First Evidence for the Decay B-s(0) -> mu(+) mu(-)

A search for the rare decays B-s(0) -> mu(+) mu(-) and B-s(0) -> mu(+) mu-is performed with data collected in 2011 and 2012 with the LHCb experiment at the Large Hadron Collider. The data samples comprise 1.1 fb(-1) of proton-proton collisions at root s = 8 TeV and 1.0 fb(-1) at root s = 7 TeV. We observe an excess of B-s(0) -> mu(+) mu-candidates with respect to the background expectation. The probability that the background could produce such an excess or larger is 5.3 x 10(-4) corresponding to a signal significance of 3.5 standard deviations. A maximum-likelihood fit gives a branching fraction of B(B-s(0) -> mu(+) mu(-)) = (3.2(-1.2)(+1.5)) x 10(-9), where the statistical uncertainty is 95% of the total uncertainty. This result is in agreement with the standard model expectation. The observed number of B-s(0) -> mu(+) mu-candidates is consistent with the background expectation, giving an upper limit of B(B-s(0) -> mu(+) mu(-)) < 9.4 x 10(-10) at 95% confidence level. DOI: 10.1103/PhysRevLett.110.021801

Observation of the rare B-s(0)->mu(+)mu(-) decay from the combined analysis of CMS and LHCb data

Muhammad Ahmad, Liupan An, Georgios Anagnostou, Konstantin Androsov, Alexandre Aubin, Aurelio Bay, Marc-Olivier Bettler, Frédéric Blanc, Roberto Castello, Yixing Chen, Tian Cheng, Peter Clarke, Victor Coco, Giuseppe Codispoti, Greig Alan Cowan, João Miguel das Neves Duarte, Adam Davis, Michel De Cian, Alessandro Degano, Charles Dietz, Hans Dijkstra, Milos Dordevic, Mirco Dorigo, Frédéric Guillaume Dupertuis, Paolo Durante, Dipanwita Dutta, Matthias Finger, Francesco Fiori, Christoph Frei, Martin George Friedl, Sebastiana Gianì, Elena Graverini, Ruchi Gupta, Guido Haefeli, Csaba Hajdu, Xiaoxue Han, Pierre Jaton, Alexis Kalogeropoulos, Chitsanu Khurewathanakul, Joo Yeon Kim, Donghyun Kim, Ji Hyun Kim, Doohyun Kim, Ilya Komarov, Ajay Kumar, Sanjeev Kumar, Ekaterina Kuznetsova, Ho Ling Li, Yiming Li, Hao Liu, Shuai Liu, Werner Lustermann, Alessandro Mapelli, Pietro Marino, Matteo Marone, Maurizio Martinelli, Bastien Luca Muster, Tatsuya Nakada, Matthew Needham, Niko Neufeld, Ioannis Papadopoulos, Luca Pescatore, Vladimir Petrov, Cédric Potterat, Jessica Prisciandaro, Quentin Python, Barinjaka Rakotomiaramanana, Gerhard Raven, Federico Leo Redi, Andrea Rizzi, Paolo Ronchese, Julien Rouvinet, Olivier Schneider, Sourav Sen, Varun Sharma, Ashish Sharma, Lesya Shchutska, Muhammad Shoaib, Gurpreet Singh, Jan Steggemann, Liang Sun, Wei Sun, Frédéric Teubert, Mark Tobin, Minh Tâm Tran, Andromachi Tsirou, Joao Varela, Horst Vogel, Qian Wang, Rui Wang, Zheng Wang, Jian Wang, Matthias Weber, Jean Wicht, Matthias Wolf, Zhirui Xu, Yong Yang, Kai Yi, Lei Zhang, Yi Zhang

The standard model of particle physics describes the fundamental particles and their interactions via the strong, electromagnetic and weak forces. It provides precise predictions for measurable quantities that can be tested experimentally. The probabilities, or branching fractions, of the strange B meson (B-s(0)) and the B-0 meson decaying into two oppositely charged muons (mu(+) and mu(-)) are especially interesting because of their sensitivity to theories that extend the standard model. The standard model predicts that the B-s(0)->mu(+)mu(-) and B-0 ->mu(+)mu(-) decays are very rare, with about four of the former occurring for every billion B-s(0) mesons produced, and one of the latter occurring for every ten billion B-0 mesons(1). A difference in the observed branching fractions with respect to the predictions of the standard model would provide a direction in which the standard model should be extended. Before the Large Hadron Collider (LHC) at CERN2 started operating, no evidence for either decay mode had been found. Upper limits on the branching fractions were an order of magnitude above the standard model predictions. The CMS (Compact Muon Solenoid) and LHCb(Large Hadron Collider beauty) collaborations have performed a joint analysis of the data from proton-proton collisions that they collected in 2011 at a centre-of-mass energy of seven teraelectronvolts and in 2012 at eight teraelectronvolts. Here we report the first observation of the B-s(0)->mu(+)mu(-) decay, with a statistical significance exceeding six standard deviations, and the best measurement so far of its branching fraction. Furthermore, we obtained evidence for the B-0 ->mu(+)mu(-) decay with a statistical significance of three standard deviations. Both measurements are statistically compatible with standard model predictions and allow stringent constraints to be placed on theories beyond the standard model. The LHC experiments will resume taking data in 2015, recording proton-proton collisions at a centre-of-mass energy of 13 teraelectronvolts, which will approximately double the production rates of B-s(0) and B-0 mesons and lead to further improvements in the precision of these crucial tests of the standard model.

Nature Publishing Group2015

Search for dark matter produced with an energetic jet or a hadronically decaying W or Z boson at $ \sqrt{s}=13 $ TeV

Muhammad Ahmad, Benjamin William Allen, Georgios Anagnostou, Konstantin Androsov, Tagir Aushev, Roberto Castello, Xin Chen, Yixing Chen, Tian Cheng, Davide Cieri, Giuseppe Codispoti, Alessandro Degano, Milos Dordevic, Dipanwita Dutta, Matthias Finger, Francesco Fiori, Daniel Gonzalez, Seungkyu Ha, Csaba Hajdu, Peter Hansen, Ali Harb, Alexis Kalogeropoulos, Viktor Khristenko, Donghyun Kim, Ji Hyun Kim, Sanjeev Kumar, Ajay Kumar, Vineet Kumar, Ekaterina Kuznetsova, Wei Li, Ho Ling Li, Hao Liu, Zhen Liu, Shuai Liu, Werner Lustermann, Bibhuprasad Mahakud, Maren Tabea Meinhard, Thomas Muller, Ioannis Papadopoulos, Vladimir Petrov, Quentin Python, Andrea Rizzi, Paolo Ronchese, Sourav Sen, Ashish Sharma, Varun Sharma, Lesya Shchutska, Muhammad Shoaib, Gurpreet Singh, Jan Steggemann, Xin Sun, Marco Trovato, Andromachi Tsirou, David Vannerom, Joao Varela, Yi Wang, Hui Wang, Rui Wang, Mingkui Wang, Jian Wang, Siyuan Wang, Qian Wang, Zheng Wang, Muhammad Waqas, Matthias Weber, Matthias Wolf, Fan Xia, Meng Xiao, Zhirui Xu, Yong Yang, Kai Yi

A search for dark matter particles is performed using events with large missing transverse momentum, at least one energetic jet, and no leptons, in proton-proton collisions at

\sqrt{s}=13

TeV collected with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 12.9 fb

^{−1}

. The search includes events with jets from the hadronic decays of a W or Z boson. The data are found to be in agreement with the predicted background contributions from standard model processes. The results are presented in terms of simplified models in which dark matter particles are produced through interactions involving a vector, axial-vector, scalar, or pseudoscalar mediator. Vector and axial-vector mediator particles with masses up to 1.95 TeV, and scalar and pseudoscalar mediator particles with masses up to 100 and 430 GeV respectively, are excluded at 95% confidence level. The results are also interpreted in terms of the invisible decays of the Higgs boson, yielding an observed (expected) 95% confidence level upper limit of 0.44 (0.56) on the corresponding branching fraction. The results of this search provide the strongest constraints on the dark matter pair production cross section through vector and axial-vector mediators at a particle collider. When compared to the direct detection experiments, the limits obtained from this search provide stronger constraints for dark matter masses less than 5, 9, and 550 GeV, assuming vector, scalar, and axial-vector mediators, respectively. The search yields stronger constraints for dark matter masses less than 200 GeV, assuming a pseudoscalar mediator, when compared to the indirect detection results from Fermi-LAT.

2017

Search for dark matter produced with an energetic jet or a hadronically decaying W or Z boson at $ \sqrt{s}=13 $ TeV

A search for dark matter particles is performed using events with large missing transverse momentum, at least one energetic jet, and no leptons, in proton-proton collisions at

\sqrt{s}=13

TeV collected with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 12.9 fb

^{−1}

2017

First Evidence for the Decay B-s(0) -> mu(+) mu(-)

Observation of the rare B-s(0)->mu(+)mu(-) decay from the combined analysis of CMS and LHCb data

Measurement of the B-s(0)-> mu(+) mu(-) Branching Fraction and Effective Lifetime and Search for B-0 ->mu(+) mu(-) Decays

Search for dark matter produced with an energetic jet or a hadronically decaying W or Z boson at $ \sqrt{s}=13 $ TeV

Observation of the rare B-s(0)->mu(+)mu(-) decay from the combined analysis of CMS and LHCb data

Measurement of the B-s(0)-> mu(+) mu(-) Branching Fraction and Effective Lifetime and Search for B-0 ->mu(+) mu(-) Decays

Search for dark matter produced with an energetic jet or a hadronically decaying W or Z boson at $ \sqrt{s}=13 $ TeV