Charmonium Production in Media

Martin zur Nedden, HU Berlin QWG Meeting, Nara 2008, p. 1Charmonium Production in Media

Charmonium Production in Media

Martin zur NeddenHumboldt-Universität zu Berlin

for the HERA-B Collaboration

International Workshop on

Heavy Quarkonia 2008December 2 – 5 2008, Nara Women University, Japan

Quarkonia in Media / Production


920 GeV protons

p + A X , s = 41.6 GeV

The HERA-B Experiment

data taking up to march 2003

Spectrometer at the HERA storage ring: proton-fixed target


Contents

• Introduction• HERA-B Detector• J/ψ: Kinematical Distributions• J/ψ: Nuclear Dependence• χc Production


Contents: Part 1



Hadronic Production of Heavy Quarks

ij

FRijFjFi dxdxppxfxf 2122

212

22

1 ),,,(ˆ),(),(

production in hadronic interaction

Parton-Density-Functionwithin the hadron

partoniccross setion

hadronisation:formation ofhadrons withheavy quarksor quarkonia stats

factorisation of the process


Quarkonia Formation

Hadronization: formation of Quarkonia (J/ψ, ψ’, χc, Υ)long distance (~1/(mcv)) process:non-perturbative calculations andinput from experiments needed, model dependence:CSM, COM, CEM, NRQCD

qq formation: production of heavy quarks in mediashort distance (~1/mc) / high momentum process:perturbative calculation

PDF


based on Glauber-model:

≠ 1 „dependence”

Nuclear Effects for Charmonium Production

p

μ/e+

μ/e-

J/

final state formation effects:• nuclear absorption• comover absorption• multiple scattering + energy lossinitial state effects:

• shadowing (nuclear PDFs)• parton energy loss • intrinsic charm

ApNpA

HERA-B: acsess to production in media measurement of using C and W wires:

C

W

W

C

W

C

C

W

C

W

C

W

AA

LL

NN

AA

ln

ln

ln

ln


xF-Dependence of Nuclear Effects

for c = 0.5 fm

xF [fm]

0.2 30

0 10

-0.2 4

p

μ/e+

μ/e-

J/

formation time and length: (xF) = c

= (xF) boost of J/ w.r.t. nucleus


Contents: Part 2



HERA-B Detector and Trigger

p-beam

z [cm]

C

Ti

W

Muon-TriggerElectron-Trigger


•150 M di-lepton trigger events (e+e- / μ+μ- triggers) ~ 300 000 J/ψ ~ 15 000 c

~ 5 000 ψ’

• 210 M minimum bias events

HERA-B Data Samples

m(ee) [GeV/c2]

en

trie

s/(3

0 M

eV

/c2)

103

104

2.5 3.0 3.5 4.0

~ 120 000 J/ψ ~ 2 200 ψ′

σJ/ψ ~ 64 MeV

~ 120 000 J/ψ ~ 2 200 ψ′

σJ/ψ ~ 64 MeV

e+e-

J/J/ψψJ/J/ψψ

ψ′ψ′ψ′ψ′

en

trie

s/(2

5 M

eV

/c2)

m(μμ) [GeV/c2]

103

104

2.8 3.2 3.6 4.0

μ+μ-

J/J/ψψJ/J/ψψ

ψ′ψ′ψ′ψ′

~ 170 000 J/ψ ~ 3 000 ψ′

σJ/ψ ~ 44 MeV

~ 170 000 J/ψ ~ 3 000 ψ′

σJ/ψ ~ 44 MeV

Three target materials:pC,pW and pTi collisions

absolute cross section measurements for di-lepton triggered data need independent reference cross section

measured with minBias events: σ(J/ψ) = (502 ± 44) nb/nucl.


Contents: Part 3



J/ pT Distributions

HERA-B combined result

Increase of <pT2> with

A (radius of nucleus):

linear dependence on the nuclear path length of the incident parton

GeV1.29/4.27s

GeV8.38s

GeV6.41s

NA50

E672/706/771/789

HERA-B

2

2

2

11

T

TT

T p

pp

dp

dN


J/ψ xF - Distribution

Fx

FF

F w

xx

dx

dN2lnexp

wxF : widthΔxF : shift

width increasing withRadius of nucleus

shift increasing withRadius of nucleus

• pT distribution:• increase of <pT

2> with radius• xF distribution:

• increasing width and shift with radiusboth effects compatible with initial state energy loss

HERA-B combined result


Contents: Part 4



Measurement of Nuclear Dependence

TF

C

C

TF

W

W

C

W

TF

dpdx

ddpdx

d

A

Apx

/1

/1

ln

ln

1)/(

XJpAA /

sys.stat. 016.0004.0981.0

C

W

C

W

A

A

nuclear dependence parameter α extracted from the ratioof carbon and tungsten J/ψ production cross sections

Final result form HERA-B:

result based on double wire runs only

Measurement of the xF and pT dependence of α based on full data sample:

Using the measured kinematical distributions of carbon and tungsten (normalized)(full data sample of single and double wire runs)


Nuclear Dependence Measurement: pT

Good agreement of E866 anHERA-B measurement in thecommon region of pT

pT broadening effect as seen by E866 confirmed


Theoretical Models for xF Dependence

Separate description and integration:

• final state absorption• interaction with co-movers• energy loss (EL)• shadowing of nuclear PDFs• intrinsic charm quark components (IC)

Nuclear Parton Density Functions:

• Eskola, Kolhinen, Salgado (EKS, Eur.Phys.JC9(1999)61)• scale dependence of a proton within a nucleon via DGLAP• initial PDF from CTEQ4L and LO-GRV

• Eskola, Paukkunen, Salgado (EPS, arXiv:0802.0139)• improved leading order DGLAP including NLO

• Hirai, Kumano, Nagai (HKN, Phys.Rev.C70(2004)044905)• nuclear structure functions and Drell-Yan cross sections• weak anti-shadowing at negative xF

Initial state energy loss:

• Gavin, Milana (GM, Phys.Rev.Lett.68(1992)1834)• based on multiple scattering approach• elastic scatterings of quarks and gluons

• Brodsky, Hoyer (BH, Phys.Lett.B298(1993)165)• modification of GM

Model calculation by R. Vogt:

- Phys.Rev.C61(2000)035203- Phys.Rev.C71(2005)054902- Private communication


Theoretical Descriptions: Overview

All calculations done by Ramona Vogt in 2007/2008


Nuclear Dependence Measurement: xF

average α measurement form HERA-B:

sysstat 016.0004.0981.0 .

Final result form HERA-B, to be published in Eur.Phys.J


Reggeon Phenomenology Model

Boreskov and Kaidalov (JEPT Lett.D77(2003)599):

predicts anti-screening effects in negative xF region- color less state containing quarks (i.e. D-Mesons) propagates trough the nucleus- large size (consisting of D-mesons), large interaction cross section: energy loss- J/ψ projected out of energy dependent color-less state

HERA-BE866

cc

HERA-B result within uncertainties qualitatively compatible


Contents: Part 5



χc Production

)/(

)/()(2

1,

J

JBRR i

cic

c

Relative measurement of χc to J/ψ production

eeJ

Jc

//

/

HERA-B:

Selection by γ Selection (Eγ) andinvariant mass measurement: )()( llMllMM

• making use of J/ψ production cross section from min.Bias data• disentangle χc1 and χc2 by double Gaussian fits: separate cross section measurements• background subtraction by mixed events• separate analysis for electrons and muons• full statistics in both channels: 15000


χc Event Counting

electronsmuons

Separation of χc1 and χc2 in the ΔM spectra:• double Gaussian fit with some fixed parameters predicted by MC• free parameters are the ratio and sum of event numbers


A-Dependence

C

W

C

W

J

A

A

R

R

c

c

c

log

log

/

averaged result of

HERA-B:

Δα = 0.05 ± 0.04

Atomic mass number dependence:

• same principle as for J/ψ• no significant difference in A-dependence within the statistical limits


Production Cross Section Ratio R(c)

[GeV]s

CDF CDF ((p-pp-p))

ISR ISR ((p-pp-p))

E771 E771 ((p-p-SiSi))

E705 E705 ((p-p-LiLi))

E369/ E369/ 610/ 610/ 673 673

((p-p-BeBe))

2002/3 final

ππ-A-A

Final result: Rχc = (18.8 ± 2.8)%

of the produced J/ψ’s come from χc decays

HERA-B

HERA-B 2000

[%]c

R

97015200)(#

6605630)(#

7109570)(#

tot

ee

c

c

c

available statistics:


Final Results of χc

eon61)nb/nucl(231)(

nb/nucleon)35133()(

23.057.0)(

)(

04.005.0

40.002.1

188.0

c2

1

2

1

12

028.0026.0

c

c

c

R

Rc

Final result form HERA-B, accepted for Phys.Rev.D (arXiv:0807.2167)


Summary

HERA-B collected 300000 J/, 15000 χc and 220 Mio minimum bias events on nuclear targets (mainly carbon and tungsten)

Final Results on charmonium production:

• J/: inclusive production cross section• J/: xF and pT distributions in a new negative xF range J/: nuclear dependence: tendency of enhancement in at xF <0• c : production ratio, disentanglement of χc1 and χc2

Final results on kinematics of J/ production, nuclear dependence of J/ψ and c production are final and published (during 2008)

Documents

Charmonium Production in Media