Transcript TESLA - TeV-Energy Superconducting Linear Accelerator The Detector and Interaction Region for a Photon Collider at TESLA Aura Rosca DESY Zeuthen Aachen, Germany, 17-23 July.

TESLA - TeV-Energy Superconducting Linear Accelerator
The Detector and Interaction Region
for a Photon Collider at TESLA
Aura Rosca
DESY Zeuthen
Aachen, Germany, 17-23 July 2003
TESLA - TeV-Energy Superconducting Linear Accelerator
Motivation
• Higgs Physics
– Measure two-photon partial width and search for
heavy Higgs states in extended Higgs models
• Electroweak Physics
– Excellent W factory allowing precision study of
anomalous gauge boson interactions
• Physics beyond SM
– Search for new charged particles, such as
supersymetric particles, leptoquarks, excited states
of electrons, etc.
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TESLA - TeV-Energy Superconducting Linear Accelerator
Principle of a Photon Collider
Crab Crossing Angle
2 deg.
IP
CP
CP
2 mm
2 mm
• Run in e - e - mode
• Convert electrons in high energy photons via
Compton backscattering of laser photons
• High energy photons follow electron direction
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TESLA - TeV-Energy Superconducting Linear Accelerator
Layout of the Beams
Electrons Out
Electrons Out
IP
Laser in
Laser Out
Electrons In
Electrons in

-
• Disruption angle is larger then in e e because of
beam-laser interaction
– Outgoing beam no longer fits through final quadrupole
• need crossing angle to have separate beam pipe for in- and
outgoing beam
– Four beam pipes will enter the detector from each side.
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TESLA - TeV-Energy Superconducting Linear Accelerator
Laser Requirements
•
•
•
•
•
•
Laser wavelength:
Laser energy:
Pulse duration:
Rayleigh length:
Repetition rate:
Average power:
  1 m
Epulse  5 J
  1 - 3 ps
Zr  0.4 mm
TESLA collision rate
P  70 kW
– Pulsed laser with correct time structure and relaxed
power requirements feed a resonant cavity with
quality factor Q ~ 100
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TESLA - TeV-Energy Superconducting Linear Accelerator
Proposed Ring Cavity
• Cavity mounted around detector
– Round trip time = repetition rate of the electron bunches
•
T  300 ns  L  100 m
– Stabilization of the cavity length within about 0.5 nm
Detector
focusing
mirror
Φ  80 cm
e
e
focusing
mirror
12 m
laser
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TESLA - TeV-Energy Superconducting Linear Accelerator
Laser-Electron Crossing Angle
• Need crossing angle electron beam-laser
- opening angle laser
ηθ  43 mrad
(3.58 divergence )
- distance to e-beam
β  17 mrad
Laser crossing angle
α 0  60 mrad
• Laser collision angle reduces conversion
– Compensated by higher laser energy
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Aura Rosca
DESY-Zeuthen
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TESLA - TeV-Energy Superconducting Linear Accelerator
Electron-Photon Conversion
Probability
s  500 GeV
0.35
 = 3.58,

 = 1.0 p s,      , z r,m ax = 0.45 m m
E p u lse = 5.6 J

 = 2.0 p s,      , z r,m ax = 0.41 m m
2
0.30
0.25

 = 3.0 p s,      , z r,m ax = 0.44 m m
0.20

 = 4.0 p s,      , z r,m ax = 0.43 m m
2
k =(N  / N e)
C om pton conversion coefficient
ee
0.15
0.10
0.05
0.0
0.5
1.0
1.5
2.0
2.5
3.0
R ayleigh
m]
le ngth
of foc allen
regth
gionz r z[m
r [m m ]
(R ayle igh length)
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DESY-Zeuthen
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TESLA - TeV-Energy Superconducting Linear Accelerator
s ee  500 GeV
E pulse  7.5 J
unpolarized
32
-2 -1
dL /d sγγ [10 cm s / GeV]
Luminosity
L( s γ γ  0.8 s max, γ γ )
- 2 -1
 0.34 10 cm s
34
helicity --
s γ γ [GeV ]
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TESLA - TeV-Energy Superconducting Linear Accelerator
Background
Background can be a factor 10 higher than in e  e -LC
• Disrupted beam

-
– larger than in e e case and
additionally widened by crab
crossing
• Beam-beam interactions:
– Incoherent pair production (ICP)
– Coherent pair production (CP)
• Neutrons from beam dump
Energy distribution on calorimeter
face from one BX at z=3.8 m
e

e
• Background from physics
processes, ex.   hadrons
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s ee  500 GeV

14 mrad
Units: GeV/mm
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TESLA - TeV-Energy Superconducting Linear Accelerator
Design of the Mask
ECAL HCAL
• Redesign of TESLA
detector in forward
region to minimize
background in TPC
and VTX
TPC
outer mask
(tungsten)
tungsten
parts
IP
– Two masks
– Longer outer mask
– Tungsten parts
inner mask
(tungsten)
100 cm
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DESY-Zeuthen
183 cm
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TESLA - TeV-Energy Superconducting Linear Accelerator
Background in VTX
• With Mask
• Hits per layer for ICP
– Incoherent pairs
s ee  500 GeV
1 layer
• ~ 368 hits
– Coherent pairs
• ~ 1 hit in the first layer
and 3 hits in three last
layers, from one event
each
2 layer
2
 0.03 hits/mm in L1
3 layer 4 layer 5 layer
no change necessary
wrt e  e - design
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TESLA - TeV-Energy Superconducting Linear Accelerator
Background in TPC
• No mask:
– Incoherent pairs
• ~ 12900 photons / bunch
– Coherent pairs
• ~ 400000 photons / bunch
• With Mask
– Incoherent pairs
• ~ 927 photons / bunch
– Coherent pairs

• ~ 2440 photons / bunch
– Reduction by a factor ~ 125
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DESY-Zeuthen
< 1% occupancy
factor 2.4 higher
than in e  e OK for TPC
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TESLA - TeV-Energy Superconducting Linear Accelerator
Beam Steering
• Feedback e-e IP: 88 nm x 4.3 nm
• Feedback Compton IP: 14 m x 14 m
Work in progress..
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DESY-Zeuthen
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TESLA - TeV-Energy Superconducting Linear Accelerator
Beam Steering
1•
Electron beams are stabilized by fast feedback system
measuring beam deflection at IP
– BPMs need large aperture because disrupted beam is larger
• Solution: undisrupted Pilot bunches for beam steering
– Electron bunches stable over one train
– Photon beams follow electron direction
2•
Separate electrons and photons on dump
IP
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Dump
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DESY-Zeuthen
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TESLA - TeV-Energy Superconducting Linear Accelerator
Beam Dump
• Photons cannot be deflected electrically
or magnetically
– Direct line of sight from IP to dump
• High neutron flux at vertex detector
– Narrow photon beam cannot be spread out
and will always hit same window
• High thermal load on window
• High radiation damage to window
WIP…
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DESY-Zeuthen
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TESLA - TeV-Energy Superconducting Linear Accelerator
Conclusion
• Tesla offers the possibility to work as a
Photon Collider
• The expected luminosity might be ~20% of
the luminosity at the LC
• Beam-beam backgrounds are larger but can
be reduced redesigning the forward region
• Some more items need to be studied for a
realistic design of a Photon Collider
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TESLA - TeV-Energy Superconducting Linear Accelerator
Acknowledgements
• Many thanks to all my colleagues for
providing me with their results.
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DESY-Zeuthen
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