Electroweak physics and QCD in the forward direction at...

Electroweak physics and QCD in the forward direction at LHCb

Victor Coco, on behalf of the LHCb Collaboration

University of Cincinnati

March 22, 2016

Rencontres de Moriond - QCD and High Energy Interactions50th anniversary meeting

LHCb and the forward region

Complementary to central detectors

I Low pT , low mass triggersI Interesting domain of phase space for MPI

studiesI J/ψC , CC [JHEP 06 (2012) 141]I ΥC [LHCb-PAPER-2015-046]

I Low pile-up environmentI Allow studies of central exclusive productionI J/ψ and ψ(2S) CEP [JPG41 (2013) 055002].I Double Charmonium [JPG 41(2014)115002]I Upsilon CEP [JHEP 09 (2015) 084]

I Forward region: high/low-x partons involved:I Heavy flavour production:

large impact on low-x gluonI W/Z production:

large impact on u/d PDFs.

I Outline:I W,Z inclusive production @ 7,8,13 TeVI AFB and sin2(θw )I W,Z+jet production @ 8 TeVI W+(b,c)-jet production @ 7,8 TeV

Victor Coco, on behalf of the LHCb Collaboration Electroweak physics and QCD in the forward direction at LHCb March 22, 2016 1 / 16

http://cds.cern.ch/record/1446466?ln=en

https://cds.cern.ch/record/2061215



https://cds.cern.ch/record/2020686/files/arXiv:1505.08139.pdf

LHCb detector2008 JINST 3 S08005

I Designed for CP violation studies in b and c hadrons decays and their rare decays.

I Single arm spectrometer, ∼ 30% of bb pairs produced in the acceptance.

I Fully instrumented forward 2 < η < 4.5

I Excellent tracking and vertexing performances

I Particle identification through RICH, Calorimeter and Muon chambers


http://iopscience.iop.org/1748-0221/3/08/S08005

LHCb detector2008 JINST 3 S08005

I During Run I, pp collisions:I 1 fb−1 @

√s = 7 TeV ,

I 2 fb−1 @√

s = 8 TeV .

I RunII: Expect ∼ 5 fb−1 @√

s = 13 TeV .I 320 pb−1 recorded in 2015.

I Luminosity levelling

→ Stable average pile-up ∼ 2

I Luminosity measurement combines Van der MeerScan and Beam Gas Imaging [JINST 9(2014)12005]

→ 1.7% uncertainty in 2011 and 1.2% in 2012


http://iopscience.iop.org/1748-0221/3/08/S08005


Inclusive W and Z production at√s = 7, 8, 13 TeV

I @ 7 TeVI W (µν) [JHEP 12 (2014) 079]I Z(µµ) [JHEP 08 (2015) 039],I Z(ee) [JHEP 02 (2013) 106]

I @ 8 TeVI Z(ee) [JHEP 05 (2015) 109]I W (µν), Z(µµ)[JHEP 01 (2016) 155]

I @ 13 TeV *NEW*I Z(µµ) LHCb-CONF-2016-002

I Muon final statepTµ > 20 GeV ,2.0 < ηµ < 4.5

I W sample purity ∼ 79%:

I Z sample purity > 99%

I Efficiencies from tag-and-probemethods.

]c [GeV/µT

p)c

Can

dida

tes

/ (1

GeV

/

20000

40000

60000

= 8 TeVsLHCb +µ −µ < 4.5µη2.0 <

Data QCD

Fit Electroweak

νµ→W Heavy flavour

]c [GeV/µT

p

Dat

a/Fi

t

0.80.9

11.11.2

20 30 40 50 60 70 20 30 40 50 60 70








Inclusive Z production

JHEP 01 (2016) 155

NNLO fixed order FEWZ LHCb-CONF-2016-002

I Total uncertainty on the cross section:I @ 8 TeV 1.79% dominated by luminosity

and beam energy.I @ 13 TeV 4.6% dominated by luminosity

(3.9%).

I Good agreement of the total cross sectionwith NNLO predictions.

I Good agreement of the differentialdistributions (y(Z),pT (Z),φ∗(Z))


Inclusive W production[JHEP 01 (2016) 155]

[pb]

µ η/d νµ

→W

σd

200

400

600

800

1000= 8 TeVsLHCb,

)+W(statData CT14

)+W(totData MMHT14

)−W(statData NNPDF30

)−W(totData CT10

ABM12

HERA15

c> 20 GeV/µT

p

µη2 2.5 3 3.5 4 4.5T

heor

y/D

ata

µη

0.91

1.1

0.91

1.1

NNLO fixed order (FEWZ)

µη

µA

0.4−

0.2−

0

0.2

0.4 = 8 TeVsLHCb,

statData CT14

totData MMHT14NNPDF30CT10ABM12HERA15

c > 20 GeV/µT

p

µη2 2.5 3 3.5 4 4.5T

heor

y-D

ata

0.04−0.02−

00.020.04

I Total uncertainty on the cross-section ∼ 1.6% :I dominated by luminosity and beam energy.I other systematic uncertainties sums up to ∼ 0.65%.

I Good agreement of the total cross-section with NNLO predictions.

I Good agreement with prediction from various PDF sets



Cross section Ratios[JHEP 01 (2016) 155]

I Cancellation of many experimental uncertainties in the ratios

I Dominated by W purity and tracking uncertainties (total 0.5-0.7%)

I Sensitivity to PDFs



Dependency to√s

[JHEP 01 (2016) 155]

LHCb

statData

totData

CT14

MMHT14

NNPDF30

CT10

ABM12

HERA15

c > 20 GeV/µT

p

< 4.5µη2.0 < 2c < 120 GeV/µµM: 60 < Z

1.15 1.2 1.25 1.3 1.35 7TeV−µ+µ→Zσ

8TeV−µ+µ→Zσ

1.15 1.2 1.25 1.3 1.35 7TeVν+µ→+W

σ

8TeVν+µ→+W

σ

1.1 1.15 1.2 1.25 1.3 7TeVν−µ→−

Wσ

8TeVν−µ→−

Wσ

LHCb

statData

totData

CT14

MMHT14

NNPDF30

CT10

ABM12

HERA15

c > 20 GeV/µT

p

< 4.5µη2.0 < 2c < 120 GeV/µµM: 60 < Z

0.94 0.96 0.98 1 1.02 1.04 8TeV−µ+µ→Zσ

7TeV−µ+µ→Zσ

7TeVν+µ→+W

σ

8TeVν+µ→+W

σ

0.9 0.92 0.94 0.96 0.98 1 8TeV−µ+µ→Zσ

7TeV−µ+µ→Zσ

7TeVν−µ→−

Wσ

8TeVν−µ→−

Wσ

0.92 0.94 0.96 0.98 1 1.02 8TeV−µ+µ→Zσ

7TeV−µ+µ→Zσ

7TeVνµ→Wσ

8TeVνµ→Wσ

1 1.02 1.04 1.06 1.08 1.1 8TeVν−µ→−

Wσ

7TeVν−µ→−

Wσ

7TeVν+µ→+W

σ

8TeVν+µ→+W

σ

I PDF uncertainties largely cancel in 8/7 TeV ratio.

I Cancellation of the luminosity uncertainties in the ratios of ratio.

I Provide precise test of the pQCD.



AFB and sin2θw[JHEP 11 (2015) 190]

I AFB in qq → Z/γ∗ → `` is sensitiveto the effective weak mixing angle.

I Large asymmetry of u/u and d/dPDFs gives better knowledge of thequark-antiquark direction

→ larger AFB in the forward region

I Same selection than for inclusiveZ → µµ measurement.

I AFB = f (mµµ) unfolded for detectoreffects.

I Main uncertainty from momentumscale calibration.


.

AFB and sin2θw[JHEP 11 (2015) 190]

I AFB = f (mµµ) templates with different sin2θw values generated usingPowheg+Pythia

effWθ2sin

0.228 0.229 0.23 0.231 0.232 0.233 0.234 0.235

2 min

χ -

2 χ

0

2

4

6

8

10Combined

= 7 TeVs = 8 TeVs

LHCb

effWθ2sin

0.224 0.226 0.228 0.23 0.232 0.234effWθ2sin

0.224 0.226 0.228 0.23 0.232 0.234

0.0002±0.2315

0.0003±0.2322

0.0003±0.2310

0.0010±0.2315

0.0005±0.2315

0.0032±0.2287

0.0012±0.2308

0.0011±0.2314

LEP + SLD

(b)FBLEP A

LRSLD A

D0

CDF

ATLAS

CMS

LHCb

Phys. Rept. 427 (2006) 257

Phys. Rept. 427 (2006) 257

Phys. Rev. Lett. 84 (2000) 5945

Phys. Rev. Lett. 115 (2015) 041801

Phys. Rev. D 89 (2014) 072005

JHEP 09 (2015) 049

Phys. Rev. D 84 (2011) 112002

JHEP 11 (2015) 190

I Largest theory uncertainty from template fit due to PDFs:

→ will improve in the next years with production measurements.

I Statistically limited:

→ Run II should provide 4 times more statistics.



W,Z plus jet production at√s = 8 TeV *NEW*

[PAPER-2016-011]

I Sensitive to high-x u/d PDFs and to higher order pQCD effects.

I Particle Flow jets build with anti-kT , R=0.5.

I Leading jet with pT > 20 GeV , 2.2 < η < 4.2I For Wj final state:

I pT (jµ + j) > 20 GeV to reduce the QCD background.I signal from fit of isolation pT (µ)/pT (jµ)

Preliminary Preliminary

I Backgrounds from:I multi-jets 30-70%, templates from data.I electroweak processes 5-10%, templates from simulation, corrected and normalised

using data-driven methods




[PAPER-2016-011]

stat. syst. lumi.[JHEP 07(2014)079]

[JHEP 01(2011)095][JHEP 06(2010)043]Preliminary

I Total cross-section and ratios in agreement with NLO calculation.

I Uncertainties dominated by W purity fit (2-7%) and Jet energy scale (3-10%)


.


Preliminary Preliminary Preliminary

Preliminary PreliminaryPreliminary

I Good agreement of differential distributions with NLO+LL predictions.

I Largest theoretical uncertainty from re-normalisation and factorisation scale.



[PAPER-2016-011]

Preliminary Preliminary

I Dominant prediction uncertainty due to PDFs.

I With Run II statistics expect to reduce d-quark PDF uncertainties by up to 30%at x ∼ 0.7 [arXiv:1505.01399]


.

http://arxiv.org/abs/1505.01399

Measurement of W + (b, c)-jet ratios and asymmetries[PRD92 (2015) 052001]

I W+c sensitive to s-quark PDF for Q ∼ 100 GeV and x down to 10−5

I Same selection as in previous measurement, (b,c)-jets identification from [JINST 10 P06013]

I A(Wq) = σ(W +q)−σ(W−q)

σ(W +q)+σ(W−q).

I Main uncertainties from heavy flavour fraction determination (5-10%), tagging efficiency(10%), isolation fit (4-10%), and for W + b the Top background (13%)

I Predictions @NLO: MCFM[PRD62(00)114012] and CT10 PDF set,[PRD82(10)074024].

c-jets c-jetsb-jets b-jets

(Wx)

0.2−

0

0.2

0.4

0.6

0.8

100

×(W

j)σ

(Wx)/

σ

0

1

2

3

4

5

6

7

8

c-jets c-jetsb-jets b-jets

LHCb measurement

SM Prediction

I Overall good agreement with NLO predictions.

I |A(Wc)| is 2σ lower than predictions using CT10 PDFs.



.

http://arxiv.org/abs/hep-ph/0006304


Outlook

I Large program of QCD and EW measurements involving vector boson production.

I Constraints on PDFs and test of pQCD predictions.

I First measurement of W,Z+jet just released.

I Measurements can be extended with heavy flavour jets.

Already performed Z+b @ 7 TeV[JHEP 01(2015)064],W+(b,c)-jet @ 7,8 TeV [PRD 92(2015)052001]

and Top production [PRL 115(2015)112001]

I Analysis of 13 TeV data on-going.


https://cds.cern.ch/record/1967222?ln=en


https://cds.cern.ch/record/2021262?ln=en

BACKUP


Predictions


Inclusive W and Z production at√s = 7, 8 TeV



Source Uncertainty [%]RW± RW+ RW− RW

Statistical 0.30 0.33 0.36 0.31Purity 0.25 0.35 0.30 0.30

Tracking 0.05 0.22 0.24 0.23Identification 0.01 0.11 0.11 0.11

Trigger 0.04 0.10 0.09 0.09GEC 0.13 0.22 0.23 0.21

Selection 0.10 0.24 0.24 0.23Acceptance and FSR 0.21 0.21 0.19 0.17

Systematic 0.37 0.59 0.56 0.54Beam energy 0.14 0.15 0.29 0.21

Total 0.50 0.69 0.73 0.66



Source Uncertainty [%]

R8/7W+ R

8/7W− R

8/7Z R

8/7RW± R

8/7RW+

R8/7RW− R

8/7RW

Statistical 0.30 0.37 0.49 0.48 0.58 0.62 0.55Purity 0.41 0.45 — 0.65 0.41 0.45 0.29

Tracking 0.33 0.27 0.53 0.09 0.23 0.26 0.24Identification 0.07 0.07 0.13 0.03 0.07 0.06 0.07

Trigger 0.27 0.25 0.09 0.08 0.19 0.16 0.17GEC 0.15 0.14 0.09 0.07 0.09 0.09 0.08

Selection 0.17 0.17 — 0.04 0.17 0.17 0.16Acceptance and FSR 0.05 0.06 0.04 0.08 0.07 0.07 0.06

Systematic 0.64 0.63 0.56 0.66 0.55 0.59 0.46Beam energy 0.06 0.05 0.10 — 0.04 0.05 0.05Luminosity 1.45 1.45 1.45 — — — —

Total 1.61 1.62 1.63 0.82 0.80 0.86 0.72


Z production at√s = 13 TeV


AFB and sin2θw

Source of uncertainty√

s = 7 TeV√

s = 8 TeVcurvature/momentum scale 0.0102 0.0050

data/simulation mass resolution 0.0032 0.0025unfolding parameter 0.0033 0.0009

unfolding bias 0.0025 0.0025

Uncertainty average ∆|ApredFB |

PDF 0.0062scale 0.0040αs 0.0030

FSR 0.0016


b and c jet tagging @ LHCb[JINST 10 P06013]

I Inclusive SV reconstruction: light jet mistag rate well below 1%

for b tag efficiency ∼ 65%, c tag efficiency ∼ 25%.

I SV properties (displacement, kinematics, mulitplicity,...) and jet propertiescombined in two BDTs.

I BDTbc|udsg optimised for heavy flavour versus light discrimination.I BDTb|c optimised for b versus c discrimination.

)udsg|bcBDT(-1 -0.5 0 0.5 1

)c|bB

DT

(

-1

-0.5

0

0.5

1

LHCb simulation

-jetsb

)udsg|bcBDT(-1 -0.5 0 0.5 1

)c|bB

DT

(

-1

-0.5

0

0.5

1

LHCb simulation

-jetsc

)udsg|bcBDT(-1 -0.5 0 0.5 1

)c|bB

DT

(

-1

-0.5

0

0.5

1

LHCb simulation

-jetsudsg

I Enrich the sample by cut or extract the flavour content from 2D fit of the BDTs.



Top production in the forward regionCross section measurements

PRL 115 (2015) 112001

I The observed excess above Wb prediction is used to measure σ(tt + t + t).

σ(top)[7 TeV ] = 239± 53(stat)± 33(syst)± 24(theory) fbσ(top)[8 TeV ] = 289± 43(stat)± 40(syst)± 29(theory) fb

I b-tagging, jet energy scale and isolation fit related uncertainties dominates thesystematics uncertainties.

) [GeV]b+µ(Tp

)W+b

(N

0

100

200Data

+topWbWb

LHCb

20 45 70 95 ∞(top) [fb]σ

100 200 300 400

7TeV

8TeV

LHCbMCFM (NLO)

Figure 4: From Ref. [4]: (left) Yield of the W + b final state vs transverse component of thesum of the muon and b-jet momenta. The SM prediction obtained using MCFM at NLO isshown with (Wb+top) and without (Wb) a top quark contribution. (right) Comparison ofthe measured and SM predicted cross sections for �(top) ⌘ �(tt + t + t). The LHCb errorbars include statistical, experimental systematic, and theory uncertainties.

trigger stage one (HLT1). The output rate of HLT1 is about 150 kHz. Finally, the full trackreconstruction is run on events selected by HLT1; this is HLT2. Phil and I re-optimized theHLT1 single-displaced-track trigger for Run 2 to make it more e�cient for b- and c-hadrondecays – and for many BSM scenarios. We also worked with Tatiana Likhomanenko andAndrey Ustyuzhanin (Yandex Corporation) to develop a new HLT1 secondary-vertex-basedalgorithm that significantly enhances the e�ciency for charm physics. Furthermore, we re-optimized the inclusive b trigger used in HLT2. The vast majority of LHCb papers producedusing Run 2 data will use our HLT1 trigger(s), while most will use our HLT2 trigger.

4.1.8 Other NSF-Supported Work

QCD Factorization

I worked with two MIT undergraduate students (Aviv Cukierman and Connor Dorothy) tomeasure a collection of b-hadron decay ratios involving both b mesons and baryons. Thiswork – published in PRL [6] – provided a number useful tests of QCD factorization, alongwith the most precise measurement of the mass of a b baryon (useful for building/testinghadronic models).

Z Boson Production

Phil worked with J. Anderson and K. Muller (Zurich), S. Bifani (Birmingham), S. Farry(Liverpool), and R. Wallace (University College Dublin) to measure the Z boson productioncross section in the forward region at

ps = 7 TeV [9]. The precision achieved is about 2%

(to our knowledge, this is the most precise cross section measurement made at a hadroncollider), which permits placing important constraints on proton PDFs. The ratio of Wboson to Z boson production cross sections was also measured with a precision of betterthan 1%.

Cross sections at√

s = 7, 8 TeVare consistent with NLO SM predictions.



Double parton scattering

I The ”simple” paradigm:I Independent hard scattering processes.

I Assuming factorisation of the double PDF: σABDPS =

δA,B2

σASPSσ

BSPS

σeff .

I σeff assumed to be a energy and process independent factor.

I Experimental tests:I Is σeff really universal?

I Is the ”pocket formula” for σABDPS always valid?


DPS studies @ LHCbJ/ψC , CC [JHEP 06 (2012) 141, JHEP 03(2014)108] and ΥC LHCb-PAPER-2015-046

I Production of multiple heavy flavour: pQCD (SPS), double parton scatt. (DPS)

I Measurement of J/ψC , CC , ΥC production with:

I J/ψ → µµ, Υ→ µµI C = D0(K−π+),D+(K−π+π+),D+

s (K−K +π+), Λ+c (pK−π+)

I Expect 1− 6% contribution from SPS.

9 9.5 10 10.5 110

50

100

150

200

250

300

1.82 1.84 1.86 1.88 1.9 1.920

50

100

150

200

250

1.82 1.84 1.86 1.88 1.9 1.920

10

20

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100

1.82 1.84 1.86 1.88 1.9 1.920

10

20

30

40

50

60

70

80C

andid

ates

/(20

MeV/c

2)

Can

did

ates

/(2

MeV/c

2)

Can

did

ates

/(2

MeV/c

2)

Can

did

ates

/(2

MeV/c

2)

mµ+µ−[GeV/c2

]mK−π+

[GeV/c2

]

mK−π+

[GeV/c2

]mK−π+

[GeV/c2

]

a)LHCbΥD0 b)

LHCbΥ(1S)D0

c)LHCbΥ(2S)D0 d)

LHCbΥ(3S)D0



.

ΥC production @√s = 7, 8 TeV

Cross section and ratios LHCb-PAPER-2015-046

I Cross section in good agreement with DPS expectations.

predictionmeasurement

I Ratios show clear excess with respect to SPS contribution.

SPS

Fragmen

tation

fracti

on

prediction

measurement

I Other ratios lead to the same conclusionσ

Υ(1S)D0

σΥ(1S)D+∼ σ

D0

σD+or

σΥ(2S)D+

σΥ(1S)D+∼ σΥ(2S)

σΥ(1S)


ΥC production @√s = 7, 8 TeV

Differential cross sections LHCb-PAPER-2015-046

I Predictions assumes uncorrelated production of Υ(1S) and D0.

I Deduced from open charm production measurement and Υ measurement

I Good agreement with DPS expectation.


σeff and the DPS pocket formula

I Excellent agreement between J/ψCand ΥC

I Agreement with γ + 3j and W + 2j

I Slight tension with J/ψJ/ψ andJ/ψΥ at 1.96 TeV .

I Will be interesting to compare withRunII results at 13 TeV .

I (W ,Z) + C allow to probe a differentkinematic range

I Z+C @√

s = 7 TeV was observed atLHCb, [JHEP 1404(2014)91]

I Not enough data to disentangle SPSfrom DPS at RunI

Supplementary material for LHCb-PAPER-2015-046

0 10 20 30 40 50

σeff [mb]

AFS, 4 jets, pp,√s = 63 GeV (no errors)

UA2, 4 jets, pp,√s = 630 GeV (lower limit)

CDF, 4 jets, pp,√s = 1.8 TeV

CDF, γ/π0+3 jets, pp,√s = 1.8 TeV

D0, J/ψΥ, pp,√s = 1.96 TeV

D0, J/ψJ/ψ , pp,√s = 1.96 TeV

D0, γ+ b/c+2 jets,pp,√s = 1.96 TeV

D0, γ+3 jets, pp,√s = 1.96 TeV

D0, γ+3 jets, pp,√s = 1.96 TeV

ATLAS, Z + J/ψ , pp,√s = 7 TeV (lower limit)

ATLAS, 4 jets, pp,√s = 7 TeV

ATLAS, W+2 jets, pp,√s = 7 TeV

CMS+Lansberg,Shao, J/ψJ/ψ , pp,√s = 7 TeV

CMS, W+2 jets, pp,√s = 7 TeV

LHCb, J/ψD0, pp,√s = 7 TeV

LHCb, J/ψD+, pp,√s = 7 TeV

LHCb, J/ψD+s , pp,

√s = 7 TeV

LHCb, J/ψΛ+c , pp,

√s = 7 TeV

LHCb, Υ(1S)D0 , pp,√s = 7 TeV

LHCb, Υ(1S)D+ , pp,√s = 7 TeV

LHCb, Υ(1S)D0,+, pp,√s = 7 TeV

LHCb, Υ(1S)D0 , pp,√s = 8 TeV

LHCb, Υ(1S)D+ , pp,√s = 8 TeV

LHCb, Υ(1S)D0,+, pp,√s = 8 TeV

LHCb, Υ(1S)D0,+, pp,√s = 7&8 TeV

Figure 1: Summary of recent measurements of the effective DPS cross-section σeff [1–16] Whentwo error bars are shown, the inner error bars indicate the statistical uncertainty whilst the outererror bars indicate the sum in quadrature of the statistical and systematic uncertainties.Victor Coco, on behalf of the LHCb Collaboration Electroweak physics and QCD in the forward direction at LHCb March 22, 2016 30 / 16

Central exclusive productionMotivation

I p + p → p + X + p with exchange of a colourless objects (γ or Pomeron).

(DPE)

I Laboratory at the interface between soft (non-perturbative) and hard(perturbative) QCD.

I Sensitive to very low-x gluon PDF (down to x ∼ 10−5) where saturation effectsoccurs.

I Very clean experimental environment which can allow spectroscopy studies(exotic quarkonia, glueball,...)


Central exclusive production @ LHCbExperimental challenge

I Data taking with luminosity levelling

→ for Run I stable average pile-up ∼ 2, ∼ 20% single pp interaction.

I X detected in the LHCb detector, and requires a rapidity gap

→ No other activity in LHCb. Backward coverage from VELO −3.5 < η < −1.5.

I Several measurement performed during Run I:I J/ψ and ψ(2S) production through γP exchange JPG41 (2013) 055002.I χc (0, 1, 2) production through PP exchange LHCb-CONF-2011-022.I Non-resonant di-µ production through γγ exchange LHCb-CONF-2011-022.I Double Charmonium in CEP JPG 41(2014)115002


Central exclusive production @ LHCbUpsilon CEP JHEP 09 (2015) 084

I Two well reconstructed µ.

I Rapidity gap: No other tracksbackward or forward.

I Fit of the p2T of the di-µ candidate

after subtraction of thenon-resonnant contribution.

I Exclusive Y (nS) and feed-downχb(mP) shapes from SuperChiCEPJC 69(2010)179.

I Inelastic background assumedexponential.

I CEP represent 54± 11% of theΥ(nS) production.

I Dominant uncertainty from χb(mP)p2

T description and description ofexclusive signal.



Central exclusive production @ LHCbUpsilon CEP JHEP 09 (2015) 084

I Cross section average for 7 and 8 TeV:

I Sensitive to a region of W (γp c.m.e) where the LO 6= NLO predictions diverge.

I NLO predictions agree with data well [JHEP 1311 (2013) 085]

I Reasonable agreement with models varying the Υ wave function and t-channelexchange.




Central exclusive production @ LHCbHerschel

I Limitation from inelastic background with activity outside of LHCb:

→ Need to increase the rapidity gap coverage

I High Rapidity Shower Counter for LHCb (HeRSCheL) installed during TS1.

I Increases the tagging of rapidity gap by 6 units of rapidity (5 < |η| < 8).

I Five stations located along the beamline, 2 in the forward (F) LHCb region and 3in the backward (B).


Central exclusive production @ LHCbHerschel

I All stations installed and readout system included in the LHCb DAQ system.

I Tested during 50ns and 25ns intensity ramp-up.

I Took > 90% of the RunII pp collisions with LHCb, as well as the AA run.

Mix of triggered events (∼ 7 pb−1). Inclusive, single diffractive and double diffractiveenriched contributions are visible.

HeR

SC

heL

Pre

lim

inar

y Inclusive

SD EnrichedSD

Enri

ched

CEP Enriched

HeR

SC

heL

Pre

lim

inar

y


A glimpse through RAW dataHerschel versus VeLo

Sum ADC B side0 5000 10000

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1HeRSCheL PreliminaryHeRSCheL Preliminary

# v

elo

trac

ks

in -

3.5

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.9I Visible correlation between VeLo activity and Herschel activity.

I Still large Herschel activity in events with ”signal-like” topology in LHCb (lowactivity).


A glimpse through RAW dataResponse to ”signal”-like events

I Optimised settings to minimize the spillover effect.

I First ”empty-empty” bunch after a ”beam-beam” train:

→ shape of the signal (event with no activity).

B0 B1 B2

F1 F2

Random trigger on bb crossing First empty crossing after a bb train

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Electroweak physics and QCD in the forward direction at...

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