共查询到20条相似文献,搜索用时 31 毫秒
1.
Abazov VM Abbott B Acharya BS Adams M Adams T Alexeev GD Alimena J Alkhazov G Alton A Alverson G Alves GA Aoki M Askew A Åsman B Atkins S Atramentov O Augsten K Avila C BackusMayes J Badaud F Bagby L Baldin B Bandurin DV Banerjee S Barberis E Baringer P Barreto J Bartlett JF Bassler U Bazterra V Bean A Begalli M Belanger-Champagne C Bellantoni L Beri SB Bernardi G Bernhard R Bertram I Besançon M Beuselinck R Bezzubov VA Bhat PC Bhatnagar V Blazey G Blessing S Bloom K Boehnlein A Boline D 《Physical review letters》2012,108(12):121802
We report on a search for charged massive long-lived particles (CMLLPs), based on 5.2 fb(-1) of integrated luminosity collected with the D0 detector at the Fermilab Tevatron pp collider. We search for events in which one or more particles are reconstructed as muons but have speed and ionization energy loss (dE/dx) inconsistent with muons produced in beam collisions. CMLLPs are predicted in several theories of physics beyond the standard model. We exclude pair-produced long-lived gauginolike charginos below 267 GeV and Higgsino-like charginos below 217 GeV at 95% C.L., as well as long-lived scalar top quarks with mass below 285 GeV. 相似文献
2.
Aseshkrishna Datta A. Djouadi 《The European Physical Journal C - Particles and Fields》2002,25(4):523-537
In the context of the minimal supersymmetric extension of the standard model, we analyze the production at future high-energy
e
+
e
-
colliders of second and third generation scalar leptons as well as scalar quarks in association with neutralinos and charginos,
. In the case of third generation squarks, we also discuss the associated production with gluinos. We show that the cross
sections for some of these three-body final state processes could be significant enough to allow for the detection of scalar
fermions with masses above the kinematical two-body threshold, . We then discuss, taking as a reference example the case of scalar muons, the production cross sections in various approximations
and make a comparison with the full four-body production process, , in particular around the two-sfermion threshold.
Received: 27 June 2002 / Published online: 20 September 2002 相似文献
3.
Aseshkrishna Datta A. Djouadi M. Mühlleitner 《The European Physical Journal C - Particles and Fields》2002,25(4):539-551
We analyze the associated production at future high-energy e
+
e
-
colliders, of first generation sleptons with neutralinos and charginos in the modes e
+
e
-
and , in the framework of the minimal supersymmetric extension of the standard model. We show that the production rates, in particular
for associated production of right-handed selectrons and the lightest neutralino which in general is the first accessible
kinematically, can be much larger than the corresponding ones for second and third generation scalar leptons and for scalar
quarks. With the high luminosities expected at these colliders, the detection of first generation sleptons with masses significantly
above the kinematical two-body threshold, , is thus possible in favorable regions of the parameter space.
Received: 27 June 2002 / Published online: 20 September 2002 相似文献
4.
S. Heinemeyer F. von der Pahlen C. Schappacher 《The European Physical Journal C - Particles and Fields》2012,72(2):1892
We evaluate two-body decay modes of charginos in the Minimal Supersymmetric Standard Model with complex parameters (cMSSM).
Assuming heavy scalar quarks we take into account all decay channels involving charginos, neutralinos, (scalar) leptons, Higgs
bosons and Standard Model gauge bosons. The evaluation of the decay widths is based on a full one-loop calculation including
hard and soft QED radiation. Special attention is paid to decays involving the Lightest Supersymmetric Particle (LSP), i.e.
the lightest neutralino, or a neutral or charged Higgs boson. The higher-order corrections of the chargino decay widths involving
the LSP can easily reach a level of about ±10%, while the corrections to the decays to Higgs bosons are slightly smaller,
translating into corrections of similar size in the respective branching ratios. These corrections are important for the correct
interpretation of LSP and Higgs production at the LHC and at a future linear e
+
e
− collider. The results will be implemented into the Fortran code FeynHiggs. 相似文献
5.
In this paper the charged Higgs signal through the decay to a pair of muon and neutrino (H
±→μν) is analyzed. The analysis attempts to estimate the amount of muonic signal of the charged Higgs at LHC at a center of mass
energy of 14 TeV. The signal process is the top quark pair production with one of the top quarks decaying to a charged Higgs
(non SM anomalous top decay) and the other decaying to a W boson which is assumed to decay hadronically to two light jets.
Due to the small branching ratio of charged Higgs decay to muon, results are quoted for data corresponding to an integrated
luminosity of 300 fb−1 which is expected to be collected at the LHC high luminosity regime. It is shown that a signal significance close to 5σ down to below 1σ is achievable for a charged Higgs mass in the range 80 GeV<m(H
±)<150 GeV taking the top quark pair production with both top quarks decaying to W bosons as the main irreducible background. 相似文献
6.
In total 1317 di-lepton events with significant missing transverse momentum were identified in a total data sample of 680 pb-1 collected at e + e- centre-of-mass energies ranging from 183 GeV to 209 GeV. The number of di-lepton events, the dependence on centre-of-mass energy, and the event properties are consistent with expectations from Standard Model processes, predominantly W + W- production with both W bosons decaying leptonically. This topology is also an experimental signature for the pair production of new particles that decay to a charged lepton accompanied by one or more invisible particles. No evidence for new phenomena is apparent. Upper limits are presented on the production cross-section multiplied by the relevant branching ratio squared for sleptons, leptonically decaying charginos and charged Higgs bosons. Mass limits are also given.Received: 14 July 2003, Published online: 9 January 2004 相似文献
7.
We present a detailed calculation of the contributions of charginos, scalar quarks, and charged Higgs boson to theK
+→π
+
vv andK
L
0
→μ
+
μ
− decays. We include mixings: that of charginos and that of the scalar partners of the left and right handed top quark. We
find that the box contribution to the amplitudes is much smaller than the penguin contribution, which can be ∼10% of the Standard
Model contribution, even for relatively large SUSY masses. The charged Higgs contribution can be as large as 25% of the SM
contribution in the first decay and as much as 40% of the SM contribution in the second decay. 相似文献
8.
YANG Xin-E 《中国物理C(英文版)》1985,9(5):537-541
We propose a composite model of leptons and quarks containing two constituent fermions of spin 1/2 and a constituent scalar. The constituent fermions are massless and color singlets. Leptons, quarks and weak vector bosons are composites confined by SU(3)H local gauge interaction, where leptons are made of three constituent fermions and quarks are two-body composites of a scalar and a fermion. The number of the constituent particles is less in our model. There are less exotic leptons and quarks. Quark-lepton parallelism holds. Weak interactions appear only at the composite level as residual short-range interactions among hypercolor singlets. The violation of parity occurs by the mechanism of dynamical symmetry breaking. 相似文献
9.
We present a general approach to get the anomalous weak charged current of leptons and quarks in a substructure mode1,in which quarks, leptons and W-bosons are composed of preons (fermions and scalar bosons). We have shown that the (V+A) current can be determined by the structure of leptons and quarks and the anomalous weak current can be very small. In particular, it can approach zero, if the wave function of leptons (or quarks) has aspinor structure (I-P/mf)F. 相似文献
10.
The top quark mass in dileptonic top quark pair decays was measured using 4.7 fb–1 of √s = 7 TeV proton-proton (pp) collision data recorded by the ATLAS experiment at the LHC in 2011. The event topology is characterized by the presence of two charged leptons, at least two neutrinos and several jets, two of which originate from bottom quarks. Using the template method and the m ?b observable, defined as the average invariant mass of the two charged lepton plus b-jet pairs in each event, the top quark mass is measured to be 173.09 ± 0.64(stat) ± 1.50(syst) GeV. This proceeding is based on a preliminary result, which has been superseded meanwhile. 相似文献
11.
G. Köpp D. Schaile M. Spira P. M. Zerwas 《Zeitschrift fur Physik C Particles and Fields》1995,65(3):545-549
Leptons, quarks and gauge bosons are assumed to be pointlike particles in the Standard Model. Stringent bounds on the radii of quarks and leptons and their weak anomalous magnetic moments can be derived from the high-precision measurements at LEP and SLC. We find a model-independent bound ofR?10?17 cm for quark and lepton radii. HERA will provide complementary information on the electromagnetic static properties of the quarks and the parameters of the charged quark currents. 相似文献
12.
A search for pair produced scalar fermions with couplings that violate R-parity has been performed using a data sample corresponding to an integrated luminosity of 56 pb at a centre-of-mass energy of 183 GeV collected with the OPAL detector at LEP. An important consequence of R-parity breaking interactions is that the lightest supersymmetric particle is expected to be unstable. Searches for R-parity violating decays of charged sleptons, sneutrinos and stop quarks have been performed under the assumptions that the
lightest supersymmetric particle decays promptly and that only one of the R-parity violating couplings is dominant for each of the decay modes considered. Such processes would yield multi-leptons,
jets plus leptons or multi-jets, with or without missing energy, in the final state. No significant excess of such events
has been observed. Limits on the production cross-sections of scalar fermions in R-parity violating scenarios are obtained. Mass exclusion regions are also presented in the framework of the Constrained Minimal
Supersymmetric Standard Model.
Received: 16 March 1999 / Published online: 14 October 1999 相似文献
13.
DELPHI Collaboration P. Abreu et al. 《The European Physical Journal C - Particles and Fields》1999,6(3):385-401
Data taken by DELPHI during the 1995 and 1996 LEP runs have been used to search for the supersymmetric partners of electron,
muon and tau leptons and of top and bottom quarks. The observations are in agreement with standard model predictions. Limits
are set on sfermion masses. Searches for long lived scalar leptons from low scale supersymmetry breaking models exclude stau
masses below 55 GeV/c at the 95% confidence level, irrespective of the gravitino mass.
Received: 13 July 1998 / Published online: 19 November 1998 相似文献
14.
A large forward-backward asymmetry is seen in both the top quark rapidity distribution A(FB)(t) and in the rapidity distribution of charged leptons A(FB)(?) from top quarks produced at the Tevatron. We study the kinematic and dynamic aspects of the relationship of the two observables arising from the spin correlation between the charged lepton and the top quark with different polarization states. We emphasize the value of both measurements, and we conclude that a new physics model which produces more right-handed than left-handed top quarks is favored by the present data. 相似文献
15.
《Nuclear Physics B》1988,308(4):791-812
Differential cross sections for electroproduction of charm, bottom and top quarks are calculated via all contributing 2 → 2 and 2 → 3 QCD subprocesses. Fragmentation of heavy quarks to heavy hadrons and effects due to weak chain decays of the heavy quarks are taken into account. We also calculated background contributions given by the production of two or three light-quark jets both via the neutral and charged current processes. We point out that, similarly to the case of hadron colliders, it will be necessary to require final state lepton(s) to suppress the jet background. To separate charm and bottom production we have to require at least one hard muon or two isolated leptons and one jet in the final state. We show that two or more jet production via the charged current mechanism and bottom production with hard gluon bremssrahlung are the most important background contributions in top search. However, we also show that they become negligible by requiring one lepton, two or three jets and large missing energy in the final state. We estimate that the discovery limit on the top quark mass value is about 70 GeV at HERA. 相似文献
16.
In this paper we present a discussion on anomalous magnetic moment of a massive fermion and leptons in a substructure model, in which quarks and leptons are composed of a massive fermion and a massive scalar boson. we have obtained some limitations on their masses and charges. 相似文献
17.
A selection of di-lepton events with significant missing transverse momentum has been performed using a total data sample
of 237.4 pb at centre-of-mass energies of approximately 183 GeV and 189 GeV. The observed numbers of events – 78 at 183 GeV and 301 at 189
GeV – are consistent with the numbers expected from Standard Model processes, which arise predominantly from production with both W bosons decaying leptonically. This topology is also an experimental signature for the pair production
of new particles that decay to a charged lepton accompanied by one or more invisible particles. Discrimination techniques
are described that optimise the sensitivity to particular new physics channels. No evidence for new phenomena is apparent.
Upper limits on the production cross-section times branching ratio squared for sleptons and for leptonically decaying charginos
and charged Higgs are presented in a manner intended to minimise the number of model assumptions. Assuming a 100% branching
ratio for the decay , where is the lightest neutralino, we exclude at 95% CL: right-handed smuons with masses below 82.3 GeV for GeV and right-handed staus with masses below 81.0 GeV for GeV. Right-handed selectrons are excluded at 95% CL for masses below 87.1 GeV for GeV, within the framework of the Minimal Supersymmetric Standard Model assuming GeV and . Charged Higgs bosons, H, are excluded at 95% CL for masses below 82.8 GeV, assuming a 100% branching ratio for the decay .
Received: 6 September 1999 / Published online: 6 April 2000 相似文献
18.
We propose a composite model for quarks and leptons based on an exact SU(3)C × SU(3)H gauge theory and two fundamental fermions: a charged T-rishon and a neutral V-rishon. Quarks, leptons and W-bosons are SU(3)H-singlet composites of rishons. A dynamically broken effective SU(3)C × SU(2)L × SU(2)R × U(1)B?L gauge theory emerges at the composite level. The theory is “natural”, anomaly free, has no fundamental scalar particles, and describes at least three generations of quarks and leptons. 相似文献
19.
A. Bartl W. Majerotto K. Mönig A. N. Skachkova N. B. Skachkov 《Physics of Particles and Nuclei Letters》2012,9(1):29-46
We study pair production of scalar top quarks (stop, \(\tilde t_1\)) in polarized photon-photon collisions with the subsequent decay of the top squarks into b quarks and charginos \(\tilde t_1 \to b\tilde \chi _1^ \pm\). We simulate this process by using PYTHIA6.4 for an electron beam energy \(2E_{beam}^e = \sqrt {s_{ee} } = 1000 GeV\). The energy spectrum of back-scattered photons is generated by CIRCE2 program. A set of criteria for physical variables is proposed which leads to a good separation of stop signal events from top quark pair production, being the main background. These criteria allow us to reconstruct the mass of the top squark, provided that the neutralino mass is known. 相似文献
20.
Abazov VM Abbott B Abolins M Acharya BS Adams M Adams T Agelou M Agram JL Ahn SH Ahsan M Alexeev GD Alkhazov G Alton A Alverson G Alves GA Anastasoaie M Andeen T Anderson S Andrieu B Arnoud Y Askew A Asman B Assis Jesus AC Atramentov O Autermann C Avila C Badaud F Baden A Baldin B Balm PW Banerjee S Barberis E Bargassa P Baringer P Barnes C Barreto J Bartlett JF Bassler U Bauer D Bean A Beauceron S Begel M Bellavance A Beri SB Bernardi G Bernhard R Bertram I Besançon M Beuselinck R Bezzubov VA 《Physical review letters》2005,95(15):151805
A search for associated production of charginos and neutralinos is performed using data recorded with the D0 detector at a pp center-of-mass energy of 1.96 TeV at the Fermilab Tevatron Collider. This analysis considers final states with missing transverse energy and three charged leptons, of which at least two are electrons or muons. No evidence for supersymmetry is found in a data set corresponding to an integrated luminosity of 320 pb-1. Limits on the product of the production cross section and leptonic branching fraction are set. For the minimal supergravity model, a chargino lower mass limit of 117 GeV at the 95% C.L. is derived in regions of parameter space with enhanced leptonic branching fractions. 相似文献