new dynamics in parton distributions at a 100 tev hadron collider

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Parton Distributions at a 100 TeV Hadron Collider Juan Rojo CERN, PH Division, TH Unit Future Circular Colliders Kick-off Meeting Geneva, 14.02.2014 Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

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LHC, high-energy physics, QCD, Higgs Boson

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Page 1: New dynamics in parton distributions at a 100 TeV hadron collider

Parton Distributions at a 100 TeV Hadron Collider

Juan RojoCERN, PH Division, TH Unit

Future Circular Colliders Kick-off MeetingGeneva, 14.02.2014

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 2: New dynamics in parton distributions at a 100 TeV hadron collider

Exploratory first study on the role of Parton Distributions at a Future Circular Collider with CoM of 100 TeV

Concentrate on the basic results, avoid technical details (choice of PDF set etc), and explore the new qualitative features of PDFs at the FCC

Outline of this talk: Kinematic coverage from LHC 14 TeV to FCC 100 TeV PDF luminosities from 14 to 100 TeV New qualitative features of PDF in 100 TeV collisions: top-quark PDFs, LO

small-x PDFs, Electroweak corrections, high-energy BFKL resummation Physics case for polarized collisions at the FCC

2 Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 3: New dynamics in parton distributions at a 100 TeV hadron collider

Kinematic Coverage andPDF Luminosities:

From LHC14 to FCC100

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 4: New dynamics in parton distributions at a 100 TeV hadron collider

At Born level, for the production of a particle at rapidity y with mass M, the PDFs are evaluated at

Going from Ecm=14 TeV to Ecm=100 TeV, for a given M and y knowledge of PDFs at smaller x is required:

x1,20( �S=100 TeV ) = 0.14 x1,20( �S=14 TeV )

In addition, for fixed M, the increased range in y allows to prove even further smaller x

Conversely, fixing x1,20 and y, the increased center of mass energy implies that higher masses will be probed:

M( �S=100 TeV ) = 7.14 M( �S=14 TeV )

But recall that hadronic cross-sections fall as 1/M2 so this is not how BSM mass reach scales!

Some consequences:

For Higgs and SM probes (tt, W, Z), PDFs will be proved (at least) one order of magnitude smaller x

For possible new high-mass particles of mass M, large-x PDFs (required at 14 TeV) turn into medium-x PDFs (at 100 TeV), not only leading to larger cross-sections but with less uncertainties

For small masses M, a completely new kinematical range opens that has never been explored

4 Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 5: New dynamics in parton distributions at a 100 TeV hadron collider

5

x-1010 -910 -810 -710 -610 -510 -410 -310 -210 -110

( G

eV )

XM

1

10

210

310

410

510

Kinematics of a 100 TeV FCC

y=0y=-4y=-8 y=4 y=8

FCC 100 TeV

LHC 14 TeV

Plot by J. Rojo, Dec 2013Kinematics of a 100 TeV FCC

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 6: New dynamics in parton distributions at a 100 TeV hadron collider

6

x-1010 -910 -810 -710 -610 -510 -410 -310 -210 -110

( G

eV )

XM

1

10

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Kinematics of a 100 TeV FCC

y=0y=-4y=-8 y=4 y=8

FCC 100 TeV

LHC 14 TeV

Plot by J. Rojo, Dec 2013Kinematics of a 100 TeV FCC

DY, low-pt jets

W,Z

Higgs, top

2 TeV squarks

20 TeV Z’

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 7: New dynamics in parton distributions at a 100 TeV hadron collider

7

x-1010 -910 -810 -710 -610 -510 -410 -310 -210 -110

( G

eV )

XM

1

10

210

310

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510

Kinematics of a 100 TeV FCC

y=0y=-4y=-8 y=4 y=8

FCC 100 TeV

LHC 14 TeV

Plot by J. Rojo, Dec 2013Kinematics of a 100 TeV FCC

x-510 -410 -310 -210 -110 1

]2 [

GeV

2 T /

p2

/ M

2Q

1

10

210

310

410

510

610

710NMC-pdNMCSLACBCDMSHERAI-AVCHORUSFLH108NTVDMNZEUS-H2ZEUSF2CH1F2CDYE605DYE886CDFWASYCDFZRAPD0ZRAPCDFR2KTD0R2CONATLAS-WZ-36pbCMS-WEASY-840PBLHCB-WZ-36pbATLAS-JETS-10

NNPDF2.3 dataset

Compare kinematical coverage to that of the NNPDF2.3 set:

Current PDF determinations have essentially no constraints for x < 10-4

The region of masses for M>1 TeV also unconstrained: rely on DGLAP evolution extrapolation

Poor constraints on high-x PDFs, relevant for high masses M For M > 10 GeV, constraints from HERA only available for x > 10-3

Global PDF fits rely on QCD evolution, but EW effects will be required in multi-TeV region

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 8: New dynamics in parton distributions at a 100 TeV hadron collider

[ GeV ]X M210 310 410

PDF

lum

inos

ity ra

tio 1

00 T

eV /

14 T

eV

1

10

210

310

410

510

610

710

810

100 TeV vs 14 TeV PDF Luminosities, NNPDF2.3 NNLO100 TeV vs 14 TeV PDF Luminosities, NNPDF2.3 NNLO

8

Compare the ratio of PDF luminosities between 100 TeV and 14 TeV in different channels as a function of the final state mass

gg lumi ratio For final state masses M < 1 TeV moderate increase in PDF luminosity, between a factor 10 and 100

For M > 1 TeV, much steeper increase (since 14 TeV lumis damped by large-x PDFs), up to a factor 108 for M = 10 TeV

Qualitative similar behavior for other PDF luminosities

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 9: New dynamics in parton distributions at a 100 TeV hadron collider

New qualitative features of PDFs in 100 TeV collisions

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 10: New dynamics in parton distributions at a 100 TeV hadron collider

10

At FCC100, the production of 100 GeV particles might require knowledge of PDFs down to x=1e-6, 1e-7, depending on acceptance

For other processes, both perturbative (low mass Drell-Yan, Quarkonium production, low pt photons and jets) and non-perturbative (Underlying Event, Minimum Bias) we need PDFs down to x=1e-8, 1e-9

Compare various PDFs at very small x out of the box using LHAPDF5.9.0: small-x PDFs frozen between 1e-6 and 1e-8 depending on the PDF set

x -910 -810 -710 -610 -510 -410 -310

)2x

g ( x

, Q

210

310

410

Small-x NNLO PDFs for FCC studies

NNPDF2.3CT10cteq6MSTW08

Small-x NNLO PDFs for FCC studies

x -910 -810 -710 -610 -510 -410 -310

)2x

u ( x

, Q

210

310

410

Small-x NNLO PDFs for FCC studies

NNPDF2.3CT10cteq6MSTW08

Small-x NNLO PDFs for FCC studies

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 11: New dynamics in parton distributions at a 100 TeV hadron collider

11

This is not a fundamental problem: is easy enough to provide a extrapolation down to very small-x ...

... but this extrapolation must be driven by theory + methodology, since no data available

The NNPDF2.3LO set can be extrapolated down to 1e-9 using the neural network extrapolation: huge PDF uncertainties, but central values turn out to have a reasonable behavior

NNPDF2.3LO PDF set is already available as standalone code in Pythia8, where there is an ongoing tuning effort. Torbjorn has been using it to provide UE predictions for FCC finding reasonable results

x-910 -810 -710 -610 -510 -410 -310 -210 -110 1

0

100

200

300

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500xg(x,Q), NNPDF23_lo_as_0119_qed.LHgrid members

MembersCentral valueStd. deviation68% c.l.Q = 1.41 GeV

Gen

erat

ed b

y A

PFEL

2.0.

0: V

.Ber

tone

, S.C

arra

zza,

J.R

ojo

(arX

iv:1

310.

1394

)

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 12: New dynamics in parton distributions at a 100 TeV hadron collider

12

In the Variable-Flavor-Number (VFN) scheme, heavy quark PDFs for charm and bottom are generated radiatively from the gluon PDF

For very high-mass production at a 100 TeV FCC, the top quark can be considered as approximately massless, and thus we need to generate a top quark PDF t(x,Q) just as we have a charm and bottom PDF

Note that missing the top PDF also feeds back into all other PDFs due to the different DGLAP evolution

]2 [ GeV2Q10 210 310 410

)2xg

(x, Q

0.85

0.9

0.95

1

1.05

1.1

1.15

-2Ratio to NNPDF2.1 GM-VFN, x=10

NNPDF2.1

=3FNNPDF2.1 FFN N

=4FNNPDF2.1 FFN N

-2Ratio to NNPDF2.1 GM-VFN, x=10

]2 [ GeV2Q10 210 310 410

)2 (x

, Q�x

0.7

0.8

0.9

1

1.1

1.2

-2Ratio to NNPDF2.1 GM-VFN, x=10

NNPDF2.1

=3FNNPDF2.1 FFN N

=4FNNPDF2.1 FFN N

-2Ratio to NNPDF2.1 GM-VFN, x=10

missing charm

missing charm

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 13: New dynamics in parton distributions at a 100 TeV hadron collider

13

Currently, only the NNPDF Collaboration provides sets with top quark PDF included (as well as sets in the other VFN schemes, NF=3, NF=4 and NF=5)

At 10 TeV, the top quark PDF t(x,Q) is only a factor 2 smaller that all other quark PDFs (charm and bottom are very close to light quark PDFs): should be included in theoretical predictions

x -510 -410 -310 -210 -110

= 1

0 Te

V )

2x

PDF

( x, Q

-110

1

10

210

= 6FNNPDF2.3 NNLO N

GluonUpCharmBottomTop

= 6FNNPDF2.3 NNLO N

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Gluon PDF

Top PDF

Up quark PDF

Page 14: New dynamics in parton distributions at a 100 TeV hadron collider

14

As mentioned in the case of top quark, when Q >> mt it makes sense computationally to resum large collinear-like logarithms into a top PDF

With a similar motivation, it might be efficient to resum multiple initial state emissions of W and Z bosons into the corresponding parton distributions, FW(x,Q), FZ(x,Q)

The analogous of DGLAP evolution equations in QCD can be derived in the electroweak sector of the Standard Model, but the resulting equations are very different (Ciafaloni and Comelli, 2002,2005)

The purely electroweak evolution equations must be supplemented with the QED evolution equations and the determination of the photon PDF �(x,Q2) from experimental data (NNPDF2.3QED)

An important difference between QED and EW evolution is that in the later case W and Z boson PDFs are always generated dynamically, while there is an intrinsic photon PDF in the proton

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 15: New dynamics in parton distributions at a 100 TeV hadron collider

15

The analogous of DGLAP evolution equations in QCD can be derived in the electroweak sector of the Standard Model, but the resulting equations are very different (Ciafaloni and Comelli, 2002,2005)

No numerical implementation of EW evolution equations exist. Very different flavor/coupling structure as compared to QCD evolution equations

In addition, EW must be combined with pure QED evolution, and then combined with QCD into a complete set of Standard Model PDF evolution equations

Evolution equation for the structure function of W bosons

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 16: New dynamics in parton distributions at a 100 TeV hadron collider

16

Once QED corrections to PDFs are taken into account, photon-initiated contributions are relevant at the LHC, could be even more the case at the FCC

Many examples, like photon-initiated corrections substantially modify the lepton pt in high-mass Drell-Yan

They also induce substantial uncertainties for high-mass WW production, up to 100%

More FCC-specific studies required

( GeV )cutWWM

0 1000 2000 3000 4000 5000 6000 7000 8000

(WW

) [Q

CD

] !

(WW

) [Q

CD

+Q

ED

] /

!

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WW production @ LHC 100 TeV, 68% CL

qNNPDF2.3 QED, q

qMRST04 QED, q

"" + qNNPDF2.3 QED, q

"" + qMRST04 QED, q

WW production @ LHC 100 TeV, 68% CL

Boughezal, Li, Petriello 2013 Snowmass QCD report

WW at FCC100

(QCD+QED)/QCD

high-mass DY

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 17: New dynamics in parton distributions at a 100 TeV hadron collider

17

The kinematical coverage of the FCC reaches the small-x region where the usual DGLAP PDF evolution might need to be completed with BFKL high-energy (small-x) resummation

Combining DGLAP and BFKL stabilizes the perturbative expansion of DGLAP evolution at small-x

The theory for DIS known (Altarelli, Ball, Forte 08, Ciafaloni, Colferai, Salam, Stasto 07), more theoretical progress is required for computation of relevant hadronic cross sections at the FCC

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

DGLAP NNLO

DGLAP+BFKL

gluo

n-gl

uon

DG

LAP

kern

el

Page 18: New dynamics in parton distributions at a 100 TeV hadron collider

18 Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Crucial milestone for the next years is to produce a global PDF fit which combines NNLO DGLAP evolution with NLL BFKL resummation

This would be a pre-requisite to study the relevance of high-energy resummation at the FCC, specially for benchmark processes like Higgs, W, Z and top production

High-energy resummation affects mostly the gluon PDF, and then feeds to all the quark PDFs

DGLAP NNLO

DGLAP+BFKL

Rat

io g

(x,Q

)/gN

LO(x

,Q)

x=10-4

Page 19: New dynamics in parton distributions at a 100 TeV hadron collider

The Physics Case for Polarized Collisions at the FCC

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 20: New dynamics in parton distributions at a 100 TeV hadron collider

20

x -210 -110

)2

x q (

x, Q

-0.1

0

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2 GeV4 = 102NNPDF2.3, Q

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x u

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q (

x, Q

#x

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2 GeV4 = 102NNPDFpol1.1, Q

g #x

u#x

d#x

s#x

2 GeV4 = 102NNPDFpol1.1, Q

Different qualitative behaviors of PDFs wrt unpolarized PDFs Polarized PDFs smaller than unpolarized due to positivity condition and suppressed at small-x due to different DGLAP splitting functions Only asymmetries which involve high-x polarized PDFs (final states with large invariant mass)

will be large enough to be accessible experimentally

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

What are the BSM opportunities for the polarized option of a 100 TeV machine? Polarized beams could provide a useful tool for BSM characterization, where differences in polarized

asymmetries provide a handle on SM vs BSM discrimination

Page 21: New dynamics in parton distributions at a 100 TeV hadron collider

21

Measurement of sign of AL will discriminate between different BSM scenarios (different production modes)

A more precise measurement of AL leads to enhanced discrimination, ie, qq vs gg production mechanisms

Fuks, Proudom, Rojo, Schienbein, in preparation

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 22: New dynamics in parton distributions at a 100 TeV hadron collider

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Parton Distributions play a central role at the LHC program, will continue to do so at a Future Circular Collider at 100 TeV

Many new qualitative features of PDFs need to be studied: top PDF, PDFs at very large-x, PDFs with electroweak corrections, PDFs with high-energy resummation

It will be useful to provide specific PDF sets for FCC studies, with suitable extrapolations at very small and very large-x as well as to a very large Q2 (and include top PDF)

A polarized mode of the FCC might provide a unique way of characterizing BSM dynamics uncovered in unpolarized collisions

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 23: New dynamics in parton distributions at a 100 TeV hadron collider

23

High-mass production at FCC will probe PDFs at very high-x, we want to make sure that available PDF sets properly extrapolate in this region

Michelangelo reported some weeks ago that using CTEQ at very large x returns zero

I have tried using LHAPDF5.9.0 with CT10, MSTW08 and NNPDF2.3. Consider only central PDF sets (ignore for the time being PDF uncertainties), for Q = 10 TeV

Large-x PDFs seems to behave properly at very large-x, though MSTW08 extrapolation has a peculiar behavior, at least using the LHAPDF library

Note substantial differences for d(x,Q) at high-x

x 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95

)2x

g ( x

, Q

-810

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Large-x NNLO PDFs for FCC studies

NNPDF2.3

CT10

MSTW08

Large-x NNLO PDFs for FCC studies

x 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95

)2x

d ( x

, Q

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Large-x NNLO PDFs for FCC studies

NNPDF2.3

CT10

MSTW08

Large-x NNLO PDFs for FCC studies

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 24: New dynamics in parton distributions at a 100 TeV hadron collider

24

Q ( GeV ) 210 310 410

= 6

)F

= 5

) / (

NF

Ratio

( N

0.98

0.99

1

1.01

1.02

1.03

1.04

1.05

1.06-2NNPDF2.3 NNLO, x = 10

GluonUpDown

-2NNPDF2.3 NNLO, x = 10

At 10 TeV, the top quark PDF t(x,Q) is only a factor 2/3 smaller that all other quark PDFs (charm and bottom are very close to light quark PDFs): should be included in theoretical predictions

The missing contribution from t(x,Q) also feeds back to the gluon PDF: up to 4% differences due to the missing top quark PDF

NF=6 vs NF=5

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014

Page 25: New dynamics in parton distributions at a 100 TeV hadron collider

25

Gluon-initiated processes grow faster than quark initiated from 14 to 100 TeV

Very large PDF uncertainties affect QQbar luminosities since large-x antiquarks poorly known

Using these results, it is possible to estimate how the cross-sections for different processes will increase when going from 14 TeV to 100 TeV

[ GeV ]X M210 310 410

PDF

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100 TeV vs 14 TeV PDF Luminosities, NNPDF2.3 NNLO

GGQGQQbarQQ

100 TeV vs 14 TeV PDF Luminosities, NNPDF2.3 NNLO

Juan Rojo FCC Kick-off Meeting, Geneva, 14/02/2014