nikolić ,C.-E Wulz,L Lyons,G P Siroli ,C Eskew,M H Zoeller,D Wang,P Vitulo,U Gebbert,J Asaadi,C H Jiang,Shilpi Jain ,H Arfaei,I Chakaberia,N Bacchetta,E Brownson,F Golf,A Snigirev,M Kasemann,P T Cox,A Parenti,M Wang,P Bellan,J Vaughan,R Granier De Cassagnac ,R Gonzalez Suarez,D Hits,S Maselli,J Haas,T Karaman,T Kolberg,J Hammer,F Odorici,B Caponeri,M Maity,M Arneodo,S Wimpenny,J Slaunwhite,D Creanza,C Roland,A Scheurer,P Schieferdecker,C Liu,Yu Andreev,A Sill,J Hauk,A Pfeiffer,Y Kim,M Ata,V Krychkine,L Mundim,A Rýd ,J Flix,Y Tschudi,M Finger,R Vilar Cortabitarte ,A Jafari,A Mussgiller,W Waltenberger,L Vanelderen,S Popescu,B K Heltsley ,C Foudas,V E Barnes,L K Saini,V E Bazterra,C Prescott,S Ovyn,M C Sawley ,R Carlin,C Tully,J C Yun,G Flucke,F Palla,G B Cerati,C Newman-Holmes,O Buchmüller ,D Kovalskyi,I.-A Melzer-Pellmann,J Richman,B C Choudhary,J P Gomez ,M Pierini,M Renz,Y Ban,U Nauenberg,R Volpe,M Grothe,M Kirakosyan,F L Navarria,M Z Mehta,R Horisberger,G Polese,T Ferguson,I Lokhtin,I Volobouev,M Besançon ,L Demortier,R Stone,T Y Ling,A Gurtu,D Vishnevskiy,R Kinnunen,W T Chen,G A Alves,A Rose,T Yetkin,Ali O Ayhan ,M Heinrich,H Jensen,L Mucibello,J Jackson,V Kim,A Zabi,A Heikkinen,Y Pakhotin,P Lariccia,J Olson,J Tomaszewska,E Friis,E James,J Pálinkás ,P Petrov,K Freudenreich,O Sengul,I Vila,M A Mahmoud,M Chadwick,M Dželalija ,A Morelos Pineda,D J Karmgard,N Akchurin,A Kapusi,F R Cavallo,D Berry,D Mesa,H Schettler,D Ryckbosch,V Buege,S F Novaes,I Smirnov,R Ranieri,W Carvalho,M Galanti,M Merschmeyer,P Verrecchia,J Babb,M Cerrada,Z Kim,T Lindén,G Wrochna,K A Ulmer,Ashok Kumar ,B Roland,M Mulders,B Klein,J Wetzel,S V Gleyzer,S Rahatlou,J Seixas,F Chlebana,O Devroede,M Jindal,P Kokkas,V Roinishvili,D Loukas,L Agostino,G Eckerlin,K Yi,R Redjimi,M Davids,P Sellers,M Ahmad,W Dominik,H Kluge,D Acosta,L Apanasevich,J H Liu,M Pernicka,J A Coughlan,R Travaglini,J P Chou,G Zito,C Botta,J Han,N Schul,S Girgis,J Williams ,A Petrilli,M A Reyes-Santos,J Freeman,A Mestvirishvili,F M Stober,S Nuzzo,B Kreis,A Khan,F Palmonari,M Kirn,A Volkov,F Ferri,A Benaglia,B Ille,K Y Kao,Α Μάρκου ,G Y Jeng,M Zeise,J Callner,D Tsirigkas,P Kreuzer,A M Sirunyan,A Dimitrov,F J M Geurts,K Hatakeyama,B Hegner,J Nachtman,J Santaolalla,G Ball,J.-P Merlo,H W K Cheung,K Sung,A Ruiz-Jimeno ,E C Chabert,E Dusinberre,T Rohe,P Everaerts,C Zorbilmez,K Nirunpong,Z Chen,K Nawrocki,S Petrushanko,B Pavlov,A Calderón ,V Gaultney,A Sanchez ,J Hirschauer,P Schlein,H Méndez ,G M Bilei,A Tumasyan,D Fasanella,J Fulcher,Z Wan,M Boutemeur,A Raspereza,E Tuominen,J Butt,J Alcaraz Maestre,S Troitsky,T Caebergs,K Harder,A Yagil,M Yan,K Cankoçak ,O Actis,K Klein,M H.g Souza ,A Fahim,G Cappello,A Besson,T Hebbeker,G Bagliesi,M Tosi,P Shukla,M Özbek,B Hong,M Pelliccioni,V Savrin,J Zhang,S Tourneur,W Bender,C Bardak,J H Kim,E Migliore,G Hall,M Simon,P Jarry,V Karimäki,S Paoletti,P Maksimović ,C Markou,F Bostock,L Raposo,F Pauß ,S Sala,G Davies,J G Shiu,P Giacomelli,F Ambroglini,P Faccioli,J Keller,C Magass,Y Hsiung,H Malbouisson,G A Pierro,C Rogan,P Demin,U E Surat,P Govoni,C Battilana,M Hashemi,C H Shepherd‐Themistocleous ,A Ledovskoy,S Stoynev,M Zieliński ,W Bertl,J Smith,L Perchalla,S Bolognesi,M Paulini,A K Mohanty,R K Shivpuri,T Kamon,D Ćutts ,A Vartak,H Held,K Krajczár ,S Gninenko,D Mercier,P G Ferreira Parracho,R Musenich,P Giubilato,M Balazs,Л Дімітров ,J Gu,S Ventura,C Fabjan,C Riccardi,O Militaru,D Soares,G Gomez Ceballos,A S Yoon,Humberto Antonio Salazar Ibarguen ,L Lista,T Speer,J N Butler,D Green,J Hollar,S R Wagner,S Lynch,K Stenson,A De Benedetti,M Krammer,B Huckvale,V Oguri,M Voutilainen,R Wilkinson,I K Furic,G Della Ricca ,V Chetluru,L Cremaldi ,H Reithler,I Vodopiyanov,H Prosper,M Mooney,M Ivova Rikova,I P J Shipsey ,M Tripathi,H Flächer ,E Gurpinar,R Sacchi,D Ungaro,I Vankov,Z Wang,D Benedetti,T Miao,J Lykken,N Almeida,M Kossov,D Cussans,K S Grogg,M Biasini,T Rommerskirchen,G Selvaggi,A Starodumov,N Van Remortel,B Heyburn,E Gottschalk,I Puljak,D Nguyen,A Polatöz,M Sasseville,P Luukka,C Loizides,M Janulis,F Marinho,J Steggemann,R Frühwirth,T Bose,T Klimkovich,V Chiochia,T Danielson,V Litvine,B De La Cruz,M Margoni,G Kozlov,K Gunthoti,G Iaselli,A Flossdorf,C Park,S Erhan,L Masetti,В Е Кузнецов ,E Locci,I Redondo,M Anderson,A Pin,J Klem,W To,M Raidal,C Rovelli,H B Rhee,S Naumann-Emme,V Matveev,W Kiesenhofer,P A Razis,E Boos,J Wang,A Venturi,Z Gecse,L Lusito,S Başeğmez ,D Polic,C Wissing,J Hays,M Choi,G Pásżtor ,N Varelas,G Codispoti,S P Singh,D Carlsmith,D Demir,A Kropivnitskaya,T Whyntie,D Teyssier,P Levchenko,M Mohammadi Najafabadi ,V Zhukova,S Thomas,L Rebane,J Goldstein,P Traczyk,C Saout,Andreas Oehler ,M Bluj,H Mermerkaya,G Flügge,L Quertenmont,L Sonnenschein,N Béni ,P Milenović ,Thomas Schwarz ,D M Morse,A Rosowsky,P Meridiani,C Leonidopoulos,M Herndon,F Fabozzi,F Glege,W Behrenhoff,B P Padley,U Behrens,C Vander Velde,I Azhgirey,K Rossato,B Curé,C Mesropian,A Colaleo,N Leonardo,A Ferapontov,G Nicolas Kaufman,A Heister,E Conte,A.-M Magnan,H Kalakhety,F Özok ,E Longo,L Borrello,C Dragoiu,C Jorda,R Pleština ,V Ciulli,A F Osório Oliveros ,G Cirino,A Anastassov,P Moisenz,F Ratnikov,R Cavanaugh,J Merz,A Bornheim,M Weber,M Górski,V Stolin,J Rohlf,B Safarzadeh,O Hindrichs,H Rykaczewski,R Harr,J Anderson,A K Srivastava,J Molnár ,A Bodek,G Hu,D Mason,P Avery,P Sauerland,P J Bell ,M Pioppí ,K Doroba,G Majumder,S De Visscher,M Paganoni,K Theofilatos,J Suarez Gonzalez ,T Bolton,N Cartiglia,S Boutle,A Zuranski,V Maroussov,H Rohringer,P Chang,H Geenen,M Della Negra,S Reucroft,C Hajdú ,A Kraan,A Baden,C Amsler,V Petrov,H Breuker,Z Zhang,J Bunn,F Fassi,G Mantovani,Alan S Go ,H El Mamouni ,A Ivanov,G B Mohanty,M Kadastik,C Baty,V Reković ,G Tonelli,G Segneri,S Wakefield,A Özpineci ,D Bodin,S K Kataria,D C Miner,D Dobur,J Puzović ,L Di Matteo,G P Heath,W Hopkins,C A Carrillo Montoya ,J Królikowski ,K H Chen,A Moeller,G Giurgiu,E Auffray,J H Wu,A.-C Le Bihan ,Y.-J Lee,L Tauscher,J Thom,L Perrozzi,P Fabbricatore,D Cebra,J Puerta Pelayo,C Hof,A Hervé,M J Ryan,Y M Tzeng,D J Kong,M Pesaresi,P R Dudero,D D’Enterria,G Iles,P Piroué,M Jeitler,O Boeriu,L Martini,K Shin,N Godinović ,D Engh,D Toback,S Ahuja,E M Gregores,D Sabes,Z L Trocsanyi,P Sharp,B Dahmes,M Buehler,K Klapoetke,F Ptochos,Pedro Ribeiro ,W Li,F Liu,N Rompotis,V Tancini,G Miní ,T Schum,G P Di Giovanni,T Medvedeva,G R Snow,J Malclès ,S Blyweert,R Erbacher,N De Filippis,E A Albayrak,L Pape,L Benucci,E Meschi,S H Chuang,I Bloch,J M Kohli,Y Zheng,A Everett,W J Womersley,J Y C Tam ,W.-S Hou,M Grassi,M Bachtis,A García-Bellido ,R Trayanov,A M Guler,A Guneratne Bryer,R Loveless,X Janssen,J Veverka,K Burkett,A Macpherson,B Kim,S Song,G N Kim,M Searle,E M Da Costa,S Eno ,A F Garfinkel,E Nesvold,K Piotrzkowski,P Baesso,J G Acosta,D Lopes Pegna,J G Branson,I Belotelov,R Démina ,B Işıldak ,N Pozzobon,J Haupt,J Ribnik,A Kubik,S Metson,J A Bakken,C Maguire,J Hrubec,A Sobol,H Sakulin,M Marone,H Xiao,S Banerjee,R Cousins,J F De Trocóniz,A Cimmino,K F Johnson,R Kroeger,G De Lentdecker,H Nogima,N Nishu,R Sharma,A Dierlamm,S Morovic,S Malik,C J Edelmaier,K Banzuzi,J M Hernández ,S Lehti,H C Kaestli,M Guchait,M Thomas,Z Demir,G Quast,S Guragain,E Cano,A Zhokin,D A Sanders,P Killewald,J Morales,G Sguazzoni,K Deiters,M Zeinali,S L Zang,D Bourilkov,G Petrillo,L M Lebolo,A Sabellek,C Plager,T Tabarelli De Fatis,A Lopez Virto,E Halkiadakis,P H Butler,A Attikis,S Kang,A Biselli,I Segoni,R Beuselinck,K Bloom,R Wilken,R Gray,R Stringer,C Grab,S Kuleshov,G Benelli,R Carroll,J Marrouche,S Dasu,D Dammann,J S Wood,S Somalwar,R Salerno,G Cerminara,I González Caballero ,P Sheldon,B Camanzi,C Genta,L Malgeri,R Rougny,N Krasnikov,K Lannon,M M Obertino,M Cutajar,G Gökbulut,P Van Mulders,W Haj Ahmad ,Y Mikami,E Petrakou,Th Müller,I Dremin,E De La Cruz Burelo,L Romero,S Cihangir,J Kolb,J Weng,S Marcellini,A Zarubin,R G Kellogg,K Lelas,S Abdullin,G Safronov,N Saoulidou,R Fereos,A Lath,H Bakhshiansohi,R Hadjiiska,C Marchica,M Barrett,H Kim,R Lander,J Sibille,E E Kangal,F Beaudette,J Lazo-Flores,D Rousseau,W A Khan,M Saelim,C Hill,P Verdier,G Lungu,M Marienfeld,M E Dinardo,D Liko,V Perelygin,C Martínez Rivero ,D Gelé,E Luiggi Lopez,J.-L Agram,J Dolen,A Palma,M Jones,A Bean,A H Ball,Y J Lei,D Ferenček ,M Dias ,M De Gruttola,P Azzurri,A Hektor,J Andreä ,J R Vlimant,W Wu,S Kunori,M Edelhoff,P Lawson,M Abbrescia,V Veszprémi ,N Parashar,I C Park,F Borcherding,N Bondar,M Mateev,J E Ramirez Vargas,R Covarelli,M Haguenauer,J Zablocki,D Pedrini,R Frazier,O Charaf,K Ranjan,S Fonseca De Souza ,A Ershov,K Petridis,F Yumiceva,L Scodellaro,S Đurić ,P Van Mechelen,S Albergo,R Ralich,F Fedele,C Campagnari,K M Ecklund,Y Roh,R Rossin,N Adam,V D Elvira,M Vazquez Acosta,D J A Cockerill,D Evans,C Hackstein,A Nayak,E Castro,P Mane,I Manolakos,D Lange,R Moser,E Olaiya,F Moortgat,C Palmer,J Damgov,D Konstantinov,F Cavallari,M Niegel,S Gollapinni,F Meier,M Rovere,A López ,C K Mackay,S Costa,S Bitioukov,S Choi,Biao Zhu ,P Adžić ,P E Karchin,R Wallny,J Ott,A Kopecký ,M Lebourgeois,A Geiser,B Akgün ,M Zeyrek,J J Brooke,M Kazana,D Giordano,N Wickramage,S Malvezzi,C Mavrommatis,B Tali,A Çakır ,B R Drell,K Gabathuler,A.s Clough ,M Lethuillier,W Busza,M Jenkins,A David,F Stöckli,H Gerwig,P Sphicas,S W Li,S A Koay,S Chauhan,M Duda,J Varela,J Thomsen,R Montalvo,J Mnich,A Ostapchuk,U Baur,K Höepfner ,J Swanson,Z Szillási ,D Fehling,S Costantini,R Gokieli,G Önengüt,C Diez Gonzalez,N Beliy,S Colafranceschi,D Cline,S Bansal,S K Park,X T Huang,S Bose,S S Yu,G Kasieczka,Magdalena Djordjevic ,S Sengupta,E Carrera Jarrin,K A Hahn,A Fanfani,F Duru,L Ceard,N Redaelli,B A Barnett,S König,A Lanev,K H Hoffmann,J Hanlon,N Mohr,A Gaddi,D Favart,P Lenzi,J W Gary,S Harper,M Blume,H Topakli,A Staiano,I Villella,M Hildreth,D Piccolo,F De Guio,C Tuvé ,G Pugliese,A Soha,P Wittich,K F Chen,A Lucaroni,S Sen,M Maes,J Alexander,M Sobron Sañudo ,A Panagiotou,I Dumanoğlu ,G Organtini,V Radicci,H Jung,J R Patterson,V Karjavin,T Mäki,A Safonov,A Castro,S Liang,B Millán Mejías ,F Thyssen,P D Luckey,A De Cosa,B Kilminster,B Ujvári ,V Brigljević ,P Kurt,W Van Doninck,C E Gerber,J Swain,G Bauer,C Ceron,T Aliev,M Albrow,B Klima,V Epshteyn,S Slabospitsky,M Sani,R Sever,N Sönmez ,J Bendavid,A Adıgüzel ,K Kadija,T Dorigo,M Goncharov,D Hidas,S Shmatov,T Maënpaä ,S M Spanier ,A Giammanco,P Torre,A York,H J Simonis,A T Serban,A Vorobyev,P Azzi,M Stoye,D Tornier,S Lowette,D Krpic,P Arce,J Harvey,A Gurrola,A Nappi,J Conway,J Gronberg,I Hoş ,L Muñiz ,Y Weng,S Jabeen,A Meyer,D Wood,P Silva,S Taroni,S Chang,A Bonato,L Tourtchanovitch,L M Villaseñor-Cendejas,J Gruschke,M D’Alfonso,W Lin,K Buńkowski ,P Katsas,V Kaftanov,C Neu,F Blekman,S Mrenna,G Brona,M Fernández ,P Zotto,S Paktinat Mehdiabadi ,A Singovsky,N Shumeiko,K Rose,F Lacroix,A Krokhotin,K Potamianos,G Vesztergombi,John Michael Marraffino ,M Hoch,L Spiegel,J Fernández Menéndez ,U Heintz,L Gray,M Zakaria,Y W Chang,M Weinberg,J 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doi:10.1140/epjc/s10052-010-1453-9

Abstract

A measurement of the underlying activity in scattering processes with transverse momentum scale in the GeV region is performed in proton-proton collisions at sqrt(s) = 0.9 TeV, using data collected by the CMS experiment at the LHC. Charged hadron production is studied with reference to the direction of a leading object, either a charged particle or a set of charged particles forming a jet. Predictions of several QCD-inspired models as implemented in PYTHIA are compared, after full detector simulation, to the data. The models generally predict too little production of charged hadrons with pseudorapidity eta < 2, p_T > 0.5 GeV/c, and azimuthal direction transverse to that of the leading object.

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