Post on 27-Mar-2015
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
The COMPASS spin physics The COMPASS spin physics programprogram
Stefano Panebianco (CEA/Saclay)on behalf of the COMPASS Collaboration
XXXXth Rencontres de Moriond
QCD and High Energy Hadronic Interactions
La Thuile, March 12th -19th 2005
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
OverviewOverview
• Spin structure of the nucleon• Polarized quark PDF• Gluon polarization
– High pt hadron pair leptoproduction
– Open charm leptoproduction
• Transversity• Conclusions
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
Nucleon parton distributionsNucleon parton distributions
• Unpolarized DIS :
q(x,Q2) and g(x,Q2)
• Here Polarized DIS :
q = q - q, G = g - g
μ
P
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
The spin of the nucleonThe spin of the nucleon
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
Deep inelastic scatteringDeep inelastic scattering
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
The COMPASS spectrometerThe COMPASS spectrometer
RICH
Sci-FibersGEM & MWPC
Sci-FibersSilicon
• Two stage spectrometer (SM1: 1Tm, SM2: 5.2 Tm)
• Track reconstruction (new technologies: Sci-Fibers, GEMs, Micromegas, straws)
• Particle identification (RICH, ECAL, HCALs, Filters)
SM2
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
• -nucleon asymmetry:
• COMPASS has:– high energy– high luminosity– high dilution factor for
a solid state target
•
• Unique result in the low x region important to test QCD sum rules
The inclusive asymmetry The inclusive asymmetry AA11 qq
(hep-ex/0501073, accepted Phys. Lett. B)
111 FAg
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
How to measureHow to measure GG/G/G
PGFg
PGFg
LLa
ˆ
ˆ
’
NX
g
q
q
Photon-Gluon Fusion (PGF)
G
GaA LL
PGFN
Two tagging methods:-High pt hadron pairs-Open charm
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
HighHigh p ptt hadron pair production @ Qhadron pair production @ Q22>1>1
5.222
21 TT pp
From Monte-Carlo
tot
QCDCQCDCLL
tot
LOLOLL
d
tot
pgfpgfLL
hhXN aaAaG
GA
ˆˆˆ 1
GeV2
to reduce LODIS
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
G/G from highG/G from high p ptt hadron pair, Qhadron pair, Q2 2 > 1> 1
2002/2003 data:
A||/D = - 0.015 ± 0.080 (stat.) ± 0.013 (syst.)
ΔG/G = 0.06 ± 0.31stat. ± 0.06syst.
BUT...
10% ofstatistics
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
G/G from highG/G from high p ptt hadron pair, all Qhadron pair, all Q2 2
At Q2 < 1 additional background
Resolved photon processes
High statisticsProjection for 2002-2004 data (all Q2) (ΔG/G) = 0.05
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
ΔΔG/G from open charmG/G from open charm
G
GaA LL
ccN
D0 K- π+ (BR 4%)
D*+ D0 π+ + c.c.
c
c
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
Open charm raw asymmetry Open charm raw asymmetry
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
Measurement of the quark transversityMeasurement of the quark transversity
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
Collins and Sivers asymmetriesCollins and Sivers asymmetries
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
ConclusionsConclusions
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
Pairs of hadrons with high pPairs of hadrons with high pTT
Photon Gluon Fusion
h1
h2
• current fragmentation:
• event cuts:
xF > 0.1z > 0.1
pt > 0.7 GeV/cpt1
2+pt22 > 2.5 (GeV/c)2
m(h1h2) > 1.5 GeV/c2
• 2 high pt hadrons:
N
Q2 > 1 (GeV/c)2 , xBj < 0.050.1 < y < 0.9
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
The COMPASS spin physics program Rencontres de Moriond S. Panebianco
Future Fixed Target Programme at CERNFuture Fixed Target Programme at CERN
Villars meeting, 22-28 Sept.
CERN seminar Villars by John DAINTON
“ FT hadron program remains very competitive ……………………. COMPASS complete in medium term
- ΔG/G, transversity, polarisability, spectroscopy- SPSC p.o.t. concern prioritise
COMPASS longer term- GPD measurements would be unique”
Conclusions (personal) by Michelangelo MANGANO
“ COMPASS beam … flagship experiment ”