S. Grünendahl

A study of events containing at least four high transverse momentum jets and a search for double parton scattering (DPS) have been performed using data collected with the UA2 detector at the CERN pp Collider (√s=630 GeV). The results are in good agreement with leading order QCD calculations. A value of σDPS<0.82 nb at 95% confidence level (CL) is obtained for the DPS cross section.

The two-jet invariant mass spectrum as measured in the UA2 experiment is used to search for additional heavy vector bosons decaying to two-jets. The mass of an additional W boson that couples to fermions with a V+A form is constrained to be greater than 261 GeV to the 90% confidence level. A limit on the production cross section of additional W and Z bosons is given as a function of the boson mass. A limit on the production of excited quarks is also given as a function of the excited quark mass.

The W and Z bosons masses, mw and mz, are measured using saing samples of W→ev and Z→e+e− decays observed in pp collisions at √s=630 GeV. The ration is found to be mwmz=0.8813±0.0036 ± 0.0019. This gives a value sin2 θw = 0.2234 ± 0.0064 ± 0.0033, and in combination with precise mz measurements from LEP yields mw=80.35±0.33±0.17 GeV. This result is in good agreement with other experiments, and with the standard model for a top quark mass lighter than 250 GeV.

A search has been made with the upgraded UA2 experiment at the CERN pp Collider at s=630 GeV for multi-jet events with large transverse momentum imbalance in a data sample corresponding to an integrated luminosity of 7.4 pb−1. Under the assumption that the photino is the lightest stable supersymmetric (SUSY) particle, the data have been used to deduce lower limits in a minimal SUSY model for the squark (mq) and the gluino (mg) masses. The 90% CL bounds are mg> 74 GeV independent of mg, mg> 79 GeV independent of mg, and and m> 106 GeV for mq=mq=m.

The UA2 experiment has collected large samples of W and Z events during recent runs at the CERN pp Collider at s = 630 GeV. These samples have been used to perform precise measurements of the masses of the W and Z bosons. After a careful analysis of systematic errors, an improved result is obtained for the mass ratio mwmz. This provides a new value for the weak mixing parameter sin2θw. Furthermore, it can be combined with recent measurements of the Z mass from e+e− colliders to give an absolute measurement of the W mass, leading to the result mw=80.49±0.43 (stat) ± 0.24 (syst) GeV.

A study of the two-jet mass spectrum measured with the UA 2 calorimeter has revealed a signal from hadronic decays ofW andZ bosons above a large background. Production and decay properties of the signal have been measured. The combined production cross-section σ·B(W, Z → two jets) is 9.6±2.3 (stat.)±1.1 (syst.) nb, compared with an expectation of 5.8 nb calculated to order α s 2 . A limit on the production cross-section of additional heavy vector bosons decaying into two jets is given as a function of the boson mass.

The process pp→evγ+X is studied as √s=630 GeV. The observed signal is used to extract a direct measurement of the parameters κ and λ which define the magnetic dipole and electric quadrupole moments of the W boson and therefore the WWγ coupling. We find κ=1+2.6−2.2 and λ=0+1.7−1.8 and their 95% confidence limits −3.5<κ<5.9 and −3.6<λ<3.5. The results are model indepedent and in good agreement with the standard model values, κ=1 and λ=0.

The inclusive jet cross-section has been measured at the CERN pp Collider (s = 630 GeV) as a function of the jet transverse momentum (pT) and pseudorapidity (η) for pT values up to 180 GeV and for−2<η<2. The results are consistent with leading order QCD calculations, and a lower limit Λc>825 GeV (95% CL) is set on the quark compositeness scale Λc.

The large sample of W→eν events collected by the UA2 experiment at the CERN pp̄ collider between 1988 and 1990 has been used to determine the strong coupling constant αs. From a measurement of the ratio of the production rate of W events with one jet to that with no jets, αs has been extracted to second order in the MS̄ scheme: αs(M2w)=0.123±0.0.18(stat.)±0.017 (syst.).

The decays W → ev and Z → e+e− are studied in [ovbar|p]p collisions at √s=630 GeV. The products of production cross section and branching ratio are measured as σew=682±12±40 pb and σew=65.6±4.0±3.8 pb. The results are in good agreement with O(α2s) calculations of the production cross sections. Many systematic effects cancel in the ratio, R=10.4±0.70.6±0.3, which can be used to give an indirect measurement of the total width of the W boson: Γw=2.10±0.13±0.09 GeV. The width gives a limit on the top quark mass, mtop>53 GeV (95% CL), which is independent of the top decay mode.

A measurement of the inclusive cross-section for production of direct photons in p̄p collisions at a centre of mass energy of 630 GeV is presented as a function of the photon transverse momentum. The data correspond to a total integrated luminosity of 7.4 pb−1. The results support predictions from QCD theory.

The Do/ detector is being upgraded in preparation for the next collider run at Fermilab. The Central Fiber Tracker discussed in this report is a major component of the Do/ upgrade. The expected Tevatron luminosity of 2×1032 cm−2 sec−1, the 132ns bunch crossing time, and the Do/ detector constraints of a 2 Tesla solenoid and a 52 cm lever arm, make a scintillating fiber based tracker an optimal choice for the upgrade of the Do/ detector.

A measurement of the cross-sections for single and double prompt photon production in pp interactions at s = 630GeV is presented. The data sample corresponds to an integrated luminosity of 13.2 pb−1. The results are in good agreement with the predictions of perturbative QCD. The signal from double prompt photon production has a statistical significance of 4.3 standard deviations.

The upgraded UA 2 detector has collected data corresponding to a total integrated luminosity of 7.5 pb−1 from $$\bar pp$$ collisions at a centre of mass energy of 630 GeV during 1988 and 1989. A search has been performed for the production and decay of the top quark (t) or a member of a hypothetical fourth family (b′). No evidence has been found for such processes. Using the expected rates for production and decay branching ratios from the Standard Model, this implies that the top quark mass is greater than 69(71) GeV/c2, and that theb′ mass is greater than 54(57) GeV/c2, at 95(90)% confidence.

The upgraded DØ detector at the Tevatron collider will use about 100 000 pixels of Visible Light Photon Counters (VLPCs) readout for its scintillating fiber tracker and preshower detectors. VLPCs are solid state photodetectors that are operated at the temperature of a few degrees Kelvin, capable of detecting single photons. All VLPC chips were characterized in the presence of a 20 MHz background of photoelectrons. The acceptance rate was 87%. The operating bias ranges from 5.8 to 8.0 V, the gain from 20 000 to 60 000, and the threshold from 5 to 15 fC. All 8 pixels belonging to one chip have very similar efficiencies, thresholds and gains.

The process t→H+b, H+→τ+v, τ+→hadrons+v and its charge conjugate are investigated by seeking an excess in number of observed τ's beyond that expected from the standard model under the assumption of e-τ universality. No such excess is found and new regions of the mH−mt plane are excluded for B(H+→τv) = 0.5 and 1.0. In addition, the ratio of couplings of the τ and e to the W is precisely measured as gwτ/gwe = 1.02 ± 0.04(stat.)±0.04(syst.).

A search has been made for scalar leptoquark pair production with the upgraded UA2 detector at the CERN pp Collider at √s = 630 GeV, investigating decays of the leptoquark into a quark and either an electron or an electron neutrino. From an event sample corresponding to an integrated luminosity of 13 pb−1 a lower limit has been determined for the mass of first generation leptoquarks, yielding 67 GeV (95% CL) for a scalar leptoquark decaying with a 50% branching ratio into a quark and an electron.

A measurement of the gluon structure fusion using direct photon events observed with the UA2 detector in pp collisions at √s=630 GeV is presented. The x-range covered by this analysis is between 0.049 and 0.207 and the Q2 range is between 280 GeV2 and 3670 GeV2. The data sample corresponds to an integrated luminosity of 7.14 pb−1. The results are found to be in good agreement with the gluon distributions measured in deep inelastic scattering experiments extrapolated to the UA2 Q2 values.

The DØ preshower detector consists of scintillator strips with embedded wavelength-shifting fibers, and a readout using Visible Light Photon Counters. The response to minimum ionizing particles has been tested with cosmic-ray muons. We report results on the gain calibration and light-yield distributions. The spatial resolution is investigated taking into account the light sharing between strips, the effects of multiple scattering and various systematic uncertainties. The detection efficiency and noise contamination are also investigated.

An overview of the system architecture and algorithms used for the DO Central Track Trigger (CTT) in the Run 2 of the Fermilab Tevatron Proton-Antiproton Collider is presented. This system uses information from the newly commissioned Central Fiber Tracker and Preshower Detectors to generate Level 1 trigger decisions. It also generates lists of seed tracks and preshower clusters that are sent to the Level 1 Muon Trigger, L2 Silicon Track Trigger, and Central and Forward Preshower Level 2 preprocessors. The system consists of modular boards which utilize field-programmable gate arrays (FPGAs) to implement trigger algorithms. The system delivers trigger decisions every 132 ns, based on input data flowing at a maximum sustained rate of 475 gigabits per second. The first results of trigger efficiency studies are presented.

The ratio of branching fractions of theW decaying to τ ande leptons is measured using $$\bar pp$$ collisions at $$\sqrt s = 630$$ GeV. The ratio of the electroweak charged current couplings to theW is then determined to beg /g =0.997±0.056 (stat.)±0.042 (syst.). The decay modeZ→τ+→τ+ is observed and also found to be consistent withe-τ universality.

Characterization of a large number of visible light photon counters (VLPC) is an integral part of the scintillating fiber system test for the DO upgrade, currently underway at Fermilab. We report results from our investigation of 4200 channels of HISTE IV VLPC's, for use in a cosmic ray test. We have studied the dependence of critical device characteristics like quantum efficiency, gain, and noise as a function of operating temperature and VLPC bias voltage, and the variation of these characteristics over the large sample. We also discuss the general operation of the devices and the problems encountered during the characterization.

The performance of a large scale scintillating fiber tracker with VLPC readout has been studied in a cosmic-ray test. Approximately 9.6 photoelectrons per single layer per trigger were detected at a VLPC bias voltage of 6.5V. The doublet efficiency was nearly 100% at a 0.1% noise level and a position resolution of about 140μm was measured. We also studied the relationship between VLPC performance and VLPC bias voltage by measuring single fiber efficiency as a function of VLPC bias in the range 6.2V to 7.OV at a fixed temperature of 6.5 °K. We observed no significant variation in VLPC performance within this bias range.

We report on results of a cosmic ray test of a scintillating fiber tracker using Visible Light Photon Counter (VLPC) readout. Two different detector configurations have been constructed and operated, the first with a total of 3072 channels and the second with 1,785 channels. The 3072 channel system is a prototype for the DO detector tracking upgrade and represents a configuration that is similar to that in the final detector. The second, smaller test was specifically designed to study the position resolution capabilities of the fiber tracker. A description of the cosmic ray test including trigger, fiber configuration, undoped lightguides, VLPC cassettes and cryogenics, and calibration system is given. Final results from the 3072 channel test will be presented, including measurements of resolution, light yield per minimum ionizing particle, singlet and doublet efficiency, and long-term stability. Resolution results from the second, 1785 channel test will be compared to the predicted resolution from Monte Carlo studies.

A fast tracking trigger system based on a new scintillating fiber tracker is being built for the upgraded DO detector for the Collider Run II at Fermilab. This fiber tracker trigger provides a first level hardware trigger, supplies track seeds for the first level muon trigger and for the second level trigger. The physics requirements and the corresponding algorithms for the hardware trigger will be described. Particularly, PLD (programmable logical device) chips are used to implement our trigger algorithms to achieve pattern recognition from scintillating fiber hits and to format that information for delivery to other trigger systems. Detector trigger efficiency studies will also be presented.

We report on the digital front end board for the D0 Upgrade tracking trigger. Each board receives discriminated signals from 1/40th of the fiber tracker detector scintillating fiber channels over 10 low voltage differential signal, 1 vds, links each capable of 186 Mbytes per second. This data is shared between two daughter cards containing FPLD chips where eight layer tracks, and single layer preshower clusters are found. On the mother board the tracks and clusters are matched to produce a list for a level 1 trigger of tracks, electrons and photons, in Pt ranges and with isolation information. The board also contains FIFO's which hold 32 crossings (224 clock cycles). The FIFO's are read out to a level 2 trigger when a level 1 accept is received.

A search for supersymmetric decays of the Z boson into a pair of scalar electrons or winos (partners of the electron and W boson) has been made with the upgraded UA2 experiment at the CERN pp collider at s= 630GeV. The analysis of the sample of electron pairs, corresponding to an integrated luminosity of 7.4 pb−1, shows no evidence for such exotic decays. The 90% confidence level lower mass limits obtained exclude selectron masses up to e40 GeV/c2 in the case of a light photino, and wino masses up to 45 GeV/c2 in the case of a light scalar neutrino.

The general purpose DO collider detector, located at Fermi National Accelerator Laboratory, is operated in the high luminosity (L=2/spl times/10/sup 32/ cm/sup -2//spl middot/s/sup -1/) and high-collision-rate environment (396 ns between beam crossings) of the upgraded Tevatron proton anti-proton accelerator. DO uses a three-tiered trigger system to select events for offline storage and analysis. This paper describes the architecture and performance of the DO central track trigger (CTT) system based on the new central fiber tracker, central preshower and forward preshower detectors, with emphasis on the interface to and integration with the second tier L2 Trigger system.

Results are given on a search for the decay W±→π±γ with the UA2 detector in pp collisions at √s=630 GeV. No signal for such a process is observed and upper limits on the ration R=Γ(W±→π±γ)/Γ(W±→e±v)<4.9×10−3 and on the branching ratio BR(W±→π±γ)<5.4×10−4 are derived at 95% confidence level.

The DØ experiment at the Fermilab pp¯ Tevatron collider (Batavia, IL, USA) has undergone significant upgrades in anticipation of high luminosity running conditions. As part of the upgrade, the capabilities of the Central Track Trigger (CTT) to make trigger decisions based on hit patterns in the Central Fiber Tracker (CFT) have been much improved. We report on the implementation, commissioning and operation of the upgraded CTT system.

An overview of the DO Central Track Trigger (CTT) for the Tevatron Run 2 program is presented. This newly commissioned system uses information from the DO Central Fiber Tracker and Preshower Detectors to generate trigger information for the first level of the three-tiered DO Trigger. The system delivers tracking detector trigger decisions every 132 ns, based on input data flowing at a rate of 475 Gbit per second. Initial results indicate excellent performance of the CTT. First studies of efficiency and trigger performance of the CTT are presented.

A large scale scintillating fiber tracker using visible light photon counter (VLPC) readout was built as a prototype for the upgraded DO central tracker. This prototype has been under test at Fermilab for six months using cosmic rays. A description of the components of the tracker including the photodetector, fibers, lightguides, ribbons, and DAQ is given. Preliminary results indicate a mean detected yield of about 10 photoelectrons per fiber, position resolution of 140 /spl mu/m for a fiber doublet, and a doublet efficiency greater than 99%.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A tracking detector using scintillating fibers is being developed for the D0 collaboration at Fermilab. The scintillating fibers will be coupled to clear fibers that will transport light to the photodetectors. We have developed connectors which couple the two types of fibers. The first 128-channel prototypes were machined using Delrin plastic to have v-shaped grooves. Fibers were glued into the grooves and their ends were finished with diamond fly-cut tools. Mating connectors were optically coupled by optical grease. Using a green light-emitting diode and a silicon photodiode, we measured average light transmission between 97% and 99%. Later versions of the v-groove connectors were made of acrylonitrile-butadiene-styrene plastic by injection molding.

The DOslash experiment was upgraded in spring 2006 to harvest the full physics potential of the Tevatron accelerator at Fermi National Accelerator Laboratory, Batavia, Illinois, USA. It is expected that the peak luminosity delivered by the accelerator will increase to over 300 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . One of the upgraded systems is the central track trigger (CTT). The CTT uses the central fiber tracker (CFT) and preshower detectors to identify central tracks with p <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> > 1.5 GeV at the first trigger level. Track candidates are formed by comparing fiber hits to predefined track equations. In order to minimize latency, this operation is performed in parallel using combinatorial logic implemented in FPGAs. Limited hardware resources prevented the use of the full granularity of the CFT. This leads to a high fake track rate as the occupancy increases. In order to mitigate the problem, new track-finding hardware was designed and commissioned. We report on the upgrade and the improved performance of the CTT system.

The DO level 1 tracking trigger uses data from the scintillating fiber tracker, the central and forward preshower detectors, the muon system and the calorimeter. Tracks are found in the scintillating fiber tracker with transverse momentum greater than 1.5 GeV/c. The tracks are matched with hits in the central preshower detector and the muon system for electron and muon tagging. Preshower dusters are also used for identifying photon candidates. These multi detector triggers are then sent to the level 1 Trigger Framework where they are further combined with the calorimeter to create the final level 1 trigger. This paper presents an overview of the level trigger system with emphasis on the use of large programmable logic devices (PLD's) in an extensible system architecture that allows complex, multi detector triggers.

Recent results on jet physics from the DØ experiment at the Fermilab Tevatron Collider are reported. Data taken from 1994 – 1995 in protonantiproton collisions at √s=1.8 GeV have been analysed; preliminary measurements of the central inclusive jet cross section, the dijet mass spectrum, and the dijet angular distribution are compared with next-to-leading order QCD theory.

The D0 level 1 tracking trigger uses data from the scintillating fiber tracker, the central and forward preshower detectors, the muon system and the calorimeter. Tracks are found in the scintillating fiber tracker with transverse momentum greater than 1.5 GeV/c. The tracks are then sent to the central preshower detector for electron tagging and to the muon system for muon tagging. Preshower clusters are also used for identifying photon candidates. These multi detector triggers are then sent to the level 1 Trigger Framework where they are further combined with the calorimeter to create the final level 1 trigger. This paper presents an overview of the level 1 trigger system with emphasis on the use of large programmable logic devices (PLD�s) in an extensible system architecture that allows complex, multi detector triggers.