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Status of energy calibration at LHC

Status of energy calibration at LHC. J. Wenninger. Proton-ion calibration principle. LHC. ~4.5 kHz. At 4 TeV the effect is small and systematic errors dominate the measurement uncertainty. ~59 Hz. ~20 Hz.

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Status of energy calibration at LHC

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  1. Status of energy calibration at LHC J. Wenninger

  2. Proton-ion calibration principle LHC ~4.5 kHz At 4 TeV the effect is small and systematic errors dominate the measurement uncertainty ~59 Hz ~20 Hz Energy calibration at the LHC The difference in speed (or corresponding RF frequency) of protons and ions can be used to determine the momentum P of the beam:

  3. Cogging at 4 TeV x • Proton and lead beams after cogging: • Same RF frequencyfor p and Pb, ~ average of p and Pb, • Protons move to the outside, Lead ions to the inside. Dx Df x • Proton and lead beam at flat top: • Different RF frequencies for p and Pb, • Both beams ~ centered. Energy calibration at the LHC

  4. Example : proton & lead orbits We are looking for an accuracy of ~ 10 mm on the radial position Protons – B1 Lead – B2 Proton-Pb orbits at 4 Z TeV after cogging (at same RF frequency) revealing the revolution frequency difference  radial position offsets. Energy calibration at the LHC

  5. Measurement method • The frequency offset is deduced from the orbit offsets of the 2 beams – sensitive to the average BPM offsets wrtcenter of the LHC quadrupoles ! x d1 d2 R2 R1 R2 R1 Dfmeas,A = Df + (d1 + d2) Dfmeas,B = Df - (d1 + d2) • The systematic error from BPM offsets cancels out on the average of the measurements of p-Pb (A) and Pb-p (B) ! Energy calibration at the LHC

  6. Results - PRELIMINARY !! p-Pb Mean value 4 TeV Pb-p Mean value p-Pb + Pb-b : 3.99 TeV± (to be evaluated) Energy calibration at the LHC

  7. Systematics p-Pb Pb-p • Correlation Pb – p frequency – no anomaly. • Changing values: tides etc Energy calibration at the LHC

  8. To do • Collect more fills.. • Systematic analysis of BPM scale and offset. • Scale calibrations are all consistent: • Can be checked in every fill during the cogging, • Dedicated calibration (5 mins each). • Offset dependence on bunch intensity, bunch length and time. • Time: split the sample and look for significant changes etc… • Intensity and bunch length: • Could try to estimate it from the data itself. • ~1 hour exercise at injection with scraping and RF voltage. Energy calibration at the LHC

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