charm production: from hera to lhc

Martin zur Nedden, HU Berlin Charm at Panda (2009), Mainz, p. 1Charm Production at HERA/Tevatron/LHC

Charm Production:from HERA to LHC

Martin zur NeddenHumboldt-Universität zu Berlin

International Conference

November 19 – 20 2009, Mainz, Germany


Content● Charm Production

– Introduction– Hadronic Interaction– Electron-Proton Interaction

● Experiments– HERA, TEVATRON and LHC– Detectors and Spectrometers

● Physics Results– D*-Production and F2

c

– Charm Fragmentation– Charmonium Production– W + charm-Jet production– Rare Decays and Flavor Changing Neutral Currents






c

– Charm Fragmentation– Charmonium Production– W + charm-Jet Production– Rare Decays and Flavor Changing Neutral Currents


Charm Production

At HERA:• open Charm• contribution to F2

• charm fragmentation• charmonium spectroscopy• excited charmed states• production in media (HERA-B)

At LHC• charmonium spectroscopy• charmonium polarization• detector calibration• trigger commissioning

At TEVATRON:• D0 mixing and CP violation• excited charmed states• FCNC• charm fragmentation, W + c-jets• charmonium spectroscopy and polarization

Not all can be covered here…


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


Heavy-Quark Production in Hadron Collisions

Leading Order and Next to Leading Order

gluon splitting

flavor excitationg

g

gg

Q

Q

radiative corrections

B/D-hadrons and/or b/c-jets are the observables for b/c-quark

DF

cbpd

cXbqgggqqd

DBpd

DXBppd DBcbpp

TT

//

/

///

/

/

NLO QCD

proton structure: HERA

fragmentation: HERA/TEVATRON

flavor creation


Quarkonia Formation

hadronization/fragmentation: formation of final state wiht charmlong distance (~1/(mcv)) process:non-perturbative calculations and

input 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


Quarkonia Production Models

Color Singlet Model

- can’t produce color-neutral JP = 1- cc pair by simple gluon fusion.- produce a colored state and one hard gluon carries away color- pT spectrum does not match data- underestimates cross sections by factors of 10 - 50

From NRQCD, Color OctetMechanism

- color radiated off by soft gluons- adjustable hadronisation parameter: → match measured pT spectra and cross section- predicts transverse polarization, increasing with pT


Heavy Quark Production in Electron-Proton Scattering

direct process:boson gluon fusionmain contribution

indirect process:resolved photon

indirect process:flavor excitation

charmoniumformation at HERAJ/ (pJ)

two kinematic regimes:• photoproduction (PHP) with Q2 ~ 0• electroproduction (DIS) with Q2 > 2 GeV2






c



The HERA Experiments

HERA I: 1994 – 2000HERA II: 2004 - 2007

total lumi on tape:~ 0.5 fb-1 per experiment

H1

ZEUS

e+p: s = 320 GeV


920 GeV protons

p+A X , s = 41.6 GeV

The HERA-B Spectrometerspectrometer at the HERA storage ring: proton-fixed target

•150 M di-lepton trigger events ~ 300 000 J/ψ ~ 15 000 c

~ 5 000 ψ’

• 210 M minimum bias events


Tevatron Experiments

p+ p: √s = 1.96 TeV CDF

D0

total lumi on tape:~ 3 fb-1 per experiment


The ATLAS Experiment at LHC

p + p: √s = 14 TeV


A transverse slice through CMS (LHC)

p + p: √s = 14 TeV


The LHCb Spectrometer

pp collision Point

Vertex Locator

Tracking System

Muon SystemRICH Detectors

Calorimeters

~ 1 cm

B

p + p: √s = 14 TeV




● Experiment– HERA, TEVATRON and LHC– Detectors and Spectrometers


c



Selection of charmed Mesons

ss KDDc 0*

ss KDDc 0*

KMKMM s

production of charm-quarks in ep-interaction via boson-gluon-fusion

identification of D*+ via the mass difference ΔM of the invariant masses

looking for charm within the decaychanel of D*-mesons

momentum transfer Q2 = -q2 = (k’-k)2

momentum fraction x of scattered quark


D-Meson Decay Signature

example fromZEUS/HERA

using vertex detector to reconstructsecondary vertices


Open Charm-Production at HERA

HERA I : PDF – central measurement of HERA

– PDF obtained from the fits to inclusive F2

– inclusive F2 experimentally very precise

– contribution of events with charm to F2 high

– measurement of F2c has large uncertainties

HERA II: precise PDF – crucial importance for the LHC

– combined HERA - PDF are of unprecedented precision

– dependent on parameterization of the QCD fit

– need a cross check / direct access to the gluon

– final state measurements (jets, heavy quarks) extremely important

– F2c at HERA II on the way to precision measurement


D* Production, Q2 dependence

measurement for DIS (5 GeV2 < Q2 < 100 Q2) and high Q2 data (up to Q2 = 103 GeV2)

good description by NLO calculations

full HERA statistics:~ 350 pb-1


D* in DIS (low Q2)

differential cross sections measured in Q2, x, pT and ηreasonable described by NLC QCD calculation

double differential cross section in x and Q2 enables the extraction of F2c

double differential:

η in bins of pT

nedden


HERA Measurement of F2c

)()(

)()( 22 theoryF

theory

datadataF cc

vis

viscc

problem: detector acceptance of ~ 30%→ strong model dependence due to large extrapolation factors

comparison of different analysis methods - inclusive lifetime (H1, HERA I + II) - μ pT

rel (ZEUS, HERA II) - D+, D0, Ds cross sections (ZEUS, HERA II) - D* cross sections (H1, ZEUS, HERA I+II) - D+ and lifetime (ZEUS, HERA II)

theory prediction differ for Q2 < (2mc)2


HERA Measurement of F2c

different methods agree well combination of all available measurements (H1 / ZEUS, different analyses) improve precision

strong rise towards low x at lager Q2

different inputs to thetheoretical predictions: - parton densities - mass treatment - charm fragmentation






c



Charm Fragmentation

)(ˆ*/ zDF D

cpg

p

parton density function(non perturbative)

parton scattering cross section(perturbative)

fragmentation function(non perturbative)

D*

zzzDDc 1)(

* α

2

11

1

1)(

*

zzz

zDDc

ε

c

D

E

Ez

*

Kartvelishvili:

Peterson:


Fragmentation Function

ET(Jet) > 9 GeV, inclusive kT algorithm

data described by NLC QCD calculations withPeterson (ε = 0.079) or Kartvelishvili (α = 2.67) fragmentation

jet

D

E

pEz

2

*

||


Fragmentation Function

for shape comparison toother experiments

normalization to 1/binwithfor z > 0.3

with PYTHIA phase space extrapolated to pT(D*) =0 and finite bin size to extract the mean value of z

.)(028.0.)(024.0565.0 sysstatz






c

– Charm Fragmentation– Charmonium Production at HERA-B and LHCb– W + charm-Jet Production– Rare Decays and Flavor Changing Neutral Currents


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 targets:

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


J/ pT Distributions of HERA-BHERA-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 of HERA-B

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


Nuclear Dependence Measurement: pT

good agreement of E866 and HERA-B measurement in thecommon region of pT

pT broadening effect as seen by E866 confirmed

TF

C

C

TF

W

W

C

W

TF

dpdxd

dpdxd

AA

px

/1

/1

ln

ln

1)/(

sys.stat. 016.0004.0981.0


Nuclear Dependence Measurement: xF

average α measurement form HERA-B:

sysstat 016.0004.0981.0 .


J/ Production at LHCb

prompt J/ production not fully understood

- NRQCD (Colour Octet Model) successful in reproducing pT spectrum

at TEVATRON

- but predicts increasing transverse polarization at high pT (not observed)

cross-section + polarization important probes of charmonium production

- LHCb has unique acceptance

coverage in pT and

- synergy with b production

measurement


Identifying Prompt J/

combinatorical background

J/ from B-meson decay: exponential

prompt component:Gaussian

+

primary vertex

-

dz

separate J/ from prompt and b decays

J/ signal in 19 million min bias events

(1.1 s of running with nominal luminosity)

• mass resolution ~ 11 MeV

• S/B ~ 4

• Expect 3.2 106 events in 5 pb-1 at 8 TeV


χc Production at HERA-B

)/(

)/()(2

1,

J

JBRR i

cic

c

relative measurement of χc to J/ψ production

llJ

Jc

/

/selection by γ reconstruction (Eγ) andinvariant mass measurement

)()( llMllMM

• disentangle χc1 and χc2 by double Gaussian fits: separate cross section measurements• background subtraction by mixed events

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


Event Counting

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

Signal in inclusive J/ events

ΔM ~ 27 MeV (cf M(c2 ) - M(c1 ) = 55 MeV )

Some sensitivity to ratio (c2 ) / (c1 )

HERA-B LHCb


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

HERA-B: final result: Rχc = (18.8 ± 2.8)%

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

HERA-B

HERA-B 2000

[%]c

R






c

– Charm Fragmentation– Charmonium Production at ATLAS/CMS– W + charm-Jets– Rare Decays and Flavor Changing Neutral Currents


• large number of J/ψ → μ+μ- andΥ → μ+μ- decays is expected at LHC:

→ alignment and calibration of trigger and tracking→ test for QCD calculations→ prompt quarkonia is a main source of background to (rare) B processes

• key player in the early data taking:

→ at low luminosity lower pT threshold possible to collect large physics sample → ATLAS reach larger pT as TEVATRON: enhance its analysis power

Motivation for Charmonium at LHC

• Pb-Pb collisions at high energies and luminosities: → The Pb-Pb runs will occur at 5.5 TeV per NN collision, with 1027 cm-2s-1 Pb-Pb instantaneous luminosity → quarkonium states will be produced with very high rates


Expected Quarkonia at early LHC data

85 pb-1

60 pb-1

ATLAS

D0 1.3 fb-1

CDF 1.1 fb-1

Tevatron

1x106 J/ψ

4.2x105

~1000 J/ψ’s per hour expected

60 pb-1 should allow for competitive measurement of quarkonium polarization,

with enough statistics in the crucial high pT region.

High pT data is important since TEVATRON suffers from statistics in this region.

With 10 pb-1 ATLAS will be able to measure ratios of quarkonia cross sections,

which can help to constrain NRQCD octet matrix elements.


•observed J/ yield results from:• direct production

• decays from ’ and c states

• decays from B hadrons

•CMS will measure the inclusive,

prompt and non-prompt (B decays)

production cross sections

•in 1 or 2 days at 1031 cm-2s-1

(1 pb-1 of integrated luminosity),

CMS will collect ~ 25 000 J/ events

•J/ yield is extracted by fitting the dimuon mass distribution, separating the signal peak

from the underlying background continuum

Inclusive Differential J/ψ cross sections

CMS simulation


Quarkonium production cross-sectionOnia production pT (MC) and the differential cross-section contributions from color singlet, color octet and singlet/octet of .

The dominant contribution at highpT range is the 3S1 color octet fragmentation (dashed dotted line).

J/ prod. cross section production cross section

LHC MC (14 TeV)

Tevatron (1.8 TeV)


Differential J/ψ cross section

corrJT

fitJ

JT ApLdt

NJBr

dp

d

/

/

/)/(

A: convolution between the detector acceptanceand the trigger and reconstruction efficiencies, which depend on the assumed polarization

corr : needed if MC does not match “reality”

pp at 14 TeV3 pb-1 ~ 75 000 J/

CMS simulation

A

Competitive with TEVATRON results after only 3 pb-1

CMS simulation


Quarkonium production in Pb-Pb collisions

dNch

/dh = 3500


J → : Acceptances and Mass Resolutions

barrel +endcaps

barrel

• material between the silicon tracker and the muon chambers (ECAL, HCAL, magnet iron) prevents hadrons from giving a muon tag but impose a minimum muon momentum of 3.5–4.0 GeV/c. This is no problem for the Upsilons but sets a relatively

high threshold on the pT of the detected J/ψ’s.

• low pT J/ψ acceptance: better at forward rapidities.

• dimuon mass resolution is 35 MeV

barrel +endcaps

pT (GeV/c)

J/

Acc

epta

nce

p T (G

eV/c

)

CMS simulation


pT reach of quarkonia measurements

J/

● produced in 0.5 nb-1

■ rec. if dN/dη ~ 2500○ rec. if dN/dη ~ 5000

0.5 nb-1 : 1 month at 4x1026 cm2s-1

expected quarkonia yields:J/ψ : ~ 180 000, : ~ 26 000

statistical accuracy (with trigger) of’/ ratio vs. pT should be good enough to rule out some models

CMS simulation

CMS simulation






c

– Charm Fragmentation– Charmonium Production– W + charm-Jets– Rare Decays and Flavor Changing Neutral Currents


W + charm● possible background to top, stop-quark and SM charged Higgs production● |Vcd|2 suppresses d-quark-gluon fusion production● ⇒ Wc production provides direct sensitivity to s-quark PDFs● s-quark PDF is important for these processes at TEVATRON/LHC:

● a probe of s-quark PDF at hadron colliders tests QCD evolution

“μ-tagged jet” method:- consider the electric charge correlation of μ from c-quark and lepton from W- require events with opposite charge NOS N≫ SS

HcsppppHiggsWgsppppSM /:,/:


W+c-Jet Fraction

017.0071.0)(

)(

jetspp

jetcWppR

W+c-jet selection• all lepton channels considered for W boson decay• Z →μμ rejected by requiring Mμμ<70 GeV for μ-channel• σ(W+c-jet) fraction compared with theory prediction in jet pT: ALPGEN calculates the matrix element PYTHIA does showering and hadronization

• measurement is consistent with theory prediction

.)(005.0.)(029.0093.0

.)(.)(021.0060.0 005.0007.0

sysstatR

sysstatRe


W+c-Jet Cross Section

CDF measurement of total cross section for W+c-jet production with ~1.8 fb-1 dataelectron and muon channels considered for W boson decayc-jet with pT(c) > 20 GeV/c and |η(c)|< 1.5:c-jet identified from semileptonic decay by looking for a muon within jet

measurement agrees with NLO calculation

pblumsysstatlWBRWc .)(6.0.)(.)(8.28.9)( 4.16.1

pbSMWc

4.10.30.11

4.0 coneR

6.0),(

3,

axisjetR

GeVpT






c

– Charm Fragmentation– Charmonium Production– W + charm-Jets– Rare Decays and Flavor Changing Neutral Currents


Upper limit for D0→μ+μ–

● search for a signal of the FCNC decay D0→μ+μ– in all di-muon samples

● observed events: 3

● expected background: 6

● limit (90% CL):

● best limit at publication time

60 100.2 DBR

ucD 0


experimental strategy CDF:

• events from two-track trigger using first 69 pb-1 of data

• to cancel acceptance effects normalize to D0→

Search for FCNC D0→• SM expectation BR ~ 3∙10-13

• best limit: <4.1∙10-6 90% CL, Beatrice/WA92,E771

• enhanced in N.P. (R-Parity Violation Susy: ~3.5*10-6)

BR(D0→) < 2.4*10-6 at 90% CLResult:

Comment: muon fake rate set limit (~10-6)


Summary

Charm production is an issue at many experiments

Still a very active field on hadron colliders

Important measurements form TEVARTON concerning - polarisation - D0 – mixing and CP-Violation - charmonium production process (color octet model) - charm fragmentation

Fundamental inputs form HERA-measurements - charm contribution to structure functions - charm fragmentation - charmonium production and polarisation

Input form HERA/TEVATRON needed for LHC - understanding detector and trigger - charmonium production important for many measurements in B-Physics program - many new inputs expected from LHCb

charm production: from hera to lhc

Documents