Interaction Region Issues

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Interaction Region Issues

• Jeff Gronberg / LLNL
• Santa Cruz Linear Collider Retreat
• June 26-29 2002

This work was performed under the auspices of the
U.S. Department of Energy by the University of
California, Lawrence Livermore National
Laboratory under Contract No. W-7405-Eng-48.
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Outline

• Backgrounds which drive the detector design
• Good Luminosity related
• Bad Machine backgrounds
• SVX is closest to the IP and least shielded from
  machine backgrounds, it is the primary driver of
  the design
• Photon Collider design
• Basic principles
• TESLA and NLC/JLC differences
• Opportunities at SLC
• Final quad stabilization
• Beam Halo reduction through non-linear optics
• Photon Collider test bed

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The NLC beam delivery group has been actively
studying the IR for many years

• IR Design and Backgrounds
• Takashi Maruyama, Lew Keller, Rainer Pitthan
• Tor Raubenheimer, Andrei Seryi, Peter Tenenbaum,
  Nan Phinney, Pantaleo Raimondi, Mark
  Woodley, Yuri Nosochkov
• Stan Hertzbach (U. Mass)
• Jeff Gronberg, Tony Hill (LLNL)
• RD Efforts
• Joe Frisch, Linda Hendrickson, Tom Himel
• Eric Doyle, Leif Eriksson, Knut Skarpaas, Steve
  Smith
• Tom Mattison Students (UBC)
• Phil Burrows, Simon Jolly, Gavin Nesom, Glen
  White, Colin Perry (Oxford)
• Brett Parker (BNL)

University groups are already involved in the IR
design
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Beam-Beam InteractionSR photons from individual
particles in one bunch when in the E field of the
opposing bunch
Slide of T. Markiewicz

• Beams attracted to each other reduce effective
  spot size and increase luminosity
• HD 1.4-2.1
• Pinch makes beamstrahlung photons
• 1.2-1.6 g/e- with E3-5 E_beam
• Photons themselves go straight to dump
• Not a background problem, but angular dist. (1
  mrad) limits extraction line length
• Particles that lose a photon are off-energy

NLC-1 TeV
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Pair ProductionPhotons interact with opposing
e,g to produce e,e- pairs and hadrons
Slide of T. Markiewicz
500 GeV designs

• Pair PT
• SMALL Pt from individual pair creation process
• LARGE Pt from collective field of opposing bunch
• limited by finite size of the bunch

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Pair Stay-Clear from Guinea-Pig Generator and
Geant
Slide of T. Markiewicz
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e,g,n secondaries made when pairs hit high Z
surface of LUM or Q1
High momentum pairs mostly in exit beampipe
N.B. Major TESLA / NLC difference TESLA has zero
crossing angle, low energy particles travel
farther down the beam pipe before hitting anything
Low momentum pairs trapped by detector solenoid
field
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The basic design drivers are the same for TESLA
and NLC
The solenoidal field is the primary defense
against the pair backgrounds
pairs scales w/ Luminosity 1-2x109/sec
Low energy particles will shower in the material
of the beam line
The detector must be protected by masks against
secondary particles
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Neutron Backgrounds at the SVXThe closer to the
IP a particle is lost, the worse

• Off-energy e/e- pairs hit material near the IP
  Pair-LumMon, beam-pipe and Ext.-line magnets
• Radiative Bhabhas Lost beam
• Showering particles produce neutrons which can
  damage the SVX
• Solutions
• Move L away from IP
• Open extraction line aperture
• Low Z (Carbon, etc.) absorber where space permits

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Design IR to Control ee- Pairs
Slide of T. Markiewicz

• Direct Hits
• Increase detector solenoid field
• Increase minimum beam pipe radius at VXD
• Move beampipe away from pairs ASAP
• Secondaries (e,e-, g,n)
• Point of first contact as far from IP/VXD as
  possible
• Increase L if possible
• Largest exit aperture possible to accept
  off-energy particles
• Keep extraneous instrumentation out of pair
  region
• Masks
• Instrumented conical M1 protrudes at least 60cm
  from face of PAIR-LumMon
• Longer more protection but eats into EndCap CAL
  acceptance
• M1,M2 at least 8-10cm thick to protect against
  backscattered photons leaking into CAL
• Low Z (Graphite, Be) 10-50cm wide disks covering
  area where pairs hit the low angle W/Si Pair
  Luminosity monitor

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HALO Synchrotron Radiation Fans with Nominal 240
mrad x 1000 mrad Collimation
Slide of T. Markiewicz
Stan Hertzbach
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Neutrons from the Beam Dump

• Neutrons from Beam Dump(s)
• Solutions Geometry Shielding
• Shield dump, move it as far away as possible, and
  use smallest window
• Constrained by angular distribution of
  beamstrahlung photons
• Minimize extraction line aperture
• Keep sensitive stuff beyond limiting aperture
• If VXD Rmin down x2 Fluence UP x40

Neutrons per Year
Limiting Aperture
Radius (cm)
z(m)
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Muon Backgrounds from Halo CollimatorsNo Big
Bend, Latest Collimation Short FF
Slide of T. Markiewicz
FF
Energy
18m 9m Magnetized steel spoilers
Betatron
BetatronCleanup
If Halo 10-6, no need to do anything If Halo
10-3 and experiment requires add magnetized tunnel filling shielding Reality
probably in between
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Background Projects

• Iterate all results for consistent set of results
• Beam parameters, detectors, solenoid design,
  beamlines not consistent
• Detector response to known backgrounds
• TPC, Cal, Lum, Pol, etc.
• Dose calculations on SC or REC QD0
• Collimator scattering study
• Locations, apertures, beam loss,
• GEANT4 beamline model
• gg-Hadron production

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Realistic IR Layout

• Masking Support
• VXD support alignment
• Instrumented Masks
• Lum_Pair Mon
• Vacuum req.
• REC QD0
• SC QD0
• Beampipe support
• Apertures
• Optical lines of sight
• Detector access

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A Photon Collider requires additional hardware
in the IP
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NLC/JLC Photon Collider Hardware
Beam Splitter
MERCURY Laser
Laser Plant
1, 100 Joule pulse - 100, 1 Joule pulses
12 Lasers x 10Hz 120Hz
1 pulse 100 Joules 1 train
Optics Assembly
Interferometric Alignment System
Beam Pipe
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MERCURY commissioning has begunOne amplifier
head with 4 of 7 crystals installed

• Status
• Producing 10 Joule pulses at 0.1 Hz
• Theoretical max 14 Joules w/ 4 crystals
• Operation of two heads with 14 crystals
• within the next year
• Installation of new front end for 10Hz
  operation

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NLC solution might be adapted to TESLA, but TESLA
bunch spacing opens new options

• A single light pulse can travel around the ring
  and hit every bunch in the TESLA train
• DESY and Max Born Institute will prototype a
  scale model
• Tolerances are tight, but enormous savings in
  laser power

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All detector elements are affected by the photon
collider environment

• Outgoing beam Compton backscattering leaves a
  large energy spread
• On-energy peak (30 of particles)
• Low-energy tail (Multiple backscatters)
• Hard cutoff at 5 GeV
• Solution
• Zero field extraction line to the dump, no
  diagnostics
• Increase extraction line aperture, SVX sees the
  beam dump!

• gg ? hadrons resolved photon events
• Every bunch crossing has tracks
• 730 GeV / train into the calorimeter with
  cos(q)
• Events look more like those from a hadron machine
  than a lepton machine

TESLA bunch spacing makes it easier to isolate a
single bunch crossing
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System Integration Optics/Beampipe
LCD - Large with new mirror placement

• Essentially identical to ee- IR
• All masking preserved
• 30 mRad x-angle
• Extraction line 10 mRadian
• New mirror design 6 cm thick, with central hole 7
  cm radius.
• Remove all material from the flight path of the
  backgrounds

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Photon Collider projects
The photon collider has all of the issues of the
regular ee- IR and then some

• Detector studies
• Rad-hard SVX design
• Resolved photon backgrounds
• SVX b-tagging
• Jet resolution
• Timing requirements
• Complete background and reconstruction simulation

• Machine studies
• Optics / beampipe integration
• Crossing angle minimization
• Realistic IR layout
• Radiation damage to the optics
• Coupon tests

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Engineering Test Facility at SLC

• An ee- linear collider exists and could be
  resurrected as a test facility for
• Test of final quad stabilization
• Beam halo reduction
• Photon collider demo

NLC 250 GeV 300 / 2 360 / 3.5 same 0.11 mm
245/2.7nm 7.5E9
SLC 30 GeV 1100 / 50 1600 / 160 8 / 0.1 mm 0.1
1.0 mm 1500/55nm 6.0E9

• Beam Energy
• DR emittances g?x,y (m-rad)
• FF emittances g?x,y (m-rad)
• IP Betas ?x / ?y
• Bunch length ? z
• IP spot sizes ?x,y
• Beam currents N?

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IP Girder Testbed
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Nanometer Stability of Colliding Beams
Beam-Beam Deflection gives 1nm stability
resolution
BPMres
400nm

• Colliding beams provide a Direct
  Model-Independent Test of any engineering
  solution to the final doublet stability problem
• Not possible in FFTB

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Controlling Beam Backgrounds with Non-Linear
Optical Elements

• Tail Folding via Octupole Pairs has the promise
  of relaxing collimation depths
• Confidence that comes from an Actual
  Demonstration may permit a great savings in
  collimator design, radiation shielding, and muon
  shielding

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SLC Photon Collider testbed hardware
Pulses at 30 Hz at SLC, 11,000 Hz at NLC The
laser is easy for a SLC testbed
Laser Plant
Beam Splitter
MERCURY Laser
A small 30Hz, 15W average power laser is
sufficient for this experiment
Optics Assembly
Interferometric Alignment System
Beam Pipe
½ size to fit in SLC
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Particle spectra in SLC photon collider

• A 0.1 Joule laser pulse converts 25 of the
  incoming electrons.
• Maximum energy transfer is 1/3 of the beam energy
• First direct production of gg luminosity
• Look for 2 ? 2 processes in the SLD calorimeter
  to measure luminosity
• ee- ? ee-
• eg ? eg
• gg ? ee-

Particles
g
e
GeV/c
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Summary

• The optimization of the IR is not complete
• Understanding and mitigation of backgrounds
• Realistic engineering of the machine / detector
  interface
• A photon collider presents new challenges
• Detector backgrounds are worse
• The impact on physics reconstruction must be
  studied
• Additional detector constraints must be
  understood
• SLC has great potential as a test facility
• Proof-of-principle for colliding nm beams
• Beam halo reduction through non-linear optics
• Photon collider demonstration