HIGHLIGHTS%20FROM%20THE%20COMPASS%20EXPERIMENT%20@%20CERN

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HIGHLIGHTS FROM THE COMPASSEXPERIMENT _at_ CERN

• F. Bradamante
• University of Trieste and INFN Trieste
• on behalf of the
  Collaboration
• WE Heraeus Seminar on Polarized Antiprotons
• Bad Honneff, June 23-25, 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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the target system
solid state target operated in frozen spin mode
2002-2004 6LiD (polarised deuteron)
dilution factor f 0.38 polarization PT
50 two 60 cm long cells with opposite
polarisation (systematics)

• 2006
• PTM replaced with the large acceptance COMPASS
  magnet (180 mrad)
• 2 target cells ? 3 target cells

2007 NH3 (polarised protons) dilution factor
f 0.14 polarization PT 90
during data taking with transverse
polarisation, polarisation reversal in the cells
after 4-5 days
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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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A1d from COMPASS

• Inclusive DIS asymmetry Q2gt1 (GeV/c)2

PLB 647(2007)8

• good agreement with previous experiments
• significantly improved statistics at low x !

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COMPASS QCD fit
using these results plus the same
asymmetries on p and n from the other
experiments
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LONGITUDINAL SPIN CASE

• direct measurement of
• ?G/G
• main objective of the
• longitudinal run

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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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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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• 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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conclusions from COMPASS deuteron data

• the unpolarised azimuthal asymmetries are
  different from zero and different for positive
  and negative hadrons

• all the transverse spin asymmetries have been
  measured to be compatible with zero

HERMES, COMPASS, BELLE data consistent
picture first fits, extractions of the new
DFs, and predictions for other experiments

• still, a lot of expectation for the higher energy
  COMPASS proton data

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2007 Transverse data statistics

• 2007 run May to November equally
  shared between transverse and longitudinal
• Transverse polarization
• data taking

Period Weeks Target Polarization
1 25 / 26 - - / -
2 27 / 28 - - / -
3 30 / 31 - / - -
4 39 / 40 - / - -
5 41 / 42a - - / -
6 42b / 43 - / - -
Period Weeks Target Polarization
1 25 / 26 - - / -
2 27 / 28 - - / -
3 30 / 31 - / - -
4 39 / 40 - / - -
5 41 / 42a - - / -
6 42b / 43 - / - -
Data used for these results

• several stability tests have been performed
• detectors and triggers performances
• event reconstruction
• K0 reconstruction
• distributions of kinematical variables
• ( zvtx, Em, fm, xBj Q2,y, W, Ehad, fhadLab ,
  qhadLab , fhadGNS , qhadGNS , pt)

20 of the total collected data has been used
for this analysis
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Collins asymmetry proton data
integrated over x and z
statistical errors only systematic errors 0.3
sstat
at small x, the asymmetries are compatible with
zero in the valence region the asymmetries are
different from zero, of opposite sign for
positive and negative hadrons, and have the
same strength and sign as HERMES
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Collins asymmetry proton data
comparison with M. Anselmino et al. predictions
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Sivers asymmetry proton data
integrated over x and z
statistical errors only systematic errors 0.5
sstat
the measured symmetries are small, compatible
with zero
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Sivers asymmetry proton data
comparison with the most recent predictions from
M. Anselmino et al.
arXiv0805.2677
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Results Sivers asymmetry
comparison with predictions from
S.Arnold, A.V.Efremov, K.Goeke, M.Schlegel and
P.Schweitzer, arXiv0805.2137
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conclusions

• COMPASS preliminary results on
• unpolarised hadron asymmetries on deuteron for
  positive and negative hadrons
• Collins and Sivers asymmetries on protons
• Collins asymmetry different from zero the
  effect is there at COMPASS energies
• Sivers asymmetry smaller, compatible with zero
  to be understood

near future analysis of the whole 2007 proton
data sample
longer term transverse spin physics is one of
the items being spelled out for the future
COMPASS program the study of transverse spin
effects needs further precise measurements and
the COMPASS facility is the only place where
SIDIS can be measured at high energy