Several recent results from the NA48 experiment are presented: a measurement
$|\eta_{+-}|$, search for CP violating phenomena in $K^\pm\to3\pi$ decays, and
a measurement of $|V_{us}|$.Comment: A talk given at the 2007 Europhysics Conference on High Energy
  Physics. 3 page

Batley J R

E Goudzovski

Gámiz E

Shabalin E P

Journal of Physics : Conference Series

English

arXiv

Several recent results from the NA48 experiment are presented: a measurement $|\eta_{+-}|$, search for CP violating phenomena in $K^\pm\to3\pi$ decays, and a measurement of $|V_{us}|$

Goudzovski, Evgueni

CERN Document Server

arXiv:0709.3048v1  [hep-ex]  19 Sep 2007R ecent results from the N A 48 experim ent at C ER N :C P violation and C K M param eter jVusjEvgueniG oudzovskiScuola Norm ale Superiore,Piazza deiCavalieri7,I-56100 Pisa,ItalyE-m ail:goudzovs@mail.cern.chA bstract. Severalrecent results from the NA48 experim ent are presented: a m easurem entj+   j,search forCP violating phenom ena in K! 3 decays,and a m easurem entofjVusj.1. IntroductionThe NA48 series of experim ents represents the long-term CERN program in experim entalkaon physics. During the 10 years of operation since 1997, several physics program s wereaccom plished. The experim ental setup has been upgraded in the course of operation; itsprincipalcom ponentsarea kaon beam lineand a vacuum decay volum efollowed by a m agneticspectrom eterconsisting offourdriftcham bers,a triggerscintillatorhodoscope,a liquid kryptonelectrom agnetic calorim eter,and a m uon detector[1].The present paper contains a num ber recent precise m easurem ents based on various datasets: 1) m easurem ent ofthe indirectCP violation param eter j+   jwith K L ! +   decays;2) m easurem ent ofthe direct CP violating Dalitz plot slope asym m etries A g in K ! 3and K  !  00 decays;3)m easurem entofthe CK M m atrix elem entjVusjbased on partialwidthsofthesem ileptonic K  ! 0l  decays.2. M easurem ent ofthe indirect C P violation param eter j+   jThe interest in the m easurem ent ofthe param eter j+   j= A(K L ! +   )=A(K S ! +   )stem s,in particular,from thefactthatprecision m easurem entsofthisvaluebyK TeV and K LO Eexperim entspublished in 2004and 2006,respectively,weredisagreem entwith thepreviousworldaverage by 5% ,orm orethe fourstandard deviations.The NA48 m easurem ent ifj+   j[2]is based on the data taken during 2 days ofdedicatedrunning in 1999. The directly m easured quantity isthe ratio ofthe decay ratesR =   (KL !+   )=  (KL ! e); these decays are characterized by sim ilar signatures involving tworeconstructed tracksofcharged particles.Then j+   jiscom puted asj+   j=s  (KL ! +   )  (KS ! +   )=sBR(K L ! +   )BR(K S ! +   )K SK L: (1)In thisapproach theK L and K S lifetim esK L and K S,and thebranching fractionsBR(K L !e)and BR(K S ! +   )are externalinputstaken from thebestsingle m easurem ents.The data sam ple containsabout80 106 2-track triggers. Eventselection israthersim ilarfortheK L ! +   and K L ! e m odes.A crucialdi erenceiselectron vspion identi cationbased on the ratio ofenergy deposition in the electrom agnetic calorim eterto track m om entumm easured by thespectrom eter.Identi cation e ciency wasm easured and corrected for.Sam plesof47 103 K L ! +   and 5:0 106 K L ! ecandidateswereselected,with about0:5% background contam ination in each. Acceptance corrections and background subtractionwere perform ed by M onte Carlo sim ulation. Trigger e ciencies were m easured directly withthe data and corrected for. The m ostrelevantsystem atic uncertaintiescom e from precision ofsim ulation ofkaon energy spectrum ,precision ofradiative corrections,and precision oftriggere ciency m easurem ent.The nalresultis  (KL ! + )=  (KL ! e)= (4:835 0:022stat: 0:016syst:) 10  3: (2)Thisleads,subtracting the K L ! +    directem ission contribution,butretaining the innerbrem sstrahlung contribution,toBR(K L ! + )= (1:941 0:019) 10  3: (3)Finally,theCP violating param eteriscom puted according to (1)to bej+   j= (2:223 0:012) 10  3: (4)The result in in agreem ent with the recent K LO E and K TeV m easurem ents, while incontradiction to the world average asof2004.3. M easurem ent ofthe direct C P violation param eter A g in K ! 3 decaysThe K  !  +   and K  !  00 decays are am ong the m ost prom ising processes inkaon physicsfora search forCP violating phenom ena. The K  ! 3 m atrix elem entsquaredisconventionally param eterized by a polynom ialexpansionjM (u;v)j2 1+ gu + hu2+ kv2; (5)whereg,h,k aretheso called linearand quadraticDalitz plotslopeparam eters(jhj;jkj jgj),and the two Lorentz invariantkinem atic variablesu and v are de ned asu =s3   s0m 2; v =s2   s1m 2; si= (PK   Pi)2;i= 1;2;3; s0 =s1 + s2 + s33: (6)Herem  isthecharged pion m ass,PK and Pi arethekaon and pion four-m om enta,theindicesi= 1;2 correspond to the two pionsofthe sam e electricalcharge,and the index i= 3 to thepion ofdi erent charge. A non-zero di erence  g between the slope param eters g+ and g describing the decays ofK + and K   ,respectively,is a m anifestation ofdirect CP violationexpressed by thecorresponding slopeasym m etryA g = (g+  g )=(g++ g )  g=(2g): (7)Theaboveslopeasym m etry isexpected to bestrongly enhanced with respectto theasym m etryofintegrated decay rates.A recentfullnext-to-leading orderChPT com putation [3]predictsA gto beoftheorderof10  5 within theSM .Calculationsinvolving processesbeyond theSM [4,5]allow a widerrange ofA g,including substantialenhancem entsup to a few 10  4.A m easurem entofthequantityA g wasperform edwith arecord datasam plecollected in 2003{04 with sim ultaneousK + and K   beam s[6]. The m easurem entm ethod exploitscancellationsofm ajorsystem atice ectsdueto sim ultaneousbeam sand regularinversionsofm agnetic  eldsin the beam line and setup. The sam ples ofevents selected are 3:11  109 K  !  +  candidates,and 9:13 107 K  !  00 candidates,practically background-free.TheCP violating charge asym m etriesofthelinearslopeparam eterofthe Dalitz plotoftheK  !  +   and K  !  00 decayswere found to beA cg = (  1:5  1:5stat:  1:6syst:) 10  4 = (  1:5  2:2) 10  4;A ng = (1:8  1:7stat:  0:6syst:) 10  4 = (1:8  1:8) 10  4:(8)The archived precision is m ore than an order ofm agnitude better that those ofthe previousm easurem ents.Theresultsdonotshow evidencesforlargeenhancem entsduetonon-SM physics,and can beused to constrain extensionsoftheSM predicting large CP violating e ects.4. M easurem ent ofthe C K M param eter jVusjw ith the K ! 0l  decaysPrecise m easurem ents ofthe CK M m atrix param eter jVusjare ofinterest for tests ofCK Munitarity.TheKl3decay rates,including the internalbrem ssrahlung process,isgiven by [7]  (Kl3())=G 2F m5K3843SE W jVusj2jf+ (0)j2IK (1+ K ); (9)wheref+ (0)isa form factoratq2 = 0,SE W = 1:0232 isa shortdistanceelectroweak correction,IK isthephasespaceintegraldepending on form factors,(1+ K )isa long-distancecorrection.The analysisisbased on a m easurem entofthe ratiosBR(K  ! 0e )=BR(K  !  0)and BR(K  ! 0 )=BR(K  !  0)using thedata collected during 3 daysofa dedicatedrun in 2003 [8]. The data sam ples are 87  103 K e3 candidates with 0.02% background,and77 103 K 3 candidateswith 0.2% background.Thefollowing partialwidthsare m easured:BR(K e3) = 0:05168  0:00019stat:  0:00008syst:  0:00030norm :;BR(K 3) = 0:03425  0:00013stat:  0:00006syst:  0:00020norm ::(10)Herethelast(dom inatingand correlated)uncertaintiesareduetoprecision oftheexternalinputBR(K 2).Thefollowing valuesofjVusjf+ (0)were com puted from K e3 and K 3 decays:jVusjf+ (0) = 0:2193  0:0012; [Ke3]jVusjf+ (0) = 0:2177  0:0013: [K3](11)Here the dom inating contribution to the uncertainty com esfrom the long-distance corrections.Com bining these resultsassum ing   e universality and using f+ (0)= 0:961 0:008 [7],itisobtained:jVusj= 0:2277 0:0013 0:0019theor:; (12)wherethesecond and largestuncertainty owestotheprecision off+ (0)com putation.Theabovem easurem entisfound to beconsistentwith unitarity ofthe CK M m ixing m atrix [8].C onclusionsA num berofrecent kaon m easurem ents by the NA48 collaboration at CERN were presented.Theachieved precisionsare sim ilarto orbetterthan thebestpreviousones.R eferences[1] V.Fantietal.(NA48),Nucl.Inst.M ethodsA 574 (2007)433.[2] A.Laietal.(NA48),Phys.Lett.B 645 (2007)26.[3] E.G am iz,J.Prades,I.Scim em i,JHEP 10 (2003)042.[4] E.P.Shabalin,ITEP preprint8-98 (1998).[5] D ’Am brosio,G .Isidori,G .M artinelli,Phys.Lett.B 480 (2000)164.[6] J.R.Batley etal.(NA48/2),CERN-PH-EP/2007-021,subm itted to Eur.Phys.J.C.[7] H.Leutwylerand M .Roos,Z.Phys.C 25 (1984)91.[8] J.R.Batley etal.(NA48/2),Eur.Phys.J.C 50 (2007)329,erratum subm itted ibid.;hep-ex/0702015.

Recent results from the NA48 experiment at CERN: CP violation and CKM parameter |$V_{us}$|

University of Birmingham Research Portal

Recent results from the NA48 experiment at CERN: CP violation and CKM parameter |Vus|

Crossref

Recent results from the NA48 experiment at CERN: CP violation and CKM parameter |
                    V

Recent results from the NA48 experiment at CERN: CP violation and CKM
  parameter Vus

Recent results from the NA48 experiment at CERN: CP violation and CKM parameter Vus

Abstract

Similar works

Full text

Available Versions

CERN Document Server

University of Birmingham Research Portal

Crossref

University of Birmingham Research Portal