Semi-Inclusive DIS in COMPASS Present and Future

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Semi-Inclusive DIS in COMPASS Present and Future

• Massimo Lamanna
• CERN and INFN Trieste

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Plan of the talk

• Physics motivations
• Detector performances in 2001
• Highlights (not all detectors!)
• Conclusions and outlook

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COMPASS programme

• Nucleon structure
• Gluon polarisation ?G(x)
• Flavour-dependent helicity functions ?q(x)
• Transverse-spin distribution functions ?Tq(x)
• Spin-dependent fragmentation (?D?q)

• Spectroscopy
• Primakov reactions
• Polarizability of ? and K
• Glueballs and hybrids
• Charmed mesons and baryons
• Semileptonic decays
• HQET
• Observe double-charmed baryons

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Semi Inclusive Deep-Inelastic Scattering
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DG measurements

• Single out gg fusion graphs
• Heavy quark lines (cc)
• High transverse momentum
• Experimentally
• DIS D0 (e.g. via ?pK-)
• DIS D (?pD0)
• DIS with high Pt hadrons

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DG measurements
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D0 reconstructed via Kp decay

• Signal over background 1/30 (DM ? 20 MeV/c2)
• Signal over background ? 1/3-1/4 (cosqlt0.5 and
  zgt0.25 (zED0/n))

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Other methods to assess DG

• More abundant channels
• Hadron pairs (with opposite charge)
• High Pt (Pt?1GeV)
• KK- pairs
• More difficult interpretation
• Systematic effects (concurrent microscopic
  mechanisms with the same final channel)
• Theoretical interpretation
• Originally proposed by A. Bravar, D. von Harrach
  and A. Kotziniam

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Flavour-dependent helicity functions ?q(x)

• Flavour decomposition of quark contribution to
  nucleon spin DS Duv Ddv
  6 D q
• Pioneered in SMC using AgN?h ?X
• Particle identification AgN?p ?X and
  AgN?K?X
• Unique in COMPASS low x (x0.003 at E190 GeV)

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2001 Apparatus
Muon Wall
Muon trigger
Spectrometer Magnet 1
Calorimetry
Spectrometer Magnet 2
Muon Wall
Polarised Target
Calorimetry
RICH
SPS 160 GeV m beam
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COMPASS 2001

• All types of detectors on the floor
• Many systems fully commissioned
• Many novel detectors operated in nominal
  conditions (2 108 m/s)
• Tracking half of the channels
• RICH fully equipped
• The target is hosted in the SMC magnet

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Target system
Two-cell target solid target (2X60 cm) with
opposite polarisation 2.5 T solenoid
field 3He-4He dilution refrigerator
(T50mK) Dynamic Nuclear Polarization 6LiD Dilutio
n factor 50 Preliminary P values P- -43
(max 48) P 48 (max 55)
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MicroMegas

• Novel tracking detector
• High rate gaseous detector
• High precision (?70 mm)
• High fluxes (before first dipole)
• Very good efficiency

Spatial resolution
Efficiency
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GEMs

• High rate gaseous detector
• High precision (?70 um)
• Small area tracking in SM1 and SM2

Efficiency
Spatial resolution
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STRAWs

• Drift tubes (STRAW tubes) arranged in double
  layers to provide high resolution (150-200 mm)
  after SM1

Installation of a double layer

• Very large area (8 m2)
• Low material budget
• First modules could be installed and operated (4
  double layers). Basic principle demonstrated
  10 double layers are expected in 2002

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RICHRing Imaging Cherenkov

• 90 m3 (3 m C4F10)
• 120 mirrors (3.3 m focal length)
• Over 20 m2 UV detectors
• MWPC CsI photon-sensitive cathods
• 8x8 mm2 pads
• 83k channels
• p/K/p separation up to 60 GeV

Photon detector (Up)
Beam halo
Photon detector (Down)
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RICH
Ring event
The cross indicates the track image The blue
dots are the pads The black dots are the selected
cluster
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2001 data taking
Beg. Jul? Beg. Oct

• Setting up period
• New detectors put in place and commissioned
• On-line system fully commissioned
• First look to the data
• Two week smooth data taking
• Event size close to nominal (30 kB)
• Event rate close to nominal (35 MB/s)

15 TB of data
Smooth data taking (2 weeks)
15 TB of data
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2001 events
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Muon vertex (primary vertex)
preliminary
IT, LT, MT different trigger combinations
(different angles/Q2)
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Vertex ? invariant mass
preliminary
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Conclusions and outlook

• Successful 2001 pilot run
• All detectors tested in realistic environment
• Excellent perspectives for 2002
• This is our initial setup
• Complete the first phase of the tracking
• Measure DG!!!
• Room for upgrades and further evolution

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Spare transparencies

• Just In Case

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Complex apparatus to allow a wide range of
measurements
COMPASS experiment

• Hadron beams (up to 300 GeV energy)

• ? beams and polarised nucleon targets

Large dynamical range (angles and momenta)
Particle identification
High-rate capabilities
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Spin of the Nucleon?

• DS 1 (Static QPM)
• DS 0.58 ?0.03 (Baryons Weak decays and Ds0)
• DS 0.24 ? 0.03 and Ds
  ?0.11 ? 0.01 (DIS)

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DG in COMPASS
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COMPASS semi-inclusive
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Em
100 GeV
n
lt 85 GeV
35 lt
cosJK
lt 0.5
zD0
gt 0.25
D0 (D) method
Invariant mass (GeV/c2)
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GEM picture
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CCF

• COMPASS Computing Farm (200 CPUs) commissioned
• Event distribution over all nodes tested
  (parallel access to event data bases)

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RICH n-1
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2001 events
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2001 events
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Straw

• First residual plots obtained
• Resolution not yet measured
• Basic principle OK

preliminary
preliminary
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Straw
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DAQ ONLINE

• Layered architecture
• Front end
• Read-out buffers
• Event building stage
• Recording
• Hardware
• Custom COMPASS solutions
• Mainstream PC and networking
• Software
• ALICE DATE
• ROOT (COOOL)

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CCF
To tape
On-line events to Objectivity DB
200 CPUs 35 MB/s input rate 300 TB/year