COMPASS Status Report 2009/2010
description
Transcript of COMPASS Status Report 2009/2010
Bernhard Ketzer
Technische Universität München
for the COMPASS Collaboration
SPSC, CERN
29 June 2010
COMPASS Status Report2009/2010
Outline
New results from 2004 p- pilot run
New results from 2008 hadron run
• 3p final states
• Multi-particle final states (>3)
• Kaonic final states
• Data with proton beam
Hadron run 2009
• Performance of spectrometer
• First analysis of data
New results from muon scattering
• Helicity distributions
• Collins and Sivers asymmetries
• Update on DG from open charm
Preparation and status of 2010 muon run
SM1
SM2
Beam
MuonWall
MuonWall
E/HCAL
E/HCAL
RICHTarget
The COMPASS Experiment
Two-stage spectrometer• large angular acceptance• broad kinematical range • ~250000 channels• > 1000 TB/year
Two-stage spectrometer• large angular acceptance• broad kinematical range • ~250000 channels• > 1000 TB/year
50 m
[COMPASS, P. Abbon et al., NIM A 577, 455 (2007)] [COMPASS, P. Abbon et al., NIM A 577, 455 (2007)]
Data taking periods:• 2002-2004: 160 GeV/c m+
• 2004: 2 weeks 190 GeV/c p-
• 2006-2007: 160 GeV/c m+
• 2008-2009: 190 GeV/c p-
• 2010: 160 GeV/c m+
Data taking periods:• 2002-2004: 160 GeV/c m+
• 2004: 2 weeks 190 GeV/c p-
• 2006-2007: 160 GeV/c m+
• 2008-2009: 190 GeV/c p-
• 2010: 160 GeV/c m+
RPD
Hadron Reactions at COMPASS
Three production mechanisms
studied in parallel using proton, pion and kaon projectiles
Three production mechanisms
studied in parallel using proton, pion and kaon projectiles
Central production Diffractive dissociationPhotoproduction
• Rapidity gap between pslow, hfast, X
• Beam particle looses ~10% of its energy• Particles at large angles from X decays• Possible source of glueballs (DPE)
• Forward kinematics• Need to separate particles at
very small angles• Study of JPC-exotic mesons
Analysis of 2004 Data
Beam: 190 GeV/c p-, 5·106 pps
Target: 3 mm Pb
Trigger: Multiplicity
Analysis:
• p-p-p+ final state
• High-t’: observation of spin-exotic resonance with JPC=1-+
• Low-t’: new results on photoproduction / diffraction
• p-p-p-p+p+ final state
• acceptance corrections done
• optimization of wave set ongoing
JPC=1-+ Exotic Wave in p-p-p+
p-p-p+ Final State at low t’
Coherent production on Pb nucleus
Contributions at very low t’:
• Diffraction:
• Photoprod.: Prim2'
Prim( ') , 2050 GeV/b tt e b c
Diff2'
Diff( ') , 400 GeV/b tt e b c
• Fit of 2 exponentials for t’ < 0.006 GeV2/c2
• Steep fall-off for photoproduced events dominated by experimental resolution
• Statistical subtraction of diffractive contribution
Partial Wave Analysis
Photoproduction Prim '( ') b tt e
'( ') ' btt t e
0.0015 < t’ < 0.01 GeV2/c2
t’ < 0.5·10-3 GeV2/c2
vanishes for t’→0
a2(1320) (M=1) present in both t’-ranges different production mechanisms?
Diffraction
Two clearly separated regions:
Phase difference a2(1320) - a1(1260): offset for two t’-regions!
Phase Difference a2-a1
Experiment Theory[G. Faeldt et al., Phys. Rev. C 79 014607 (2009)]
Plot by N. Kaiser, TUM
smooth transition between a2 photoproduction
to diffractive production with increasing t‘ possibility to cleanly separate photoproduction from diffraction
PWA in t’ bins for single mass bin 1.26 < m3p < 1.38 GeV/c2 (a2 region)
F(a1)F(a2)
(DF a2-a1)
determination of radiative width of a2(1320), p2(1670)
Analysis of 2008 Data
Beam: 190 GeV/c p-, 2.5·107 pps, protons
Target: 40 cm liquid hydrogen
Trigger: Recoil proton (DT0)
Analysis:
• p-p-p+ final state
• full 2008 statistics available
• M=1 production suppressed
• acceptance corrections being finalized (MC description)
• final states containing neutral particles
• ECAL optimization close to being finished
• p-p0p0 final state: isospin symmetry
• other states
• kaonic final states
p-p-p+ Final State
Adobe Acrobat Document
• Full 2008 statistics available: 96M events in high-t’, 5.8M a2(1320)
• M=1 production on H suppressed compared to Pb
• Acceptance corrections being finalized (MC description)
• Wave set being optimized
p-p0p0 Final State
• Partial 2008 statistics, no acceptance correction
• Normalization to a2(1320) intensity
• Charged and neutral mode rely on different detectors systematics
• Isospin symmetry
• expect same intensity for isovector isobars (e.g. r)
• expect half the intensity in neutral mode for isoscalar isobars (f0, f2)
• acceptance being finalized, ECAL reconstruction being optimized
Multi-Particle (>3) Final States
Motivation:• Higher masses accessible many disputed states: 0-+, 1++, 2-+,...• p1(1400) observed in hp
• p1(1600) observed in h’p, b1p, f1p
• p1(2000) observed in b1p, f1p• JPC=1-+ hybrid decay modes [Page, Swanson, Szczepaniak, PRD 59, 034016 (1999)]
establishedneed confirmationfurther states
mp1 b1p f1p h(1295)p
r(1450)p r(770)p
1.6 GeV
24 5 2 9
2.0 GeV
43 10 27 12 16
p-h Final State
0
PWA required to resolve small contributions, e.g. p1(1400)
p-p+p0 invariant mass
Select
gg invariant mass
Select
h
w
a2(1320)
p-p-p+h Final State
0 p - p +h invariant mass
h’f1(1285)
h’f1(1285)
'Select
Hybrid p1(1600) expected in this channel
p-hh Final State
COMPASS53% of 2008 data
No cut for central production applied both diffractively and centrally produced states
Kaonic Final States
• Access to exotics, glueballs
• Clarify flavor content and structure of resonance
• Expand knowledge on kaon spectrum
• Requires CEDAR & RICH PID
• Channels: K p K p
0 0S Sp K K p p K K p
Diffractive states at 1.7 GeV/c2 and 2.2 GeV/c2, decaying to K*(892)
Kaonic Final States
01f K K p X p
1X f Diffractive dissociation:
• >10 × BNL statistics
• very clean spectrum
• possibly also f1(1420) seen
Data with Proton Beam
Only very short test in 2008 (early shutdown of North Area):
• Beam: 190 GeV/c, 71.5% p, 25.5% p, 3.0% K
• CEDARs tagging protons
• Trigger: Recoil proton
• ~10% of total 2008/2009 statistics
• Baryon spectroscopy:
•
•
• Central Production
•
•
•
f spp p p
f spp p K K p
f spp p p f spp p p
f spp p KK p
Baryon Spectroscopy
f spp p p f spp p K K p
Central Production
L LF max
L
20.88fp p p
xp s
f spp p K K p
• cut on
0 0S Sf spp p K K p
Hadron Run 2009
Goals:
• collect data sample with positive beam on lH2 target (central production)
• increase data sample with negative beam on lH2 target (central production)
• complete data taking with negative beam on lH2 target (diffr., low-t)
• take data with negative beam on nuclear targets (M-dep., statistics)
• PS/SPS efficiency ~70% rather than 80% as assumed for request
• lower data taking efficiency for COMPASS for low-t’ and ECAL trigger
New Equipment for 2009 Run
Silicon Microstrip Detectors: all five stations at 200K, stability < 1K
ECAL2 upgrade: Pipelined readout completed (1000 ch. MSADC)
ECAL1 monitoring: LED replaced by laser system
Nuclear targets: Pb, W, Ni
New trigger elements:
• Multiplicity trigger
• Digital trigger for ECAL
Trigger
Diffractive Trigger DT0 = BT RPD !Veto
high-t’: t’>0.07 GeV2/c2
Multiplicity Trigger: Cover full range of t’
• 12 trapezoidal scintillator slabs, ø 62 cm
• central disk scintillator with 83 cm air light guide
• acceptance 180 mrad
• LT1 = [≥ 1(2) outer slabs] BT !Veto
LT3 = [> 1.6(2.5) MIPS disk] BT !Veto
Digital Trigger for ECAL: high-energy photons
• Implemented in existing FPGA of MSADC
• Time and amplitude extraction for each cell
• Prim = Esum(12×12 cells) > Ethr(50/70 GeV)
• Efficiency > 98%, energy resolution = 3.3 GeV
• Time resolution 0.8 ns
Nuclear Targets
Goals:
• study dependence of M-population on A
• increase statistics on nuclear targets
• Target holder: carbon fiber / fiber glass
• Thin disks of Pb, W, Ni: 25-250 mm
First Look at 2009 Data
Nuclear Targets: p-p-p+ final state
2009: 8.1M events3 × statistics of 2004
2009: 2.3M events6 × statistics of 2004
Conclusions on Hadron Analysis
• Very high statistics, 10 – 200 × existing data sample
• Many new channels being analyzed
Conclusions on Hadron Analysis
• Very high statistics, 10 – 200 × existing data sample
• Many new channels being analyzed
• Monte Carlo acceptance corrections
• very good description of setup necessary (no asymmetries!)
• new hardware (2008/2009) implemented
• very large data samples required
• Calorimetry:
• improvement & unification of reconstruction code (ECAL1/ECAL2)
• calibration: electron beam + Laser/LED + p0 signal
• PWA:
• three different programs
• careful selection of wave set for PWA due to small statistical errors
• combined PWA of diffractive and central production
• new formalism for baryonic resonances
• new international task PWA force: COMPASS, JLAB, PANDA, …
Conclusions on Hadron Analysis
Future data taking: based on results of ongoing analyses
• Higher beam energies for cleaner separation of central production
• All neutral final states with full ECAL trigger
• Primakoff measurements with p-, p+, K
Addendum to COMPASS II Proposal
New Results with Muon Beam
Muon beam 2007 with NH3 target:
• Helicity distributions
• Collins and Sivers asymmetries
Gluon polarisation from open charm (2002-2007 data)
Longitudinal spin transfer to L and Lbar in polarised DIS
Helicity Distributions
[COMPASS, M.Alekseev et al., Phys. Lett. B 690, 466 (2010)]
Longitudinal spin asymmetry:
11
b t 1
( )1
( )
g xN NA
P P f D F xN N
• Pb ≈ -80%
• Pt ≈ 90%• f = 0.1-0.2
• improved precision of at low x
• Q2[1,100] GeV2
no Q2 dependence of A1
• data compatible with g1=const.
for x→0.004
Bjorken Sum Rule
Non-singlet spin structure function
NS 2 p 2 n 21 1 1, , ,g x Q g x Q g x Q
• Q2 evolution independent of singlet quark
and gluon densities
• both g1p and g1
n measured at COMPASS
• 3-parameter NLO QCD fit
1st moment Bjorken sum rule
NS 2 NS 2 NS 2A1 1 1
V
1d ,
6
gQ x g x Q C Q
g
• ~92% of G1NS from measured region
• saturation of integral only at lowest x
2 2 20 3GeV /Q c
A
V
1.28 0.07 0.10g
g
Collins Asymmetry
Fragmentation of transversely polarised quarks to unpolarised hadrons
Coll2h,sin
T TTColl 2
NN
hq qq
hq qq
e q DAA
D f P e q D
Comparison with HERMES COMPASS data with x>0.050
Sivers Asymmetry
Modulation of transverse momentum of unpolarised quarks in a transversely polarised nucleon
Siv2 Th,sin
0TSiv 2
hq qq
hq qq
e q DAA
f P e q D
Comparison with HERMES COMPASS data with x>0.032
Gluon Polarisation from Open Charm
stat syst
2
0.08 0.21 0.11
0.11, 13 GeVgx c
G G
(2002-2007 data)
p0
Muon Run 2010
ColdSilicon
PolarizedTarget
H1hodoscope
MMcooling
Pixel-Gem
H2hodoscope
PA03-05MWPC
SciFi 15
Muon Run 2010
Installation: May 21 May 20
Triggers:
• (modified) 2007 triggers fully operational
• Two new hodoscopes (H1, H2) not yet ready
Muon Run 2010
Triggers:
• (modified) 2007 triggers fully operational
• Two new hodoscopes (H1, H2) not yet ready
to be operational by end of July
Polarized target: operational• Upgrade of control system for liq. 4He delivery system• New control system for new 4He pumps for cryogenic operation• Modification of cooling water infrastructure
24 h
June 10, 20102007
Muon Run 2010
Triggers:
• (modified) 2007 triggers fully operational
• Two new hodoscopes (H1, H2) not yet ready
to be operational by end of July
Polarized target: operational
Detectors: all operational
Physics data taking with transversely polarized target:
started June 12
Publications
Since 2009 status report:
• Measurement of the Longitudinal Spin Transfer to Λ and Λ-bar Hyperons
in Polarized Muon DIS, Euro. Phys. J. C 64, 171 (2009).
• Observation of a JPC = 1–+ exotic resonance in diffractive dissociation
of 190 GeV/c π– into π–π–π+, Phys. Rev. Lett. 104, 241803 (2010).
• The spin-dependent structure function of the proton g1p and a Test
of the Bjorken Sum Rule, Phys. Lett. B 690, 466 (2010).
• Measurement of the Collins and Sivers asymmetries on transversely
polarised protons, submitted to Phys. Lett. B (2010), 1005.5609v1 [hep-ex].
Conferences & Workshops
2009: 91 COMPASS presentations
• DIS2009: 9 talks
• CIPANP 2009: 4 talks
• HEP 2009: 3 talks
• HADRON 2009: 9 talks
2010: >20 COMPASS presentations
• DIS 2010: 10 talks
• MENU 2010: 3 talks
• MESON 2010: 3 talks
• QCD 2010: 3 talks
Spare Slides
Longitudinal Spin Transfer to L and L
Polarised m (-0.80) DIS on unpolarised target (2003-2004):
• Q2>1 GeV2/c2
• Fractional virtual photon
energy 0.2 < y < 0.9
• 30·107 DIS events
Spin transfer to L small
(compatible with 0)
Spin transfer to L 0.4-0.5
Flavor Separation
• Longitudinal spin asymmetries
for identified pions and kaons in
SIDIS on NH3 target
• combined with data on d and inclusive DIS
LO QCD analysis
• Ds, Dsbar compatible with 0• sea quark distributions small
• no sizable x-dependence