Underlying Event measurements in pp collisions at $ \sqrt {s} = 0.9 $ and 7 TeV with the ALICE experiment at the LHC
Authors:   The ALICE collaboration, Abelev Betty , Quintana Arian Abrahantes , Adamova Dagmar , Adare Andrew Marshall , Aggarwal Madan , Rinella Gianluca Aglieri , Agocs Andras Gabor , Agostinelli Andrea , Salazar Saul Aguilar , Ahammed Zubayer , Ahmad Nazeer , Ahmad Arshad , Ahn Sang Un , Akindinov Alexander , Aleksandrov Dmitry , Alessandro Bruno , Molina Jose Ruben Alfaro , Alici Andrea , Alkin Anton , Avina Erick Jonathan Almaraz , Alt Torsten , Altini Valerio , Altinpinar Sedat , Altsybeev Igor , Andrei Cristian , Andronic Anton , Anguelov Venelin , Anson Christopher Daniel , Anticic Tome , Antinori Federico , Antonioli Pietro , Aphecetche Laurent Bernard , Appelshauser Harald , Arbor Nicolas , Arcelli Silvia , Arend Andreas , Armesto Nestor , Arnaldi Roberta , Aronsson Tomas Robert , Arsene Ionut Cristian , Arslandok Mesut , Asryan Andzhey , Augustinus Andre , Averbeck Ralf Peter , Awes Terry , Aysto Juha Heikki , Azmi Mohd Danish , Bach Matthias Jakob , Badala Angela , Baek Yong Wook , Bailhache Raphaelle Marie , Bala Renu , Ferroli Rinaldo Baldini , Baldisseri Alberto , Baldit Alain , Pedrosa Fernando Baltasar Dos Santos , Ban Jaroslav , Baral Rama Chandra , Barbera Roberto , Barile Francesco , Barnafoldi Gergely Gabor , Barnby Lee Stuart , Barret Valerie , Bartke Jerzy Gustaw , Basile Maurizio , Bastid Nicole , Bathen Bastian , Batigne Guillaume , Batyunya Boris , Baumann Christoph Heinrich , Bearden Ian Gardner , Beck Hans , Belikov Iouri , Bellini Francesca , Bellwied Rene , Belmont-Moreno Ernesto , Beole Stefania , Berceanu Ionela , Bercuci Alexandru , Berdnikov Yaroslav , Berenyi Daniel , Bergmann Cyrano , Berzano Dario , Betev Latchezar , Bhasin Anju , Bhati Ashok Kumar , Bianchi Nicola , Bianchi Livio , Bianchin Chiara , Bielcik Jaroslav , Bielcikova Jana , Bilandzic Ante , Blanco F. , Blanco Francesco , Blau Dmitry , Blume Christoph , Boccioli Marco , Bock Nicolas , Bogdanov Alexey , Boggild Hans , Bogolyubsky Mikhail , Boldizsar Laszlo , Bombara Marek , Book Julian , Borel Herve , Borissov Alexander , Bortolin Claudio , Bose Suvendu Nath , Bossu Francesco , Botje Michiel , Bottger Stefan , Boyer Bruno Alexandre , Braun-Munzinger Peter , Bregant Marco , Breitner Timo Gunther , Broz Michal , Brun Rene , Bruna Elena , Bruno Giuseppe Eugenio , Budnikov Dmitry , Buesching Henner , Bufalino Stefania , Bugaiev Kyrylo , Busch Oliver , Buthelezi Edith Zinhle , Caffarri Davide , Cai Xu , Caines Helen Louise , Villar Ernesto Calvo , Camerini Paolo , Roman Veronica Canoa , Romeo Giovanni Cara , Carena Francesco , Carena Wisla , Filho Nelson Carlin , Carminati Federico , Montoya Camilo Andres Carrillo , Diaz Amaya Ofelia Casanova , Caselle Michele , Castellanos Javier Ernesto Castillo , Hernandez Juan Francisco Castillo , Casula Ester Anna Rita , Catanescu Vasile , Cavicchioli Costanza , Cepila Jan , Cerello Piergiorgio , Chang Beomsu , Chapeland Sylvain , Charvet Jean-Luc Fernand , Chattopadhyay Sukalyan , Chattopadhyay Subhasis , Cherney Michael Gerard , Cheshkov Cvetan , Cheynis Brigitte , Chiavassa Emilio , Barroso Vasco Miguel Chibante , Chinellato David , Chochula Peter , Chojnacki Marek , Christakoglou Panagiotis , Christensen Christian Holm , Christiansen Peter , Chujo Tatsuya , Chung Suh-Urk , Cicalo Corrado , Cifarelli Luisa , Cindolo Federico , Cleymans Jean Willy Andre , Coccetti Fabrizio , Coffin Jean-Pierre Michel , Colamaria Fabio , Colella Domenico , Balbastre Gustavo Conesa , del Valle Zaida Conesa , Constantin Paul , Contin Giacomo , Contreras Jesus Guillermo , Cormier Thomas Michael , Morales Yasser Corrales , Cortese Pietro , Maldonado Ismael Cortes , Cosentino Mauro Rogerio , Costa Filippo , Cotallo Manuel Enrique , Crescio Elisabetta , Crochet Philippe , Alaniz Emilia Cruz , Cuautle Eleazar , Cunqueiro Leticia , Dainese Andrea , Dalsgaard Hans Hjersing , Danu Andrea , Das Indranil , Das Kushal , Das Debasish , Dash Ajay Kumar , Dash Sadhana , De Sudipan , De Azevedo Moregula Andrea , de Barros Gabriel , De Caro Annalisa , de Cataldo Giacinto , de Cuveland Jan , De Falco Alessandro , De Gruttola Daniele , Delagrange Hugues , Del Castillo Sanchez Eduardo , Deloff Andrzej , Demanov Vyacheslav , De Marco Nora , Denes Ervin , De Pasquale Salvatore , Deppman Airton , D’Erasmo Ginevra , de Rooij Raoul Stefan , Di Bari Domenico , Dietel Thomas , Di Giglio Carmelo , Di Liberto Sergio , Di Mauro Antonio , Di Nezza Pasquale , Divia Roberto , Djuvsland Oeystein , Dobrin Alexandru Florin , Dobrowolski Tadeusz Antoni , Dominguez Isabel , Donigus Benjamin , Dordic Olja , Driga Olga , Dubey Anand Kumar , Ducroux Laurent , Dupieux Pascal , Majumdar Mihir Ranjan Dutta , Majumdar A.K. 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, Harris John William , Hartig Matthias , Hasegan Dumitru , Hatzifotiadou Despoina , Hayrapetyan Arsen , Heckel Stefan Thomas , Heide Markus Ansgar , Helstrup Haavard , Herghelegiu Andrei Ionut , Corral Gerardo Antonio Herrera , Herrmann Norbert , Hetland Kristin Fanebust , Hicks Bernard , Hille Per Thomas , Hippolyte Boris , Horaguchi Takuma , Hori Yasuto , Hristov Peter Zahariev , Hrivnacova Ivana , Huang Meidana , Huber Sebastian Bernd , Humanic Thomas , Hwang Dae Sung , Ichou Raphaelle , Ilkaev Radiy , Ilkiv Iryna , Inaba Motoi , Incani Elisa , Innocenti Pier Giorgio , Innocenti Gian Michele , Ippolitov Mikhail , Irfan Muhammad , Ivan Cristian George , Ivanov Marian , Ivanov Vladimir , Ivanov Andrey , Ivanytskyi Oleksii , Jacholkowski Adam Wlodzimierz , Jacobs Peter , Jancurova Lucia , Jang Haeng Jin , Jangal Swensy Gwladys , Janik Rudolf , Janik Malgorzata Anna , Jayarathna Sandun , Jena Satyajit , Bustamante Raul Tonatiuh Jimenez , Jirden Lennart , Jones Peter Graham , Jung Won 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Lohn Stefan Bernhard , Lohner Daniel , Loizides Constantinos , Loo Kai Krister , Lopez Xavier Bernard , Torres Ernesto Lopez , Lovhoiden Gunnar , Lu Xianguo , Luettig Philipp , Lunardon Marcello , Luo Jiebin , Luparello Grazia , Luquin Lionel , Luzzi Cinzia , Ma Rongrong , Ma Ke , Madagodahettige-Don Dilan Minthaka , Maevskaya Alla , Mager Magnus , Mahapatra Durga Prasad , Maire Antonin , Malaev Mikhail , Cervantes Ivonne Alicia Maldonado , Malinina Ludmila , Mal’Kevich Dmitry , Malzacher Peter , Mamonov Alexander , Manceau Loic Henri Antoine , Mangotra Lalit Kumar , Manko Vladislav , Manso Franck , Manzari Vito , Mao Yaxian , Marchisone Massimiliano , Mares Jiri , Margagliotti Giacomo Vito , Margotti Anselmo , Marin Ana Maria , Markert Christina , Martashvili Irakli , Martinengo Paolo , Martinez Mario Ivan , Davalos Arnulfo Martinez , Garcia Gines Martinez , Martynov Yevgen , Mas Alexis Jean-Michel , Masciocchi Silvia , Masera Massimo , Masoni Alberto , Massacrier Laure Marie , 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, Salgado Carlos Albert , Sambyal Sanjeev Singh , Samsonov Vladimir , Castro Xitzel Sanchez , Sandor Ladislav , Sandoval Andres , Sano Masato , Sano Satoshi , Santo Rainer , Santoro Romualdo , Sarkamo Juho Jaako , Scapparone Eugenio , Scarlassara Fernando , Scharenberg Rolf Paul , Schiaua Claudiu Cornel , Schicker Rainer Martin , Schmidt Christian Joachim , Schmidt Hans Rudolf , Schreiner Steffen , Schuchmann Simone , Schukraft Jurgen , Schutz Yves Roland , Schwarz Kilian Eberhard , Schweda Kai Oliver , Scioli Gilda , Scomparin Enrico , Scott Rebecca , Scott Patrick Aaron , Segato Gianfranco , Selioujenkov Ilya , Senyukov Serhiy , Seo Jeewon , Serci Sergio , Serradilla Eulogio , Sevcenco Adrian , Sgura Irene , Shabetai Alexandre , Shabratova Galina , Shahoyan Ruben , Sharma Natasha , Sharma Satish , Shigaki Kenta , Shimomura Maya , Shtejer Katherin , Sibiriak Yury , Siciliano Melinda , Sicking Eva , Siddhanta Sabyasachi , Siemiarczuk Teodor , Silvermyr David Olle Rickard , Simonetti Giuseppe , Singaraju Rama Narayana , Singh Ranbir , Singha Subhash , Sinha Bikash , Sinha Tinku , Sitar Branislav , Sitta Mario , Skaali Bernhard , Skjerdal Kyrre , Smakal Radek , Smirnov Nikolai , Snellings Raimond , Sogaard Carsten , Soltz Ron Ariel , Son Hyungsuk , Song Jihye , Song Myunggeun , Soos Csaba , Soramel Francesca , Sputowska Iwona , Spyropoulou-Stassinaki Martha , Srivastava Brijesh Kumar , Stachel Johanna , Stan Ionel , Stan Ionel , Stefanek Grzegorz , Stefanini Giorgio , Steinbeck Timm Morten , Steinpreis Matthew , Stenlund Evert Anders , Steyn Gideon Francois , Stocco Diego , Stolpovskiy Mikhail , Strabykin Kirill , Strmen Peter , do Passo Suaide Alexandre Alarcon , Vasquez Martin Alfonso Subieta , Sugitate Toru , Suire Christophe Pierre , Sukhorukov Mikhail , Sultanov Rishat , Sumbera Michal , Susa Tatjana , de Toledo Alejandro Szanto , Szarka Imrich , Szostak Artur Krzysztof , Tagridis Christos , Takahashi Jun , Takaki Daniel Jesus Tapia , Tauro Arturo , Munoz Guillermo Tejeda , Telesca Adriana , Terrevoli Cristina , Thader Jochen Mathias , Thomas Jim , Thomas Deepa , Tieulent Raphael Noel , Timmins Anthony , Tlusty David , Toia Alberica , Torii Hisayuki , Toscano Luca , Tosello Flavio , Traczyk Tomasz , Truesdale David Christopher , Trzaska Wladyslaw Henryk , Tsuji Tomoya , Tumkin Alexandr , Turrisi Rosario , Tveter Trine Spedstad , Ulery Jason Glyndwr , Ullaland Kjetil , Ulrich Jochen , Uras Antonio , Urban Jozef , Urciuoli Guido Marie , Usai Gianluca , Vajzer Michal , Vala Martin , Palomo Lizardo Valencia , Vallero Sara , van der Kolk Naomi , Vyvre Pierre Vande , van Leeuwen Marco , Vannucci Luigi , Vargas Aurora Diozcora , Varma Raghava , Vasileiou Maria , Vasiliev Andrey , Vechernin Vladimir , Veldhoen Misha , Venaruzzo Massimo , Vercellin Ermanno , Vergara Sergio , Vernekohl Don Constantin , Vernet Renaud , Verweij Marta , Vickovic Linda , Viesti Giuseppe , Vikhlyantsev Oleg , Vilakazi Zabulon , Baillie Orlando Villalobos , Vinogradov Leonid , Vinogradov Yury , Vinogradov Alexander , Virgili Tiziano , Viyogi Yogendra , Vodopianov Alexander , Voloshin Sergey , Voloshin Kirill , Volpe Giacomo , von Haller Barthelemy , Vranic Danilo , vrebekk Gaute , Vrlakova Janka , Vulpescu Bogdan , Vyushin Alexey , Wagner Boris , Wagner Vladimir , Wan Renzhuo , Wang Yifei , Wang Mengliang , Wang Dong , Wang Yaping , Watanabe Kengo , Wessels Johannes , Westerhoff Uwe , Wiechula Jens , Wikne Jon , Wilde Martin Rudolf , Wilk Grzegorz Andrzej , Wilk Alexander , Williams Crispin , Windelband Bernd Stefan , Karampatsos Leonidas Xaplanteris , Yang Hongyan , Yang Shiming , Yano Satoshi , Yasnopolsky Stanislav , Yi JunGyu , Yin Zhongbao , Yokoyama Hiroki , Yoo In-Kwon , Yoon Jongik , Yu Weilin , Yuan Xianbao , Yushmanov Igor , Zach Cenek , Zampolli Chiara , Zaporozhets Sergey , Zarochentsev Andrey , Zavada Petr , Zaviyalov Nikolai , Zbroszczyk Hanna Paulina , Zelnicek Pierre , Zgura Sorin Ion , Zhalov Mikhail , Zhang Xiaoming , Zhou Fengchu , Zhou You , Zhou Daicui , Zhu Xiangrong , Zichichi Antonino , Zimmermann Alice , Zinovjev Gennady , Zoccarato Yannick Denis , Zynovyev Mykhaylo 
Published: July 2012

Abstract

We present measurements of Underlying Event observables in pp collisions at
$ \sqrt {s} = 0.9 $
and 7TeV. The analysis is performed as a function of the highest charged-particle transverse momentum p
T,LT in the event. Different regions are defined with respect to the azimuthal direction of the leading (highest transverse momentum) track: Toward, Transverse and Away. The Toward and Away regions collect the fragmentation products of the hardest partonic interaction. The Transverse region is expected to be most sensitive to the Underlying Event activity. The study is performed with charged particles above three different p
T thresholds: 0.15, 0.5 and 1.0 GeV/c. In the Transverse region we observe an increase in the multiplicity of a factor 2–3 between the lower and higher collision energies, depending on the track p
T threshold considered. Data are compared to Pythia 6.4, Pythia 8.1 and Phojet. On average, all models considered underestimate the multiplicity and summed p
T in the Transverse region by about 10–30%.