Squark Production at the Tevatron

AC-coupling and the Factor 1.0 rule1. Introduction to the AC-Coupling conceptAlready familiar with the concepts of AC-coupling and regulating PV inverter output power by frequency shifting? Skip to the requirements and limitations:Factor 1.0 rule chapter1.2.Minimum battery capacity chapter3.Requirement of adding DC-Coupling (MPPT Solar Chargers)1.1 What is AC-coupling?In an AC-coupled system, a grid-tied PV inverter is connected to the output of a Multi, Inverter or Quattro. PV power is first used to power the loads, then to charge the battery, and any excess PV power can be fed back to the grid.When the Multi or Quattro is connected to the grid, this excess PV inverter power will automatically be fed back to the grid.When the Multi or Quattro is operating in inverter-mode, disconnected from its AC input, it will create a local grid: a micro-grid. The PV Inverter will accept this micro-grid and will therefore operate even during a black-out. The PV power can even be used to charge the batteries: when there is more PV power available than used by the loads, the power will automatically run through the inverter in reverse direction and charge the batteries. It is necessary to regulate that power to prevent overcharging the batteries as well as overloading the inverter/charger. This is where 'frequency shifting' comes in to the picture, see next section.Highlights:AC-coupling is available in single-phase, split-phase and also three-phase systems.Victron Multis and Quattros can prevent feeding back PV power to grid.Systems with only a grid-tied PV inverter will fail when there is a grid black-out. A micro-grid system will continue to operate, and even keep using solar power.It is also possible to run a AC-coupled micro-grid on a generatorMost brands of PV inverters can be used for these systems, they need to be setup to support frequency shifting, often called the island-mode or micro-grid mode. For SolarEdge settings, see Integrating with SolarEdge, for Fronius settings, see AC-coupled PV with Fronius PV Inverters & for reading and controling ABB/Fimer inverters, see AC-coupled PV with ABB/Fimer PV Inverters.To read out SMA inverters, see AC-coupled PV with SMA PV Inverters.If power will be fed back into the grid an anti-islanding device may have to be added to thesystem, depending on local regulations.1.2 What is frequency shifting?Frequency shifting is used to regulate the output power of a Grid-tie PV Inverter, or Grid-tie Wind inverter, by changing the frequency of the AC. The MultiPlus (or Quattro) will automatically control the frequency to prevent over charging the battery. See also the chapter 'Example & background'.For how to configure, see chapter 4.2. The Factor 1.0 ruleThe max PV power must be equal or less than the VA rating of the inverter/charger2.1 Rule definitionIn both grid-connected and off-grid systems with PV inverters installed on the output of a Multi, Inverter or Quattro, there is a maximum of PV power that can be installed. This limit is called the factor 1.0 rule: 3.000 VA Multi >= 3.000 Wp installed solar power. So for a 8.000 VA Quattro the maximum is 8.000 Wp, for two paralleled 8000 VA Quattros the maximum is 16.000 Wp, etc.2.2 Example and backgroundTo understand the background, consider the following situation: the PV inverter is at full power, supplying a big load. The Multi is in inverter mode. Then, suddenly and at once, this load is switched off. At that moment the PV inverter will continue operating at full power until the AC frequency has been increased. Increasing this frequency will take a very short time, but during that time all power will be directed into the batteries as there is no other place for it to go. This causes the following: When batteries are (nearly) full, the battery voltage will spike, possibly causing the Multi toswitch off in DC over-voltage alarm.The same spike will cause the AC output voltage of the Multi to spike, as these two are directly related, and when the spike on the battery voltage is high and fast enough, the Multi can never regulate its PWMs down fast enough to prevent the spike on AC. This spike can damage the PV inverter, the Multi and also any connected loads and other equipment.Another problem is that the Multi starts charge current protection.In the best case it might switch the grid inverter off immediately by setting the AC frequency tothe disconnect frequency as configured in the assistant.It is no problem to overpower the grid inverter by installing more solar panels. Some people do this to increase the generated solar power in winter time or rainy weather. Refer to the PV Inverter datasheet to maximum allowed installed PV power. Two times the inverter nameplate rating or even more is not uncommon!2.3 Charge current limitAnother question frequently asked is how can this factor be 1.0? Since the charger inside a 3000 VA Multi is not 3000 VA but closer to 2000 VA? The explanation lies in the fact that it will regulate. In other words: when there is too much power coming in, causing the charge current to exceed the limit, it will increase the output frequency again and will keep regulating the AC output frequency to charge with the limit.An example, a 3000 VA Multi, with 3000 W of solar power coming out of a PV inverter: 1.When the Multi is connected to the grid, all 3000 W can be fed back to the grid through theMulti, no problem.2.In case the Multi is not connected to the grid, the 3000 Wp is more than the charger in a Multi 3000 VA can handle. The charger is around 2000 W. Therefore the grid inverter assistant will automatically increase the frequency to reduce the output of the grid inverter, to matchmaximum charge current.2.4 Should you look at the total PV array, or the PV inverter rating?The mentioned 3000 Wp and 8000 Wp is the Watt-peak which can be expected from the solar system. So for an oversized PV array, where the total Watt-peak installed PV panels exceeds the power of the PV Inverter, you take the Wp from the inverter. For example 7000 Wp of solar panels installed, with an 6000 Watt PV grid inverter, the figure to be used in the calculations is 6000 Wp.And for an undersized PV array, where the total Wp of installed PV panels is less than the installed PV grid inverter, you use the Wp from the PV panels in your calculation.3. Minimum battery capacityBesides the relation between installed PV Power and the inverter/charger VA rating, it is also important to have a sufficiently sized battery. The minimum battery capacity depends on the type of battery, lead or lithium.Note that, besides the minimum battery capacity, the mentioned sizes are often also the most economical battery size. In case used for self-consumption purposes that is. In case the goal is to increase autonomy, of course installing a large battery increases the system autonomy in case of a grid failure.3.1 Lead batteries1 kWp installed PV power requires approximately 5kWh of lead acid battery:100 Ah at 48 Vdc200 Ah at 24 Vdc400 Ah at 12 VdcEach additional 1 kWp of AC PV will require an additional proportional 5 kWh increase in lead acid battery storage.3.2 Lithium batteries1,5 kWp installed AC PV power requires 4.8 kWh of battery storage:100 Ah at 48 Vdc200 Ah at 24 Vdc400 Ah at 12 VdcEach additional 1.5 kWp of AC PV will require an additional proportional 4.8 kWh increase in battery storage.4 Requirement of adding DC-Coupling - MPPT Solar Chargers Not required for Energy Storage Systems in Germany or other reliable grid situations.Required for offgrid systems as well as backup systems that need to overcome extended grid failures. Reason: recover from deadlock situation of AC-Coupling only situation.There is no Factor 1.0 limit that applies for DC coupled PV through a Victron MPPT. Nor is there a specific minimum amount of battery storage capacity, though please follow battery manufacture specifications for maximum charge rates. A rule of thumb is C10 (10% of Ah capacity in A) for lead acid batteries, and C2 (50% of Ah capacity in A) for lithium batteries.5 Software configurationMultis and Quattros with factory settings will not shift the AC output frequency to regulate charge current. When setting up an AC Coupled system, install either the ESS Assistant (for grid-connected systems) or the PV Inverter Support Assistant (for off-grid systems).The Inverter RS will automatically shift frequency without any additional configuration required when a surplus/back-feed of AC is detected on the AC-output.Other options, all deprecated, are:1.Self-consumption Hub-2 v3 assistantHub-4 Assistant in combination with the PV Inverter support Assistant 2.3.Use the Inverter period time settings on the Virtual switch tab. MonitoringSee Connecing a PV inverter section of the GX manual.DISQUSView the discussion thread.。

a r X i v :h e p -e x /0506030v 1 12 J u n 2005TOP QUARK MASS MEASUREMENTS AT THE TEV ATRONMARTIJN MULDERS(on behalf of the CDF and DØcollaborations)Fermi National Accelerator Laboratory,Batavia,IL 60510,USAIn the year 2004several milestones in the measurement of the top quark mass were reached.The DØcollaboration published a significant improvement of their Run I measurement of the top quark mass,and both Tevatron experiments released preliminary measurements based on Run II data sets collected in the period 2002-2004.The preliminary Run II results presented here do not yet surpass the current world average in precision,but this is expected to change soon.With larger data sets ready to be analyzed,a better understanding of the Run II detectors and improved analysis methods,2005promises to be a remarkable year for Top physics.1IntroductionThe recent publication of the improved Run I measurement of the top mass by DØ1was exciting for two reasons.First of all it demonstrated how much improvement in measurement precision could be achieved using a more advanced analysis technique like the Matrix Element method.Secondly,it was a reminder of how little we yet know about the properties of the top quark and that new experimental information about the top quark can have big implications for electroweak fits in the Standard Model.The current (Run I only)world average value for the top quark mass is 178.0±4.3GeV /c 2.In the coming years the measurements of CDF and DØcombined should lead to a precision of about 2GeV.Together with expected improvements in the measurement of the W boson mass this will allow to further constrain the Higgs boson mass to a relative precision of approximately 30%,as discussed elsewhere in these proceedings 2.Since the start of Run II both CDF and DØhave recorded more than 600pb −1of data,already 5times the Run I luminosity.The preliminary results presented here are based on fraction of the recorded data ranging from 160to 230pb −1.Figure1:Reconstructed mass distributions for the CDF di-lepton neutrino weighting analysis(left),and the DØTemplate method with b-tagging(right).2Run II Top mass resultsIn p¯p collisions with √Table1:Overview of preliminary Run II top mass resultstop mass(GeV/c2)CDF neutrino-weighting168.1+11−9.8(stat)±8.6(sys)CDF M reco Template+t¯t p z176.5+17.2−16.0(stat)±6.9(sys)CDF M reco Template+φofν1andν2170.0±16.6(stat)±7.4(sys) DØDalitz and Goldstein155+14−13(stat)±7(sys)CDF Template with b-tagging177.2+4.9−4.7(stat)±6.6(sys)CDF Multi-Variate Template179.6+6.4−6.3(stat)±6.8(sys)CDF Dynamic Likelihood177.8+4.5−5.0(stat)±6.2(sys)DØIdeogram177.5±5.8(stat)±7.1(sys)DØTemplate topological169.9±5.8(stat)+7.8−7.1(sys)DØTemplate with b-tagging170.6±4.2(stat)±6.0(sys)2.2Final states with one lepton plus jetsWhile the lepton+jets channel benefits from a higher branching ratio,it suffers from significant backgrounds from W+jets and non-W multi-jet events.Since only one neutrino is present thefinal state can be fully reconstructed.Some analyses use a constrained kinematicfit to further improve the measurement of lepton and jets beyond detector resolution.The CDF Dynamic Likelihood Method(DLM)follows a different approach, similar to the DØMatrix Element method1;transfer functions are derived from Monte Carlo simulation describing the jet energy resolution.These functions are subsequently used in a multi-dimensional integration over phase space calculating the likelihood that the event is compatible with matrix elements describing top pair production and decay.In order to reconstruct the invariant mass of the top decay products,a choice has to be made to assign jets and lepton to the corresponding top or anti-top quark.In a lepton+jets event12ways exist to do this assignment.Some analyses take only one jet assignment per event in consideration.The CDF Dynamic Likelihood Method and the DØIdeogram analysis include all possible jet assignments in thefit.The CDF and DØtemplate methods use an overallfit of Monte Carlo templates to the data in order to extract the mass.The CDF Dynamic Likelihood Method and DØIdeogram analysis derive an event-by-event likelihood to maximize the statistical information extracted from each event.The Ideogram method also includes the hypothesis that the event could be background, weighted according to an estimated event purity.Both experiments apply b-tagging in some of the top mass analyses.One advantage of b-tagging is to strongly reduce the backgrounds.A second advantage of b-tagging for the top mass measurement in the lepton+jets channel is the reduction of the number of possible jet assignments in the case that one or two jets are b-tagged.The CDF Template analysis combines the0-tag,1-tag and double tagged event samples in thefit to optimize the statistical precision. DØ’sfirst top mass analysis with b-tagging uses events with at least one tag,which applied to a data set of230pb−1leads to the most precise preliminary Run II top mass result presented so far.Figure1shows thefitted mass for the lowest-χ2solution for the b-tagged DØTemplateanalysis,compared to the Monte Carlo prediction.An overview of the current preliminary results is shown in Table1.3Prospects for the Top mass measurementIn all results reported here the dominant component of the systematic uncertainty is the uncer-tainties related to the jet energy scale.In the last year a lot of work has been done to improve the calibration of the reconstructed jet energies.CDF reports an improvement of a factor two or more in jet energy scale uncertainties compared to a year ago.Similar improvements are expected in DØ.This will have a direct effect on the systematic uncertainties quoted.Further improvements in understanding the Jet Energy Scale can come from performing an in-situ calibration of the light-jet energy scale using the jets from the hadronic decay of the W in the same t¯t events used to measure the top mass,and from studies in progress aimed at determining the b-jet energy scale from data.Other systematics that are being studied are the modeling of initial state andfinal state gluon radiation in the t¯t Monte Carlo.Very soon both experiments hope to present preliminary results with updated jet energy scale and an integrated luminosity of more than300pb−1.All together the prospects are very good for having new top mass results this year with a precision comparable to or better than the current world average for each of the Tevatron experiments.This will open the door to an exciting new area of top physics to be further explored in the coming years at the Tevatron.References1.DØCollaboration,Nature429(2004)p638.2.C.Hays,these proceedings,hep-ex/0505064.3.J.Nielsen,these proceedings,hep-ex/0505051.4.CDF Collaboration,/physics/new/top/top.html5.DØCollaboration,/Run2Physics/WWW/results/top.htm。

Energy Meters start pageAt Victron Energy, we stock several types of Energy Meters.The Energy Meters are used in systems with a GX device. To measure the output of a PV inverter (more info in the Venus-OS manual here. Or as a Grid Meter in an ESS installation, more information in the ESS manual.1. Selection guideEnergy Meter ET112ET340EM24AppearanceDisplay no display no display LCD DisplayManual and Wiring Diagrams ET112 Manual ET340 Manual EM24 ManualPart Number REL300100000REL300300000REL200100000Supported Phases 1 phase 3 phase 3 phaseMaximum Current Rating100A65A per phase65A per phaseMeasurement Type Shunt Shunt ShuntFirst decide if you need single- or three phase metersFor a three phase utility connection, use a three phase meter. For a three phase PV Inverter, use a three phase meter as well. For a single phase utility connection, use a single phase meter. And in an installation with a single phase utility connection, that also has a PV Inverter that needs measuring with a Victron meter, then you can use Rutger 2 pieces of ET112; or use the ET340.Now, based on current, select the modelRequirement Type Model / SolutionSingle phase up to 100A Shunt ET112Three phase up to 65A/phase Shunt EM24/ET340*Single phase more than 100A/phase CT Not available, use the three phase CT solutionThree phase more than 65A/phase CTs Carlo Gavazzi EM24DINAV53DISX (see FAQ Q8)The EM24 meter counts energy in a different way than the ET340. For Germany and most other countries; the EM24 is the advised model. See FAQ Q5 and Q9 for further details.1.1 Support for other Carlo Gavazzi metersBesides above listed meters, there are many more meters available from Carlo Gavazzi. Use this list to see which ones are compatible.Type Support RemarksEM111Supported Compatible with ET112.ET111Supported Compatible with ET112.EM112Supported Compatible with ET112.ET340Supported None.EM340Not supported does not report exported energy per phase (unlike the ET340)EM21 72D Not supported does not report exported energy,com protocol not compatible with supported grid metersEM271Not supported does not report exported energy,com protocol not compatible with supported grid meters3. FAQQ1: Can I combine three ET112s for a three phase system?No. Use a real three-phase meter.Q2: Can I use other meters, for example from other brands?No.Q3: I already have a Fronius SmartGrid meter, can I use that?No.Q5: What are the differences between the various three phase meters?EM24 - REL200100000 - Carlo Gavazzi EM24DINAV93XISXET112 - REL300100000 - Carlo Gavazzi ET112-DIN.AV01.X.S1.XET340 - REL300300000 - Carlo Gavazzi ET340-DIN.AV23.X.S1.XDifferences:The ET meters don't have a front selector that the installer needs to put in a different setting than it comes out of the box: easier, less mistakes to be made.The ET meters have no display. The only thing they have is an LED, which blinks in case ofactive communication.The new meters have 2 RJ45 sockets for the Modbus RS485 connection. But they are not used.Note the possible confusion because of yet another RJ-45 socket in the Victron world though.Don't mix that with VE.Bus, VE.Can or . Besides the RJ-45 sockets, the meters still also have screw terminals access below the sockets for the RS485 wiring, which is how we advise to connect a meter to the RS485 to USB interface and then CCGX.Since there is no display, the Modbus address can no longer be changed on the meter.Combining multiple of those meters on one RS485 network is therefore not supported byVictron. You are advised to use multiple RS485 to USB interfaces.Three-phase new meter only (ET340):Measuring Energy from single phase PV Inverter on the second phase of the new meter, ET340, actually works. Where-as with the old meter, the EM24, only the Power Metering (Watts) works.The Energy Metering (kWh) for a single phase PV Inverter on the second phase of the EM24does not work. See Q9 for the details.Q6: Will you keep shipping both 3 phase meters? (ET340 & EM24)Yes. There are still situations suitable for each. See Q9.Q7: Can I buy those meters directly from Carlo Gavazzi instead of from you?Yes. That is also why we make no secret of the CG part numbers.Q8: I want to use Current Transformers (CTs), is that possible?Yes. You can buy the CG EM24DINAV53DISX directly from Carlo Gavazzi or one of their distributors. Even though Victron does not stock that type of meter, we do support it in our software.The EM24DINAV53DISX is the solution for three-phase systems that go over 65A per phase.Q9: What’s the difference between ET340 and EM24 in 3 phase systems?These meters have a different way of calculating the total of energy imported and exported.In the ET340 - the energy imported and exported is counted at each individual phase and then the Total is provided from the sum of those values.In the EM24 - the energy imported and exported is counted as a total power, with net differential readings from each phase cancelling each other out.Which meter is best to use with depend on your countries own metering configuration. It is most common in Australia and Germany for example to only be billed for the total in a 3 phase system. So it is more accurate to use an EM24 to match the billing.So if you are exporting from one phase, and importing from another phase after the energy meter, but before the billing meter then you will not be charged for this, and the meter should not count it as an import and an export.This is also how Victron’s phase compensation feature works, to make the most of the cost savings for an ESS system when there is a differential in generation and load across different phases.Q10: Can I use an isolated USB-RS485 interface?Yes. The interfaces we sell are non isolated; suitable for most use cases.In case an isolated one is needed; purchase it dirsctly from Hjelmslund Electronics.USB485-STIXL : Isolated USB to RS485 converterDISQUSView the discussion thread.。

QuarksQuarks and Leptons are the building blocks which build up matter, i.e., they are seen as the "elementary particles". In the present standard model, there are six "flavors" of quarks. They can successfully account for all known mesons and baryons (over 200). The most familiar baryons are the proton and neutron, which are each constructed from up and down quarks. Quarks are observed to occur only in combinations of two quarks (mesons), three quarks (baryons). There was a recent claim of observation of particles with five quarks (pentaquark), but further experimentation has not borne it out.Quark Symbol Spin Charge BaryonNumberS C B T Mass*Up U 1/2 +2/3 1/3 0 0 0 0 1.7-3.3 MeV Down D 1/2 -1/3 1/3 0 0 0 0 4.1-5.8 MeV Charm C 1/2 +2/3 1/3 0 +1 0 0 1270 MeV Strange S 1/2 -1/3 1/3 -1 0 0 0 101 MeV Top T 1/2 +2/3 1/3 0 0 0 +1 172 GeVBottom B 1/2 -1/3 1/3 0 0 -1 0 4.19 GeV(MS) 4.67 GeV(1S)*The masses should not be taken too seriously, because the confinement of quarks implies that we cannot isolate them to measure their masses in a direct way. The masses must be implied indirectly from scattering experiments. The numbers in the table are very different from numbers previously quoted and are based on the July 2010 summary in Journal of Physics G, Review of Particle Physics, Particle Data Group. A summary can be found on the LBL site. These masses represent a strong departure from earlier approaches which treated the masses for the U and D as about 1/3 the mass of a proton, since in the quark model the proton has three quarks. The masses quoted are model dependent, and the mass of the bottom quark is quoted for two different models. But in other combinations they contribute different masses. In the pion, an up and an anti-down quark yield a particle of only 139.6 MeV of mass energy, while in the rho vector meson the same combination of quarks has a mass of 770 MeV! The masses of C and S are from Serway, and the T and B masses are from descriptions of the experiments in which they were discovered.Each of the six "flavors" of quarks can have three different "colors". The quark forces are attractive only in "colorless" combinations of three quarks (baryons), quark-antiquark pairs (mesons) and possibly larger combinations such as the pentaquark that could also meet the colorless condition. Quarks undergo transformations by the exchange of W bosons, and those transformations determine the rate and nature of the decay of hadrons by the weak interaction.Why "quark"?Has anyone ever seen a quark?What is the evidence for quarks inside protons?What is the evidence for six quarks?IndexParticle conceptsReferenc es Serway Ch. 47Rohlf Ch. 17Griffiths Ch. 1HyperPhysics***** Quantum Physics R Nave Go BackWhy "Quark"?The name "quark" was taken by Murray Gell-Mann from the book "Finnegan's Wake"by James Joyce. The line "Three quarks for Muster Mark..." appears in the fancifulbook. Gell-Mann received the 1969 Nobel Prize for his work in classifying elementary particles.IndexParticleconceptsHyperPhysics ***** Quantum PhysicsR Nave Go BackUp and Down QuarksThe up and down quarks are the most common and least massive quarks, being the constituents of protons and neutrons and thus of most ordinary matter.The fact that the free neutron decaysand nuclei decay by beta decay in processes likeis thought to be the result of a more fundamental quark processTable of quark propertiesIndexParticle conceptsHyperPhysics ***** Quantum PhysicsR Nave Go BackThe Strange QuarkIn 1947 during a study of cosmic ray interactions, a product of a proton collision with a nucleus was found to live for much longer time than expected: 10-10 seconds instead ofthe expected 10-23 seconds! This particle was named the lambda particle (Λ0) and the property which caused it to live so long was dubbed "strangeness" and that name stuck to be the name of one of the quarks from which the lambda particle is constructed. The lambda is a baryon which is made up of three quarks: an up, a down and a strange quark.The shorter lifetime of 10-23seconds was expected because the lambda as a baryon participates in the strong interaction, and that usually leads to such very short lifetimes. The long observed lifetime helped develop a new conservation law for such decays called the "conservation of strangeness". The presence of a strange quark in a particle is denoted by a quantum number S=-1. Particle decay by the strong or electromagnetic interactions preserve the strangeness quantum number. The decay process for the lambda particle must violate that rule, since there is no lighter particle which contains a strange quark - so the strange quark must be transformed to another quark in theprocess. That can only occur by the weak interaction, and that leads to a much longer lifetime. The decay processes show that strangeness is not conserved:The quark transformations necessary to accomplish these decay processes can be visualized with the help of Feynmann diagrams.The omega-minus, a baryon composed of three strange quarks, is a classicexample of the need for the property called "color" in describing particles.Since quarks are fermions with spin 1/2, they must obey the Pauliexclusion principle and cannot exist in identical states. So with threestrange quarks, the property which distinguishes them must be capable ofat least three distinct values.Conservation of strangeness is not in fact an independent conservation law, but can be viewed as a combination of the conservation of charge, isospin, and baryon number. It is often expressed in terms of hypercharge Y, defined by:Isospin and either hypercharge or strangeness are the quantum numbers often used to draw particle diagrams for the hadrons.Table of quark properties IndexParticle conceptsHyperPhysics***** Quantum Physics R Nave Go BackThe Charm QuarkIn 1974 a meson called the J/Psi particle was discovered. With a mass of 3100 MeV,over three times that of the proton, this particle was the first example of another quark, called the charm quark. The J/Psi is made up of a charm-anticharm quark pair.The lightest meson which contains a charm quark is the D meson. It provides interesting examples of decay since the charm quark must be transformed into a strange quark by the weak interaction in order for it to decay.One baryon with a charm quark is a called a lambda with symbol Λ+c . It has a composition udc and a mass of 2281 MeV/c2.Table of quark properties IndexParticle conceptsHyperPhysics***** Quantum Physics R Nave Go BackThe Top QuarkConvincing evidence for the observation of the top quark was reported by Fermilab's Tevatron facility in April 1995. The evidence was found in the collision products of 0.9 TeV protons with equally energetic antiprotons in the proton-antiproton collider. The evidence involved analysis of trillions of 1.8 TeV proton-antiproton collisions. The Collider Detector Facility group had found 56 top candidates over a predicted background of 23 and the D0 group found 17 events over a predicted background of 3.8. The value for the top quark mass from the combined data of the two groups after the completion of the run was 174.3 +/- 5.1 GeV. This is over 180 times the mass of a proton and about twice the mass of the next heaviest fundamental particle, the Z0 vector boson at about 93 GeV.The interaction is envisioned as follows: IndexParticle concept sReferen ce Ladbur yD-ZeroTable of quark propertiesHyperPhysics***** Quantum Physics R Nave Go BackConfinement of QuarksHow can one be so confident of the quark model when no one has ever seen an isolated quark? There are good reasons for the lack of direct observation. Apparently the color force does not drop off with distance like the other observed forces. It is postutated that it may actually increase with distance at the rate of about 1 GeV per fermi. A free quark is not observed because by the time the separation is on an observable scale, the energy is far above the pair production energy for quark-antiquark pairs. For the U and D quarks the masses are 10s of MeV so pair production would occur for distances much less thana fermi. You would expect a lot of mesons (quark-antiquark pairs) in very high energy collision experiments and that is what is observed.Basically, you can't see an isolated quark because the color force does not let them go, and the energy required to separate them produces quark-antiquark pairs long before they are far enough apart to observe separately.One kind of visualization of quark confinement is called the "bag model". One visualizes the quarks as contained in an elastic bag which allows the quarks to move freely around, as long as you don't try to pull them further apart. But if you try to pull a quark out, the bag stretches and resists.Another way of looking at quark confinement is expressed by Rohlf. "When we try to pull a quark out of a proton, for example by striking the quark with another energetic particle, the quark experiences a potential energy barrier from the strong interaction that increases with distance." As the example of alpha decay demonstrates, having a barrier higher than the particle energy does not prevent the escape of the particle - quantum mechanical tunneling gives a finite probability for a 6 MeV alpha particle to get through a 30 MeV high energy barrier. But the energy barrier for the alpha particle is thin enough for tunneling to be effective. In the case of the barrier facing the quark, the energy barrier does not drop off with distance, but in fact increases.Evidence for quarks in deep inelastic scattering IndexParticle conceptsReferenc eRohlf Sec 6-6HyperPhysics***** Quantum Physics R Nave Go Back The Bottom QuarkIn 1977, an experimental group at Fermilab led by Leon Lederman discovered a new resonance at 9.4 GeV/c^2 which was interpreted as a bottom-antibottom quark pair and called the Upsilon meson. From this experiment, the mass of the bottom quark is implied to be about 5 GeV/c^2. The reaction being studied waswhere N was a copper or platinum nucleus. The spectrometer had a muon-pair mass resolution of about 2%, which allowed them to measure an excess of events at 9.4 GeV/c^2. This resonance has been subsequently studied at other accelerators with a detailed investigation of the bound states of the bottom-antibottom meson.Table of quark properties IndexParticle conceptsReferenc eRohlf Ch. 17HyperPhysics***** Quantum Physics R Nave Go Back。