Presentation on theme: "The SLHC prospects at ATLAS and CMS"— Presentation transcript:
1The SLHC prospects at ATLAS and CMS IntroductionPhysics motivationLHC machine upgradeExperiment upgradesNew inner trackers for SLHCConclusionsIan Dawson,University of SheffieldEPS 2007, Manchester
2IntroductionATLASATLAS and CMS will exploit physics in TeV regime. First collisions expected in 2008.Rich physics programme -Higgs, SUSY etc.CMSExtend the physics potential of the LHC with a luminosity upgrade around ~2016Rich physics programme for ATLAS and CMS.
3Time scale of an LHC upgrade Radiation damagelimit ~700fb-1designluminosityultimateL at end of yeartime to halve errorintegrated LJim Strait, 2003Hypothetical lumiscenarioLife expectancy of LHC inner-triplet (focusing) magnets estimated to be <10 years due to high radiation dosesStatistical error halving time exceeds 5 years by It is reasonable to plan a machine luminosity upgrade based on new inner-triplet focusing magnets around ~
4Physics motivation The physics potential of a luminosity upgrade will be better known withLHC data. In general:See: Eur.Phys.J.C39(2005)293Extend the mass reach by 0.5TeV->1Tev (increased statistics of high-x parton interactions)Extra gauge bosons, heavy Higgs-bosons, resonances in extra-dimension models, SuperSymmetry particles (if relatively heavy).For example, extra gauge bosons (W,Z) like appear in various extensions of the SM symmetry group.Consequences of a ten-fold increase in statistics for the experiments can be divided into 3 area:Extending the mass reach is a consequence of hadron colliders - the probability of very high-x parton interactions is increased by a factor of ten. As an example, shown here is a ~1TeV incease in mass reach in the search for additional gauge bosons. Extra gauge bosons appear in many extensions of SM - usually with couplings similar as for SM Z.Example of improved mass reach - taking into account CMS acceptance and e/ reconstruction efficiency and pile-up noise.
5Increased precision in Standard Model Physics Higgs couplingsStrongly coupled vectorboson scattering (if no Higgs)Triple and quarticgauge couplingsRare top decays through FCNCQGC final state statistics with 6000fb-1.Physics beyond SM (if relatively light and discovered at LHC).For example -SUSYRequires 5 years of SLHCDark Matter?Extend particle spectrumImprove precision and access rare decay channels.2) Improving precision measurements - for example, tripke and quartic couplings statistically limited at LHC.3) Basically, if physics BSM then with more data can make more precise and extensive measurements - especially if the physics is on the heavy side. For example, improving SUSY search for heavy Higgs.Measure coupling of neutralino to Higgs. Determine its higgsino component.
6LHC machine upgradeBig challenge to increase luminosity by factor of ten. Machine R&D has to start now.Two upgrade scenarios currently being considered - both are based on first replacing the inner triplet magnets to achieve ultimate LHC luminosity of ~2x1034cm-2s-1parameter25ns, small *50ns, longprotons per bunch1.74.9bunch spacing2550beam current0.861.22longitudinal profileGaussFlatrms bunch length7.5511.8beta* at IP1&50.080.25full crossing angle381peak luminosity15.510.7peak events per crossing294403initial lumi lifetime2.24.5effective luminosity (Tturnaround=5h)3.63.5Improve beam focusingMachine magnets inside experiments25ns or 50ns bunch crossingIncrease beam currentsMore demanding on machine50ns bunch crossingReducing the bunch spacing is not possible due to electron cloud heating.
725 nsspacingPeak luminosities different for 25ns versus 50ns scenarios, but average luminosity similar.50 nsspacingaverageluminosityThe 25ns scenario will require magnets inside the experiments!Peak luminosities may be too difficult for experiments to cope with - possibility of ”luminosity levelling” being explored.For experiments, what’s important is not peak luminosity but average luminosity - which is similar for 50ns and 25ns scenarios.From experiments point of view - not clear which is preferred solution. 25ns greater peak lumi variance and magnets interfering in experiements, but 50ns has more avergae pile-up.The large peak luminosity variations and associated pile-up will be difficult for experiments to cope with - hence the motivation for luminosity levelling. Various methods for doing this being investigated - blah
8Experiment upgrades From the LHC to the SLHC 103310351032 cm-2 s-11034I. OsborneThe ATLAs and CMS experiemtents will need to upgrade to work in higher radiation backgrounds. The inner trackers will need to be replaced due to -1) Radiation damage, 2) Big increases in occupancies.Both ATLAS and CMS in process of determining upgrade requirements - but the inner trackers need replacing and likely to be most of cost.
9ATLAS Muon chambers Forward calorimeters In general, most of calorimetry should be OKFCAL (|η|>3.1) particularly subject to beam radiationSimulations show possible heating of LarImprove cooling? Or new “warm” FCAL?Background rates very uncertain (factor ~5x)Need LHC experienceEffect of slim quads?Use existing chambers as far as possibleBeryllium beampipe will reduce by factor of 2.
10CMS Calorimeters Level 1 trigger Muon system Electromagnetic calorimeters should be OK at SLHC.Hadronic calorimeter scintillator may suffer radiation damage for >2R&D requiredImpact on HF if machine magnet insertions?There may not be enough rejection power using the muon and calorimeter triggers to handle the higher luminosity conditions at SLHCLevel 1 Muon Trigger has no discrimination for pT > 20GeV/c, therefore problem to keep Level 1at ~100kHz.Adding tracking information at Level 1 gives the ability to adjust PT thresholdsMuon systemHigh momentum tracks are straighter so pixels line upSearchWindowγIn general, expected to be quite robust, but some electronics “less” radiation hard and most likely need replacing.As with ATLAS, need experience with running at LHC.2 layers about 1mm apart could communicate
11New trackers for SLHC Both ATLAS and CMS need new inner trackers Started looking at new layouts. Simulations crucial to ascertain:Track reconstruction performanceOccupanciesMaterial effectsSilicon trackers at LHC use p-in-n sensors - requires full depletion high depletion voltages already at LHC.n-in-p or n-in-n can operate under-depleted - promising progress being made on n-in-p.For both ATLAS and CMS the inner trackers will need to be replaced. There are two reasons for this: 1) Radiation damage, 2) Big increases in occupancies.Fluences at larger radii dominated by neutron-albedo, greatest near endcaps.Fluences at small radiidominated by particlesfrom interaction point.
12Possible sensor technology for the SLHC tracker Long strips(present p+-nor n+-p)Short strips(n+-p)Pixel b-layer(3D? Diamond?thin-Si? Gas?)n+-p pixelsThe most challenging will be engineering work (cooling, cabling, shielding, other services)
13For innermost layers - new technology required 3D silicon sensors ?Uses MEMS (Micro Electro Mechanical Systems) technology to engineer structures.Both electrode types are processed inside the detector bulk instead of being implanted on the wafer's surface.Electric field between electrodes - shorter signal collection distances compared with planar devices:Lower depletion voltage (and therefore power)Faster and more efficient charge collection.Large scale production? Timescale? Cost ?CVD Diamond ?Gas ?Now well established with several applications (eg beam conditions monitoring)Large band gap and strong atomic bonds give excellent radiation hardnessLow leakage current and capacitance = low noiseLarge band gap means ~2 less signal than Si for same X0For innermost layers, certainly the b-layer - extremely high radiation - several new technologies being looked at.1) A novel new technology being developed are 3D silicon detectors. The short signal collection distance (d = 50->70m) ensures efficient charge collection.The signal is proportional to Leff(1-exp(-d/Leff)) so if Leff similar between 3D and planar devices (which is case if both Silicon) then 3D is better. Leff is reduced with increasing irradiation because of introduction of traps so that Leff ~ 1/fluence.Alternative 3D geometries/designs are now being investigated, eg single-type-column, partial-columns2) Diamond is now well established and found several applications (eg BCM, pixel modules fabricated and tested succesfully by ATLAS)Eg GOSSIP (micromegas) low mass but gas issues such as sparking?
14Some initial comparison data Plot on left shows signal charge versus irradiated fluence. For inner most layers we expect 1.6x1016 where 3D looks promising. However, it is the signal/noise which is important and the plot on the right gives an indication of noise - diamond has very low noise and seems competitive.Pixel n-in-n or n-in-p may also play a role should the novel new technologies not be ready on time - or too costly - but thinner wafers need to be used to avoid very high voltages for depletion.Planar silicon n-in-p or n-in-n can still play a role for inner most layers should new technologies not be readyTried and tested solution but high operating voltages unless thin ?
15ConclusionsThe implications of a major luminosity upgrade (SLHC) sometime around are being studied by the LHC machine and experiments.Long lead times require this work starts now.But the main priority is physics exploitation of the LHC.The baseline bunch crossing rate at the SLHC is 20MHz, with 40MHz as a backup.The 80MHz option is no longer considered due to beam heating.ATLAS and CMS need new inner trackersCMS will need to revise Level 1 trigger strategy.ATLAS forward calorimeter unlikely to survive at SLHCA better understanding of upgrade requirements for ATLAS and CMS will be gained from running at LHC.
16Backup slidesFor both ATLAS and CMS the inner trackers will need to be replaced. There are two reasons for this: 1) Radiation damage, 2) Big increases in occupancies.
17The European strategy for particle physics “The LHC will be the energy frontier machine for theforeseeable future, maintaining European leadership in thefield; the highest priority is to fully exploit the physics potential of the LHC, resources for completion of the initial programme have to be secured such that machine and experiments can operate optimally at their design performance. A subsequent major luminosity upgrade (SLHC), motivated by physics results and operation experience, will be enabled by focussed R&D; to this end, R&D for machine and detectors has to be vigorously pursued now and centrally organized towards a luminosity upgrade by around 2015.”(http://council-strategygroup.web.cern.ch/council-strategygroup/)
18Luminosity levelling etc. 25 ns50 nsaverageluminosityThe relatively fast luminosity decay and high multiplicity call for Luminosity Leveling.…but the issue is how to do it efficiently:dynamic beta*: uses existing hardware; probably complex due to large number of side-effects in IR’s AND arcs.dynamic bunch length: needs new RF; possible side effects in whole machine related to modification of peak current.dynamic crossing angle: using the early separation hardware, no side effects identified. Even better: crabbing.
19Simulations for the inner tracker 1 MeV fluences obtained by convolving particle spectra predicted by FLUKA2006 with “displacement-damage” curves (RD48).1 MeV equivalent neutron fluences assuming anintegrated luminosity of 3000fb-1 and 5cm ofmoderator lining the calorimeters.av18 is current baseline geometry for upgrade studies5cm neutron moderator lining all the calorimetersno tracker materialThe beneficial moderating effect of the TRT is lost in an all silicon system. Can be recovered with 5cm of moderator lining barrel (as shown in Genova).
20Parameterisation of 1MeV-neq fluences Several requests to parameterise inner tracker backgrounds.Z(cm)a1a2a3a41.4x10173.7x10151.7x1014-1.0x10121507.0x10169.5x10159.7x1013-5.7x10113004.9x10161.2x10163.0x1014-2.0x1012Parameterise also pion and neutron contributions separately.Fluences at small radiidominated by particlesfrom interaction point.Mention no safety factors.Future investigations = moderator, material in front of FCALFluences at larger radii dominated by neutron-albedo, greatest near endcaps.Use these types of plots for future investigations (Eg moderator design, impact of extra material etc.)
21Uncertainties/Safety-factors? Until we have better benchmarking data, the uncertainties assumed at the LHC still apply.Event generators ~20%Transport codes ~20%Displacement damage cross sections ~50%At the SLHC, the goal seems to be 3000fb-1 for the integrated physics luminosity. What safety factors do we assume?At present, 2 × 3000fb-1 being usedAlso, until we know what an upgraded detector and machine look like, there may be additional contributions to inner tracker fluences …Concerning safety factors at LHC … if designed to deliver 300fb-1, then by designing tracker to ~700fb-1 and applying a further “simulation” safety factor of 1.5 to give ~1000fb-1, then we have effectively a total safety factor greater than 3.
22Impact of additional mass in front of FCAL on Inner Tracker fluences Can ‘alcove’ region in front of FCAL be used for machine magnets?Look at 1MeV-neq fluences in tracker volume. (Saying nothing about FCAL).Fill ‘alcove’ with iron. Should be pessimistic? If so, results below give worse case?av185cm polyZ=300cmav18 withFe mass~2.7~2.0Factor ~2.7 increase due mainlyto increase in neutron albedo.