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Interpretation of Fermilab Crystal Collimation Experiment

This article discusses the possible interpretation and findings of the Fermilab crystal collimation experiment conducted by Dick Carrigan. Topics covered include the E853 geometry, Tevatron crystal collimation, beam halo effects, moving crystals or collimators, and potential explanations for the observed effects. The article provides a comprehensive overview of the experiment and its implications.

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Interpretation of Fermilab Crystal Collimation Experiment

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  1. Possible interpretation of Fermilab crystal collimation experiment Dick Carrigan Fermilab CARE Crystal channeling workshop CERN March 9, 2006

  2. Channeling collimation related issues • E853 geometry and collimation • Tevatron crystal collimation • Fliller-Still shoulder • Does Tevatron crystal deflect, collimate? • Channeling information needed • Radiation damage • Self-monitoring crystals? Interpretation of TeV results CARE channeling collimation workshop D. Carrigan http://imapserver1.fnal.gov/~carrigan/ March 9, 2006

  3. At crystal Lambertson, crystal C0 at the time of E853 “Murphy geometry” U counters Interpretation of TeV results CARE channeling collimation workshop D. Carrigan http://imapserver1.fnal.gov/~carrigan/ March 9, 2006

  4. Relative rate Xc (mm) Series of ~100 m step collimator retraction Beam halo effects and collimation Moving crystals or collimators gives information on halo retracting crystal 200 microns cut signal by 4. In 2 minutes recovered somewhat. moving in-initial spurt for several minutes followed by 1/e decays of 0.5 to 5 hours • Extraction rate depended on shadowing of crystal by collimator • 5 mm retraction to behind collimators precipitously cut rate • Characteristically the D0 proton loss rate rose by 5% to 20% as the collimators were opened.

  5. FNAL PROPOSAL FOR CRYSTAL COLLIMATION Blm Detector T:LE033 LE03 pin L shaped tungsten E0 Pin diode ? Current collimation system in Tevatron is somewhat different compared to the one planned before Run-II. Based on detailed modeling, Carrigan, Drozhdin, Mokhov and Still, proposed to implement a bent crystal in the EØ straight section. Done in 2004-2005. Interpretation of TeV results CARE channeling collimation workshop D. Carrigan http://imapserver1.fnal.gov/~carrigan/ March 9, 2006

  6. CRYSTAL COLLIMATOR SYSTEM Laser – angular measurement PIN Diode BLM E0 Scintillator Paddles 23.8 m BLM 31.542 m 14 mm crystal channeled beam Pin Diode E03H 2nd Collimator E03 Secondary Collimator E0 Crystal Collimator Assembly

  7. Fliller-Still Effect: 980-GEV BEAM at E0 (5.5 σ fit) Oct. 6, 2005 Jan. 31, 2006 With E03H out, LE033C BLM is proportional to nuclear interact. rate in crystal Full arc coherent Channeling Peak width is 22±4 mrad (rms) 440 microrad Interpretation of TeV results CARE channeling collimation workshop D. Carrigan http://imapserver1.fnal.gov/~carrigan/ March 9, 2006

  8. Possible explanations for whole bend effect Volume capture Volume reflection Miscut angle for crystal Something else What to call effect? • Whole arc channeling (gets at characteristic of process) • Volume reflection (probably correct) • Volume capture (probably wrong) • Vorobiev-Taratin effect (sort of predicted but does not include accelerator) • Fliller shoulder (yes, but Tevatron confirmation helped) • Fliller-Still shoulder (includes Tevatron confirmation) • L5 effect (silly but 42% of Fliller-Still is ls) Interpretation of TeV results CARE channeling collimation workshop D. Carrigan http://imapserver1.fnal.gov/~carrigan/ March 9, 2006

  9. Potential picture for volume reflection, volume capture (Ivanov) Volume reflection (Taratin-Vorobiev) Particle bounces off plane at some place in passage through a curved crystal. Deflection order of ψc Volume capture (Sumbaev/PNPI) Particle scatters into channel with lower transverse energy and remains there. Continues to end of bend.

  10. where p is the momentum and R is the radius of curvature Volume capture • “Volume capture” is the putative process whereby particles outside a channel in a bent crystal diffuse into the channel. It was first investigated at Gatchina by Samsonov, Sumbaev and their colleagues at 1 GeV. Volume capture should deflect in the direction of the bend. This diffusion process is an analog of dechanneling where the particles diffuse in to the channel. Process occurs over the whole arc of the bend. Deflections can range up to the whole arc of the bend. • In their book BCK (Crystal channeling …) give a formula (BCK 5.27) for the transition probability to diffuse into the channel as: Thus as the energy goes up, volume channeling goes down. As R gets smaller (tighter bend) it also decreases. Biryukov, et al., have shown that this relation holds true for 70 GeV protons and is characteristically small compared to ordinary bent crystal channeling (Fig. 3.30 in BCK) Interpretation of TeV results CARE channeling collimation workshop D. Carrigan http://imapserver1.fnal.gov/~carrigan/ March 9, 2006

  11. Volume reflection • Volume reflection was discovered in simulations by Taratin and Vorobiev in the eighties [Phys. Lett A, 119, 425 (1987 for English language version]. In essence particles reflect off of planes when they are nearly parallel and are deflected on the order of a critical angle away from the bend. The process will occur over the whole arc of the bend. It can be cumulative for many passes. Since the expected deflection is O(θc) the deflection will go as 1/(pβ)½. R does not appear but θc for a bent crystal will be a function of R. As a result the effect will diminish more slowly than volume capture as the energy increases. This is why many expect the whole arc effect seen at RHIC and the Tevatron is due to volume reflection. Useful to understand p, R scaling since we are extrapolating to LHC Interpretation of TeV results CARE channeling collimation workshop D. Carrigan http://imapserver1.fnal.gov/~carrigan/ March 9, 2006

  12. Possible volume reflections in E853 at the Tevatron Normal extraction did not see whole arc effects. Needed kick almost whole bend for extraction. Interaction (U counter) often drifted, was disregarded. Figure is selected (bad science but also wide variety of running conditions). Note that more negative angle is convex side, the volume reflection side. Interpretation of TeV results CARE channeling collimation workshop D. Carrigan http://imapserver1.fnal.gov/~carrigan/ March 9, 2006

  13. Summary of coherent bend effects Interpretation of TeV results CARE channeling collimation workshop D. Carrigan http://imapserver1.fnal.gov/~carrigan/ March 9, 2006

  14. E03 COLLIMATOR SCAN FOR DIFFERENT CRYSTAL ANGLES (Mokhov) Channeled beam produces a shoulder 7 mm from the core The channeled beam should have been ~10.5 mm from the core. First data set suggested the channeled beam was hitting an aperture. But on 1/10/2006, after moving the crystal 10mm, new data proved there was no aperture limit. Scatter Channel Reflections Beam probe w/out crystal

  15. E03 data fitted and differentiated Puzzle Apparent deflected angle is 296 micro radians. Should be 440. But maybe appropriate beam center is not E03H = 0. Channeling peak is 50% of deflected beam. Remainder dechanneling? Sigma is twice critical angle, some due to beam divergence.

  16. Negative hadron and e+/e- channeling? • Could one collimate antiprotons at the Tevatron? • Could one collimate e+/e- at ILC? • In TOTEM, etc. at LHC could one deflect negative particles including leptons? e+/e- channeling • channeling radiation impact must be considered • crystal lengths must be short • not so much dependence on charge • little of no experimental information at high energy, particularly for bending Negative hadron bending Bak et al. did studies of negative particle axial deflection at 10 - 12 Gev with pions [S. Anderson et al., Nucl. Phys. B167, 1 (81), J. Bak, et al., Nucl Phys. A389, 533(82)] Schiott simulated their data in Carrigan and Ellison (Relativistic Channeling, NATO 165, Plenum (87)). Saw only small effects on order of critical angle. Taratin & Vorobiev, Phys. Lett. A119, 425 (1987) also discuss negative bending simulation.

  17. + - Negative hadron and e+/e- channeling -continued More recently Greenenko and Shul’ga [NIM B90, 179 (94)] studied negative deflection with a simulation program. For axial channeling at 400 GeV they saw deflection at the same scale as the Schiott simulation. Their distributions for 100 GeV hadrons bent in a 3 cm crystal are shown below. Note that the negative deflection is of the same order as the positive case but very diffuse. In thinking about the possibility of negative particle deflection in the early eighties I discounted it because I thought in terms of discrete angular deflections in the spirit of an external beam. The situation is different for collimation where the important thing is to give the particles a kick, any kick, provided it is more than the multiple scattering. Multi-pass channeling also helps. High energy may also help. We need more information on negative channeling, negative bending!

  18. Scale 1/16 in/div Some radiation damage experience • E853: 70 hours of halo on crystal, no effect • Baker et al NIMB90, 119 (1994) – 3*10^19 protons @ 28 GeV (BNL) or fluence of 4*10^20/cm^2. Channeling minimum yield went from 2.3% to 4.1%. Related to crystal disorder. From Dynamitron study with energy there was a suggestion • it may have been dislocations • This article also considers relative impacts of dislocations, point defects • CERN saw 25% degradation of bending efficiency for 2*10^20p/cm^2 • IHEP bent crystal with temperature to 150 degree, 1 W beam power Issues • temperature effects (see later slides) • controlling damages • material? • types of defects • extrapolation to 7 TeV

  19. Bad things happen to crystals break radiation damage bend relaxes… Bad things happen to collimators melt fuse strip diode electrode xtal diode electrode ground plane Self monitoring? radiation damage via depletion voltage, leakage current ala Si strip detectors bend via capacitance? continuity via plated on fuse surface? Self monitoring crystal?

  20. Summary • Tevatron crystal collimation has been a big success • puzzle concerning apparent deflection angle • improvements ahead! • Channeling • Fliller-Still shoulder is probably volume reflection • understand scaling with p, Θb? • Negative particles, leptons? • Radiation damage • extrapolation to 7 GeV, very intense beams • Are self monitoring crystals useful? Interpretation of TeV results CARE channeling collimation workshop D. Carrigan http://imapserver1.fnal.gov/~carrigan/ March 9, 2006

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