Multiple Volume Reflections in a Series of Crystals

1. Vincenzo Guidi Multiple Volume Reflections in a SeriesofCrystals Department of Physics and INFNUniversity of Ferrara, Italy UA9 collaboration meeting Geneva, 10 November 2009

2. Multistrip MST14 Campaign of measurements in 2008 at external line H8 • 14 silicon strips • 1 mm spacing • 1 mm along the beam • 0.3 mm thickness • bending radius 4.5 m

3. Data Analysis 2008:Channeling Peaks of 12 strips

4. Data Analysis 2008:Volume Reflection Region of 12 strips Regionwithout channeling peaks

5. Data Analysis:“Amorphous region” 97.5% particles in 3 region; cut@10rad

6. Data Analysis:MVR region 88.2% particles in 3 region; cut@10rad  = 91.2%

7. Data Analysis:MVR region 88.2% particles in 3 region  = 91.2%  = 92.6% Particleswith negative deflection Difference between the two efficiency definitions

8. Data Analysis: single strip parameters PRL 101 (2008) 234801

9. Some observations • On assuming the stochastic independence in performance of the strips, expected efficiency is about 0.98Nstrips= 0.9812~0.78. Measured efficiency was 0.92. • Volume reflection peak is broader than for a single crystal. • There is a small fraction of particles—probably channeled particles—with a deflection angle less than the bending angle. • Maximum efficiency occurs at the end of volume reflection region θVR θVR θVR θacc

10. Volume Capture-Assisted Multiple Volume Reflection • Non channeled particles at the first crystal are volume-captured and emerge at the end of the first crystal • Due to some misalignment between the strips, volume-captured particle may be volume-reflected at the second crystal and be recycled in the mechanism of MVR 98% α>0 2% θref

11. Volume Capture-Assisted Multiple Volume Reflection • Reversing the sign of the angle between the strips does not allow re-capture of volume-captured particle at previous strip. • If such particle will not interact with other strips it results in deflection to an angle opposite as that of MVR α<0 θref

12. Modelling • We emulated the behavior of a twelve multi-strip with experimentally measured parameters including misalignment • Particle interaction with the crystal was assumed as a “black-box” process adapted with measured parameters θref

13. Emulation: resultsfortwelvemisalignedcrystalswithdifferentincident angle multistrip

14. Emulation: resultsfortwelvemisalignedcrystalswithdifferentincident angle multistrip

15. Emulation: resultsfortwelvemisalignedcrystalswithdifferentincident angle multistrip

16. Emulation: resultsfortwelvemisalignedcrystalswithdifferentincident angle multistrip

17. Emulation: resultsfortwelvemisalignedcrystalswithdifferentincident angle multistrip

18. Emulation: resultsfortwelvemisalignedcrystalswithdifferentincident angle multistrip

19. Emulation: resultsfortwelvemisalignedcrystalswithdifferentincident angle multistrip

20. Emulation: resultsfortwelvemisalignedcrystalswithdifferentincident angle multistrip

21. Emulation: resultsfortwelvemisalignedcrystalswithdifferentincident angle multistrip

22. Volume capturedparticles Broadeningofdeflectedpeak Volume capturedparticleslaterreflectedbyotherstrips Volume captured particles not reflected by other strips

23. Conclusions • Multi-volume reflection is a high-efficiency method for particle deflection • Insight into the mechanism of MVR, importance of controlled misalignment • A model of MVR assisted by volume capture was presented, which provides an explanation for higher efficiency than for the independent-strip model and for the other features. • Need for more precise simulations