HEP2005, 21 July 2005 V. Chekelian, Charm and Beauty SF 1

Charm and beauty proton structure functions F2

cc and F2bb

at HERA Vladimir Chekelian (Shekelyan)

MPI for Physics, Munich

Measurements of F2cc and F2

bb using the H1 vertex detector

at high Q2: Q2 > 150 GeV2 (scattered positron in Lar calorimeter) Eur. Phys. J. C40 (2005) 349 [hep-ex/0411046]

at low Q2: 6.3 < Q2 < 120 GeV2 (scattered positron in Spacal) DESY-05-110 (July 2005), submitted to Eur. Phys. J. C [hep-ex/0507081] ’ the e+p data 1999-2000, int= 57.4 pb-1

--

HEP2005, 21 July 2005 V. Chekelian, Charm and Beauty SF 2

Structure Functions, Heavy Quarks and QCD

22

4 2

22

2 2

2(1 (1 ) )

1 (1 )[ ]

pC

L

eN F

yd yydxd xQ QF

DIS cross section and SFs

2 22 ( , ) ( )

iq i iF x Q x e q q in QPM:

Boson Gluon Fusion (BGF)Q2 ~M2

HQ

QPMQ2 >>M2

HQ

’ exp. checks of HQ calculations in pQCD (calculation techniques, pdfs from QCD fits) direct access to gluon via BGF

Treatment of HQ in QCD mc

2 2.5 GeV2, mb2 25 GeV2

Q2 >>M2HQ massless scheme

Q2 ~ M2HQ massive approach (FFNS)

full Q2 range: Variable FNS (VFNS: ACOT,MRST)

,b

- ,b

HEP2005, 21 July 2005 V. Chekelian, Charm and Beauty SF 3

Main methods used so far to study HQ at HERA

Open Charm:

- exclusive D* and D meson production - small branching (-> limited statistics) - large extrapolation to get F2

cc

ptrel

( ) ( )slowm K m K

’ see talk of S. Fourletov

’ see talk of B. Naroska

Open Beauty:

b ’ X make use of large b mass and long lifetime: pt

rel ( transverse to b-jet)

(impact parameter)

HEP2005, 21 July 2005 V. Chekelian, Charm and Beauty SF 4

The H1 vertex detector

used in this analysis:

CST(30o < < 150o)

- 2 cylindical layers of double-sided silicon strip detectors surrounding the beam pipe

- radii 5.7 cm and 9.7 cm

- hit resolution: 12 μm in r-φ 25 μm in z

- impact parameter resolution (for central tracks with CST hits in both layers):

9033 [ ]

T

mm GeV

P

FST CST BST Forward, Central and Backward Silicon Trackers e p27.6 920 GeV

HEP2005, 21 July 2005 V. Chekelian, Charm and Beauty SF 5

Inclusive lifetime tagging of HQ

secondary vertex

- use impact parameter in r-φ plane for

- all tracks with pt> 500 MeV and 2 hits in CST

- sign of impact parameter is defined using φ of the HQ direction:

Goal: be as inclusive as possible

-> the method is cross checked at high Q2 by using explicit reconstruction of the secondary vertex

primary vertex

x

y

r-φ plane

(resolution + secondary vertices) (due to resolution only)

-> high acceptances for long lived c (b) hadrons: 82% (96%) at low Q2; 93% (96%) at high Q2

-> small extrapolation to the full phase space

HEP2005, 21 July 2005 V. Chekelian, Charm and Beauty SF 6

Reference axis (HQ direction) Reference axis in r-φ plane ref. axis = jet of the highest transverse momentum jet with pt>2.5 GeV

low Q2 : jet is found for 81% (95%) c(b) events

ref. axis = 180o – scattered elec. if no jet found

Checks of the resolution:

D* - ref. axis : azimuthal difference between reconstructed D* and reference axis

jet no jetfound

Resolution in is 5o for events with jets and 35o if jet is not found

’ data are well described by MC

HEP2005, 21 July 2005 V. Chekelian, Charm and Beauty SF 7

Signed impact parameter and SignificanceTracks matched to the reference axis |trref. axis

Significance S = /() of the track (in r-φ plane) - remove ||>1mm (to suppress long lived strange particles, e.g. Ks

0)

/ ( )S

Signed impact parameter Significance

(r-φ plane)

distributions are well described by MC

HEP2005, 21 July 2005 V. Chekelian, Charm and Beauty SF 8

Significance distributions at low Q2

S1 – highest absolute significance track

S2 – 2nd highest absolute significance track

with the same sign as S1

S3 – 3d highest absolute significance track

with the same sign as S1 and S2

S1 S2

S3

HEP2005, 21 July 2005 V. Chekelian, Charm and Beauty SF 9

Subtracted significance distributions at low Q2

subtract the contents of negative bins from the contents of the corresponding positive bins -> substantially reduce uncertainty due to resolution of and light quark normalisation

-> dominated by c with increasing b fraction at high Si

Simultaneous fit to the subtracted S1,S2,S3 distributions

and total number of inclusive events before track selection using c, b and uds shapes from MC 3 parameters:

- Pc scale factor for charm MC (b decays are excluded)

- Pb scale factor for beauty MC

- Pl scale factor for light quark MC

S1 S2

S3

For complete low Q2 sample: 1.28 0.04, 1.55 0.16, 0.95 0.01c b lP P P

’ individual fit for each x-Q2 interval

HEP2005, 21 July 2005 V. Chekelian, Charm and Beauty SF 10

Reduced cross sections and F2cc, F2

bb

2 2( , ) ( , )MCgen

cccBCCMCgen MCgen MCgen

c b l

cc

l

c

bc

Nx Q x Q

N N N

P

P PP

’ F2cc,bb are obtained using FL

cc,bb from the NLO QCD predictions

2 4 2

2 2 2 22

22 (1 (1 )(

),

))

1 (1HQ

HH QQ

QHL

d xQ yF

dx Q

xdQ yF

y

2 2( , ) ( , )MCgen

bbcBCCMCgen MCgen MCgen

cc l

bb

l

b

bb

Nx Q x Q

N N N

P

PP P

2( , )x Q measured inclusive reduced cross section

bin center correction to convert the bin average to x-Q2 point,cc bb

BCC

Pc , Pb , Pl defined for each x-Q2 interval

HEP2005, 21 July 2005 V. Chekelian, Charm and Beauty SF 11

Charm structure function F2

cc

lifetime results are consistent with H1 and ZEUS D* measurements

extention of H1 measurements to higher Q2

consistent with gluon from scaling violations

HEP2005, 21 July 2005 V. Chekelian, Charm and Beauty SF 12

Beauty reducedcross section

the first measurement of bb (and F2bb)

consistent with pQCD prediction

important for LHC experiments (e.g. bb->H)

bb

MRST04: VFNSCTEQ6HQ: VFNSCCFM: massive (BGF)

HEP2005, 21 July 2005 V. Chekelian, Charm and Beauty SF 13

F2cc vs Q2 F2

bb vs Q2

Scaling violations of F2cc, F2

bb are increasing with decreasing of x (similarly to F2)

Compared with NLO and NNLO QCD predictions:

’ the data are more precise than the spread of QCD predictions

HEP2005, 21 July 2005 V. Chekelian, Charm and Beauty SF 14

Cross section fractions2 2 2

2 2 2

( , )/

( , )

HQ HQHQ d d x Qf

dxdQ dxdQ x Q

Charm fraction fcc

- roughly constant with Q2

- slightly decreasing with x

- around 24% on average

Beauty fraction fbb - increases rapidly with Q2 from ~0.3% to ~3% (i.e. by a factor of 10)

fcc

fbb

Well described by MRST04 (VFNS)

HEP2005, 21 July 2005 V. Chekelian, Charm and Beauty SF 15

Charm and beauty structure functions F2cc and F2

bb are measured in the Q2 range from 12 GeV2 to 650 GeV2 using lifetime tagging (impact parameter method)

Charm contribution to F2 is around 24% on average

Beauty contribution to F2 changes from 0.3% to 3% F2

bb is measured for the first time

Both F2cc and F2

bb are well described by NLO/NNLO QCD

Summary

Large potential for HERA II:

H1: CST, FST, BST ZEUS: MVD (see talk of M. Corradi)