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, 10th MIB WG, 15.06.2007

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?

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BCM

Team from Dortmund University: M. Domke, Ch. Ilgner, M. Lieng, M. Nedos, K. Rudloff, B. Spaan, K. Warda

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

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BCM

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, 2.8x109 p/s of the halo are lost in

IR7 collimators. At temporary inefficiencies this number is 3.8x1011 p/s

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IR7 / IR8 Collimators. LHC Design Report Vol 1.

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 3x106 p/s at normal running conditions

● Effects of the LHCb shielding on the background is calculated

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Available source files for:

● Vertical or horizontal tertiary collimators

● Hadrons or muons

● Full shield, staged shield or no shield

● Vertical Halo for Beam 1LHCb upstream shielding

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.

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Muon and Charged Hadron Background

from Vertical Tertiary Collimators. Staged

Shield. (V. Talanov, 01.06.06)

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

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Muon Background from Vertical Tertiary Collimators. Staged Shield. In background estimates, and as sampled in the MIB tool.

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

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Center of hadronic and muonic Background for Vertical Tertiary Collimators. Staged Shield.(particles/cm2/s)

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

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Energy of particles hitting BCM. Minimum biasand hadrons from vertical tertiary collimator

incident angle of particles hitting BCM. Minimum biasand hadrons from vertical tertiary collimator

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

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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

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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)

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