tesla - tev-energy superconducting linear accelerator the detector and interaction region for a...

TESLA - TeV-Energy Superconducting Linear Accelerator

The Detector and Interaction Region for a Photon Collider at

TESLAAura RoscaDESY Zeuthen

Aachen, Germany, 17-23 July 2003

17 July 2003 Aura Rosca DESY-Zeuthen 2


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.



Principle of a Photon Collider

• Run in mode• Convert electrons in high energy photons via

Compton backscattering of laser photons• High energy photons follow electron direction

--ee

CPIP

CP2 mm 2 mm

Crab Crossing Angle 2 deg.



Layout of the Beams

• Disruption angle is larger then in 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.

Electrons Out

Laser Out

Laser in

Electrons in

IP

Electrons Out

Electrons In

-ee



Laser Requirements

• Laser wavelength:• Laser energy:• Pulse duration:• Rayleigh length:• Repetition rate: TESLA collision rate• Average power:

– Pulsed laser with correct time structure and relaxed power requirements feed a resonant cavity with quality factor Q ~ 100

m 1 J5Epulseps 3-1

kW 70P

mm 0.4Zr



Proposed Ring Cavity• Cavity mounted around detector

– Round trip time = repetition rate of the electron bunches•

– Stabilization of the cavity length within about 0.5 nm

m 100L ns 300T

Detector

12 m

cm 80Φ

laser

ee

focusing mirror

focusing mirror



Laser-Electron Crossing Angle

• Need crossing angle electron beam-laser

- opening angle laser

- distance to e-beam

mrad 43 ηθ

mrad 17β

f= /2

x

laserbeam

2 a

electronbeam

• Laser collision angle reduces conversion– Compensated by higher laser energy

mrad 600 αLaser crossing angle

)divergence(3.58



Electron-Photon Conversion Probability

0.0 0.5 1.0 1.5 2.0 2.5 3.00.05

0.10

0.15

0.20

0.25

0.30

0.35

=4.0 ps, , zr,max

=0.43 mm

=3.0 ps, , zr,max

=0.44 mm

=2.0 ps, , zr,max

=0.41 mm

=1.0 ps, , zr,max

=0.45 mm=3.58, E

pulse=5.6 J

Com

pton

con

vers

ion

coef

fici

ent

k2 =(N

/ N

e)2

Rayleigh length zr [mm]length of focal region z [mm]r

(Rayleigh length)

GeV 500see



Luminosity

]GeV[sγγ

]G

eV/

scm

10[s

/dL

12

32

γγ

unpolarized

helicity --

d 1234

max,

scm1034.0

)s8.0s(L

γγγγ

J 5.7Epulse GeV 500see



Background

Energy distribution on calorimeter face from one BX at z=3.8 m

• Disrupted beam– larger than in case and

additionally widened by crab crossing

• Beam-beam interactions:– Incoherent pair production (ICP)– Coherent pair production (CP)

• Neutrons from beam dump

• Background from physics processes, ex.

Units: GeV/mm2

-ee

hadrons

e

e14 mrad

Background can be a factor 10 higher than in LC

-ee

GeV 500see



Design of the Mask

• Redesign of TESLA detector in forward region to minimize background in TPC and VTX

– Two masks– Longer outer mask– Tungsten parts outer mask

(tungsten)

TPC

HCALECAL

tungstenpartsIP

100 cm 183 cm

inner mask(tungsten)



Background in VTX

• Hits per layer for ICP

• With Mask– Incoherent pairs

• ~ 368 hits

– Coherent pairs• ~ 1 hit in the first

layer and 3 hits in three last layers, from one event each

0.03 hits/mm in L1

1 layer

2 layer

5 layer4 layer3 layer

2

no change necessary wrt design

-ee

GeV 500see



Background in TPC

< 1% occupancy factor 2.4 higher than in OK for 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

-ee



Beam Steering

• Feedback e-e IP: 88 nm x 4.3 nm• Feedback Compton IP: m 14 x m 14

Work in progress..



Beam Steering• 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

• Separate electrons and photons on dump

DumpIP

1

2



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…



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



Acknowledgements

• Many thanks to all my colleagues for providing me with their results.

tesla - tev-energy superconducting linear accelerator the detector and interaction region for a...

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pulsed laser

angle laser distance

ebeam laser collision

aura rosca desyzeuthen6

laser e e

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