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.