共查询到20条相似文献,搜索用时 15 毫秒
1.
A gauge model featuring a chiral color symmetry of quarks was considered, and possible manifestations of this symmetry in
proton-antiproton and proton-proton collisions at the Tevatron and LHC energies were studied. The cross section st[`(t)]\sigma _{t\bar t} for the production of t[`(t)]t\bar t quark pairs at the Tevatron and the forward-backward asymmetry AFBp[`(p)]A_{FB}^{p\bar p} in this process were calculated and analyzed with allowance for the contributions of the G′-boson predicted by the chiral color symmetry of quarks, the G′-boson massm
G′ and the mixing angle θ
G
being treated as free parameters of the model. Limits on m
G′ versus θ
G
were studied on the basis of data from the Tevatron on st[`(t)]\sigma _{t\bar t} and AFBp[`(p)]A_{FB}^{p\bar p}, and the region compatible with these data within one standard deviation was found in the m
G′-θ
G
plane. The region ofm
G′-mass values that is appropriate for observing the G′-boson at LHC is discussed. 相似文献
2.
R. H. K. Kadala P. G. Mercadante J. K. Mizukoshi Xerxes Tata 《The European Physical Journal C - Particles and Fields》2008,56(4):511-528
The branching fraction for the decays of gluinos to third generation quarks is expected to be enhanced in classes of supersymmetric
models where either third generation squarks are lighter than other squarks, or in mixed-higgsino dark matter models constructed
so as to be in concordance with the measured density of cold dark matter. In such scenarios, gluino production events at the
CERN Large Hadron Collider should be rich in top and bottom quark jets. Requiring b jets in addition to E
T
miss should, therefore, enhance the supersymmetry signal relative to Standard Model backgrounds from V + jet, VV and QCD backgrounds (V=W,Z). We quantify the increase in the supersymmetry reach of the LHC from b-tagging in a variety of well-motivated models of supersymmetry. We also explore “top tagging” at the LHC. We find that while
the efficiency for this turns out to be too low to give an increase in reach beyond that obtained via b-tagging, top tagging can indeed provide a confirmatory signal if gluinos are not too heavy. We also examine c jet tagging but find that it is not useful at the LHC. Finally, we explore the prospects for detecting the direct production
of third generation squarks in models with an inverted squark mass hierarchy. This is signaled by b jets + E
T
miss events being harder than in the Standard Model, but softer than those from the production of gluinos and heavier squarks.
We find that while these events can be readily separated from the SM background (for third generation squark masses ∼300–500 GeV),
the contamination from the much heavier gluinos and squarks remains formidable if these are also accessible. 相似文献
3.
In this study a systematical analysis of various polarization asymmetries in inclusive b→s
ℓ
+
ℓ
− decay in the standard model (SM) with four generation of quarks is carried out. We found that the various asymmetries are
sensitive to the new mixing and quark masses for both of the μ and τ channels. Sizable deviations from the SM values are obtained. Hence, b→s
ℓ
+
ℓ
− decay is a valuable tool for searching physics beyond the SM, especially in the indirect searches for the fourth-generation
of quarks (t′,b′). 相似文献
4.
George W S Hou 《Pramana》2006,67(5):773-782
There are currently two hints for new physics involving CP violation in b → s transitions: ΔS ≡ S
f − S
J
ϕK
≠ 0, and difference in direct CP asymmetry ΔA
Kπ
≡ A
K+π
0
− A
K+π
−
≠ 0. We explore the two scenarios with a large and unique new CP phase in b ↔ s transitions. Motivated by ΔS ≠ 0, we update on the right-handed strange-beauty squark sb
1R at TeV scale. Motivated by ΔA
Kπ
≠ 0, we explore sequential fourth generation t′ and b′ quarks. Both scenarios can survive constraints such as SM level b → sγ, sll and B
s mixing, and predict sizable CP violation in B
s mixing. The fourth generation picture predicts sizable K
L → π
0
vv. Direct search for sb
R, b′ and t′ at hadronic colliders, such as Tevatron Run II and LHC, can complement further CP violation studies at these machines, as
well as at the future Super B factory. 相似文献
5.
6.
Using the responsible form factors calculated via full QCD, we analyze the ?? b ?? ???+?? transition in the standard model containing fourth-generation quarks (SM4). We discuss the effects of the presence of the t?? fourth-family quark on related observables like branching ratio, forward-backward asymmetry, baryon polarization as well as double-lepton polarization asymmetries. We also compare our results with those obtained in the SM as well as with predictions of the SM4 but using form factors calculated within heavy-quark effective theory. The obtained results on the branching ratio indicate that the ? transition is more probable in full QCD comparing to the heavy-quark effective theory. It is also shown that the results on all considered observables in the SM4 deviate considerably from the SM predictions when m t?? ?? 400 GeV. 相似文献
7.
E. Gotsman E. Levin U. Maor J. S. Miller 《The European Physical Journal C - Particles and Fields》2008,57(4):689-709
In this paper we develop an approach to soft scattering processes at high energies which is based on two elements: the Good–Walker
mechanism for low mass diffraction and multi-pomeron interactions for high mass diffraction. The principal idea, which allows
us to specify the theory for pomeron interactions, is that the so called soft processes occur at rather short distances (r
2
∝1/〈p
t
〉2
∝
α′ℙ≈0.01 GeV−2), where perturbative QCD is valid. The value of the pomeron slope α′ℙ is obtained from a fit to the experimental data. Using this theoretical approach, we suggest a model that fits all soft data
in the ISR-Tevatron energy range: total, elastic, single and double diffractive cross sections, as well as the t dependence of the differential elastic cross section, and the mass dependence of single diffraction. In this model we calculate
the survival probability of diffractive Higgs production, and we obtain a value for this observable that is smaller than 1%
at the LHC energy range. 相似文献
8.
Ahmed Ali Fernando Barreiro Javier Llorente 《The European Physical Journal C - Particles and Fields》2011,71(9):1737
We present an analysis with improved sensitivity to the light charged Higgs (mH+ < mt-mbm_{H^{+}} < m_{t}-m_{b}) searches in the top quark decays t→bH
+→b(τ
+
ν
τ
)+c.c. in the t[`(t)]t\bar{t} and single t/[`(t)]t/\bar{t} production processes at the LHC. In the Minimal Supersymmetric Standard Model (MSSM), one anticipates the branching ratio
B (H+ ?t+nt) @ 1{\mathcal{B}} (H^{+} \to\tau^{+}\nu_{\tau})\simeq1 over almost the entire allowed tanb\tan\beta range. Noting that the τ
+ arising from the decay H
+→τ
+
ν
τ
are predominantly right-polarized, as opposed to the τ
+ from the dominant background W
+→τ
+
ν
τ
, which are left-polarized, a number of H
+/W
+→τ
+
ν
τ
discriminators have been proposed and studied in the literature. We consider hadronic decays of the τ
±, concentrating on the dominant one-prong decay channel τ
±→ρ
±
ν
τ
. The energy and p
T
of the charged prongs normalised to the corresponding quantities of the ρ
± are convenient variables which serve as τ
± polariser. We use the distributions in these variables and several other kinematic quantities to train a boosted decision
tree (BDT). Using the BDT classifier, and a variant of it called BDTD, which makes use of decorrelated variables, we have
calculated the BDT(D)-response functions to estimate the signal efficiency vs. the rejection of the background. We argue that
this chain of analysis has a high sensitivity to light charged Higgs searches up to a mass of 150 GeV in the decays t→bH
+ (and charge conjugate) at the LHC. For the case of single top production, we also study the transverse mass of the system
determined using Lagrange multipliers. 相似文献
9.
The rare t-quark decays t → cl
j
+
l
k
−
and t → cṽ
j
k
k
induced by scalar-leptoquark doublets are considered within the minimal model involving four-color quark-lepton symmetry
and the Higgs mechanism of quark and lepton mass splitting. The partial widths with respect to the decays being considered
and the total widths Γ(t → cl
+′l
−) = Σj,k Γ(t → cl
j
+
l
k
−
) and Γ(t → cl
+′l
−) = Σj,kΓ(t → cṽ
j
v
k
) with respect to, respectively, the charged leptonic and neutrino modes are calculated. It is shown that, at scalar-leptoquark
masses higher than the t-quark mass (m
S > m
t), the branching ratios for these modes are Br(t → cl
+′l
−) ≈ (3.5−0.4) × 10−5 and Br(t → cṽ′v) ≈ (7.1−0.8) × 10−5 at m
s
= 180–250 GeV and an appropriate value of the leptoquark-mixing angle (sin β ≈ 0.2) and can increase for m
S < m
t to Br(t → cl
+′l
−) ≈ 0.03−0.002 and Br(t → cl
+′l
−) ≈ 0.46−0.05 for the charged mode at m
S
= 150–170 GeV for sin β ≈ 1 and sin β ≈ 0.2, respectively. In the cases being considered, t-quark decays to pairs of charged leptons can be accessible to detection at LHC. In the last case, these decays could manifest
themselves (for example, in dilepton events) at the Tevatron as well.
Original Russian Text ? P.Yu. Popov, A.D. Smirnov, 2006, published in Yadernaya Fizika, 2006, Vol. 69, No. 6, pp. 1006–1016. 相似文献
10.
Mixing angles of η and η′ mesons are obtained in the scheme of octet-singlet mixing θη = −15.4°, θ′η = −17.9°, and in the scheme connected with expansion in the quark basis $
\bar q
$
\bar q
q − $
\bar s
$
\bar s
s φ = 39.3°. The constants gV
ηγ, g
η′
V
γ of radiative decays η′ → V
γ and V → ηγ (V ≡ ρ, ω, φ) and the ratios of constants of weak decays of η and η′ mesons are calculated. The numerical values that were found
are in agreement with the experimental data. 相似文献
11.
M. Carena S. Heinemeyer C. E. M. Wagner G. Weiglein 《The European Physical Journal C - Particles and Fields》2006,45(3):797-814
The Higgs boson search has shifted from LEP2 to the Tevatron and will subsequently move to the LHC. The current limits from
the Tevatron and the prospective sensitivities at the LHC are often interpreted in specific MSSM scenarios. For heavy Higgs
boson production and subsequent decay into
or τ+τ–, the present Tevatron data allow one to set limits in the MA–tan β plane for small MA and large tan β values. Similar channels have been explored for the LHC, where the discovery reach extends to higher values
of MA and smaller tan β. Searches for MSSM charged Higgs bosons, produced in top decays or in association with top quarks, have
also been investigated at the Tevatron and the LHC. We analyze the current Tevatron limits and prospective LHC sensitivities.
We discuss how robust they are with respect to variations of the other MSSM parameters and possible improvements of the theoretical
predictions for Higgs boson production and decay. It is shown that the inclusion of supersymmetric radiative corrections to
the production cross sections and decay widths leads to important modifications of the present limits on the MSSM parameter
space. The impact on the region where only the lightest MSSM Higgs boson can be detected at the LHC is also analyzed. We propose
to extend the existing benchmark scenarios by including additional values of the higgsino mass parameter μ. This affects only
slightly the search channels for a SM-like Higgs boson, while having a major impact on the searches for non-standard MSSM
Higgs bosons. 相似文献
12.
The diffractive vector meson photoproduction with hadron dissociation in coherent hadron-hadron interactions at LHC energies
is studied assuming that the color singlet t-channel exchange carries large momentum transfer. We estimate the rapidity distribution and total cross-section for the processes
pp → pVX and PbPb → PbVX (V = ρ or ϒ considering the non-forward solution of the BFKL equation at high energy and large momentum transfer. Our results indicate
that the experimental identification of these processes can be feasible at the LHC. 相似文献
13.
In this paper we consider soft processes at LHC energies in the framework of the constituent quark model. We show that this
rather naive model is able to describe all available soft process data at lower energies and to predict the behavior of the
total cross section, the elastic and diffractive cross sections at LHC energy. It turns out that the “input” pomeron that
has been used in this approach has parameters that are close to the so called “hard” pomeron with rather large intercept Δ≈0.12
and small value of the slope α′
P≈0.08 GeV-2. We show that the elastic amplitude has a minimum at impact parameter b=0 and a maximum at b≈2 GeV-1. Such a behavior is the result of overlapping of the parton clouds that belong to the different quarks in the hadron. 相似文献
14.
Fritzsch like mass matrices with non-zero 22-elements both in U sector and D sector have been investigated in the context
of latest data regardingm
t
phys
, |V
ub|, |V
cb|, |V
td| and |V
ts|. Unlike several other phenomenological models, the present model not only accommodates the value ofm
t
phys
in the range 150–240 GeV, encompassing the CDF and D0 values, but is also able to reproduce |V
cb| ≊0.040 and |V
ub/Vcb| = 0.08±0.02 and |V
td| is predicted to lie in the range 0.005–0.014. Further, the angles of the unitarity triangle, related to the CP-violating
asymmetries, are calculated to be in the ranges −1.0⩽sin2α⩽−0.1, 0.6 ⩽sin2α⩽1.0 and 0.48⩽sin2β⩽0.56, which are in agreement
with other recent calculations. 相似文献
15.
Lorenzo Basso Stefano Moretti Giovanni Marco Pruna 《The European Physical Journal C - Particles and Fields》2011,71(8):1724
We investigate the phenomenology of the Higgs sector of the minimal B−L extension of the Standard Model at a future e
+
e
− Linear Collider. We consider the discovery potential of both a sub-TeV and a multi-TeV machine. We show that, within such
a theoretical scenario, several novel production and decay channels involving the two physical Higgs states, precluded at
the LHC, could experimentally be accessed at such machines. Amongst these, several Higgs signatures have very distinctive
features with respect to those of other models with enlarged Higgs sector, as they involve interactions of Higgs bosons between
themselves, with Z′ bosons as well as with heavy neutrinos. In particular, we present the scope of the Z′ strahlung process for single and double Higgs production, the only suitable mechanism enabling one to access an almost decoupled
heavy scalar state (therefore outside the LHC range). 相似文献
16.
We investigate the phenomenological implication of the discrete symmetry S3 × P on flavor physics in SO(10) unified theory. We construct a minimal renormalizable model which reproduce all the masses and mixing angle of both quarks and leptons. As usually the SO(10) symmetry gives up to relations between the down sector and the charged lepton masses. The underlining discrete symmetry gives a contribution (from the charged lepton sector) to the PMNS mixing matrix which is bimaximal. This gives a strong correlation between the down quark and charged lepton masses, and the lepton mixing angles. We obtain that the small entries V
ub, V
cb, V
td, and V
ts in the CKM matrix are related to the small value of the ratio δ m2
solΔ m2
atm: they come from both the S3×P structure of our model and the small ratio of the other quark masses with respect to m
t. Wonderfully, with our model, we fit 17 experimental data %with only 13 free relevant combinations of vevs. 相似文献
17.
Wenna Xu Xuelei Wang Zhen-jun Xiao 《The European Physical Journal C - Particles and Fields》2007,51(4):891-897
In the topcolor-assisted technicolor (TC2) model, the typical physical particles, top-pions and top-Higgs, are predicted and
the existence of these particles could be regarded as robust evidence for the model. These particles are accessible at the
Tevatron and LHC, and furthermore the flavor-changing (FC) feature of the TC2 model may provide us with a unique opportunity
to probe them. In this paper, we study some interesting FC production processes of top-pions and top-Higgs particles at the
Tevatron and LHC, i.e., cΠt
- and cΠt
0(ht
0) productions. We find that the light charged top-pions are not favorable by the Tevatron experiments, and the Tevatron has
little capability to probe the neutral top-pion and top-Higgs particles via these FC production processes. At LHC, however,
the cross section can reach the level of 10–100 pb for cΠt
- production and 10–100 fb for cΠt
0(ht
0) production. So one can expect that enough signals could be produced at the LHC experiments. Furthermore, the SM backgrounds
should be clean due to the FC feature of the processes, and the FC decay modes Πt
-→bc̄, Πt
0(ht
0)→tc̄ can provide us with the signal typical for the detection of the top-pions and top-Higgs particles. Therefore, one may
have hope to find the signal of top-pions and top-Higgs particles with the running of LHC via these FC processes.
PACS 12.60.Nz; 14.80.Mz; 12.15.LK; 14.65.Ha 相似文献
18.
An empirical mass formula is tested for the basic fermion sequences of charged quarks and leptons. This relation is a generalization
of Barut’s mass formula for the lepton sequence (e, μ, τ......). It is found that successful mass extrapolation to the third and possibly to other higher generations (N>2) can be obtained with the first and second generation masses as inputs, which predicts the top quark massm
t to be around 20 GeV. This also leads to the mass ratios between members of two different sequences (i) and (i′) corresponding to the same higher generations (N>2). 相似文献
19.
A 3-D Gross-Neveu model with Lorentz-violating term b
μ is studied. The effective potential V
eff with a real or imaginary Lorentz-violating term b
μ is calculated. The gap equation is obtained and the influence of the presence of an additional term b
μ on the symmetry of the theory is examined. 相似文献
20.
G. M. Molchan 《Communications in Mathematical Physics》1999,205(1):97-111
Let b
γ (t), b
γ(0)= 0 be a fractional Brownian motion, i.e., a Gaussian process with the structure function , 0 < γ < 2. We study the logarithmic asymptotics of P
T
= P{b
γ (t) < 1,□t∈TΔ} as T→∞, where Δ is either the interval (0,1) or a bounded region that contains a vicinity of 0 for the case of multidimensional
time. It is shown that ln P
T
= - D ln T(1 + o(1)), where D is the dimension of zeroes of b
γ (t) in the former case and the dimension of time in the latter.
Received: 28 September 1998 / Accepted: 19 February 1999 相似文献