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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
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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
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•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
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Goals:
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Desirable to have two bending angles in θ (30 and 80) for HF and HE.
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Proton energy – ejection energy (400 GeV).
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The beam intensity in the range of <103 p/sec.
Construction limitations:
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Strong magnetic field – 4 T.
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High vacuum.
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Minimal cross section of the device to minimize the shadow for
upstream apparatus.
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Limited space defined by the vacuum pipe.
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12.2°
LAYOUT OF CALIBRATION SCHEME
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BENDING CRYSTAL
Maximum bending angle for available crystal position corresponding to the
bellows position.
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CRYSTAL BENDING SYSTEM
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TOWER NUMBER
BENDING CRYSTAL
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LAYER NUMBER
IP
The tower which corresponds to maximum bending angle.
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BEAM PIPE & DESIGN CONSIDERATIONS
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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
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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
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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
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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
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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 yplane.
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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
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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
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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
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• 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.
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