Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLocalized $4sigma$ and $5sigma$ Dijet Mass Excesses in ALEPH LEP2 Four-Jet Events
205
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We investigate an excess observed in hadronic events in the archived LEP2 ALEPH data. This excess was observed at preselection level during data-MC comparisons of four-jet events when no search was being performed. The events are clustered into four jets and paired such that the mass difference between the two dijet systems is minimized. The excess occurs in the region $M_1+M_2sim 110mbox{ GeV}$; about half of the excess is concentrated in the region $M_1sim 80mbox{ GeV}$, $M_2sim 25mbox{ GeV}$, with a local significance between $4.7sigma$ and $5.5sigma$, depending on assumptions about hadronization uncertainties. The other half of the events are in a broad excess near $M_1sim M_2sim 55mbox{ GeV}$; these display a local significance of $4.1-4.5sigma$. We investigate the effects of changing the SM QCD Monte Carlo sample, the jet-clustering algorithm, and the jet rescaling method. We find that the excess is remarkably robust under these changes, and we find no source of systematic uncertainty that can explain the excess. No analogue of the excess is seen at LEP1.
rate research
Read More
We use the SHERPA Monte Carlo generator to simulate the process $e^+e^-rightarrowmbox{hadrons}$ using matrix elements with up to six partons in the final state. Two samples of SHERPA events are generated. In the LO sample, all final states are generated with leading order matrix elements; in the NLO sample, matrix elements for final states with up to four partons are generated at next-to-leading order, while matrix elements for final states with five or six partons are generated at leading order. The resulting samples are then passed through the ALEPH detector simulation. We compare the Monte Carlo samples to each other, to samples generated using the KK2f generator interfaced with PYTHIA, and to the archived ALEPH data at both LEP1 and LEP2 energies. We focus on four-jet observables with particular attention given to dijet masses. The LO and NLO SHERPA samples show significant improvement over the KK2f generation for observables directly related to clustering events into four jets, while maintaining similar performance to KK2f for event-shape variables. We additionally reweight the dijet masses using LEP1 data and find that this greatly improves the agreement between the three Monte Carlo samples at LEP2 energies for these observables.
A search for the production and non-standard decay of a Higgs boson, h, into four taus through intermediate pseudoscalars, a, is conducted on 683 pb-1 of data collected by the ALEPH experiment at centre-of-mass energies from 183 to 209 GeV. No excess of events above background is observed, and exclusion limits are placed on the combined production cross section times branching ratio, xi^2 = sigma(e+e- --> Zh)/sigma_{SM}(e+e- --> Zh) x B(h --> aa)x B(a --> tau^+tau^-)^2. For mh < 107 GeV/c2 and 4 < ma < 10 GeV/c2, xi^2 > 1 is excluded at the 95% confidence level.
The production of two high-p_T jets in the interactions of quasi-real photons in e+e- collisions at sqrt{s_ee} from 189 GeV to 209 GeV is studied with data corresponding to an integrated e+e- luminosity of 550 pb^{-1}. The jets reconstructed by the k_T cluster algorithm are defined within the pseudo-rapidity range -1 < eta < 1 and with jet transverse momentum, p_T, above 3 GeV/c. The differential di-jet cross-section is measured as a function of the mean transverse momentum ptmean of the jets and is compared to perturbative QCD calculations.
We present a coherent model that combines jet production from perturbative QCD with strongly-coupled jet-medium interactions described in holography. We use this model to study the modification of an ensemble of jets upon propagation through a quark-gluon plasma resembling central heavy ion collisions. Here the modification of the dijet asymmetry depends strongly on the subleading jet width, which can therefore be an important observable for studying jet-medium interactions. We furthermore show that the modification of the shape of the leading jet is relatively insensitive to the dijet asymmetry, whereas the subleading jet shape modification is much larger for more imbalanced dijets. Finally, we compare the results of our holographic model to a recent CMS measurement.
The first measurements of anti-$k_{T}$ jet energy spectrum and substructure in hadronic $Z$ decays are presented. The archived $e^+e^-$ annihilation data at a center-of-mass energy of 91 GeV were collected with the ALEPH detector at LEP in 1994. The jet substructure was analyzed as a function of jet energy. The results are compared with the perturbative QCD calculations and predictions from the PYTHIA v6.1, SHERPA, and HERWIG v7.1.5 event generators. In this note, jet reconstruction procedure, jet energy calibration, and the performance with archived ALEPH data and Monte Carlo simulations are also documented.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
