[PPT] - COMPASS - a facility to study QCD Eva-Maria Kabu, Institut f ur PowerPoint Presentation

SLIDE 1

COMPASS - a facility to study QCD

Eva-Maria Kabuß, Institut f¨ ur Kernphysik, Mainz University for the Compass collaboration Hadron 2011 M¨ unchen, 13.-17.11.2011 – Compass experiment – What we have done – What we want to do

COMPASS

SLIDE 2

COMPASS

What have we done

Compass is data taking since 2002 studying Nucleon spin puzzle: SN = 1

2 = 1 2∆Σ + ∆G + L

muon scattering on polarised p(NH3) and d(6LiD)

with long. and transv. target polarisation

addendum in 2010 (transv. p) and 2011 (long. p)
all three leading twist PDFs investigated (f1, g1, h1)

Results: quark spin responsible for 30% of nucleon spin gluon contribution small in x range covered hardly any information on orbital angular momentum

N (E, p) q e (E, p )

’ ’ *

γ u d u π

+

h h π

Hadron spectroscopy

190 GeV/c hadron beams (π, p, K) on unpol. targets (liquid H2, Pb, Ni, Cu ,W)
searches for exotics, hybrids and glueballs
pion polarisabilities
E. Kabuß, Munich, 14.6.2011

1

SLIDE 3

COMPASS

What will we do

Improve the 1-dimensional picture of the nucleon Generalized parton distribution (GPD) longitudinal momentum structure plus transverse spatial structure accessible in exclusive reaction like DVCS or DVMP Flavour separation and fragmentation in semi-inclusive deep inelastic scattering (SIDIS) improvement of strange quark distribution and fragmentation Transverse momentum dependent distributions (TMD) dynamic picture using intrinsic transverse momenta of partons accessible in SIDIS and Drell-Yan processes QCD at very low momentum transfers using Primakoff reactions to access inverse Compton scattering pion/kaon polarisabilities, testing chiral perturbation theory Compass II proposal: submitted in May 2010 for 5 years of data taking in the first phase approved in December 2010 for initially 3 years of data taking

E. Kabuß, Munich, 14.6.2011

2

SLIDE 4

COMPASS

LHC SPS proton beam: 1.4 1013/spill of 4.8s, 400 GeV/c Secondary hadron beams (8 /spill, 150-270 GeV/c Tertiary muon beam (80% pol): 2.108 /spill, 100-200 GeV/c

> Luminosity ~ 5 × 1032 cm-2 s-1 with polarised targets

SPS CNGS Gran Sasso 732 kms COMPASS

3

SLIDE 5

COMPASS

LHC

high energy beam(s), broad kinematic range, large angular acceptance

SPS proton beam: 1.4 1013/spill of 4.8s, 400 GeV/c Secondary hadron beams (8 /spill, 150-270 GeV/c Tertiary muon beam (80% pol): 2.108 /spill, 100-200 GeV/c

> Luminosity ~ 5 × 1032 cm-2 s-1 with polarised targets

SPS CNGS Gran Sasso 732 kms COMPASS

4

SLIDE 6

COMPASS

COMPASS spectrometer

H E/ CAL2 H E/ CAL1 RICH Muon Wall 1 Muon Wall 2 SM2 SM1 Trigger Hodoscopes Target

µ

Polarised target

He−Precooler

3

Dilution refrigerator

Acceptance (70mrad)

Targets Solenoid Superconducting 1m

target material: 6LiD, NH3 polarisation: 50%, 90%

x

6

10

5

10

4

10

3

10

2

10

1

10 1

)

2

(GeV

2

Q

4

10

3

10

2

10

1

10 1 10

2

10

3

10

4

10

5

10

6

10

COMPASS 2002-03 data

E. Kabuß, Munich, 14.6.2011

5

SLIDE 7

Primakoff experiments with π, K

π−Z → π−Zγ chiral perturbation theory predicts low energy behaviour dσπγ dΩcm = dσπγ dΩcm

point

+ C · s − m2

π

s2 P(απ, βπ) P(απ, βπ) = (1−cos θcm)2(απ − βπ)+(1+cos θcm)2(απ + βπ) s2 m4

π

+(1 − cos θcm)3(α2 − β2)(s − m2

π)2

24s

deviation from pointlike due to pion polarisabilities
measurements: απ − βπ (at backward angles), απ + βπ

2-loop chiral prediction απ − βπ = (5.7 ± 1.0)10−4 fm3 experiments: απ − βπ from 4 to 14 · 10−4 fm3

π π

θπ

γ

θ

E γ Q2

(A,Z) (A,Z)

Primakoff

π π γ γ θ

Inverse Compton

E. Kabuß, Munich, 14.6.2011

6

SLIDE 8

Pion polarisability measurement

CM

θ cos

1
0.8
0.6
0.4
0.2

0.2 0.4 0.6 0.8 1 b] µ [

CM

Ω /d σ d 0.02 0.1 0.2 0.3 0.4 E < 20 GeV γ

2 π

s=3m

2 π

s=5m

2 π

s=8m

2 π

s=15m

= -2.86

π

β = 3.00,

π

α

- -
effect increases with s2
effects due to απ − βπ much

larger than for απ + βπ unique at Compass :

kaon component in hadron beam: kaon polarisability accessible
availability of a muon beam (point like) for comparison and systematics
switching between pion and muon beam within few hours possible
E. Kabuß, Munich, 14.6.2011

7

SLIDE 9

COMPASS

Projections for polarisabilities

already two (test)measurements performed, clear signal from Primakoff events

]

2

[(GeV/c)

2

Q

0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01

Number of Events

1 10

2

10

3

10

4

10

COMPASS 2004 Hadron

− Pb 3.0 mm π − Pb 2.0+1.0 mm π − Pb 1.6 mm π − Cu 3.55 mm π − C 23.5 mm π − Pb 2.0+1.0 mm µ

expected precision of the new measurement:

in 120 d απ − βπ απ + βπ α2 − β2 90 d with π, 30 d of µ beam (10−4 fm3) (10−4 fm3) (10−4 fm5) 2-loop ChPT prediction 5.70 ± 1.0 .016 ± 0.10 16 Compass sensitivity ±0.66 ±0.25 ±1.94

E. Kabuß, Munich, 14.6.2011

8

SLIDE 10

Generalised parton distributions

x + ξ

γ*

hard soft ∆2 t = − x − ξ

γ

p p’ q q’ GPDs

Factorisation for Q2 large, t < 1 GeV2

generalised parton distributions for quarks

Hf, Ef, Hf, Ef(x, ξ, t)

limits:

q(x) = H(x, 0, 0) normal PDF F(t) =

dx H(x, ξ, t)

elastic form factor

Ji’s sumrule

Jf = 1 2 lim

t→0

1

−1

dx x

Hf(x, ξ, t) + Ef(x, ξ, t)
Jf: total angular momentum contribution of quark f
E. Kabuß, Munich, 14.6.2011

9

SLIDE 11

Nucleon tomography

GPDs allow simultaneous measurement of longitudinal momentum and

transverse spatial structure

for ξ → 0:

t = −∆2

⊥ purely transverse and

qf(x, b⊥) = d2∆⊥ (2π)2 e−i∆⊥·b⊥Hf(x, 0, −∆2

⊥)

b⊥ distance to center of momentum (b in figure is b⊥)
E. Kabuß, Munich, 14.6.2011

10

SLIDE 12

COMPASS

Why GPDs at Compass?

CERN high energy muon beam:

– 100–160 GeV, 80% polarisation – µ+ and µ− with opposite polarisation

x Q2 (GeV2)

ZEUS +H1 JLab 11 GeV HERMES 27 GeV COMPASS 160 GeV

COMPASS y=0.9 y=0.05

1 2 3 4 5 6 7 8 9 10 20 10

2

10

1

1

unique kinematic range

between HERA and HERMES/JLab – intermediate x: = ⇒ sea and valence quarks – high x limit from acceptance – Q2 up to 8GeV2 = ⇒ limit from cross section with L = 1032 cm−2s−1

planned measurements:

– deeply virtual Compton scattering – deeply virtual meson production Phase 1: 2.5 m long unpolarised liquid H2 target = ⇒ GPD H Phase 2: transversely polarised liquid NH3 target = ⇒ GPD E

E. Kabuß, Munich, 14.6.2011

11

SLIDE 13

COMPASS

Experimental requirements

µp − → µγp

two competing processes: DVCS and BH
Bethe-Heitler dominates at low x,

used a reference yield

measurement with µ+ and µ− with
pposite polarisation

SCS,U ≡ dσ+↓ + dσ−↓ DCS,U ≡ dσ+↓ − dσ−↑

yield Re(H) and Im(H)
additionally deeply virtual meson production

Experimental set-up

2.5 m long liquid hydrogen target
4 m long recoil proton detector

(2 layers)

’hermetic’ coverage with electro-
magnetic. calorimetry
E. Kabuß, Munich, 14.6.2011

12

SLIDE 14

COMPASS

Test measurement 2009

data taking with µ+ (8 times more stat.) and µ− at about nominal intensity
40 cm liquid H2 target and small recoil proton detector
measure BH events plus relative DVCS and DVMP contributions
comparison of µ+ and µ− data: µ− flux is factor of 3 lower at 160 GeV

= ⇒ limitation on overall luminosity

(deg) φ

150 -100
50

50 100 150

nb of events

10 20 30 40 50 60 70 80

< 0.01

Bj

0.005 < x

278 events

PRELIMINARY

2

|BH+DVCS|

2

|BH|

(deg) φ

150 -100
50

50 100 150

nb of events

5 10 15 20 25 30 35

< 0.03

Bj

0.01 < x

134 events

PRELIMINARY

2

|BH+DVCS|

2

|BH|

(deg) φ

150 -100
50

50 100 150

nb of events

1 2 3 4 5 6 7 8

> 0.03

Bj

x

54 events

PRELIMINARY

2

|BH+DVCS|

2

|BH|

= ⇒ clear DVCS signal observed at Q2 > 1 GeV2, x > 0.03

E. Kabuß, Munich, 14.6.2011

13

SLIDE 15

COMPASS

Projected results

projections with 2 years of data εglobal = 10% L = 1222 pb−1

Transverse imaging:

B(x) ∼ 1/2 r2

⊥(x)

no model dependence

Azimuthal dependence:

comparison to different models = ⇒ cI

1 ∝ Re(F1H)

2

2 4 6 8 10

4

10

3

10

2

10

1

B (GeV-2)

COMPASS ZEUS H1-HERA I H1-HERA II < Q2 > < Q2 > < Q2 > < Q2 > = 2 GeV2 = 3.2 GeV2 = 4 GeV2 = 8 GeV2 280 days at 160 GeV α' = 0.125 α' = 0.26

0.2
0.1

0.1 0.2 0.3 20 40 60 80 100 120 140 160 180

VGG Factorized (x,t)-dependence VGG Reggeized (x,t)-correlation Mueller fit on world data (with JLab Hall A) (without JLab Hall A)

φ Beam Charge and Spin Asymmetry

Eµ=160 GeV 1 Q2 4 GeV2 0.03 xB 0.07 ≤ ≤ ≤ ≤

E. Kabuß, Munich, 14.6.2011

14

SLIDE 16

Transverse Momentum Dependent Distributions

dynamic picture of the nucleon

using intrinsic transverse momentum kT of partons

sensitivity to quark orbital

angular momentum

at leading twist:

full description with 8 TMDs

3 survive integration over kT:

f 1, g1 and h1

TMDs are accessed by azimuthal asymmetries
studied in SIDIS using unpolarised and transversely polarised target
in SIDIS convolution with fragmentation function
E. Kabuß, Munich, 14.6.2011

15

SLIDE 17

COMPASS

Boer-Mulders and Sivers DF in SIDIS

BM function h⊥

1 : correlation of quark kT and transverse spin in unpol. nucleons

Bj

x

2

10

1

10 φ cos 2

A

0.05

0.05 0.1 positive hadrons COMPASS 2004 deuteron prelim. COMPASS proj. 1 week Bj

x

2

10

1

10

0.05

0.05 0.1 negative hadrons COMPASS 2004 deuteron prelim. COMPASS proj. 1 week

2004 data on deuteron target: non-zero

Boer-Mulders asymmetry (Acos 2φ

LU

)

Boer-Mulders on proton will be measu-

red in parallel with DVCS Sivers function f ⊥

1T: correlation of quark kT and nucleon transverse spin

COMPASS 2007 proton data x

−2

10

−1

10 p Siv

A

−0.1 0.1 z

0.5 1

−0.1 0.1

positive hadrons negative hadrons

) c (GeV/

h T

p

0.5 1 1.5

−0.1 0.1

Sivers asymmetry (AsinφS

LT

) measured at Compass with pol. deuteron and proton target

positive asymmetry for h+ on proton,

but smaller than seen by HERMES Boer-Mulders and Sivers function are T-odd → process dependent h⊥

1 (SIDIS) = −h⊥ 1 (DY )

f ⊥

1T(SIDIS) = −f ⊥ 1T(DY )

− → Crucial test of non-perturbative QCD and of TMD approach

E. Kabuß, Munich, 14.6.2011

16

SLIDE 18

COMPASS

Drell-Yan at Compass

π−p↑ → µ+µ−X

Ha(Pa) X γ∗(q) l−(l) l+(l′) Hb(Pb, S) ¯ u(ka) u(kb)

π− beam 190 GeV/c DY 4 – 9 GeV/c2 generated accepted

DY: convolution of two TMDs measured
access to 4 azimuthal modulations:

Boer-Mulders, Sivers, pretzelosity and transversity PDFs

ideal DY measurement: ¯

pp

good compromise π−p
dominated by annihilation of valence

anti-quark from π− and valence quark from polarised proton

large acceptance of Compass in the

valence region of p and π where large SSA are expected

E. Kabuß, Munich, 14.6.2011

17

SLIDE 19

COMPASS

Experimental requirements

high intensity 190 GeV/c pion beam

(up to 109/spill)

transversely polarised NH3 target
hadron absorber downstream of target
dimuon trigger system

Results from 2009 beam test

300
250
200
150
100
50

50 100 100 200 300 400 500 600 700 800

COMPASS DY test run 2009 M> 2.5 GeV

Preliminary

M, GeV 1 2 3 4 5 6 7 1 10

2

10

3

10

ψ J/ 70 events ± 3170 0.005 GeV ± M=3.092 0.004 GeV ± =0.227

M

σ

Preliminary

COMPASS DY beam test 2009

E. Kabuß, Munich, 14.6.2011

18

SLIDE 20

COMPASS

Projections for azimuthal asymmetries

4 GeV/c2 < Mµ+µ− < 9 GeV/c2

↑

p

x

π

= x

F

x

0.8
0.6
0.4
0.2

0.2 0.4 0.6 0.8

0.1
0.05

0.05 0.1 0.15 0.2 0.25

S

φ sin T

A

↑

p

x

π

= x

F

x

0.8
0.6
0.4
0.2

0.2 0.4 0.6 0.8

0.1
0.05

0.05 0.1 0.15 0.2 0.25

φ cos 2 U

A

↑

p

x

π

= x

F

x

0.8
0.6
0.4
0.2

0.2 0.4 0.6 0.8

0.1
0.05

0.05 0.1 0.15 0.2 0.25

)

S

φ + φ sin (2 T

A

↑

p

x

π

= x

F

x

0.8 -0.6 -0.4 -0.2

0.2 0.4 0.6 0.8

0.1
0.05

0.05 0.1 0.15 0.2 0.25 )

S

φ

φ

sin (2 T

A

Sivers Boer-Mulders BM ⊗ pretzelosity BM⊗ transversity projections with 2 years of data 6 · 108 π spill (9.6 s) 1.1 m pol. NH3

key measurements:

TMD universality, change of sign from SIDIS to DY, study of J/ψ production me- chanism

E. Kabuß, Munich, 14.6.2011

19

SLIDE 21

Conclusions and Outlook

New proposal (Compass II) with

DVCS and DVMP for the study of GPDs in a kinematic region not yet

covered by experiments

in parallel with GPD measurement rich programme in unpolarised DIS

and SIDIS

first polarised Drell-Yan experiment to study TMDs
measurement of pion (kaon) polarisabilities

= ⇒ at least 5 years of data taking, can start from 2012 Program accepted in December 2010 for a first period of 3 years Compass has a great potential in new fields and work is started to get the spectrometer upgraded for the new programmes

E. Kabuß, Munich, 14.6.2011

20