Dijet Invariant Mass Research Articles

R-parity violating supersymmetric explanation for the CDFWjjexcess

Recently CDF has reported a 4.1 sigma excess in the distribution of the dijet invariant mass between 120-160 GeV in Wjj event sample in 7.3 fb^{-1} of data, which has generated considerable interest. We offer a possible explanation of this observation in the general framework of MSSM with R-parity violation through resonance production of tau sneutrino decaying into the LSP stau_1 and W boson. We also give the predictions of this scenario for the LHC operating at 7 TeV center of mass energy.

Color-octet-electroweak-doublet scalars and the CDF dijet anomaly

We study the phenomenology of color-octet scalars in the (8,2)1/2 representation in the context of the 3.2σ excess, in the dijet invariant mass spectrum of the W+jj final state, recently observed by the CDF Collaboration. We consider the region of parameter space with a sizable mass splitting between the charged and neutral color-octet scalars and consistent with electroweak precision data. We implement the principle of Minimal Flavor Violation (MFV) in order to suppress FCNC currents and reduce the number of free parameters. The excess in the W+jj channel corresponds to the charged current decay of the heavier neutral octet scalar into its lighter charged partner which decays into the two jets. In the MFV scenario, the production of the neutral color-octet is dominated by gluon fusion due to the Yukawa suppression of production via initial state quarks. As a result, no visible excess is expected in the γ+jj channel due to Yukawa and CKM suppression. Contributions to the Z+jj final state are suppressed for a mass spectrum where the decay of the heavier color-octet to this final state is mediated by an off-shell neutral color-octet partner. MFV allows one to control fraction of bottom quarks in the final state jets by a single ratio of two free parameters.

Top Quark Asymmetry andWjjExcess at CDF from Gauged Flavor Symmetry

We show that the scalar sector needed for fermion mass generation when the flavor symmetry of the standard model is maximally gauged can consistently explain two anomalies reported recently by the CDF Collaboration-the forward-backward asymmetry in tt pair production and the dijet invariant mass in the Wjj channel. A pair of nearly degenerate scalar doublets with masses in the range 150-200 GeV explain these anomalies, with additional scalars predicted in the mass range 100-400 GeV. Consistency of such low scale flavor physics with flavor-changing processes is shown, and expectations for the LHC are outlined.

Gluon excitations intt¯production at hadron colliders

We argue that a relatively light massive gluon with mass <= 1 TeV, small purely axial couplings to light quarks and sizable vector and axial couplings to the top quark can reproduce the large forward-backward asymmetry observed at the Tevatron without conflicting with the t tbar and the dijet invariant mass distributions measured at the Tevatron and the LHC. We show that realistic Higgsless models with warped extra dimensions naturally fulfil all the necessary ingredients to realize this scenario. While current data is unable to discover or exclude these heavy gluons with masses 850 GeV, they should be observed at the (7 TeV) LHC with a luminosity of the order of 300 pb^{-1}.

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).

An explanation of the CDF dijet anomaly within a [formula omitted] Stueckelberg extension

We discuss the recent excess seen by the CDF Collaboration in the dijet invariant mass distribution produced in association with a W boson. We analyze the possibility of such a signal within the context of a U(1)X Stueckelberg extension of the Standard Model where the new gauge boson couples only to quarks. In addition to the analysis of the Wjj anomaly we also discuss the production of Zjj and γjj at the Tevatron. The analysis is then extended to the Large Hadron Collider with s=7 TeV and predictions for the dijet signals are made.

New color-octet vector boson revisited

Motivated by CDF Collaboration recent measurements on di-jet invariant mass spectrum, where di-jet is associated with charged leptons ($e/\ensuremath{\mu}$) and missing energy, we reexamined the previous proposed massive color-octet axial-vectorlike boson ${Z}_{c}$. Our simulation showed that the di-jet bump around 120--160 GeV can be induced by ${Z}_{c}$ with effective coupling ${g}_{{Z}_{c}q\overline{q}}=0.2{g}_{s}$ ($q$ represents the quark other than top and ${g}_{s}$ is the strong coupling constant). Moreover our numerical investigation indicated that the top quark forward-backward asymmetry ${A}_{\mathrm{FB}}^{t}$ can be reproduced without distorting shape of differential cross section $d\ensuremath{\sigma}/d{M}_{t\overline{t}}$, provided that the ${Z}_{c}$ and top quark coupling is appropriately chosen (${g}_{{Z}_{c}t\overline{t}}\ensuremath{\simeq}4.5{g}_{{Z}_{c}q\overline{q}}$). Our results also showed that the theoretical ${A}_{\mathrm{FB}}^{t}$ as functions of $\ensuremath{\Delta}y$ and ${M}_{t\overline{t}}$ can be consistent with data within $1\ensuremath{\sigma}$ and $1.8\ensuremath{\sigma}$, respectively.

O(100 GeV)deci-weakW′/Z′at Tevatron and LHC

Recently Tevatron released their measurements on invariant mass spectrum of electron/positron, as well as the di-jet arising from WW+WZ production with one W leptonically decay. Though the statistics is not significant, there are two bumps around 240 GeV and 120-160 GeV respectively. We proposed that the two bumps correspond to the extra light gauge bosons $Z^\prime$ and $W^\prime$, which couple with quarks with the deci-weak strength. In this brief report, we also simulated di-jet invariant mass distribution at the current running LHC.

Standard model explanation of a CDF dijet excess inWjj

We demonstrate the recent observation of a peak in the dijet invariant mass of the $Wjj$ signal observed by the CDF Collaboration can be explained as the same upward fluctuation observed by CDF in single-top-quark production. In general, both $t$-channel and $s$-channel single-top-quark production produce kinematically induced peaks in the dijet spectrum. Since CDF used a Monte Carlo simulation to subtract the single-top backgrounds instead of data, a peak in the dijet spectrum is expected. The D0 Collaboration has a small upward fluctuation in their published $t$-channel data; and hence we predict they would see at most a small peak in the dijet invariant-mass spectrum of $Wjj$ if they follow the same procedure as CDF.

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.

Determining the squark mass at the LHC

We propose a new way to determine the squark mass based on the shape of di-jet invariant mass distribution of supersymmetry (SUSY) di-jet events at the Large Hadron Collider (LHC). Our algorithm, which is based on event kinematics, requires that the branching ratio $B(\tilde{q} \rightarrow q \tilde{z}_1)$ is substantial for at least some types of squarks, and that $m_{\tilde{z}_1}^2/m_{\tilde{q}}^2 \ll 1$. We select di-jet events with no isolated leptons, and impose cuts on the total jet transverse energy, $E_T^{tot}=E_T(j_1)+E_T(j_2)$, on $\alpha = E_T(j_2)/m_{jj}$, and on the azimuthal angle between the two jets to reduce SM backgrounds. The shape of the resulting di-jet mass distribution depends sensitively on the squark mass, especially if the integrated luminosity is sufficient to allow a hard enough cut on $E_T^{tot}$ and yet leave a large enough signal to obtain the $m_{jj}$ distribution. We simulate the signal and Standard Model (SM) backgrounds for 100 fb$^{-1}$ integrated luminosity at 14 TeV requiring $E_T^{tot}> 700$ GeV. We show that it should be possible to extract $m_{\tilde{q}}$ to within about 3% at 95% CL --- similar to the precision obtained using $m_{T2}$ --- from the di-jet mass distribution if $m_{\tilde{q}} \sim 650$ GeV, or to within $\sim 5$% if $m_{\tilde{q}}\sim 1$ TeV.

Measurement of the differential dijet production cross section in proton–proton collisions at [formula omitted

A measurement of the double-differential inclusive dijet production cross section in proton–proton collisions at s=7 TeV is presented as a function of the dijet invariant mass and jet rapidity. The data correspond to an integrated luminosity of 36 pb−1, recorded with the CMS detector at the LHC. The measurement covers the dijet mass range 0.2 TeV to 3.5 TeV and jet rapidities up to |y|=2.5. It is found to be in good agreement with next-to-leading-order QCD predictions.

Measurement of Dijet Angular Distributions and Search for Quark Compositeness inppCollisions ats=7 TeV

Dijet angular distributions are measured over a wide range of dijet invariant masses in pp collisions at √s = 7 TeV, at the CERN LHC. The event sample, recorded with the CMS detector, corresponds to an integrated luminosity of 36 pb⁻¹. The data are found to be in good agreement with the predictions of perturbative QCD, and yield no evidence of quark compositeness. With a modified frequentist approach, a lower limit on the contact interaction scale for left-handed quarks of Λ⁺ = 5.6 TeV (Λ⁻ = 6.7 TeV) for destructive (constructive) interference is obtained at the 95% confidence level.

Dijet Cross Section and Longitudinal Double Spin Asymmetry Measurements in Polarized Proton-proton Collisions at √s = 200 GeV at STAR

These proceedings show the preliminary results of the dijet cross sections and the dijet longitudinal double spin asymmetries \U0001d49cLL in polarized proton-proton collisions at √s = 200 GeV at the mid-rapidity |η) ≤ 0.8. The integrated luminosity of 5.39 pb−1 collected during RHIC Run-6 was used in the measurements. The preliminary results are presented as functions of the dijet invariant mass Mjj. The dijet cross sections are in agreement with next-to-leading-order pQCD predictions. The \U0001d49cLL is compared with theoretical predictions based on various parameterizations of polarized parton distributions of the proton. Projected precision of data analyzed to date from Run-9 are shown.

Erratum: Quark fragmentation within an identified jet [Phys. Rev. D81, 074009 (2010)

We derive a factorization theorem that describes an energetic hadron h fragmenting from a jet produced by a parton i, where the jet invariant mass is measured. The analysis yields a "fragmenting jet function" G_i^h(s,z) that depends on the jet invariant mass s, and on the energy fraction z of the fragmentation hadron. We show that G^h_i can be computed in terms of perturbatively calculable coefficients, J_{ij}(s,z/x), integrated against standard non-perturbative fragmentation functions, D_j^{h}(x). We also show that the sum over h of the integral over z of z G_i^h(s,z) is given by the standard inclusive jet function J_i(s) which is perturbatively calculable in QCD. We use Soft-Collinear Effective Theory and for simplicity carry out our derivation for a process with a single jet, B -> X h l nu, with invariant mass m_{X h}^2 >> Lambda_QCD^2. Our analysis yields a simple replacement rule that allows any factorization theorem depending on an inclusive jet function J_i to be converted to a semi-inclusive process with a fragmenting hadron h. We apply this rule to derive factorization theorems for B -> X K gamma which is the fragmentation to a Kaon in b -> s gamma, and for e^+e^- -> (dijets)+h with measured hemisphere dijet invariant masses.

Measurement of theWW+WZproduction cross section using a matrix element technique inlepton+jetsevents

We present a measurement of the $WW+WZ$ production cross section observed in a final state consisting of an identified electron or muon, two jets, and missing transverse energy. The measurement is carried out in a data sample corresponding to up to 4.6~fb$^{-1}$ of integrated luminosity at $\sqrt{s} = 1.96$ TeV collected by the CDF II detector. Matrix element calculations are used to separate the diboson signal from the large backgrounds. The $WW+WZ$ cross section is measured to be $17.4\pm3.3$~pb, in agreement with standard model predictions. A fit to the dijet invariant mass spectrum yields a compatible cross section measurement.

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.

Measurement of the dijet invariant mass cross section in [formula omitted] collisions at [formula omitted

The inclusive dijet production double differential cross section as a function of the dijet invariant mass and of the largest absolute rapidity of the two jets with the largest transverse momentum in an event is measured in pp¯ collisions at s=1.96 TeV using 0.7 fb−1 of integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider. The measurement is performed in six rapidity regions up to a maximum rapidity of 2.4. Next-to-leading order perturbative QCD predictions are found to be in agreement with the data.

Quark fragmentation within an identified jet

We derive a factorization theorem that describes an energetic hadron $h$ fragmenting from a jet produced by a parton $i$, where the jet invariant mass is measured. The analysis yields a ``fragmenting jet function'' ${\mathcal{G}}_{i}^{h}(s,z)$ that depends on the jet invariant mass $s$, and on the energy fraction $z$ of the fragmentation hadron. We show that ${\mathcal{G}}_{i}^{h}$ can be computed in terms of perturbatively calculable coefficients, ${\mathcal{J}}_{ij}(s,z/x)$, integrated against standard nonperturbative fragmentation functions, ${D}_{j}^{h}(x)$. We also show that $\ensuremath{\sum}_{h}\ensuremath{\int}dz{\mathcal{G}}_{i}^{h}(s,z)$ is given by the standard inclusive jet function ${J}_{i}(s)$ which is perturbatively calculable in QCD. We use soft collinear effective theory and for simplicity carry out our derivation for a process with a single jet, $\overline{B}\ensuremath{\rightarrow}Xh\ensuremath{\ell}\overline{\ensuremath{\nu}}$, with invariant mass ${m}_{Xh}^{2}\ensuremath{\gg}{\ensuremath{\Lambda}}_{\mathrm{QCD}}^{2}$. Our analysis yields a simple replacement rule that allows any factorization theorem depending on an inclusive jet function ${J}_{i}$ to be converted to a semi-inclusive process with a fragmenting hadron $h$. We apply this rule to derive factorization theorems for $\overline{B}\ensuremath{\rightarrow}XK\ensuremath{\gamma}$ which is the fragmentation to a Kaon in $b\ensuremath{\rightarrow}s\ensuremath{\gamma}$, and for ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}(\mathrm{\text{dijets}})+h$ with measured hemisphere dijet invariant masses.

Dijet angular distributions at $\sqrt{s}=14$ TeV

We present a Monte Carlo study of dijet angular distributions at $\sqrt{s}=14$ TeV. First we perform a next-to-leading order QCD study; we calculate the distributions in four different bins of dijet invariant mass using different Monte Carlo programs and different jet algorithms, and we also investigate the systematic uncertainties coming from the choice of the parton distribution functions and the renormalization and factorization scales. In the second part of this paper, we present the effects on the distributions coming from a model including gravitational scattering and black hole formation in a world with large extra dimensions. Assuming a 25% systematic uncertainty, we report a discovery potential for the mass bin $1 < M_{jj} < 2$ TeV at 10 pb$^{-1}$ integrated luminosity.