SLAC Linear Collider Research Articles

Controlling refractive index and reducing the Global Warming Potential of Cerenkov gas radiators: a challenge in the era of diminishing fluorocarbon availability

Saturated fluorocarbons (SFCs) of the form CnF(2n+2) are chosen for their optical properties (high transparency in the near UV, adapted refractive index and low chromatic dispersion over wavelength ranges of interest) for use as Cherenkov radiators. The COMPASS and LHCb experiments currently use C4F10 and CF4 gas radiators. SFCs have high Global Warming Potentials (GWPs), however (in the range 5000–9000). There is thus an impetus to reduce their use and wastage through leaks in existing installations.Newer fluids of the form CnF2nO, including the 3M NOVEC® range, can offer similar optical performance to SFCs of the same order, n, but with GWPs equivalent to CO2. These GWPs are, however, geometry-specific: closed molecular rings having an oxygen atom as a link can have GWPs as high as those of SFCs, and should be avoided.While the optical constraints of RICH detectors can motivate a “special case” argument to retain the use of preferred SFCs, legislation and external market forces will limit their future availability, leaving “holes” in the CnFx spectrum that might not be filled by NOVEC equivalents. This situation might require the blending of low molar concentrations of heritage-stock higher-order SFCs and NOVEC vapours with transparent light gases such as nitrogen, and is the subject of this paper.While continuous optical measurement of refractive index in dynamically changing gas mixtures is very demanding, the monitoring of sound velocity has been historically shown to provide simple, reliable and continuous real time mixture information. Indeed the speed of sound is, in itself, a monitor of the speed of light and the Cherenkov threshold in a gas radiator.This ultrasonic (“sonar”) technique was first used for controlling the real-time blending C5F12 with N2 in the SLD CRID at the SLAC linear collider. The technique could become important again in future operation to meet the optical and low GWP constraints of future Cherenkov gas radiators. Some examples are explored in this paper.

From the speed of sound to the speed of light: Ultrasonic Cherenkov refractometry

Despite its success in the SLD CRID at the SLAC Linear Collider, ultrasonic measurement of Cherenkov radiator refractive index has been less fully exploited in more recent Cherenkov detectors employing gaseous radiators. This is surprising, since it is ideally suited to monitoring hydrostatic variations in refractive index as well as its evolution during the replacement of a light radiator passivation gas (e.g. N2, CO2) with a heavier fluorocarbon (e.g. C4F10[CF4]; mol. wt. 188[88]). The technique exploits the dependence of sound velocity on the molar concentrations of the two components at known temperature and pressure. The SLD barrel CRID used an 87%C5F12/13%N2 blend, mixed before injection into the radiator vessel: blend control based on ultrasonic mixture analysis maintained the β=1 Cherenkov ring angle to a long term variation better than ±0.3%, with refractivity monitored ultrasonically at multiple points within the radiator vessel.Recent advances using microcontroller-based electronics have led to ultrasonic instruments capable of simultaneously measuring gas flow and binary mixture composition in the fluorocarbon evaporative cooling systems of the ATLAS Inner Detector. Sound transit times are measured with multi-MHz transit time clocks in opposite directions in flowing gas for simultaneous measurement of flow rate and sound velocity. Gas composition is evaluated in real-time by comparison with a sound velocity/composition database.Such instruments could be incorporated into new and upgraded gas Cherenkov detectors for radiator gas mixture (and corresponding refractive index) measurement to a precision better than 10−3. They have other applications in binary gas analysis - including in Xenon-based anaesthesia. These possibilities are discussed.

First results with prototype ISIS devices for ILC vertex detector

The vertex detectors at the International Linear Collider (ILC) (there will be two of them, one for each of two general purpose detectors) will certainly be built with silicon pixel detectors, either monolithic or perhaps vertically integrated. However, beyond this general statement, there is a wide range of options supported by active R&D programmes all over the world. Pixel-based vertex detectors build on the experience at the SLAC large detector (SLD) operating at the SLAC linear collider (SLC), where a 307 Mpixel detector permitted the highest physics performance at LEP or SLC. For ILC, machine conditions demand much faster readout than at SLC, something like 20 time slices during the 1 ms bunch train. The approach of the image sensor with in-situ storage (ISIS) is unique in offering this capability while avoiding the undesirable requirement of ‘pulsed power’. First results from a prototype device that approaches the pixel size of 20 μm square, needed for physics, are reported. The dimensional challenge is met by using a 0.18 μm imaging CMOS process, instead of a conventional CCD process.

Phenomenology of a three-family model with gauge symmetry SU(3)c ⊗ SU(4)L ⊗ U(1)X

We study an extension of the gauge group SU(3)c ⊗ SU(2)L ⊗ U(1)Y of the standard model to the symmetry group SU(3)c ⊗ SU(4)L ⊗ U(1)X (3-4-1 for short). This extension provides an interesting attempt to answer the question of family replication in the sense that models for the electroweak interaction can be constructed so that anomaly cancellation is achieved by an interplay between generations, all of them under the condition that the number of families must be divisible by the number of colours of SU(3)c. This method of anomaly cancellation requires a family of quarks transforming differently from the other two, thus leading to tree-level flavour changing neutral currents (FCNC) transmitted by the two extra neutral gauge bosons Z′ and Z′′ predicted by the model. In a version of the 3-4-1 extension, which does not contain particles with exotic electric charges, we study the fermion mass spectrum and some aspects of the phenomenology of the neutral gauge boson sector. In particular, we impose limits on the Z − Z′ mixing angle and on the mass scale of the corresponding physical new neutral gauge boson Z2, and establish a lower bound on the mass of the additional new neutral gauge boson Z′′ ≡ Z3. For the analysis we use updated precision electroweak data at the Z-pole from the CERN LEP and SLAC Linear Collider, and atomic parity violation data. The mass scale of the additional new neutral gauge boson Z3 is constrained by using updated experimental inputs from neutral meson mixing in the analysis of the sources of FCNC in the model. The data constrain the Z − Z′ mixing angle to a very small value of , and the lower bounds on and are found to be of and , respectively.

SU(4)L⊗U(1)Xthree-family model for the electroweak interaction

An extension of the gauge group SU(2){sub L} x U(1){sub Y} of the standard model to the symmetry group SU(4){sub L} x U(1){sub X} (3-4-1 for short) is presented. The model does not contain exotic electric charges and anomaly cancellation is achieved with a family of quarks transforming differently from the other two, thus leading to FCNC. By introducing a discrete Z{sub 2} symmetry we obtain a consistent fermion mass spectrum, and avoid unitarity violation of the Cabibbo-Kobayashi-Maskawa mixing matrix arising from the mixing of ordinary and exotic quarks. The neutral currents coupled to all neutral vector bosons are studied, and by using CERN LEP and SLAC Linear Collider data at Z-pole and atomic parity violation data, we bound parameters of the model related to tree-level Z-Z{sup '} mixing. These parameters are further constrained by using experimental input from neutral meson mixing in the analysis of sources of FCNC present in the model. Constraints coming from the contribution of exotic particles to the one-loop oblique electroweak parameters S, T and U are also briefly discussed. Finally, a comparison is done of the predictions of different classes of 3-4-1 models without exotic electric charges.

Phenomenology of theSU(3)c⊗SU(3)L⊗U(1)Xmodel with exotic charged leptons

A phenomenological analysis of the three-family model based on the local gauge group $SU(3{)}_{c}\ensuremath{\bigotimes}SU(3{)}_{L}\ensuremath{\bigotimes}U(1{)}_{X}$ with exotic charged leptons, is carried out. Instead of using the minimal scalar sector able to break the symmetry in a proper way, we introduce an alternative set of four Higgs scalar triplets, which combined with an anomaly-free discrete symmetry, produce quark and charged lepton mass spectrum without hierarchies in the Yukawa coupling constants. We also embed the structure into a simple gauge group and show some conditions to achieve a low energy gauge coupling unification, avoiding possible conflict with proton decay bounds. By using experimental results from the CERN-LEP, SLAC linear collider, and atomic parity violation data, we update constraints on several parameters of the model.

STUDY OF THE SU(3)c⊗SU(3)L⊗U(1)X MODEL WITH THE MINIMAL SCALAR SECTOR

A study of the three-family local gauge group SU (3)c⊗ SU (3)L⊗ U (1)X with right-handed neutrinos is carried out. We use the minimal scalar sector able to break the symmetry in a proper way and produce, at the same time, masses for the fermion fields. We embed the structure into a simple gauge group and, by using experimental results from the CERN LEP, SLAC linear collider and atomic parity violation data, we also constrain relevant parameters for the new neutral and charged currents. We discuss the mass spectrum for the gauge boson sector and for the spin 1/2 particles. With the use of discrete symmetries and the introduction of extra scalar fields, a consistent mass spectrum could be constructed.

Phenomenology of the $SU(3)_c\otimes SU(3)_L\otimes U(1)_X$ model with right-handed neutrinos

A phenomenological analysis of the three-family model based on the local gauge group $SU(3)_c\otimes SU(3)_L\otimes U(1)_X$ with right-handed neutrinos is carried out. Instead of using the minimal scalar sector able to break the symmetry in a proper way, we introduce an alternative set of four Higgs scalar triplets, which combined with an anomaly-free discrete symmetry, produces a quark mass spectrum without hierarchies in the Yukawa coupling constants. We also embed the structure into a simple gauge group and show some conditions for achieving a low energy gauge coupling unification, avoiding possible conflict with proton decay bounds. By using experimental results from the CERN-LEP, SLAC linear collider, and atomic parity violation data, we update constraints on several parameters of the model.

Measurement of the branching ratios of theZ0into heavy quarks

We measure the hadronic branching ratios of the Z0 boson into heavy quarks: Rb=ΓZ0→bb¯/ΓZ0→hadrons and Rc=ΓZ0→cc¯/ΓZ0→hadrons using a multitag technique. The measurement was performed using about 400 000 hadronic Z0 events recorded in the SLC Large Detector experiment at SLAC between 1996 and 1998. The small and stable SLAC Linear Collider beam spot and the CCD-based vertex detector were used to reconstruct bottom and charm hadron decay vertices with high efficiency and purity, which enables us to measure most efficiencies from data. We obtain, Rb=0.21604±0.00098(stat.)±0.00073(syst.)∓0.00012(Rc) and, Rc=0.1744±0.0031(stat.)±0.0020(syst.)∓0.0006(Rb).1 MoreReceived 18 May 2005DOI:https://doi.org/10.1103/PhysRevD.71.112004©2005 American Physical Society

Unitarity violation of the CKM matrix in a nonuniversal gauge interaction model

We explore the unitarity violation of the Cabibbo-Kobayashi-Maskawa (CKM) matrix in the model where the third generation fermions are subjected to the separate SU(2){sub L} gauge interaction. With the recent LEP and SLAC linear collider (SLC) data at Z-pole and low-energy neutral current interaction data, the analysis on the parameter space of the model is updated, and the unitary violation is predicted under the constraint.

Direct Measurements ofAbandAcUsing Vertex and Kaon Charge Tags at the SLAC Detector

Exploiting the manipulation of the SLAC Linear Collider electron-beam polarization, we present precise direct measurements of the parity-violation parameters A(c) and A(b) in the Z-boson-c-quark and Z-boson-b-quark coupling. Quark-antiquark discrimination is accomplished via a unique algorithm that takes advantage of the precise SLAC Large Detector charge coupled device vertex detector, employing the net charge of displaced vertices as well as the charge of kaons that emanate from those vertices. From the 1996-1998 sample of 400 000 Z decays, produced with an average beam polarization of 73.4%, we find A(c)=0.673+/-0.029(stat)+/-0.023(syst) and A(b)=0.919+/-0.018(stat)+/-0.017(syst).

$SU(3)_c\otimes SU(4)_{\mathrm {L}}\otimes U(1)_X$ model for three families

An extension of the standard model to the local gauge group $SU(3)_c\otimes SU(4)_{\mathrm {L}}\otimes U(1)_X$ as a three-family model is presented. The model does not contain exotic electric charges and we obtain a consistent mass spectrum by introducing an anomaly-free discrete Z 2 symmetry. The neutral currents coupled to all neutral vector bosons in the model are studied. By using experimental results from the CERN LEP, SLAC Linear Collider and atomic parity violation data we constrain the mixing angle between two of the neutral currents in the model and the mass of the additional neutral gauge bosons to be $-0.0032\leq\sin\theta\leq 0.0031$ and $0.67 \hbox{TeV}\leq M_{Z_2} \leq 6.1$ TeV at $95 \%$ C.L., respectively.

SU(3)c⊗SU(4)L⊗U(1)Xwithout exotic electric charges

We present an extension of the Standard Model to the local gauge group $SU(3)_c\otimes SU(4)_L\otimes U(1)_X$ with a family non-universal treatment and anomalies canceled among the three families in a nontrivial fashion. The mass scales, the gauge boson masses, and the masses for the spin 1/2 particles in the model are analyzed. The neutral currents coupled to all neutral vector bosons in the model are studied, and particular values of the parameters are used in order to simplify the mixing between the three neutral currents present in the theory, mixing which is further constrained by experimental results from the CERN LEP, SLAC Linear Collider, and atomic parity violation.

HIGHLIGHTS OF THE SLD PHYSICS PROGRAM AT THE SLAC LINEAR COLLIDER

▪ Abstract Starting in 1989, and continuing through the 1990s, high-energy physics witnessed a flowering of precision measurements in general and tests of the standard model in particular, led by e+e− collider experiments operating at the Z0 resonance. Key contributions to this work came from the SLD collaboration at the SLAC Linear Collider. By exploiting the unique capabilities of this pioneering accelerator and the SLD detector, including a polarized electron beam, exceptionally small beam dimensions, and a CCD pixel vertex detector, SLD produced a broad array of electroweak, heavy-flavor, and QCD measurements. Many of these results are one of a kind or represent the world's standard in precision. This article reviews the highlights of the SLD physics program, with an eye toward associated advances in experimental technique, and the contribution of these measurements to our dramatically improved present understanding of the standard model and its possible extensions.

The search for B s0 oscillations at SLD

The SLD experiment at the SLAC Linear Collider has updated three searches for the time dependence of B s 0 oscillations. One search uses events with a reconstructed D s meson; a second search uses events with a lepton and a topologically identified charmed meson; and the third uses events in which both a secondary and tertiary vertex are distinguished. The combined analyses are sensitive to values of Δ m s , the oscillation frequency, up to 13.0 ps −1 . A preliminary maximum likelihood analysis excludes Δm s<7.6 ps −1 and 11.8< Δm s<14.8 ps −1 at 95% CL. Including this data, the combined world data now imply Δm s>15.0 ps −1 at 95% CL, and are not incompatible with a signal near the expected value, Δm s∼15 ps −1 .

Light quark fragmentation in polarized Z0 decays at SLD

We report results on two physics topics from the SLD experiment at the SLAC Linear Collider, using our full sample of 550,000 events of the type e + e − → Z 0 → q q . The electron beam was polarized, enabling the quark and antiquark hemispheres to be tagged in each event. One physics topic is the first study of rapidities signed such that positive rapidity is along the quark rather than antiquark direction. Distributions of ordered differences in signed rapidity between pairs of particles are analyzed, providing the first direct observation of baryon number ordering along the q q axis. The other topic is the first direct measurement of A s , the parity-violating coupling of the Z 0 to strange quarks, by measuring the left-right forward-backward production asymmetry in polar angle of the tagged s quark. We obtain A s = 0.895 ± 0.066( stat.) ± 0.062( syst.), which is consistent with the Standard Model and is currently the most precise measurement of this quantity.

Improved direct measurement of leptonic coupling asymmetries with polarized Z bosons.

We present final measurements of the Z boson-lepton coupling asymmetry parameters A(e), A(mu), and A(tau) with the complete sample of polarized Z bosons collected by the SLD detector at the SLAC Linear Collider. From the left-right production and decay polar angle asymmetries in leptonic Z decays we measure A(e) = 0.1544+/-0.0060, A(mu) = 0.142+/-0.015, and A(tau) = 0.136+/-0.015. Combined with our left-right asymmetry measured from hadronic decays, we find A(e) = 0.1516+/-0.0021. Assuming lepton universality, we obtain a combined effective weak mixing angle of sin (2)theta(eff)(W) = 0.230 98+/-0.000 26.

The fundamental fermions and bosons

AbstractRecent progress in understanding the properties of the fundamental fermions and bosons is presented. The masses and couplings of the heavy Z and W bosons are accurately known from experiments at the CERN electron‐positron storage ring LEP, the SLAC Linear Collider SLC, and the Fermilab proton‐antiproton collider Tevatron. The mass of the top quark has been measured at Fermilab and yields, together with the W mass, an important consistency test of the Minimal Standard Model. Detailed investigations of the properties of quark and gluon jets have been performed, some of the results are summarised. Constraints on the mass of the yet undiscovered Higgs boson are discussed and the perspectives for future searches for new fermions and bosons at the LHC are briefly mentioned.

High-precision measurement of the left-right Z Boson cross-section asymmetry.

We present a measurement of the left-right cross-section asymmetry ( A(LR)) for Z boson production by e(+)e(-) collisions. The measurement includes the final data taken with the SLD detector at the SLAC Linear Collider during the period 1996-1998. Using a sample of 383 487 Z decays collected during the 1996-1998 runs we measure the pole value of the asymmetry, A(0)(LR), to be 0.150 56+/-0.002 39 which is equivalent to an effective weak mixing angle of sin (2)straight theta(eff)(W) = 0.231 07+/-0.000 30. Our result for the complete 1992-1998 data set comprising approximately 537 000 Z decays is sin (2)straight theta(eff)(W) = 0.230 97+/-0.000 27.

Recent tests of QCD at SLD

We present selected results on strong interaction physics from the SLD experiment at the SLAC Linear Collider. We report on several new studies of 3- and 4-jet hadronic Z 0 decays, in which jets are identified as quark, antiquark or gluon. The 3-jet Z 0 → b bg rate is sensitive to the b-quark mass; prospects or measuring m b are discussed. The gluon energy spectrum is measured over the full kinematic range, providing an improved test of QCD and limits on anomalous bbg couplings. The parity violation in Z 0 → b bg decays is consistent with electroweak theory plus QCD. New tests of T- and CP-conservation at the bbg vertex are performed. A new measurement of the rate of gluon splitting into b b pairs yields g b b = 0.0031 ± 0.0007(stat.) ± 0.0006(syst.) (Preliminary). We also present a number of new results on jet fragmentation into identified hadrons. The B hadron energy spectrum is measured over the full kinematic range using a new, inclusive technique, allowing stringent tests of predictions for its shape and a precise measurement of < χ B > = 0.714 ± 0.0005(stat.) ± 0.0007(syst.) (Preliminary). A detailed study of correlations in rapidly y between pairs of identified π ±, K ± and p p confirms that strangeness and baryon number are conserved locally, and shows local change conservation between meson-baryon and strangenonstrange pairs. Flavor-dependent long-range correlations are observed for all combinations of these hadron species, yielding new information on leading particle production. The first study of correlations using rapidities signed such that y > 0 corresponds to the quark direction provides additional new insights into fragmentation, including the first direct observation of baryon number ordering along the q q axis.