Direct di- Production @ Tevatron On behalf of the & Collaborations Liang HAN University of Science & Technology of China (USTC)

Direct di- Production @ Tevatron

On behalf of the & Collaborations

Liang HANUniversity of Science & Technology of China (USTC)

2010/03/13 L.Han@Moriond-QCD 2010

1st motivation: SM Higgs search@Tevatron

2

Searching for light Higgs(~130GeV)

“inaccessible” ggHbb, S/B(QCD) ~ 10-9

“common” qqbarW(l)/Z(ll,) + H(bb)

“extra” ggH,with Br(H) ~ 0.2%

Direct photon pair production at O(1)fb

Gluon-gluon fusion

W/Z associate

W fusion (VBF)

135GeV

Production 1. Gluon-gluon fusion ggH

2. W/Z associate qqW/Z+H

3. W fusion (VBF) qqqq+H


SM prediction on direct diphoton production

LO (2EM):

Quark annihilation:NLO (s2

EM): virtual + real emission infra-safe

(Box) (ISR)

Gluon fusion:LO (

s2EM): gluon PDF density enhancement at low mass

+

Fragmentation: FSR collinear singularity

+

• photon isolation • pT()<M()

Suppressed by:

(no theory)

3


2nd motivation: precise test of QCD predictions

RESBOS, Phys. Rev. D 76, 013009 (2007) :

+ Quark Scattering qqbar and Gluon Fusion gg up to NLO

+ Fragmentation at LO, with additional NLO approximation

+ Resummation of soft/collinear terms of initial gluons up to all orders, cancelling divergence at NLO as pT()0

DIPHOX, Eur. Phys. J. C 16, 311 (2000) :

+ qqbar up to NLO + gg at LO

+ Fragmentation up to NLO

+ asymmetry di-photon pT(pT()

PYTHIA, Comp. Phys. Comm. 135, 238(2001) :

+ qqbar and gg at LO

+ Resummation via parton shower

4


CDF results

First di- measurement @ Tevatron: 207pb-1, PRL 95, 022003 (2005)

pT(1)>14GeV, pT(2)>13GeV; |1,2|<0.9; ETiso<1GeV

• Bump of pT()~30GeV dominated by events of /2 and pT()>M(), described in DIPHOX as final state radiation + Fragmentation on the same quark

Reasonable agreements between data and QCD predictions in different region :

• Low pT ()~0GeV and , DIPHOX unstable due to the lack of resummation

)(1'21 Fragqqqqgg

5

DIPHOXRESBOSPYTHIA

M (GeV) pT (GeV) (rad)


• pT(1)>21GeV, pT(2)>20GeV, |1,2|<0.9, dR(1,2)>0.4

• Isolation requirement(jet and Fragmentation) + track veto(electron)

• pT()<M() remove Fragmentation, reduce theoretical uncertainty

• Neutral Network discriminator ONN to separate from EM-like jet

D0 analysis based on 4.2fb-1 data:

D0 di-photon measurement

6

Loose


Background composition

Electron misidentified in Drell-Yan Z/*ee :

• Estimated with GEANT simulation, normalized up to NNLO and 4.2fb-1

Jet-misidentified in +jet and jet+jet :

• Split data(Zee deducted) into 4 groups based on tighter ONN normalization

+ Npp : both pass+ Npf : leading passes, trailing fails+ Nfp : vice-versa+ Nff : both fail

N

N

N

N

E

N

N

N

N

j

j

jj

pp

pf

fp

ff

4×4 /j ONN>0.6 efficiency matrix

• Line shapes estimated by reversing ONN<0.1

7

Loose Tight


Theoretical predictions:+ RESBOS and DIPHOX, with CTEQ6.6M, R=F=f=M+ PYTHIA 6.420 with CTEQ5L

Data.vs.MC comparison:

• RESBOS with resummation demonstrates better agreement with data

• data shows harder pT() and excess in low ()

Differential cross section

8

M (GeV) (rad)pT (GeV) cos*=tanh[()/2]


Double-differential cross section:

• The pT() inconsistence occurs in M< 50GeV region, where the gluon fusion is significant. NNLO correction to gg at low mass?

9

• distributions tell the same story


Systematic uncertainty

• Dominated by uncertainty of di-photon purity, ~10-15%, followed by luminosity ~ 6%

• the accuracy is around O(1)fb, statistics are close to systematic

10


Impact on Higgs search Reducible background (Zee, +j, jj)subtracted, sideband fitting into signal region Combine all signal channels (ggH, W/Z+H, VBF) to increase sensitivity

D0:

CDF:

11


Summary

Direct di- production at Tevatron has been studied both by CDF and D0

• DIPHOX treats the Fragmentation better; impose pT()<M() would reduce the discrepancy to RESBOS;

•RESBOS, with NLO gg, gives the best agreement with data; hints the need of NNLO corrections for low mass region (<50GeV)

Data are compared with theoretical predictions, RESBOS, DIPHOX and PYTHIA. None of these calculations provides full description of data in all kinematic regions.

Provide extra the sensitivity to SM Higgs search in the most interested mass region ~130GeV

12


Backup Slides

13


CDF & DØ

Preshower: to distinguish vs. neutral jets

Calorimeter : fine granularity and good energy resolution

)2.0(4.0

T

dR

iT

isoT EEE

• CDF : •D0 :

Isolation requirement to suppress fragmentation

• D0 : lead + scintillating strip Central Preshower (CPS)• CDF : Preshower detector + shower maximal CES

Shower shape difference between single and multi- from neutral hadron (e.g. 0)

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FSR

ISR

15

Loose

+ Input : Preshower & Calorimeter shower shapes + tracker activities

+ Training : MC EM-like jet vs. + Validation : data ZllFSR


Double-differential cross section:

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2010/03/13 L.Han@Moriond-QCD 2010 17

Documents

Direct di- Production @ Tevatron On behalf of the & Collaborations Liang HAN University of Science & Technology of China (USTC)