Neutral Hadrons Research Articles

Resonance Search and Particle Production at HERA

Searches for exotic strange baryon resonances decaying into K s 0 p , K s 0 p ¯ , and Ξ π were performed by the H1 collaboration in deep inelastic scattering (DIS) at HERA. Upper limits are given for the production rates. Deuterons and anti-deuterons were observed by the ZEUS collaboration and their production rates in DIS were compared to those of p ( p ¯ ) . Strange neutral hadrons were produced and cross-sections, baryon to meson ratios and relative yields of strange to light mesons were measured by ZEUS. Excited charm non-strange and strange mesons were produced and the fraction of charm quark fragmenting to these mesons was measured by ZEUS.

LOW pT HADRONIC PHYSICS WITH CMS

The pixel detector of CMS can be used to reconstruct very low pT charged particles down to about 0.1 GeV /c. This can be achieved with high efficiency, good resolution and a negligible fake rate for elementary collisions. In the case of central PbPb collisions the fake rate can be kept low for pT > 0.4 GeV /c. In addition, the detector can be employed for identification of neutral hadrons (V0s) and converted photons.

Measurement of K0 S, Λ and Λ̄ production at HERA

The production of the neutral strange hadrons K0 S, Λ and Λ̄ has been measured in ep collisions at HERA using the ZEUS detector. Cross sections, baryon-to-meson ratios, relative yields of strange and charged light hadrons, Λ (Λ̄) asymmetry and polarization have been measured in three kinematic regions: Q2 > 25 GeV2; 5 < Q2 < 25 GeV2; and in photoproduction (Q2≃0). In photoproduction the presence of two hadronic jets, each with at least 5 GeV transverse energy, was required. The measurements agree in general with Monte Carlo models and are consistent with measurements made at e+e- colliders, except for an enhancement of baryon relative to meson production in photoproduction.

Measurement of azimuthal asymmetries in neutral current deep inelastic scattering at HERA

The distribution of the azimuthal angle of charged and neutral hadrons relative to the lepton plane has been studied for neutral current deep inelastic $ep$ scattering using an integrated luminosity of 45 pb-1 taken with the ZEUS detector at HERA. The measurements were made in the hadronic centre-of-mass system. The analysis exploits the energy-flow method, which allows the measurement to be made over a larger range of pseudorapidity compared to previous results. The dependence of the moments of the azimuthal distributions on the pseudorapidity and minimum transverse energy of the final-state hadrons are presented. Although the predictions from next-to-leading-order QCD describe the data better than do the Monte Carlo models incorporating leading-logarithm parton showers, they still fail to describe the magnitude of the asymmetries. This suggests that higher-order calculations may be necessary to describe these data.

Particle production at forward rapidity in d+Au and Au+Au collisions in the STAR experiment at RHIC

We present the recent results from the STAR experiment on charged and neutral particle measurements at the forward rapidity in d+Au collisions at s NN = 200 GeV and Au+Au collisions at s NN = 62.4 GeV . The nuclear modification factor for charged and neutral hadrons in d+Au collisions are presented. Measurements of Λ and Λ ¯ production at forward rapidity and the variation of net baryon density as a function of collision centrality are discussed. We have also studied the limiting fragmentation of photons and charged particles in Au+Au collisions. The photons and charged particles separately follow the energy independent limiting fragmentation behaviour. However they have been observed to follow a different centrality dependence of limiting fragmentation.

Electric polarizability of neutral hadrons from lattice QCD

By simulating a uniform electric field on a lattice and measuring the change in the rest mass, we calculate the electric polarizability of neutral mesons and baryons using the methods of quenched lattice QCD. Specifically, we measure the electric polarizability coefficient from the quadratic response to the electric field for 10 particles: the vector mesons ${\ensuremath{\rho}}^{0}$ and ${K}^{*0}$; the octet baryons n, ${\ensuremath{\Sigma}}^{0}$, ${\ensuremath{\Lambda}}^{0}$, and ${\ensuremath{\Xi}}^{0}$; and the decuplet baryons ${\ensuremath{\Delta}}^{0}$, ${\ensuremath{\Sigma}}^{*0}$, and ${\ensuremath{\Xi}}^{*0}$. Independent calculations using two fermion actions were done for consistency and comparison purposes. One calculation uses Wilson fermions with a lattice spacing of $a=0.10$ fm. The other uses tadpole-improved L\"uscher-Weisz gauge fields and clover quark action with a lattice spacing $a=0.17$ fm. Our results for neutron electric polarizability are compared to experiment.

Formation of dense partonic matter in relativistic nucleus–nucleus collisions at RHIC: Experimental evaluation by the PHENIX Collaboration

Extensive experimental data from high-energy nucleus-nucleus collisions were recorded using the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The comprehensive set of measurements from the first three years of RHIC operation includes charged particle multiplicities, transverse energy, yield ratios and spectra of identified hadrons in a wide range of transverse momenta ( p T ), elliptic flow, two-particle correlations, nonstatistical fluctuations, and suppression of particle production at high p T . The results are examined with an emphasis on implications for the formation of a new state of dense matter. We find that the state of matter created at RHIC cannot be described in terms of ordinary color neutral hadrons.

Neutral pions with large transverse momentum in d+Au and Au+Au collisions

Measurements of transverse-momentum (pT) spectra of neutral pions in Au+Au and d+Au collisions at and 62.4 GeV by the PHENIX experiment at RHIC are presented. The spectra are compared to p+p reference spectra at the same . In central Au+Au collisions at a factor 4–5 suppression for neutral pions and charged hadrons with pT > 5 GeV/c is found relative to the p+p reference scaled by the nuclear overlap function ⟨TAB⟩. In contrast, such a suppression of high-pT particles is absent in d+Au collisions independent of the centrality of the collision. To study the dependence of the suppression Au+Au collisions at and 62.4 GeV are compared.

Inclusive production of single hadrons with finite transverse momenta in deep-inelastic scattering at next-to-leading order

We calculate the cross section for the inclusive production of single hadrons with finite transverse momenta in deep-inelastic scattering at next-to-leading order (NLO), i.e., through O ( α s 2 ) , in the parton model of QCD endowed with non-perturbative parton distribution functions (PDFs) and fragmentation functions (FFs). The NLO correction is found to produce a sizeable enhancement in cross section, of up to one order of magnitude, bringing the theoretical prediction to good agreement with recent measurements for neutral pions and charged hadrons at DESY HERA. This provides a useful test for the universality and the scaling violations of the FFs predicted by the factorization theorem.

BaBar forward endcap upgrade

The muon and neutral hadron detector (instrumented flux return or IFR) in the forward endcap of the BaBar detector at SLAC was upgraded by the installation of a new generation of resistive plate chambers (RPCs) and by increasing the absorber. The chamber replacement was made necessary by the rapid aging and efficiency loss of the original BaBar RPCs. Based on our experience with those original RPCs and 24 RPCs with thinner linseed oil treatments, improvements in the design, construction, and testing of the new generation RPCs were implemented and are described in detail.

BaBar forward endcap RPCs

The BaBar detector has operated over 2000m2 of resistive plates chambers (RPCs) as muon and neutral hadron detectors since 1999. Most of the RPCs of the original production underwent a significant efficiency loss and many are now completely inefficient. During the summer 2002 new RPCs from a recent production were therefore installed to replace the old chambers in the forward endcap. The experience of the first 8 months of operation is described here.

Results on high particle production from the PHENIX experiment at RHIC

Transverse momentum ( p T ) spectra of neutral pions and charged hadrons measured in Au+Au and d+Au collisions at √s NN = 200GeV by the PHENIX experiment at RHIC are compared to p+p reference spectra at the same √ s NN. In central Au+Au collisions a factor 4 – 5 suppression for neutral pions and charged hadrons with p T > 5GeV/c is found relative to the p+p reference scaled by the nuclear overlap function˚ T AB «. In contrast, such a suppression of high p T particles is absent in d+Au collisions.

Results on high p T particle production from the PHENIX experiment at RHIC

Transverse momentum ( p T ) spectra of neutral pions and charged hadrons measured in Au+Au and d+Au collisions at √s NN = 200GeV by the PHENIX experiment at RHIC are compared to p+p reference spectra at the same √ s NN. In central Au+Au collisions a factor 4 – 5 suppression for neutral pions and charged hadrons with p T > 5GeV/c is found relative to the p+p reference scaled by the nuclear overlap function˚ T AB«. In contrast, such a suppression of high p T particles is absent in d+Au collisions.

Performances of RPCs in the BaBar experiment

The BaBar experiment uses a big system based on RPC detectors to discriminate muons from pions and to identify neutral hadrons. About 2000 m 2 of RPC chambers have been working at SLAC since the end of 1998. We report on the performances of the RPC chambers focusing on new problems discovered in the RPC behaviour. These problems started very soon after the installation of the chambers on the detector when the high-ambient temperature triggered an increase of dark currents inside the chambers and a reduction of the efficiency. Careful analysis of the BaBar data and dedicated R&D efforts in the laboratory have helped to identify the main source of the trouble in the linseed oil varnish on the bakelite electrodes.

High pT measurements from PHENIX

We present recent high transverse momentum measurements by the PHENIX experiment for Au+Au and p+p collisions at S N N = 200 GeV at the Relativistic Heavy Ion Collider (RHIC). We show particle spectra for neutral pions and charged hadrons, define and show the nuclear modification factor, and discuss particle composition. By means of the nuclear modification factor, we observe a suppression factor of 5–6 for neutral pions and 3–4 for charged hadrons in central collisions at high p T . We find that the ratio of π 0 to ( h + + h −)/2 remains nearly constant at ∼ 0.5 for p T = 2 − 9GeV/c. Finally we present strong evidence for the observation of jets in Au+Au collisions.

The BaBar instrumented flux return performance: lessons learned

Abstract The BaBar Collaboration has operated an instrumented flux return (IFR) system covering over 2000 m 2 with resistive plate chambers (RPCs) for nearly 3 years. The chambers are constructed of bakelite sheets separated by 2 mm . The inner surfaces are coated with linseed oil. This system provides muon and neutral hadron detection for BaBar. Installation and commissioning were completed in 1998, and operation began mid-year 1999. While initial performance of the system reached design, over time, a significant fraction of the RPCs demonstrated significant degradation, marked by increased currents and reduced efficiency. A coordinated effort of investigations have identified many of the elements responsible for the degradation. This article presents our current understanding of the aging process of the BaBar RPCs along with the action plan to combat performance degradation of the IFR system.

Resistive plate chamber performance in the BaBar IFR system

The BaBar Collaboration has operated a system covering over 2000 m/sup 2/ with resistive plate chambers for nearly three years. The chambers are constructed of bakelite sheets separated by 2 mm. The inner surfaces are coated with linseed oil. This system provides muon and neutral hadron detection for BaBar. Installation and commissioning were completed in 1998, and operation began mid-1999. While initial performance of the system reached design, over time, a significant fraction of the resistive plate chambers demonstrated significant degradation, marked by increased currents and reduced efficiency. A coordinated investigative effort has identified many of the elements responsible for the degradation.

The RPC-based IFR system at BaBar experiment: preliminary results

The IFR system is a RPC-based detector used to identify muons and neutral hadrons in the BaBar experiment at PEP II machine in SLAC. The RPC system can be used to reconstruct the trajectory of muons, pions and neutral hadrons interacting in the iron of the IFR. The different range and hit pattern allow to discriminate different particles crossing the IFR. An overview of the system design and the preliminary results on the IFR performances are reported.

Radiation hard silicon detectors—developments by the RD48 (ROSE) collaboration

The RD48 (ROSE) collaboration has succeeded to develop radiation hard silicon detectors, capable to withstand the harsh hadron fluences in the tracking areas of LHC experiments. In order to reach this objective, a defect engineering technique was employed resulting in the development of Oxygen enriched FZ silicon (DOFZ), ensuring the necessary O-enrichment of about 2×10 17 O/cm 3 in the normal detector processing. Systematic investigations have been carried out on various standard and oxygenated silicon diodes with neutron, proton and pion irradiation up to a fluence of 5×10 14 cm −2 (1 MeV neutron equivalent). Major focus is on the changes of the effective doping concentration (depletion voltage). Other aspects (reverse current, charge collection) are covered too and the appreciable benefits obtained with DOFZ silicon in radiation tolerance for charged hadrons are outlined. The results are reliably described by the “Hamburg model”: its application to LHC experimental conditions is shown, demonstrating the superiority of the defect engineered silicon. Microscopic aspects of damage effects are also discussed, including differences due to charged and neutral hadron irradiation.

Overview of the BTeV program

BTeV is a dedicated experiment to carry out precision studies of CP violation, mixing, and rare decays of beauty and charm hadrons in the forward direction at the Fermilab Tevatron Collider. The detector is designed to have excellent particle identification for charged and neutral hadrons and photons, excellent mass and decay time resolutions, and a trigger system capable of selecting both hadronic and leptonic final states using detached vertices at the lowest level of the trigger. Some specific goals of the experiment include precision measurements of the CKM angles γ using B s→D s ±K ∓ (and other methods), α using B 0→ρπ, and the important but small CP asymmetry in the final state B s→ψη′. We discuss the performance of BTeV for the first of these methods after giving an overview of the detector.