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Dive into the research topics where K. Sobczak is active.

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Featured researches published by K. Sobczak.


Physical Review Letters | 2013

First evidence for the decay Bs -> mu+ mu-

R. Aaij; S. Barsuk; O. Callot; J. He; B. Jean-Marie; J. Lefrançois; F. Machefert; A. Martín Sánchez; M. Nicol; P. Robbe; M. H. Schune; B. Viaud; I. Videau; E. Ben-Haim; M. Benayoun; P. David; L. Del Buono; Z. Ajaltouni; O. Deschamps; E. Cogneras; I. El Rifai; Pierre Henrard; M. Hoballah; Marwa Jahjah-Hussein; R. Lefèvre; L. Li Gioi; S. Monteil; V. Niess; Pascal Perret; Diego Alejandro Roa Romero

A search for the rare decays B(s)(0)→μ+ μ- and B(0)→μ+ μ- 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 sqrt[s]=8  TeV and 1.0  fb(-1) at sqrt[s]=7  TeV. We observe an excess of B(s)(0)→μ+ μ- candidates with respect to the background expectation. The probability that the background could produce such an excess or larger is 5.3×10(-4) corresponding to a signal significance of 3.5 standard deviations. A maximum-likelihood fit gives a branching fraction of B(B(s)(0)→μ+ μ-)=(3.2(-1.2)(+1.5))×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(0)→μ+ μ- candidates is consistent with the background expectation, giving an upper limit of B(B(0)→μ+ μ-)<9.4×10(-10) at 95% confidence level.


Journal of High Energy Physics | 2013

Measurement of

R. Aaij; C. Adrover; E. Aslanides; J. Cogan; R. Legac; O. Leroy; G. Mancinelli; E. Maurice; M. Perrin-Terrin; M. Sapunov; J. Serrano; A. Tsaregorodtsev; S. Barsuk; O. Callot; J. He; B. Jean-Marie; J. Lefrançois; F. Machefert; A. Martín Sánchez; M. Nicol; P. Robbe; M. H. Schune; B. Viaud; I. Videau; E. Ben-Haim; M. Benayoun; P. David; L. Del Buono; Z. Ajaltouni; E. Cogneras

A bstract The production of J/ψ mesons is studied with the LHCb detector using data from pp collisions at


Journal of High Energy Physics | 2013

J/\psi

R. Aaij; S. Barsuk; O. Callot; J. He; B. Jean-Marie; J. Lefrançois; F. Machefert; A. Martín Sánchez; M. Nicol; P. Robbe; M. H. Schune; B. Viaud; I. Videau; E. Ben-Haim; M. Benayoun; P. David; L. Del Buono; Z. Ajaltouni; O. Deschamps; E. Cogneras; I. El Rifai; Pierre Henrard; M. Hoballah; Marwa Jahjah-Hussein; R. Lefèvre; L. Li Gioi; S. Monteil; V. Niess; Pascal Perret; Diego Alejandro Roa Romero

\sqrt{s}=2.76


Journal of High Energy Physics | 2013

production in

R. Aaij; S. Barsuk; O. Callot; Jibo He; B. Jean-Marie; J. Lefrançois; F. Machefert; A. Martín Sánchez; M. Nicol; P. Robbe; M. H. Schune; B. Viaud; I. Videau; E. Ben-Haim; M. Benayoun; P. David; L. Del Buono; Z. Ajaltouni; O. Deschamps; E. Cogneras; I. El Rifai; Pierre Henrard; M. Hoballah; Marwa Jahjah-Hussein; R. Lefèvre; L. Li Gioi; S. Monteil; V. Niess; Pascal Perret; Diego Alejandro Roa Romero

TeV corresponding to an integrated luminosity of 71 nb−1. The differential cross-section for inclusive J/ψ production is measured as a function of its transverse momentum pT. The cross-section in the fiducial region 0 < pT  < 12 GeV/c and rapidity 2.0 <


European Physical Journal C | 2012

pp

R. Aaij; S. Barsuk; O. Callot; Jibo He; B. Jean-Marie; J. Lefrançois; F. Machefert; A. Martín Sánchez; M. Nicol; P. Robbe; M. H. Schune; B. Viaud; I. Videau; E. Ben-Haim; M. Benayoun; P. David; L. Del Buono; Z. Ajaltouni; O. Deschamps; Pierre Henrard; Marwa Jahjah-Hussein; R. Lefèvre; L. Li Gioi; S. Monteil; V. Niess; Pascal Perret; Diego Alejandro Roa Romero; K. Sobczak; C. Adrover; E. Aslanides

y


European Physical Journal C | 2012

collisions at

R. Aaij; I. De Bonis; D. Decamp; Ph. Ghez; P. Hopchev; J. P. Lees; I. V. Machikhiliyan; M.-N. Minard; B. Pietrzyk; S. T'Jampens; V. Tisserand; E. Tournefier; S. Barsuk; O. Callot; Jibo He; B. Jean-Marie; J. Lefrançois; F. Machefert; A. Martín Sánchez; M. Nicol; P. Robbe; M. H. Schune; B. Viaud; I. Videau; Z. Ajaltouni; E. Cogneras; O. Deschamps; Pierre Henrard; Marwa Jahjah-Hussein; R. Lefèvre

< 4.5 is measured to be 5.6 ± 0.1 (stat) ± 0.4 (syst) μb, with the assumption of unpolarised J/ψ production. The fraction of J/ψ production from b-hadron decays is measured to be (7.1 ± 0.6 (stat) ± 0.7 (syst))%.


Journal of High Energy Physics | 2012

\sqrt{s}=2.76

R. Aaij; S. Barsuk; O. Callot; Jibo He; B. Jean-Marie; J. Lefrançois; F. Machefert; A. Martín Sánchez; M. Nicol; P. Robbe; M. H. Schune; B. Viaud; I. Videau; E. Ben-Haim; M. Benayoun; P. David; L. Del Buono; Z. Ajaltouni; E. Cogneras; O. Deschamps; I. El Rifai; Pierre Henrard; M. Hoballah; Marwa Jahjah-Hussein; R. Lefèvre; L. Li Gioi; S. Monteil; V. Niess; Pascal Perret; Diego Alejandro Roa Romero

A search for the decay K0S→μ+μ− is performed, based on a data sample of 1.0 fb−1 of pp collisions at √ s =7 TeV collected by the LHCb experiment at the Large Hadron Collider. The observed number of candidates is consistent with the background-only hypothesis, yielding an upper limit of B(K0S→μ+μ−) < 11(9) × 10−9 at 95 (90)% confidence level. This limit is a factor of thirty below the previous measurement.A bstractA search for the decay


Nuclear Physics | 2012

TeV

R. Aaij; S. Barsuk; O. Callot; J. He; B. Jean-Marie; J. Lefrançois; F. Machefert; A. Martín Sánchez; M. Nicol; P. Robbe; M. H. Schune; B. Viaud; I. Videau; E. Ben-Haim; M. Benayoun; P. David; L. Del Buono; Z. Ajaltouni; E. Cogneras; O. Deschamps; I. El Rifai; Pierre Henrard; M. Hoballah; Marwa Jahjah-Hussein; R. Lefèvre; L. Li Gioi; S. Monteil; V. Niess; Pascal Perret; Diego Alejandro Roa Romero

K_{\mathrm{S}}^0\to {\mu^{+}}{\mu^{-}}


Physics Letters B | 2012

Search for the rare decay K^0_S -> mu+ mu-

R. Aaij; L. Arrabito; I. De Bonis; D. Decamp; Ph. Ghez; P. Hopchev; J. P. Lees; I. V. Machikhiliyan; M.-N. Minard; B. Pietrzyk; S. T'Jampens; V. Tisserand; E. Tournefier; S. Barsuk; O. Callot; B. D'Almagne; J. He; B. Jean-Marie; J. Lefrançois; F. Machefert; A. Martín Sánchez; M. Nicol; P. Robbe; M. H. Schune; B. Viaud; I. Videau; Z. Ajaltouni; O. Deschamps; Pierre Henrard; Marwa Jahjah-Hussein

is performed, based on a data sample of 1.0 fb−1 of pp collisions at


Journal of High Energy Physics | 2012

Differential branching fraction and angular analysis of the B +→ K+μ+μ- decay

R. Aaij; S. Barsuk; O. Callot; J. He; B. Jean-Marie; J. Lefrançois; F. Machefert; A. Martín Sánchez; M. Nicol; P. Robbe; M. H. Schune; B. Viaud; I. Videau; E. Ben-Haim; M. Benayoun; P. David; L. Del Buono; Z. Ajaltouni; E. Cogneras; O. Deschamps; I. El Rifai; Pierre Henrard; M. Hoballah; Marwa Jahjah-Hussein; R. Lefèvre; L. Li Gioi; S. Monteil; V. Niess; Pascal Perret; Diego Alejandro Roa Romero

\sqrt{s}=7\;\mathrm{TeV}

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S. Barsuk

Université Paris-Saclay

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Z. Ajaltouni

Blaise Pascal University

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J. Lefrançois

Université Paris-Saclay

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F. Machefert

Université Paris-Saclay

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