COMPASS PLANS

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COMPASS PLANS

Stephane Platchkov

Institut de Recherche sur les lois Fondamentales de l’Univers CEA/IRFU, Saclay, France

(for the COMPASS Collaboration)

EIC workshopStony Brook, June 24-27, 2014

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COMPASS – a fixed target experiment A very versatile setup

Several beams available: µ+, µ-, h+, h-, e- => Several physics goals

S. Platchkov EIC 2014 2

50 m

“Minor” changes to the setup – switch between various physics programs

Energy: 100 – 200 GeVIntensity: up to 109 /spillLarge acceptance, PID detectorsSeveral particles in the final stateLarge (1.2 m) polarized target

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COMPASS – a fixed target experiment

A very versatile setup Several beams available: µ+, µ-, h+, h-, e- => Several physics goals


Measurements with muon beams

Gluon polarization Spin-flavor decomposition Transversity Transv. Mom. Distributions

Measurements with hadron beams

Pion polarizability Light meson spectroscopy Baryon spectroscopy Search for hybrids

COMPASS - I (2002 – 2011)

DVCS and HEMP Unpolarized SIDIS and TMDs

Drell-Yan studies Pion and Kaon polarizabilities

COMPASS - II (2012, 2015 – 2017/2018)

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Nucleon structure studies – physics goals


Drell-Yan

TMD (x,kT) GPD (x,bT)PDF (x)

from Bacchetta from Bacchetta

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DVCS and HEMP studies


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DVCS characteristics in COMPASS


Beams 100 – 200 GeV Beam polarization: ~80% Both m+ and m- beams

x domain: ≈ 0.01 – 0.1 Q2 domain: 1 to 10 (GeV/c)2

Luminosity: 1032 cm-2s-1

(with a 2.5 m long LH2 target)

Detect both outgoing photon and recoiling proton

+ EIC

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DVCS and BH cross section for µ+ and µ-

Cross section for µp -> µpγ :

COMPASS beams: opposite charge/spin Charge-and-Spin Sum:

Charge-and-Spin Difference

small for COMPASS


DVCS BH

Access both Re(H) and Im(H) by measuring the Sum and the Difference

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DVCS – SUM of m+ and m- cross sections


Goal: transverse size of the nucleon as a function of xB

- Nucleon “tomography” -

Expected statistics in 2 x 140 days of data taking

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Beam Charge and Spin Difference


Expected statistics in 2 x 140 days of data taking

Kroll, Moutarde, Sabatié, EPJC 73(2013)2278

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DVCS – the COMPASS xB regions – SIMULATION


DVCS BH

DVCS

BH

0.005 < xB <0.01 0.01 < xB < 0.03 xB > 0.03

Large relative amplitude variation as a function of x

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Test run – 4 days with a 40 cm long H2 target

DVCS – the COMPASS xB regions – REAL DATA


DVCS278

134

54

BH dominance Interference DVCS dominance

2009 data

Successful feasibility measurement

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DVCS run – main new equipment


2x2 m2 electromagnetic

calorimeter, ECAL0

4.0 m longTime-Of-Flight detector: 24 inner and 24 outer

slabs

50 m

ECAL1 ECAL2

2.5 m long LH target

ECAL0

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2012 DVCS setup – 4 weeks data taking


Full scale recoil proton detector

Partially ready ECAL0

ECAL1ECAL2

Liquid H2 target

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Transverse size of the nucleon


2012 data: expected uncertainty

Test data taking in 2012 – 4 weeks

Data analysis is underway

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Semi-inclusive unpolarized DIS

Features Pure hydrogen target, 2.4 m long High-performance particle identification for p+,p-,p0,K+,K-,K0 etc…

Measurements of: Multiplicities

Input to global FF analysis Strange quark pPDF

down to x=0.004


1 week of beam

Phys. Rev. D 89 (2014) 097101

will s(x) continue to raise?

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Beyond GPD H

Hard Exclusive Meson production Vector mesons: sensitive to H, E

► allows for flavour separation

Present studies at COMPASS : Transversely polarized target No recoil proton detection (From transversity data: 2007/2010)

► First example: exclusive r production S. Platchkov EIC 2014 16

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Exclusive r0 production


Measurement: μ + p μ’ + r0 + p p+p-

Access to different E and H combinations Analysis of w ongoing

First possible indication for a non-vanishing HT

COMPASS: PLB 731 (2014) 19NPB 865 (2012) 1

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DVCS and HEMP on a transversely polarized target

2 years of data, NH3 target, 160 GeV, global efficiency ~10%

Distant future (beyond 2018)


Main challenge: development of dedicated superconducting magnetPlanned proposal/addendum

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Overview of past/planned GPD experiments


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Drell-Yan studies


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.

COMPASS setup advantages Beam energy: 100 – 200 GeV Hadron (pion) beam Transversely polarized NH3 target Large muon angular acceptance With a negative pion beam: u/u annihilation

COMPASS acceptance (MC simulation) Dominated by valence quarks (x ≥ 0.1)

Polarized Drell-Yan measurements


Drell and Yan, PRL 25 (1970), 316, 902.

COMPASS is an ideal place for DY studies

I R F UTung-Mow Yan (SLAC, 1998): “The process (1970) has been so well understood that it has become a powerful tool for precision measurements and new physics” Full formalism for two spin ½ hadrons

COMPASS: access 4 TMDs: Boer-Mulders, Sivers, Pretzelosity, Transversity

Access 4 TMDs – asymmetry modulations:

DY (polarized) cross section expansion


Arnold, Metz and Schlegel, Phys. Rev. D79 (2009) 034005.

Boer-Mulders

Sivers

Pretzelosity

Transversity

Worm-Gear

All four TMDs are also measured in SIDIS

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TMDs in Drell-Yan and SIDIS

SIDIS vs TMD SIDIS: TMD and FF Drell-Yan: two TMDs

Factorization TMDs (unlike PDFs) can be process dependent (“non-universality”) Opposite sign in SIDIS and DY processes:


Collins, Soper, Sterman, Adv. Ser. High En Phys. 5, 1988.

Crucial test of the QCD factorization approach

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Sivers asymmetry (SIDIS) Compass data on a proton target

pions

kaons


Hermes data: PRL 103 (2009) 152002

COMPASS data: PLB 692 (2010) 240PLB 717 (2012) 383+ preliminary

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Drell-Yan acceptances (COMPASS vs E615)


E615(1989)

COMPASS(2014)

0.4

0.04

An order of magnitude improvement

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SIDIS vs Drell-Yan (x - Q2) regions


Kinematical overlap between SIDIS and Drell-Yan

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COMPASS Drell-Yan setup


Upgrade of the spectrometer• Beam telescope (Sci-Fi)• Thick hadron absorber/beam dump• Vertex detector • Polarized target moved 2.2 m upstream

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COMPASS Drell-Yan setup


Small cross sections – high intensity h beam (~109/spill of 10 sec) Possible use of thin nuclear targets (inside the absorber)

pion beam 190 GeV

Hadron absorber: Tungsten, Alumina

and Stainless steel

Nominal COMPASS setup (minor modifications)Dimuon trigger system

Polarized Target

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Test setup (3 days in 2009) 190 GeV negative pion beam, I ≤ 1.5x107/s (instead of 108/s) “poor-man” hadron absorber ( concrete and steel) two polyethylene target cells preliminary DY trigger

Results Count rate confirmed Mass resolution as expected Good vertex resolution Low background at high masses

Drell-Yan – test data taking


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Expected statistical accuracy

Assumptions: Ibeam = 108p/s, L = 2.3x1033, P=90%, f = 0.22, t = 140 days, spill length = 10 s, every 34 s

► ~ 2000 DY events/day in the mass region 4 < Mµµ < 9 GeV/c2

J/Ψ cross section: about 50 times largerS. Platchkov EIC 2014 30

Boer-Mulders SiversPretzelosityTransversity

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Polarized Drell-Yan – expected results


Sivers Boer-Mulders

Pretzelosity Transversity

140 days of data

6.108 pions/spill

2 x 55 cm NH3 target

4 < Mmm< 9 GeV

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Further Drell-Yan studies


DY on nuclear targets

flavour-dependent EMC effect

Dutta et al., PRC83:042201,2011

First glimpse from the 2015 data

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Drell-Yan: further possibilities

Medium term DY on nuclear targets

Flavour dependent EMC, Violation of the Lam-Tung relation Polarized deuteron ( 6LiD) target

Flavour separated TMDs

Long term RF separated K- and p beams

Recall: at 190 GeV: p-/K-/p = 96.5%/2.5%/1% Aim at 1 to 2 orders of magnitude improvement for K- and p


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COMPASS OUTLOOK 2014

Preparation for DY run Refurbished PT magnet, PT installation, hadron absorber 2 months of data taking (October-December)

2015 Drell - Yan data taking (1 “year” ≈ 140 days)

End 2015, beg. 2016 Removal of PT, Installation of LH target, CAMERA, ECAL0

2016/2017 DVCS data taking (2 “years” ≈ 2x140 days)

2018 and beyond Long Shutdown 2 Extensions of DY and DVCS programs (definition underway)

EIC 2014S. Platchkov 34

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The End


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Exclusive r0 production


Measurement: μ + p μ’ + r0 + p p+p-

5 single-spin (UT) asymmetries 3 double-spin (LT) asymmetries

Curves: Goloskokov and Kroll, EPJ C74(2014)2725Data: Compass, PLB, 731(2014)19.

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Boer-Mulders asymmetry (SIDIS)

Compass data on deuteron (6LiD)

Significantly different from zero Larger for negative hadrons Dependence on all three variables: x, z, pT


COMPASS preprint, hep-ex:1401.6284

also HERMES: PRD 87 (2013)012010.

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COMPASS PLANS