Detector challenges for future HEP experiments

Detector challengesfor future HEP experiments

Lucie Linssen (CERN)

Granada ESPPU symposium, May 14th 2019

With many thanks to many colleagues for presentation materialMogens Dam, Dominik Dannheim, Richard Jacobsson, Chang Kee Jung, Luciano Musa, Chris

Parkes, Petra Riedler, Werner Riegler, Andreas Schopper, Alfons Weber and many others

Scope of the talk

Linssen, Granada symposium 2019 2

Scope: Detector requirements for future accelerator-based HEP experiments,placed in a context of today’s technology achievements.

• High-energy collider detectors• Fixed target experiments (“high energy”)• Accelerator-based neutrino experiments

Focus on experiments/detectors/upgrades that are “proposed”,so ≠ already approved, under construcLon or built

With apologies to all interesting EPPSU detector input not covered in the talk

The main focus of the talk: detector requirementsThe development of detectors for future experiments is mostly driven by:• physics objectives (momentum, energy, particle ID, late decays etc.)• experimental conditions and other constraints encountered

To all evidence: generic exploratory R&D is also of high importance !

FCC-hh hadron collider


100 TeV FCC-hh, proton-protonÞ See next slides

PbPb collisions at FCC-hh:Þ See next slides

27 TeV HE-LHC, proton-protonLarger luminosity than HL-LHC => increased radiation and pile-up effects with respect to ATLAS/CMS. Much of the challenges will be similar to FCC-hh, though more modest (approx. half-way between HL-LHC and FCC-hh).

↑ Study of 5 TeV jets

parameters LHC, HL-LHC, HE-LHC, FCC-hh


FCC-hh: pp collisions at 100 TeVUltimate ! = 3×1035 cm-2s-1

Aim to collect ∫ ℒ of 30 ab-1

High rates: pp collision rate of 31 GHz, and charged track rate of 4 THzIn the first vertex barrel layer (at 25 mm radius):

=> fluence ~10 GHz/cm2

Pile-up of 1000 events per bunch crossing=> average distance between vertices is 125 %m (1/7 wrt HL-LHC)

High radiation levels, for 30 ab-1:=> ~1018 1 MeV neq /cm2 and ~300 MGy in the inner tracking layers

FCC

-hh

slid

es, C

DR

https://indico.cern.ch/event/789349/contributions/3298692/attachments/1805766/2946875/fcc_hh_detector_cdr_presentation_feb_2019.pdf

FCC-hh reference detector


• 4T, 10m solenoid, unshielded• Forward solenoids, unshielded• Silicon tracker• Barrel ECAL LAr• Barrel HCAL Fe/Scint• Endcap ECAL/HCAL LAr• Forward ECAL/HCAL LAr

‘general’ purpose detector with very large η acceptance and extreme granularityMuon detection up to η = 4 (! ≈ 2°) Calorimetry up to η = 6 (! ≈ 0.5°)

50 m long, 20 m diameter

FCC-

hh sl

ides

, CDR


FCC-hh tracker considerations


• High occupancies => small cells sizes (~25×50 "m2

in inner layers)

• Two-track separation in boosted objects • small cell sizes + better hit resolution <5 "m

• Tilted layout to minimize multiple scattering

• High-E => significant fraction of displaced vertices outside acceptance

• Radiation ×100 higher than present technologies

tilted layout conventional layout

Tracker radius 1.6 m, half-length 16 m, initial baseline hit position resolution 7−$ %m in R&

FCC-

hh sl

ides

, CDR

20% -


main FCC-hh detector challenges


• Magnet systems:• Very large solenoid bore diameter of 10 m (cf. 6 m in CMS); unshielded coil in baseline design

=> stray field in cavern. Large (and costly) engineering challenge, but in principle doable in available technology.

• Radiation levels:• The radiation for <40 cm radius of the tracker for FCC-hh is up to 100 times larger than what

present sensors can sustain• For most parts of the calorimeter Liquid Argon is only viable known technology, but requires

development towards high granularity (!"×!$ = 0.01×0.01 in ECAL, 0.025×0.025 in HCAL). Silicon or scintillator technologies could be used in regions with milder radiation levels.

• Pile-up and boost:• Requires much increased granularity in most regions of the detector• High precision timing required (~5ps per track) and computing power for reconstruction, both

significantly above HL-LHC• Very accurate tracker hit position resolution (<5 %m), for 2-track separation in boosted objects

• Data rate:• High collision rate and high granularity => data rate of 1-2 Pbyte/s, mostly dominated by the

tracker. Studies to be done whether this is possible and what triggering is required (year 20xx)

• Activation:• => impact on access conditions after several yrs of operation => maximise automated access

=> engineering challengeCour

tesy

Wer

ner R

iegl

er


heavy ion collisions at FCC


The general purpose FCC-hh detector will also do well for PbPb collisions

Will profit from: • Continuous readout• PID from time-of-flight with very precise timing detectors

In case of optimising a detector for ion-ion:Running at lower B-field (<4T) would be an advantageProfiting from lower radiation levels would allow for more optimised solutions

Like at LHC, one of four interaction regions could host a dedicated experiment

FCC-

hh sl

ides

, CDR


FCC-ee => CLD and IDEA√s: 90 - 365 GeV

CEPC => baseline and low-B√s: 90-240 GeV

9Linssen, Granada symposium 2019

ILC => ILD and SiD: √s: 250 – 500 GeV (1 TeV)

high-energy e+e- collider detectors

CLIC => CLICdet, √s: 380 GeV, 1.5 TeV, 3 TeV

linear: ILC / CLIC beam parameters

Parameter 250 GeV

500GeV

380 GeV

1.5 TeV

3 TeV

Luminosity L (1034cm-2sec-1) 1.35 1.8 1.5 3.7 5.9

L above 99% of √s (1034cm-2sec-1) 1.0 1.0 0.9 1.4 2.0

Repetition frequency (Hz) 5 5 50 50 50

Bunch separation (ns) 554 554 0.5 0.5 0.5

Number of bunches per train 1312 1312 352 312 312

Beam size at IP σx/σy (nm) 515/7.7 474/5.9 150/2.9 ~60/1.5 ~40/1

Beam size at IP σz (μm) 300 300 70 44 44

Drives timingrequirementsCLIC detector

Very small beams + high energy => beamstrahlung


ILC: Crossing angle 14 mrad, electron polarization ±80%, positron polarization ±30%, CLIC: Crossing angle 20 mrad, electron polarization ±80%

Very low duty cycleat ILC/CLIC allows for:

Triggerless readoutPower pulsing

Beams arrive in “bunch trains”

ILC CLIC

CLIC

201

8 Su

mm

ary

ILC

stra

tegy

https://arxiv.org/abs/1812.06018

http://ilchome.web.cern.ch/content/ilc-european-strategy-document

circular: FCC-ee /CEPC beam parameters


Z Higgs ttbar Z (2T) Higgs

√S [GeV] 91.2 240 365 91.2 240

Luminosity per IP (1034cm-2sec-1) 230 8.5 1.7 32 1.5

no. of bunches / beam 16640 393 48 12000 242

Bunch crossing separation (ns) 20 994 3000 25 680

Beam size at IP σx/σy (μm) 6.0/0.04 20.9/0.06

Bunch length (SR / BS) (mm) Beam size at IP σz (mm)

3.5 / 12.1 3.3 / 5.3 2.0 / 2.5 8.5 4.4

At Z-peak very high luminosities and very high e+e- cross section (40 nb)Þ Statistical accuracies at 10-4 -10-5 level ⇒ drives detector performance requirementsÞ Small systematic errors required to matchÞ This also drives requirement on data rates (physics rates 100 kHz)Þ Triggerless readout likely still possible

Beam-induced background, from beamstrahlung + synchrotron radiation• Most significant at 365 GeV• Mitigated through MDI design and detector design

Beam transverse polarisation => beam energy can be measured to very high accuracy (~50 keV)

FCC-ee CEPC

FCC-

ee s

lides

, CD

RCE

PC C

DR

https://indico.cern.ch/event/789349/contributions/3298691/attachments/1805339/2946724/FCCCDR4March-MD.pdf

http://cepc.ihep.ac.cn/CEPC_CDR_Vol2_Physics-Detector.pdf

e+e- physics performance requirements


Note: differences between requirements ILC, CLIC, FCC-ee, CEPC rather small

+ requirements from experimental conditions

« impact parameter resolution:e.g. c/b-tagging, Higgs branching ratios

�E

E⇠ 3.5 � 5 %

�pT /p2T ⇠ 2 ⇥ 10�5 GeV�1

« angular coverage, very forward electron tagging

« momentum resolution:e.g, HZ recoil, gHμμ, Smuon endpoint

(for high-E jets, light quarks)

« jet energy resolution:e.g. W/Z/H di-jet mass separation, Z and W width, HZ with Zèqq, background reduction

�r� = 5 � 15/(p[GeV] sin32 ✓) µm

e+e- forward region, machine-detector-interface


example: FCC-ee example: CLIC

FCC-ee magnet shielding schemefor beam quality preservation

CLIC 3 TeV: hit densities from beam-induced background near beam pipe and vertex detector. Therefore:• First pixel layer at 31 mm radius• Pixel size 25*25 !m2 for occupancy

reasons• ~5 ns hit time resolution needed

Experimental conditions are taken into account in all e+e- detectorsÞ Additional performance requirements or constraints for the detectorsÞ Minimal impact on physics performance

FCC-

ee sl

ides

, CDR

CLIC detector CDR

beam pipe

vertex detector

https://indico.cern.ch/event/789349/contributions/3298691/attachments/1805339/2946724/FCCCDR4March-MD.pdf


highly granular calorimetry


To reach jet energy resolution of ~3%, most e+e- detectors choose:

Highly granular calorimetry and Particle Flow Analysis technique

• Separate individual particles in jets + use best information

(tracker or calorimeter) for each particle

• Separate ”physics event” particles from beam-induced

background particles (CLIC example)

• General asset for particle identification

Example: ILD detector @ ILC, proposing CALICE collab. technologies

ECAL option ECAL option HCAL option HCAL optionActive layer silicon scint+SiPM scint+SiPM glass RPC

Absorber tungsten tungsten steel steel

Cell size (cm×cm) 0.5×0.5 0.5×4.5 3×3 1×1

# layers 30 30 48 48

Readout analog analog analog Semi-dig (2 bits)

Depth # (X0/Λint) 24 X0 24 X0 5.5 Λint 5.5 Λint

# channels [106] 100 10 8 70

Total surface 2500 2500 7000 7000

PFA calorimetry

also adopted by:

CLIC

FCC-ee

CEPC

FCC-hh

CMS HGCal

DUNE ND

ESPPU input, ID=107

https://indico.cern.ch/event/765096/contributions/


same event before cuts on beam-induced background

e+e- è ttH è WbWbH è qqb τνb bb--- - -

CLIC 1.4 TeV

Highly granular calorimetry + hit timing O(1ns)⇓

Very effective in suppressing backgroundsfor fully reconstructed particles

(much better than hit-level cuts)

ESPPU input, ID=146


Main e+e- collider detector challenges


Vertex detectors:• Very high spatial resolution, very low mass + O(5 ns) hit timing (CLIC)• Linear Colliders: Engineering challenge to combine low mass with air cooling• Circular Colliders: Maintain low mass for position resolution without power pulsing

PFA calorimetry:• Much experience gained through CALICE; CMS HGCal will be a benchmark• Very large area of silicon for ECAL => cost driver • Engineering challenge overall

Power pulsing:• Much experience gained with laboratory set-ups, and with system tests of CALICE prototypes• Power pulsing not yet tested at system level for vertex/tracker • Power pulsing can become an obstacle for e.g. cosmic ray calibration

Systematics on energy scale, luminosity measurement, calibration:• Keep systematics below level of statistical errors

=> most challenging at Z-peak, but also for top quark mass and per-mille level Higgs couplings

Combination makes it challenging

27 cm

ITS2 → ITS3 pixel detector upgrade ALICE


ALICE “ITS2” pixel detector is under constructionA “Pioneering project” in Monolithic HR-CMOS

Expression of interest: ALICE “ITS3” Building on the ITS2 experience with ALPIDE sensorDetailed device simulation => faster signal, more radiation hardMore advanced technology: 180 nm => 65 nmPush technology further: thinner, large sensors through stitching

parameter ITS2 ITS3X/X0 per layer 0.3% 0.05%

HR-CMOS technology 180 nm 65 nm

Pixel size 28×28 #m2 O(10 #m×10 #m)

Chip dimensions 15×30 mm2 up to 280×100 mm2

Sensor thickness 50 #m (first 3), 100 #m thinned to ~30 #m

Sensor shape flat curved

Position resolution ~5 #m <3 #m

Hit timing O(#s) O(100ns)

Radiation* NIEL 1.7×1013 MeV neq /cm2 1.7×1013 MeV neq /cm2

Radiation* TID 2.7 Mrad 2.7 Mrad

ALI

CE-P

UBL

IC-2

018-

013

Bending20 #m silicon

* Radiation levels include factor 10 safety

https://cds.cern.ch/record/2644611

example: LHCb upgrade-II (LS4)


Luminosity L = 1.5×1034 cm-2s-1, 56 evts/BX, 2500 charged particles /BX Calls for major detector overhaul, with accurate hit timing (~50-100 ps), high granularity, radiation hardness and huge data rateDetector challenges have lots of synergies with other projects

VELO vertex locator:<50 "m square pixels (down to ~28×28 "m). Time resolution of 50 ps allows 4D pattern recogn. Hybrid technology considered. Target ASIC technology: 28 nm. Continuous triggerless readout ⇒huge data rate.

Silicon tracker:Monolithic CMOS or HV-CMOS sensors (with embedded analog processing) considered. Total 25 m2, pixel sizes <100 × 500 "m2, O(1014 - 1015) 1 MeV neq/cm2

New ECAL:5D (space+time+energy), radiation hard (~1MGy), high granularity (1.5 × 1.5 or 2 × 2 cm2 cells).Small Moliere radius (overlapping showers), very accurate timing O(few 10 ps).Considering sampling calorimeter of spacal or shashlik design with crystal fibers (e.g. GAGG and YAG).

Particle ID detectors (RICH, TORCH):More granularity, very accurate timing: down to 10 ps for RICH, 15 ps for TORCH)

LHCb

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Cb-u

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http://cdsweb.cern.ch/record/2636441

http://cdsweb.cern.ch/record/2244311

high-energy collider, tracking challenges


Exp.Parameter

LHC HL-LHC SPS FCC-hh FCC-ee CLIC 3 TeV

Fluence [neq/cm2/y] N x 1015 1016 1017 1016 - 1017 <1010 <1011

Max. hit rate [s-1cm-2] 100 M 2-4 G****) 8 G****) 20 G 20 M ***) 240k

Surface inner tracker [m2] 2 10 0.2 15 1 1

Surface outer tracker [m2] 200 200 - 400 200 140

Material budget per layer [X0] 0.3%*) - 2% 0.1%*) - 2% 2% 1% 0.3% 0.2%

Pixel size inner layers [µm2] 100x150-

50x400

~50x50 ~50x50 25x50 25x25 <~25x25

Hit position resol. inner [!m] 3 3

Hit position resol. outer [!m] 7 7

Bunch Crossing spacing [ns] 25 25 >109 25 20-3400 0.5

Hit time resolution [ns] <~25–1000*) 0.2**)–1000*) 0.04 ~10-2 ~1000 ***) ~5

Silicon vertex and tracking detector parameters

Hadron colliders and (some) fixed target expts:• Very high radiation levels• Very high hit rates• Very precise timing (down to ~10 ps)

Lepton colliders (and ALICE ITS3):• Ultimate precision, very low material budget

Note that ps-level timing was not part of

initial HL-LHC detector requirements

⇓Became available through pioneering R&D on

LGAD / MCP / precise timing with silicon⇓

Now well motivated for vertex separation / pattern reco

CE

RN

-OP

EN

-20

18

-00

6

http://cds.cern.ch/record/2649646

Physics Beyond Colliders (PBC)


A wealth of proposed experiments and facilities,at precision frontier / intensity frontierVery wide spread of detector requirements:

• Very precise timing• High radiation levels• Ultimate precision• Very large surfaces or volumes• High demands on particle ID

A few examples, only (sorry), on the next slides MuonE !" → !"Hadronic leading order correction to g-2

NA64++ Dark sector and BSM, here with ! beamKLEVER KL → $0%%

ESPP

U in

put,

ID=4

2


PBC examples: SHiP and TauFV


Magnetized volume

SHiP: Dark matter search behind SPS beam dump facility1020 Protons on Target (PoT)

Neutrino physics, !" interactions

Some of the detector technology challenges:• Background tagger ~250 m3 liquid scintillator, SiPM readout, O(3500) systems <= large volume, SiPM• Straw tracker in vacuum, 16000 straws, 5 m length, horizontal <= large surface, engineering challenge• Spectrometer timing layer, 50 m2, <100 ps <= very precise timing• Neutrino detection with lead-emulsion spectrometer <= high precision

~5.6 m

Detector challenges, similar to LHCb upgrade II:• Silicon pixel VELO, similar to LHCb upgrade• TORCH particle ID detector (70 ps per photon)• Fast rad-hard ECAL (e.g. using GAGG crystal)All components:• High radiation hardness• Very precise timing (<70 ps)• High data rates

Using primary SPS proton beam, ∫ =1018 PoT

TauFV

ESPP

U in

put,

ID=4

2, 1

2ES

PPU

inpu

t, ID

=42,

102



100 m

PBC examples: MATHUSLA, LDMX@eSPS


LDMX@eSPSLight Dark Matter eXperiment at ~16 GeV e- beam.Measurement of soft recoiling electron with large pT

• High-precision strip tracker• Highly granular ECAL, with ~50 ps time resolution

per calorimeter cluster• HCAL, scintillator bars wit SiPM readout

Detector requirements overlapping with:• e+e- colliders for the tracking• HL-LHC (CMS HGCal) for calorimetry

MATHUSLA, long-lived particles produced at LHCMeasurement of a displaced vertex, at ~100 m from IPDetector:Surface 100×100 m2, height 20 m, 5 tracking layersO(cm) spatial resolution, O(ns) time resolutionBoth RPC and scintillator considered

Main detector challenge:Very large surface at low cost

ESP

PU

inp

ut,

ID=4

2, 7

5ES

PP

U in

pu

t, ID

=42,

36



neutrino long baseline and near detector


DUNE far detectorBaseline 1300 km, on-axis beamBeam power: 1.2 MW (2.4 MW)Far detector: four 10 kt target LAr-TPCPossible mix of single phase and dual phase

ProtoDUNE Dual Phase ⇔ DP field cage assembled and tested at CERN neutrino platform

ProtoDUNE Single phase

example: DUNE

ESPP

U in

put,

ID=1

26DU

NE N

D pr

es. D

resd

en

Longe baseline " has challenges in common with non-accelerator " expts and dark matter searches large mass, purity, large area photodetectors


https://indico.desy.de/indico/event/21211/session/5/contribution/17

neutrino long baseline and near detector


DUNE Near Detector (ND) has multiple purposes:

• Understand beam, detector + many systematic effects

> Multiple devices will be needed

• Physics programme on its own

Current DUNE ND design approach:A. Have a capable Multi-Purpose Detector (MPD) to:

o constrain ( flux (target nucleus does not matter)

o measure as many differential cross sections as possible on argon

- sensitive to pions, protons, neutrons, electrons, photons

- other nuclear targets might be useful (especially H)

B. Have a LAr TPC to measure

o reactions on argon (mostly inclusive)

o constrain detector effects

Synergies with other detector developmentse.g. CALICE ECAL, gas TPC applications

ESP

PU

inp

ut,

ID

=1

26

DU

NE

ND

pre

s. D

resd

en

ND LAr TPC

with pixel readout (as required for high intensity)

MPDwelcoming new collaborators


https://indico.desy.de/indico/event/21211/session/5/contribution/17

and much more……


Apologies for the many inspiring future experiments not covered in this talk

Several other neutrino experimentsaccelerator-based

non-accelerator based

Many of the PBC projectsESPPU input, ID=42

New study for an experimentat a muon collider link

Experiments at the Super Charm-Tau (SCT) e+e-

colliderESPPU input, ID=49

etc.




driven by requirements ⇔ generic R&D


From past and present experience:

Experiments made different technology choices

Yet, thanks to high-level efforts invested:

physics outcome is very similar !

Cost-effectiveness is obviously important

Maximising chances to observe the unexpected is also a key asset

Some level of generic “blue sky” R&D is important

To open doors to new opportunities and new physics discoveries

Summary


Future experiments require very challenging detector technologiesDepending on the application:• Much improved spatial resolutions (few !m per hit, low mass)• Much improved time resolutions (down to ~10 ps per hit)• High-performance photodetectors• Very high tolerance to radiation• Combined features in the same detector (5D imaging)• Very large numbers of channels, very high readout speed• Very large area coverage at low cost• Accompanied with a large diversity of engineering challenges

Electronics (CMOS technologies), high speed links and optoelectronics play increasingly important rolesAdvanced detector simulation tools are necessary to reach ultimate performances

R&D priorities • To be driven by requirements of future experiments• New ideas from generic R&D are also indispensable

Advanced detector technologies are essential for the progress in particle physics. They require high-level professional physics and engineering skills,

the ability to generate original ideas and dedicated effort over many years.Detector R&D needs strong support !


CERN EP Detector R&D programmeIn view of the challenging detector requirements for future experiments, the CERN EP department engages in a long-term advanced detector R&D effort.

The EP R&D programme focuses on those technology areas where CERN has significant expertise and infrastructure and already plays a unique role (ASICs, links, magnets, infrastructure for detector construction).

The developments will be carried out jointly with external groups. Enlarging the collaborative efforts with other research institutes and with industrial partners is an integral part of the objectives.

The selection of topics and the established work plans are the result of a transparent and open process, which took place in 2017-2018.

ESPP

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ID=1

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http://cds.cern.ch/record/2649646


RESERVEMATERIAL

30

Interesting pp events need to be foundwithin many simultaneous collisions

Linssen, Granada symposium 2019

pp collisions / e+e- collisions

e+e- events are more “clean”

collision energy

e+e- processes

factor > 107

pp cross section

collision energy

Impact on detector requirementsHigh radiation levels in the detector Much lower radiation levels (<10-4 LHC)

Complex triggering schemes needed No triggers needed

Collisions have strong forward boost Less forward boost, but increases with √s

O(10 ps) timing requirement (minimum bias) No or O(1 ns) timing requirement (beam background)

Somewhat more relaxed accuracy requirements Very high accuracy requirements

pp e+e-

Comparison to ATLAS and CMS


• Compared to ATLAS / CMS, the forward calorimeters are moved far out in order to reach larger η, to reduce radiation load and increase granularity.

• Forward solenoid (or forward dipole) adds about 1 unit of η to tracking acceptance.• A large shielding (brown) stops neutrons from escaping to cavern and muon system

experimental conditions e+e-


Linear Colliders• Beam-induced background:

• Beamstrahlung (incoherent pairs and !! → hadrons)

• High occupancies in the detector => small readout cells needed

• O(1-5 ns) timing required at CLIC

• Low duty cycle • Power pulsing of electronics possible

• Triggerless readout • Beam crossing angle 14 mrad (ILC), 20 mrad (CLIC)

Circular Colliders• Beam-induced background

• Beamstrahlung (incoherent pairs and !! → hadrons) + Synchrotron radiation

• Circulating beams• Maximum detector solenoid field of ~2 T (3 T) => requires large tracker radius• Complex magnet shielding schemes near the beam

• Beam focusing quadrupole closer to IP (~2.2m)

• No power pulsing

• High luminosity and many bunches at Z pole• Drives detector performance, moderate timing requirements, high data rates

• Larger challenge to keep systematics very low• Beam crossing angle 30 mrad (FCC-ee), 33 mrad (CEPC)

Stronger engineering and layout constraints

CLIC detector


Final beam focusing is outside the detector

FCC-ee detectors


comparison CLIC and CLD detector


CLD is derived from the CLIC detector modelAdapted to FCC-ee conditions

Detector solenoidal field ↓ 2 T (4 T for CLIC)Outer tracker radius ↑ 2.15 m (1.5 m for CLIC)Beam pipe radius ↓ 15 mm (29 mm for CLIC)Inner vertex radius ↓ 17 mm (31 mm for CLIC)Max collision energy ↓ 365 GeV (3 TeV for CLIC)Hadronic calorimeter depth ↓ 5.5 λI (7.5 λI for CLIC)Layout respects the ±150 mrad cone for FCC-ee detector

Constraint from FCC-ee continuous operationPower pulsing not possibleIncreased tracker “mass” in simulation model

6 m

CLICFCC-ee

Beam-induced background at CLIC


Beam-beam background at IP:§ Small beams => very high E-fields

s Beamstrahlung

s Pair-backgroundsHigh occupancies

s γγ to hadronssEnergy deposits

�/�� q

q�/��

Simplified picture:Design issue (small cell sizes)

Impacts on the physicsNeeds suppression in data

Beamstrahlung è important energy lossesright at the interaction point

Most physics processes are studied well above production threshold => profit from full spectrum

Luminosity spectrum can be measured in situ using large-angle Bhabha scattering events,to 5% accuracy at 3 TeVEur.Phys.J. C74 (2014) no.4, 2833

http://link.springer.com/article/10.1140/epjc/s10052-014-2833-3

Documents

Detector challenges for future HEP experiments