Fc measurements at HERA 2€¦ · 2 @ HERA II on the way to precision measurement 0.4 0.2 10-5 10-3...

New trends in HERA Physics, Ringberg 2008

Katerina Lipka

Fc2 measurements at HERA

Charm production at HERA: why now?

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 Fc2 has large uncertainties

now: precise PDF – crucial importance for the LHC

• Combined HERA PDF are of unprecedented precision

• BUT dependent on parameterization of the QCD fit

• Need a cross check / direct access to the gluon

• Final state measurements (jets, heavy quarks) extremely important

• Fc2 @ HERA II on the way to precision measurement

10-5 10-3 x

HERA I Fc / F22

Q2 = 11 GeV2

K. Lipka Charm production and Fc2 at HERA 2

Dominated by Boson – Gluon Fusion (BGF)

• gluon directly involved:

include in a global PDF fit

important cross-check of the g(xg)

• charm mass – additional hard scale:

pQCD calculations possible;

multiple scales: calculations complicated

Charm production at HERA

Factorization:

σ(ep→D*X)=Proton Structure ⊗ Photon Structure ⊗ Matrix Element ⊗ Fragmentation

to learn something about PDFs:

calculate hard ME, measure cross section, understand fragmentation

Presented in this talk

Hard ME:

• NLO calculations and Monte-Carlo simulations

Charm tag methods and extraction of Fc2 :

• Charm tag via reconstruction of charmed mesons

• Extrapolation to the full phase space

• Fragmentation measurement

• Charm tag via track displacement measurement

Results and discussion

Models of charm productionMassive calculation, fixed order QCD calculation, FFNS

• correct threshold suppression, no collinear divergences, terms ~log(μ/m)

• no factorization, no conceptual necessity fo FFs, no resummation

• valid for 0 ≤ pt2≤ mc

2, fixed order logarithms ln(pt2/mc

2) large for pt2>>mc

Models for charm at HERA: FMNR (Photoproduction), HVQDIS (DIS),

Massless calculation (ZM-VFNS)• large collinear ln (μ2/m2

c)-terms resummed in evolved PDFs and FFs (LL, NLL), good for large μ2~pt

2>>mc2

• universality of PDFs and FFs via factorization theorem, global analysis

• terms (mc/pt)n neglected in the hard part – breaks down @ threshold

Not appropriate for charm production at HERA (close to threshold)

Generalized mass calculation (GM-VFNS) → Hubert’s talkAvailable for charm production in γp at HERA, DIS is on the way

RAPGAP• matrix element calculated in LO QCD

• higher order contributions via parton showers

• parton evolution in collinear approximation (DGLAP equations)

• charm is massive in BGF

CASCADE• gluon density unintegrated in gluon transverse momentum kT

• only gluons in proton

• higher order contributions via initial state parton showers

• based on CCFM equations

• charm is massive in BGF

Hadronization via Lund String model (Jetset)

Monte-Carlo models for data corrections

Liquid ArCalorimeter

“Spaghetti” Calorimeter

central tracking detector

D*+→D0 πs+ → K-π+ πs

+ (+ c.c.)

Kinematics regimes:

DIS: 5 <Q2< 1000 GeV2

Photoproduction Q2< 2 GeV2

Charm tag via D*± production

) [GeV]π) - M(KππM(K0.14 0.15 0.16 0.17

282±N(D*) = 20803

) [GeV]π) - M(KππM(K0.14 0.15 0.16 0.17

6000 slow±π ±π +Κ

H1 Preliminary

HERA II

2 < 100 GeV25 < Q0.02 < y < 0.7

(D*)| < 1.5η| (D*) > 1.5 GeV

Electron reconstructed in

SpaCal: Q2<100 GeV2

LAr: Q2>100 GeV2

(D*)η-1.5 -1 -0.5 0 0.5 1 1.5

η/dσd

(D*)η-1.5 -1 -0.5 0 0.5 1 1.5

η/dσd

e+D*+X→ep

-1ZEUS (prel.) 162 pb

HVQDIS

(D*)η-1.5 -1 -0.5 0 0.5 1 1.5

(D*) < 2.5 GeVT

1.5 < p

H1 PreliminaryHERA II

2 < 100 GeV25 < Q0.02 < y < 0.7

D* in DIS

(D*)η-1.5 -1 -0.5 0 0.5 1 1.5

(D*) < 3.5 GeVT

2.5 < p

H1 data (prel.)

HVQDIS (MRST2004FF3nlo)

HVQDIS (CTEQ5f3)

D* in DIS

(D*)η-1.5 -1 -0.5 0 0.5 1 1.5

(D*) < 5.5 GeVT

3.5 < p

< 1.6 GeVc1.3 < m2c + 4m2 = Q2

μ/f,r

0.4±(Kartvelishvili) = 3.3 α

D* in DIS

(D*)η-1.5 -1 -0.5 0 0.5 1 1.5

(D*) < 14.0 GeVT

5.5 < p

D* in DIS

D* production in DIS (5<Q2<100 GeV2)

H1: FFNs NLO does good job describing the D* kinematics,

but underestimates forward region ay low pT(D*)

ZEUS: no forward access in the data seen. Data precision will improve

D* production in DIS (Q2>100 GeV2)

(D*)η-1 0 1

η/dσd

1502D* production at high Q

(D*)η-1 0 1

η/dσd

H1 data (prel.)

RAPGAP (CTEQ65m)

CASCADE (A0)

H1 Preliminary HERA II

2 < 1000 GeV2100 < Q0.02 < y < 0.7

(D*) > 1.5 GeVT

(D*) [GeV/c]T

p5 10 15 20

2D* production at high Q

(D*) [GeV/c]T

p5 10 15 20

210H1 data (prel.)

RAPGAP (CTEQ65m)

CASCADE (A0)

2 < 1000 GeV2100 < Q0.02 < y < 0.7

(D*) | < 1.5η|

• D* production at high Q2: description by the LO Monte-Carlo gets worse

• NLO FFNs describes data very well

D* production in DIS: Q2 slope

]2 [GeV2Q10 210 310

D* production in DIS

H1 data (prel.)

RAPGAP (CTEQ65m)

RAPGAP (CTEQ6l)

CASCADE (A0)

0.02 < y < 0.7 (D*) | < 1.5η| (D*) > 1.5 GeV

]2 [GeV2Q10 210 310

Monte-Carlo models don’t describe the Q2 slope of the D* cross section

]2 [GeV2Q10 210 310

H1 data (prel.)

0.02 < y < 0.7 (D*) | < 1.5η| (D*) > 1.5 GeV

]2 [GeV2Q10 210 310

NLO FFNs calculation does good job (surprising, should break down for high Q2)

1 10 102

Q2 (GeV2)

ZEUS (prel.) 162 pb-1

ZEUS BPC (prel.) 98-00

ZEUS 98-00

HVQDIS

) 2 (GeV2Q10 210 310

10ZEUS

+ X0 e + D→ep

HERA I-1ZEUS 65 pb

HERA II-1ZEUS (prel.) 135 pbNLO + Fragmentation

) 2 (GeV2Q10 210 310

More to charmed meson production

-1.5 -1 -0.5 0 0.5 1 1.5

3 + X0 e + D→ep

HERA II-1ZEUS (prel.) 135 pbNLO + Fragmentationbeauty contribution (RAPGAP)

-1.5 -1 -0.5 0 0.5 1 1.5

±Dη-1.5 -1 -0.5 0 0.5 1 1.5

±D η

1.4 + X± e + D→ep

HERA II-1ZEUS (prel.) 135 pbNLO + Fragmentationbeauty contribution (RAPGAP)

±Dη-1.5 -1 -0.5 0 0.5 1 1.5

±D η

1.4ZEUS

• HERA-II, L=135pb-1

5<Q2<1000 GeV2 ,

pT(D)>3 GeV, Iη(D)I<1.6

• Lifetime information from the ZEUS Micro Vertex Detector used

• NLO FFNS describes data well

Visible cross section: pT(D*)>1.5 GeV, |η(D*)|<1.5

0.02<y<0.7, 5<Q2<1000 GeV2

Problem: detector sees only 30% of the phase space for c→D*

→ strong model dependence due to large extrapolation factors

Extrapolation problems:

1) Different extrapolation models

2) Unknown parameters within a single model:

mass of charm quark, scales,

fragmentation model → experimentally measurable: see next slides

(exp)(exp) 22 theoryFtheory

Extraction of Fc2 from meson cross section

Measurement of charm fragmentation in epMethods to reconstruct the energy of the parent quark:

Jet containing D*; problem: only small region of phase space accessible

• DIS: inclusive k⊥ algorithm applied in the γp frame, ET(D*-jet)>3 GeV

• significant contribution only from ŝ > 100 GeV² (much above threshold)

Hemisphere containing D*:

• experimental setup similar to e+e- , works at threshold, ŝ ≈ 4m²c

γp-system

cut:η>0

- take all particles towards γ

- project onto the plane ⊥ to the γ

- get Thrust axis

- Σ momenta of all particles in the D* hemisphere

⊥ γ direction

Charm fragmentation in photoproduction

Parent quark approximated by a jet containing D*

• data: HERAI, L =120 pb-1, Q2<1GeV2;

• pT ( D*) >2 GeV, Iη(D∗)I<1.5

• inclusive k⊥ algorithm, ET(D*-jet)>9 GeV

2)( *+

• compared to the NLO FFNS (FMNR)

fragmentation model: Kartvelishvili

best fit α=2.67

)1()(* zzzDDc −∝ α

0.2 0.4 0.6 0.8 1z

σ/dz ZEUS (120 pb-1)

FMNR×CPYThad(Kartvelishvili α=2.67

+0.25- 0.31)

FMNR×CPYThad(Kartvelishvili α=1.2)

FMNR×CPYThad(Kartvelishvili α=4.0)

Hemisphere method should include more final state gluon radiation than jet method

⇒ Measured distributions of the fragmentation variable should be different

⇒ Extracted parameters of the non-perturbativefragmentation function should agree

Data: H1 HERA I, L=75 pb-1 both methods used: ,

Differences between the methods:jet

DLjet pE

pEz)()( *

DLhem pE

pEz)()( *

• Measure in the common phase space: require presence of a D* jet

• Extract parameters for n.-p. FF using MC/ HVQDIS.

• Expect : parameters agree for different methods, different for MCs and HVQDIS

• Any differences at the threshold (absence of a D*-jet)?

Measurement of charm fragmentation in DIS

Hemisphere method Jet methodRAPGAP MC: NLO (HVQDIS):

Fragmentation measurement: D*- Jet sample

• Distributions on hadron level look different (as expected)• MC (Rapgap) with standard n.p. FF yield reasonable description of data• Extracted n.p. FF parameters from zhem (α=4.5±0.6) and zjet (α=4.3±0.4) agree• HVQDIS ⊗ Kartvelishvili fragmentation: extracted parameters zhemi and zjet agree

Hemisphere method

Fragmentation c → D*. No D*- jet sample

MC: Extracted parameters (α=10.3 ) inconsistent with jet-sample (α=4.5±0.6)HVQDIS: “no jet” (α=6.0 ) inconsistent with jet-sample (α=3.3±0.4)Fragmentation at threshold significantly harder than expected from the jet-sample

Treatment in extrapolation models: ŝ-dependent fragmentation

+ 1.7- 1.6

+ 1.0- 0.8

Extrapolation Models in use:

• NLO: Riemersma et al: integrated form; HVQDIS: differential form,

fixed order massive calculation, Nf=3, FFNS, evolution: DGLAP

Parameters: PDFs: MRST04F3, mc = 1.43 GeV , μr=μf=μ=√ Q2+4mc2

Fragmentation: ŝ<70 GeV2: α =6.0, otherwise α=3.3

• CASCADE: massive LO ME + Parton showers,

proton structure: gluons only, evolution: CCFM

Parameters: PDFs: A0, mc = 1.43 GeV, μr=μf=μ=√ Q2+4mc2

Fragmentation: ŝ <70 GeV2; α = 8.2, otherwise α = 4.3

Back to extrapolation of σ(D*) to the Fc2

ep → e D* X

2 σ/d

Q =2 7 GeV2 11GeV2 18GeV2

200 32GeV2 65GeV2 120GeV2

200 200GeV2

y10 -2 10 -1 10 -2 10 -1 1

440GeV2H1Preliminary

Data HERA-II

HVQDIS(MRST04FF3)total theoryuncertainty

fragmentationuncertainty

0 2 = 7 GeV2Q

0 211 GeV

0 218 GeV

0 232 GeV

0 265 GeV

02120 GeV

02200 GeV

02440 GeV

Data HERA II

CASCADE (A0)

H1 Preliminary

eD*X→ep

σ 2 d4Q

1-1 10-2 10-1 10-210 0

Lowest y (highest x) overestimated by NLO, underestimated by CASCADE

D* cross sections vs NLO/CASCADE

Extrapolation factors (σtot/σvis)

differ in NLO vs CASCADE:

3%-10% (low x) -100% (high x)

Differences in the models:

• LO+PS vs NLO

• Evolution

• Hadronization

Possible reason:

Hadronization

More studies have to be done

7 GeV2 11 GeV2 18 GeV2

32 GeV2 65 GeV2 120 GeV2

200 GeV2 440 GeV2

x10 -5 10 -3 10 -5 10 -3 10 -1

Extrapolation factors NLO/CASCADE

Results: Fc2 from D* measurement

2 = 7 GeV2Q

211 GeV

218 GeV

232 GeV

265 GeV

2120 GeV

2200 GeV

2440 GeV

GraphGraphGraph

< 1.6 GeVc1.3 < mμ < 2

rμ < μ0.5

D* HERA IICASCADE (A0)theoryuncertainty:

H1 Preliminary

in the CCFM scheme (CASCADE)cc2F

-1 10-3 10-5 10-3 10-5 10 0

0.6Fcc

2 in the NLO DGLAP scheme (HVQDIS)

7 GeV2 11 GeV2 18 GeV2

32 GeV2 65 GeV2 120 GeV2

200 GeV2 440 GeV2

x10 -5 10 -3 10 -5 10 -3 10 -1

H1Preliminary

Data HERA-II

total theoryuncertainty

PDF variation

MRST04FF3CTEQ5F3

Experimental errors will further decrease – we are on the way to the final precision

Charm/beauty via other tag methods• Charm comes alone with beauty:

- More experimental details in Massimo’s talk

• Large mass : transverse momentum to Jet axis: muon ptrel

• Large lifetime: impact parameter δ, Significance S=δ/σ(δ)

• Semileptonic decays (e,μ)

• Different systematic uncertainties wrt. D-meson measurements

/ cmδ-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2

bb2 and Fcc

2Measurement of F

H1 PreliminaryH1 Data (Prel.)Total MCudscb

/ cmδ-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2

0 1 2prel (GeV)

T (GeV)

ZEUS (prel.) HERA II 125 pb-1

MC sumcbuds

Charm in semileptonic events

-1.5 -1 -0.5 0 0.5 1 1.5 2

ep→ eQQ–

X→ e μ X

ZEUS (prel.) HERA II 125 pb-1

Beauty

HVQDISHVQDIS

dημ (

Reasonable description

by the NLO FFNS

Q2=30 GeV2

F2 cc_

Q2=130 GeV2

F2 cc_

Q2=1000 GeV2Charm

ZEUS (prel.) HERA II, 125 pb-1 (μ)ZEUS HERA I, 82 pb-1 (D*)H1 HERA I, 57 pb-1 (VTX)

ZEUS-S-FF mc=1.5, mb=4.75 GeVPDF uncertaintymc=1.3, mb=4.5 GeVmc=1.7, mb=5.0 GeV

Charm cross sections via lifetime tag vs D*H1 CHARM CROSS SECTION IN DIS

Q2= 6.5 GeV2σ∼cc_

Q2= 12 GeV2 Q2= 20 GeV2

Q2= 35 GeV2 Q2= 60 GeV2

Q2= 120 GeV2

Q2= 200 GeV2

H1 Preliminary

Q2= 400 GeV2

H1 HERA IH1 HERA II (Prel.)H1 D✽ HERA II (Prel.)

Charm cross sections vs VFNS (TR)

H1 CHARM CROSS SECTION IN DIS

Q2= 6.5 GeV2σ∼cc_

Q2= 12 GeV2 Q2= 20 GeV2

Q2= 35 GeV2 Q2= 60 GeV2

Q2= 120 GeV2

Q2= 200 GeV2

H1 Preliminary

Q2= 400 GeV2

H1 HERA IH1 HERA II (Prel.)

CTEQ6.6MSTW08 (Prel.)CCFM

Fc2 from lifetime tag vs MSTW NNLO

H1 F2cc_(x,Q2)

10 102

x=0.0002, i=10

x=0.00032, i=9

x=0.0005, i=8

x=0.0008, i=7

x=0.0013, i=6

x=0.002, i=5

x=0.0032, i=4

x=0.005i=3

x=0.008i=2

x=0.013i=1

x=0.02i=0

H1 Preliminary

MSTW08 (Prel.)MSTW08 NNLO (Prel.)

H1 HERA II (Prel.)

Q2 / GeV2

F 2cc_ × 4

Recall Robert’s talk on Monday:

NNLO better fits the measured Fc2

Only Lifetime data of H1 are shown

Data will get better !

HERA measurement of Fc2

• Plenty of measurements

• Nice agreement between methods

• Experimental precision of several measurements will further improve

• Different methods will be combined: orthogonal errors!

• H1 and ZEUS results will be combined

• Sensitivity to the models (PDFs)

• Need proper (precise) theory

1 10 102

Q2 (GeV2)

F2 cc–

HERA F2 cc–

H1 HERA I (D*)H1 HERA I (VTX)ZEUS HERA I (D*)ZEUS HERA I (D+, D0, Ds

+)ZEUS (prel.) HERA II:

D* D+ μH1 (prel.) HERA II:

D* VTX

NLO QCD:CTEQ5F3MRST2004FF3

x = 0.00003 (× 420)

x = 0.00005 (× 419)x = 0.00007

(× 418)x = 0.00013

(× 417)x = 0.00018 (× 416)

x = 0.0003 (× 415)

x = 0.00035 (× 414)

x = 0.0005 (× 413)

x = 0.0006 (× 412)

x = 0.0008 (× 411)

x = 0.001 (× 410)

x = 0.0012 (× 49)

x = 0.0015 (× 48)

x = 0.002 (× 47)

x = 0.003 (× 46)

x = 0.004 (× 45)

x = 0.006 (× 44)

x = 0.008 (× 43)x = 0.012

(× 42)

x = 0.02 (× 41)

x = 0.03(× 40)

Conclusions

Experimentally charm measurements at HERA get very precise:

We will get soon

• D* measurement at H1 on the way to 5% precision measurement

• D* measurements at ZEUS full HERA-II on the way

• Combination of different measurement methods

• Combination of H1 and ZEUS: cross calibration

• Enlarge the visible phase space (H1)

Extrapolation to the full phase space model dependent

Theory: massive NLO pQCD describes the data quite well

Model uncertainties larger than experimental errors

We still need:

• GMVFNS for DIS : proper charm treatment in the global fit

• NNLO

F2 cc–

HERA F2 cc–

Q2 = 2 GeV2

H1 HERA I:D* VTX

ZEUS HERA II:D* D+, D0, Ds

H1 (prel.) HERA II:D* VTX

ZEUS (prel.) HERA II:D* D+ μ

NLO QCD:CTEQ5F3MRST2004FF3

4 GeV2 7 GeV2

11 GeV2 18 GeV2 30 GeV2

60 GeV2

130 GeV2

500 GeV2

Outlook:

Precision will improve

Results will be combined

10-5 10-3 x

HERA I Fc / F22

Q2 = 11 GeV2

Backup

D* in photoproduction (Q2 < 2 GeV2)

(D*)η-1.5 -1 -0.5 0 0.5 1 1.5

40H1 data (prel.)

FFNS (CTEQ5F3) < 1.7 GeV c1.3 < m

cm / r,f

μ0.5 <

GMVFNS (CTEQ6.5)

D* in Photoproduction

(D*)η-1.5 -1 -0.5 0 0.5 1 1.5

(D*)[GeV]t

p2 4 6 8 10 12

210H1 data (prel.)

cm / r,f

μ0.5 <

GMVFNS (CTEQ6.5)

2 < 2 GeV2Q < 285 GeV Pγ100 < W

(D*) > 1.8 GeVt

(D*)| < 1.5η|

(D*)[GeV]t

p2 4 6 8 10 12

[GeV] pγW100 150 200 250

0.8H1 data (prel.)

cm / r,f

μ0.5 <

GMVFNS (CTEQ6.5)

[GeV] pγW100 150 200 250

0.8• Measurement in the visible range:

PT(D*)>1.8 GeV, Iη(D*)I<1.5

Q2 < 2 GeV2, 0.1<y<0.8

• Good agreement with both NLO

• Large model uncertainties due to variation of the scales

D* in photoproduction

(D*)η-1.5 -1 -0.5 0 0.5 1 1.5

30H1 PreliminaryHERA II (D*) < 2.5 GeV

t1.8 < p

(D*)η-1.5 -1 -0.5 0 0.5 1 1.5

10H1 PreliminaryHERA II (D*) < 4.5 GeV

t2.5 < p

(D*)η-1.5 -1 -0.5 0 0.5 1 1.5

0.5H1 PreliminaryHERA II (D*) < 12.5 GeV

t4.5 < p

H1 data (prel.)

+p2cm /

r,fμ0.5 <

GMVFNS (CTEQ6.5)

GM VFNS underestimates the forward region at high pT

Fc measurements at HERA 2€¦ · 2 @ HERA II on the way to precision measurement 0.4 0.2 10-5 10-3...

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