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Monitoring p-p collision rates at LHC

Monitoring p-p collision rates at LHC. Monitoring p-p collision rates at LHC. E. Bravin CERN AB-BI. Many inputs from LBNL - US-LARP. Introduction. The aim of LHC is to produce collisions inside the 4 detectors: ATLAS , ALICE , CMS and LHC-b

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Monitoring p-p collision rates at LHC

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  1. 12th LHCCWG - CERN Monitoring p-p collision rates at LHC Monitoring p-p collision rates at LHC E. Bravin CERN AB-BI Many inputs from LBNL - US-LARP

  2. 12th LHCCWG - CERN Introduction • The aim of LHC is to produce collisions inside the 4 detectors: ATLAS, ALICE, CMS and LHC-b • For ATLAS and CMS the collision rate should be as high as possible • For ALICE and LHC-b the rate should be set and kept at optimal levels

  3. Luminosity An offset of 1 produces a 20% reduction in luminosity • The collisions rate at an interaction point (IP) is proportional to the Luminosity and depends on many machine parameters Beam offsets Beam parameters For identical round beams the value under sqroot becomes 22 Due to the large number of variable parameters it is very difficult to compute L from beam observables like currents, emittances and machine parameters like beta functions  Need a dedicated monitor 12th LHCCWG - CERN

  4. 12th LHCCWG - CERN Collision Rate Monitors (aka “Luminosity monitors”) Monitor the collisions rate by detecting the flux of forward neutral particles generated in the interactions

  5. 12th LHCCWG - CERN The new scenario is to collide beams at 450 GeV with = 11m. (ref. = 18m) The range of operation Old Day 1 Full specifications in LHC document LHC-B-ES-0007 rev 1.0

  6. 12th LHCCWG - CERN The nominal performances 1026 is the lowest luminosity compatible with the integration time limits, but still quite uncomfortable to work with @ 450 GeV the p-p  is also slightly lower than at 7 TeV (80 mb) Full specifications in LHC document LHC-B-ES-0007 rev 1.0

  7. 12th LHCCWG - CERN The Monitors LBNL is committed to develop and install fast ionization chambers in the 4 TANs around IP1 and IP5 CERN will install solid state CdTe detectors produced by CSA-LETI around IP2 and IP8 The challenge of these detectors is to be sufficiently radiation hard to survive 20 years of LHC operation (this means several GGy of integrated dose) and to be sufficiently fast and sensitive to allow the bunch by bunch measurement for luminosities in the range 1028 1034

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  10. 12th LHCCWG - CERN The LBNL Ionization Chamber

  11. 12th LHCCWG - CERN Status of LBNL detector • The Ionization chamber final design is ready • First chamber will be delivered by end 2006, remaining 3 chambers by mid 2007 • Front end electronics well advanced and on track (most sensible item now.) B-by-B resolution is just right… • Acquisition system based on the DAB card and FBCT integrators mezzanine. Programming of on board FPGA just started • Gas control to be designed and installed. Gas pipings being installed

  12. 12th LHCCWG - CERN LBNL detector signals • The signal induced in the detector by a p-p event is almost linearly dependent on the beam energy (rule of thumb). • At low luminosity the small rate of events requires single events counting, possibly using left-right coincidence. • At the moment the IC has a signal to noise of ~30 at 14Tev c.m. Reducing the energy by a factor 15 would bring the signal at the level of the noise. • In this situation it is impossible to use the detectors in counting mode. • Signal spectrum has tails, exploiting this would reduce considerably the counting rate.

  13. 12th LHCCWG - CERN LBNL detector signals Energy deposition for neutrons of 1Tev and 100GeV in a copper absorber at a depth of 29cm. Plots on the left have linear energy scale, plots on the right have logarithmic energy scale. Top plot 80% of events are above threshold Bottom plot only 6.3% of events are above threshold 1 TeV Neutrons 100 GeV Neutrons

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  16. 12th LHCCWG - CERN The LETI CdTe detector

  17. 12th LHCCWG - CERN CdTe detectors integration IP The CdTe detector goes here beyond a Cu block of between 4 and 20 cm depth

  18. 12th LHCCWG - CERN Status of CdTe detector • The design of the detector has been ready for a while… Technology stretched to the limit in terms of rad-hardness  can not be used in IP1 and IP5 • Design of mechanical supports undergoing (probably the same moveable support for IP2 and IP8) • Decision to proceed with this technology taken only at the end of 2005 …Order to LETI sent end of April • LETI needs about 12 months to produce 4 monitors… looks just ok, delivery of first monitor expected for end October 2006 • Front end electronics being designed (FOTEC). In contact with ATLAS (BCM) • For the acquisition system we plan to use the DAB as for the IC thus profiting from the development done by LBNL

  19. 12th LHCCWG - CERN Signals of CdTe detector • The CdTe detector has an intrinsically higher signal: • Higher density -> higher deposited energy • Smaller pair production energy • At 14 TeV c.m. the average signal from the CdTe detector per p-p event is of the order of 5 mV before the F.E. amplifier. (detector current over a 50 Ohm resistor). Noise is not going to be a big issue as the F.E. amplifier will be close to the detector (~1m). • The gain of the F.E. amplifier will be adjusted to the range of the DAQ electronics some 50m away.

  20. 12th LHCCWG - CERN Colliding beams... • Set up beams using BPM near Q1. Expected overlap incertitude ~200m • This leaves 13 separation at m, 7 TeV and 1.5 separation at =11m, 450 GeV, pretty close already • Many unknowns about background • Detector signals will have to be “understood” at this moment (not much can be done beforehand without beam for this…)

  21. 12th LHCCWG - CERN Process Scaling Rate [s-1] L=1034 14 TeV 2808 x 1.15 1011 Rate [s-1] L=1027 900 GeV 1 x 3.5 1010 p-p inelastic collisions Ib2, Nb, L 8 108 80 Beam –Gas collisions Ib, Nb 3.5 104 3.8 Beam halo scraping Ib, Nb 8 104 8.7 Background Estimated event rates for vacuum pressure of 10-10 Torrs >>>Very rough indicative background estimations<<<

  22. 12th LHCCWG - CERN … Background • At high beta the ratio between p-p collisions and unwanted effects like beam-gas and beam losses is much worse • It might be necessary to use coincident detection on both sides of the IP. The system is currently being modified in that sense (*need to improve the understanding of the events typology)

  23. 12th LHCCWG - CERN Conclusions / Remarks • Present schedule for the monitors is compatible with the machine installation • All 4 IP’s will be equipped with monitors • Measurement of collisions of few low intensity bunches will be very difficult due to statistics • The Ionization Chamber may not be able to discriminate single events at 450 GeV

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