the compass spin physics program rencontres de moriond s. panebianco the compass spin physics...

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


OverviewOverview

• Spin structure of the nucleon• Polarized quark PDF• Gluon polarization

– High pt hadron pair leptoproduction

– Open charm leptoproduction

• Transversity• Conclusions


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 spin of the nucleonThe spin of the nucleon


Deep inelastic scatteringDeep inelastic scattering


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


• -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


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


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


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


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


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


Open charm raw asymmetry Open charm raw asymmetry


Measurement of the quark transversityMeasurement of the quark transversity


Collins and Sivers asymmetriesCollins and Sivers asymmetries


ConclusionsConclusions


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


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 ”

the compass spin physics program rencontres de moriond s. panebianco the compass spin physics...

Documents

panebianco slide

nucleon slide

panebianco gg

lodis slide

b slide

compass complete

g g p slide

panebianco conclusions