14h50 - 15h10 Teratron review talk

A. Bhatti Rockfeller University

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15h10 - 15h30 HERA review talk

J. Phillips Liverpool University

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1- Studies of Jet Energy Resolution. 15 mn

Stefano Lami Rockfeller University

The jet energy resolution comes from many sources, which can be grouped into two categories: (1) detector effects such as calorimeter resolution, and (2) physics effects such as fluctuations in the energy outside a clustering cone. We studied the physics uncertainties using simulated $W\rightarrow jj$ events in order to improve the low-mass tail in the di-jet mass distribution. For the detector resolution we used both CDF detector simulation and data. For the first time the full granularity of the CDF detector is used to perform corrections at ``tower level'' rather than at ``jet level''. The track momenta measured by the Central Tracking Chamber and the neutral cluster energies measured by the Central Shower Max detector are used to correct the calorimeter tower energies. When tested on photon+jet data, our new algorithm has shown an improvement on the jet energy resolution better than 25\% compared to the standard CDF jet corrections.

2- Mass reconstruction in fully hadronic boson-boson decays 15 mn

Celso Martinez-Rivero CERN

The use of energy and momentum conservation in high energy multijet events allow to resconstruct kinematics and specially the masses of the underlying bosons. The kinematical information, together with the jet btag content, is used to build up optimal mass estimators for searches of new particles such as Higgs bosons. The treatment of jet pairings and final states with more than four jets is reviewed taking as an example analysis used actually in the DELPHI collaboration of LEP at CERN. In the DELPHI W mass determination similar techniques have been used and the results will be mentioned.

3-Energy Flow reconstruction in analyses involving 2-jet or 4-jet toplogies at LEP2 15 mn

Franco Ligabue Pisa

The impact of calorimeters on LEP2 physics is illustrated via the use of Energy Flow reconstruction in analyses involving 2-jet or 4-jet toplogies at LEP2 (especially WW physics). The interplay between calorimeter calibration and offline corrections applied at various stages of reconstruction and analysis is discussed, with a particular emphasis on systematic issues.

4-Jet energy scale calibration for the ATLAS detector at the LHC. Presentey 15 mn

R. Lefevre LPC Clermont

Precision measurements at the LHC, like the measurement of the top quark or SUSY particle masses, set the challenging goal of understanding the jet energy scale at the percent level. The jet energy reconstructed with the detector is affected both by experimental effects, like calorimeter non-compenstation or dead material, and physics effects like fragmentation, jet reconstruction in a finite region, etc. In-situ calibration methods with physics processes available at the LHC are investigated.

5-Reconstruction of narrow resonances decaying to hadronic jets 15 mn

P.Grenier CERN

Many physics studies foreseen at the LHC involve decays of narrow resonances into hadronic jets. A good mass resolution is needed for good identification and background rejection capabilities. Various channels involving dijets and multijets final states have been studied with full simulation of the ATLAS detector. Expected performances for the reconstruction of W -> jj, t ->bW(jj), H->bb or bbbb and H/A->tautau decays are presented.

6-Hadronic energy resolution Improvement in calorimeterswith fine transverse segmentation. 15 mn

A. Savine Arizona University

The fine transverse segmentation of the ATLAS Forward Calorimeter allows a significant improvement in the hadronic energy resolution by a weighting technique. The scheme was implemented on the 1998 'Module-0' beam test data analysis. It performs a 'software compensation', bringing the e/pi ratio closer to 1. Optimization of the cluster radius for the signal/noise ratio and coherent noise suppression are intrinsic features of this approach. The present report considers the single hadron optimization, but this technique is also applicable to the analysis of jets. In addition it has strong potential for pile-up background reduction on an event-by-event basis. We expect this scheme can be applied to other calorimeters with fine transverse segmentation.

7-The Calibration of the H1 Liquid Argon Calorimeter 15 mn

Cigdem Issever Dortmund University

The calibration of the Liquid-Argon-Calorimeter of the H1 Detector at HERA is described. Due to the high statistics sample of high Q2 neutral current events in the data taken in 1994-97 the uncertainties on electromagnetic and hadronic energy scales were reduced for the publication on neutral and charged current cross sections. For the calibration of the electromagnetic energy scale the calorimetrically measured energy of the scattered electron is compared to the energy predicted from the angles of the electron and the hadronic system. For the calibration of the hadronic energy scale the balance in transverse momentum between the hadronic system and the electron in neutral current events is exploited. After these calibrations an uncertainty of0:7

8- Measurement of Absolute Jet Energies in the H1 Liquid Argon Calorimeter 15 mn

Marie-Claude Jacquet LAL Orsay

The procedure used to correct the measured jet energy response of the H1 detector at HERA to the true energy is given. The energy and angular resolution of jets is optimised by combining measurements of charged particle tracks in the central tracking detectors with calorimeter energy deposits. The reconstructed jet energies are then corrected to the true energy scale by applying a correction function obtained from a full Monte Carlo simulation of the H1 detector. The results are checked by comparing with the correction fuction obtained from a sample of high Q 2 neutral current single jet events, where trans- verse energy of the jet is accurately predicted from the transverse energy of the scattered electron.

9- Precise Measurement of Jet Energies with the ZEUS Detector 15 mn

Mathew Wing Mc Gill University

A method to correct the jet transverse energy has been developed for the ZEUS detector which attains an uncertainty better than 3%. The procedure is based on a combination of tracking and calorimeter information that optimises the resolution of reconstructed kinematic variables. The selected calorimeter clusters and tracks are referred to as Energy Flow Objects (EFOs). The conservation of energy and momentum in neutral current deep inelastic e^+p scattering events is exploited to determine the required energy corrections by balancing the scattered positron with the hadronic final state. The method has been applied to data and simulated events independently. The corrected EFOs are used as input to a$k_T$-cluster jet algorithm to reconstruct the jets and to determine kinematic variables. In addition, the corrected EFOs allow an improved measurement of the internal structure of a jet.

10- Optimization of Jet Algorithm Inputs in the ZEUS Detector 15 mn

Steve Magill Argonne

Building on the studies of energy-scale and energy-correction of jets using the ZEUS Barrel Presampler (BPRE), jet algorithm inputs in the barrel region are constructed which optimize the total performance of the ZEUS detector. By using tracks from charged hadrons to replace matching calorimeter (hadronic) clusters, it is shown that the jet energy resolution is significantly improved for two reasons. First, the substition of some hadronic clusters with the information from their associated tracks takes advantage of the superior momentum resolution of the central tracking detector. Second, because the remaining clusters are predominantly electromagnetic and BPRE corrections to electromagnetic clusters contain a larger contribution to the total correction from dead material than the corresponding hadronic corrections, the sensitivity to dead material effects is significantly enhanced, leading to optimal jet energy resolutio