Highlights from the COMPASS experiment QNP09, Beijing, September 2009 G. K. Mallot CERN/PH for the...
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![Page 1: Highlights from the COMPASS experiment QNP09, Beijing, September 2009 G. K. Mallot CERN/PH for the Collaboration.](https://reader035.fdocuments.in/reader035/viewer/2022070409/56649e985503460f94b9b99e/html5/thumbnails/1.jpg)
Highlights from the COMPASS experiment
QNP09, Beijing, September 2009
G. K. MallotCERN/PH
for the Collaboration
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Plan
• COMPASS• Helicity structure (quarks)• Gluon polarisation• Transverse spin-structure of the nucleon
• A glimpse a hadron spectroscopy• Outlook
G. Mallot QNP09, Beijing, September 2009
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COMPASS: QCD structure of hadronsdata taking since 2002
nucleon spin-structure• helicity distributions of
qluons and quarks• transverse spin structure
hadron spectroscopy• light mesons• glue-balls • exotic mesons• polarisability of
pion and kaon
COMPASS RICH
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COMPASS key figures (muon beam)
• Large solid polarised target• proton target (NH3, 3 cells, e.g. +−+, ~85%, f 0.18 )
• deuteron target (6LiD, 2 cells, e.g. +−, ~50%, f 0.4)
• Polarised muon beam• ~80% polarisation• 5 107 muons/s, duty factor 20 − 33 %
• Nominal luminosity • 51032 cm-2 s-1
• Particle ID• RICH (π/K: 9−50 GeV/c), ECals, HCals, Muon walls
• DAQ• 250k channels• up to 30 kHz, several PByte/year (hadron runs)
G. Mallot QNP09, Beijing, September 2009
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G. Mallot QNP09, Beijing, September 2009
Three twist-2 PDFs
Parton Distribution Functions
q(x)f1
q (x)
Dq(x) g1
q(x)
DTq(x)
h1q(x)
chiral odd, poorly known
unpolarised PDFquark with momentum xP in a nucleon well known – unpolarised DIS
helicity PDFquark with spin parallel to the nucleon spin in a longitudinally polarised nucleon known – polarised DIS
transversity PDF quark with spin parallel to the nucleon spin in a transversely polarised nucleon
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TMD parton distributions
• 8 intrinsic transverse momentum dependent PDFs at LO• Asymmetries with different angular dependences on
hadron and spin azimuthal angles, Φh and Φs
G. Mallot QNP09, Beijing, September 2009
Sivers
Boer–Mulders
Transversity
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Results from transverse
polarisation
G. Mallot QNP09, Beijing, September 2009
longitudinal
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Longitudinal asymmetries
Semi-inclusive asymmetries
with
Inclusive asymmetry
G. Mallot QNP09, Beijing, September 2009
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Incl. & semi-incl. asymmetries
• proton, first measurement of AK, preliminary
G. Mallot QNP09, Beijing, September 2009
K+
K−
π+
π –
incl.
new
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Incl. & semi-incl. asymmetries
• deuteron
G. Mallot QNP09, Beijing, September 2009
K+
K−
π+
π –
incl.
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Incl. deuteron asymmetry
• most precise measurement for x<0.03 and Q2 > 1 GeV2
G. Mallot QNP09, Beijing, September 2009
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Structure function g1(x,Q2)
• very precise data• only data below
x < 0.01 (Q2 > 1)
• deuteron data:a0 =
0.33±0.03±0.05Δs+ Δs
=−0.08±0.01±0.02
(evol. to Q2=∞)
G. Mallot QNP09, Beijing, September 2009
p
d
new
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g1 proton and g1NS
G. Mallot QNP09, Beijing, September 2009
new
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proton & deuteron g1(x,Q2)
• unique kinematic domain• important for global QCD analyses
G. Mallot QNP09, Beijing, September 2009
CLAS
HER
MES
dpnew
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The role of quark flavours
LO analysis, preliminary
G. Mallot QNP09, Beijing, September 2009
new
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Flavour asymmetry?
• considerable asymmetry in the unpolarised case • model predicts naturally asymmetry for pol. case• only small effect (if at all)
G. Mallot QNP09, Beijing, September 2009
new
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17G. Mallot QNP09, Beijing, September 2009
Angular momentum of the nucleon
small ~0.15
poorly known
unknown
quarks gluons orbital
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• measure
• calculate , and background by Monte Carlo
Principle: Gluon polarisation enters via photon-gluon fusion (PGF)
G. Mallot QNP09, Beijing, September 2009
Hadron production in DIS via PGF
18
q
q
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cleanest process• little physics background (LO, QCDC)
observe asymmetry in D meson production• statistics limited• only one D meson via D→πK (BR ~ 4%)• combinatorial background large• drastically reduced when looking to D* decay
in coincidence with slow pion
Δg/g from open charm
G. Mallot QNP09, Beijing, September 2009 20
sππsπ0* KDD
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Update on open charm
• 2002–2006 deuteron data • new channels in D* sample
• sub-threshold kaons• 3-body decay with
non-observed π0
• old• new
G. Mallot QNP09, Beijing, September 2009
)( 00 KD
update
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G. Mallot QNP09, Beijing, September 2009
ΔG = 2.5
ΔG = 0.2
ΔG = 0.6
GRSV
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Δg/g from hadron pairs (LO)
Panic, 10 November 2008
G.K. Mallot 23
high-Q2
charm
low-Q2
(2004)
(2000)
single h
• LO data points at different scales 1 – 13 GeV2
• NLO fits to g1 at 3 GeV2
Δg/g is small around x 0.1
PLB 633 (2006) 25-32
confirmed by RHIC
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Results from longitudinal polarisation
G. Mallot QNP09, Beijing, September 2009
transverse
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Couple to chiral odd Collins FF
Transversity PDF
G. Mallot QNP09, Beijing, September 2009
Azimuthal cross-section asymmetry:
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Collins Asymmetries
G. Mallot QNP09, Beijing, September 2009
h+
h−
new
new: full 2007 proton data set (statistics tripled)
h+
h−
proton
deuteron
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Comparison to HERMES
• large asymmetry ~10% • good agreement in common x range• zero deuteron result important opposite sign of u and d
quark transversity PDF
G. Mallot QNP09, Beijing, September 2009
h+ h-
COMPASS HERMES
proton
sign change andDnn y appliedfor HERMES data
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Global Fit
Fit to COMPASS d, HERMES, BELLE (FF, e+e-)
in good agreement with new proton data
G. Mallot QNP09, Beijing, September 2009
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Alternative: couple to chiral odd 2-hadron interference FF
Transversity PDF
G. Mallot QNP09, Beijing, September 2009
cross-section asymmetry:
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two-hadron asymmetry
• large asymmetries• interference FF and transversity sizable
G. Mallot QNP09, Beijing, September 2009
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Comparison to a recent Fit
• Recent fit (COMPASS p not yet in)
G. Mallot QNP09, Beijing, September 2009
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Sivers Asymmetry:
• proposed (1990, Sivers)• though to vanish (1993, Collins)• resurrected (2002, Brodsky,
Hwang, Schmitt)• different sign in DY and SIDIS
Sivers function
G. Mallot QNP09, Beijing, September 2009
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Proton Sivers Asymmetry
• compatible with zero for the deuteron• large effect seen by HERMES, not confirmed by COMPASS• clarification needed
G. Mallot QNP09, Beijing, September 2009
h−h+
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Longitudinal spin transfer to &
G. Mallot QNP09, Beijing, September 2009
ΛΛ
• non-zero DLL related to polarisation of strange (anti) quarks (?)
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Physics with hadron beams
2004: Pilot run with 190 GeV/c π− beam and heavy targets (Pb), few days only
2008: full year with LH2 target (40 cm) with recoil detector, mainly π− beam (4% K), some datawith p/ π+ beam (75/25%)
2009: LH2 target, Pb, Ni positive and negative beams
more: Ismail UMAN: Thu, 24.09. Parallel 5C Room:B326
G. Mallot QNP09, Beijing, September 2009
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Hadron Spectroscopy @ COMPASS
Central production Diffractive dissociation
• Rapidity gap between pslow, hfast, X
• Beam particle looses little of its energy
• Particles at large angles from X decays
• Possible source of glueballs (DPE)
• Forward kinematics• Particles at small angles• Study of JPC-exotic mesons
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Example: 3π final state (2004 data)
COMPASS: pπ=190 GeV/c• 4M events in 3 days (full t range)• 450k events in 0.1<t’<1.0 GeV2/c2
COMPASS: pπ=190 GeV/c• 4M events in 3 days (full t range)• 450k events in 0.1<t’<1.0 GeV2/c2
BNL852: pπ=18 GeV/c
• 250k events π1(1600)
BNL852: pπ=18 GeV/c
• 250k events π1(1600)
this and following slides: from B. Ketzer
Pb Pb
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Invariant Mass of 3p System
Acc
epta
nce
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a1(1260) and p2(1670) from PWA
42 waves considered in PWA6 dominant waves in mass fit
B. Ketzer, Int. J. Mod. Phys. A 24, 245 (2009)
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p1(1600) and p2(1670)
JPC=1−+ exotic wave in p-p-p+
slow phase motion wrt p2(1670)
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p1(1600) and a1(1260)
strong phase motion wrt a1(1260)
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Leakage Study
• 1150000 events generated from 15 dominant waves
• including JPC=2−+ M=0,1• excluding JPC=1−+ exotic wave
• full reconstruction + PWA
less than 5% leakage into 1−+ wave less than 5% leakage into 1−+ wave
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Outlook
• huge amount of spectroscopy data collected in 2008/2009
• approved 2 year measurements with muon beam and pol. proton target• transversity, Sivers, Boer-Mulders• longitudinal: g1, g1
NS, flavour separation, Δs
• plans for measurements of the pion and (maybe) kaon electrical and magnetic polarisabilities and further spectroscopy studies after analysis 08/09 data
• proposal for GPD and Drell-Yan measurements in preparation
G. Mallot QNP09, Beijing, September 2009
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G. Mallot QNP09, Beijing, September 2009
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G. Mallot QNP09, Beijing, September 2009
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G. Mallot QNP09, Beijing, September 2009
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G. Mallot QNP09, Beijing, September 2009
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Transverse spin structure
Collins asymmetry:• match HERMES precision at large x • improve precision at small x
• higher Q2
G. Mallot QNP09, Beijing, September 2009
h+ h−
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Longitudinal Spin Structure
proton g1(x)• small x behaviour very interesting• only COMPASS can provide further data until the advent
of a pol. ep collider
G. Mallot QNP09, Beijing, September 2009
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Non-singlet structure function
non-singlet structure function: Bjorken sum rule
G. Mallot QNP09, Beijing, September 2009
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Flavour separated PDFs
projection for flavour separation from semi-inclusive asymmetries
G. Mallot QNP09, Beijing, September 2009
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PWA Technique
• t-channel Reggeon exchange• Reflectivity basis in G-J frame• At high s: e = h of Regge trajectory• Isobar model
1. Mass-independent PWA of angular distributions in 40 MeV mass bins2
2
indep1 1
( (( )rN
ir
ii
ir dT
• 42 partial waves i=JPCMe[...]L
[...]=isobar (pp)S, f0(980), r(770), f2(1270), r3(1690)
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Waves used in PWA
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Summary of Waves
Publication being prepared, to be submitted
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Summary of Waves