HIGHLIGHTS FROM THE COMPASS EXPERIMENT @ CERN

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HIGHLIGHTS FROM THE COMPASSEXPERIMENT _at_ CERN

• F. Bradamante
• University of Trieste and INFN Trieste
• on behalf of the
  Collaboration
• Sixth International Conference on Perspectives in
  Hadronic Physics
• Trieste, May 16, 2008

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COmmon Muon and Proton
Apparatus for
Structure and
Spectroscopy NA58

• Czech Republic, Finland, France, Germany, India,
  Israel, Italy, Japan, Poland, Portugal, Russia
• Bielefeld, Bochum, Bonn, Burdwan, Calcutta, CERN,
  
• Dubna, Erlangen, Freiburg, Heidelberg, Helsinki,
  Lisbon,
• Mainz, Miyazaky, Moscow, Munich, Nagoya, Prague,
  Protvino,
• Saclay, Tel Aviv, Torino, Trieste, Warsaw
• 28 Institutes, 230 physicists

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COMPASS

experiment thought of in April 94 Nov. 94 Trento workshop Trieste workshop _at_ICTP
LoI encouraged March 95 June 95 SPSLC in Cogne
Proposal recommended approved by RB March 96 Sept. 96 Feb. 97 as NA58
Technical run 2000 2000
Commissioning 2001 2001

• since 2002 taking data with
• a new spectrometer with outstanding performances

• merging of two programmes

HMC (muon beam) CHEOPS (hadron beam)
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Physics program of COMPASS

• Experiments with hadron beams
• Pion and Kaon polarizabilities
• Diffractive production of exotic states
• Search for glueballs
• Light meson spectroscopy
• Production of double charmed baryons

• Experiments with muon beam
• ?G/G
• g1
• Transverse spin effects
• Flavor decomposition of spin distribution
  functions
• Vector meson production
• Spin transfer in ?-hyperon production

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luminosity 5 . 1032 cm-2 s-1 beam
intensity 2.108 m/spill (4.8s/16.2s) beam
momentum 160 GeV/c
longitudinally polarised muon beam longitudinally
or transversely polarised target calorimetry
particle identification

LHC
SPS
N
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The Spectrometer for the Muon Programme
Trigger-hodoscopes
µ Filter
ECal HCal
50 m
RICH
MWPC
Straws
TWO STAGE SPECTROMETER
Gems
Drift chambers
Polarized beam and target
Micromegas
SAT,
LAT,
PID
Silicon
SciFi
0.003 lt x lt 0.5 10-3 lt Q2 lt 10 GeV2
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WHERE ARE WE ?

• in 2002, 2003, 2004, 2006 and 2007 COMPASS has
  taken data in the muon program configuration

160 GeV, polarized m beam2002-2006 6LiD
polarized target (polarized deuterons)
2007 NH3 polarized target (polarized
protons)
2000 TB 51010 events

• pilot run in 2004 for hadron program

• 2008 hadron beam at 190 GeV for diffractive and
  central production

• physics results
• DG/G 1.
  pion polarizability
• DS
  2. PWA in diffractive
• Transversity
  scattering
• Cahn asymmetry
• Pentaquark
• Exclusive ?0
• ? physics

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THE COMPASS MUON PROGRAM

• TWO CLASSES OF PHENOMENA
• LONGITUDINAL SPIN CASE
• TRANSVERSE SPIN CASE

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LONGITUDINAL SPIN CASE the beginning
EMC 1988
G1p 0.123 ? 0.013 ? 0.019 DS 0.12 ? 0.17
? SPIN CRISIS
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LONGITUDINAL SPIN CASE

• from polarised lepton polarised nucleon DIS

with
and
first moments
from measurement of EMC in 1988 and using
complementary information from neutron and
hyperon ßdecay one obtained
at variance with naïve expectation
since
necessity for measuring
SMC, SLAC, HERMES
and in SIDIS
SMC, HERMES, COMPASS
in SIDIS
HERMES, COMPASS
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LONGITUDINAL SPIN CASE

• physics results
• ?G/G

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MEASUREMENTS OF THEGLUON POLARIZATION

• FOUR LINES OF ATTACK
• Double spin asymmetry of the OPEN CHARM
  cross-section in high energy µD scattering
• Double spin asymmetry of the HIGH-pt HADRON PAIRS
  in high energy µD DIS (Q2 gt 1 GeV2)
• Double spin asymmetry of the high-pt hadron pairs
  in high energy µD scattering (Q2 lt 1 GeV2)
• Measurement of g1 of the deuteron and QCD fit of
  all the world data

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DG/G at COMPASS
Photon Gluon Fusion

• q c cross section differencein charmed
  meson production
• ? theory well understood
• ? experiment challenging
• q u,d,s cross section difference in 21 jet
  productionin COMPASS events with 2 hadrons
  with high-pt
• ? experiment easy
• ? theory more difficult

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• ?G/G
• from Open Charm

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D mass spectra
APS, 13 April 2008
G.K. Mallot
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DG/G from open charm

• 2002 2006 data D0 D
• ?G/G -0.49 0.27 (stat) 0.11 (syst)
• _at_ ltxggt 0.11, ltm2gt 13 (GeV/c)2

preliminary
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• ?G/G
• from High-pt hadron pairs

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?G/G from High-pt hadrons, Q2 gt 1 (GeV/c)2

• PGF and background

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?G/G from High-pt hadrons, Q2 gt 1 (GeV/c)2

• 2002 2004 data High pT, Q2 gt 1 GeV/c2
• ?G/G 0.08 0.10 (stat) 0.05(syst)
• _at_ ltxggt 0.082 (range 0.055 0.123), m2
  3 (GeV/c)2

preliminary
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?G/G from High-pt hadrons
all Q2
low Q2
resolved photon
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?G/G from High-pt hadrons, Q2 lt 1 (GeV/c)2

• 2002 2004 data High pT, Q2 lt 1 GeV/c2
• ?G/G 0.016 0.058 (stat) 0.055 (syst)
• _at_ ltxggt 0.085, m2 3 GeV2

preliminary
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Gluon Polarization
COMPASS preliminary results
high-pT pairs, Q2gt1GeV2
20022004

• ?G/G 0.08 0.10 (stat) 0.05(syst)
• _at_ ltxggt 0.082 (range 0.055 0.123), m2
  3 (GeV/c)2

high-pt pairs, Q2lt 1GeV2
20022004

• ?G/G 0.016 0.058 (stat) 0.055 (syst)
• _at_ ltxggt 0.085, m2 3 GeV2

open charm
20022006

• ?G/G -0.49 0.27 (stat) 0.11 (syst)
• _at_ ltxggt 0.11, ltm2gt 13 (GeV/c)2

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Summary of results
new high-pT point
new charm point
G.K. Mallot
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• g1d

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g1 of the deuteron (2002-2003)
Phys Lett B 612 (2005) 154

• most precise measurement for 0.004 lt x lt 0.03
• new NLO QCD fit, precision of a0 improves factor
  2 (Q2 4 GeV2)

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CONCLUSION from ?G MEASUREMENTS
?G SMALL
more precise measurements will come soon
COMPASS 2006 RHIC RUN6 .
interest in orbital angular momentum GPDs
Jis SUM RULE
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more on LONGITUDINAL SPIN CASE
MEASUREMENT OF VALENCE QUARK POLARISATION
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valence quark polarisation

• hadron asymmetries

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valence quark polarisation

• comparison with other experiments

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• The Transverse Spin Case

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Transverse Spin case

• Large effects observed in hadronic interactions

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Transverse Spin case

• Large effects observed in hadronic interactions

at leading order a third PDF is necessary for a
complete description of the structure of the
nucleon
Theoretical developments

• DTq(x) being chiral-odd, it can be measured
  only in conjunction
• with another chiral-odd partner

Collins function
SIDIS
DY
measurable in ee-? hadrons

• relevance of transverse momentum dependent
  (TMD) PDF and FF

Sivers function
Many Workshops in recent years on Transverse
Momentum, spin, and position distributions of
partons in hadrons
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Collins and Sivers angles
Transversity single hadron - 1

• ?C ?h - ?S
• ? S ?h - ?S
• ?S azimuthal angle of spin vector of
  fragmenting quark (?S p - ?S)
• ?h azimuthal angle of hadron momentum

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Transversity single hadron - 2

• first measurements of transverse spin asymmetries
  in DIS of high energy
• muons on a transversely polarized deuteron target
  
• published single hadron asymmetries from
  2002-2004 runs
• Collins related to transverse quark
  distributions
• Sivers related to intrinsic kT

Phys Rev Lett 94 (2005) 202002 Nucl Phys B765
(2007) 31
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Collins asymmetry for pions and kaons
preliminary 2002-2004 data proton (virtual photon
asymm)
(lepton beam 2002-05 ? DIS07)
final CERN-PH-EP/2008-002hep-ex/0802.2160
(PRL) 2003-2004 data deuteron (virtual photon
asymm)
COMPASS sign convention
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Independent Measurement of the Collins FF

• measurable in ee annihilation
• first attempts to measured it from the
  correlation between the azimuthal angles of ps
  from ee annihilation using LEP data

last years great news from BELLE
the Collins FF is being measured in ee
annihilation, and it is different from zero!
measurement of the correlation between the
azimuthal angles of ps in the near jet and in
the far jet from ee annihilation

• 547 fb-1 charm corrected data sample,
• UL and UC double ratios

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Collins asymmetries SUMMARY

• The facts
• HERMES has measured on a proton targetnon-zero
  Collins asymmetries for p and p-
• COMPASS has measured on a deuteron targetCollins
  asymmetries compatible with zero
• BELLE has produced the first results on Collins
  FF
• Conclusion
• Collins mechanism is a real phenomenon
• universality of Collins FF
• transversity can be measured in SIDIS

• Present picture
• Collins DTu - DTd DT0D(fav.) -
  DT0D(unfav)
• To extract TMD DF and FF GLOBAL ANALISYS are
  necessary

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HERMES, COMPASS, BELLE
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Sivers asymmetry for pions and kaons
preliminary 2002-2005 data proton
(DIS07)
CERN-PH-EP/2008-002hep-ex/0802.2160
(PRL) 2003-2004 data deuteron
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Sivers asymmetry
the measured asymmetry on deuteron compatible
with zero has been interpreted as Evidence for
the Absence of Gluon Orbital Angular Momentum in
the Nucleon S.J. Brodsky and S. Gardner, PLB643
(2006) 22
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SUMMARY AND OUTLOOK

• a technically challenging new experiment is IN
  OPERATION SINCE 2002

LHC technologies detectors read-out data handling

• a privileged situation at CERN

• MANY PHYSICS RESULTS have been produced
  MANY MORE IN THE PIPE-LINE

• COMPASS is foreseen to run up to the end of the
  present mid-term plan of CERN (2010)

BIG DISCOVERY POTENTIAL

• with some upgrade COMPASS might be an interesting
  option even in the second decade of this century

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• SPARE SLIDES

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Transversity two hadrons - 1
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Transversity two hadrons - 2
all /- combinations

• precise measurement of few
• systematics seems well under control
• also compatible with zero
• interesting to see proton in 2006

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• Exclusive ?0 production

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Exclusive ?0 production (2002 data) - 1
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Exclusive ?0 production - 2
ANGULAR DISTRIBUTIONS
preliminary, statistical errors only, limited by
MC
corrected for acceptance, smearing and efficiency
(MCDIPSI gen) background not subtracted
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measurement of r
Exclusive ?0 production - 3
04 00

distribution

Spin density matrix element
T?? ?? are helicity amplitudes
meson photon
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measurement of rand Im r
Exclusive ?0 production - 4
0 4 1-1
3 1-1

distribution
beam polarisation

Spin density matrix element
if SCHC holds
weak violation
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• Pentaquark search

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F(1860) Pentaquark search - 1

• motivated by NA49 report of pentaquark candidate
• COMPASS has large sample of the double-strange ?
  baryon (18000 ?, 11000 ?) from 2002-2003 data
• search for ? p resonance
• F(1860) ? ? p ? ?p p ? p ppp

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F(1860) Pentaquark search - 2
Eur Phys J C41 (2005) 469

• compare to yields
• opposite-sign pairs ?(1530)0 ? ? p , 1700
  and 920 evts
• like-sign pairs evts lt79 and lt89 at 99 CL
• (expected 400)

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Transversity ? polarization
2002-2003 data
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• Longitudinal polarization
• of ? and anti? in DIS

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Event selection
? POLARIZATION (2002 data) - 1

N(?) N(??)
E665 750 650
NOMAD 8087 649
HERMES1996-2000 10568 1687
COMPASS2002 7919 5062
COMPASS2003 34789 20651
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? POLARIZATION
2002 data
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? POLARIZATION
2002 data