Experimental SummaryMoriond QCD 2015

Tom LeCompte

High Energy Physics DivisionArgonne National Laboratory

2

Necessary preliminaries

Thanks to the organizers for the privilege of giving this talk!

Forty-five minutes is too short to really do justice to the wide variety of interesting experimental outcomes presented. I apologize to those whose material I under-represnted here: which is everybody.Any mistakes you see here are entirely my own

There is some conclusion and opinion in these slides.– I’ll try and label what is opinion

3

Themes of this Summary

At this time in particle physics, we are faced with two problems– The Higgs mass seems to be telling us there is new physics at around the TeV

scale• The mass is too light to be heavy and too heavy to be light

– Flavor, on the other hand, seems to be telling is there isn’t– We need to reconcile this

– Most of the universe is composed of a kind of matter not present in the Standard Model

– We need to (at least!) identify this

QCD is…– Necessary to answer the above questions (signals, backgrounds, initial

conditions…)– A beautiful theory in its own right: a non-Abelian gauge theory in its purest

form

4

Onto QCD…

5

Heavy Ions

Work shown by– Redmer Bertens– Frederike Bock– Bingchu Huang– Matt Lamont– Emilia Leogrande – Valery Pozdnyakov – Christof Roland– Shengquan Tuo– Julia Velovska– Kryztof Wozniak

6

Heavy Ion Cheat Sheet for HEP-ers

AA collisions = nucleus-nucleus collisions– Where you expect to see the Quark-Gluon Plasma (or other new physics)

pp collisions = proton-proton collisions– Reference data

pA collisions = proton-nucleus collisions– Reference data but with nuclear size and structure effects included

Centrality = the degree of overlap in collisions– Defined so that “10%” means “only 10% of the events are more central”– Defined so that “90%” means “only 90% of the events are more central”

• So these are more peripheral– Unmeasurable – so people use a proxy like energy, multiplicity, etc.

Cut me out and take me home!

LHC just finished a p-Pb run, so lots of new pA results

RAA – nuclear modification with respect to pp collisions

RCP – nuclear modification comparing central to peripheral

The basic paradigm:

7

Nuclei and PDFs

A proton in a nucleus is different than a free proton

Nuclei are made largely of neutrons – (15% more d-quarks tha u-quarks)

The same PDF probes used in pp can be used in pA (e.g. pPb)

Proton direction

These measurements should be very familiar to PDF fitters from the pp community.

8

What is Flow?

Flow is a collective motion of particles produced in collisions.

– Implicitly assumes a large number of particles

2 dN/d = 1 + 2v1 cos()

+ 2v2 cos(2)

+ 2v3 cos(3) + …

Directed Flow(similar to MET)

Elliptical Flow

Triangular Flow

9

The Flow Mystery in pA Collisions

pA collisions show evidence of hydrodynamic collective behavior, even though the system size is “small”.

Seen by multiple experiments using multiple techniques.

10

Possibly Related – the Ridge in pA

No/small “ridge” in pp

Large ridge in AAWhy the large “ridge” in pA?

11

A Jet Mystery

It is common in RHI physics to make jets exclusively from charged particles This is RpA for p-Pb collisions at CMS for charged particle jets and “regular” jets

Why is this different? Remember, RpA is a ratio.

12

For Lack of Time

Jet quenching– A parton moving through a QGP dramatically loses

energy, causing its jet to vanish.– The world’s hottest substance is the world’s best

refrigerator

Quarkonium dissociation– Proposed by Matsui and Satz (1986)– In a QGP, the free color charges

interfere with the q-qbar binding. The less bound the system, the easier it is to “melt”.

I encourage everyone to look at the proceedings

13

Heavy Ion Mini-Summary

The idea of “pA is a reference dataset – nothing interesting happens” may not be entirely correct

– The flow measurements suggest some sort of hydrodynamic behavior even in “small” systems

– Observed in multiple experiments– Improve the measurements and the effect persists– Oddly, Cu-Au data (a “large” system) suggests no QGP.– Is the existence of a “ridge” in pA evidence of the same phenomena?

The RpA results from CMS seems hard to explain– ALICE does not see this– The biggest difference between the experiments is their 7 TeV pp reference datasets

• Possibly a clue?

Tremendous amount of work – one could easily spend the entire summary talk just on Heavy Ions.

14

QCD: Light Quarks, PDFs and EWK

Work shown by– Sabine Lammers– Daniel Johnson– Daniel Britzger– Stefano Carmada– Andreas Hafner– Milena Misheva– Peter Svoisky – Georgios Mavromanolakis – Brian Lindquist

15

QCD: Light Quarks, PDFs and EWK

Work shown by– Sabine Lammers– Daniel Johnson– Daniel Britzger– Stefano Carmada– Andreas Hafner– Milena Misheva– Peter Svoisky – Georgios Mavromanolakis – Brian Lindquist

Work on using Belle and BaBar data to constrain HVP and LBL in muon magnetic moment experiments doesn’t really fit anywhere in this talk, but it is important.

16

“Extreme QCD”

Experiment is confronting theory at scales that we couldn’t imagine just a few years ago:

– W/Z + 7 or more jets– V+Jets out to a TeV

Agreement is overall good, but this does expose some areas for improvement

Not just interesting as a QCD measurement – these are key backgrounds to many searches.

17

A Puzzle

It’s not clear why the shape of the ratio is right, but the magnitude is off by 20%– Shouldn’t that only depend on the vector and axial charges of the quarks?

18

More “Extreme QCD”

LHCb provides a unique window into the forward region – it’s well-instrumented at high .

Looking at W production gives access to very low x sea quarks.

– The kinematics are such that you have one high-x and one low-x parton collide; the product of x’s has one in a well-measured region and one relatively unknown.

19

The Higgs and QCD

Among other things, the Higgs discovery gives us a new window to the gluon PDF

– Theory is known to ~8%– You have two gluons in the initial state

Higgs + Njet production is a new place to test our calculational understanding

This is a good place to mention HERAfitter: in my view, the importance of HERAfitter is that it lets us “crowdsource” PDF fitting – it lowers the barrier to people asking the question “how would/does this measurement affect the PDFs?”

“We are lucky to be at the LHC where gluon fusion dominates” – Bernhard Mitslberger

20

Dibosons

Why should this be in Moriond QCD? Because the experiments are starting to use hadronic W/Z’s decays, especially in

cases where the jets are boosted.– Sensitivity to AGCs is largest at high pT – limiting yourself to resolved bosons really cuts

into your sensitivity– A key thing to watch

We heard mostly about leptonic W/Z’s– Experiments are starting to use VBF production (ideas from the Higgs search)– Experiments are start to see triboson final states

21

QCD: Onia and Heavy Flavor

Work shown by– Ruslan Chistov– Martino Gagliardi– Tomasz Skwarnicki– Wenbiao Yan – Kai Zhu

22

Charmonium Spectrum

Below threshold, things look like the positronium spectrum.

With one major exception, things are well understood.

23

Charmonium Spectrum

Below threshold, things look like the positronium spectrum.

With one major exception, things are well understood.

Above threshold, things are confusing – many unpredicted particles!

24

Where are all the 1’s coming from?

Corrected for branching fractions this tells us the 2/1 ratio is ~1

Other predictions– Spin-counting: 5/3– Ratio of hadronic partial widths:

~25– CSM: ~100

The NRQCD curves rely on matrix elements fit from the data – they do not predict (although in some cases a measurement of one quantity allows calculation of another)

This shows about twice as many 1 as 2.

Pretty much everyone sees the same thing here.

25

The X(3872)

The first of the unpredicted “charmonium” states

Unequivocal – everyone who could see it did

– There were even pre-observations in the record from FNAL E-705

Spin-parity 1++ – with few assumptions, as we

heard

Produced both promptly and from b-decays

26

The Z(3900)

The Z(3900) cannot be a q-qbar state: it has hidden charm and electric charge We now know - for sure – that it has isospin: BES sees its neutral partner

BESIII Preliminary

27

This Isn’t The First Time

There are two analogues in the strange sector: a0(980) and f0(980) They are right at kaon threshold

– The upper end of the resonance decays to KK– The lower end, below threshold, decays to or .– Evidence that they contain a lot of strangeness

The quantum numbers are 0++

– In the quark model, this means a 3P0 state.• How does this end up lighter than the (1020), which is 3S1?

• Why is it not near the 3P1,2 states?• How to explain the other 0++ states?

Unlikely to be a q-qbar state– I leave discussions about tetraquark vs. hadronic molecule to theorists.

History doesn’t repeat itself, but it sometimes rhymes.

This might have been discussed at the 1st Moriond. (Then called the S* and the )

Opinion

28

What Are these States?

I believe that the X and Z are fundamentally the same kind of particle.

– That means not q-qbar

It’s not at all obvious to me that the models to the right truly differ, and are not simply idealizations to expand about.

The X(3872) has been argued to have a significant c-cbar admixture because:

– 1. The prompt production rate at hadron colliders is large

– 2. The significant radiative branching fractions.

Opinion

29

What Are these States? (2)

I believe that the X and Z are fundamentally the same kind of particle.

– That means not q-qbar

It’s not at all obvious to me that the models to the right truly differ, and are not simply idealizations to expand about.

The X(3872) has been argued to have a significant c-cbar admixture because:

– 1. The prompt production rate at hadron colliders is large, and therefore the particle is “small”

– 2. The significant radiative branching fractions.

Opinion

I think #1 is a bad reason. The f0 has a production rate of 0.5-2.0x of the (1020), and it is not small.

I think #2 is a good reason.

30

What About Bottom?

The X-analog in bottomonium is not seen by ATLAS

The X(3872) J/ + 2 decay appears to be dominated by the isospin violating decay J/ +

– It would be good if LHCb, Belle or BESIII could confirm this by measuring the absence of decays.

– The proximity of the state to the DD* threshold makes this possible.

The X(3872) is in a very special place. The Xb doesn’t have to be.

– And apparently isn’t.

31

Onia Mini-Summary

We see a fundamentally new kind of color singlet in particles like the X, Z and f.

– Near KK or DD* threshold, as appropriate.

This system contains a substantial admixture of 2 quarks and 2 antiquarks, although there is no consensus on the dynamics. Different particles may have different internal dynamics.

When possible, these particles have an admixture of q-qbar as well.

Opinion

32

Searches for BSM Particles

Work shown by– Zach Marshall – Santiago Folgueras – H. Wells Wulsin – Enrique Kajomovitz – Oleg Ruchayskiy

33

The Bottom Line: No Sign of New Physics

Either a generic SUSY limit plot, or the view downhill from a snowboarder in thick fog

34

Next Key Idea: Combinations

Combining multiple channels can slightly (~50 GeV) improve limits over a single channel.

This is much easier to do if planned for from the beginning – one can keep the subsamples orthogonal.

One only gains sensitivity beyond “use the best region” when multiple channels are comparably sensitive.

– This is usually the middle of the rage

35

Next Key Idea: Filling The Holes

If the stop is just a bit heavier than the top, its signal can be hidden by the larger top signal.

– Mass plots are no good.– One can look for an excess of spin-0 “top”

pairs as opposed to the SM (where the top production goes through a gluon)

Similarly, one can design searches around Higgs decays or VBF Production

– The VBF tools were developed for the Higgs search

36

It’s not all SUSY

There are well over 100 searches – no evidence for BSM physics.

To pick just one, CMS searches for a b* by b-tagging the q* dijet search:

– This would be TeV physics involving flavour

37

Long-Lived or Weakly Interacting Particles

27% of the p19MSSM models have long-lived particles

– Presumably through near-degenerate LSP and NLSP

Experiments have developed a number of searches to go after these signatures

– Unfortunately, without success

These are very difficult searches: the detectors were designed to do very different things.

– Even things like luminosity become tricky

SAIL: a beam dump proposal to look for ultraweakly interacting particles

38

Dark Matter & Gravity

Work Shown By– Zeynep Demiragli – Greg Landsberg – Jim Hirschauer

39

The Basic Paradigm*

The remarkable thing is that the same objects we are interested in for traditional collider searches (jets, leptons, missing ET) are the same ones we are interested in for DM searches.

In some sense, the collider experimenters get DM searches for “free”.

So far, no significant excesses have been observed.

* From the Greek “para”, plot and “digm”, overused.

40

The Problem

We are sure about the left side. The right is far more model dependent. Going from one to the other is, at best, tricky. (We heard a suggestion on moving forward)

How do we go from this… To this?

41

The More General Issue

So long as we don’t see an excess, it doesn’t matter which model we use. Once we see a signal, sorting it out will take some time. If we saw a signal in the m(ttbar) channel, would we conclude “extra dimensions”

or “topcolor Z-prime?”

42

Searches Summary

SUSY colored objects are excluded up to masses around 0.7-1.4 TeV Electroweak SUSY has limits more like 0.2-0.7 TeV Nothing new outside of SUSY seen either Caveat: these limits often make assumptions about branching fractions

– Especially “Simplified models” Your favorite model might not be excluded!

LHC Run 2 is about to start:

43

Flavor: Top

Work shown by– Fabrice Balli – Gabriele Benelli – Oleg Brandt – Yuan Chao – Matteo Cremonesi – Carlos Escobar

44

The |Vtb| Story (I)

Shortly after discovery, CDF made the measurement

This really measures |Vtb| relative to |Vts| and |Vtd| This could be done before single top was expected to be visible.

Now we see new results from CDF:

222

2

||||||

||

)(

)(

tbtstd

tb

VVV

V

WqtB

WbtBR

45

The |Vtb| Story (II)

Now that single top production is visible, one can use it to measure |Vtb| without recourse to |Vts| and |Vtd|: ~ |Vtb|2.

46

The |Vtb| Story (III)

The R measurement and the single top measurement have comparable uncertainties.

These are systematics limited

|Vtb| is far better known through unitarity than through any measurement, and the Higgs is telling us that there are only 3 sequential familes.

I predict soon that you will see these measurements turned around – using |Vtb| from unitarity and these measurements to control the b-tagging systematics, thereby improving searches. Opinion

47

The Top Asymmetry Story (I)

CDF reported a top forward-backward asymmetry that was 3 above the then-current QCD prediction.

– Many exotic explanations (axigluons, etc.) were tendered. We have new results from D0 and the LHC

– The LHC asymmetry changes from front-back to marrow-wide

48

The Top Asymmetry Story (II)

Meanwhile, the theory asymmetry moved up. The original measurement is now much less improbable, and today is just on the

high side of an ensemble of measurements consistent with QCD. Also, no effect is seen in bottom (granted, the physics is similar, not identical)

I think we can close the book on this.Opinion

49

The Top Mass (1)

Theorists would like experimenters to tell them the pole mass What we actually measure is the W-b system invariant mass These differ by ~1 GeV

It weighs about 173 GeV, with statistical uncertainties typically between 0.1 and 1 GeV, and systematics between 0.5 and 1.5 GeV.

This means it’s Yukawa coupling to the Higgs is 0.996 ± 0.004– This is a clue, I am sure.

The statistical error will fall with the start of LHC Run 2, so the name of the game will switch to beating down systematics.

– The dilepton, lepton+jets and all hadronic modes have different systematics, but they are still similar in approach

– We saw some very different approaches, with wildly different systematics

Opinion

50

The Top Mass (2)

In addition to the in-situ JES calibration, we heard about, One can use the cross-section (including +1 jet) to infer the pole mass.

One can also look at single top production

These are less sensitive than the other channels – but have systematics from very different sources.

Expect more of these alternative methods to appear in the future

Opinion

51

Flavor: Bottom/Weak Interactions

Work shown by– Angelo Carbone – Andreas Crivellin– Francesco Dettori– Leonid Gladilin – Nazim Hussain – Cai-Dian Lu – Donatalla Lucchesi – Derek Strom

52

The Big Picture

Key fact – despite a few ~2 anomalies, the CKM picture holds up remarkably well over many, many measurements (many shown here).

53

Charm

In the SM, charm CP-violation is “small”

Any observation of “large” CP violation isa sign of new physics– U-type CP violation

has never been seen.

No evidence seen so far– My favorite plot is on the

right.– Nearing limits that might

be accommodated in the SM

54

The B Anomalies

A. Crivellin

+ a tension in extracting |Vub| from different datasets

Much theoretical discussion on how these might be accommodated in BSM physics

55

The B Non-Anomaly

Right on the SM value for Bs– If anything, it’s a little small. BSM physics can interfere destructively, but the amplitude

can’t be very large. I really want to get excited about the 2.3s excess in Bd…but I just can’t.

56

Bs J/ +

Another SM Success

57

Higgs

Work shown by– Christos Anastopoulos – Tatsuya Masubuchi – Andrew Mehta – Aruna Nayak– Roko Plestina – Si Xie

I’m impressed by the N3LO work shown by Bernhard Mitslberger, and the wisdom of adopting “N3LO” over NNNLO.

58

Does the Higgs Decay to Fermions?

I am convinced that the Higgs decays to fermions The decay to taus is the most significant, and is what is driving the above

certainty The best evidence for decays to b’s is still from the Tevatron.

5.3 5.72.2Combined

Caveat: this is my combination, not anything official, simply using Fisher’s method

59

Couplings and Searches

Searches for a 2nd Higgs have come up negative

Couplings look as predicted, to within the experiments’ ability to measure

– Note that the top coupling comes from the production, not from ttH

60

Higgs Mass

125.09 ± 0.21 ± 0.11 GeV

Completely consistent with one particle, as opposed to two, one that decays to ZZ* and one that decays to .

We’ve come a long way since July 4, 2012 – but still statistically limited.

ZZ

61

A Word About Spin and Parity

This looks complicated:

And it is! And so is the giant fit that the experiments use.The ideas behind the fit, though, are simpler. For instance, energy conservation.

I

LZmZmHm

2*)()()(

2

I

LZm

2*)( GeV 34

2

The Z* mass tells you something about the possible values of L.

62

Higgs Scoreboard

Couples to Bosons – Unequivocal Couples to 3rd Family Fermions – Very Strong Evidence Couples to 1st and 2nd Family Fermions – No Evidence Yet Spin 0 – Very Strong Evidence Even Parity – Very Strong Evidence Has Only Even Parity – Probable (but one can only ever set limits on the

admixture)

Production rate tells us that there are only 3 sequential generations– More quarks must be either vector-like or children of another Higgs

Agrees with SM Properties to the best we can tell No evidence yet for another Higgs

– In many models, these two statements are coupled: the more SM-like the 1st Higgs is, the harder it is to spot the 2nd one.

63

“The Past”

Despite having stopped running years ago, we see that ZEUS, H1, NA48/2, CDF and D0 are still producing excellent physics.

We need to find a way to better support these efforts – the community has invested tremendous resources into mounting these experiments, sowe should make sure to get the most return from these investments. Opinion

64

The Future

What is this?

65

The Future

The point of this is to show that a ~50% measurement of via di-Higgs production at the HL-LHC does not describe the Higgs potential with as much resolution as we would like.

The LHC is not the end of the story – we will want something that goes beyond it.

My favorite of the future candidates (ILC, FCC, CLIC, etc…)? Whichever one can be built.

It’s a Mexican Hat

66

The Summary of the Summary (of the Summaries)

No signs of new physics - yet Plenty of signs of extreme cleverness in getting the absolute

most out of the data that is in hand.

More to come – not just from LHC Run 2, but from the Fermilab neutrino program, g-2, Belle-2, etc…

Thanks once again to the organizers, the secretariat, and especially all of you for giving me so much to summarize.