1. Observation of a $$ {\varLambda}_b^0 $$ − $$ {\overline{\varLambda}}_b^0 $$ production asymmetry in proton-proton collisions at $$ \sqrt{s} $$ = 7 and 8 TeV
- Author
-
B. Pietrzyk, Thomas Peter Jones, Cheryl Pappenheimer, Andrea Lampis, G. Carboni, Y. H. Zheng, Xiaolong Hu, C. J. G. Onderwater, X. Han, Alexander Inglessi, M. Brodski, Elena Graverini, D. E. Hutchcroft, Pascal Vincent, L. Zhang, Christoph Hasse, G. Passaleva, Christopher James Pawley, Lukas Calefice, Eliane Epple, Harris Conan Bernstein, S. Ferreres Sole, Marcel Materok, Valeriia Lukashenko, Christopher Burr, L. M. Garcia Martin, Alina Zharkova, Rizwaan Adeeb Mohammed, V. Gibson, C. Bozzi, Davide Fazzini, K. Carvalho Akiba, T. Ruf, Sevda Esen, Anton Philippov, Nicola Serra, Xiao-Rui Lyu, Dmitry Popov, Simon Akar, Vitalii Lisovskyi, Dawid Gerstel, P. Spradlin, Malte Hecker, Almagul Kondybayeva, D. Hynds, Marina Artuso, Vladimir Macko, Jake Alexander Ward, Y. Li, G. Lanfranchi, M.-N. Minard, A. Vorobyev, F. Dordei, D. Vom Bruch, Andrew Beiter, U. Marconi, R. J. Barlow, E. L. Gkougkousis, L. Garrido, Marta Calvi, Hans Dembinski, E. Grauges, I. Nasteva, Yury Guz, A. Bay, Chenzhi Dong, X. K. Zhou, Jake Lewis Amey, Julian Alexander Boelhauve, Marco Adinolfi, A. Fernandez Prieto, Emmy Gabriel, Alessandro Minotti, Ph. Charpentier, Daniel Berninghoff, R. Nandakumar, R. Silva Coutinho, B. T. Meadows, Ryan Newcombe, G. Raven, D. Decamp, Kevin Heijhoff, Lorenzo Capriotti, Alexander Malinin, Marie Bachmayer, Yang Yang, G. Mancinelli, Conor Fitzpatrick, A. Brea Rodriguez, Dmitrii Ilin, A. Lai, A. Golutvin, M. D. Sokoloff, Andrea Mauri, Wenbin Qian, P. Gandini, Luca Minzoni, Dylan Jaide White, Michela Garau, Ryunosuke Hugo O'Neil, A. G. Morris, Shuaiyi Liu, A. Dovbnya, J. J. Walsh, Davide Lancierini, Claudia Bertella, Aleksandra Snoch, Y. G. Gao, Benedetto Gianluca Siddi, Jascha Peter Grabowski, V. Shevchenko, Yiheng Luo, Deepanwita Dutta, Stefano Petrucci, W. Wislicki, Adam Davis, Alessandro Scarabotto, Aleksei Andreianov, Lingzhu Bian, Evgenii Shmanin, R. Santacesaria, S. Perazzini, M. Franco Sevilla, Alexey A. Petrov, Joseph David Shupperd, A. Jawahery, Jie Yu, Ahmed Sameh Wagih Abdelmotteleb, J. Maratas, Ifan Williams, Sergei Popov, T. E. Latham, G. Valenti, Agnieszka Oblakowska-Mucha, Victor Renaudin, T. J. V. Bowcock, Anthony Gavin Downes, Elisabet Golobardes, A. B. Rodrigues, D. Websdale, B. Couturier, R. A. Fini, C. Abellán Beteta, Shuangli Yang, Sandra Amato, A. Bondar, B. Schmidt, Ivan Belyaev, Artur Ishteev, C. Parkes, Silvia Gambetta, Daniel Patrick O'Hanlon, O. Lantwin, Paul Andre Günther, C. Haen, Artem Maevskiy, C. B. Van Hulse, Matteo Salomoni, Kenenbek Arzymatov, A. Pereiro Castro, C. Santamarina Rios, Thomas Grammatico, P. K Resmi, M. van Veghel, G. Martellotti, V. Bellee, W. D. Hulsbergen, Aidan Richard Wiederhold, Konstantinos Petridis, J. A. Rodriguez Lopez, A. Brossa Gonzalo, P. Gironella Gironell, Tabitha Halewood-leagas, Carmen Giugliano, Silvia Borghi, S. Farry, Razvan Daniel Moise, Julien Cogan, Oleg Yushchenko, Kuzma Ivshin, Benjamin Audurier, Joan Mauricio, Philipp Ibis, David Anthony Friday, K. Belous, Jolanta Brodzicka, Biljana Mitreska, Stefano Cali, George Coombs, Jan-Marc Basels, Holger Stevens, Hang Yin, M. Karacson, Qundong Han, Maksim Karpov, M. J. Bradley, Zhihong Shen, Christoph Langenbruch, S. Schael, A. Artamonov, Martina Ferrillo, Niladribihari Sahoo, Hongrong Qi, Michal Kazimierz Mazurek, Frederic Machefert, Sheldon Stone, A. Petrolini, Marco Petruzzo, R. Matev, B. Rachwal, Y. Zhou, Victor Egorychev, O. Boente Garcia, Daniel Vieira, Alastair Roger Tanner, Ming Zeng, O. Steinkamp, Jordy Sebastiaan Butter, Fabio Ferrari, C. Marin Benito, Hongjie Mu, Thomas Boettcher, L. De Paula, Baasansuren Batsukh, Marcin Kucharczyk, Maximilien Chefdeville, Konrad Klimaszewski, Marian Stahl, Veronique Puill, Naomi Veronika Raab, Gianluigi Casse, E. van Herwijnen, Jonas Rademacker, Felix Johannes Kress, Shantam Taneja, Marianna Fontana, D. R. Johnson, Zishuo Yang, Laurent Dufour, Nicola Neri, T. T. H. Pham, Alexander Vagner, Alexandru Ene, Anatoly Konoplyannikov, E. Thomas, Anna Danilina, Angelo Loi, Mario Edgardo Olivares, G. D. Lafferty, Ivan Shchemerov, M. Palutan, Aodhan Tomas Burke, C. A. Chavez Barajas, Jana Crkovská, R. McNulty, P. Krokovny, Eduardo Rodrigues, Yawen Wang, L. Dieste Maronas, Samuel Belin, A. Romero Vidal, Sebastian Neubert, Da Yu Tou, F. Teubert, Maciej Witold Majewski, S. Mariani, C. R. Jones, Matthew Scott Rudolph, Z. A. Zhu, E. Spadaro Norella, Jozef Tomasz Borsuk, Patrick Robbe, P. Baladron Rodriguez, G. Wilkinson, Hangyi Wu, Ross John Hunter, Jakub Jacek Malczewski, Li Xu, Michael Becker, Dmitry Golubkov, R. Le Gac, Felicia Carolin Volle, D. Galli, Stephen M. Stahl, V. Franco Lima, J. A. de Vries, N. Neufeld, A. Lobo Salvia, Richard Lane, Martha Hilton, F. Archilli, A. Alfonso Albero, Tatiana Ovsiannikova, G. Wormser, A. Sergi, Vladimir Chulikov, D. Wiedner, Constantin Weisser, Quentin Fuehring, Phillip John Marshall, A. Dzyuba, M. Tobin, Guillaume Pietrzyk, M. Senghi Soares, M. Witek, Tara Shears, Alex Daniel Fernez, Ivan Solovyev, Sergey Didenko, W. Baldini, Cynthia Nunez, Simone Bifani, Anton Poluektov, Lorenzo Sestini, Edoardo Franzoso, Dana Bobulska, H. Li, Danila Saranin, Matteo Bartolini, B. Malecki, Aristeidis Fkiaras, R. Schwemmer, Roger Forty, Alexander Battig, E. Santovetti, Alex Seuthe, Harald Viemann, C. Chen, N. Tuning, M. De Cian, M. Rama, F. Fontanelli, E. Jans, Daniel Joachim Unverzagt, Gabriele Simi, Lukas Witola, Marko Petrič, M. Needham, Krzysztof Swientek, Ning Qin, Dmitrii Pereima, Fedor Ratnikov, Olga Madejczyk, Franco Bedeschi, Andrii Usachov, J. van Tilburg, Wojciech Krzemien, Arthur Marius Hennequin, S. De Capua, Alessandra Gioventù, M. Rotondo, Serhii Cholak, Renata Kopecna, Michele Veronesi, S. Meloni, Robbert Erik Geertsema, Eduard Ursov, Evelina Gersabeck, Barbara Passalacqua, Simon Nieswand, Sofia Kotriakhova, Davide Zuliani, Patrick Mackowiak, Bo Fang, Annarita Buonaura, Valery Zhukov, Ouail Kitouni, Johannes Albrecht, Floris Keizer, D. Pinci, Malcolm John, Tai-hua Lin, Olli Lupton, Jihyun Bhom, Luca Tomassetti, Liupan An, D. Torres Machado, Eleonora Luppi, N. G. Polukhina, Blaise Delaney, B. Dey, Paul Seyfert, Simone Capelli, Matthew Birch, Igor Kostiuk, Ia. Bezshyiko, Nikolay Nikitin, S. Gomez Fernandez, Mauro Morandin, Srishti Bhasin, X. Cid Vidal, Alessandro Pastore, Zhenzi Wang, Veronica Soelund Kirsebom, Salvatore Aiola, Philip Ilten, M. S. Rangel, Zakariya Aliouche, Camille Normand, S. Zucchelli, M. Gandelman, Mauro Piccini, L. Kravchuk, Y. Zhang, F. Stagni, Mariia Poliakova, Laura Promberger, Denis Derkach, R. Vazquez Gomez, E. Gushchin, Phoebe Meredith Hamilton, D. Savrina, Alessandro Cardini, Philippe d'Argent, Jan Buytaert, M. Pepe Altarelli, Thomas Harrison, Edward James Millard, Marco Gersabeck, Chishuai Wang, J. M. De Miranda, S. Simone, J. M. Otalora Goicochea, Piera Muzzetto, G. Punzi, F. Ferreira Rodrigues, Giulia Tuci, E. Vilella Figueras, Christopher Betancourt, A. Satta, Ling-Yun Dai, Xiaotao Huang, Eluned Smith, Jakub Moron, Wolfgang Funk, Roberta Cardinale, Mark Richard James Williams, Kodassery Prasanth, A. Leflat, John Gordon Smeaton, M. Veltri, G. Haefeli, Mikhail Zavertyaev, S. Li, M. R. J. Williams, Naomi Cooke, Konstantin Gizdov, Wiktor Byczynski, M. Martinelli, Nikolai Voropaev, I. V. Gorelov, K. Müller, Giovanni Bassi, P. E. L. Clarke, Niklas Stefan Nolte, Jennifer Clare Smallwood, L. Calero Diaz, Yuyue Gan, Anatoly Butkevich, Luciano Pappalardo, Tamaki Holly Mcgrath, Roberto Ribatti, S. Lopez Solino, M. Shapkin, Patrick Owen, Z. Xiang, Alessio Sarti, Mika Vesterinen, M. Vieites Diaz, Jonathan Edward Davies, Mark Hatch, Lucio Anderlini, G. Manca, O. Schneider, Giovanni Cavallero, Sebastien Ponce, C. M. Costa Sobral, Anja Beck, Kayleigh Anne Thomson, Johannes Heuel, Sebastian Schulte, Ulrik Egede, J. Baptista Leite, Gennady Panshin, Svende Braun, M. Poli Lener, M. Plo Casasus, Daniele Manuzzi, Brij Kishor Jashal, Lorenzo Pica, A. C. dos Reis, Minaugas Sarpis, P. Billoir, Fabrice Desse, Fionn Caitlin Ros Bishop, Dominik Stefan Mitzel, Loris Martinazzoli, Marco Guarise, Sara Sellam, Valery Pugatch, P. Naik, Yunyun Fan, Ryan Calladine, Gianfranco Morello, A. Palano, Tomasz Szumlak, Mauricio Féo, Pawel Kopciewicz, Nicola Skidmore, Tommaso Colombo, Vasyl Dobishuk, Stephane T'Jampens, Ina Carli, Vlad-Mihai Placinta, Stanislav Poslavskii, Saliha Bashir, Imanol Corredoira, Basem Khanji, Y. Xie, Kimberley Vos, Nikolay Bondar, O. Maev, Abhijit Mathad, Thomas Blake, Jennifer Brigitta Zonneveld, F. J. P. Soler, C. Satriano, Matthew George Chapman, A. Contu, Marko Milovanovic, Xiaofeng Zhu, C. Remon Alepuz, A. Papanestis, Ao Xu, Mara Senghi Soares, Jakob Haimberger, R. Lindner, Elisabeth Maria Niel, Yuya Shimizu, R. Jacobsson, Rafal Dominik Krawczyk, Adam Benjamin Morris, Ph. Ghez, Georgios Chatzikonstantinidis, Sonia Amina Bouchiba, Mateusz Goncerz, G. Alkhazov, Claudio Gotti, Andrea Villa, Martino Borsato, Diego Alejandro Milanes, Barbara Sciascia, Vladimir Romanovskiy, A. Zhelezov, Henryk Karol Giemza, M. Schmelling, M. J. Morello, Dong Xiao, Dominik Müller, H. Schindler, Marek Idzik, P. Garcia Moreno, M. Xu, Thomas Hadavizadeh, Samuel Maddrell-Mander, V. V. Gligorov, A. Grecu, L. Sun, Karol Hennessy, R. I. Rabadan Trejo, L. G. Scantlebury Smead, M. Charles, Andrey Ustyuzhanin, J. J. Back, Jordan Daniel Roth, David Gerick, J. Ruiz Vidal, M. Pappagallo, Hossein Afsharnia, Tomasz Skwarnicki, G Falmagne, Sebastian Bachmann, Mikhail Hushchyn, M. van Beuzekom, Scott Ely, Gediminas Sarpis, Maria Elena Stramaglia, S.I. Eidelman, A. Hicheur, Kurt Rinnert, V. Obraztsov, M. De Serio, L. R. Madhan Mohan, Lesya Shchutska, M. Lucio Martinez, Stephan Eisenhardt, Heather Mckenzie Wark, Olivier Leroy, Giulia Frau, Lishuang Ma, Tengiz Kvaratskheliya, B. R. Gruberg Cazon, D. Lacarrere, C. L. Da Silva, Polina Kravchenko, T. Mombächer, A. Bursche, Bernardo Adeva, Lex Marinus Greeven, P. Perret, Sergey Barsuk, Xuhao Yuan, Jiayin Sun, Adam Dendek, B. Garcia Plana, Anastasia Smetkina, H. B. Liu, Sune Jakobsen, Preema Rennee Pais, E. Cogneras, Peilian Li, Ruiting Ma, E. Dall’Occo, M. McCann, Carina Trippl, Lucia Grillo, S. Ricciardi, D. Martinez Santos, Aleksandr Solovev, S. A. Wotton, J. Z. Fan, Sophie Katharina Kretzschmar, M. Calvo Gomez, Alexsei Chubykin, J. Marks, Antje Mödden, M. Straticiuc, J. García Pardiñas, Mick Mulder, F. Blanc, Halime Sazak, H. V. Cliff, Milosz Zdybal, Federico Alessio, Maciej Wojciech Dudek, G. Corti, C. Matteuzzi, Daniel James David Thompson, A. McNab, V. Vagnoni, Roland Bernet, Christoph Frei, Abbie Jane Chadwick, A. Bitadze, R. Lefèvre, Martin Stefan Bieker, Mark Whitehead, Shulei Zhang, Tommaso Pajero, Lucas Mcconnell, François Fleuret, D. Zhang, B. Leverington, D. Yang, M. Chrzaszcz, Fanghua Jiang, Hannah Louise Pullen, M. Korolev, Daniel Charles Craik, J. He, Mateusz Rafal Kmiec, Surapat Ek-In, Aleksandr Terentev, Marcel Merk, Alexandre Boyer, A. F. Campoverde Quezada, Fidan Suljik, Sara Celani, Ivan Polyakov, F. Maciuc, John Jake Lane, Rudolf Oldeman, Roberto Calabrese, P. Durante, Louis Lenard Gerken, Stephan Escher, G. Graziani, S. Easo, Miroslaw Firlej, Massimiliano Fiorini, Ilaria Neri, Lauren Emma Yeomans, P. Campana, L. Giubega, A. Oyanguren, A. Gallas Torreira, M. Ramos Pernas, Paolo Carniti, Meril Reboud, A. Bertolin, Qiang Xu, M. T. Tran, J. Lomba Castro, P. Vazquez Regueiro, D. De Simone, Igor Slazyk, I. A. Monroy, Patrick Koppenburg, Viacheslav Matiunin, Lars Eklund, William Barter, Martina Pili, B. D. C. Westhenry, Sandro Cadeddu, Alexander Berezhnoy, Alexander Mclean Marshall, Flavio Pisani, Leon David Carus, Marco Cattaneo, Ziad Ajaltouni, Valeriia Zhovkovska, Cameron Thomas Dean, Francesco Dettori, Yue Pan, T. J. Gershon, Angelo Carbone, Gianluca Zunica, D. Melnychuk, M. Van Dijk, Peter Griffith, Elie Aslanides, B. Souza De Paula, Michele Piero Blago, N. Valls Canudas, Nathan Allen Grieser, Dillon Scott Fitzgerald, Andreas Güth, Aravindhan Venkateswaran, Jaap Velthuis, Peter Svihra, Thomas Ackernley, T. D. Nguyen, F. F. Wilson, Sara Elizabeth Mitchell, Michael Alexander, D. Lucchesi, Sergei Kholodenko, N. Sagidova, O. Zenaiev, Thomas Henry Hancock, A. Falabella, Biagio Saitta, Stanislav Luchuk, Shakhzod Dadabaev, S. Malde, Jonas Nathanael Eschle, A. Gomes, Federico Betti, L. A. Granado Cardoso, Z. Mathe, Veronika Chobanova, Jan Langer, E. R. R. Rodriguez Rodriguez, Serhii Koliiev, Alexandra Paige Rollings, John Leslie Cobbledick, E. Ben-Haim, Maxime Schubiger, Maria Flavia Cicala, Petr Andreevich Gorbounov, Ekaterina Govorkova, O. De Aguiar Francisco, Miroslav Saur, Paul Nathaniel Swallow, A. Lusiani, Lucian Cojocariu, Jonathan Plews, P. De Simone, Ignacio Bediaga, Desmond Mzamo Shangase, B. Spaan, Ilia Belov, Louis Henry, J. Closier, A. Massafferri, Zhuyin Ren, Wojciech Kucewicz, Yiduo Shang, Mark Smith, Roel Aaij, Vadym Denysenko, P. Roloff, Aleksei Chernov, J. H. Lopes, V. Balagura, T. Gys, Wenhua Hu, Youen Kang, S. Blusk, Z. Xu, P. Di Nezza, Vukan Jevtic, K. M. Fischer, Fedor Baryshnikov, Donal Hill, Quan Zou, S. Klaver, J. J. Saborido Silva, Chung Nguyen-Mau, Gregory Ciezarek, G. H. Gong, Jeremy Dalseno, Amanda May Donohoe, William Parker, F. Polci, Carmelo D'Ambrosio, Jean François Marchand, Paolo Ciambrone, Oleg Stenyakin, Mikhail Mikhasenko, Andrea Bizzeti, Marco Santimaria, R. Currie, C. A. Aidala, L. Del Buono, S. Hansmann-Menzemer, Gerd Joachim Kunde, A. Schopper, Roman Litvinov, Jakub Ryzka, Oleksander Kot, Timothy Evans, R. Mountain, S. H. Lee, Rui Wang, Davide Brundu, Colm Harold Murphy, C. Patrignani, T. Lesiak, Renato Quagliani, C. Göbel, V. Tisserand, M. Andreotti, Adam Szabelski, A. Ukleja, Antonio Pellegrino, F. Redi, E. Polycarpo, Tatsuya Nakada, G. Bencivenni, M. Patel, Anastasiia Kharisova, Federico Lazzari, N. K. Watson, Marie Helene Schune, Michele Atzeni, James Vincent Mead, F. Goncalves Abrantes, G. Liu, Olivier Deschamps, Moran Wang, Ying Lu, Mark Wilkinson, Roland Waldi, Timofei Maltsev, S. Vecchi, Matthieu Marinangeli, S. J. Chen, Yasmine Amhis, C. Sanchez Gras, Matteo Giovannetti, Alexey Boldyrev, Mark Slater, Vladislav Belavin, Anna Ossowska, Nathan Jurik, Jixing Qin, I. Longstaff, L. Shekhtman, Maciej Pawel Szymanski, U. Uwer, Jiangqiao Hu, Xixin Liang, Chun-wei Gu, F. Martinez Vidal, Tjeerd Ketel, Victor Coco, Zhuoming Li, Liliana Congedo, P. Alvarez Cartelle, W. Huang, J. Fu, Emilie Maurice, Andrea Valassi, Tara Nanut, V. Kudryavtsev, Donal Murray, A. Casais Vidal, L. Meyer Garcia, Markus Frank, Matthew Kenzie, Daria Strekalina, Xavier Vilasis-Cardona, B. Quintana, J. J. Xu, Sophie Elizabeth Hollitt, Tatiana Gaintseva, Alexander Semennikov, John Matthew Durham, Kevin Heinicke, Kara Renee Mattioli, M. Cruz Torres, K. De Bruyn, Andrea Merli, Jacopo Cerasoli, Dmitrii Maisuzenko, Hans Dijkstra, Maxim Borisyak, C. Gaspar, Jing Wang, Alex Pearce, Viacheslav Duk, Daniele Marangotto, Artem Ryzhikov, Franz Muheim, Nis Meinert, Alison Tully, Michal Kreps, B. Jost, Hanna Malygina, Edward Brendan Shields, Marco Clemencic, Mikkel Bjørn, F. A. Garcia Rosales, Sergey Legotin, L. Ferreira Lopes, F. L. Souza De Almeida, S. Filippov, V. Vorobyev, H. Cai, M. Romero Lamas, M. Ferro-Luzzi, P. Camargo Magalhaes, Yuezhe Yao, Ekaterina Trifonova, l. Soares Lavra, Anna Lupato, S. Monteil, George Holger Lovell, Shinichi Okamura, C. Vázquez Sierra, F. Reiss, Manuel Schiller, Lauren Douglas, Wojciech Krupa, Gary Robertson, Sergey Gromov, Bhagyashree Pagare, Hilbrand Steffen Kuindersma, A. Di Cicco, Tomasz Fiutowski, P. Collins, Y. Sun, Gerwin Meier, Serena Maccolini, S. Kandybei, J. A. B. Coelho, Jan Patrick Hammerich, T. Kirn, A. Dziurda, Claire Prouve, Neville Harnew, Ettore Zaffaroni, K. Wyllie, and S. G. Weber
- Subjects
Physics ,Semileptonic decay ,Nuclear and High Energy Physics ,Particle physics ,Luminosity (scattering theory) ,Hard scattering ,Proton ,010308 nuclear & particles physics ,Keywords: Hadron-Hadron scattering (experiments) ,media_common.quotation_subject ,01 natural sciences ,Asymmetry ,B physics ,Keywords: Hadron-Hadron scattering (experiments), Heavy quark production, proton- proton scattering, Hard scattering, B physics ,Baryon ,Heavy quark production ,proton- proton scattering ,0103 physical sciences ,CP violation ,Production (computer science) ,Rapidity ,010306 general physics ,media_common - Abstract
This article presents differential measurements of the asymmetry between $$ {\varLambda}_b^0 $$ Λ b 0 and $$ {\overline{\varLambda}}_b^0 $$ Λ ¯ b 0 baryon production rates in proton-proton collisions at centre-of-mass energies of $$ \sqrt{s} $$ s = 7 and 8 TeV collected with the LHCb experiment, corresponding to an integrated luminosity of 3 fb−1. The $$ {\varLambda}_b^0 $$ Λ b 0 baryons are reconstructed through the inclusive semileptonic decay $$ {\varLambda}_b^0 $$ Λ b 0 → $$ {\varLambda}_c^{+} $$ Λ c + μ−$$ \overline{\nu} $$ ν ¯ μX. The production asymmetry is measured both in intervals of rapidity in the range 2.15 < y < 4.10 and transverse momentum in 2 < pT< 27 GeV/c. The results are found to be incompatible with symmetric production with a significance of 5.8 standard deviations for both $$ \sqrt{s} $$ s = 7 and 8 TeV data, assuming no CP violation in the decay. There is evidence for a trend as a function of rapidity with a significance of 4 standard deviations. Comparisons to predictions from hadronisation models in Pythia and heavy-quark recombination are provided. This result constitutes the first observation of a particle-antiparticle asymmetry in b-hadron production at LHC energies.
- Published
- 2021
- Full Text
- View/download PDF