Yesterday:
• Physics goals and LHC detector requirements
• Experimental environment
• Overall detector concepts
(ATLAS,CMS - ALICE and
LHCb more briefly)
• Magnetic configurations and momentum measurements
• A reminder about basic detector physics
• Inner Detector status and
Silicon Detectors
S.Stapnes SSI -Aug09
Today:
• Calorimeters
• Gas detectors (in Inner
Detectors and as Muon
Systems)
• Particle identification systems
• Status, commissioning and early physics
• Upgrades for SLHC
1

Sources used:
(1) Technical papers about the LHC experiments:
6) K.Kleinknecht; Detectors for particle radiation. Cambridge University Press, http://www.iop.org/EJ/toc/1748-
0221/3/08
ISBN 0-521-64854-8.
7) G.F.Knoll; Radiation Detection and
(2) Lectures at the fourth CERN-Fermilab Measurement. John Wiley & Sons, ISBN
Hadron Collider Physics Summer
School (G.Herten
– Tracking Detectors):
0-471-07338-5
8) CERN summer school 2009: Particle http://indico.cern.ch/conferenceOtherVi
Detectors. Lectures by W.Riegler ews.py?confId=44587&view=nicecomp
9) Particle Detectors; CERN summer act student lectures 2002 by C.Joram,
(3) W.R.Leo; Techniques for Nuclear and
CERN. These lectures (7 and 8) can be
Particle Physics Experiments. Springerfound on the WEB via the CERN pages,
Verlag, ISBN-0-387-57280-5; Chapters also video-taped.
2,6,7,10.
10) Status talks of Gianotti, Virdee,
(4 and 5)
Giubellino and Golutvin at EPS conf.
D.E.Groom et al.,Review of Particle
Physics; section: Experimental
Methods and Colliders; see http://pdg.web.cern.ch/pdg
/
Krakow July 09
In several cases I have included pictures from (1),(2),(8), (9) and (10) and text directly in my slides.
Section 27: Passage or particles through matter
Chapter 28 : Particle Detectors.
I would recommend all those of you needing more information to look at these sources of wisdom, and the references.
Steinar Stapnes 2

3

Electrons/positrons; modify Bethe Bloch to take into account that incoming particle has same mass as the atomic electrons
Bremsstrahlung in the electrical field of a charge Z comes in addition :
 goes as 1/m 2
S.Stapnes SSI -Aug09
The critical energy is defined as the point where the ionisation loss is equal the bremsstrahlung loss.
4

The differential cross section for Bremsstrahlung
(v : photon frequency) in the electric field of a nucleus with atomic number Z is given by
(approximately) http://prola.aps.org/pdf/PR/v93/i4/p768_1 : d
 
Z
2 dv v
The bremsstrahlung loss is therefore : where the linear dependence is shown.
The
 function depends on the material (mostly); and for example the atomic number as shown.
N is atom density of the material (atoms/cm 3 ).

( dE dx
)

N v
0

E o
0

/ h hv d
 dv dv

A radiation length is defined as thickness of material where an electron will reduce it energy by a factor 1/e; which corresponds to 1/N
 as shown on the right (usually called

0
).

( dE
E giving
)

N
 dx
E

E
0 exp(
1 /
 x
N

)

( Z
2
)
5 S.Stapnes SSI -Aug09

S.Stapnes SSI -Aug09 6

Radiation length parametrisation :
A formula which is good to 2.5% (except for helium) :
A few more real numbers (in cm) : air = 30000cm, scintillators = 40cm,
Si = 9cm, Pb = 0.56cm, Fe = 1.76 cm.
S.Stapnes SSI -Aug09 7

Photons important for many reasons :
• Primary photons
• Created in bremsstrahlung
• Created in detectors (de-excitations)
• Used in medical applications, isotopes
They react in matter by transferring all (or most) of their energy to electrons and disappearing. So a beam of photons do not lose energy gradually; it is attenuated in intensity (only partly true due to Compton scattering).
8 S.Stapnes SSI -Aug09 S.Stapnes SSI -Aug09

Three processes :
Photoelectric effect (Z 5 ); absorption of a photon by an atom ejecting an electron. The cross-section shows the typical shell structures in an atom.
Compton scattering (Z); scattering of a photon again a free electron (Klein Nishina formula). This process has well defined kinematic constraints (giving the so called
Compton Edge for the energy transfer to the electron etc) and for energies above a few
MeV 90% of the energy is transferred (in most cases).
Pair-production (Z 2 +Z); essentially bremsstrahlung again with the same machinery as used earlier; threshold at 2 m e
= 1.022 MeV. Dominates at a high energy.
S.Stapnes SSI -Aug09
Plots from C.Joram
9

Ph.El.
Pair Prod.
Compton
Considering only the dominating effect at high energy, the pair production cross-section, one can calculate the mean free path of a photon based on this process alone and finds :
Photon mfp


 x exp(

N
 exp(

N
 pair pair x ) dx x ) dx

9
7

0

10 S.Stapnes SSI -Aug09

Considering only Bremsstrahlung and Pair
Production with one splitting per radiation length
(either Brems or Pair) we can extract a good model for EM showers.
From C.Joram
S.Stapnes SSI -Aug09 11

More :
Text from C.Joram
Text from C.Joram
S.Stapnes SSI -Aug09 12

The total track length :
Intrinsic resolution
:
T

N

( E )
E
 tracks 0


( T )
T

E
0
E
C


1
0
T

1
E
Text from C.Joram
S.Stapnes SSI -Aug09 13

From Leo
Text from C.Joram
FYS4550, 2005 Steinar Stapnes 14

CRAFT*: Cosmics Run at Four Tesla
* Operating field of CMS is 3.8T
Ran CMS for 6 weeks (Oct-
Nov’08) continuously to gain operational experience, stability of infrastructure.
Collected 300M cosmic events . About 400 TB of data distributed widely. e
~ 70% (24/7)
First analyses of these data used s/w release destined for
2008 data-taking & LHC grid infrastructure.
Re-reconstruction and analyses with more advanced versions of the release.
15

Alignment in Inner Tracker
Distn of Mean Residuals
Energy deposited by muons
Muon Chambers
Point Resolution
MB4
ECAL total
Si Trkr
Modules
TOB x
3.2 um
Points- data
MB3

~250um radiative ionisation
MB2
HCAL
Bpix
Modules
PXB x
3.1 um
MB1
S.Stapnes SSI -Aug09 16
16

Barrel calorimeter (EM Pb/LAr + HAD Fe/scintillator Tiles) in its final position at Z=0.
November 2005
18

19

Calorimeters:
• CMS homogeneous
• ATLAS sampling
• Readout (in a magnetic field): not easy but not covered here
20

Text from C.Joram
Define hadronic absorption and interaction length by the mean free path (as we could have done for

0
) using the inelastic or total crosssection for a high energy hadrons
(above 1 GeV the cross-sections vary little for different hadrons or energy).
S.Stapnes SSI -Aug09 21

Text from C.Joram
S.Stapnes SSI -Aug09 22

S.Stapnes SSI -Aug09 23

S.Stapnes SSI -Aug09 24

25

HB
HE
Before After
HF
HB HE HF
BPTX adjusted on-the-fly to be in time with HF
L1 Trigger Timing
# orbits
26

White areas: masked from readout
ECAL Endcaps (lhs), Barrel (rhs)
> 99% of ECAL channels alive, ~200 TeV energy deposited in EB+EE
Inter-crystals timing established (< 1ns), inter-crystal calibration EB (1.5-2.5% test beam + cosmics), EE (~7% from splash events)
HCAL Endcap : un-captured (lhs) and captured circulating beam (rhs)
27

28
See D. Froidevaux & P. Sphicas An. Re. Nucl. Part. Sci 56 (375) 2006
E p [ GeV ]
ATLAS CMS p
T
10
Mass [tons] 7000 12500
Diameter 22 m 15 m
E Length 46 m 22 m / 2 E
Solenoid 2 T 4 T
|
η|<2.7 : Muon spectrometer


(1TeV muons)
/ 100
| η|<2.6 : Muon spectrometer


(1TeV muons)
Joe Incandela UC Santa Barbara

• Verified in testbeams, and by in situ calibration methods in labs and after installation
• Can check partly with cosmic muons - but limited as seen in previous slide
• Timing also partly checked using single beam splashes in 2008
• Will need beam to reduce energy resolution towards final values
• However, overall status very good
29 S.Stapnes SSI -Aug09

S.Stapnes SSI -Aug09

S.Stapnes SSI -Aug09 31

The different regions :
Recombination before collection.
Ionisation chamber; collect all primary charge. Flat area.
Proportional counter (gain to 10 6 ); secondary avalanches need to be quenched.
Limited proportionality (secondary avalanches distorts field, more quenching needed).
Geiger Muller mode, avalanches all over wire, strong photoemission, breakdown avoided by cutting HV.
Again I recommend:
Particle Detection with Drift Chambers,
W.Blum, W.Riegler and L.Rolandi, Springer
Verlag, ISBN 3-540-76683-4.
Concerning: amplification, mobility, drift, diffusion, induced signal
32 Steinar Stapnes

Muon Spectrometer
Precision chambers
Trigger chambers
~ 700 barrel precision chambers (Monitored
Drift Tubes), ~ 600 barrel trigger chambers
(Resistive Plate Chambers)
33

S.Stapnes SSI -Aug09 34

35

36

37

CSC chambers
6 Staggered planes of strips
Near the strip edges
Top Leg 1
Bottom Leg
Momentum Resolution <2-leg>
Near the centre
1/

2 (chamber) = 3/

1
2 + 3/

2
2

(ME2/1) = 161 m m (TDR = 150 m m)
T. Virdee EPS Jul09 38

130 mm active area 70 mm
Flat cable connector
Differential signal sent from strip to interface card
M5 nylon screw to hold fishing-line spacer connection to bring cathode signal to central read-out PCB honeycomb panel
(10 mm thick)
PCB with cathode pickup pads external glass plates
0.55 mm thick internal glass plates
(0.4 mm thick)
PCB with anode pickup pads
Mylar film
(250 micron thick)
5 gas gaps of 250 micron
PCB with cathode pickup pads
Honeycomb panel
(10 mm thick)
Silicon sealing compound
W. Riegler/CERN
Several gaps to increase efficiency.
Stack of glass plates.
Small gap for good time resolution:
0.25mm.
Fishing lines as high precision spacers !
Large TOF systems with 50ps time resolution made from window glass and fishing lines !
Before RPCs  Scintillators with very special photomultipliers – very expensive. Very large systems are unaffordable.
39

Time projection chamber :
Drift to endplace where x,y are measured
Drift-time provides z
Analogue readout provide dE/dx
Magnetic field provide p (and reduce transverse diffusion during drift)
CLAF 2005 Steinar Stapnes
From Leo
40

Gas volume with parallel E and B Field.
B for momentum measurement. Positive effect:
Diffusion is strongly reduced by E//B (up to a factor 5).
Drift Fields 100-400V/cm. Drift times 10-100 m s.
Distance up to 2.5m !
gas volume y
B drift
E z x charged track
Wire Chamber to detect the tracks
W. Riegler/CERN
41

• Largest TPC:
– Length 5m
– Diameter 5m
– Volume 88m 3
– Detector area 32m 2
– Channels ~570 000
• High Voltage:
– Cathode -100kV
• Material X
0
– Cylinder from composite materials from airplane industry
(X
0
= ~3%)
W. Riegler/CERN 42

TPC installed in the ALICE Experiment
4/9/2020
W. Riegler, CERN

MICROMEGAS
Narrow gap (50100 µm) PPC with thin cathode mesh
Insulating gap-restoring wires or pillars
GEM
Thin metal-coated polymer foils
70 µm holes at 140 mm pitch
Y. Giomataris et al, Nucl. Instr. and Meth. A376(1996)239
4/9/2020
F. Sauli, Nucl. Instr. and Methods A386(1997)531
W. Riegler, Particle Detectors 44

In addition we should keep in mind that EM/HAD energy deposition provide particle ID, matching of p (momentum) and EM energy the same (electron ID), isolation cuts help to find leptons, vertexing help us to tag b,c or

, missing transverse energy indicate a neutrino, etc so a number of methods are finally used in experiments.
Steinar Stapnes 45

46


A particle with velocity
 in a medium with refractive index n

=v/c may emit light along a conical wave front if the speed is greater than speed of light in this medium : c/n q
Cherenkov
The angle of emission is given by cos q  c / nt
 ct
 1
 n
5 4
CERN-Claf, O.Ullaland
3 2 eV and the number of photons by
N
 
1
 
2
 
4.6

10
6


2
1
( A )


1
1
( A )

L ( cm )sin
2 q
Steinar Stapnes
FYS4550, 2005 47

W. Riegler/CERN 48

10 September 2008, ~10h am : waiting for first beams in the ATLAS Control Room
49

50

(examples ….)
Slides for Fabiola Gianotti - EPS, Krakow
51

52

53

54

55

T. Virdee EPS Jul09 56

57

58


Detector commissioning – much already done using cosmics/testbeam,..



Early beam - collisions, up to 10pb -1 @ 10 TeV

Detector synchronization, alignment with beam-halo events, minimum-bias events. Earliest in-situ alignment and calibration

Commission trigger, start “physics commissioning” – “rediscover SM”:


Physics objects; measure jet and lepton rates; observe W, Z, top
And, of course, first look at possible extraordinary signatures…
Collisions, 100pb -1 measure Standard Model, start search

Per pb-1: 6000 W
 l

(l = e, m
); 600 Z
 ll (l =e, m
); 40 ttbar
 m
+X


Improved understanding of physics objects; jet energy scale from
W
 j j’; extensive use (and understanding) of b-tagging

Measure/understand backgrounds to SUSY and Higgs searches
Early look for excesses from SUSY & Z’ resonances.
Collisions, 1000pb -1 entering Higgs discovery era

Also: explore large part of SUSY and resonances at ~ few TeV
59








A factor 10 higher luminosity …
Replace complete Inner Detectors
Electronics for calorimeters and muon chambers might need changes
Possible some detectors in the forward/endcap regions (muon chambers, calorimeters)
Shielding and beampipe optimisation
Trigger to cope with increases complexity of events
Costs: 40-50% of current detectors, one year shutdown of LHC to do it
Steinar Stapnes SLHC detectors, 2008
6
0




300 – 400 pile-up events at start of spill
(unless luminosity leveling)
Want to survive at least 3000 fb -1 data taking
B-layer at 37 mm:


~30 tracks per cm -2 per bunch crossing
>10 16 1 MeV n-equivalent non-ionising
 Few 10s of MGray
Steinar Stapnes SLHC detectors, 2008
6
1

 Inner Tracker Triggers at Level-1
 Muon trigger rate ~constant above ~20-30



GeV/c; both ATLAS and CMS
Current understanding is this is due to multiple scattering at CMS and width of RPC strips at ATLAS
Cannot improve muon situation at CMS; difficult at ATLAS (new muon trigger chamber layer with higher resolution?)
Several ideas to investigate Inner Tracker triggers (ASIC development demanding)
 Both Pt and vertex displacement triggers
High momentum tracks are straighter so elements line up in nearby layers
Search
Window
Pairs of stacked layers can give a P
T measurement
Steinar Stapnes SLHC detectors, 2008
6
2



Depending on backgrounds, either minimal or very large fraction of ATLAS muon system needs replacing, unless backgrounds can be reduced
(in relation to luminosity)
Both ATLAS and CMS have to wait for data
Steinar Stapnes SLHC detectors, 2008
6
3

• The LHC detectors are (remarkably well) ready for datataking
• Their designs are well optimized for the job and cover most issues one can imagine related to detector physics and instrumentation
• Early physics has to the promise of being exiting from day 1 – critical elements, beyond the currently tested detector performance, will be triggering, calibration, fast turn around of initial data analyses
• Long term performance and reliability of the detectors, as well radiation damage and background conditions will determine the need for improvements – and the scale of upgrades needed.
• Any sLHC scenario will require need Inner Detectors around 2018-2020.
S.Stapnes SSI -Aug09 64

S.Stapnes SSI -Aug09 65

• Three major systems
– Calorimeter Trigger
– Muon Trigger
– Central Trigger Processor
(CTP)
• Other triggers and signals also integrated by CTP
– Minimum bias
– Luminosity triggers
– Beam Pick-up
• CTP distributes all timing information

• Dataflow view of TDAQ infrastructure:
Underground
Detectors
Surface
Permanent Storage
Readout Drivers
Dedicated Optical Links
Readout Buffers
Readout
System
Node
Sub Farm Output
Sub Farm Input
Data Network
Data Flow
Manager

Thanks to James Stirling
HWW search
NLO MCFM x-sec (14:10TeV) gg  H 1 : 0.54
WW and WZ tt
W+jets and DY
1 : 0.65
1 : 0.45
1 : 0.68
68