Document 11412989

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Experiments  Basics    

–  based  on  D.  Green,  M.  Thomson,  Braibant  et  al  &  LHC,  Tevatron,  ATLAS,  

CMS,  …    

19/03/15 1

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Accelerators  and  detectors  –  briefly  

SM  Particles  -­‐  Mapping  into  Detector  Subsystems  

Tracking  and  b  Tagging  

Electromagnetic  Calorimetry  -­‐  e  and  

γ

 

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  

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N

=

L

.

σ

§

N :  Distribution  of  number  of  events  

Distribution  measured  by  detector  

§

L :  Luminosity  

Accelerator  

§

σ

:  Cross-­‐section  

Fermi’s  golden  rule  

M:  matrix  element  –  transition  probability  i

à f  calculable   using  Feynman  diagram  rules    

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Hadron  colliders  

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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  

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Precision  machines  

Linear  colliders    as  a  solution  to  the   synchrotron  radiation  problem  of   circular  colliders  

Bigger  circular  machines  

Muon  colliders?   ep-­‐colliders  

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…    

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

-

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19/03/15  

Once  good  energy  budget  …  give  a  chance  to  rare  processes  …  

F.  Ould-­‐Saada:  HEPP  &  ATLAS   5  

Number  of  collisions  

N  =  L  .  

σ

( pp

 

 X)    

19/03/15  

Luminosity L

n. of protons per bunch n. of bunches

L

=

N

2 k b

f

4

πσ

x

σ

y

n. of turns per second beam size at IP

(

σ

x,y

= 16

µ

m)

F.  Ould-­‐Saada:  HEPP  &  ATLAS  

Cross-section

σ

Very small for new processes

6  

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Particles  

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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  

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Detect  SM  particles  by  way  of  their  characteristic  interactions  

Particle

g e

,

γ

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

λ

Detector

Calorimeter

τ

W

µ

,

τ

→ µ + ν

µ

µ

+

ν

τ

Z

τ

+

ν

µ

Electromagnetic Shower

(

X o

)

“Missing” transverse energy

Calorimeter (ECAL)

Calorimeter

Only ionization interactions Muon Absorber

Decay with

c

τ

>

100

µ

m

Silicon Tracking

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A  fast  charged  particle  moving  in  given  medium    

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loses  energy  almost  constantly     is  slightly  deflected  from  its  initial  direction.    

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Two  types  of  collisions:  

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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  

 Bremstrahlung  important  for  light  relativistic   particles  (electrons)  

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

+

,

-

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  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

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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  

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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

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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

 Proton  of  200MeV  energy  (M~1GeV)    

βγ

 ~  0.2  

à

 R/M  x  M  ~  1  g  cm -­‐2 ,    

~1  cm  of  water.    

2

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

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 )

2

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

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Important  application  of  the  concept  of    range  of  a   particle  in  the  medical  field.    

Hadron  therapy    

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  is  the  most  recent  relative  of  conventional   radiotherapy,  which  uses  X-­‐rays.    

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  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.  

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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.    

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The  dose  received  at  the  tumor  can  therefore  be  very   high  while  the  healthy  tissue  is  saved.    

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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.  

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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  …  

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http://en.wikipedia.org/wiki/Proton_therapy    

19/03/15 F. Ould-Saada 15

"

$

#

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Bremsstrahlung    

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  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  

§

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  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

     

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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

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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  

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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

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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  

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In  time  t  particle  travels  d=

β ct  

In  t  wavefront  emitted  at  t=0   travelled  d’=ct/n  

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¡

Cerenkov  radiation  only  when  

β

>1/n  

Threshold  behaviour  

è

 identification   of  particles  of  given  p  

β =

pc

=

E

β >

1 /

n p p

2

+

m

2

c

2

$

%

"

$

# ⇒

mc

< cos

θ

=

1

n

β

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

ln(2)

E 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

]

¡

Detection  of  quarks  

§

Jet  energy  

60%  (charged,  mainly  

π

±

)  

30%  (

γγ

 from  

π

0

)  

10%  (neutral  hadrons,  mainly  K l

,K s

)  

p mis

= −

i p i

¡

Jet  of  hadrons  with  b-­‐quark  

§

§

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  

Particle  detection  

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

§

bb  

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

30

Muon system

Hadronic

Tracker

EM

CDF

Coarse Hadronic

(Tail catcher)

Muon system

Magnetized iron

Fine Hadronic

EM

Tracker

Large  Hadron  Collider  

   27km  in  circumference,  100  m  underground  

   proton  bunches  with  1000  billion  protons    circulate  nearly   at  the  speed  of  light  :    

     v=0.99999991  c  

    proton  bunches  collide  every  25  /  50  ns:    

     100

µ s  per  round  …  10  000  rounds  per  second  

   energy  released  enables  creation  of  new  particles  

19/03/15   F.  Ould-­‐Saada:  HEPP  &  ATLAS   34  

q

Particle  collisions   at  LHC  

Ø

Ø

Simulated   proton  +  proton  

à

 black  hole   candidate  

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

W

2

Γ

W

)

4

m

10

GeV

τ

c

τ

=

!

/

Γ

~ 1

µ

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

And small angle production

à limited P

T

,

π

=

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

(

Δ

p

T

)

MS

)

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

.  

Many  interactions  per  beam  crossing?  

§

§

§

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) = 174

2 secondary vertices from b-decays

45 GeV E

T miss = 113 GeV,

19/03/15  

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