Beam profile measurements based on modern vertex detectors and beam-gas interactions

1. Beam profile measurements based on modern vertex detectors and beam-gas interactions Rhodri Jones (CERN) SLAC Halo Workshop (IBIC14) Slides from: Colin Barschel - TIPP 2014 third international conference on Technology and Instrumentation in Particle Physics Plamen Hopchev - 9th DITANET Topical Workshop on Non-Invasive Beam Size Measurement for High Brightness Proton and Heavy Ion Accelerators, 16 April 2013

2. Beam profile Experiments - Measure (calibrate) instantaneous luminosity • Accelerator • Monitor emittance • Optimize luminosity • Transverse beam profile • Crossing angle • Beam offset • Beam profiles (and emittance) are difficult to measure (in particular with low emittance of 2 μm vs. 3.75 μm nominal) • Multiple instruments are used in the LHC: • Wire Scanners • Synchrotron Light monitor • Beam-Gas Ionization monitor • (beta functions are measured by other instruments) • In LHCb experiment: • Van der Meer method • Beam-gas imaging Colin Barschel

3. LHCb detector • LHCb VELO (Vertex LOcator) is ideally suited to measure beam-gas vertices: • Large acceptance in forward region • Good spatial vertex accuracy • (15-50 μm) • Sensors close to the beam (8 mm) • Excellent hit resolution • (σhit ≈ 5 μm) • Dedicated beam-gas trigger Beam 2 Beam 1 Beam-gas vertices are used to measure the beams overlap Colin Barschel

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5. Beam-Gas Imaging (BGI) Single bunch density function of colliding bunch pair • Overlap integral depends on: • Single bunch spatial dimensions (X,Y shape) • Beam crossing angle • Offset (head-on or displaced) LHCb data Enough data (rate) + good resolution Goal of BGI method: measure overlap integral using beam-gas interactions to measure single beam shapes and position We need: Colin Barschel

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8. Beam-gas can do more Measurement of unbunched charges (ghost charge faction) Relative measurement of bunch charges Compared with LHC FBCT instrument (LHC fill 3563 2.76 TeV Feb 2013) Knowledge of ghost charge is important for the experiments during a luminosity calibration Colin Barschel

9. From LHCb to mini LHCb BGV Colin Barschel

10. BGV Goal and constraints - Provide non-disruptive measurement of transverse beam shapes (stat. and sys. uncertainty <5% in 3 minutes for 1011 protons) - Provide meaningful measurements during the energy ramp period of the LHC cycle - Overcome the limitations and complement the existing beam profile monitors Develop, build and install a new tracker for beam profile monitoring. Using the beam-gas vertexing technique (BGV = Beam Gas Vertex monitor). A demonstrator system is prepared for installation on one beam at the LHC. 2 main requirements: • Sensor technology • Detector geometry and acceptance • Material budget Precise vertex resolution • Gas type and pressure • Detector acceptance Sufficient beam-gas rate Optimize resolution and rate while keeping costs and complexity low Colin Barschel

11. BGV collaboration Colin Barschel

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15. Beam-gas rate Retention fraction of “good” events Number of “good” events (enough track multiplicity) Proton-gas inelastic rate Integration time Ngood = fgoodRinelΔt ρΔz N f σpA ≈ 70 Hz 10-7 mbar over 1 m Neon cross-section (243 mb) 1011 protons/bunch LHC frq. 11245 Hz Retention fraction fgood evaluated with MC studies fgood≈ 0.14 for xenon fgood≈ 0.02 for neon -> Can reach ≈3% statistical uncertainty in 1 minute (pushing P≈10-6 mbar with neon) Colin Barschel

16. BGV design 8 SciFi modules in 2 tracking stations Each module has 2 mattresses of SciFi (250 μm fibers) with σhit ≈ 60 μm Synergy with LHCb Upgrade fiber tracker Colin Barschel

17. Ongoing MC data sets are available (thanks to LHCb and G. Corti) Ongoing work: Modules are now being build by Aachen and EPFL Vacuum chamber is in final stage Detector support and cooling solution DAQ setup, trigger, computing farm Full MC, software, analysis, LHC interface, … extremely aggressive schedule for the BGV demonstrator First design ideas started in Oct 2012 and aiming for a commissioning in 2015. Colin Barschel

18. Status • Beam-gas imaging technique was a success for LHCb • - Precise luminosity calibration • - Multiple additional measurements were provided to the other experiments and the LHC (i.e. ghost charge, beam factorizability) • BGV instrument based on LHCb technology and knowhow • Synergy with LHCb Upgrade fiber tracker • Overcome the limitations and complement the existing emittance monitors at the LHC • - Identify possible constraints for long and large SciFi module for LHCb • Gain experience in SciFi+SiPM operation and aging (expect 16 Gy/year) Vacuum chamber Exit window We are working on installing everything by the end of the year and operate the BGV in 2015 Colin Barschel

19. BGV for Halo? • No experience with trying to measure the halo at 4-6 sigmas • Need to deconvolve with tail of vertex resolution • Beam-gas rate will be orders of magnitude smaller at this radial distance • Currently aim at 100Hz beam-gas per nominal bunch. • Sampling 0.1% of bunch tail of the bunch  0.1 Hz / bunch Increasing the interaction rate • Measurement of “average” beam halo possible (2808 bunches) • Increase the pressure (limited by vacuum interlocks) • factor 10 to 100 may be possible for short times • Combine with gas sheet? Colin Barschel