Newsletter Issue 12 - Institute of PhysicsIOP HEPP GROUP NEWSLETTER: ISSUE 12 DECEMBER 2014 IoP HEPP...

IOP HEPP GROUP NEWSLETTER: ISSUE 12DECEMBER 2014

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Alexander Mahmoud

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This Years IoP Half Day Meetings

IoP Prizes – awarded in 2014.

Student Conference Fund maximum Increased to £300

Meet the Committee

NewsletterIssue 12

Happy New Year From The IoP HEPP Committee

What's Inside:

Report From our incoming Chairman – Dr Yoshi Uchida

Particle fever returns to the Large Hadron Collider – Dr Chris Hays

Recent highlights and future plans of the LHCb experiment – Dr. Greig Cowan

IOP HEPP GROUP NEWSLETTER: ISSUE 12 DECEMBER 2014

IoP HEPP group Chairperson’s Report

In April, at the Annual Confer-ence at Royal Holloway, I hadthe honour of being asked to bethe next chair of the High En-ergy Particle Physics Commit-tee. I have been on the commit-tee since shortly after I arrived inthe UK in 2004, having spentten years based in the UnitedStates, and I have had the privi-lege of seeing three differentcommittee chairs at work, MikeGreen, Phil Allport and my pre-decessor, Mark Lancaster. Eachone of these brought with themtheir own distinct style, and I be-lieve that I have learnt enoughfrom them all to carry on theirexcellent work, while also intro-ducing something new of myown to the role.

In these ten years I have alsolearnt much about the way inwhich particle physics is carriedout in the UK and Ireland, and Iam proud to be part of this com-munity and I look forward toworking with my colleagues tohelp us pursue particle physicsin all its forms.

We are experiencing some ofthe most exciting times in ourfield, where high-energy colliderexperiments have justified one

of the most extraordinary pre-dictions that has ever beenmade, the Higgs boson, whileneutrino experiments continueto show us that the StandardModel is not complete and ev-ery new measurement points ustowards new discoveries thatare within our reach. As we con-tinue to probe the predictions ofthe Standard Model, every pre-cision measurement whose re-sult is not ‘unexpected’ repre-sents a triumph in its own right—something which is easily for-gotten.

The IoP HEPP group spansmany things; from the huge andextraordinary experiments atthe LHC, to the smaller comple-mentary experiments measuringthe properties of particles tofantastic precision, and many inbetween, all of which have thepotential to make revolutionarydiscoveries—it encompasses students, postdocs, researchersand academics, as well as re-tired physicists, educators andthose who have a connectionwith our field in other ways. I amproud to be chair of a commit-tee that serves all of these dif-ferent aspects of our commu-nity, and I do hope that we cando our bit to help our field flour-ish through these times that areboth exciting and challenging.



Whatever our individual involve-ment may be, I am certain weshare a desire for the field ofparticle physics to be as vibrantas it can be, and each one ofyou can participate actively inour group in many ways; by sug-gesting a half-day meeting to beheld on a favoured topic, orreaching out to the world atlarge with your knowledgethrough our outreach events, orby simply letting us know yourthoughts on how things can bemade better, and of course,through joining the committee it-self to coordinate new initiatives.We can also help co-sponsoryour events and fund postgradu-ate students as they presenttheir research at internationalconferences. For any of theseand more, please do not hesi-tate to contact me personally [email protected] I would be happy to do mybest to help.

Our Annual Conference in 2015will be at Manchester Universityfrom 30th March until 2nd April,to be held jointly with the As-troparticle and Nuclear physics groups, where we will also holdour General Meeting. I verymuch look forward to seeingmany of you there,

Dr. Yoshi Uchida

Particle fever returns to theLarge Hadron Collider

By any measure, the first threeyears of collisions at the LHCwere an historic success. In2012 the ATLAS and CMS ex-periments dramatically ob-served a new form of funda-mental matter, a Higgs boson,nearly fifty years after it was firstproposed. But just as notable iswhat was not discovered. Thesource of dark matter remainselusive, perhaps awaiting thenext significant increase in ex-perimental sensitivity. With theLHC set to provide more than a60% increase in collision energynext year, the anticipation ishigh for the next discovery, adiscovery that would be evenmore dramatic than the last.

To prepare for the expected col-lisions, LHC physicists are por-ing over the wealth of informa-tion provided by the existingdata. The newly observed parti-cle appears to have one of thekey features of a Higgs boson: itinteracts with other particleswith a strength proportional totheir masses (see Fig 1). Theboson has been unambiguouslyobserved in its decays to Wbosons, Z bosons, and photons,and each experiment hasdemonstrated strong evidence



for its decay to tau leptons. Themeasurements of the rates forHiggs boson production and de-cay to these particles have aprecision of 20-40% (see Fig 2),

Figure 1: The inferred couplingof Standard Model particles to

the Higgs boson as a function ofeach particle's mass, based onmeasurements of Higgs boson

production and decay rates withthe CMS experiment [CMS-PAS-HIG-14-009 (https://cd-s.cern.ch/record/1728249)].

impressive accuracy for a newlyobserved particle with challeng-ing decay signatures. LHCphysicists aim to improve theaccuracy of these measure-ments by factors of 2-3 in thenext three years of collisions.The collisions will also allow forthe first observation of interac-tions between the Higgs boson

and top quarks, and betweenthe Higgs boson and bottomquarks. If there are other Higgsbosons contributing to themasses of any of the StandardModel particles, deviationscould be observed in the pre-dicted rates of Higgs boson pro-duction and decay.

Figure 2: The measurementsof several Higgs boson produc-tion and decay rates with theATLAS experiment, relative to

the Standard Model predictions[https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/Com-binedSummaryPlots/HIGGS]



Now that a Higgs-like boson hasbeen observed, one of the long-term goals is the observation ofits self-couplings. These self-couplings are required by theHiggs mechanism; the particlecan not be called a Higgs bosonwithout them. While it will takethe lifetime of the LHC to mea-sure the self-couplings with anyprecision, the experiments arealready constraining their valuesusing the existing data. A non-zero value of the self-couplingcould be demonstrated with thedata to be collected over thenext three years.

Another important property ofthe Higgs boson is its mass.Prior to the Higgs boson discov-ery, the self-consistency of theStandard Model required itsmass to be less than about 150GeV. The ATLAS and CMS ex-periments have measured thenew boson's mass to be about125 GeV, consistent with thisprediction and with the predic-tion of a range of models that in-clude an as-yet unobserved su-persymmetry relating fermionsto bosons. The mass can alsobe used to fix the form of theHiggs potential and determinethe stability of the vacuum underquantum corrections. If one as-sumes that there are no unob-served particles affecting the

Higgs potential, the vacuum ap-pears to be meta-stable but witha lifetime that is considerablylonger than the age of the uni-verse, and with the possibilitythat gravitational interactionscould stabilize the vacuum.

While the vacuum may be sta-ble without new interactions be-low the Planck scale, quantumcorrections to the Higgs bosonmass suggest that such interac-tions should appear at the TeVscale. Top-quark loops in theHiggs boson propagator contrib-ute to the boson's mass, andshould drive it to large valueswithout the presence of new in-teractions at this scale. In theabsence of such interactionsthere must be a fine-tuned can-cellation between the top-quarkloop and high-scale contribu-tions to the Higgs boson mass.If the high scale is taken to bethe Planck scale, the cancella-tion in the Lagrangian mass-square parameter must be apart in 1034 .

The seemingly low value of theHiggs boson mass in the face ofquantum corrections is a curi-ous mystery. A more concretedeficiency of the StandardModel is its failure to accountfor the observed dark matter inthe universe. Here again the



LHC is primed for discovery: ifthe source of dark matter is aparticle with natural weak cou-plings, it should be observableat the LHC. Supersymmetry pre-dicts a particle with such cou-plings, and is made more ap-pealing by its ability to also ex-plain the low value of the Higgsboson mass: supersymmetricquantum corrections approxi-mately cancel those due toStandard Model particles. Oneof the surprises of the first threeyears of LHC data was the ab-sence of any evidence for su-persymmetry. With the addi-tional energy in next year's colli-sions, this evidence could bejust around the corner.

Measurements of the Higgs bo-son and searches for dark mat-ter and supersymmetry are justa taste of the broad array of theongoing measurements andsearches at the LHC. Nextyear's collisions will explorecompletely new territory, promis-ing a return of “particle fever” tothe LHC.

Dr. Chris Hays

Recent highlights and futureplans of the LHCb experiment

The LHCb experiment is a dedi-cated flavour-physics laboratoryat the LHC. Since 2010 it hassuccessfully recorded hugesamples of b and c hadron de-cays that provide fertile groundto further our understanding ofCP violation, the mechanism ofthe strong interaction and thesearch for very rare heavy-flavour decay processes. Witheach precision measurementLHCb can test the StandardModel (SM) to a new level, look-ing for the first signs of newphysics effects that could openup new avenues of discovery.Analysis of the Run-1 dataset,collected in 2011–2012, has ledto over 220 published paperswith many more in preparation.

The LHCb collaboration has re-cently published the most pre-cise measurement of the CP-vi-olating phase phi_s and B0

s me-son lifetimes using B0

s -> J/ψ φs

decays. In the SM φs predictedto be very small with almost notheoretical uncertainty. Newphysics contributions in B0

s-mix-ing diagrams could substantiallyincrease φs and the measure-ment is therefore a very sensi-tive probe for physics beyond



the SM. The published resultsare in good agreement with SMpredictions and significantly con-strain possible new physicsmodels such as supersymmetry.

One of the main objectives ofthe LHCb experiment is tosearch for and study the decaysof B mesons that are controlledby quantum processes involvingparticle loops. These loops typi-cally mean that the decays arevery rare (e.g. 1 decay for every300 million B mesons produced)and so are challenging to detectbut this also makes them verysensitive to the effects that parti-cles from beyond-the-SM theo-ries could have in these loops.The benchmark B0

s -> μ+ μ-

mode has recently been ob-served by LHCb and the CMScollaboration (another experi-ment at the LHC), with a mea-sured decay rate that is consis-tent with the SM prediction. An-other rare decay is B0 -> K*μ+ μ-,the analysis of which allowsmany theoretically clean observ-ables to be measured. LHCbhas published results (usingonly the 2011 dataset) that aregenerally in good agreementwith SM predictions, except forthe variable called P5', which isshowing a discrepancy from theSM prediction in a single bin ofthe di-muon invariant mass by

3.7 sigma. LHCb is currentlypreparing the analysis of its fullRun-1 dataset for B0 -> K* μ+ μ-

and is certainly something topay attention to in the future!

Our understanding of the stronginteraction that binds quarksinto hadrons has been ad-vanced through the exciting dis-covery of two new particles: theχ b’- and χi b*- baryons. Theseare composed of one b quark,one s quark and one d quarkand have long been predicted toexist but had never previouslybeen observed. By preciselymeasuring properties such asthe mass and widths of thesebaryons it is possible to makestringent tests of theorists pre-dictions using QCD. In addition,LHCb has confirmed the exis-tence of the Z(4430)- charmo-nium state, measured its quan-tum numbers and demonstratedthat it indeed behaves like aparticle. Together, these mea-surements confirm the exoticnature of this state, which is be-lieved to be composed of fourquarks or a combination of twoquarks and two anti-quarks, un-like anything other hadron previ-ously studied.

The second proton-proton runof the LHC will start in mid-2015, operating with 25 ns colli-



sions at a centre-of-mass en-ergy of 13 TeV until the end of2018. The LHCb detector willcollect data at an instantaneousluminosity of 4x1032 cm-2s-1, afactor two above the design, al-lowing an additional 6 fb-1 of ppcollision data to be recorded, ef-fectively tripling the total datasetavailable. In the period betweenRun-1 and Run-2 the LHCb col-laboration have been very activein preparing the detector sub-systems and computing infra-structure so that it is fully opera-tional for the first collisions in2015. Run-2 will provide LHCbphysicists the chance to buildupon their impressive pro-gramme of flavour physics mea-surements, which will allowthem to look for the effects ofnew physics in quantum loops atunprecedented precision.

Dr. Greig Cowan

IoP Half Day Meetings 2014

A half day meeting on “VectorBoson Fusion" (VBF) was heldat the University of Warwick inJune. It was well attended by agood mix of experimentalists(ATLAS and CMS) and theo-rists. The program included re-views of recent experimental ev-idence for the VBF process in

Higgs and W/Z boson produc-tion and a discussion of futureexperimental measurements us-ing VBF to probe, for example,the CP properties of the Higgsboson. The theory status wasreviewed and the talks on thestate of the art of QCD calcula-tions and higher order Higgsprocess simulations led to spir-ited discussions. Effective FieldTheory (EFT) is likely to be thelanguage of future Higgs bosonmeasurements at the LHC andwe were led through this in athought-provoking talk. Theoutcome was a clear view of thefuture experimental methodsusing VBF and the future lan-guage in which measurementsshould be couched, namelyEFT.

The Dark Matter at the LargeHadron Collider (DM@LHC)meeting held in Oxford in Sep-tember saw the launch of a newinternational workshop seriesdedicated to the search for DarkMatter at the LHC. The work-shop featured many new experi-mental results from the LHC,ideas for improving thesearches and also discussion ofthe limitations of the current the-oretical interpretations. TheIoP-sponsored Half-Day Meet-ing within the workshop (on



September 27) brought togetheran international panel of expertswith a focused and ambitiousgoal; to create a "simplifiedmodel" structure for Dark Matterinterpretation that will allow adetailed and fair comparison be-tween the different channels,and also comparison with direct-detection searches for DarkMatter. More than 60 partici-pants joined the Half-Day Meet-ing, which spawned a workinggroup that has grown to wellover 100 people engaged inwriting up the conclusions of theworkshop. The plans for DarkMatter simplified model genera-tion for use by CMS and ATLASare now well underway, andshould be ready for the newdata in 2015.

All of our half-day meetings areintended to be accessible for ageneral particle-physics audi-ence, not just for people workingin a specific area. Please sup-port the IoP HEPP group andyour colleagues who organisethese events by attending asmany of our upcoming meetingsas you can.

More information can be found at http://www.iop.org/activity/groups/subject/hepp/calendar/index.html

IoP Particle Accelerator andBeams Newsletter

Our friends of the IoP PABgroup also have a newsletterwhich may be of interest andyou can be viewed through thefollowing link.

http://www.iop.org/activity/groups/subject/pab/news/page_40592.html


http://www.iop.org/activity/groups/subject/hepp/calendar/index.html




IoP HEPP Prizes 2014

Group Prize:

Justin Evans – For his contri-butions to world-leading neutrinooscillation measurements at MI-NOS.

Poster Prize:

Emily Grace – Liquid ArgonNeutrino Detectors

Science in Society Prize:

Tom Whyntie – For his work in establishing the nationwide CERN@school programme thathas brought CERN technology into the classroom.


http://www.iop.org/activity/groups/subject/hepp/prize/society/page_40789.html


Meet the Committee


Sinead Farrington (Warwick): treasurer/secretary

Alexandra Wilcock (Durham): theory student representative

Thomas Bird (Manchester): student experimental rep.

Melissa Uchida (Imperial): newsletter & PAB group liaisonYoshi Uchida (Imperial): chair

Franz Muheim (Edinburgh)


We have ex-officio/cross members to provide links with other IoP and STFC groups:

Neville Hollingworth, Penny Woodman (STFC Science and Society)Paul Newman (STFC PPAP)Peter Williams (Particle Beamsand Accelerators group)

Disclaimer: views expressedherein are not necessarily thoseof the Institute of Physics, norare they indicative of any cur-rent or future policy of the Insti-tute.


Celine Boehm (Durham)

Mrinal Dasgupta (Manchester)

Newsletter Issue 12 - Institute of PhysicsIOP HEPP GROUP NEWSLETTER: ISSUE 12 DECEMBER 2014 IoP HEPP...

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