Yury CHESNOKOV

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CALIBRATION of CMS CALORIMETERS with LHC
PROTON BEAM DEFLECTED BY CRYSTAL

• Yury CHESNOKOV
• Crystal Collimation workshop, March 7, 2005

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INTRODUCTION

• Calibration of collider calorimeters with fixed
  target beam is practically impossible
• As a rule the extracted beam has much lower
  energy than the secondary particles in
  proton-proton collider interaction (the
  dynamical range is limited).
• In case the calorimeters are placed in a magnetic
  field any calibration outside of magnetic field
  is a rough approximation because a sandwich
  calorimeter response depends on magnetic field
  value and its orientation.
• Transportation of calibration coefficients
  obtained with external beams is not an easy task
  (requires some corrections connected, for
  example, with influence of magnetic field on the
  scintillator and calorimeter response, exact
  knowledge of isotope composition to correct for
  life time).

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INTRODUCTION

• Often (CMS case) at fixed target beam test the
  final apparatus is not ready (no EE SE).
• Interfering material (support structure,
  electronics, cabling etc) is not easy to imitate
  to take into account during calibration.
• Some part of the apparatus can not be tested
  (HE-HF transition, for example).
• If longitudinal uniformity has changed (cable
  connectors, radiation damage etc) no way to
  correct it .
• Calibration in situ, utilizing some physical
  processes, is time consuming procedure providing
  only limited precision.
• Proposal to steer the LHC protons (halo) into
  HF/HE by crystal.

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REQUIREMENTS

• Goals
• Desirable to have two bending angles in ? (30 and
  80) for HF and HE.
• Proton energy ejection energy (400 GeV).
• The beam intensity in the range of lt103 p/sec.
• Construction limitations
• Strong magnetic field 4 T.
• High vacuum.
• Minimal cross section of the device to minimize
  the shadow for upstream apparatus.
• Limited space defined by the vacuum pipe.

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LAYOUT OF CALIBRATION SCHEME
Maximum bending angle for available crystal
position corresponding to the bellows position.
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CRYSTAL BENDING SYSTEM

The tower which corresponds to maximum bending
angle.
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BEAM PIPE DESIGN CONSIDERATIONS

• Design considerations
• available space
• acceptable materials
• cabling
• servicing
• possible movers
• cross-section structure
• of the beams.

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CHANNELING APPLIED for BEAM EXTRACTION
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PREVIOUS EXPERIENCE
In 1994-2004 IHEP operated a channeling crystal
100 mm long to bend 70 GeV beam a huge angle of
150 mrad (9 degrees) !!! 1 V.M. Biryukov et
al. IHEP Preprint 95-14 (1995). 2 V.M.
Biryukov et al. PAC Proceedings (Dallas, 1995).
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SCHEME of 150-MRAD CRYSTAL BEAM LINE OPERATED at
IHEP at 106 PROTONS in 1994-2004
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EXAMPLE with SILICON CRYSTAL and LOW-END ENERGY
Our preliminary calculations assumed 50 cm
crystal size a reasonable figure. IHEP used up
to 15 cm long Si crystals. Details of
calculations in V.M. Biryukov et al. Crystal
Channeling and Its Application at High Energy
Accelerators (Springer, 1997).
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MAIN PROBLEM of REALIZATION
Installation of moving parts into vacuum pipe.
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UNIVERSAL IHEP DEVICE for LONG CRYSTAL BENDING
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POSSIBLE VARIANT - SPECIAL CRYSTAL without
GONIOMETER
Crystal with distributed acceptance due to
triangular shape of end face allows exclude any
mechanical devices for rotation and movement.
This crystal can simply placed in fixed
position inside vacuum pipe!!! Channeling can
achieved by changing incident beam position in
y-plane.
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PROTOTYPE CRYSTAL DEVICE for LHC
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PROTOTYPE PARAMETERS 150 MRAD BEND, 100 MM
LENGTH and 12 MM WIDTH

• Next steps before installation in CMS
• design and production of full scale prototype
• test with SPS extracted beam and HF and HE
  prototypes (H2 beam line).

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Simultaneous calibration of many calorimeter cells
Positive feature of large crystal bending for
calibration is wide angular region of the
deflected particles there are present not only
fully deflected particles, but also some
particles dechanneled in a crystal bulk and
thus deflected at smaller angle.
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SUMMARY

• In situ calibration can provide unprecedented
  precision of energy scale determination for real
  environment .
• Allows to measure characteristics which are
  inaccessible for other methods.
• Can be used for regular control of the apparatus.
  
• The method is widely used and is a mature one
  therefore the efforts and cost are not looked
  prohibitive.