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