共查询到20条相似文献,搜索用时 515 毫秒
1.
Affolder T Akimoto H Akopian A Albrow MG Amaral P Amendolia SR Amidei D Anikeev K Antos J Apollinari G Arisawa T Asakawa T Ashmanskas W Atac M Azfar F Azzi-Bacchetta P Bacchetta N Bailey MW Bailey S de Barbaro P Barbaro-Galtieri A Barnes VE Barnett BA Barone M Bauer G Bedeschi F Belforte S Bellettini G Bellinger J Benjamin D Bensinger J Beretvas A Berge JP Berryhill J Bertolucci S Bevensee B Bhatti A Bigongiari C Binkley M Bisello D Blair RE Blocker C Bloom K Blumenfeld B Blusk BS Bocci A 《Physical review letters》2000,84(25):5704-5709
We have searched for direct pair production of scalar top and scalar bottom quarks in 88 pb-1 of pp collisions at sqrt[s]=1.8 TeV with the CDF detector. We looked for events with a pair of heavy flavor jets and missing energy, consistent with scalar top (bottom) quark decays to a charm (bottom) quark and a neutralino. The numbers of events that pass our selections show no significant deviation from standard model expectations. We compare our results to the next-to-leading order scalar quark production cross sections to exclude regions in scalar quark-neutralino mass parameter space. 相似文献
2.
Aad G Abbott B Abdallah J Abdelalim AA Abdesselam A Abdinov O Abi B Abolins M AbouZeid OS Abramowicz H Abreu H Acerbi E Acharya BS Adamczyk L Adams DL Addy TN Adelman J Aderholz M Adomeit S Adragna P Adye T Aefsky S Aguilar-Saavedra JA Aharrouche M Ahlen SP Ahles F Ahmad A Ahsan M Aielli G Akdogan T Åkesson TP Akimoto G Akimov AV Akiyama A Alam MS Alam MA Albert J Albrand S Aleksa M Aleksandrov IN Alessandria F Alexa C Alexander G Alexandre G Alexopoulos T Alhroob M Aliev M Alimonti G Alison J 《Physical review letters》2012,108(18):181802
The results of a search for pair production of the scalar partners of bottom quarks in 2.05 fb(-1) of pp collisions at sqrt[s]=7 TeV using the ATLAS experiment are reported. Scalar bottom quarks are searched for in events with large missing transverse momentum and two jets in the final state, where both jets are identified as originating from a bottom quark. In an R-parity conserving minimal supersymmetric scenario, assuming that the scalar bottom quark decays exclusively into a bottom quark and a neutralino, 95% confidence-level upper limits are obtained in the b(1) - χ(1)(0) mass plane such that for neutralino masses below 60 GeV scalar bottom masses up to 390 GeV are excluded. 相似文献
3.
Tkaczyk S Tollefson K Tollestrup A Toyoda H Trischuk W de Troconiz JF Tseng J Turini N Ukegawa F Valls J Vejcik S Velev G Vidal R Vilar R Volobouev I Vucinic D Wagner RG Wagner RL Wahl J Wallace NB Walsh AM Wang C Wang CH Wang MJ Watanabe T Waters D 《Physical review letters》2000,84(23):5273-5278
We have searched for direct production of scalar top quarks at the Collider Detector at Fermilab in 88 pb(-1) of p&pmacr; collisions at sqrt[s] = 1.8 TeV. We assume the scalar top quark decays into either a bottom quark and a chargino or a bottom quark, a lepton, and a scalar neutrino. The event signature for both decay scenarios is a lepton, missing transverse energy, and at least two b-quark jets. For a chargino mass of 90 GeV/c(2) and scalar neutrino masses of at least 40 GeV/c(2), we find no evidence for scalar top production and present upper limits on the production cross section in both decay scenarios. 相似文献
4.
We report the results of a one-loop calculation of , where is a gluino, the proposed supersymmetric partner of a gluon. Depending on the masses of the scalar quarks and of the top quark, the branching ratio for the decay is in the 10?5 to 10?4 range for gluino mass below about 40 GeV. The signature for gluinos should allow detection in this range. 相似文献
5.
S. Heinemeyer C. Schappacher 《The European Physical Journal C - Particles and Fields》2012,72(3):1905
We evaluate all two-body decay modes of the gluino, in the Minimal Supersymmetric Standard Model with complex parameters (cMSSM).
This constitutes an important step in the cascade decays of SUSY particles at the LHC. The evaluation is based on a full one-loop
calculation of all two-body decay channels, also including hard QED and QCD radiation. The dependence of the gluino decay
to a scalar quark and a quark on the relevant cMSSM parameters is analyzed numerically. We find sizable contributions to the
decay widths and branching ratios. They are, roughly of O(±5%)\mathcal{O}({\pm 5\%)}, but can go up to ±10% or higher, where the pure SUSY QCD contributions alone can give an insufficient approximation to the
full one-loop result. Therefore the full corrections are important for the correct interpretation of gluino decays at the
LHC. The results will be implemented into the Fortran code FeynHiggs. 相似文献
6.
We address the question of the Lorentz nature of the effective long-range interquark interaction generated by the QCD string with quarks at the ends. Studying the Dyson-Schwinger equation for a heavy-light quark-antiquark system, we demonstrate explicitly how a Lorentz scalar interaction appears in the Dirac-like equation for the light quark as a consequence of chiral symmetry breaking. We argue that the effective interquark interaction in the Hamiltonian of the QCD string with quarks at the ends stems from this effective scalar interaction. 相似文献
7.
Chatrchyan S Khachatryan V Sirunyan AM Tumasyan A Adam W Bergauer T Dragicevic M Erö J Fabjan C Friedl M Frühwirth R Ghete VM Hammer J Hänsel S Hoch M Hörmann N Hrubec J Jeitler M Kiesenhofer W Krammer M Liko D Mikulec I Pernicka M Rahbaran B Rohringer H Schöfbeck R Strauss J Taurok A Teischinger F Wagner P Waltenberger W Walzel G Widl E Wulz CE Mossolov V Shumeiko N Suarez Gonzalez J Bansal S Benucci L De Wolf EA Janssen X Maes T Mucibello L Ochesanu S Roland B Rougny R Selvaggi M 《Physical review letters》2011,107(10):101801
A search for three-jet hadronic resonance production in pp collisions at a center-of-mass energy of 7 TeV has been conducted by the CMS Collaboration at the LHC, using a data sample corresponding to an integrated luminosity of 35 pb(-1). Events with high jet multiplicity and a large scalar sum of jet transverse momenta are analyzed using a signature-based approach. The number of expected standard model background events is found to be in good agreement with the observed events. Limits on the cross section times branching ratio are set in a model of gluino pair production with an R-parity-violating decay to three quarks, and the data rule out such particles within the mass range of 200 to 280 GeV/c2. 相似文献
8.
We summarize the effects of some unknown supersymmetry breaking mechanism by the addition to the super-QCD lagrangian of explicit, and different, mass terms for the scalar superpartners of quarks and antiquarks. Allowing also a possible Majorana mass for the gluino, we then calculate cross sections for e+e? → two gluinos, a process which may be observable if the gluino is sufficiently long-lived. 相似文献
9.
Stefano Moretti Ramon Muñoz-Tapia Kosuke Odagiri 《The European Physical Journal C - Particles and Fields》1998,4(2):351-362
Heavy flavour tagging provides a broad range of possibilities in testing QCD features at LEP. We present here a study of
4jets events at LEP I where the so-called light gluinos could be directly produced. We show that microvertex techniques offer
a unique chance to exploit simple kinematical distributions in order to optimise the signal coming from gluino production
with respect to the background of ordinary QCD events. Our results indicate that experimental analyses along the lines suggested
here can exclude or reveal the presence of a gluino for masses up to 10 GeV and lifetimes below 10 sec. We also point out that a large fraction of gluino events could decay in configurations carrying large missing energy,
so to escape the usual selection criteria of 4jet samples. In our study, mass effects of quarks and gluinos have been taken
into account exactly. Our results are independent from both the jet algorithm and its resolution parameter.
Received: 25 July 1997 / Revised version: 16 September 1997 / Published online: 20 February 1998 相似文献
10.
Yujiang Bi Hao Cai Ying Chen Ming Gong Zhaofeng Liu Hao-Xue Qiao Yi-Bo Yang 《中国物理C(英文版)》2016,40(7):073106-073106
We calculate diquark correlation functions in the Landau gauge on the lattice using overlap valence quarks and 2+1-flavor domain wall fermion configurations. Quark masses are extracted from the scalar part of quark propagators in the Landau gauge. The scalar diquark quark mass difference and axial vector scalar diquark mass difference are obtained for diquarks composed of two light quarks and of a strange and a light quark. The light sea quark mass dependence of the results is examined. Two lattice spacings are used to check the discretization effects.The coarse and fine lattices are of sizes 24~3×64 and 32~3×64 with inverse spacings 1/a = 1.75(4) Ge V and 2.33(5) Ge V,respectively. 相似文献
11.
Acosta D Affolder T Akimoto H Albrow MG Ambrose D Amidei D Anikeev K Antos J Apollinari G Arisawa T Artikov A Asakawa T Ashmanskas W Azfar F Azzi-Bacchetta P Bacchetta N Bachacou H Badgett W Bailey S de Barbaro P Barbaro-Galtieri A Barnes VE Barnett BA Baroiant S Barone M Bauer G Bedeschi F Behari S Belforte S Bell WH Bellettini G Bellinger J Benjamin D Bensinger J Beretvas A Berryhill J Bhatti A Binkley M Bisello D Bishai M Blair RE Blocker C Bloom K Blumenfeld B Blusk SR Bocci A Bodek A 《Physical review letters》2004,92(5):051803
We present the results of a search for pair production of scalar top quarks (t(1)) in an R-parity violating supersymmetry scenario in 106 pb(-1) of pp collisions at square root of s=1.8 TeV collected by the Collider Detector at Fermilab. In this mode each t(1) decays into a tau lepton and a b quark. We search for events with two tau's, one decaying leptonically (e or mu) and one decaying hadronically, and two jets. No candidate events pass our final selection criteria. We set a 95% confidence level lower limit on the t(1) mass at 122 GeV/c(2) for Br(t(1)-->tau b)=1. 相似文献
12.
Heinz König 《Zeitschrift fur Physik C Particles and Fields》1997,73(1):161-167
I present a detailed and complete calculation of the gluino and neutralino contribution to the direct CP violating parameter ? within the MSSM. I include the complete mixing matrices of the neutralino and of the scalar partners of the left and right handed down quarks. I find that the neutralino contribution is generally small but can be larger than the gluino contribution for small values m s ≤ 400 GeV of the supersymmetric breaking scale. 相似文献
13.
The recently observed collider events with large missing PT are analysed in terms of a supersymmetric model with a light photino and scalar quarks with mass in the range 20 to 35 GeV. A lower bound of O(60 GeV) on the gluino mass in this scenario is found. 相似文献
14.
Fragmentation functions for charged particles in events have been measured for bottom (b), charm (c) and light (uds) quarks as well as for all flavours together. The results
are based on data recorded between 1990 and 1995 using the OPAL detector at LEP. Event samples with different flavour compositions
were formed using reconstructed mesons and secondary vertices. The distributions and the position of their maxima are also presented separately for uds, c and b quark events. The fragmentation function for b quarks is significantly softer
than for uds quarks.
Received: 29 May 1998 / Published online: 25 January 1999 相似文献
15.
16.
S.P. Das A. Datta M. Guchait M. Maity S. Mukherjee 《The European Physical Journal C - Particles and Fields》2008,54(4):645-653
The estimation of the backgrounds for gluino signals in focus point supersymmetry is extended by including the backgrounds
from the production of four third generation quarks in the analysis. We find that these backgrounds are negligible if one
uses the strong selection criteria proposed in the literature (including this analysis) for heavy gluino searches. Softer
selection criteria often recommended for lighter gluino searches yield backgrounds that are small but numerically significant.
We have also repeated the more conventional background calculations and compared our results with the other groups. We find
that the size of the total residual background estimated by different groups using different event generators and hard kinematical
cuts agree approximately. In view of the theoretical uncertainties in the leading order signal and background cross sections
mainly due to the choice of the QCD scale, the gluino mass reach at the LHC cannot be pinpointed. However, requiring a signal
with ≥3 tagged b-jets (instead of the standard choice of ≥2) it is shown that gluino masses close to 2 TeV can be probed at
the LHC for a range of reasonable choices of the QCD scale for an integrated luminosity of 300 fb-1.
PACS 11.30.Pb; 12.60.Jv; 14.80.Ly; 95.35.+d 相似文献
17.
We compute, for the first time, the absorptive part of the massless correlator of two quark scalar currents in five loops. As physical applications, we consider the [symbol: see text](alpha(s)4) corrections to the decay rate of the standard model Higgs boson into quarks, as well as the constraints on the strange quark mass following from QCD sum rules. 相似文献
18.
D. Ebert T. Feldmann C. Kettner H. Reinhardt 《Zeitschrift fur Physik C Particles and Fields》1996,71(1):329-335
We present a phenomenological ansatz for coupling a heavy quark with two light quarks to form a heavy baryon. The heavy quark is treated in the heavy mass limit, and the light quark dynamics is approximated by propagating scalar and axial vector ‘diquarks’. The resulting effective lagrangian, which incorporates heavy quark and chiral symmetry, describes interactions of heavy baryons with Goldstone bosons in the low energy region. As an application, the Isgur-Wise form factors are estimated. 相似文献
19.
G. Degrassi S. Di Vita P. Slavich 《The European Physical Journal C - Particles and Fields》2012,72(6):1-11
We present a calculation of the two-loop top–stop–gluino contributions to Higgs production via gluon fusion in the MSSM. By means of an asymptotic expansion in the heavy particle masses, we obtain explicit and compact analytic formulas that are valid when the Higgs and the top quark are lighter than stops and gluino, without assuming a specific hierarchy between the Higgs mass and the top mass. Being applicable to the heaviest Higgs scalar in a significant region of the MSSM parameter space, our results complement earlier ones obtained with a Taylor expansion in the Higgs mass, and can be easily implemented in computer codes to provide an efficient and accurate determination of the Higgs production cross section. 相似文献
20.
D. Ebert T. Feldmann C. Kettner H. Reinhardt 《The European Physical Journal C - Particles and Fields》2011,71(1):329-335
We present a phenomenological ansatz for coupling a heavy quark with two light quarks to form a heavy baryon. The heavy quark is treated in the heavy mass limit, and the light quark dynamics is approximated by propagating scalar and axial vector ??diquarks??. The resulting effective lagrangian, which incorporates heavy quark and chiral symmetry, describes interactions of heavy baryons with Goldstone bosons in the low energy region. As an application, the Isgur-Wise form factors are estimated. 相似文献