1. Background Simulations for the LHCb Beam Condition Monitor Overview: ● The LHCb Beam Condition Monitor (BCM) – Purpose, Design and Function – Implementation in Simulation Software ● The Machine Induced Background (MIB) Tool – Estimates Available for Simulation – Functionality of the Tool ● Resulting Machine Induced Background in the BCM – Comparison to Minimum Bias Signal – Situation for Non-Nominal Conditions ● Conclusions 1 M. Lieng, 10 th MIB WG, 15.06.2007

2. The Beam Condition Monitor ● BCM monitors the behaviour of the beam and protects the LHCb from adverse beam condition ● The BCM provides real-time radiation monitoring with 40us integration time; not synchronized with the trigger and always active ● It is connected to the beam interlock system ● Two BCM stations exist; upstream and downstream of IP, at a non-sensitive angle of the LHCb ● Radiation hard CVD diamonds are used as sensors ● Could be used in the Background 1 & 2 signal? 2 M. Lieng, 10 th MIB WG, 15.06.2007 BCM Team from Dortmund University: M. Domke, Ch. Ilgner, M. Lieng, M. Nedos, K. Rudloff, B. Spaan, K. Warda

3. The Beam Condition Monitor in Software ● The BCM is implemented in the LHCb Detector Description ● The simulations are conducted in the Gauss program of the LHCb software suit – Uses Geant4 – Works on an event by event basis ● BCM should be sensitive to: – Collimator background – Beam gas background – Offsets of beam in detector – Any and all adverse beam and background conditions 3 M. Lieng, 10 th MIB WG, 15.06.2007 BCM

4. The Collimator Background at LHCb ● Tracking of particle losses in the machine gives information about expected rates in the collimators. ● Estimates for “perfect machine” with full collimator system in IR7 (phase 2?) ● Separate estimates for vertical and horizontal halo ● For standard 30h collimation beam lifetime, 2.8x10 9 p/s of the halo are lost in IR7 collimators. At temporary inefficiencies this number is 3.8x10 11 p/s 4 M. Lieng, 10 th MIB WG, 15.06.2007 IR7 / IR8 Collimators. LHC Design Report Vol 1.

5. The Collimator Background at LHCb ● About 78% of the tertiary collimator losses are caused by the vertical halo, thus only this halo is used in further estimates ● Particle cascade from the tertiary collimators is transported to 1m upstream of IP8 ● Loss rate in tertiary collimators is about 3x10 6 p/s at normal running conditions ● Effects of the LHCb shielding on the background is calculated 5 M. Lieng, 10 th MIB WG, 15.06.2007 Available source files for: ● Vertical or horizontal tertiary collimators ● Hadrons or muons ● Full shield, staged shield or no shield ● Vertical Halo for Beam 1 LHCb upstream shielding

6. The Collimator Background at LHCb ● Particle distributions given at entrance of cavern and can be imported by other programs from there ● Each particle in distribution is given a weight to represent its relative likelihood to exist. ● The sum of the particle weights give the average particle flux through the plane. ● Each particle is represented by its position, direction, type and kinetic energy. 6 M. Lieng, 10 th MIB WG, 15.06.2007 Muon and Charged Hadron Background from Vertical Tertiary Collimators. Staged Shield. (V. Talanov, 01.06.06)

7. The Machine Induced Background Tool ● Tool created to import particles from background simulations into the LHCb simulation software ● Samples random particles from the given distribution using the particle weights ● Can be run together with other generators, or stand- alone ● Generated distribution consistent with expectations ● A series of options exist to make the tool dynamic enough to cover most use cases 7 M. Lieng, 10 th MIB WG, 15.06.2007 Muon Background from Vertical Tertiary Collimators. Staged Shield. In background estimates, and as sampled in the MIB tool.

8. The MIB Tool Used on the BCM ● Simulations of the BCM with the MIB tool – Nominal background signal in BCM is about 0.5% of the minimum bias signal. In average a sensor is hit by a background particle every 6-10 period – Hadrons from Vertical Tertiary Collimator dominates (97%) – The shielding has little effect on the distribution in the BCM region as it is located in the shield “hole” – Signal from muons is very low as the distribution has a minimum close to the beam line 8 M. Lieng, 10 th MIB WG, 15.06.2007 Center of hadronic and muonic Background for Vertical Tertiary Collimators. Staged Shield. (particles/cm 2 /s)

9. The MIB Tool Used on the BCM ● Some comparison of background to minimum bias signal – Particles from the background are in general more energetic than min. bias – Angular distribution of particles are similar. This is also related to the angular coverage and position of sensors 9 M. Lieng, 10 th MIB WG, 15.06.2007 Energy of particles hitting BCM. Minimum bias and hadrons from vertical tertiary collimator incident angle of particles hitting BCM. Minimum bias and hadrons from vertical tertiary collimator

10. The MIB Tool Used on the BCM ● Background effects not taken into account in the simulations – Temporary inefficiencies can cause an increase by a factor 136 – Other protons on collimators: Losses in arcs can cause an increase by a factor 5 (29.09.06 I. Bayshev) – Beam 2 simulations are currently done by “flipping” Beam 1 distributions. This is an ad-hoc solution – What can one expect from a non-optimal beam situation in the collimators? – Beam gas background not taken into account. Import tool need to be created. Estimates are for old beam gas and without shielding 10 M. Lieng, 10 th MIB WG, 15.06.2007

11. Conclusions ● The LHCb BCM is being created to protect the sensitive parts of the LHCb from adverse background conditions ● Simulations of the Machine Induced Background gives expectations to what one will see at nominal conditions and how sensitive we are to various failure scenarios ● A tool has been created to import the background estimates into the Gauss simulations software ● Estimates of beam 2 and failure scenarios are necessary to improve our understanding of both nominal and adverse conditions 11 M. Lieng, 10 th MIB WG, 15.06.2007

12. Spare: Preliminary Expected Signal in Real BCM ● One MIP traversing one BCM sensor within the 40us period should create a signal that is large enough to be seen over the continuous bias signal of 10pA ● At minimum bias the expected signal is in the range of 1.8nA, and thus well within the sensitive range (10pA to 1mA) 12 M. Lieng, 10 th MIB WG, 15.06.2007