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2 Progress report

2.1 The D0 Experiment The D0 detector had its first data run in the period May 1992 till June 1993. The first two thirds of the run period were characterized by low luminosity and frequent machine development periods. The luminosity gradually climbed, and the machine ultimately delivered 31 pb_1 to the experiment. The detector performed admirably well, and data analysis tracked data taking closely. The overall D0 efficiency was 54% and 16.7 pb_1 of data were collected; due to high backgrounds during Main Ring injection and transition, and beam gas interactions in the MR pipe that intersects our calorimeter, triggers in D0 were vetoed for about 29% of the store time; data acquisition busy (7%), experiment down time (5%), and run startup overhead (5%) added another 17% to the inefficiency. Many cycles of reconstruction software upgrade were done as experience with real data was gained, bugs were corrected, and new data corrections were added. First results were presented at the Spring 1993 APS meeting, the Summer conferences, and at the Fall 1993 pp symposium in Tsukuba. Several papers (See Attached [LeptoQuark PRL, RapGap PRL, Top PRL]) have appeared in print, a lepto-quark search, a rapidity-gap study, and. a lower mass limit on the Standard Model top quark where we also present a spectacular event that has laxge $y, a high energy electron and a high momentum muon, both isolated, and two sizable jets. When interpreted as a it event, a top mass around 145 GeV (with a large 30 GeV error) is obtained. The current run began in December 1993, and machine efficiency started to improve only recently. At this date about 5 pb-1 has been collected.

2.1.1 The D0 detector, Calibrations, Maintenance and Data Taking Our group is active in many areas. We are contributing to the running and maintenance of the detector: Guida leads the calorimeter group, responsible for all aspects of the operation of the calorimeter. Guida is participating in an effort to reduce the MR veto time by making it an active veto. She has responsibility for maintaining the calorimeter online database, and its associated software. We are contributing to online software for the trigger: Claes, Rajagopalan, and H. Li have been contributing to online hit finding, hit block size compression (tracking information represents about 80% of the raw event data), fast tracking, and online vertex finding with the Stony Brook central drift chamber (CDC). Claes is responsible for the maintenance, documentation, and simulation of all Level 2 trigger code. Trigger simulators are of utmost importance in estimating efficiencies and background rejec• tion for a large variety of physics processes. Over the course of Run la, the trigger code evolved through more than two dozen versions, and for the current run we are already at the eighth version of the Level 2 code. All versions, together with parameters, constants, and related simulation code have to be maintained as long as the data will be used. Special trigger runs, coordinated and analyzed by Claes, ensure proper operation. We are involved in the online calibration. Guida has cross-calibrated the online pulser system. Yanagisawa is working on a program to measure calorimeter pedestals from "calibration events" taken in between collider bunches, and compares this pedestal data with pedestal data from special MASTER -••••-".>; i~CN OF TH;3 DOCUMENT 18 UNLfMfTS DISCLAIMER

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. runs with no bunches in the machine, to check for luminosity dependent effects. Rajagopalan, working on the online calibration, has produced effective tools to allow the reconstruction packages quick access to compressed run calibration data. Thompson, until his graduation, had responsibility for the CDC built at Stony Brook by the NSF and DOE supported groups. Feher, with Stony Brook support, constructed the scintillating fiber calibration detector that is used for tQ and drift velocity calibration of the CDC and covers a 17° section of the azimuth. This detector uses a single Multi-anode PMT for readout and time- multiplexes its signals into sixteen spare channels of the D0 FADC data acquisition system. In addition, Feher was responsible for the determination of the tracking alignment parameters with minimum bias events. H. Li has been involved with the offline reconstruction passes of all the data. This was a major effort, as the wealth of data, and its tremendous size (3000 8mm raw data tapes), make this a bookkeeping nightmare. The latest reconstruction passes were done on UNIX clusters, which entailed porting the code developed under VAX CMS to the IBM and Silicon Graphics Unix environment, and the development of monitoring and bookkeeping tools.

2.1.2 Search for the Top Quark Although the discovery of the top quark was recently announced at Fermilab, the evidence for it in the data is still marginal. CDF has reported a 2.8 a effect in the cross section of several decay channels combined, while D0 sees no statistically significant effect. In Figure 1 the it cross sections measured by D0 are shown as function of mtop- The D0 95% CL contour is indicated as well, together with the recently announced CDF measurement (scaled to the total pp cross section at 1.8 TeV used by D0), and the NNLO QCD calculation by Laenen et ai.. However, D0 has a few spectacular candidates. We are strongly involved in the top analysis. Two graduate students recently defended their theses on searches for the top quark in the '92-'93 data. Both students have accepted postdoctoral positions in High Energy Physics. Cochran was instrumental in calculating the backgrounds in the e/x decay mode of the it pair. His thesis, "Search for Truth in the ep channel at D0" (Dec 1993), was the main ingredient in our top publication in PRL that establishes a lower limit of 131 GeV on the top mass at 95% CL. Thompson graduated in February 1994 with a thesis titled "Search for the Top Quark in the Muon + Jets Channel at D0". This work contributed to raise the top mass limit significantly by 8 GeV compared to the limit derived from the other top decay modes. In the fi + jets channel two events were found with a calculated background of 0.5 ± 0.3 events. Both events are spectacular and a it mass fit yields a miop value in the neighborhood of 170 GeV. Work is continuing on lepton plus jets with a /z-tag (a soft muon close to a jet). One of these events, an event with a /n-tag is shown in Figure 2. The threefold increase in statistics expected from the current run should settle the question of the top's existence in the 160-190 GeV mass range. Reports of recent results from SLC are somewhat in conflict with a LEP plus SM prediction of the top mass, raising the lower top mass limit above 200 GeV. It is clear that only a direct measurement with better statistics at the FNAL collider will be decisive. Feher is investigating multivariate approaches to the search for it production in the all-jets

3 DJ Preliminary Top Limit and Cross Section - 50

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110 120 130 140 150 160 170 180 190 200 Top Mass (GeV/cJ) Figure 1: D0 Preliminary limit on the it cross section. The single measurement labeled "CDF" is the recent CDF measurement scaled to use the same total pp cross section as D0. decay channel. Topological variables, like the generalized sphericity tensor, may improve QCD background reduction. An online multi-jet trigger is in development for run lb which aims to improve signal efficiency and reduce background rates. The current multi-jet filter selects events with 5 and more jets. Efficiency and rejection power of this filter are shown in Figure 3.a. The cross section as a function of the ET of the 5th jet for the data sample (dark boxes) and for a simulated it {mtop = 150 GeV) sample (open boxes) is shown. This filter is more than 80% efficient at -ErQets) > 10 GeV, where the signal-to-noise ratio is about 7 X 10-4. A sum of jet transverse energy, ^,\ET\, requirement offers additional discrimination power (a factor two for a threshold at 125 GeV) without complicating the triggering logic. Figure 3.b shows the cross section for events passing the existing multi-jet filter as function of the J2 \ET\ threshold. Figure 3.c shows the signal efficiency vs. background cross section for various multi-jet ET thresholds including a J2 \ET\ threshold requirement.

2.1.3 Precision Determination of the W Mass

The physics of W's and Z's is at the heart of the Collider program. The precision measurement of the W mass is an important goal of D0 because it will, together with a good mass determination of the top, limit the mass range available to the Higgs boson and constrain possible extensions of the Standard Model. The identification of W's and Z's in the electron and muon channels is crucial for the top search in leptonic channels. Looking for energetic isolated direct photons produced together with the W or Z tells us about the strength of the trilinear vector boson vertices WW7, ZZ-j and Z77 that are all precisely predicted in the SM, but are allowed "anomalous" values in various CP conserving and CP-non-conserving extensions. These trilinear couplings are directly related to the W magnetic

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Figure 3: Simulation results for the online Top to Multi-jets filter together with data cross section for thresholds of two different selection variables: a) the E? of the 5"* jet, and in b) the ^ \Ej\ (Ht) of all jets. In c) both variables are compared.

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi• bility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer• ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom• mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. dipole and electric quadrupole moments. The Z —y e+e~ mode, given the very precise LEP determination, serves as an accurate EM calibration gauge for the W mass determination. The tails of the Z mass and the W transverse mass distributions are examined to set limits on recurrences of the W and Z bosons that are needed in some extensions of the SM (as the left-right symmetric model). These topics, and many more, are studied in the Electroweak Physics Analysis group of which Bijssenbeek was co-convener till April 1994. Rajagopalan and others are in the process of analysing the data collected over the past year. The W boson is generated at various masses and smeared using a fast simulation program. A maximum likelihood fit of the transverse ev mass spectrum yields the W mass. A very detailed and complete understanding of the detector effects is required to allow us to satisfactorily model the transverse W mass and resolution. With 15 pb~\ we have collected 10,346 W ->• ev and 782 Z -> ee events at D0. The pre• liminary W mass measurement using only central electrons, is 79.86 ± Q.l6(stat) ± 0.20(syst) ± 0.31(EMscale) GeV and has been reported at recent conferences. The final transverse mass fit is shown in Figure 4. This is to be compared to the CDF W mass measurement, reported at Tsukuba, of 80.47 ± 0.l5(stat) ± 0.25{syst) GeV for the electron channel.

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The D0 systematic errors come primarily from our understanding of the detector resolution effects modeled in the toy monte carlo and the limits of the theoretical understanding of the W boson production. We use our Z sample to set the overall energy scale using the LEP Z mass of

7 91.187 ± 0.007 GeV. Our energy scale error is thus tied directly to the statistics of the Z boson production and will improve with our next run. We are also exploiting low mass resonance states of 7T° and J/fj} to reduce the scale error. Rijssenbeek has been studying the possibility of comparing the W and Z transverse mass dis• tributions directly and thereby extracting the W mass without many of the various systematics that plague W transverse mass and Z mass differently. Using the Z, and "discarding" each elec• tron in turn, one determines the Z transverse mass which is then subject to very much the same systematics as the W transverse mass. The two transverse masses that can be reconstructed from Z —> e+e_ are mostly uncorrelated because of the large smearing effect of the underlying event in the transverse mass determination. It turns out that many of the systematics in the ratio cancel, because of the very similar production characteristics of W's and Z's. The effect of the trigger is under study and appears to be minimal. The method is limited by Z-statistics and will need around 50 pb_1 of data to become competitive with the current method that leads to errors of 400 MeV (stat + syst -f scale) on the W mass. The goal for D0 is to reduce the error on the W mass to less than about 100 MeV before LEP II turns on.

2.1.4 r Physics H. Li, Yanagisawa, and Jung have studied the data for a W —» rv signal. The search has been difficult because an efficient and stable r-trigger only became operational late in the run. Eventually about 1.31 pb_1of data were collected with a working -r-trigger and this data was used to sift out the r in its hadronic decay modes from the large QCD backgrounds. The result,

2.1.5 New Phenomena

Squark and Gluino Search Supersymmetry cures the quadratic mass divergencies in the SM scalar Higgs field and thus avoids the "fine tuning" problem that occurs in all orders. The MSSM model used is inspired by supergravity, and adds a second Higgs doublet to the scalar sector. The model is preferred by theorists because it allows the least freedom in the choice of model parameters, and limits us to tan/3 (relating the two vacuum expectation values of the Higgs doublets), the Higgsino mixing parameter /x (determining the mixing in the various gaugino states), and the masses of the lightest squark and gluino. The mass of the lightest neutralino (LSP), which is stable, is determined by the gluino mass to roughly one sixth of the gluino mass. The charged Higgs mass is presumably large and set to 500 GeV. Due to the mixing in the gaugino sector, the squarks and gluinos decay preferentially via multiple intermediate states with gauginos, to the final state in which the stable LSP is emitted. Paterno has put much effort into algorithms to bring the D0 $j measurement to its full potential. Large $? is the main tool to lift a possible SUSY signal above the QCD background. The SUSY search, by its reliance on i?-^ collects all the extremely rare problems that occur:

8 isolated noisy cells, baseline subtraction units that went bad, non-vetoed Main Ring depositions, and mis-identified interaction vertices, all have to be detected, and corrected or removed from the sample. Patemo has just defended his thesis this May. His topic is "A Search for Squarks and Gluinos in pp Collisions at y/s = 1.8 TeV with the D0 Detector". The data sample is from 15 pb_1 of

events with three jets and $T.

The final sample contains 14 events with $T > 75 GeV, and is used to calculated lower mass limits on squarks and gluinos. Paterno puts a lower limit on Minimal Supersymmetric gluinos of

157 GeV (at 95% CL) and limits squarks, for the scenario m,- = mg, to above 218 GeV. Both limits are a substantial improvement from previously published limits, and a paper by Jung and Paterno is in preparation. The excluded region in m, vs. mg space is indicated in Figure 5.

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S-toy Search

Claes and Jung begun a search for the light supersymmetric scalar-top particle. Most squark studies assume all flavors to be effectively mass-degenerate. But given that top appears to be so much heavier than all other quark flavors, Yukawa interactions (insubstantial for the first two quark generations) should drive s-top eigenmasses considerably lower than all the others. It is conceivable

9 that only one squark (the light s-top £[) is within the reach of the TeVatron, with a signal that may well have escaped all previous searches. Such light top squarks will dominantly decay via i\ —* cZ\ yielding a signal of two acollinear jets with $?. An initial selection of events with $j > 35 GeV and 2 large Ej jets was performed; after acollinearity requirements, only a handful of candidate events remain. This first pass through the data makes the search look promising. The known backgrounds, principally W/Z A- jets, do appear to give expected candidates at the level seen in the data.

2.1.6 QCD

Feher coordinated the work of D0's Parton Distribution Function group. The group provided a forum to broaden knowledge and deepen understanding of parton distributions and helped carrying out physics results. Feher wrote a program to calculate leading order triple differential di-jet cross sections. D0, with its large forward angle coverage and fine segmentation can probe the parton distri• butions down to x = 0.002. At these x values the cross sections are dominated by gluons providing an unique way to probe the gluon distribution at the TeVatron. Figure 6 illustrates the result of our calculation. We used CTEQ 2L LO parton distributions and a scale of Q2 = E\. In the plot the solid curve is the total triple differential di-jet cross section plotted versus ^(j'e^), with rj(jeti) held fixed to 0.5.

2.2 Super-Kamiokande

Two large underground water Cerenkov detectors, 1MB (8k tons) and Kamiokande (4.5k tons), have produced fruitful physics: the search for nucleon decays, first detection of neutrinos from a supernova explosion, first real-time detection of solar neutrinos and confirmation of a deficit in the solar neutrino flux, observation of inconsistencies in atmospheric neutrino fluxes, search for dark matter, search for monopoles etc.. Based on their experience with Kamiokande, the collaboration studied the feasibility of con• structing a larger water Cerenkov detector with better capabilities called Super-Kamiokande. The Super-Kamiokande project plans to build a water Cerenkov detector of the next generation (50k tons) and has been approved by the Japanese government and detector construction has started. There are plans for an upgrade of the KEK-PS including a fast extraction for a neutrino-beam test, important for understanding nucleon decay backgrounds, and for a long baseline neutrino oscillation experiment which would utilize the KEK beam, Super-Kamiokande as a far detector, and an existing 1 kton water Cerenkov detector at KEK as a near detector. The mean neutrino energy is expected to be 2 GeV. The Stony Brook group was actively involved in establishing the collaboration between the 1MB group and the Super-Kamiokande group in 1992, and in the preparation of the US proposal to the DOE. The current group consists of 2 faculty (Jung, Yanagisawa), 3 graduate students (Johnson, Mauger, Viren), and an undergraduate (Einarsson). Another graduate student (Funk) worked with us at KEK, and an undergraduate (Litvak) worked on simulations and has recently graduated.

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11 2.2.1 Physics Motivation

Nucleon decay

The discovery of nucleon decay would be a critical extension of physics beyond the Standard Model, motivated by GUT and cosmology. The much improved fiducial mass (22k ton), energy resolution, track identification efficiency, background rejection capabilities, and the low energy threshold will lead to an order-of-magnitude increase in detection sensitivity for most decay modes. The present combined lower limit on the lifetime of the proton decay p —> e+7r° by the 1MB and Kamiokande collaborations is 1.1 xlO33 years. This result clearly rules out the minimal SU(5) which predicts a lifetime r/Br = 4.5 x 1029±1-7 years. There are many other theories that predict proton decay: a recent estimate by the minimal SUSY GUT theory based on SU(5) and using existing data especially from the LEP experiments, predicts a proton decay lifetime of -r/Br ~ io34±3-2 years. This is within the reach of Super- Kamiokande, and models which predict proton lifetimes from 1031 to 34 years will be tested by the experiment.

Solar neutrinos

The Kamiokande H experiment confirmed the deficit of the solar neutrino flux first observed by the 37C1 experiment. This was the first observation of solar neutrinos using real-time data. It also confirmed that these neutrinos indeed came from the Sun. In addition, two 71Ga experiments, SAGE and GALLEX, seem to observe the deficit, although they are sensitive to lower energy neutrinos from the p-p chain. A possible and very interesting explanation of the deficit is matter enhanced neutrino oscillation via the MSW effect. With a low energy threshold of 5 MeV, Super- Kamiokande will observe about 10,000 solar neutrino events from 8B per year. Such high statistics will make it possible to do detailed studies on the solar neutrino energy spectrum and provide vital information to solve the solar neutrino puzzle.

Atmospheric neutrino studies

At least two experiments (IMB-3 and Kamiokande-II) have reported an anomaly in the at• mospheric neutrino flux composition, measuring a shortage of muon neutrinos which could be interpreted as due to neutrino oscillations. Super-Kamiokande will collect high statistics data for accurate spectral and angular distribution measurements that were not possible with previous experiments.

Long baseline neutrino oscillation

There has been a great deal of interest recently in long baseline neutrino oscillation experiments using accelerator beams and distant underground detectors. The combination of the 250 km dis• tance between KEK and Super-Kamiokande, and the mean neutrino beam energy of 2 GeV, allows a sensitivity down to Am2 of a few times 10-3 eV2, the region favored by the atmospheric neutrino anomaly.

12 Neutrinos from gravitational stellar collapses It was a historic moment when 1MB and Kamiokande detected neutrinos from SN1987A, a su• pernova in the Large Magellanic Cloud. Super-Kamiokande is capable of observing several thousand neutrinos from a supernova in our galaxy. This will provide information about neutrino masses down to cosmologically interesting values (a few eV). Furthermore it may be possible to observe the neutronization burst, allowing for significant tests of supernova theories. Super-Kamiokande has great potential to uncover physics beyond the Standard Model such as baxyon/lepton number violation, finite neutrino mass and neutrino oscillations. Furthermore, as a by-product, very interesting astrophysics is probed.

2.2.2 Overview of the Detector Super-Kamiokande, shown schematically in Figure 7, is a 50,000 ton ring-imaging water Cerenkov detector to be constructed at a depth of 2,700 meters water equivalent in the Kamioka mine in Japan.

1 1.200 20' PMTs

Figure 7: Schematic view of the Super-KamiokandeDetector.

The major component of the detector will be a cylindrical water tank of 39 m in diameter and 41 m in height. The detector will be divided into two parts, the inner and outer detectors.

13 The inner detector will consist of a cylindrical part of the water tank of 34 m in diameter and 36 m in height (32k tons), and will be viewed by 11,200 photomultipliers (PMTs) with 50 cm photocathode, facing inwards providing 40% photocathode coverage. The fiducial mass for the proton decay search, defined to be 2 m inside the PMT surface, will be 22,000 tons. The outer detector, a region of 2.5 m thick, will be viewed by 2,200 20 cm PMTs facing outwards with wavelength shifter from the IMB-3 detector. The outer detector is optically isolated from the inner one, and serves as anti-coincidence detector, passive shielding against low energy gammas and neutrons, as locater for the trajectories of entering muons, and as leakage detector. Super-Kamiokande has seven times the fiducial mass of 1MB. With this large fiducial mass and unprecedented photocathode coverage, Super-Kamiokande can explore nucleon decay to significant new lifetimes. Its background rejection, muon decay and showering vs. non-showering track dis• crimination capabilities will greatly improve studies of particular nucleon decay modes and of the atmospheric neutrino spectrum. Significantly improved energy and position resolutions will be an essential feature for the elimination of background and the detection of low energy interactions. Together with the anti-coincidence capability, these features provide Super-Kamiokande with the sensitivity to detect atmospheric, solar and supernova neutrinos above 5 MeV.

2.2.3 The Trigger System

Jung is the co-responsible physicist (with Dye of BU) for the Super-Kamiokande trigger electronics. The trigger system is a crucial part of the experiment that bears directly on the physics analysis. It is also the only US contribution to the experiment that covers both inner and outer detectors. Our focus is on developing a system that can efficiently trigger on low energy proton decay events as well as on a variety of other interesting events. The trigger electronics must recognize the presence of an event within 1/is and issue a global trigger to all of the front-end electronics, Analog Timing Modules (ATMs). The ATM module han• dles 12 PMT channels, and converts PMT pulses to digital form and provides PMT hit information to the trigger. PMTSUM is an analog current sum of 12 PMT channels. It produces a 10/JA (peak) current pulse per 1.6 pC PMT pulse (corresponding to 1 p.e.). These pulses will be summed to produce a current proportional to the total instantaneous light collection in the detector. HITSUM is a current source which is modulated by the number of discriminators which are in the on-state. Although event topologies differ greatly, it is sufficient to require a minimum amount of Cerenkov light or number of PMTs which have signal above a threshold, to trigger. Therefore the trigger condition can be rather simple. When the total number of PMTs, whose signal level is higher than a certain threshold, exceeds a preset value corresponding to an energy threshold, an event can be triggered. Our goal of the energy threshold is 5 MeV. In principle one can sum up all the PMTSUM or HITSUM outputs and trigger when the current sum exceeds a preset threshold. However, considering the large number of PMTs (11,200 for the inner detector) and the long signal cable distance (50 m), it is not practical to adopt this simple trigger scheme. In addition, the accidental coincidence of dark current noise can be problematic since the diagonal transit time across the detector (210 ns) determines the time window for the coincidence. Figure 8 shows the rate of accidental coincidences due to dark noise as a function of the dark noise

14 i to4

9 10 Dork Rate (kHz) Figure 8: Accidental 34 PMT coincidence rate as function of PMT dark current.

rate for the case of 34 PMT coincidence.

The trigger rate strongly depends on the noise rate. Therefore it is desirable to have a flexible trigger system. For example, to reduce the trigger rate one might divide the detector into quadrants and require a smaller number of PMTs which are in the on-state per quadrant with a reduced time window. A requirement of a coincidence of 17 PMTs in a quadrant within 160 ns is as efficient as a coincidence of 34 PMTs in the entire detector, and the accidental rate is actually smaller if the dark rate is higher than about 4 kHz.

We are investigating many possible trigger schemes. A simple trigger design is shown in Figure 9. The HTTSTJM current pulse from each trigger group is converted to a voltage pulse and fed into a cuscriminator which generates a current proportional to the multiplicity of input signals exceeding a preset threshold. This current output is daisy-chained with other discriminator outputs and the resulting current signal is digitized by the flash ADC. The ADC provides the multiplicity information in digital form (8-bit) and sends it to programmable trigger logic modules in a control station which check whether any trigger conditions are satisfied and issue the trigger signals to DAQ stations.

We formed a US-Japanese trigger working group in August 1993. The group has produced three workable "intelligent trigger" designs, including one with pattern recognition developed at Stony Brook (See Attached [SB trigger]). Currently we are doing rigorous simulation studies of each of these designs to evaluate the expected performance of each system.

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2.3 Post-SSC Development Over the past five years our group has been heavily involved in developing experiments for the SSC. As leaders in the EMPACT and EMPACT/TEXAS proposals, and then as key players in the GEM experiment, the SSC was a major element in our planning for the future. With the cancellation of the SSC last Fall, we were thus left with a significant void in our program. We have spent much of this year exploring options for the longer term future. Our activity in GEM (apart from organizational and administrative responsibilities!) was pri• marily in the muon system, where we were involved in system design, simulations, and in develop• ment of the Cathode Strip Chambers for use as precision muon measuring and triggering elements. As part of the latter activity, Mohammadi organized GEM's participation in the RD5 test program at CERN. This activity has continued, supported originally with TNLB.C and now with SSC close- out funding. Continuation of this work has also provided a natural bridge to the CMS proposal at the LHC, which has accepted us into the collaboration.

2.3.1 RD5 experiment at CERN The RD5 experiment was first proposed in 1990. The main objectives of the experiment are: punchthrough measurements, muon momentum measurements, trigger studies, and test of large area muon chambers. The RD5 experimental setup consists of two magnets, a superconducting solenoid having a field of 3 Tesla (the old EHS magnet), and an absorber magnet having a 1.5 Tesla field. The setup can simulate a solenoidal detector with its return yoke, or a toroidal spectrometer by switching off the EHS magnet. Scintillation counters and multi-wire proportional chambers define the incoming

16 muon/hadron beam. A sampling calorimeter with a depth of 10 absorption lengths and made of steel and Honeycomb Strip Chambers is installed inside the EHS magnet. Large area muon drift chambers for accurate muon momentum measurements are located in front, in the middle, and after the absorber magnet. Resistive Plate Chambers are mounted on these muon chambers as well as inside the absorber magnet. These chambers are used to study triggering schemes and to determine to for the drift chambers. The RD5 effort at Stony Brook (Mohammadi, Sanjari, Vanyashin(visitor)) covers two major muon-system-related tasks:

• Muon backgrounds: punchthrough and muon-induced electromagnetic secondaries;

• Performance of the cathode strip chambers (CSC), which were chosen to instrument the entire GEM muon system and are in the baseline design of the CMS forward muon spectrometer.

Muon backgrounds

We have been studying hadron punchthrough and decays and muon radiation backgrounds, which have consequences in muon trigger rates and pattern recognition. We have done extensive simulations of these backgrounds, which can be compared with RD5 test beam measurements. This allows tuning of simulation parameters so that reliable predictions can be made for various detectors at multi-TeV colliders. Figure 10 shows a comparison of measured total punchthrough probability for negative pions of 30, 50, 100 and 300 GeV and GEANT+GHEISHA and GEANT+FLUKA simulations. Both simulations underestimate the amount of punchthrough compared to the real data, although the agreement with FLUKA is significantly better. This is caused by a higher percentage of pro• tons in hadronic showers generated by FLUKA. A more detailed study is under way, it should be noted, however, that the present accuracy is adequate to make predictions for LHC. (See At• tached [ED5 PunchThrough]) To study muon-induced e.m. secondaries, a CSC prototype (see below for more details) was exposed to high energy muons passing through a 40 cm thick copper block placed upstream of the chamber. The large sensitive area of the CSC chambers allowed measurements of secondaries at large distances from the muon track. These secondaries, which are predominately produced in the copper, do not compromise the position measurement but they would affect muon triggering. The CSC-based triggering scheme takes as input hits in each CSC layer of a superlayer to form track stubs for the first-level trigger. Figure 11 shows the probability of secondary tracks (charge clusters in all four CSC layers) vs. distance from muon for 200 GeV and 300 GeV incident muons. The curves are the simulation results which are in good agreement with data. From these measurements the total probability of e.m. secondaries was determined to be (7.2 ±0.2)% for 200 GeV and (8.0 ±0.2)% for 300 GeV incident muons. (See Attached [RD5 Muonsl)

Cathode Strip Chambers A cathode strip chamber (CSC) is a multiwire proportional chamber with highly segmented cathodes in which the track position is determined by interpolation of the charge induced on the precision cathode strips. In addition to the precision bend coordinate, this technology provides

17 3

2 3 4 12 3 4 Iron equivalent ( m ) Iron equivalent ( m )

Figure 10: Muon punchthrough measurements for x~'s of momenta of 30, 50, 100, and 300 GeV; compared to GEANT(GHEISHA) (left side, x), and to GEANT(FLUKA) (right side, x).

0.6 ~i i I i i i i i i—i—i—r ii> E p^ = 200 GeV/c - 15 CO •8 0.2

.1 i i i l i i i ,i i i i i i *5TTT*mo= 50 100 150 200 Distance to muon (mm)

0.6 IIII I I I I I t I I I I I I I I 1 I I I

^0.4 — ^X p^ = 300 GeV/c -_

CO - <>^<> - -§ 0.2 i "llll I I I I I I I ,'^rr ,<*rs°w5So5= 50 100 150 200 Distance to muon (mm) Figure 11: Probability of occurrence of secondary tracks in the CSC (charge clusters in all four CSC layers) vs. distance from the muon hit for 200 GeV and 300 GeV incident muons. A 40 cm Cu block was placed upstream of the CSC. The curves are the Monte Carlo results.

18 determination of non-bend coordinate by anode wires or by strips in the second cathode, as well as triggering and timing capabilities. The measurements presented here were taken with the a prototype, which was assembled at BNL, made of a set of two two-gap modules (4 layers) providing four cathode strip planes each with a sensitive area of 37 X 45 cm2 and a position sensing cathode strip readout pitch of 5 mm. This chamber was exposed to high energy (50-300 GeV) muons during the 1993 run. Figure 12.a shows the distribution of residuals for normal incident angles (polar and azimuthal). A spatial resolution of better than 40 microns was measured, in good agreement with simulations. The time of the fast OR output from each layer was used to study the trigger timing precision of the chambers. The software OR of all 4 layers is shown in Figure 12.b. It has an rms spread of 3.6 ns, which makes it possible to tag bunch crossings at collider experiments even with 4-layer superlayers. Other studies such as single layer resolution as a function of incident angles, gas gain, etc. have been done. These results are summarized in a paper, to be submitted to NIM. (See At• tached [RD5 CSC]) Cathode Strip Chambers Test

^spatiaJ^40^

-200 0 200 Residuals (um)

-1 i i i i I • i i i— | i i i i | i i i ^~2 600 (b) — 3 6nS CO ^timing = " - c 400 — — ID

L>U i 1 _ 200

1 i i i n I n i 1 20 30 40 50 60 Earliest arrival time (ns)

Figure 12: The measured resolution of the CSC for normal incident high energy muons. In (a) the spatial resolution is shown, and in (b) the timing resolution. The rms width is derived from the Gaussian fit shown.

2.3.2 High energy physics at RHIC Given the uncertainties involved in the US participation at the LHC, we felt that it was prudent to explore other long term options. A natural choice for us at Stony Brook, was to exploit the opportunities at the RHIC machine being constructed through the Nuclear Physics program at neighboring BNL. We are involved in establishing the potential of this machine to do high energy physics.

19 A new high energy machine with the capability for high energy pp collisions can extend the old ISR elastic scattering measurements to the higher energy regime. We have contributed to a feasibility study of elastic scattering measurements at RHIC. Rijssen- beek wrote an elastic scattering simulation program incorporating the projected machine parame• ters and realistic detector resolutions, to investigate the range of acceptance of the proposed small angle detector system. The simulated "data" were subsequently corrected for geometric acceptance

and fitted to obtain simulated measurement values and resolutions for the parameters atot, p, and 6 (see Figure 13).

0.0013 0.002

t— (Q«V/C)*

t : : •

S. ' i • • ..;,., .

< ; M... • \ f ; m ' . i...... ; ' &4019 1X002 &QQ1 QlOOIS &003 t_ (a»v;ej*

6 Figure 13: Errors on p,

The results are very encouraging, and show that pp at RHIC will surpass the elastic pp collider measurements in precision. The feasibility study was prominently featured in the proposal to the BNL PAC (See Attached [RHIC pp]), which approved the elastic scattering experiment in March 1994. The experiment will measure total cross section, p parameter, and nuclear slope b over a large cms energy range, 60 < -Js < 500 GeV. This requires measuring the scattered particles down to about 100/zrad with respect to the beam - deep into the Coulomb region. Second, we plan to explore the higher momentum transfer (\t\) region, 0.2 < \t\ < 2 GeV2. We will compare our measurements against the pp elastic scattering measurements at the pp collider at CERN and Fermilab. Differences in the angular distributions are seen at ISR energies at the 2 cr level, and are expected from several model calculations, with the "diffraction" dip that is present in pp at \t\ — 1.4 expected to be much more prominent in pp. Finally, we hope to use transversely polarized protons in the RHIC to measure the "Analyzing power", and the "Double- spin asymmetry parameter" both of which are functions of 5 5-channel helicity amplitudes. The

20 details of elastic pp scattering at small and medium \t\ will contribute to our understanding of the elusive Pomeron. RHIC is scheduled for commissioning in 1999, and will run primarily for nuclear physics with an anticipated availability of about 20% for high energy running. Despite this time restriction, calculations show that RHIC, operating in pp mode with 250 Gev per beam and an achievable luminosity of 4 X 1032cm~2s-1, can produce 10105's in one month. RHIC has additional nice features of 110 nsec between bunches, a short luminous region (sigma 10 cm), 60% of the B's produced at \rj\ > 1.5 with j3j significantly larger than at an asymmetric B-Factory, as illustrated in Figure 14.

B Production ot RHIC

ft. Figure 14: Integrated rate of B production vs. /3j.

In addition to the copious production of Bj which can be made at e+e~ machines, a hadron 9 9 r machine like RHIC will produce 10 B3, 10 i?-baryons and 10 Bc, opening a variety of interesting windows to rare B decays, B spectroscopy, and CP-violation. We have worked with BNL staff to bring these opportunities to the attention of the community, and to provide quantitative comparisons of the opportunities at RHIC to other possible venues for studying B decays. (See Attached [RHIC 5-physics])

21