The LHCb Muon System

and LAPE Participation

Burkhard Schmidt

CERN - EP/LHB

Presented at the CNPq Workshop

Rio de Janeiro, 12 January 1999

12/1/1999 B. Schmidt / CERN

Outline

• IntroductionMuon identification 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

• Conclusion

12/1/1999 B. Schmidt / CERN

Introduction

Lepton identification:

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

• Lepton identification in LHCb is important for the Bd J/s and Bd J/(ee)s 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 signatures is a powerful tool inparticle physics

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12/1/1999 B. Schmidt / CERN

The LHCb Detector

12/1/1999 B. Schmidt / CERN

The LHCb Detector

12/1/1999 B. Schmidt / CERN

Introduction

Hadron punch-through:

• The probability for a hadron to traverse material of thickness L and nuclear interaction length without interacting is e -L/ .

• Punch-through indicates the debris exiting an absorber and causeswrong identification of a hadron as a prompt muon.

• The length of a hadron absorber must be sufficient to reduce thepunch-through trigger rate well below the prompt rate.

• Minimum absorber length ~ 10

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

12/1/1999 B. Schmidt / CERN

Overview

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

-K X 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.

12/1/1999 B. Schmidt / CERN

Overview

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.

12/1/1999 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

12/1/1999 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

12/1/1999 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

12/1/1999 B. Schmidt / CERN

Muon System Technologies

Status of CPC R&D:

• A first prototype with pads of different sizes has been constructedtogether with its frontend-electronics at PNPI and tested using theCERN-PS beam.

• good signal/noise separations have been obtained • time resolutions are better then expected

12/1/1999 B. Schmidt / CERN

Muon System Technologies

Resistive Plate chambers (RPC) :

• Type of parallel plate chamber (therefore simple construction)

with plates of a bulk resistivity of ~ 1011cm

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

• RPCs provide excellent time resolution and a moderate rate capability.

12/1/1999 B. Schmidt / CERN

Muon System Technologies

Multigap RPCs (MRPC) :

• Improve timing properties of RPC further and reduce streamer formation

12/1/1999 B. Schmidt / CERN

Muon System Technologies

MRPC R&D:

• 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.

12/1/1999 B. Schmidt / CERN

Muon Frontend Electronics

12/1/1999 B. Schmidt / CERN

L0 Muon TriggerAlgorithm (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

12/1/1999 B. Schmidt / CERN

L0 Muon Trigger

Muon Momentum Measurement:• Muon momenta are measured by means of the magnet spectrometer.

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

• The transverse momentum PT is given by: PT = P tan2 dim. tan )

The momentum resolution is limited by:

• multiple scattering (material between IP andM2)

• the granularity of the muon chamber pads

• magnetic field map and alignment

12/1/1999 B. Schmidt / CERN

L0 Muon Trigger

Distributions of P and PT for muons:Title:ptt_rio_nor.epsCreator:HIGZ Version 1.23/09Preview:This EPS picture was not savedwith a preview included in it.Comment:This EPS picture will print to aPostScript printer, but not toother types of printers.

12/1/1999 B. Schmidt / CERN

L0 Muon Trigger

• Algorithm (II):

• calculate muon PT

(PT -resolution is ~25%)

• apply cut on PT:

1GeV< PT<2GeV

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

(region of LHCb operation)

12/1/1999 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

1998 + 1999

1998 + 1999

1998 + 1999

January 2000

July 2000

2000

January 2001

2001 - 2003

2004

12/1/1999 B. Schmidt / CERN

LAPE Participation in the Muon Group

Present situation:

Physicists from UFRJ Rio de Janeiro are involved in various aspectsof 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.

12/1/1999 B. Schmidt / CERN

Conclusion

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.