Dijet Resonance Research Articles

Tevatron topAFBversus LHC top physics

We carry out a comprehensive analysis of models for top ${A}_{\mathrm{FB}}$ at CDF in light of new top data arriving from the LHC. We begin with a careful Tevatron analysis, considering in general which sets of effective vertices give rise to a large forward-backward asymmetry while suppressing the contribution to the total $t\overline{t}$ cross-section. We show on general grounds that scalar models struggle to produce sufficient asymmetries consistent with CDF observations, while vector models can produce a large asymmetry with a less significant tension in the total cross-section and $t\overline{t}$ invariant mass distribution at the Tevatron. We examine the essential observables of these models for top physics at LHC7 with $1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data, including the total cross-section, invariant mass distribution and number of additional jets in $t\overline{t}$ events. In the case of $t$-channel mediators, the LHC total cross-section places a strong constraint on light mediators, while the Tevatron invariant mass distributions place strong constraints on heavy mediators that are able to produce the asymmetry. In particular, single mediator production at the LHC can contribute significantly to $t\overline{t}+\mathrm{\text{jets}}$ events and lead to a significant increase in the $t\overline{t}$ cross-section, as well as in the ratio of top pair events with extra jets to events with no extra jets. Heavy axigluons are becoming increasingly squeezed by LHC7 $t\overline{t}$ and dijet resonance searches. We conclude that LHC7 top analyses are rapidly closing the window for viable models of the CDF top ${A}_{\mathrm{FB}}$.

STUDY OF THE DIJET INVARIANT MASS IN W + JETS EVENTS BY THE DØ COLLABORATION

The recent claim by the CDF Collaboration of a possible anomalous dijet resonance in their data required experimental verification from other hadron collider experiments. We present a study of the dijet invariant mass spectrum in events with two jets produced in association with a W→ℓν boson at the DØ experiment. We investigate the dijet mass range between 110 GeV /c2 and 170 GeV /c2 and find no evidence for any resonant dijet production.

Dijet resonances, widths and all that

The search for heavy resonances in the dijet channel is part of the on-going physics programme, both at the Tevatron and at the LHC. Lower limits have been placed on the masses of dijet resonances predicted in a wide variety of models. However, across experiments, the search strategy assumes that the effect of the new particles is well-approximated by on-shell production and subsequent decay into a pair of jets. We examine the impact of off-shell effects on such searches, particularly for strongly interacting resonances.

Chiral U(1) flavor models and flavored Higgs doublets: the top FB asymmetry and the W jj

We present U(1) flavor models for leptophobic Z' with flavor dependent couplings to the right-handed up-type quarks in the Standard Model, which can accommodate the recent data on the top forward-backward (FB) asymmetry and the dijet resonance associated with a W boson reported by CDF Collaboration. Such flavor-dependent leptophobic charge assignments generally require extra chiral fermions for anomaly cancellation. Also the chiral nature of U(1)' flavor symmetry calls for new U(1)'-charged Higgs doublets in order for the SM fermions to have realistic renormalizable Yukawa couplings. The stringent constraints from the top FB asymmetry at the Tevatron and the same sign top pair production at the LHC can be evaded due to contributions of the extra Higgs doublets. We also show that the extension could realize cold dark matter candidates.

SEARCHES FOR DIJET RESONANCES AT HADRON COLLIDERS

We review the experimental searches for new particles in the dijet mass spectrum conducted at the CERN [Formula: see text], the Fermilab Tevatron Collider, and the CERN Large Hadron Collider. The theory of the QCD background and new particle signals is reviewed, with emphasis on the choices made by the experiments to model the background and signal. The experimental techniques, data, and results of dijet resonance searches at hadron colliders over the last quarter century are described and compared. Model independent and model specific limits on new particles decaying to dijets are reviewed, and a detailed comparison is made of the recently published limits from the ATLAS and CMS experiments.

Possible common origin of the top forward-backward asymmetry and the CDFWjjexcess

A color-singlet neutral vector boson is considered as a possible common origin of the top forward-backward asymmetry and the CDF dijet resonance. We identify chiral and flavor structures of the couplings of this new vector boson to the standard model quarks for which one could accommodate both data. We also demonstrate that non-vanishing observables involving longitudinal top polarizations can provide useful criteria for the possible existence of parity violating new physics in the q q^bar -> t t^bar process, and discrimination between the flavor-conserving and flavor-violating cases.

Top quark asymmetry and dijet resonances

CDF recently reported an anomaly in the ${m}_{jj}$ distribution of dijet events produced in association with a $W$ boson. A single $u\ensuremath{-}t\ensuremath{-}V$ flavor-changing coupling can contribute to the ${m}_{jj}$ anomaly while being consistent with other resonance searches. Furthermore, it gives a potential explanation of the observed forward-backward asymmetry in top quark production.

Signatures of resonant superpartner production with charged-current decays

Hadron collider signatures of new physics are investigated in which a primary resonance is produced that decays to a secondary resonance by emitting a $W$ boson, with the secondary resonance decaying to two jets. This topology can arise in supersymmetric theories with $R$-parity violation where the lightest supersymmetric particles are either a pair of squarks, or a slepton-sneutrino pair. The resulting signal can have a cross section consistent with the $Wjj$ observation reported by the CDF Collaboration, while remaining consistent with earlier constraints. Other observables that can be used to confirm this scenario include a significant charge asymmetry in the same channel at the LHC. With strongly interacting resonances such as squarks, pair production topologies additionally give rise to four jet and ${W}^{+}{W}^{\ensuremath{-}}+\text{ }\mathrm{\text{four}}\text{ }\text{ }\mathrm{\text{jet}}$ signatures, each with two equal-mass dijet resonances within the four jets.

Heavy octets and Tevatron signals with three or four b jets

Hypothetical color-octet particles of spin 0, pair-produced at hadron colliders through their QCD coupling, may lead to final states involving three or four b jets. We analyze kinematic distributions of the 3b final state that differentiate the scalar octets from supersymmetric Higgs bosons. Studying the scalar sector that breaks an SU(3) \times SU(3) gauge symmetry down to the QCD gauge group, we find that the scalar octet is resonantly produced in pairs via a spin-1 octet (coloron). A scalar octet of mass in the 140 - 150 GeV range can explain the nonstandard shape of the b-jet transverse energy distributions reported by the CDF Collaboration, especially when the coloron mass is slightly above twice the scalar mass. The dominant decay mode of the scalar octet is into a pair of gluons, so that the production of a pair of dijet resonances is large in this model, of about 40 pb at the Tevatron. Even when a W boson is radiated from the initial state, the inclusive cross section for producing a dijet resonance near the scalar octet mass remains sizable, around 0.15 pb.

Bounds on an Anomalous Dijet Resonance inW+jetsProduction inpp¯Collisions ats=1.96 TeV

We present a study of the dijet invariant mass spectrum in events with two jets produced in association with a W boson in data corresponding to an integrated luminosity of 4.3 fb(-1) collected with the D0 detector at √s = 1.96 TeV. We find no evidence for anomalous resonant dijet production and derive upper limits on the production cross section of an anomalous dijet resonance recently reported by the CDF Collaboration, investigating the range of dijet invariant mass from 110 to 170 GeV/c(2). The probability of the D0 data being consistent with the presence of a dijet resonance with 4 pb production cross section at 145 GeV/c(2) is 8×10(-6).

Forward-Backward Asymmetry intt¯Production from Flavor Symmetries

We show that the forward-backward asymmetry in top quark pair production can be enhanced by fields that transform nontrivially under the flavor group and satisfy minimal flavor violation, while at the same time the constraints from associated effects on the dσ(tt)/dM(tt) distribution, dijet resonance searches, same-sign top-pair production, and other phenomenology are satisfied. We work out two examples in detail: one where a scalar color antisextet field that is also an antisextet of SU(3)(U) enhances the forward-backward asymmetry and one where the enhancement arises from a vector color octet field that is also an octet of SU(3)(U).

Z′model for the CDF dijet anomaly

We adopt a bottom-up approach to constructing a new physics model to explain the CDF excess seen in dijets with an associated lepton and missing transverse energy. We find that the 145 GeV broad feature seen by CDF in the dijet invariant mass distribution can be explained by a ${Z}^{\ensuremath{'}}$ boson with a mass of 145 GeV that couples only to first generation quarks. After dijet resonance constraints are considered, a sizeable region of the parameter space favored by the CDF anomaly remains viable.

LHC predictions from a tevatron anomaly in the top quark forward-backward asymmetry

We examine the implications of the recent CDF measurement of the top-quark forward-backward asymmetry, focusing on a scenario with a new color octet vector boson at 1-3 TeV. We study several models, as well as a general effective field theory, and determine the parameter space which provides the best simultaneous fit to the CDF asymmetry, the Tevatron top pair production cross section, and the exclusion regions from LHC dijet resonance and contact interaction searches. Flavor constraints on these models are more subtle and less severe than the literature indicates. We find a large region of allowed parameter space at high axigluon mass and a smaller region at low mass; we match the latter to an SU(3)xSU(3)/SU(3) coset model with a heavy vector-like fermion. Our scenario produces discoverable effects at the LHC with only 1-2 inverse femtobarns of luminosity at 7-8 TeV. Lastly, we point out that a Tevatron measurement of the b-quark forward-backward asymmetry would be very helpful in characterizing the physics underlying the top-quark asymmetry.

Publisher’s Note: Search for Dijet Resonances in 7 TeVppCollisions at CMS [Phys. Rev. Lett.105, 211801 (2010)

A search for narrow resonances in the dijet mass spectrum is performed using data corresponding to an integrated luminosity of 2.9 inverse pb collected by the CMS experiment at the LHC. Upper limits at the 95% confidence level (CL) are presented on the product of the resonance cross section, branching fraction into dijets, and acceptance, separately for decays into quark-quark, quark-gluon, or gluon-gluon pairs. The data exclude new particles predicted in the following models at the 95% CL: string resonances, with mass less than 2.50 TeV, excited quarks, with mass less than 1.58 TeV, and axigluons, colorons, and E_6 diquarks, in specific mass intervals. This extends previously published limits on these models.

A closer look at string resonances in dijet events at the LHC

The first string excited state can be observed as a resonance in dijet invariant mass distributions at the LHC, if the scenario of low-scale string with large extra dimensions is realized. A distinguished property of the dijet resonance by string excited states from that the other "new physics" is that many almost degenerate states with various spin compose a single resonance structure. It is examined that how we can obtain evidences of low-scale string models through the analysis of angular distributions of dijet events at the LHC. Some string resonance states of color singlet can obtain large mass shifts through the open string one-loop effect, or through the mixing with closed string states, and the shape of resonance structure can be distorted. Although the distortion is not very large (10% for the mass squared), it might be able to observe the effect at the LHC, if gluon jets and quark jets could be distinguished in a certain level of efficiency.

Annihilation decays of bound states at the LHC

At the Large Hadron Collider, heavy particles may be produced in pairs close to their kinematic threshold. If these particles have strong enough attractive interactions they may form bound states. Consequently, the bound states may decay through annihilation back into the standard model. Such annihilation decays have the potential to provide much information about the bound particles, such as their mass, spin, or charges, in a manner completely complementary to standard single particle cascade decays. Many of the signatures, such as dijet resonances, will be challenging to find, but may be extremely helpful in unraveling the nature of the new physics. In the standard model, the only novel annihilation decays would be for toponium; these will be hard to see because of the relatively large width of the top quark itself. In models with supersymmetry, marginally visible annihilation decays may occur for example, from bound states of gluinos to dijets or tops. If new particles are bound through forces stronger than QCD, annihilation decays may even be the discovery mode for new physics. This paper presents various theoretical results about bound states and then addresses the practical question of whether any of their annihilation decays can be seen at the LHC.

Searching for extra-dimensions at CMS

A possible solution to the hierarchy problem is the presence of extra space dimensions beyond the three ones which are known from our everyday experience. The phenomenological ADD model of large extra-dimensions predicts a ETmiss +jet signature. Randall-Sundrum-type extra-dimensions predict di-lepton and di-jet resonances. This contribution addresses an overview of experimental issues and discovery potential for these new particles at the LHC, focusing on perspectives with the CMS detector during early data taking.

High [formula omitted] Jet Physics at CMS

We present CMS plans to search for physics beyond the standard model using high p T jets. The inclusive cross section as a function of jet p T is a first simple measure of QCD dijets which is sensitive to a 3 TeV contact interaction with only 10 pb −1 . With the dijet mass distribution we expect to be able to observe dijet resonances with large cross sections, such as a 2 TeV excited quark which produces a convincing signal with only 100 pb −1 . With the dijet ratio, a simple angular measurement, we expect to be able to discover a contact interaction scale Λ + of 4, 7 and 10 TeV for integrated luminosities of 10 pb −1 , 100 pb −1 , and 1 fb −1 respectively. Using the dijet ratio we can discover or confirm a dijet resonance, and eventually measure its spin. With 100 pb −1 a 2 TeV resonance with the production rate of an excited quark produces a convincing signal in the dijet ratio.

CMS search plans and sensitivity to new physics with dijets

The compact muon solenoid (CMS) experiment will use dijets to search for physics beyond the standard model during early LHC running. The inclusive jet cross section as a function of jet transverse momentum, with 10 pb−1 of integrated luminosity, is sensitive to contact interactions beyond the reach of the Tevatron. The dijet mass distribution will be used to search for dijet resonances coming from new particles, for example an excited quark. Additional sensitivity to the existence of contact interactions or dijet resonances can be obtained by comparing dijet rates in two distinct pseudorapidity regions.