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The LHCb Muon System and LAPE Participation Burkhard Schmidt CERN - EP/LHB Presented at the CNPq Workshop Rio de Janeiro, 12 January 1999. Introduction Muon identification in particle physics experiments The LHCb Muon System - Overview - Muon detector technologies and prototype studies

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The LHCb Muon Systemand LAPE ParticipationBurkhard SchmidtCERN - EP/LHBPresented at the CNPq WorkshopRio de Janeiro, 12 January 1999


Muonidentification in particle physics experiments

The LHCb Muon System

- Overview

- Muon detector technologies and prototype studies

- Frontend-electronics

- Level 0 muon trigger

Muon System Schedule

LAPE Participation



B. Schmidt / CERN

Lepton identification:

Many discoveries in particle physics are based on lepton (e, m) identification: J/Y, Neutral Currents, W± and Z0, top etc.

Lepton identification in LHCb is important for the

Bd J/Y(mm) Ks and Bd J/Y(ee) Ks decay channels

electrons and muons give complementary signatures due to huge differences in radiative losses:

- electrons are identified by calorimetry and E/p matching

- muons are identified by their penetration power

The complementarity of e and m signatures is a powerful tool in

particle physics


B. Schmidt / CERN

the lhcb detector
The LHCb Detector

B. Schmidt / CERN

the lhcb detector1
The LHCb Detector

B. Schmidt / CERN

Hadron punch-through:

The probability for a hadron to traverse material of thicknessL and

nuclear interaction length l without interacting is e -L/l .

Punch-through indicates the debris exiting an absorber and causes

wrong identification of a hadron as a prompt muon.

The length of a hadron absorber must be sufficient to reduce the

punch-through trigger rate well below the prompt m-rate.

Minimum absorber length ~ 10l

Total thickness of LHCb hadron absorber (muon shield) : ~ 23l


B. Schmidt / CERN

Background sources in the LHC environment:

primary background (correlated in time with the p-p interaction):

- hadron punch-through including muons generated in the hadron shower

- p,K mX decays, predominantly with PT< 10 GeV

radiation background:

neutron and photon “gas” (MeV energies from radiative n-capture) generated by hadrons interacting in the absorber. Its impact depends on the efficiency of the chamber material for photon conversions.

machine background:

energetic muons produced in beam-gas interactions and in machine elements upstream of the experimental areas.


B. Schmidt / CERN

Particle fluxes in the muon stations

The highest rates are expected in M1

(not protected by the shield)

and in the inner part of Stations 2-5.

In the outer part of station 2-5

a technology with moderate

rate capability can be used.


B. Schmidt / CERN

lhcb muon system
The Muon System must provide:

Muon identification

Reliable beam-crossing identification

(good timing resolution)

Reasonable momentum resolution for a robust PT-selective trigger

(L0 muon trigger)

Good performance for the duration of LHC in a high rate environment

LHCb Muon System

B. Schmidt / CERN

muon detector layout
Chamber pad structure:

Muon stations are devided in 4 regions with different pad size

Pad dimension scales with station number

Projectivity to interaction point

Required precision in the bending plane (x) leads to x/y aspect ratio of 1/2 in stations M1 and M2.

“Physical” pads in outer region and in the various planes per station are grouped together to “logical” pads.

total number of physical pads: ~240 k

total number of logical pads: ~45k

Muon Detector Layout

B. Schmidt / CERN

muon system technologies
Cathode Pad Chambers (CPC) :

Wire Chamber operated in proportional mode with cathode pads (strips)

providing the spatial resolution.

wire-spacing s determines

time resolution

at present: s = 2mm

Characterized by very high rate capability and moderate time resolution

30% CO2, 60% Ar and 10% CF4 is prefered gas mixture

CPC have good aging properties:

4C/cm equiv. to 50kHz/cm2/s for 10years

Muon System Technologies

B. Schmidt / CERN

muon system technologies1
Status of CPC R&D:

A first prototype with pads of different sizes has been constructed

together with its frontend-electronics at PNPI and tested using the

CERN-PS beam.

good signal/noise separations have been obtained

time resolutions are better then expected

Muon System Technologies

B. Schmidt / CERN

muon system technologies2
ResistivePlatechambers (RPC) :

Type of parallel plate chamber (therefore simple construction)

with plates of a bulk resistivity of r ~ 1011W cm

Gas mixture normally used: C2F4H2 + few % isobutane + 1% SF6

RPCs provide excellent time resolution and a moderate rate capability.

Muon System Technologies

B. Schmidt / CERN

muon system technologies3
Multigap RPCs (MRPC) :

Improve timing properties of RPC further and reduce streamer formation

Muon System Technologies

B. Schmidt / CERN

muon system technologies4

Participants: CERN and UFRJ-Rio

Objectives: - Studies of resistive plates (materials)

- Development of construction techniques

- Performance studies in testbeam

Status: - First (small) prototype has been tested last year

- prototype of 130cm x 230cm is under construction

and will be studied this year using testbeams.

Muon System Technologies

B. Schmidt / CERN

muon frontend electronics
Muon Frontend Electronics

B. Schmidt / CERN

l0 muon trigger
Algorithm (I) :

start with pad hit in M3 (seed)

extrapolate to M4 and M5 and look for hits within field of interest (FOI)

search for hits in M2 and M1 and take hits closest to centre of search window

calculate x- and y-slopes and find y-intercept at z=0

L0 Muon Trigger

B. Schmidt / CERN

l0 muon trigger1
Muon Momentum Measurement:

Muon momenta are measured by means of the magnet spectrometer.

In the bending plane the deflection angle b is given by:

The transverse momentum PT is given by: PT = P tang (2 dim. tanq )

The momentum resolution is limited by:

multiple scattering (material between IP andM2)

the granularity of the muon chamber pads

magnetic field map and alignment

L0 Muon Trigger

B. Schmidt / CERN

l0 muon trigger3
Algorithm (II):

calculate muon PT

(PT -resolution is ~25%)

apply cut on PT:

1GeV< PT<2GeV

B mX efficiency of 8% -14% MB-retention of 1% - 3%

(region of LHCb operation)

L0 Muon Trigger

B. Schmidt / CERN

muon system schedule
Optimization of the muon detector

Study of MRPC and CPC (WPC) prototypes in testbeam

Design and and develop FE-electronics

Accommodate L0 muon trigger to detector layout

Choice of technologies for detector and electronics

Finalize detecotor design

Construction and test of full scale prototypes

Technical Design Report (TDR)

Construction and test of muon chambers

Installation and commissioning of the muon system


1998 + 1999

1998 + 1999

1998 + 1999

January 2000

July 2000


January 2001

2001 - 2003


Muon System Schedule

B. Schmidt / CERN

lape participation in the muon group
Present situation:

Physicists from UFRJ Rio de Janeiro are involved in various aspects

of the muon system, in particular :

- the research and development of MRPC,

- the development of the related frontend-electronics,

- the implementation of the L0 muon trigger.

Future Possibilities:

UFRJ can be a major production-center of the muon chambers and the frontend electronics.

This will open a door to brazilian industry and result in an important technology transfer.

LAPE Participation in the Muon Group

B. Schmidt / CERN

Physicists form UFRJ Rio de Janeiro are making a major contribution to the muon project of the LHCb experiment.

The contribution of LAPE to LHCb is important for the experiment and has certainly a positive impact for science and industry in Brazil.


B. Schmidt / CERN