1. Yury CHESNOKOV Crystal Collimation workshop, March 7, 2005 CALIBRATION of CMS CALORIMETERS with LHC PROTON BEAM DEFLECTED BY CRYSTAL CALIBRATION of CMS CALORIMETERS with LHC PROTON BEAM DEFLECTED BY CRYSTAL

2. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 2 INTRODUCTIONINTRODUCTION 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).

3. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 3 INTRODUCTIONINTRODUCTION 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.

4. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 4 REQUIREMENTSREQUIREMENTS Goals: Desirable to have two bending angles in θ (3 0 and 8 0 ) for HF and HE. Proton energy – ejection energy (400 GeV). The beam intensity in the range of <10 3 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.

5. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 5 LAYOUT OF CALIBRATION SCHEME Maximum bending angle for available crystal position corresponding to the bellows position.

6. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 6 CRYSTAL BENDING SYSTEM The tower which corresponds to maximum bending angle.

7. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 7 BEAM PIPE & DESIGN CONSIDERATIONS Design considerations: available space; acceptable materials; cabling; servicing; possible movers; cross-section structure of the beams.

8. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 8 CHANNELING APPLIED for BEAM EXTRACTION

9. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 9 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). PREVIOUS EXPERIENCE

10. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 10 SCHEME of 150-MRAD CRYSTAL BEAM LINE OPERATED at IHEP at 10 6 PROTONS in 1994-2004 SCHEME of 150-MRAD CRYSTAL BEAM LINE OPERATED at IHEP at 10 6 PROTONS in 1994-2004

11. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 11 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). EXAMPLE with SILICON CRYSTAL and LOW-END ENERGY

12. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 12 Installation of moving parts into vacuum pipe. MAIN PROBLEM of REALIZATION

13. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 13 UNIVERSAL IHEP DEVICE for LONG CRYSTAL BENDING

14. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 14 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. POSSIBLE VARIANT - SPECIAL CRYSTAL without GONIOMETER

15. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 15 PROTOTYPE CRYSTAL DEVICE for LHC

16. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 16 PROTOTYPE PARAMETERS: 150 MRAD BEND, 100 MM LENGTH and 12 MM WIDTH 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).

17. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 17 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.

18. Calibration of CMS calorimeters, Yu. Chesnokov Crystal Collimation workshop, March 7, 2005 18 SUMMARYSUMMARY 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.