–  based  on  D.  Green,  M.  Thomson,  Braibant  et  al  &  LHC,  Tevatron,  ATLAS,
CMS,  …
19/03/15 1

¡
¡
¡
¡
¡
¡
¡
¡
Accelerators  and  detectors  –  briefly
SM  Particles  -­‐  Mapping  into  Detector  Subsystems
Tracking  and  b  Tagging
Electromagnetic  Calorimetry  -­‐  e  and
Hadron  Calorimetry  -­‐  Jets  of  q  and  g  and  neutrino
(missing  Et)
Muon  Systems
Complex  Event  Topologies  in  D0,  CDF,  ATLAS,  CMS
Fragmentation,  Minimum  Bias  Events,  Pile-­‐up

N
L
§
N :  Distribution  of  number  of  events
▪   Distribution  measured  by  detector
§
L :  Luminosity
▪   Accelerator
§
:  Cross-­‐section
▪   Fermi’s  golden  rule
▪   M:  matrix  element  –  transition  probability  i à f  calculable   using  Feynman  diagram  rules

¡
¡
¡
¡
Hadron  colliders
§
Discovery  machines
▪   Fraction  of  proton  momentum  carried   by  parton,  x,  varies
▪   large  domain  of  energies  investigated   simultaneously
▪   Potential  source  of  discovery  and   surprises
Electron  colliders
§
Precision  machines
▪   Linear  colliders    as  a  solution  to  the   synchrotron  radiation  problem  of   circular  colliders
▪   Bigger  circular  machines
▪   Muon  colliders?   ep-­‐colliders
§
§
…
Exploration  and  precision
Measurement  of  structure  functions,
…

Complementary role of collisions with various beams:
e+e-
ep
pp
ppbar
nuN
nue
heavy ion - HI
p HI
…
¡
19/03/15
Once  good  energy  budget  …  give  a  chance  to  rare  processes  …
F.  Ould-­‐Saada:  HEPP  &  ATLAS   5

( pp
19/03/15
Luminosity L n. of protons per bunch n. of bunches
L =
N 2 k b f
4
x
y n. of turns per second beam size at IP
( σ x,y
= 16 µ m)
F.  Ould-­‐Saada:  HEPP  &  ATLAS
Cross-section
Very small for new processes
6

¡
Particles
§
§
Stable:  e -­‐ ,  e + ,  p,   γ ,   ν
Unstable:  travel  d=
γ v
τ
▪   >10 -­‐10 s  –  quasi  stable  (several  meters  in  detectors):
µ
± ,  n,
π
± ,  K ±
▪   <10 -­‐10 s  –  short-­‐lived:  decay  in  detectors  area

¡
Detect  SM  particles  by  way  of  their  characteristic  interactions
Particle
, , → +
Fundamental elementary particles in the Standard Model, their detection
in particular detector subsystems and a signature allowing for particle identification
in those subsystems.
Signature
Jet of hadrons
Detector
Calorimeter
λ g e , γ Electromagnetic Shower Calorimeter (ECAL)
W
, ,
τ
→ µ + ν
µ
( X o
)
“Missing” transverse energy
Calorimeter
µ , τ → µ + ν
τ
+ ν
µ
Z → µ µ
τ
Only ionization interactions dE dx
Decay with c τ > 100 µ m
Muon Absorber
Silicon Tracking

¡
¡
¡
§   loses  energy  almost  constantly     is  slightly  deflected  from  its  initial  direction.     §
§
§
1.  Inelastic  collisions  with  atomic  electrons
▪    produce  ionization  and/or  excitation  of  the  atoms  of  the  medium
▪   excited  atom  de-­‐excites,  emitting  one  or  more  photons.
2.  Elastic  collisions  with  nuclei
▪    less  frequent;
▪   do  not  cause  a  loss  of  energy,
▪   lead  to  variation  in  the  direction  of  the  incident  particle
19/03/15 F. Ould-Saada 10

− dE dx
= 2 π N a m e r e
2 c 2
ρ
Z
A z 2
β 2
(
)
* ln $
"
#
2 m e
γ 2 v 2 W max
I 2
%
&
'− 2 β
2
− δ − 2
C
Z
+
,
-
¡
¡
¡
¡
¡
¡
¡
¡
¡
¡
¡
¡
¡
¡   r e
=e 2 /m e c 2  =  2.818  x  10 -­‐13  cm:  classical  electron   radius
N
2 a
π m e
=  N
N a r e
A
2
Z   m e
ρ
/A   c 2  =  0.1535MeV  g -­‐1  cm 2
=  electron  mass  =  0.55110MeV/c 2 =  9.110  x  10 -­‐31   kg
N
A
=  Avogadro’s  number  =  6.022  x  10 23  mol -­‐1
I  ~10eV=  mean  ionization  (excitation)  potential   of  the  target
Z,A  =  atomic  number  and  atomic  weight  of  the   absorber  medium
ρ
=  material  density   ze   =  charge  of  the  incident  particle
β
=v/c  of  incident  particle
γ
=1/sqrt(1-­‐
β 2 )
δ =
density  effect  correction  (important  at  high   energy)
C  =  shell  correction  (already  important  at  low   energy)
W max
=  maximum  kinetic  energy  imparted  to  an   e -­‐  in  a  single  collision  ~2m e c 2  (
βγ
) 2  for  M>>  me
19/03/15 F. Ould-Saada
(a)  Energy  loss  through  ionization  for   π
±  mesons  in  copper.  The  general   behavior  is  shown  together  with  some  definitions  and  corrections  due   to  the  density  effect  (responsible  for  the  smaller  relativistic  rise)  and   two  different  approximations  at  low  energies.     11

¡
¡
¡
¡
¡
Energy  loss  only  depends  on
βγ
§
P=Mv
γ
=M
βγ c   à
βγ
=P/Mc
§
Dependence  of  dE/dx  on  material  only   through
ρ : dE/dx  ~Z/A  ~  constant
Scaling  law
− dE
2 dx
( E
2
) ≅ − z
2
2 z
1
2 dE
1 dx
#
%
$
E
2 m
1 m
2
&
(
'
Difference  in  Energy  loss
§
Liquid  H2  (Z/A=1),  Gaseous  materials  (He,  Z/
A=0.5),  Solid  materials  (Z/A~0.5)
Specific  energy  loss
§
§
At  minimum  ionisation:  (dE/dx) min g -­‐1 cm 2
~1.5  MeV
At  high  energies:  (dE/dx)~2  MeV  g -­‐1 cm 2 for
βγ
=3  (MIPs  –  muons)
The  energy  loss  curves  show  a  minimum
19/03/15 F. Ould-Saada
10
8
6
5
4
3
2
1
0.1
0.1
H
2
liquid
He gas
Pb
Sn
Fe
A l
C
1.0
10
βγ
100
= p / M c
1000
0.1
1.0
10
Mu o n m o mentum ( Ge V/ c )
100
0.1
1.0
10
Pi o n m o mentum ( Ge V/ c )
100
1.0
10 100
Pr o t o n m o mentum ( Ge V/
1000 c )
10 000
1000
1000
10 000
12

50000
20000
10000
5000
Pb
Fe
C
¡
¡
¡
¡
Integrate  BB-­‐formula  in  order  to   determine  the  range
§
total  path  length  of  a  particle  that   looses  energy  only  through  ionization
2000
1000
500
200
100
50
20
10
“Range”  of  charged  particles,  normalized  to  the
5 mass  M  of  the  particle  as  a  function  of
βγ
à   2
1
0.1
2
Proton  of  200MeV  energy  (M~1GeV)
βγ
~  0.2   à  R/M  x  M  ~  1  g  cm -­‐2 ,
~1  cm  of  water.
0.02
0.02
1GeV  proton:  range  is  R  ~  100  g  cm -­‐2
0.1
0.2
0.05
5 1.0
2 5
βγ
= p / M c
He gas
H
2
liquid
10.0
2
0.05
0.1
0.2
0.5
1.0
Mu o n m o mentum ( Ge V/
2.0
c )
0.1
0.2
0.5
1.0
Pi o n m o mentum ( Ge V/
2.0
c )
0.5
1.0
2.0
5.0
10.0
Pr o t o n m o mentum ( Ge V/ c )
20.0
5.0
5
5.0
100.0
10.0
10.0
50.0
19/03/15 F. Ould-Saada 13

¡
¡
¡
¡
Important  application  of  the  concept  of    range  of  a   particle  in  the  medical  field.
Hadron  therapy
§   is  the  most  recent  relative  of  conventional   radiotherapy,  which  uses  X-­‐rays.
§   uses  beams  of  protons,  carbon  ions  or  neutrons.
Protons  accelerated  to  200MeV  or  carbon   ions  accelerated  to  4.7  GeV  may  be  used  to   irradiate  deep  tumors  by  following  the  tumor   contour  with  millimetric  precision,  allowing   one  to  preserve  the  surrounding  healthy   tissue.
§
The  accelerated  hadrons  are  able  to  destroy  sick  tissue   mostly  at  the  end  of  their  range  in  the  body  of  the   patient,  where  the  tumor  is  situated
A  beam  of  charged  hadrons  releases  the  greatest   part  of  its  destructive  energy  on  the  target  tumor.
§
The  dose  received  at  the  tumor  can  therefore  be  very   high  while  the  healthy  tissue  is  saved.
¡
19/03/15 F. Ould-Saada
Unlike  electrons  or  X-­‐rays,  the  dose  from  protons  to   tissue  is  maximum  just  over  the  last  few  millimeters  of   the  particle’s  range.
14

¡
¡
¡
¡
In  a  typical  treatment  plan  for  proton   therapy,  the  spread  out  Bragg  peak  (SOBP,   dashed  blue  line),  is  the  therapeutic  radiation   distribution.
The  SOBP  is  the  sum  of  several  individual
Bragg  peaks  (thin  blue  lines)  at  staggered   depths.
The  depth-­‐dose  plot  of  an  x-­‐ray  beam  (red   line)  is  provided  for  comparison.
The  pink  area  represents  additional  doses  of   x-­‐ray  radiotherapy—which  can  damage  to   normal  tissues  …
§   http://en.wikipedia.org/wiki/Proton_therapy
19/03/15 F. Ould-Saada 15

−
"
$
#
¡
¡
¡
Bremsstrahlung
§
§
§   emission  of  a  photon  from  an  electron  deflected  by  a  nucleus   process  due  to  the  EM  interaction  producing  large  energy  loss   dominates  the  energy  loss  with  respect  to  ionization  and  excitation  for  high
βγ
Given  small  electron  mass,
§   already  happens  for  a  few  tens  of  MeV  for  electrons  in  lead     and  hundreds  of  MeV  for  lighter  materials   §
Process
§
§   slowing  down  of  the  incident  electron  caused  by  the  nuclear  Coulomb  field
The  amplitude  of  the  emitted  radiation    ~1/m e
–  probability  ~1/m e
2
¡
Energy  loss  per  path  length  unit:   dE dx
19/03/15
%
'
& rad
≈
4 N a
Z 2 V α
3 em m e
2 c 4
( !
c ) 2
F. Ould-Saada
E   ln
"
$
#
183
Z 1/3
%
'
&
§
§
N a
=  N
A
Z
ρ
/A:  number  of  atoms  cm -­‐3
Logarithm  due  to  screening  of  nucleus   from  atomic  electrons   à  limitation
16

¡
¡
Low  energy
§
Energy  loss  of  electrons  dominated  by  ionisation
§
§
(Photoelectric  effect  for  photons)
E>critical  energy  E
Bremsstrahlung   c
E c
~
800
Z
MeV
¡
Muons  and  photons
§
§
Muons/electrons   à  suppression  (m e
E
µ
/m
µ
) 2
>100GeV  Bremsstrahlung  adds  to  ionisation
§
§
E
γ
~1MeV,  Compton  scattering:
γ e à
γ e
E
γ
>10  MeV,  dominated  by  e + e -­‐  pair  production  in  field  of  nucleus

¡
¡
¡
§
Charged  particle  through  medium   à  trail  of  ionised  atoms+e
2  main  tracking  detector  technologies
§
Detect  tracks  in  large  gaseous  volume  by  drifting  electrons  in  strong  E-­‐field  towards  sense   wire  where  signal  is  recorded
§
Semiconductors  using  silicon  pixels  (2D  space  points)  and  strips  (O(25
µ m)
▪   Charged  particle  traversing  doped  silicon  wafer   à  ionisation   à  e-­‐hole  pairs  (O(10  000))
▪   Potential  across  silicon   à  holes  drift  in  direction  of  E-­‐field   à  collection  by  p-­‐n  junctions
Large  solenoid  with  B//  colliding  beams  (z-­‐axis)
§
è helix  with  radius  of  curvature  R  and  a  pitch  angle
λ
–  for  single  particle
CMS:  100  GeV
π
±  in  B=4T   à R~100  m
p[GeV] cos λ = 0.3 B[T]R[m]

¡
Organic  scintillators
§
§
Detect  passage  of   charged  particles  –  no   precise  spatial   information  required
▪   à  excited  molecules   à   emission  of  UV  light
▪   Fluorescent  dyes   molecules  absorb  UV  and   reemit  blue  photons   detected  by   photomultipliers  (down   to  single  optical  photons)
Plastic  &  liquid  SC  widely   used    in  neutrino   experiments
19/03/15 F. Ould-Saada 19

¡
Charged  particle  in  dielectric   medium  (refractive  index  n)   polarises  molecules
§
Emission  of  photons
§
§
If  v>c/n   à  constructive   interference,  Cerenkov  radiation   as  coherent  wavefront  at  fixed   angle
θ
to  trajectory  of  particle
(analogous  to  sonic  boom  by   supersonic  aircraft
¡
¡
In  time  t  particle  travels  d=
β ct
In  t  wavefront  emitted  at  t=0   travelled  d’=ct/n
¡
¡
Cerenkov  radiation  only  when
β
>1/n
Threshold  behaviour   è  identification   of  particles  of  given  p
⇒
β = pc
=
E
β > 1 / n cos θ =
1 n β p p 2
+ m 2 c 2
$
%
"
$
# ⇒ mc < n 2
− 1   p ⇒ C − radiation

¡
¡
EM  shower  /  cascade   with  large  with  many   e +,   e -­‐ ,
γ
§
In  matter,  a  high   energy  photon   converts  into  an  e + e -­‐   pair;  each  able  to   radiate  energetic   photons  through   bremsstrahlung,   followed  by  e + e -­‐   pairs,  …  These   radiated
Process  stops  when
E
§   e
<E critical
Electrons  lose   energy  only  through   ionization  and   excitation
19/03/15 F. Ould-Saada 21

¡
¡
Cascade  development  as  statistical   process
§
§
§
§   primary
γ
(E
0
)  converts  into  e + e -­‐   after  L rad
à
<E e
>=E
0
/2   e
à
+ ,e
<E
-­‐   emit   i
>=E
γ after  2 nd  L rad
0
/4  ,  2 2  particles
After  3 rd   L rad
à
<E i
>=E
0
/8,  i=2 3
After  t th   L rad
à
<E
N
>=E
0
/2 t ,  N=2 t
§   t=x/L rad
Same  result  for  a  cascade  initiated   by  an  electron
19/03/15 F. Ould-Saada 22

¡
¡
Maximum  penetration  of  cascade
E t max
≅
E
0
2 t max
= E c
⇒ t max
≅ ln
#
%
$
E
0
E c
&
(
' ln 2
Maximum  number  of  particles  in   cascade  at  given  instant:
N max
≅
E
0
E c
¡
Simulation
§   electromagnetic  cascade  is   fully  contained  in  about  20–
25  radiation  lengths.
0.125
0.100
0.075
0.050
0.025
0.000
0
19/03/15 F. Ould-Saada
5
Energy
Ph o t o ns
×
1 / 6.8
Ele c tr o ns
10
30 Ge V ele c tr o n in c ident o n ir o n
15 t = depth in radiati o n lengths
20
20
0
60
40
100
80
23

¡
X
0
Radiation  length  X0
§
Average  distance  over  which  energy  of  electron  reduced  by  Bremsstrahlung  by  factor  1/e
§
≈
X0~7/9of  free  mean  path  of  e + e -­‐  pair  production  of  high-­‐energy  photon
1 e 2
4 α nZ 2 r e
2 ln
"
$
#
287
Z
%
'
&
;    r e
=
4 πε
0 m e c 2
= 2.8
× 10 − 15 m
§
For  High-­‐Z  materials  X
▪   X
0
(Fe)=1.76cm  ,  X
0
0
relatively  short
(Pb)=0.56cm
¡
§
§
EM  showers:  electrons
§
§
§
§
à
Photons  start  with  e + e -­‐  pairs
Nber  of  particles  ~  doubles  after  every   X
0
E ≈
Shower  continues  to  develop  until  <E>  <E c
Shower  maximum
E ≈ E c
⇒ x max
= ln ( E
E
/ x
E ln(2) c
)
High-­‐Z  material  (Pb):  E c
~10MeV,  100GeV  EM  shower  max  after  13X
0
~10  cm  of  Pb
Large  nber  of  particles:  2 xmax

¡
A  calorimeter  is  a  detector  that  absorbs  all  the   kinetic  energy  of  a  particle  and  provides  an   electronic  signal  proportional  to  the  deposited   energy.
§
§
§
Electrons  and  photons  lead  to  EM  showers
Hadrons  to  hadronic  showers
Muons  to  minimum  ionisation  in  both  ECAL  and  HCAL
¡
Charged  hadrons  (p,
π
± )
§
Energy  loss  by  ionisation  +   strong  interaction  with  nuclei
(also  neutral  hadrons)
§
Hadronic  showers  parametrised   by  interaction  length
λ
I
▪   Mean  distance  between  hadronic   interaction  of  relativistic  hadrons
▪   Fe:
λ
I
~17cm,  X
0
~1.8cm
▪   π
0 )
à γγ
:  EM  component
¡
EM  (CMS)
§
75000  crystals
(PbWO 4 ),  X0~0.83c
σ
E ~
E
3% − 10%
E [ GeV ]
¡
HC  (ATLAS)
σ
E
E
≥
50%
E [ GeV ]

¡
§
Jet  energy
▪   60%  (charged,  mainly
π
± )
▪   30%  (
γγ
from
π
0 )
▪   10%  (neutral  hadrons,  mainly  K l
,K s
)   p mis
= −
i p i

¡
§
§
Hadronisation   à  B-­‐meson,
τ
~1.5  ps
In  HE,  d~
β c
τ
~few  mm  before  decaying
▪   Secondary  vertex  resolved  from  primary  by  silicon  vertex  detectors
(single  hit  resolutions  of  O(10
µ m)

19/03/15   F.  Ould-­‐Saada:  HEPP  &  ATLAS   28

19/03/15 F. Ould-Saada: HEPP & ATLAS
the various particles have different signatures in different parts of the detector
by combining the various signatures, we can reconstruct how the particle moved through the detector
how the various particles are here

Experimental Particle Physics @ UiO F. Ould-Saada, 11/2012 30

Muon system
Hadronic
Tracker
EM
CDF
Coarse Hadronic
(Tail catcher)
Muon system
Magnetized iron
DØ
Fine Hadronic
EM
Tracker

v=0.99999991  c
100
µ s  per  round  …  10  000  rounds  per  second
19/03/15   F.  Ould-­‐Saada:  HEPP  &  ATLAS   34

q   Particle  collisions   at  LHC
Ø   Simulated   proton  +  proton
à  black  hole   candidate
Ø   LHC  collides   also  heavy  ions:   pb-­‐pb  and  p-­‐pb   q   Sensitivity  to  rare   phenomena  –  with   small  cross   sections  –     depends  on  the   luminosity
Higgs  and  more  -­‐  F.  Ould-­‐Saada   19/03/15   35

ATLAS superimposed to the 5 floors of building 40
24 m
45 m
7000 Tons
36

Let’s     build
ATLAS     in  ~  1   minute  …
Higgs  and  more  -­‐  F.  Ould-­‐Saada   19/03/15   37

A  real  event  in  a  detector  …
Higgs  and  more  -­‐  F.  Ould-­‐Saada   19/03/15   38

CMS: 2900 physicists
184 Institutions
38 countries
550 MCHF
LHCB 700 physicists
52 Institutions
15 countries
75 MCHF
ALICE; 1000 physicists
105 Institutions
30 countries
150 MCHF and 3 smaller experiments
TOTEM
LHCf
MoEDAL
ATLAS : 3030 Physicists
174 Institutions
38 countries
550 MCHF
F.  Ould-­‐Saada:  HEPP  &  ATLAS   39

Momentum and energy resolutions
Tracking dP / P = cP ⊕ d
Calorimetry dE / E = a / E ⊕ b
The momentum resolution for tracking increases with energy
The energy resolution for calorimetry decreases with energy
Si Tracker
pixels
strips
Crystal ECAL
HCAL
barrel
outer
endcap
forward
4 T Magnet
Muon
barrel
endcap

¡
¡
¡
Silicon  strip  detectors
§
+  3  layers  of  Si  pixels   à  space  points
¡
High  luminosity  requires  highest   rate  detector  capability
Measure  bending  angle  in  magnetic  field
§
§
à  momentum
Measurement  of  secondary  vertices
à  weak  decays  of  heavy  quarks  and  lepton
(tau)
α ∝
1 p
⇒ d α
α
∝ dp p 2
⇒ dp p
∝ ⋅ p = c ⋅ p

One  of  the  Norwegian  contributions  to  ATLAS:    “Semi  Conductor
Tracker”  (SCT)  –    Oslo,  Bergen,  Uppsala  made  320  silicon-­‐ modules  ~  15%  of  Atlas  needs
Mounting in Oslo
Experimental Particle Physics @ UiO
ATLAS  upgrade
è Insertable  pixel  B-­‐
Layer
è  3D-­‐Pixel  R&D
F. Ould-Saada, 11/2012 44

Estimate  decay  width  of  a  charm  quark,  c   c
s
+ e +
+
ν e c → s + W +
W + → e + +
ν e
⎫
⎬
⎭
W −
2 vertices → propagator
Γ
→
∝ α
W
2
Γ ∝ 1 / M 4
W
[ Dim ( Γ ) ] [ Energy ]
Γ ~ α
2
W
( /
W
) 4 m
Γ ~ 2 10 − 10 GeV
c
= !
/
~ 1
m c τ ~ ( 124 − 320 ) µ m
~ ( 468 − 495 ) µ m
~ 87 µ m c quarks b quarks
τ leptons
•   Mean decay distance in detector frame: <ct>=c τγ
•   γ >1 à Silicon detector with strip pitch of ~50 µ m enough to resolve secondary vertices due to heavy quarks and tau lepton

5 th power of mass

•   γ (c τ ) ~ γ (0.48 mm) for b quarks.
•   Since Higgs couples to mass,
•   identification of heavy quarks, Γ ~M 5 , is important - “b tagging”.

à  Efficiency  to  tag  a  b-­‐quark  jet  depends  on  jet  momentum
à   Tagging  Limited  at  lower  momenta  by  multiple  scattering
à   Higher  energy  jets  have  longer  decay  length  –  due  to  relativistic  time  dilatation
CDF

Sampling calorimeter:
Shower develops in passive heavy element plates
sampling in gaseous or other low atomic weight active detectors
- Electrons and photons make a characteristic
“shower” on a short distance scale - the radiation length- in high Z materials.
- Needed depth ~ 20Xo
E c
=energy below which radiative processes largely cease.
à   shower max, all particles ~ same energy E c
Typical materials: E c
~2.5 MeV
. 1 GeV particle à shower maxim with N=E/ E c
~400 particles
E = E c
N ⇒ dE = E c
N ⇒ dE
E
=
1
N
Stochastic term / ~ c
/
Typically σ ( E )
E
=
15 − 18 %
E ( GeV )
. The higher E, the higher N, the better the resolution!
Why do Hadronic CALs have worse resolution than ECALs?

-­‐   Transparent  scintillating   crystals
-­‐    light  produced  read  by   some  photon  transducer
-­‐    most  precise  energy   measurements,  but   sampling  calorimeters   can  have  better  angular   resolution!

•
The  W  gauge  bosons  can  decay  into  quark-­‐antiquarks,  or  into   lepton  pairs.
•
For  2  body  decays,  Et  ~  M/2.
•
There  can  also  be  radiation  associated  with  the  W,  gluons   which  evolve  into  jets
•
Azimuthal  angle
φ
vs  pseudo-­‐rapidity
η
•
à  Transverse  energy:
η
-­‐
φ pixels  each  give  independent   measurements
Rapidity : y =
1
2 ln
⎛
⎜⎜
E +
E − p
L p
L
⎞
Pseudo rapidity : η = − ln
⎡
⎢ tan
⎛
⎝
θ
2
⎞
⎠
⎤
⎥
E
T
η
φ
E
T
~ M
W
/2 ~ 40 GeV - “Jacobean peak”

π o
D0
EM  calorimeters  calibrated  in  energy  by
-­‐  exposing  them  to  well  defined  particle  beams,
-­‐  or  in  situ  using  well  known  signal
CDF
Get  data  sets  with  photons  and  look  at  resonant  peaks
π
0
→ γγ ρ ±
→ π ± π
0
M
π
0
=
0 .
14 GeV M
ρ
=
0 .
769 GeV

Hadronic calorimeters measure energy of hadrons or group of hadrons (jets)
Average distance between interactions ~interaction
length λ
0
Absorbers: Fe, λ
0
=17 cm à 10-15 λ
0
to absorb a hadronic shower
Typical resolution:
π + p → π + π + p is E
Th
~ 2 m
π
~ 0.28 GeV
200 GeV π -p Interaction dE / E = a
σ (
/
E
E )
E
40 − b
60 %
=
E ( GeV )
π
+ , π
− , π
π +
= ud , π o
=
Note large multiplicity
0
, , π
And small angle production
à limited P
T
−
= p
T du h
~ 0 .
4 GeV

Distribution  of  pseudo-­‐rapidity  of  recoil  or  “tag”  jets  produced  in
WW  fusion  process  of  Higgs  production
How small an angle to be covered?
- Calorimetry at LHC extends to
|
η
| = 5 to cover the region of
“tag jets” à polar angle of 0.8
o
Vector boson
Fusion: W W à H
η = −
.
θ

What sort of angular size needed for a Hadronic CALorimeter (HCAL)?
Jet “cone” of R ~ 0.5 ==> ~ 100
“towers” in the cone to evaluate jet substructure.
R = d φ
2
+ ( d η ) 2 e.g. Resolve 1 TeV H à ZZ
P
TZ
~ 500 GeV, Z à Jet-Jet
P
TJ
~ 45 GeV for symmetric decays
Jet-Jet opening angle ~ 0.2 rad
CMS tower size ~ 0.087: Δφ =2 π /72

Calorimeters  often  calibrated  using  prepared  beams  at  accelerators  with   well-­‐defined  momentum
-­‐  Also  with  cosmic  ray  muons  (Minimum  Ionizing  Particles)
225-GeV/c
Muon Beam
ß Pedestal: Zero-energy deposit
ß Muon - MIP
•   Because of the effect of the B field, HCAL must make an in situ, field on calibration.
•   HCAL can be used for muon ID if the muon is isolated.
•   A muon deposits ionization energy corresponding to ~ 3
GeV.

η
E
T
φ
¡
Momentum  distribution  of   hadrons  found  in  jets
Z=p(Hadron)/p(jet)
Distribution  of  form   zD(z)=(1-­‐z) a

dP / P = cP ⊕ d
Jet energy: E=E
1
+E
2
+E
3
+…
- If stochastic term (a) dominates in the error of the measurement of dE 2
=
≈ dE aE
1
2
1
+
+ dE aE
2
2
2
+
+ dE aE
3
2
3
+
+
= aE
If a~50% and b=3%
100 GeV jet
à dE individual hadrons à energy resolution of ensemble is same as that of single
/ E = a / E ⊕
accuracy of 5% on b
- If constant term dominates (very high energy case) à the ensemble is measured more accurately than the single particle.
If the energies of the jet fragments are equi-partitioned, then there are n terms of equal magnitude z i
=1 / n z i
≡ E i
/ E dE / E = b z
1
2
+ z
2
2
+ z
3
2
+
/ ~ / n
Dijet mass – stochastic (back to back)
M 2
= 2 E
1
E
2
( 1 − cos θ
12
) ≈ 4 E
1
E
2
~ 4 E 2 dM / M ~ a / 2 E ~ a / M

Mass resolution at LEP:
W à jet-jet dM ~ 2.5 GeV dM/M ~ 0.035
But the initial state constraints can be used.
Worse resolutions at the Tevatron and LHC

-­‐  Measure  the  muon  momentum  vector  in  the  tracker.
-­‐  Then  filter  out  all  hadrons  and  remeasure  the  muon  in  the  flux  return  of  the  magnet.
-­‐  Multiple  redundant  measurements  are  needed  in  searching  for  rare  processes.

Arise from decays of heavy quarks, resonances, gauge bosons, ...
Q → q µ − ν
µ
,
J / ψ , Υ ,...
→ µ + µ −
W → µ − ν
µ
, Z → µ + µ − ,...
•   A given single final state particle can have many sources.
•   Muons from B dominate a low P
T for P
T
, while W,Z dominate
~ M/2.
•   At still higher P
T
there are no known sources (W’,Z’,?)

Resonance used to check Calibration and alignement of muon chambers in situ
J / ψ → µ + µ − - Momentum determined solely from muon chambers
mu-chambers interspersed in an iron return yoke
à   Resolution in the Fe toroids is multiple scattering limited.
Δ p
B p
≈
∝
2 T
B
1
; L
L
≈ 1 m
⎫
⎪
⎬
⎪ dp p
≈
( Δ p
T
)
MS
( Δ p
T
)
B
≈ 15 %
à   Alternative: use Inner detector tracking system (ID) BUT must match muon tracks to ID tracks.
à   limitation due to multiple scattering induced by passage of muons through calorimeters, …

•
•
The  CDF  detector  has  3  main   detector  systems;
§
§
tracking  -­‐  Si  +  ionization   in  a  magnetic  field,     scintillator  sampling     calorimetry,  (EM  -­‐   e ,
γ
and
HAD  -­‐   h ),
§   and  ionization  tracking  for   muon  measurements.
Missing  energy  indicates
ν
in   the  final  state.Si  vertex   detectors  allow  one  to  identify   b   and   c   quarks  in  the  event .

§
§
§
ATLAS  detector   functioned  well   despite  recording   many  interactions  per   collision
Proof  that  the   tracking  system  of
ATLAS,  which   includes  an  important
Norwegian/
Scandinavian   contribution  (Semi
Conductor  Tracker,
SCT),  functions  very   well?
Z   boson  decay  to  μμ   with  25  reconstructed   vertices                     è
Design   value
(expected   to  be   reached  at
L=10 34   !)
Experimental Particle Physics @ UiO F. Ould-Saada, 11/2012 66

p
T
( μ )= 51 GeV p
T
(e)=66 GeV p
T
(b-tagged jets) =
2 secondary vertices from b-decays
174 45 GeV E
T miss = 113 GeV,
19/03/15